Thin films preparation

Thin films for polymer microscopy (using both EM and AFM) can he prepared in 

Film by dropping This involves dropping the dilute polymer solution onto a substrate, followed by the subsequent drying and atmealing if needed. The film thickness can be generally controlled by the concentration of polymer, but the film thickness will not be uniform. 

Spin coating This involves subjecting a drop of the polymer solution taken onto a substrate to high-speed rotation. Drying and atmealing of the films at elevated temperature may also be needed. The film thickness, which is more uniform than in the dropping technique, can be adjusted by changing the solution concentration and the speed of substrate rotation. 

Dip coating This involves slowly drawing a substrate (e.g., a rectangular plate of smooth glass, mica or silicon wafer) that has been dipped into a polymer 

The thickness of the films required for transmission electron microscopy (TEM) investigations should be in the range of 50 to 70 nm, whereas films of any thickness can be studied using either scanning electron microscopy (SEM) or/and AFM. 

One technique which has produced thin, but not epitaxial films of BaPbj.xBixOg, and which shows good promise is the use of laser evaporation methods (40). Since the compound is efficiently transported stoichiometrically from the target to the substrate at a high rate and does not require a vacuum, this method may be superior to sputtering techniques. 

The thermal instability of Baj.xKxBiOj compounds makes it desirable to utilize low temperature deposition techniques. Use of a three cell evaporation source coupled with oxygen, ionized by an electron cyclotron resonance source and accelerated toward the 

Techniques utilizing spray on of precursors or chemical vapor deposition offer considerable competition as cost effective methods of producing films and should be pursued. 

PPV and its derivatives are conventionally used in the form of thin films operating as active layers in LEDs, photodetectors, and other optoelectronic devices. An important characteristic of devices constructed with PPV is that they operate with the polymer layer submitted to high electric field strengths. To permit device operation at low voltages, on the order of a few volts, the polymer film thickness is reduced to around 10 run. The production of high-quality polymer thin films constitutes, for these reasons, an important step in the device construction process. 

Nuclear magnetic resonance (NMR) spectroscopy ( H, and other nuclei) is an extremely powerful analytical technique capable of providing unequivocal proof of a compound structure, but is usually applied to soluble materials. An interesting example in which this method provided the molecular structure, as well as information about conformations and molecular dynamics, for over 20 soluble n-alkoxy-substituted phenylene vinylene oligomers has been described [95]. 

Solid-state cross-polarization magic-angle spinning 

The method used for the preparation of thin films of PPV or its derivatives depends on the specific potymer. For those that present high solubility in common organic solvents, very simple procedures, such as casting, doctor-blade technique [98], or spin-coating of the polymer solution with further solvent evaporation can be used. In the case of spin-coating, the film morphology is sensitive to the solvent evaporation rate, density, viscosity, polarity, and solubility during the process [99]. 

For insoluble potymers, such as PPy an elaborate strategy for film production must be used. The most common is the preparation of the film using the soluble precursor sulfonium polyelectrolyte, with further conversion to PPV. This strategy has the advantage that it permits the use of the casting, doctor-blade, or spin-coating techniques for film deposition, but needs a conversion step, which in most of the cases is based on thermal annealing of the fitoi in a vacuum or inert atmosphere, at temperatures up to 300°C [75] (see also Section 2.2). 

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Both anatase and mtile are broad band gap semiconductors iu which a fiUed valence band, derived from the O 2p orbitals, is separated from an empty conduction band, derived from the Ti >d orbitals, by a band gap of ca 3 eV. Consequendy the electrical conductivity depends critically on the presence of impurities and defects such as oxygen vacancies (7). For very pure thin films, prepared by vacuum evaporation of titanium metal and then oxidation, conductivities of 10 S/cm have been reported. For both siugle-crystal and ceramic samples, the electrical conductivity depends on both the state of reduction of the and on dopant levels. At 300 K, a maximum conductivity of 1 S/cm has been reported at an oxygen deficiency of... 

Thin-film solid electrolytes in the range of lpm have the advantage that the material which is inactive for energy storage is minimized and the resistance of the solid electrolyte film is drastically decreased for geometrical reasons. This allows the application of a large variety of solid electrolytes which exhibit quite poor ionic conductivity but high thermodynamic stability. The most important thin-film preparation methods for solid electrolytes are briefly summarized below. 

Glad [37] studied the micro deformations of thin films prepared from DGE-BA/MDA by electron microscopy. His results are also shown in Fig. 7.5. The deformation of the sample with high strand density was small and consequently its image in the EM rather blurred. Therefore, the result on Mc = 0.5 kg/mol should perhaps have been omitted. 

Aylett, B. J., and Tannahill, A. A., Chemical Vapour Deposition of Metal Silicides from Organometallic Compounds with Silicon-Metal Bonds, SIRA Int. Seminar on Thin Film Preparation and Processing Technolgy, Brighton, UK (March 1985)... 

Soft metals such as In, Ag, Sn, Pb, and Au can lead to reasonably low friction coefficients, when used as solid lubricants, due to their low shear strength. The metals were generally applied as thin films prepared by the vacuum deposition process. Especially, in applications to the high temperature conditions where liquid lubricants fail due to the evaporation, the thin films of soft metals can provide effective protection to the surfaces in sliding. 

Bouroushian M, Loizos Z, Spyrellis N, Mamin G (1997) Hexagonal cadmium chalcogenide thin films prepared by electrodeposition from near-boihng aqueous solutions. Appl Surf Sci 115 103-110... 

Loizos Z, Spyrehis N, Mamin G, Pottier D (1989) Semiconducting CdSexTei x thin films prepared by electrodeposition. J Electroanal Chem 269 399-410... 

Torimoto T, Nagakubo S, Nishizawa M, Yoneyama H (1998) Photoelectrochemical properties of size-quantized CdS thin films prepared by an electrochemical method. Langmuir 14 7077-7081... 

Herrero J, Ortega J (1988) n-Type ln2S3 thin films prepared by gas chalcogenization of metalhc electroplated indium Photoelectrochemical characterization. Sol Energy Mater 17 357-368... 

Castro RJ, Cabrera CR (1997) Photovoltammetry and surface analysis of MoSea thin films prepared by an intercalation-exfoliation method. J Electrochem Soc 144 3135-3140... 

An experiment has shown that thin films prepared of various materials (Co, C03O4, Ag, Ti02, ZnO) feature C>2( Aj ) sensitivity. The highest sensitivity, 2 to 3 orders of magnitude above the sensitivity of calorimetric methods, is featured by the film prepared of partially reduced zinc oxide. During interaction with such films, the 02( ) behave as... 

An example of this process of data analysis is provided by the work of Yubero et al. (2000), who studied the structure of iron oxide thin films prepared at room temperature by ion beam induced chemical vapour deposition. Such films find important applications because of their optical, magnetic, or magneto-optical properties. They were produced by bombardment of a substrate with Oj or Oj + Ar+ mixtures, and Figure 4.15 shows RBS spectra of two iron oxide thin films prepared on a Si substrate by each of these bombardment methods. 

Figure 4.15. RBS characterisation of iron oxide thin films prepared with ion bombardment with (a) Oj or (b) Oj + Ar+ mixture. Dots raw data. Full lines RUMP simulations. (Reproduced by permission of...

Tanahashi I, Manabe Y, Tohda T, Sasaki S, Nakamura A (1996) Optical nonlinearities of Au/Si02 composite thin films prepared by a sputtering method. J Appl Phys 79 1244-1249... 

Fouad, O.A., Ismail, A.A., Zaki, Z.I. and Mohamed, R.M. (2006) Zinc oxide thin films prepared by thermal evaporation deposition and its photocatalytic activity. Applied Catalysis B Environmental, 62, 144-149. 

Coleman and Sivy also used an infrared transmission cell to undertake degradation studies under reduced pressure on a series of poly(acrylonitrile) (ACN) copolymers [30-33]. Thin films prepared from a polymer were mounted in the specially designed temperature-controlled cell mounted within the infrared spectrometer. The comparative studies were made on ACN copolymers containing vinyl acetate [30,32], methacrylic acid [30,31] and acrylamide [30,33]. The species monitored was the production of the cyclised pyridone structure. This was characterised in part by loss of C=N stretch (vC = N) intensity at 2,240 cm-1 accompanied by the appearance and increase in intensity of a doublet at 1,610/1,580 cm-1. 

Bose, F., Ayral, A., Albouy, P.A., Datas, L. and Guizard, C. (2004) Mesostructure of anatase thin films prepared by mesophase templating. Chemistry of Materials, 16 (11), 2208-2214. 

There is some need for new pH indicators with improved characteristics which allow also covalent binding. P. Makedonski report about new kind of reactive azo dyes and their application as reversible pH sensors35. They prepare a new pH indicating sensors based on thin films prepared from azo dyes that are covalently bonded by an acetal linkage to a vinylalcohol ethylene copolymer (Figure 7). The absorption spectra of the polymer bond... 

An overview of the precursors, process chemistry, and relative advantages and disadvantages of the three principal methods of inorganic electronic thin film preparation is shown in Table 2.1. Generally, sol-gel methods offer the greatest control over the nature of the solution precursor species, but they have involved... 

The above methods represent the most commonly employed methods for inorganic electronic thin film preparation. A variety of other methods, including Pechini,21 citrate,86 nitrate,23 and aqueous processes87 have also been used. For a discussion of these methods, the reader is referred to Refs. 5 through 12, which highlight these methods for the preparation of various electronic ceramic materials. 

Figure 2.10. Variations in refractive indices of zirconia thin films prepared with the drying control agent, diethanolamine (DEA), and using three different heating ramp rates.

Figure 2.15. (a) ORTEP structure of Ti02 precursor [(THME TUOPr fio] synthesized for use in thin-film preparation and (b) molecular dynamics simulation of the same precursor. [Reprinted with permission from Ref. 82. Copyright 1995 American Chemical Society.] (See color insert.)... 

Ousi-Benomar, W. Xue, S. S. I. cssard, R. A. Singh, A. Wu, Z. L. Kuo, P. K. 1994. Structural and optical characterization of BaTi03 thin films prepared by metal-organic deposition from barium 2-ethylhexanoate and titanium dimethoxy dineodecanoate. J. Mat. Res. 9 970-979. 

Haertling, G. H. 1991. PLZT thin films prepared from acetate precursors. Ferro. 116 51-63. 

Kazmerski, L. L. Ayyagari, M. S. Sandborn, G. A. 1975. Copper indium sulfide (CuInS2) thin films. Preparation and properties. J. Appl. Phys. 46 4865 869. 

Valyomana, A. G. Sajeev, T. P. 1991. Photoconductivity studies of CuInSe2 thin films prepared by the chemical bath deposition technique. Physica Status Solidi A 127 K113-K116. 

Zeenath, N. A. Pillai, P. K. V. Bindu, K. Lakshmy, M. Vijakakumar, K. P. 2000. Study of trap levels by electrical techniques in p-type CuInSe2 thin films prepared using chemical bath deposition. J. Mater. Sci. 35 2619-2624. 

Bindu, K. Lakshmi, M. Bini, S. Sudha Kartha, C. Vijayakumar, K. P. Abe, T. Kashiwaba, Y. 2002. Amorphous selenium thin films prepared using chemical bath deposition Optimization of the deposition process and characterization. Semicond. Sci. Technol. 17 270-274. 

Izu, N. Murayama, N. Shin, W. Matsubara, I. Kanzaki, S. 2004. Resistive oxygen sensors using cerium oxide thin films prepared by metal organic chemical vapor deposition and sputtering. Jpn. J. Appl. Phys. 43 6920-6924. 

Jimenez-Gonzalez, A. Nair, P. K. 1995. Photosensitive ZnO thin films prepared by the chemical deposition method SILAR. Semicond. Sci. Technol. 10 1277-1281. 

Jimenez-Gonzalez, A. Suarez-Parra, R. 1996. Effect of heat treatment on the properties of ZnO thin films prepared by successive ion layer adsorption and reaction (SILAR)./. Cryst. Growth 167 649-655. 

Qiu, J. Jin, Z. Wu, W. Xiao, L.-X. 2006. Characterization of CuInS2 thin films prepared by ion layer gas reaction method. Thin Solid Films 510 1-5. 

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