Transmission electron microscopy TEM

TEM is a very effective technique to study the morphology of polymer samples. TEM can be also used to identify the crystalline regions of polymer and the spherulitic structure of polyethylene composites. Many studies on agglomeration and dispersion of nano-particle in PE based nanocomposites have been carried out by TEM [54, 55]. 

Some TEMs have a closed circuit television system fitted so that the images can be fed directly to an automatic image analysis system. 

The detector system just described is analogous to a gas-filled detector used for x-rays. At low applied voltage it is like an ionization chamber, and when there is amplification, like a proportional counter. An x-ray proportional counter has a limited response rate, of about 10 kHz, but the x-ray systems are normally operated at pressures close to atmospheric, with local fields up to 100 MV m that give amplifications of several thousand times. These conditions can produce very high concentrations of positive ions by the central wire. The ions reduce the applied field, and the response rate is limited by the need for them to diffuse away. In the case of the HPSEM, the field is more uniform, the pressure and the field are lower. All these factors tend to reduce local ion concentrations and thus increase the response frequency. 

The amplification will work best in only a limited range of pressures. Too high a chamber pressure makes the mean free path of electrons very small a high field is then needed to accelerate them, and the high voltage required may not be practicable. Too low a pressure and the effect will be small because the electrons will have few collisions as they travel from specimen to detector. The exact form of the signal contrast is difficult to predict because of the complicated 

1 High resoludon transmission electron microscopy (HREM) 

HREM is here taken to mean the resolution of the intermolecular or interatomic spacings in ordered materials. The theory and practice of this technique is well established [74-76] and its applications to materials science [77-79], to 

The spherical aberration of the objective lens and any defocus both add phase shifts to the diffracted beams that depend on the angle 26. From Fig. 6.9 it appears that phase shifts will move the image laterally. If the scattering is weak, the transmitted wave acts as a reference phase, and the phase of the diffracted beam is naturally 90 ° to this. Then, as for phase contrast generally, there will be no contrast in a perfectly formed image. As d decreases 26 increases and the phase shift x due to defocus and aberration increases. This will cause the image contrast to appear and strengthen, then disappear at 

Transmission electron microscopy is similar to SEM, except for the fact that the beam passes 

Using appropriately prepared samples, TEM in its various modes (SEM, HREM) can routinely resolve metal crystallites and clusters down to sizes at 

Transmission electron microscopy (TEM) is similar to SEM except that the beam passes through the sample. A high-voltage (80-200 keV) highly focused electron beam is passed through a thin solid sample, typically 100-200 nm in thickness. Electrons undergo coherent scattering or diffraction from lat- 

In transmission electron microscopy (TEM), a beam of highly focused and highly energetic electrons is directed toward a thin sample ( 200 nm) which might be prepared from solution as thin film (often cast on water) or by cryocutting of a solid sample. The incident electrons interact with the atoms in the sample, producing characteristic radiation. Information is obtained from both deflected and nondeflected transmitted electrons, backscattered and secondary electrons, and emitted photons. 

Because the electron beam passes through the sample, transmission electron microscopy reveals the interior of the specimen. It is sensitive toward the internal structure of the material (size, shape, and distribution of phases within the material), its composition (distribution of elements, including segregation if present), and the crystalline structure of the phases and the character of crystal defects. 

In Transmission Electron Microscopy (TEM), a very high energy monoenergetic electron beam (100 to 400 keV) passes through a thin specimen (less than 1000 nm) of diameter less than 3 mm (necessary to fit in the electron optics column). A series of post specimen lenses transmits the emerging electrons, with spatial magnification up to 1,000,000, to a detector (fluorescent screen or video camera) viewed in real time. 

Any regions of the sample under the incident beam (usually a few pm diameter) exhibiting crystallinity, will diffract electrons away from the central spot, forming a diffraction pattern observable at the back focal plane of the objective lens. Like X-ray diffraction, this can provide identification of crystalline phase, orientation, and lattice parameters. In micro-diffraction, the incident beam is focused down to sub-micron areas, but this focusing degrades the diffraction pattern. 

Yet another mode of use is High Resolution TEM (HRTEM), in which atom positions can be established by collecting electrons from both the undeflected and diffracted beams and comparing the observed phase interference patters to a simulation. 

with its many modes, and often involving ancillary materials analysis capabilities such as EDS (see EDS summary), is the mainstay of material science and analysis of small volume (areas and thickness). A fully equipped TEM laboratory will have several microscopes with differing capabilities, plus all the necessary sample preparation techniques. See also Scanning TEM (STEM), where the incident beam is focused down to almost atomic dimensions and scanned across the sample. 

Even when the sample naturally occurs in a form that is thin enough for direct examination in the TEM (e.g. solution crystals [86-89] or samples prepared directly in the form of a very thin film [90-94]), problems are encountered as a direct consequence of the way in which the sample and the 

Castellano and co-workers [14] investigated elastomer-silica interactions by image analysis-aided TEM. 

The principle setup for STEM is shown in Fig. 3.14b and in more detail in Fig. 3.14c. The major difference compared to TEM is, that the electron beam gets focused by condenser lenses, is scanned over a sample area by scan coils and for each beam position an intensity is recorded. Further the objective lens is located before the sample and combined with an additional aperture. Two types of images can be 

The infonnation limit of a TEM depends on temporal and spatieil coherence of the e-beam, where the former is related to the eneigy spread of the electrons, the latter on the source size. In order to achieve the highest possible resolution, monochromatic tmd coherent electron sources tire applied [110]. The error of non perfect sources results in chromatic aberration and is expressed by the coefficient Cc- 

The mass-thickness contrast is the reason why denser regions with higher scattering probability of the beam appear dark and light regions appear bright in TEM [112]. 

In approximation one can argue that for thin objects a plain and ideal Z-contrast can be interpreted with a simple relation between Z number of the probed element (inch the sample thickness, i.e. particle size) and image intensity. This simple (ideal) 

In DF the obtained images are inverted, i.e. metal particles appear light (high scatter) on an dark background (low scattering). 

The tungsten filament source has a limit to the beam current that can be obtained in a small spot. Replacing it with a lanthanum hexaboride (LaB6) gun provides a beam about 30 times brighter. This results in an improved signal to noise ratio and allows better resolution at high scan speeds. The increased current is also useful for analytical microscopy. A disadvantage is that this gun requires a better vacuum which must be provided by the addition of an ion pump to the gun chamber. 

Many SEM studies involve magnifications below about lOOOOx where depth of field and minimum degradation are more important than resolution. Conditions for maximum depth of field are  

The small final aperture will reduce the beam current and increase the noise in the image unless the scan rate is reduced. 

In TEM, a focused electron beam is incident on a thin (less than 200 nm) sample. The signal in TEM is obtained from both undeflected and deflected electrons that penetrate the sample thickness. A series of magnetic lenses at and below the sample position are responsible for delivering the signal to a detector, usually a fluorescent screen, a film plate, or a video camera. Accompanying this signal transmission is a 

1st Condenser lens 2nd Condenser lens Beam tilt colls Condenser 2 aperture Objective lens 

Column vacuum block 35 mm Roll film camera Focussing screen Plate camera 16 cm Main screen 

Schematic representation for the ray paths of both unscattered and scattered electrons beneath the sample. 

The higher the operating voltj e of a TEM instrument, the greater its lateral spatial resolution. The theoretical instrumental point-to-point resolution is proportional to This su ests that simply going from a conventional TEM 

Note All scale bars shown in the figure are 150 nm. Abbreviations NPs, nanoparticles PCL, poly(e-caprolactone). 

The observation of low contrast particles in Pt/Ti02 film samples led Baker et al. to suggest that there was a strong interaction between 

Pt particles to lose their spherical symmetry and to adopt a pill-box morphology. Similar TEM effects have been observed and given the same interpretation by other As indicated above it is not 

Several different types of diffraction condition are used to characterise radiation damage. These are achieved by tilting the specimen with reference to the Kikuchi pattern. These include dynamical two-beam , bright-field kinematical and weak-beam conditions - see Jenkins and Kirk for a full description. Under dynamical two-beam conditions, small dislocation loops located close to foil surfaces exhibit black-white contrast (Fig. 9.3), and their symmetry can be used to determine the Burgers vectors and habit-planes. 

Bright-field kinematical conditions are used when it is necessary to avoid the dynamical contrast effects seen in strong two-beam (dynamical) conditions. This is achieved by tilting the foil just away from the Bragg condition. As a result, the contrast is often easier to interpret,but quantitative measurements, such as the loop sizing, should be made with caution. 

2 Schematic diagram illustrating (a) bright-field and (b) dark-field image formation. 

3 Black-white contrast of dislocation loops under dynamical two-beam imaging conditions. The figure shows the same area of a Cu specimen, containing small dislocation loops formed by irradiation with 30keV self ions. The g-vectors are (a) (111) and (b) (111).  

In addition, care must be taken to minimise fine-scale oxidation of the surfaces of the foil. In unfavourable cases, the resultant image contrast from the oxide may be extremely similar to that obtained from small clusters. Oxidation may be minimised by storing samples under water-free ethanol prior to analysis. 

Airlock Sample Stage Objective Lens Coil Objective Lens Aperature 

Freshly-cleaved mica or cleaned glass slide C 

The typical thickness of amorphous carbon films is 2-5 nm, whereas polymer films have thicknesses on the order of 30 nm. As you might expect, all plastic films are subject to decomposition by the electron beam. Sometimes, this exposure also causes further crosslinking that will cause the film to shrink and become more brittle. The surface adsorption characteristics of support films vary quite significantly between polymer and carbon varieties. In general, polymer films possess hydrophilic characteristics whereas carbonaceous support films are hydrophobic. 

The primary electron beam may also be inelastically scattered through interaction with electrons from surface atoms. In this case, the collision displaces core electrons from filled shells e.g., ns (K) or np (L)) the resulting atom is left as an energetic excited state, with a missing inner shell electron. Since the energies of these secondary electrons are sufficiently low, they must be released from atoms near the stuface in order to be detected. Electrons ejected from further within the sample are reabsorbed by the material before they reach the surface. As we will see in the next section (re SEM), as the intensity of the electron beam increases, or the density of the sample decreases, information from underlying portions of the sample may be obtained. 

An imaging mode that merges both SEM and TEM is also possible on most modem TEM instmments. This method, referred to as scanning transmission electron microscopy (STEM), uses a LaBs source that produces a focused electron beam 

The majority of STEM instruments are simply conventional TEMs with the addition of scanning coils. As a result, these non-dedicated STEMs are capable of TEM/ STEM, as well as SEM imaging for thicker samples. The development of HRTEMs and dedicated STEMs with lens aberration correction have now pushed the 

Phosphotungstic acid was used to stain PA6 for contrast in PA6/SAN blends [83]. One problem with staining techniques is that the chemical reaction can promote phase separation, thus the procedure may provide more phase differentiation than is actually present (if a mobile lower 

Tg component is stained). This could be a problem in observation of interfaces where limited phase mixing is present, such as in partially miscible blends, blends with a broad transition (microheterogeneous) and block copolymers. 

TEM has been particularly useful for observing the detailed and ordered morphologies available with block copolymers. Therefore, the morphology of blends of block copolymers with homopolymer constituents is commonly characterized with TEM, as noted with SBS BCP/PS blends [84] and SI BCP/PS blends [85, 86]. The binary blends of miscible S-SB-S triblock copolymers with different block compositions stained with OSO4 and observed by 

With the depth of field for SEM, fiber networks are clearly viewed. Blending various polymers with thermoplastic PVOH followed by orientation of the extrudate and removal of the PVOH by water extraction leads to microfiber formation [104]. SEM analysis was quite useful in observing the resultant fiber structure as illustrated in Fig. 5.19. 

A variation of SEM termed environmental scanning electron microscopy (ESEM) does not require high vacuum and can measure insulating samples without the requirement of a conductive coating [105]. Operation at up to 10 torr and wet samples are possible, permitting observation of hydrated colloidal samples. Observation of block copolymer morphology is possible via ESEM without staining procedures. Application to polymer blends, however, is relatively new. 

Objective piefield lens Specimen holder Objective postfield lens 

Local elemental distributions in a specimen can be investigated in TEM and STEM using the analytical techniques electron energy-loss spectroscopy (EELS) and X-ray microanalysis. X-ray microanalysis in TEM and STEM corresponds to EDX spectroscopy in SEM. However, the thin 

In practice, most TEM investigations of polymers make use of mass-thickness contrast, that is, specimen parts containing elements with a higher atomic number and/or which are thicker scatter electrons stronger, but not contributing to image formation. Therefore, such parts appear darker than the surroundings (see Fig. 3.11). 

The transmission electron microscope provides detailed structural information at levels down to atomic dimensions. However, such high-resolution examination is seldom possible in case of polymers. Nevertheless, it is possible to obtain information within the range 1-10 nm with varying degrees of difficulty. This range is beyond that of optical microscopy, and the TEM can provide information that can rarely be obtained by any other means. 

Generally, polymeric materials are composed of only low-atomic-number elements therefore, significant contrast due to variations of the local density in the specimen cannot be expected. Usually, a chemical staining is used, that is, treatment with heavy metal compounds, for example, OSO4 or RUO4, and deposition in different regions of the polymer (e.g., amorphous, crystalline) (see Fig. 3.12). 

---

Transmission electron microscopy (TEM) can resolve features down to about 1 nm and allows the use of electron diffraction to characterize the structure. Since electrons must pass through the sample however, the technique is limited to thin films. One cryoelectron microscopic study of fatty-acid Langmuir films on vitrified water [13] showed faceted crystals. The application of TEM to Langmuir-Blodgett films is discussed in Chapter XV. 

In many ways the nanocrystal characterization problem is an ideal one for transmission electron microscopy (TEM). Here, an electron beam is used to image a thin sample in transmission mode [119]. The resolution is a sensitive fimction of the beam voltage and electron optics a low-resolution microscope operating at 100 kV might... 

Occasionally, especially in the developmental phase of catalyst research, it is necessary to determine the oxidation state, exact location, and dispersion of various elements in the catalyst. Eor these studies, either transmission electron microscopy (TEM) or scanning electron microscopy (SEM) combined with various high vacuum x-ray, electron, and ion spectroscopies are used routinely. 

Alternatives to XRD include transmission electron microscopy (TEM) and diffraction, Low-Energy and Reflection High-Energy Electron Diffraction (LEED and RHEED), extended X-ray Absorption Fine Structure (EXAFS), and neutron diffraction. LEED and RHEED are limited to surfaces and do not probe the bulk of thin films. The elemental sensitivity in neutron diffraction is quite different from XRD, but neutron sources are much weaker than X-ray sources. Neutrons are, however, sensitive to magnetic moments. If adequately large specimens are available, neutron diffraction is a good alternative for low-Z materials and for materials where the magnetic structure is of interest. 

The field of carbon nanotube research was launched in 1991 by the initial experimental observation of carbon nanotubes by transmission electron microscopy (TEM) [151], and the subsequent report of conditions for the synthesis of large quantities of nanotubes [152,153]. Though early work was done on... 

The earliest observations of carbon nanotubes with very small (nanometer) diameters [151, 158, 159] are shown in Fig. 14. Here we see results of high resolution transmission electron microscopy (TEM) measurements, providing evidence for m-long multi-layer carbon nanotubes, with cross-sections showing several concentric coaxial nanotubes and a hollow core. One nanotube has... 

Processes that occur at a size scale larger than the individual chain have been studied using microscopy, mainly transmission electron microscopy (TEM), but optical microscopy has been useful to examine craze shapes. The knowledge of the crazing process obtained by TEM has been ably summarised by Kramer and will not be repeated here [2,3]. At an interface between two polymers a craze often forms within one of the materials, typically the one with lower crazing stress. 

The interface properties can usually be independently measured by a number of spectroscopic and surface analysis techniques such as secondary ion mass spectroscopy (SIMS), X-ray photoelectron spectroscopy (XPS), specular neutron reflection (SNR), forward recoil spectroscopy (FRES), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), infrared (IR) and several other methods. Theoretical and computer simulation methods can also be used to evaluate H t). Thus, we assume for each interface that we have the ability to measure H t) at different times and that the function is well defined in terms of microscopic properties. 

Several structural characterisations of carbon nanotubes (CNTs) with the cylindrical graphite are reviewed from the viewpoint of transmission electron microscopy (TEM). Especially, electron energy loss spectroscopy (EELS) by using an energy-fdtered TEM is applied to reveal the dependence of fine structure of EELS on the diameter and the anisotropic features of CNTs. 

Multi-walled CNTs (MWCNTs) are produced by arc discharge between graphite electrodes but other carbonaceous materials are always formed simultaneously. The main by-product, nanoparticles, can be removed utilizing the difference in oxidation reaction rates between CNTs and nanoparticles [9]. Then, it was reported that CNTs can be aligned by dispersion in a polymer resin matrix [10]. However, the parameters of CNTs are uncontrollable, such as the diameter, length, chirality and so on, at present. Furthermore, although the CNTs are observed like cylinders by transmission electron microscopy (TEM), some reports have pointed out the possibility of non-cylindrical structures and the existence of defects [11-14]. 

Silver nitrate (AgN03) is a compound that fulfills the precedent requirements (Till = 212°C), and also it can be easily decomposed into pure silver by thermal treatment at 400 °C. As mentioned before, the basic characterisation technique for this studies is transmission electron microscopy (TEM) the atoms with rather high atomic number would facilitate the detection of the nanorods. 

Fig. 2. (a) (b) Transmission electron microscopy (TEM) images of as-grown VGCFs (broken portion) with the PCNT core exposed field emission-type scanning electron microscopy (FE-SEM) image of (c) as-grown and (d) heat-treated VGCFs (broken portion) at 2800°C with PCNT (white line) exposed [20],... 

The crystallization of glassy Pd-Ni-P and Pd-Cu-P alloys is complicated by the formation of metastable crystalline phaf s [26]. The final (stable) crystallization product consists of a mixture of a (Pd,Ni) or (Pd,Cu) fee solid solution and more than one kind of metal phosphide of low crystallographic symmetry. Donovan et al. [27] used transmission electron microscopy (TEM) and X-ray microanalysis to study the microstructure of slowly cooled crystalline Pd4oNi4oP2o- They identified the compositions of the metal phosphides to be Pd34Ni45P2j and Pdg8Ni[4Pjg. 

Small needle-shaped single crystals were examined by transmission electron microscopy (TEM) and electron diffraction (ED) (see Fig. 16-17). The results show that the crystals are elongated along the b-axis, which is the direction of weak intermolecular n-n interactions, and have a well-developed (ab) top surface. It corresponds to the surface of aliphatic tails (direction of weak intermolecular interactions). There are indications of displacement of successive ( / )-laycrs along the fl-axis, in line with the other signs of disorder in the aliphatic layer. 

Also a good interface resolution is obtained with transmission electron microscopy (TEM), where, however, a dedicated sample preparation and treatment are necessary to achieve nanometer resolution and suitable contrast [64]. Thus the... 

SAXS), IR spectroscopy, NMR, transmission electron microscopy (TEM), or atomic force microscopy (AFM) and the thermal transitions by DSC and DMA. 

The nano-scale structures in polymer layered-silicate nano-composites can be thoroughly characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD is used to identify intercalated structures. XRD allows quantification of changes in layer spacing and the most commonly used to probe the nano-composite structure and... 

In the transmission electron microscopy (TEM) images, the starch nanoplatelets (SNPs) are believed to aggregate as a result of hydrogen bond interactions due to the surface hydroxyl groups [13] (Fig. lA). Blocking these interactions by relatively large molecular weight molecules obviously improves the individualization of the nanoparticles. The acetylated starch and cellulose nanoparticles (SAcNPs and CelAcNPs) appeared more individualized and monodispersed than their unmodified counterparts with a size of about 50 nm (Fig. IB C). 

SEM), and transmission electron microscopy (TEM). Study of mechanical and thermal properties shows significant improvement over the gum. The thermal results are given in Table 2.1. 

FIGURE 2.8 Transmission electron microscopy (TEM) photographs of clay nanocomposites with acrylonitrile-butadiene rubber (NBR) having (a) 50% and (b) 19% acrylonitrile content, respectively... 

FIGURE 2.13 Transmission electron microscopy (TEM) photographs of (a) FNA4 and (b) F20A4. (From Maiti, M. and Bhowmick, A.K., J. Appl. Polym. Sci., 105, 435, 2007. Courtesy of Wiley InterScience.)... 

Recent demands for polymeric materials request them to be multifunctional and high performance. Therefore, the research and development of composite materials have become more important because single-polymeric materials can never satisfy such requests. Especially, nanocomposite materials where nanoscale fillers are incorporated with polymeric materials draw much more attention, which accelerates the development of evaluation techniques that have nanometer-scale resolution." To date, transmission electron microscopy (TEM) has been widely used for this purpose, while the technique never catches mechanical information of such materials in general. The realization of much-higher-performance materials requires the evaluation technique that enables us to investigate morphological and mechanical properties at the same time. AFM must be an appropriate candidate because it has almost comparable resolution with TEM. Furthermore, mechanical properties can be readily obtained by AFM due to the fact that the sharp probe tip attached to soft cantilever directly touches the surface of materials in question. Therefore, many of polymer researchers have started to use this novel technique." In this section, we introduce the results using the method described in Section 21.3.3 on CB-reinforced NR. 

FIGURE 22.1 Transmission electron microscopy (TEM) micrograph of a carbon black network obtained from an ultrathin cut of a filled rubber sample. 

---