Property optical

Optical absorption in tetrahedral crystalline semiconductors such as Si and GaAs shows variations with energy corresponding to variations in the bonds and the details of the density of states obtained from the energy-momentum relationships [see Section 2.1]. The lowest energy absorption derives primarily from transitions from 

In all semiconductors and particularly in amorphous materials there are states in the energy gap that decrease in density roughly exponentially as one moves into the gap. These are the band tails described earlier. The resulting absorption coefficient 

The optical gap (related to the mobility gap) in amorphous Si and other amorphous semiconductors exhibits temperature-dependent behaviors that are qualitatively similar to the temperature-dependences of crystalline materials. For example, a-Si H shows a decrease in optical gap as temperature increases, as one would expect. Unlike the case for crystalline materials, the temperature dependence of a-Si H is primarily related to changes in phonon-electron interactions. Thus, rather than a linear-quadratic relationship to temperature, one finds a change in optical gap of 

In many optical, electronic, and opto-electronic applications, the main emphasis is not so much on thickness since the required thickness is submicron or at the most a few fim, but more on the deposition of pure diamond crystals without carbon, graphite, or metallic impurities. This has 

Optical properties of the azides which have been studied include optical absorption, luminescence, photoconductivity, and photoemission. As the latter 

Experimentally, the optical absorption properties are usually determined by transmission measurements. The intensities of the incident (/q) and transmitted (/) radiation are compared as a function of frequency (or wavelength X) to obtain the optical density  

When losses due to reflection are properly accounted for, the optical density is related to the absorption coefficient 

Luminescence, the emission of electromagnetic radiation in excess of that thermally generated, has been observed in several azides. The emission typically occurs in the ultraviolet, visible, or infrared regions of the electromagnetic spectrum. Some external stimulus is required prior to luminescent emission. The stimulus can take the form of photons, energetic particles, electric field, mechanical energy, or energy available from chemical reaction. 

Luminescent emission involves radiative transitions between electronic states characteristic of the radiating substance (intrinsic or extrinsic). It is usually characterized by the decay time of the emission following removal of the excitation Fluorescence will refer here to the rapidly decaying component immediately following interruption of the excitation its rate is independent of excitation intensity and of temperature. Phosphorescence will refer to the more slowly decaying component which usually involves complex kinetics. 

Optical properties of nanocrystals have been of interest for centuries (see Sect. 1.1) and have become the subject matter of several books in recent years [50,73-75] and reviews [66-69,713]. The plasmon resonance band has emerged as a probe of events taking place in the proximity of metal nanocrystals. Advances have been made in understanding the electronic structure of semiconductor nanocrystals from the excitonic absorption spectra. 

Just as Au nanocrystals, metallic nanoparticles of ReOs (Note ReOs looks like copper and conducts like copper) also exhibit a plasmon band centered around 520 nm [250]. Size-dependent changes such as a red shift of absorption band with increase in size are seen in these nanocrystals as well (see Fig.4.13). 

Optical properties of most known semiconductors have been investigated 

Other semiconductor systems in which strong confinement have been obtained include the sulphide and selenides of lead, nitrides of Ga and In. The band-gap of hexagonal InN has been recently shown to be around 0.7 eV, markedly lower than the previously accepted value of 1.9 eV. Rao and 

Electronic properties of semiconductor ensembles have been examined by absorption spectroscopy [770]. Interparticle interactions could lead to a discernable change in the optical properties of a lattice of semiconductor nanocrystals. The couphng of the electronic states could vary from weak to strong. Absorption spectra showing the results of weak coupling in CdSe nanocrystals are shown in Fig. 4.19. When present in close-packed organization, the absorption spectra of the nanocrystals are broadened and red-shifted. 

Optical properties provide another perspective on the influence of temperature and density changes on the electronic structure of cesium. 

In the liquid, the increasing role of electron interactions can be expected to affect the optical properties at low densities. On the vapor side of the equilibrium, new species forming in the dense vapor at high temperatures can be detected by their characteristic optical response. We shall discuss the optical properties of fluid cesium after we first define the fundamental optical parameters and summarize some simple relationships among them (Abeles, 1972 Ashcroft and Mermin, 1976). 

Consider the response of a sample of matter to a frequency-dependent electromagnetic field. We can describe the linear response of the material in terms of a complex dielectric constant 

When propagation of the electromagnetic wave is of interest, it is useful to express the dielectric constant (w) in terms of the complex refractive index N((o). The complex refractive index is defined as Af = n -i- ik where = e, so that ei — n — and 2 = Here, n is the refractive index and k is the extinction coefficient. The traveling wave solutions to Maxwell s equations for a lossy optical medium are of the form  

Reflectivity spectra (Knuth and Hensel, 1990 Knuth et al., 1997) R (o) versus h(o for liquid cesium are shown in Fig. 3.7. These spectra encompass the range from the normal metal, not too far above (T = 144°C p = 1.78 g cm ), to the moderately expanded metal (T = 1100°C p = 1.19 g cm ). The onset of corrosion of the sapphire windows by liquid cesium prevents extension to higher temperatures and lower densities. 

The optical properties of tungsten have been studied in more detail than those of any other metal or material, because tungsten is not only used as an incandescent lamp filament, but also as a comparison temperature standard in specially constructed strip lamps. 

TABLE 1.17. Temperature Dependence of Thermoelectric Power of Tlmgsten [1.35] 

TABLE 1.18. Tungsten and Tungsten-Rhenium Thermocouple Electromotive Forces at Various Temperatures for a Reference Junction at 0°C [1.39] 

Spectral emissivity [1.37,1.85-1.88]. The spectral emissivity of tungsten as a function of temperature is shown in Fig. 1.20. In the wavelength range of 0.3-0.5 pm, the emissivity has a maximum. The X point of tungsten, where all the emissivity wavelength isotherms cross, corresponds to Xx = 1.27 pm e = 0.33). 

Total emissivity e,. The experimental results of e, measurements can be well 

The optical properties of the nonpolar nitrides have been extensively studied [94-106] by photoluminescence (PL), cathodoluminescence (CL), and photoreflectivity (PR). All the studies consistently reported two important features of this type of material that differ significantly from the optical properties of the nitrides grown in the [0001] direction. The first difference is related to the specific microstructure of these materials and is characterized by additional emission bands attributed to structural defects such as SFs. The second difference is related to the anisotropic in-plane character of the optical properties, in agreement with the theoretical predictions. 

The other well-known emission bands in GaN, in lower energy regions such as donor-acceptor pair emission together with its phonon replicas, as well as the blue-green, yellow, and red emission bands, have also been observed in GaN films with nonpolar orientations and their origin was, in principle, related to the same defects as the respective emissions in polar materials [95, 99]. 

It should be underlined that the luminescence spectra of low-defect density nonpolar GaN material grown by optimized ELOG templates are dominated by the exciton-related emissions, and the defect-related recombinations have been significantly reduced [70]. Furthermore, for the bulk GaN material with nonpolar surfaces sliced from boules, which have been grown in the c direction, the low-defect density is reflected in a high optical quality [86, 100]. Namely, low temperature PL spectra in the NBE region show free-exciton emissions 

The origin and the behavior of the emission in GaN with [11-22], [10-1-1], and [10-1-3] semipolar orientations have been less studied [101,102]. In principle. 

The emission properties of nonpolar a-plane AlN and InN films grown on r-plane sapphire are the least explored. Only a few papers present the initial data on this topic. The NBE emissions were confirmed very close to that in polar AlN [103,104] and InN [38,105] materials with no detailed studies of the effect of strain on them. Significant improvement of the emission intensity was observed in nonpolar AlN [104] as a result of microstructure improvement in case of ELOG [104] or Pendeo [106] template employment. Similar to the observation for GaN, the AlN bulk material with nonpolar orientations sliced from boules grown in the [0001] direction was found to possess superior emission quality [103]. 

Another important optical property of a material is the index of refraction. It is defined as the ratio of the speed of light in a vacuum, Uv, to the speed of light in the material Um 

1 Rotation of Plane Polarized Light, Optical Dispersion and Circular Dichroism 

The propagation of an electromagnetic wave in a given medium is determined by the interactions between the wave and the material. Important information on these interactions can be obtained from the material s optical properties by spectroscopy. When chirality, in the form of a given enantiomer, is present at the molecular level there is a breakdown in the spatial symmetry of the medium through which the wave passes. It is this breakdown in symmetry that is responsible for the phenomenon of the rotation of the plane of polarization of light. 

In practice, the specific rotation of a substance is defined by the relationship  

At this point two important aspects of the specific rotation must be emphasized. 

The two types of optical rotatory dispersion negative values. 

After extensively reviewing the mechanical properties of polymers, let s refer to other, less general, properties that are particularly important in cases 

Transparency, in general drops with crystallinity (e.g. polyethylene), and with an increase of crystallite size which causes light scattering. Most fillers, colorants and auxiliary additives lead to opacity. Transmittance depends on the refractive index, so that some fillers may preserve full or partial transparency (translucent). There are also dyes that dissolve in the polymer, so that a colored transparent polymer is produced. It is also possible to find stabilizers (including antioxidants or UV absorbers) that do not affect the polymer transparency. Any chemical change in the polymer like degradation or oxidation, or diffusion of some components, may reduce light transmission. 

Another optical property is gloss, which is determined by light reflection. 

Most polymers have smooth surfaces and high gloss. However, it is sometimes desired to reduce the gloss by including special additives, like fibers. 

By and large, gloss is a beneficial property, mainly in household goods, transportation or toys. At present, the property of light reflection is also crucial for the storage of solar energy. 

PEN films have strong electrical luminescence (EL) properties (Table 10.6). Under DC stress, the emission threshold for PEN is 1.5MVcm 1 while for PET it is 4 MV cm-1. 

Compared with PET, PEN has five times more radiation resistance in air, four times more in O2 and ten times more resistance in vacuum under continuous-use temperature [10]. Cakmak and co-workers calculated the refractive index of PEN this parameter is highest (nc = 1.908) along the chain axis and lowest (nn = 1.36) normal to the naphthalene ring. Biaxially oriented PEN film has a 

It is widely established that graphene has numerous fascinating properties [4-9]. Though considered as a semimetal, graphene has unique electromag-netic/plasmonic effects compared to conventional noble metals [10,11]. First, its plasma frequency in the long-wavelength limit is expressed as [12-15] 

Colour is another aspect of optical properties, but here, plastics do not introduce any new phenomena, rather it is the behaviour of the colourants which is of interest they must be stable during processing and use, and should not induce any reaction, either physical or chemical, in the polymer. It has been observed that for partially crystalline polymers, colourants frequently behave as nucleating agents. 

Within materials science, the optical properties of ICP-CNT composites refer specifically to the absorption, photo luminescence, Raman and FTIR spectroscopy of ICP-CNT composites. Spectroscopic methods offer the possibiUty of quick and nondestructive characterization of relatively large amounts of ICP-CNT composites. There is a strong demand for such characterization from the industrial point 

As shown below, these spectroscopies allow quick and reliable characterization of this ICP-CNT composite quality in terms of nontubular carbon content, structure of the produced ICP-CNT composites, and structural defects. Those features determine nearly any other properties such as optical, mechanical, and electrical properties. 

Chemical Society.) (b) Photoluminescence spectra of P3FIT-MWNT nanocomposites after excitation by radiation of a 500 nm wavelength (normalized to film thickness of 1pm) (i) P3HT (ii) PCNC-1 (iii) PCNC-2.5 (iv) PCNC-8. (From Kuila, B.K., etal. [2007] Macromolecules 40, 278. Reproduced with permission from American Chemical Society.) 

Interestingly all composite samples show upshift in both the G- and D-band frequencies due to an increase in the carbon nanotube C-C bond strength. Wise et al. [66] reported the effect of electron donor-acceptor type charge 

Otherwise, a similar upshift of 10-15 cm was observed in the Raman spectra of poly(butadiene)-MWNT composites [67], The CH-ti interactions observed between nanotube and polymer are stronger than that of the n-n interactions observed between nanotube bundles, resulting in a restriction of the C-C bond vibrations and a corresponding upshift of the Raman signal. A 17 cm upshift in G-band Raman signal of MWNTs embedded in melt-blended polyethylene-MWNT composites and the evolution of a shoulder to this peak were attributed to compressive forces exerted on the MWNTs by polyethylene chains following intercalation into MWNT bundles. So, the proposed compression-induced effect on MWNT Raman G-band position appears to be consistent with the results obtained for rrP3HT-MWNT composites. 

Optical techniques have provided valuable information on many important properties of surface sihcides. The most common optical experiments include reflectance (R), transmittance (T), and elipsometric spectroscopy (SE). Although the physical process is the same, the method used to extract the optical functions from the experimental R, T, or SE measurements is different in the case of thin films, where the properties of the film itself and its purity and crystalline quality play a relevant role in the reliability of the optical constants determined. In particular, the results obtained from optical measurements on thin films can be affected by several contributions originating from the presence of the substrate. For qualitative analysis, it is sufficient to identify the spectral features of the substrate and normalize the measured spectra to this contribution. However, interference effects may also play 

In the case of semiconducting silicides, optical properties are affected by the presence of impurities, so that in most cases the best values have been obtained for thin films grown in situ. The case of P-FeSij has received special attention, and the director indirect character of the gap [181,182] as well as other properties [183-186] deserved attention for some time. In general, optical studies are important to assess definitively the semiconducting character of sihcides. 

The different modifications of Cu S crystals have been investigated in respect of their optical behaviour. Basing on the known optical constants which vary considerably in the different phases/ theoretical values of optical transmission and reflection have been derived /32/ for a large wavelength interval. These values are plotted in figure 13 which clearly indicates that the spectral transmission is sensitively affected by the chemical composition of the Cu S film, which was assumed to be 0,15 ]im thick. This characteristic behaviour presents a sensitive tool to investigate stoichiometry and film thickness. From figure 13 the absorption coefficients of Cu S can be derived, which are 

Fluorescence, both visible and infrared, and opalescence in glass-ceramics are also important optical characteristics. 

electron, and photon beams all share the same optical properties, i.e. all can be formed into collimated beams (a stream of particles following more or less parallel trajectories), which can be focused at some position in space. Likewise, all can suffer from the same set of deformations, some more so than others. This is inclusive of  

If ohmic electric contacts cannot be obtained, the solution is provided by optical properties. An example has been provided in Chap. 4. So far, we had only considered static properties now we have to investigate the response of the semiconductor to an electromagnetic wave of angular frequency oo E t) = E (o)e . The equa-ti(Mi of motion of the electron is still given by the dynamics law  

The electric current generated this electromagnetic wave is j t) = nev t) = c i)E, with c the conductivity  

If UT C 1, we recover the Ohm s law, as expected. Otherwise, friction prevents the electron from following the field the imaginary part in Eq. (13.47) implies an out-of-phase response of the electron gas. If we consider the trajectory of the electron, we write that the position x of the electron oscillate at the same frequency, i.e., x(t) = x co)e so that v(t) = dxjdt = —io)x t), which can be inserted in Eq. (13.46) to obtain  

It is important to remember the system of units when some numerical application is needed. To avoid any problem linked to the units, you may simply use the formula  

1 Limit mt for the Free Electron Gas (No Mixing with Phonons) 

The material has to simultaneously possess photoconductivity and electro-optical effect to have photorefractive properties. Typical candidate materials have low glass transition temperature, frequently reduced by the plasticizer. Diffraction efficiency is improved by addition of the plasticizer because chromophore groups have higher rotational mobility and increase their contribution of birefringence to the total refractive index modulation.  

The direct effect of the plasticizer on clarity arrd color of the resultarrt rrraterial is rarely related to the qrrality of the plasticizer. They are rrsually trarrsparertt arrd colorless liquids with clearly indicated optical properties by their rrtanrrfacturers. Clarity rrray be affected by incompatibility with resin and effect of moisture absorption, hrcorrrpatibihty is sometimes encourrtered with polymeric plasticizers. Some plasticized arrd rrrrplasticized materials become clondy and white on moisture absorption. This is a temporary state which can be reversed by drying. Before stabilizers are corrsidered, the effect of moisture 

Several of the perovskite crystals, including LiNb03, KNb03, KTa03, KNbi Ta,c03, and Ba2NaNb50i5, possess nonlinear optical properties that can be 

Fluoropol5mier-based additives performed well during extrusion, but were not detected on the surface of films using SIMS and ESCA. Also, surface tack, surface tension, and optical properties of the films were not affected. 

Several optical properties may be affected by the antiblocking, release, and slip agents, such as  

Optical properties are most likely affected by inorganic antiblocking agents. 

T - talc, HCT - high clarity talc, DE - diatoma-ceous earth. [Data from Radosta, J. A. Deutsch, 

International Plastics Additives and Modifiers Conference, Singapore, Oct. 28-29,1997, paper 18,1-6.] 

In recent years, epoxy resins have been nsed to realize optical disk matrices, lenses and prisms. However, the refractive index of conventional epoxy resins is low and their applications as optical materials where a high refractive index is reqnired are limited. For this reason, many efforts are being dedicated to synthesizing new optical epoxy resins characterized by a high refractive index, good mechanical properties and optimal thermal insulation. 

The experimental results have shown that the BEPTES/ESDGEBA cured resins have a high refractive index that increases linearly with the content of BEPTES. The introduction of ESDGEBA into the copolymerization system can improve both surface hardness and the Eg of the cured resins. For the BEPTES/TDI system, the refractive index increases linearly with the increase of molar ratio of BEPTES to TDI. 

Thanks both to their good properties and mainly to their versatility, nowadays epoxy resins find application in the following major fields coatings, electrical and electronic insulation, adhesives and construction and as matrices for FRP automotive, nautical and aerospace applications. 

In industrial manufacturing, adhesives play an important role in the production of many different kinds of product. They offer a number of advantages in comparison to the conventional joining techniques for instance, adhesive bonds are superior in the presence of dynamic stress, due to their flexible nature. Moreover rivets or bolts can only transmit forces over a very localized area, while in an adhesive bond the stress distribution is spread over the entire area of the bond. 

The low heat input, compared to welding, is another key criterion when joining parts that already have their final surface finish, for example painted metal or stainless steel. As non-conducting materials, cured adhesives also have an insulating effect, thus preventing contact corrosion. 

Nonmetallic inorganic materials are widely used for optical purposes lenses, pigments, interference filters, laser hosts, luminescent coatings, displays, solar cells, fiber optics, lamp bulbs, and tubes. For optical applications use is made of the refractory index, light absorption, luminescence, and nonlinear optical behavior of materials. These are intrinsic but may depend on the concentration of impurities. Refraction index and optical absorptivity in insulators are atomic properties and are only indirectly related to the structure, but the structure affects the selection rules and the term splitting in the atomic chromophores. The coordination number determines the intensity and wavelength of absorption and 

Spinels have anion lattices with tetrahedral and octahedral sites for transition metal dopants. Garnets have three types of cation lattice sites. Some cation sites are coordinated by eight oxide ions on the corners of a distorted cube around the cation, four-coordinated (tetrahedral), and six-coordinated (octahedral) lattice sites. By substituting the right transition metal or lanthanide ions in these sites the color and optical activity of garnet pigments can be controlled. 

The refractory index n depends on the band gap Eg (in eV) for oxides there is an empirical relation  

For perpendicular incident light the reflecting power p of an interface between two materials that differ in refractory index is 

Chemical properties of solid compounds are not intrinsic but extrinsic as the chemistry of solids is for the most part the kind of chemistry that occurs at the surface or at an interface between solid phases. Interface chemistry is the subject of Chapter 6. Bulk chemistry of solids is linked to the presence of defects. An introduction to defect chemistry in crystals is given in Chapter 10. Insofar as bulk chemistry relates to ion and electron transport it has been discussed above under electrical properties. 

The extinction of the luminous flux passing through a foam layer occurs as a result of light scattering (in the processes of reflection, refraction, interference and diffraction from the foam elements) and light absorption by the solution. In a polyhedral foam there are three structural elements, clearly distinct by optical properties films, Plateau borders and vertexes. The optical properties of single foam films have been widely studied (see Section 2.1.3) but these of the foam as a disperse systems are poorly considered. 

A conclusion has been drawn in [67] that the extinction of the luminous flux (7//o, where, 7o is the intensity of the incident light and 7 is the intensity the light passed through the foam) is a linear function of the specific foam surface area. A similar dependence has been used also for the determination of the specific surface area of emulsions [68]. Later, however, it has been shown [69,70] that the quantity 7//o depends not only on the specific surface area (or dispersity) but also on the liquid content in the foams, i.e. on the foam expansion ratio, that during drainage can increase without changing the dispersity. Since foam expansion ratio and dispersity are determined by the radii of border curvatures and film thicknesses, all the structural elements of the foam will contribute to the optical density of foams. This means that 

Because of the non-regularity of the polyhedral foam structure (lack of long-range order) the foam becomes macroscopically isotropic, the specific surface area (per unit volume) accepting the luminous flux, is uniformly distributed in direction normal to the films 

Since there are no flat surfaces in the foam borders and vertexes, the entire incident light changes its initial direction, similarly to the case of a spherical bubble. Thus, the optical cross section of borders and vertexes will equal the projection area of these structural elements on a plane perpendicular to the light beam direction (shadow area). 

For borders of random orientation the optical cross section is directly proportional to the border radius r and the specific border length l, i.e. the total length of borders per unit volume. In this case the border symmetry axis is of a third order referring to the light beam and the orientation of the border, characterised by the angle of rotation with this axis. Thus, for foam layer of thickness L 

A composition containing at least 70 wt % of PVDF and about 30 wt % of acrylic resin has been recommended as a standard coating formulation. The recommended formulation is designed to provide coatings with optimized physical properties and a resistance to the effects of long-term environmental exposure. In addition to internal research results, a literature search was done to confirm that this composition provides the best balance of optical properties, solvent resistance, hardness, mechanical strength, and weatherability. 

SHIOW-CHING LIN and KAROL ARGASINSKI Ausimont USA, Thorofare, New Jersey 08086. 

Fluoropolymers 2 Properties, edited by Hougham et al. Plenum Press, New York, 1999. 

Glass transition temperature is one of the most important parameters used to determine the application scope of a polymeric material. Properties of PVDF such as modulus, thermal expansion coefficient, dielectric constant and loss, heat capacity, refractive index, and hardness change drastically below and above the glass transition temperature. A compatible polymer blend has properties intermediate between those of its constituents. The change of glass transition temperature has been a widely used method to study the compatibility of polymer blends. Normally, the glass transition temperature of a compatible polymer blend can be predicted by the Gordon-Taylor relation  

Two methods, annealing and film-casting by slow solvent evaporation, have been used effectively to develop maximum crystallinity in PVDF blends. The 

Setchell, Teo Kuhn (1985) observed that glass-ionomer cements prepared from poly(acrylic acid) were more resistant to erosion than such cements prepared from maleic acid copolymers. This has been confirmed by Wilson et al. (1986) and by Billington (1986), even when, as in the latter case, the same glass was used in both cements. The method has been reviewed recently by Billington, Williams Pearson (1992). 

In addition to the sensitivity to ring structure, slight alterations of the hydrocarbon chain may lead to dramatic differences in electro-optic performance in chiral compounds [43]. For example, in some electroclinic Sm-A materials it has been reported that if the chain is shortened or if a double bond is localised at the end of the hydrocarbon chain, the tilt angle, electroclinic coefficient, and switching time are significantly suppressed [43]. 

As a result of the unique molecular electronic properties and geometrical structure, liquid crystals also tend to be optically nonlinear materials meaning 

The technical requirements for such applications are highly specific, and the technology is also highly specialised and beyond the scope of this book. 

For very many years it has been common practice to improve the electrical conductivity of plastics and rubbers by the incorporation of certain additives like special grades of carbon black. Such materials were important, for example, in hospital operating theatres where it was essential that static charges did not build up, leading to explosions involving anaesthetics. 

The polymers which have stimulated the greatest interest are the polyacetylenes, poly-p-phenylene, poly(p-phenylene sulphide), polypyrrole and poly-1,6-heptadiyne. The mechanisms by which they function are not fully understood, and the materials available to date are still inferior, in terms of conductivity, to most metal conductors. If, however, the differences in density are taken into account, the polymers become comparable with some of the moderately conductive metals. Unfortunately, most of these polymers also have other disadvantages such as improcessability, poor mechanical strength, instability of the doped materials, sensitivity to oxygen, poor storage stability leading to a loss in conductivity, and poor stability in the presence of electrolytes. Whilst many industrial companies have been active in their development (including Allied, BSASF, IBM and Rohm and Haas,) they have to date remained as developmental products. For a further discussion see Chapter 31. 

In addition to the refractive index (already seen to be closely linked with molecular structure) there are a number of other optical properties of importance 

For transparent plastics materials transparency may be defined as the state permitting perception of objects through or beyond the specimen. It is often assessed as that fraction of the normally incident light transmitted with deviation from the primary beam direction of less than 0.1 degree. 

Atactic PMMA is a brittle amorphous polymer with low elongation at break. Without molecular orientation, PVDF has also a low elongation under tensile stress as shown in Figine 7.9. However, the elongation of PVDF/PMMA blends 

Transparent resins are used as the materials for molded products, such as automobile components, illumination equipment, and electrical components. Transparent resins, which can be applied to such applications, include poly(carbonate) (PC)-based resins and acrylic-based resins. 

However, although acrylic-based resins offer excellent transparency, they have problems in terms of heat resistance and water resistance. In contrast, PC-based resins offer superior performance to acrylic resins in terms of heat resistance and water resistance, but suffer from different problems, such as a high birefringence. 

Certain norbornene derivatives, for example, 5-(2-naphthalene-carbonyloxy)bicyclo[2.2.1 ]hept-2-ene or 5-(4-biphenylcarbonyloxy)-bicyclo[2.2.1]hept-2-ene produce a polymer that is effective in producing molded products with excellent transparency, low water absorption, and low birefringence (29). 

The norbornene derivative is polymerized by a ring opening metathesis polymerization, followed by a hydrogenation reaction. The polymers can be used for optical disks, optical lenses, and optical films or sheets. 

FIGURE 2.26 Microscope images of PDMS channel structures constructed after assembly of square capillaries, (a) T-junction two open capillaries (100 pm i.d.) face each other (left and right). The top PDMS channel (300 pm) is blocked by a plugged capillary, (b) Straight connection The top PDMS channel is connected to the bottom one by an open capillary. Left and right channels are blocked by plugged capillaries [241]. Reprinted with permission from the American Chemical Society. 

FIGURE 2.27 UV transmittance spectra of PC, PMMA, glass, and PDMS substrates [224]. Reprinted with permission from the American Chemical Society. 

The clarity of the film is important for bottom-emissive displays, when one is viewing through the film. A total light transmission (TLT) of 85% over 400-800 nm 

Biaxially oriented films such as PET and PEN are birefringent. For LC displays which depend on light of known polarization this means that birefringent films, which would change the polarization state, are unlikely to be used as substrates. Films based on amorphous polymer are not birefringent and are more suitable for LC displays. Birefringence is not an issue with OLED, electrophoretic displays, or, indeed, some LC displays. 

Translucency or opacity is an expression of how much light can penetrate a substance. There are three levels of light transmission, the first two of which are often modified bywords such as slightly or moderately. Semi-transparent is a stage between transparent and translucent. This term is used most in describing gem materials. 

Translucency can be used to describe individual objects only, since it is not consistent for any given material. Even some metals become translucent when in very thin sheets  

Luster describes the way a surface reflects light, independent of color. There are two basic types metallic and non-metallic. Metallic luster is rarely described further, but there are a wide variety of non-metallic lusters. 

The luster of a natural translucent or transparent material is dependent on its refractive index. Something with a very high refractive index may display 

The structural and chemical causes of color in natural materials can be very complex. But basically, visible colors are caused and affected by the amount of a pigment or impurities present in a material, or the physical structure of its surface. Color is consistent for some materials, and not for others. This depends on the causes of the color. 

Values of the observed and calculated refractivity of phosgene vapour at various wavelengths are given in Table 6.9 and illustrated in Fig. 6.8 [1281]. The theoretical values were calculated according to  

For white light, the refractivity of the gas, relative to that of air, was recorded by Dulong [565b] to be 3.936, corresponding to a refractive index of 1.001153 at standard reference conditions of 0 C and atmospheric pressure [565a]. 

The simplest method for probing the band structure of semiconductors is to measure the absorption spectrum. The absorption coefficient, a, is defined as 

By analyzing the T and A or the R and A data at normal incidence, or by measuring R and T at different angles of incidence, both n and a can be obtained. 

Since the momentum of photons, h/A, is small compared with the crystal momentum, hla (a is the lattice constant), the momentum of electrons should be conserved during the absorption of photons. The absorption coefficient a hv) for a given photon energy is proportional to the probability, P, for transition from the initial to the final state and to the density of electrons in the initial state as well as to the density of empty final states. On this basis, a relation between absorption coefficient a and photon energy ph can be derived [2, 4]. For a direct band-band transition, for which the momentum remains constant (see Fig. 1.7), it has been obtained for a parabolic energy structure (near the absorption edge)  

The interpretation of the interband transition is based on a single-particle model, although in the final state two particles, an electron and a hole, exist. In some semiconductors, however, a quasi one-particle state, an exciton, is formed upon excitation [4, 8], Such an exciton represents a bound state, formed by an electron and a hole, as a result of their Coulomb attraction, i.e. it is a neutral quasi-particle, which can move through the crystal. Its energy state is close to the conduction band (transition 3 in Fig. 1.9), and it can be split into an independent electron and a hole by thermal excitation. 

Therefore, a sharp absorption peak just below the bandgap energy can usually only be observed at low temperatures, whereas at room temperature only the typical band-band transition is visible in the absorption spectrum. The situation is different in organic crystals [9] and also for small semiconductor particles (see Chapter 9). 

Color of fillers should be certainly taken into consideration at their high content, particularly when a light-colored profile is to be made. However, composite materials typically contain enough colorants to overcome color of fillers, except very dark ones, such as carbon black. Fillers effect opacity of the product, which is a negligible factor in colored composite materials. 

A Spectrum bared the Rainbow to his view. Each Element absorbs its signature  

Go add a negative Electron to Potassium Chloride it turns deep blue, 

As Chromium incarnadines Sapphire. Wavelengths, absorbed are reemitted through Fluorescence, Phosphorescence, and the higher Intensities that deadly Laser Beams require. 

A gigabit is 1 billion bits a terabit is 1 trillion bits. 

All EM radiation will interact with solids in some fashion or other. Understanding the nature of this interaction has been and remains invaluable in deciphering and unlocking the mysteries of matter. For instance, it is arguable, and with good justification, that one of the most important techniques to study the solid state has been X-ray diffraction. Other spectroscopic techniques are as varied as radiation sources and what is being monitored, i.e.. reflected, refracted, absorbed rays, etc. 

PEN is transparent in the visible fight region, but can absorb ultraviolet radiation at wavelengths below 380 nm (Eigure 10.6). 

1 Prop atiott aloi the optic axis for wavelengths 4, pitch 

The appearance of a coating involves not only color but also gloss, luster, and translucency. 

The term gloss is commonly used but is difficult to define [9.13]. The Commission Internationale de I Eclairage (CIE) defines the gloss of a surface as the mode of appearance by which reflected highlights of objects are perceived as superimposed on the surface due to the directionally selective properties of that surface.  

Arbitrary gloss scales were used initially. Little effort was made to establish perceptual gloss scales. Psychromatic scaling of gloss has recently been proposed and describes a method devised for the multidimensional assessment of gloss [9.14]. 

Specular gloss and the distinctness of image are of practical importance. In many paint uses maximum gloss is required. Humans experience gloss as particularly brilliant if images are reflected with clear definition from a plane surface. Various forms of black-white contrasts are formed on the paint surface for the visual evaluation of the distinctness of image (DOI). 

The 60° reflectometer has been supplemented by the 20° and 85° reflectometers. The 20° instrument provides better differentiation in the high-gloss range, while the 85° instrument provides a better differentiation in the low-gloss range. However, values measured with these two reflectometer geometries do not always correlate satisfactorily with visual gloss evaluation. 

The PL spectra of MEH-PPV exhibit a maximum around 640 nmJ The maximum is red-shifted with increasing annealing temperature. However, the PL emission from MEH-PPV and blend films with 2-(4-biphenyl-yl)-5-(4-ferf-butylphenyl)-l,3,4-oxadiazole becomes blue-shifted with increasing temperature.  

In PPV, with increasing static pressure a red-shift of the maximum in the PL spectra is observed. In addition, the intensity of the main peak is decreased. 

This phenomenon becomes evident as the increasing pressure of the interaction of polymeric chains becomes more pronounced. The structure tends to become more planar and the conjugated length becomes longer. 

Source Reproduced from ref. 44 with permission from John Wiley and Sons. 

The storage modulus of PLLA shows a slight increase before, and subsequently a rapid decrease at the temperature corresponding 

It is reported that the maximum achieved tensile modulus and strength, for stereocomplex PLA films with an extrusion draw ratio of 16 and prepared by solid-state coextrusion, were 9500 and 410 MPa, respectively. In addition, these films exhibited excellent thermomechanical stability showing 9500, 7000, and 3000 MPa modulus [ ] values at room temperature, 100 and 200°C, respectively [209]. 

The refractive index varies with the wavelength of the incident light. The Abbe number p is given as a measure of this dispersion. p is obtained from three refractive index measurements at the wavelengths 656.3,589.3, and 486.1 nm  

The capacity to separate the colors of white light increases as v decreases. 

The refractive index n of a material depends according to Lorenz-Lorentz relationship, on the polarizability P of all the molecules residing in a uniform field  

Counterpart Relative humidity (%) Friction coefficient, F Remarks Reference 

Steel 40 0.1. 4 Strong fluctuations, p. decreases under dry conditions [55] 

For films sputter deposited from a boron carbide target, k markedly increased at A 400 nm [55]. This indicates an effect of the incorporated carbon (5-10 at-%, see section 5.5.1) in the films. The cathodoluminescence behavior of hBN and cBN films was investigated by Taylor et al. [80] with respect to possible applications of the large band gap material BN in the deep blue and UV range. 

Most polymetallaynes have band gaps of ca. 2.4—3.2 eV, but the value can be reduced substantially to ca. 1.7 eV by the use of alternating donor (bis(phosphine)plat-inum acetylide) and acceptor (electron-deficient thienopyraane) units in the backbone, as in polymer 5.29 [70]. Similarly, donor-acceptor interactions appear to be important in polymer 5.30, which possesses a ferrocenylfluorenyl spacer and has a band gap of 2.1 eV. In the absence of the metallocene group, the analogous polymer has a substantially wider gap ( g=2.9 eV) [71]. 

Detailed studies have been performed on the photophysics of a range of Pt poly-ynes [68, 75-77], and the energy-gap law for triplet states in a series of platinum poly-ynes has been established [78]. Convincing evidence for Jt-conjugation between metal sites in the main chain has been provided by some of the experiments [75]. The photophysics of polymers with fluorene and carbazole spacers has also been investigated in depth, and the studies indicate that the singlet state extends over more than one repeat unit whereas the triplet state is strongly localized [79]. 

Studies of polymetallaynes that contain metals other than Pt are much more rare. However, the photophysical properties of rigid-rod, conjugated gold(I) polymers 5.17-5.19 have been investigated, and these materials were found to exhibit weak luminescence in the solid state at ca. 585 and 600 nm at room temperature when excited with UV light [34], 

The visible and ultraviolet (UV) light transmittance of PLA (98% LLA) has been studied and compared with that of commercial polystyrene, PET, low density PE, and cellophane films in 

The monomers of L- and D-lactic acids, LLA, and DLA, and their homopolymers, PLLA and PDLA, are optically active. The specific optical rotation ([aj sse) values of PLLA and PDLA 

The absorption of inorganic QCNs or semiconducting nanocrystals is quite broad with first sharp excitonic peak appearing in visible or near infra red 

m and hole m are the effective masses of electron and hole, h is Plank s constant, and is the bandgap of the bulk material. The second term is the kinetic energy term. Third term corresponds to the Coulombic interaction between the electron and hole. 

Like their inorganic counterparts, organic quantum confined nanomaterials (QCNs) also display size-dependent optoelectronic properties, though surface states, synthesis routes, and surface chemistry play much stronger 

4 Conjugated-Polymer/Quantum-Confined Nanomaterials (CP/QCN) Hybrids 

1 Methodologies for Making Conjugated-Polymer/ Inorganic QCNs-Based Hybrids 

The photoabsorption spectrum a(co) of a cluster measures the cross-section for electronic excitations induced by an external electromagnetic field oscillating at frequency co. Experimental measurements of a(co) of free clusters in a beam have been reported, most notably for size-selected alkali-metal clusters [4]. Data for size-selected silver aggregates are also available, both for free clusters and for clusters in a frozen argon matrix [94]. The experimental results for the very small species (dimers and trimers) display the variety of excitations that are characteristic of molecular spectra. Beyond these sizes, the spectra are dominated by collective modes, precursors of plasma excitations in the metal. This distinction provides a clear indication of which theoretical method is best suited to analyze the experimental data for the very small systems, standard chemical approaches are required (Cl, coupled clusters), whereas for larger aggregates the many-body perturbation methods developed by the solid-state community provide a computationally more appealing alternative. We briefly sketch two of these approaches, which can be adapted to a DFT framework (1) the random phase approximation (RPA) of Bohm and Pines [95] and the closely related time-dependent density functional theory (TD-DFT) [96], and (2) the GW method of Hedin and Lundqvist [97]. 

The linear response of a system (initially in the ground state 0)) to a periodic one-body perturbation Q(o)) = Q[exp(icot) -h c.c.] is fully described by the complex polarizability a(co), given by the well-known time-dependent perturbation-theory expression 

The connection with the experimentally measurable spectrum S(cu) is established by the relation 

Needless to say, the exact G(co) for the interacting system is not known, except for formal relations that cannot be applied in practice. Time-dependent DFT and RPA define a simple approximation for this Green s function, thus providing a scheme that is suitable for computations. The starting point is the noninteracting particle-hole Green s function defined by 

The scheme can be cast in a somewhat simpler, but less transparent, matrix form by using the noninteracting orbitals as a basis for the integral relations listed above. First, one has to write the (many-electron) state n) as a linear superposition of states obtained by single excitations above the ground state 0)  

In sheet extrusion where the molten sheet of polymer is forced through a set of rolls, the surface conditions are strongly determined by the surface texture of the rolls. If the rolls are polished, they will impart a polished surface onto the polymer sheet-this is why these rolls are often called polishing rolls. Obviously, a variety of different textures can be machined into the rolls and, consequently, a number of different textures can be imparted to the extruded sheet. 

Wagner, Ph. D. thesis, Technische Hochschule Darmstadt, Germany (1978) 

On the contrary, a solid material with more than one principal refractive index is called anisotropic. Anisotropic materials are divided into two subgroups  

Carla M. B. Gonsalves, Joao A. P. Coutinho, and Isabel M. Marrucho 

Since most applications of PLA-based materials are in the sohd state, flie detailed knowledge of the composition, bulk structure, and conformation of these materials is crucial. For example, it is weU known that poly(L-lactide) (PLLA) obtained from LL-lactide is usually molded at 100-120 C in industrial melt processing because of the higher crystallization rate. It has been reported that when it is crystallized within this temperature region a mixture of crystals, a- and P-forms, is formed [2]. Although infrared and Raman spectroscopy is a very promising analytical technique, as will be 

In this chapter, the main optical techniques used to characterize PLA-based polymers are discussed in four sections (1) absorption and transmission of UV-Vis radiation, (2) index of refraction, (3) specific optical rotation, and (4) infrared and Raman spectroscopy and NMR. 

Poly(lactic acid) Synthesis, Structures, Properties, Processing, and Applications, edited by R. Auras, L.-T. Lim, S. E. M. Selke, and H. Tsuji Copyright 2010 John Wiley Sons, Inc. 

FIGURE 8.1 Percent transmission versus wavelength for PLA (98% L-lactide), PS, LDPE, PET, and cellophane films. Adapted from Ref 7 with permission from Wiley-VCH Verlag GmbH Co. 

Spectral Emissivity of ThN, Eo.gs. with the Wave Length X = 0.65, im as a Function of Tempera- 

Infrared Absorption Spectra. Molecular spectra of matrix-isolated Th N and Th N at 15 K as produced by sputtering Th in Ar+Ng and in Kr+Ng mixtures have been reported by Green, Reedy [7]. The infrared spectra show a multiplet of absorption peaks (Table 8) all corresponding to one and the same stretching mode of vibration but to several different matrix sites characterized by different arrangements of the inert gas atoms. The site for Th N with the absorption peak v = 934.61 cm predominates after the matrix is annealed at 34 K. 

Infrared Absorption Spectra of Matrix-Isolated ThN in Solid Ar and in Solid Kr at 14 K. The Peaks are Assigned to the Given Harmonic and Anharmonic Vibrational Constants of ThN [7]. 

Spectra obtained with higher Ng concentrations reveal a Th-N2 complex (not a dinitride) having a sideways bonding of Ng to Th with C2v symmetry and equivalent N atoms. The N-N stretching frequencies Vn n = 1828.59 cm in Th N, 1798.47 in Th( N, N), and 1767.78 cm in Th N2 indicate a strong Th-N2 interaction and an ionic Th Nj contribution to the bonding. 

FIGURE 1.17 (a) Photograph of single-layer and bilayer graphene in transmitted light, the inset shows a 

FIGURE 1.18 (a) The energy gap of tt-tt transitions as a function of the number of fused aromatic rings, 

These are often of importance in plastic products and include colour, surface gloss, light transmittance and haze as well as refractive index. 

Most pigments that are part of any paint formulation are intended to provide visual effects - predominantly, color and opacity. 

Chemical purity The selective absorption of visible light by a pigment is predominantly decided by its chemical structure therefore, chemical purity is one of the important factors that produces consistent color. 

Crystal structure In certain cases, chemically identical pigments existing in different crystal forms (also known as polymorphisms) may exhibit a different hue. Pigments that clearly show the effect of polymorphism on hue are quinacridone pigment (Pigment Violet 19), phthalocyanine pigment (Pigment Blue 15) and lead chromates. 

Mass tone (mass color) According to ASTM, when viewed by reflected light, the color of a pigment-vehicle mixture of a thickness that completely obscures the background is known as mass tone or mass color. 

Tint color (reduced color) The color produced by mixing a predominant amount of a white pigment (generally titanium dioxide) with a colored pigment is known as tint color or reduced color. 

Eggleton B. Luther-Davies B., and Richardson K., Chalcogenide photonics. Nature Photon., 5,141-148 (2011). 

Calvez L., Ma H., Lucas J., and Zhang X., Selenium-based glasses and glass ceramics transmitting light from the visible to the far-IR, Adv. Mater., 19,129-132 (2007). 

Zhang X., Ma H., Adam J. L., and Chen G., Glass formation and crystallization behavior of novel GeS2-Sb2S3-PbS chalcogenide glass system,/. Am. Ceram. Soc., 89(7], 2154-2157 (2006]. 

An object, e. g., a paper surface, is termed white when the illumination intensity and the absorption capacity of the surface are independent of the wavelength. Deviations confer a more or less pronounced color shade on the surface. 

In the paper industry, a special process is used to characterize the brightness because this is one of the most important optical properties of paper. The determination of the reflectance factor (ISO brightness) is based on ISO 2470 (1999). For this test, a filter is used which has an intensity maximum at a wavelength of 457 nm. The reflectance (blue component) measured in a reflectometer under specified conditions is known as brightness. It is expressed as a percentage of the brightness of a white standard. 

Another optical property of paper is its transparency, i. e., a measure of its light transmittance. It is calculated from the reflectance factors Ro, 1 and R ), which are determined in accordance with DIN 53 147 (1993). The reflectance factor of the individual sheet on a completely black background is Ro, J w is the reflectance factor of the individual sheet on a white background, and J (w) is the reflectance factor of the white base. 

Most white papers and paperboards, and therefore also secondary fiber materials, currently contain an optical brightener. Brightness measurements for such materials depend on the relative proportion of UV radiation in the illuminant used for the determination. The standard test methods for ISO brightness have not defined the standard illuminant for use in the determination. The relative amount of UV has also not been defined. As a result, widely different R457 reflectance factors exist for the same kind of fluorescent material. The problem has recently been solved. A revised ISO method, ISO 2470, states that the UV radiation of the illumination must correspond to the relative amount of UV in the standard illuminant C when measuring fluorescent objects. 

The opacity is a measure of Kght-tightness. It is defined in ISO 2471 (1998) as the ratio of the reflectance factor Ro to the reflectance factor Roo. Both reflectance factors are determined in accordance to DIN 53 145 (2000). Ro is measured as the reflectance factor of an individual sheet on a completely black background and Roo as the reflectance factor of an infinitely thick stack of the same paper. 

Depending on the application, polymers are transparent, opaque, glossy, or matte. Transparent applications range from automotive tail lights and food packaging, to camera and contact lenses. Opaque applications include buckets, kitchenware, and diaper backsheets. We can tailor the surface characteristics of a polymer by the production process to be either glossy or 

Once the technique for building up multilayer materials had been developed by Langmuir and Blodgett, it soon became clear that such 

Handbook of Plastics Testing and Failure Analysis, Third Edition, by Vishu Shah Copyright 2007 by John Wiley Sons, Inc. 

In this method, a microscope having a magnifying power of 200 diameters or more is used. A specimen of convenient size, having a fair polish and two parallel 

Luminous transmittance is defined as the ratio of transmitted light to the incident light. The value is generally reported in percentage of light transmitted. Polymethyl methacrylate, for example, transmits 92 percent of the normal incident light. There is about 4 percent refiection at each polymer-air interface for normal incident light (4). 

Ti = specimen and light trap out of position, reflectance standard in position T2 = specimen and reflectance standard in position, light trap out of position Ti = light trap in position, specimen and reflectance standard out of position T4 = specimen and light trap in position, reflectance standard out of position 

The coarse grained M2Se3 obtained at 1200 C are dark colored with a metallic luster. The colors are more characteristic at lower temperature or for powders, Guittard et al. [1]. The following table summarizes data from various sources  

The transparency of most unfilled plastics is obvious in thin-fllm applications such as packaging. However, the number of polymers that are very transparent in thick sections (greater than 0.5 cm thick) is limited. Applications such as eyeglass lenses. 

FIGURE 11.5 Mechanical and dielectric loss tangents for polyfchlorotriiluoroethylene). (After Saito, N. et al., in F. Seitz and D. Turnbull, eds., Solid State Physics, vol. 14, Academic Press, New York, 1963, p. 420.) 

The first three materials listed in Table 11.6 are amorphous thermoplastics. CR-39 is a cross-linked, amorphous network (see Section 17.2). Most highly crystalline polymers are hazy because the crystals and the amorphous phases do not have the same index of refraction and light is scattered at the interfaces. Poly(4-methyl-l-pentene) is unusual in that the two phases have nearly the same index of refraction. The haze in crystalline polymers can be reduced if the crystallite size is very small. A sorbitol-based clarifier for polypropylene is bis(3,4-dimethyldibenzylidene) [25]. It acts as a nucleating agent and makes it possible to produce a water bottle with PET-like clarity. 

FIGURE 11.6 (a) Dielectric constant and (b) loss tangent as fnnctions of frequency and temperature for polyfethylene terephthalate). (Data from Reddish, W., Trans. Faraday Soc., 46, 459, 1950 redrawn by A. J. Curtis in J. B. Birks and J. H. Schuhnan, eds.. Progress in Dielectrics, vol. 2, Wiley, New York, 1960, p. 37.) 

The comparison of densities of various plastics with crown glass shows why eyeglass lenses of plastic are popular despite their generally lower scratch resistance. Contact lenses that are hydrophilic may be made from copolymers of hydroxyethyl 

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Actual crystal planes tend to be incomplete and imperfect in many ways. Nonequilibrium surface stresses may be relieved by surface imperfections such as overgrowths, incomplete planes, steps, and dislocations (see below) as illustrated in Fig. VII-5 [98, 99]. The distribution of such features depends on the past history of the material, including the presence of adsorbing impurities [100]. Finally, for sufficiently small crystals (1-10 nm in dimension), quantum-mechanical effects may alter various physical (e.g., optical) properties [101]. 

See K. Fajans, Radio Elements and Isotopes. Chemical Forces and Optical Properties of Substances, McGraw-Hill, New York, 1931. 

Chemical properties of deposited monolayers have been studied in various ways. The degree of ionization of a substituted coumarin film deposited on quartz was determined as a function of the pH of a solution in contact with the film, from which comparison with Gouy-Chapman theory (see Section V-2) could be made [151]. Several studies have been made of the UV-induced polymerization of monolayers (as well as of multilayers) of diacetylene amphiphiles (see Refs. 168, 169). Excitation energy transfer has been observed in a mixed monolayer of donor and acceptor molecules in stearic acid [170]. Electrical properties have been of interest, particularly the possibility that a suitably asymmetric film might be a unidirectional conductor, that is, a rectifier (see Refs. 171, 172). Optical properties of interest include the ability to make planar optical waveguides of thick LB films [173, 174]. 

Many phenomena in solid-state physics can be understood by resort to energy band calculations. Conductivity trends, photoemission spectra, and optical properties can all be understood by examining the quantum states or energy bands of solids. In addition, electronic structure methods can be used to extract a wide variety of properties such as structural energies, mechanical properties and thennodynamic properties. 

It is possible to make a coimection between the quantum states of a solid and the resulting optical properties of a solid. 

Cohen M L and Cheiikowsky J R 1989 Electronic Structure and Optical Properties of Semiconductors 2nd edn (Springer)... 

Roark S E and Rowlen K L 1993 Atomic force microscopy of thin Ag films. Relationship between morphology and optical properties Chem. Phys. Lett. 212 50... 

The preparation of the reflecting silver layers for MBI deserves special attention, since it affects the optical properties of the mirrors. Another important issue is the optical phase change [ ] at the mica/silver interface, which is responsible for a wavelength-dependent shift of all FECOs. The phase change is a fimction of silver layer thickness, T, especially for T < 40 mn [54]. The roughness of the silver layers can also have an effect on the resolution of the distance measurement [59, 60]. 

There are a few other surface-sensitive characterization techniques that also rely on the use of lasers. For instance surface-plasmon resonance (SPR) measurements have been used to follow changes in surface optical properties as a fiinction of time as the sample is modified by, for instance, adsorption processes [ ]. SPR has proven usefiil to image adsorption patterns on surfaces as well [59]. 

Shanthi E, Dutta V, Baneqee A and Chopra K L 1980 Electrical and optical properties of undoped and antimony-doped tin oxide films J. Appi. Rhys. 51 6243-51... 

Figure Bl.26.14. Plot of A versus K, the imaginary part of the refractive index. (B) MEASUREMENT OF FILM THICKNESS AND OPTICAL PROPERTIES...

Hevens O S 1965 Optical Properties of Thin Solid Films (New York Dover)... 

G) ILLUSTRATIVE EXAMPLES OF THE ELECTRONIC AND OPTICAL PROPERTIES OF MODERN MATERIALS... 

As an indication of the types of infonnation gleaned from all-electron methods, we focus on one recent approach, the FLAPW method. It has been used to detennine the band stmcture and optical properties over a wide energy range for a variety of crystal stmctures and chemical compositions ranging from elementary metals [ ] to complex oxides [M], layered dichalcogenides [, and nanoporous semiconductors The k p fonnulation has also enabled calculation of the complex band stmcture of the A1 (100) surface... 

Pulci O, Onida G, Shkrebtii A I, Del Sole R and Adolph B 1997 Plane-wave pseudopotential calculation of the optical properties of GaAs Phys. Rev. B 55 6685... 

Parameters (ii)-(vii) depend on the dielectric, mechanical and optical properties of the mesogens. To optimize a dis compromise between different molecular characteristics is often required and mixtures of liquid crystals are usually commercial displays. 

Furtlier details of PDLCs can be found in tire excellent monograph by Drzaic [121]. A review of tire non-linear optical properties of PDLCs has also been presented [1241. 

Blinov L M 1983 Electro-optical and Magneto-optical Properties of Liquid Crystals (Chichester Wiley)... 

Simoni F 1997 Nonlinear Optical Properties of Liquid Crystals and Polymer-Dispersed Liquid Crystals (Singapore World Scientific)... 

Guemouri L, Ogier J and Ramsden J J 1998 Optical properties of protein monolayers during assembly J. Chem. 

Some semiconductors with compositions close to ABq Gq are known to become ordered. This results in changes in the gap, and electrical and optical properties, compared to random alloys of the same composition. 

We begin our discussion of nanocrystals in diis chapter widi die most challenging problem faced in die field die preparation and characterization of nanocrystals. These systems present challenging problems for inorganic and analytical chemists alike, and die success of any nanocrystal syndiesis plays a major role in die furdier quantitative study of nanocrystal properties. Next, we will address die unique size-dependent optical properties of bodi metal and semiconductor nanocrystals. Indeed, it is die striking size-dependent colours of nanocrystals diat first attracted... 

The striking size-dependent colours of many nanocrystal samples are one of tlieir most compelling features detailed studies of tlieir optical properties have been among tire most active research areas in nanocrystal science. Evidently, tire optical properties of bulk materials are substantially different from Arose of isolated atoms of tire... 

This section will outline the simplest models for the spectra of both metal and semiconductor nanocrystals. The work described here has illustrated that, in order to achieve quantitative agreement between theory and experiment, a more detailed view of the molecular character of clusters must be incoriDorated. The nature and bonding of the surface, in particular, is often of crucial importance in modelling nanocrystal optical properties. Wlrile this section addresses the linear optical properties of nanocrystals, both nonlinear optical properties and the photophysics of these systems are also of great interest. The reader is referred to the many excellent review articles for more in-depth discussions of these and other aspects of nanocrystal optical properties [147, 148, 149, 150, 151, 152, 153 and 1541. 

An explanation for these size-dependent optical properties, tenned quantum confinement , was first outlined by Bms and co-workers in the early 1980s, [156, 158, 159, 160 and 161] and has fonned the basis for nearly all subsequent discussions of these systems. Though recent work has modified and elaborated on this simple model, its basic predictions are surjDrisingly accurate. The energy of the lowest-lying exciton state is given by the following simple fonnula ... 

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