Characterization, film functional

Because acoustic wave devices are sensitive and respond rapidly, they are ideally suited for real-time monitoring of chemical and physical systems. As discussed in the introduction to this chapter, thin films represent a growing industrial and technological concern for a variety of applications. The use of acoustic devices to characterize the physical properties of these films has been dealt with in the previous sections. Here we describe how these devices can be used to monitor film formation or dissolution processes, or to observe and characterize film properties as a function of time (similar to the monitoring of diffusion in polymers described in Section 4.2.2). 

A somewhat different behavior is found for the initial rate of growth of a diffusion layer in a flow where inertia is absent, as in the steady fully developed flow in a pipe or channel or in a fully developed thin film falling under gravity. To characterize this functional dependence, we must first define the velocity field within which the diffusion layer grows. 

Navarro, A.-E., R Pages, C. Moustrou, H. Brisset, N. Spinelli, C. Chaix, and B. Mandrand. 2005. Characterization of PEDOT film functionalized with a series of automated synthesis ferrocenyl-containing oligonucleotides. Tetrahedron 61 3947-3952. 

Scherson DA, Palencsar A, Tohnachev Y, Stefan I (2008) Transition metal macrocycles as electrocatalysts for dioxygen reduction. In Alkire RC, Kolb DM, Lipkowski J, Ross PN (eds) Electrochemical surface modification thin films, functionalization and characterization. Wiley-VCH Verlag GmbH Co. KGaA, Weinheim, Germany... 

ALkire RC, Kolb DM, Lipkowski J, Ross P (2008) Electrochemical surface modification thin films, functionalization and characterization. Wiley... 

The experimental aspects of the performance of in situ FTIR measurements are described in Refs. 33 and 34. Figure 2 shows a typical layout of cells for an in situ external reflectance mode (e.g., SNIFTIRS type measurements) and internal reflectance modes, multiple internal reflectance, ATR, and single internal reflectance mode. " The use of the ATR mode requires crystals, which have a high refractive index (> 2). The common materials that have such a high refractive index and are transparent to the IR in the 500-4000 cm range, which is the most useful optical window for the characterization of functional groups, are KRS-5, ZnSe and germanium (R.I. = 2.37, 2.4 and 4, respectively). The use of the ATR mode requires the facilities of the metal film deposition under UHV. 

In Chapter 4, we discussed an important 2-D nanoarchitecture - thin films. As long as the thickness is <100 nm, these are properly classified within the nanomaterials umbrella. Though spin-coating may be able to afford thin films of this overall thickness, these types of coatings are generally deposited using vapor deposition techniques (PVD, CVD, and ALD). The current buzz related to 2-D nanomaterials is related to the synthesis, characterization, and functionalization of the theoretical sub-unit of carbon nanotubes - graphene sheets. 

The ease of sample handling makes Raman spectroscopy increasingly preferred. Like infrared spectroscopy, Raman scattering can be used to identify functional groups commonly found in polymers, including aromaticity, double bonds, and C bond H stretches. More commonly, the Raman spectmm is used to characterize the degree of crystallinity or the orientation of the polymer chains in such stmctures as tubes, fibers (qv), sheets, powders, and films... 

The Metravib Micromecanalyser is an inverted torsional pendulum, but unlike the torsional pendulums described eadier, it can be operated as a forced-vibration instmment. It is fully computerized and automatically determines G, and tan 5 as a function of temperature at low frequencies (10 1 Hz). Stress relaxation and creep measurements are also possible. The temperature range is —170 to 400°C. The Micromecanalyser probably has been used more for the characterization of glasses and metals than for polymers, but has proved useful for determining glassy-state relaxations and microstmctures of polymer blends (285) and latex films (286). 

The principal applications of REELS are thin-film growth studies and gas-surface reactions in the few-monolayer regime when chemical state information is required. In its high spatial resolution mode it has been used to detect submicron metal hydride phases and to characterize surface segregation and difRision as a function of grain boundary orientation. REELS is not nearly as commonly used as AES orXPS. 

The chemical and electronic properties of elements at the interfaces between very thin films and bulk substrates are important in several technological areas, particularly microelectronics, sensors, catalysis, metal protection, and solar cells. To study conditions at an interface, depth profiling by ion bombardment is inadvisable, because both composition and chemical state can be altered by interaction with energetic positive ions. The normal procedure is, therefore, to start with a clean or other well-characterized substrate and deposit the thin film on to it slowly at a chosen temperature while XPS is used to monitor the composition and chemical state by recording selected characteristic spectra. The procedure continues until no further spectral changes occur, as a function of film thickness, of time elapsed since deposition, or of changes in substrate temperature. 

In this review the definition of orientation and orientation functions or orientation averages will be considered in detail. This will be followed by a comprehensive account of the information which can be obtained by three spectroscopic techniques, infra-red and Raman spectroscopy and broad line nuclear magnetic resonance. The use of polarized fluorescence will not be discussed here, but is the subject of a contemporary review article by the author and J. H. Nobbs 1. The present review will be completed by consideration of the information which has been obtained on the development of molecular orientation in polyethylene terephthalate and poly(tetramethylene terephthalate) where there are also clearly defined changes in the conformation of the molecule. In this paper, particular attention will be given to the characterization of biaxially oriented films. Previous reviews of this subject have been given by the author and his colleagues, but have been concerned with discussion of results for uniaxially oriented systems only2,3). 

One of the apparent results of introducing couple stress is the size-dependent effect. If the problem scale approaches molecular dimension, this effect is obvious and can be characterized by the characteristic length 1. The size effect is a distinctive property while the film thickness of EHL is down to the nanometre scale, where the exponent index of the film thickness to the velocity does not remain constant, i.e., the film thickness, if plotted as a function of velocity in logarithmic scale, will not follow the straight line proposed by Ham-rock and Dowson. This bridges the gap between the lubrication theory and the experimental results. 

X-ray diffraction has been applied to spread monolayers as reviewed by Dutta [67] and Als-Nielsen et al. [68], The structure of heneicosanoic acid on Cu and Ca containing subphases as a function of pH has been reported [69], as well as a detailed study of the ordered phases of behenic acid [70], along with many other smdies. Langmuir-Blod-gett films have also been studied by x-ray diffraction. Some recent studies include LB film structure just after transfer [71], variations in the structure of cadmium stearate LB films with temperature [72], and characterization of the structure of cadmium arachidate LB films [73], X-ray [74,75] and neutron reflectivity [76,77] data on LB films can be used to model the density profile normal to the interface and to obtain values of layer thickness and roughness. 

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