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Thin film materials are the key elements of continued technological advances made in the fields of optoelectronic, photonic and magnetic devices. Thin film studies have directly or indirectly advanced many new areas of research in solid state physics and chemistry which are based on phenomena uniquely characteristic of the thickness, geometry and structure of the film. The processing of materials into thin films allows easy integration into various types of devices. Thin films are extremely thermally stable and reasonably hard, but they are fragile. On the other hand organic materials have reasonable thermal stability and are tough, but are soft. Thin film mechanical properties can be measured by tensile testing of freestanding films and by the micro beam cantilever deflection technique, but the easiest way is by means of nanoindentation. Optical experiments provide a good way of examining the properties of semiconductors. Particularly measuring the absorption coefficient for various energies gives information about the band gaps of the material. Thin film materials have been used in semiconductor devices, wireless communications, telecommunications, integrated circuits, rectifiers, transistors, solar cells, light-emitting diodes, photoconductors and light crystal displays, lithography, micro- electromechanical systems (MEMS) and multifunctional emerging coatings, as well as other emerging cutting technologies.

Organic and inorganic relaxor ferroelectrics used for electrocaloric effect (ECE) applications are introduced. Relaxor ferroelectrics offer several advantages for ECE devices, e.g., infinite states without applying electric field, field-induced large polarization, no-hysteresis of heating and cooling, small-hysteresis polarization loss, room temperature phase transition, and broad temperature range. The ECE in relaxor ferroelectrics under a high electric field can be described using a theory similar to that for first-order phase transition materials. Large ECE was observed directly in high-energy electron irradiated poly(vinylidene fluoride–trifluoroethylene) (P(VDF–TrFE)) 68/32 mol% copolymers, P(VDF–TrFE–CFE) (CFE-chlorofluoroethylene) 59.2/33.6/7.2 mol% terpolymers, P(VDF–TrFE–CFE)–P(VDF–CTFE) (CTFE-chlorotrifluoroethylene) 95/5 wt% terpolymer blended films, and (PbLa)(ZrTi)O₃ (PLZT) ceramic thin films. ECE reported in Pb(Sc_1/2Ta_1/2)O₃ (PST), Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PMN–PT) thin films is also summarized. Finally, the perspective of ECE devices is illustrated.

Gold and copper thin films are widely used in microelectromechanical system (MEMS) and nanoelectromechanical system (NEMS) devices. Nanoindentation has been developed in mechanical characterization of thin films in recent years. Several researchers have examined the effect of surface roughness on nanoindentation results. It is proved that the surface roughness has great importance in nanoindentation of thin films. In this paper, the surface topography of thin films is simulated using the extracted data from the atomic force microscopy (AFM) images. Nanoindentation on a rough surface is simulated using a three-dimensional finite-element model. The results are compared with the results of finite-element analysis on a smooth surface and the experimental results. The results revealed that the surface roughness plays a key role in nanoindentation of thin films, especially at low indentation depths. There was good compatibility between the results of finite-element simulation on the rough surface and those of experiments. It is observed that on rough films, at low indentation depths, the geometry of the location where the nanoindentation is performed is of major importance.

We study a thin-shell limit of micromagnetic energy for soft small ferromagnets. The relations between thickness of the magnet t, diameter l and magnetic exchange length w are t/l → 0 and tl/w² ≲ 1. We prove a Γ-convergence of the original 3D problem to a nonlocal 2D problem.

In this research, gas sensing characteristics of undoped and zinc-doped molybdenum trioxide (MoO${}_3)$ thin films toward ethanol vapor were investigated. Thin films were deposited using low cost and simple technique of spray pyrolysis on top of glass substrates at 450${}^{\circ }$C. Effects of addition of Zn, as an impurity, on the surface morphology, structural and optical properties of MoO₃ thin films were also investigated. X-ray diffraction (XRD) pattern analysis showed that by increasing the amount of impurity, crystal structure changes from orthorhombic $\alpha$-MoO₃ to two new phases of monoclinic $\beta$-ZnMoO₄ and Mo₅O${}_{14}$ reduced phase. Field emission scanning electron microscope (FESEM) images showed that by increasing the amount of impurity up to 5at.%, grain sizes decrease to about 60nm. UV–Vis analysis showed that by increasing the percentage of impurity the band gap of thin films increases. Gas sensing properties of samples were studied at three temperatures of 200${}^{\circ }$C, 250${}^{\circ }$C and 300${}^{\circ }$C toward different concentrations of ethanol vapor. Gas response of 5at.% Zn-doped MoO₃ thin film reached the maximum value of $\sim 84$% when it exposed to 1000ppm of ethanol vapor. Response and recovery times for all samples were reported at different temperatures.

SnO₂–ZnO thin films consisting of nanoscale crystallites were obtained on glass and silicon substrates by solid-phase low-temperature pyrolysis. The synthesized materials were studied by XRD and SEM methods, electrophysical and optical properties were evaluated, as well as the band gap was calculated. It was shown that regardless of the phase composition all films were optically transparent in the visible range (310–1000 nm). The nanocrystallites’ minimum size, the highest activation energy of the conductivity and the smallest band gap calculated for indirect transitions were shown for a thin film 50SnO₂–50ZnO. It was assumed that the band gap decreasing might be attributed to the existence of surface electric fields with a strength higher than 4 × 10⁵ V/cm.

Molecular electronics is a new, exciting and interdisciplinary field of research. The main concern of the subject is to exploit the organic materials in electronic and optoelectronic devices. On the other hand, the Langmuir–Blodgett (LB) film deposition technique is one of the best among few methods used to manipulate materials at the molecular level. In this article, the LB film preparation technique is discussed briefly with an emphasis on its application towards molecular electronics.

Cobalt-doped ZnO films were grown on the glass substrates using sol–gel/spin-coating technique to investigate the effect of annealing on the structural and magnetic properties. The X-ray diffraction (XRD) patterns of the Co-doped ZnO films are dominated by the (002) peak, suggesting an up-standing array of ZnO structure hexagonal (wurtzite) with a good crystalline quality, however, the secondary phases of Co₃O₄ and Co are present in the samples. With the annealing temperature increased, the secondary phases tend to disappear completely and the intensity of the (002) peak increased, indicating a high crystallinity of the samples. For the ZnO majority phase, the lattice constant ($c)$ decreases (from 5.232 $\mathrm{\text{Å}}$ to 5.224 $\mathrm{\text{Å}}$), while the crystallite size increases (from 22.040nm to 24.018nm) as the annealing temperature varies from 380^∘C to 600^∘C. Significant changes in the dislocation density ($\delta )$, strain $({\epsilon }_c)$ and stress $({\sigma }_c)$ of the Co-doped ZnO films were also observed, by increasing the annealing temperature. All samples display a ferromagnetic behavior with variations in the saturation magnetization ($M_s=1.31\times 10^{-5}$, $1.19\times 10^{-5}$ and $1.15\times 10^{-5}$ emu/cm${}^3)$ and coercive field ($H_c=82$, 104 and 75 Oe) for the temperatures of 380^∘C, 500^∘C and 600^∘C, respectively. The magnetic behavior of Co-doped ZnO films confirms the exchange interaction between the local spin moments produced by the oxygen vacancy. In addition, the ferromagnetic existence of the samples (380^∘C, 500^∘C and 600^∘C) can be attributed to certain nanoparticles or to the binding of Co${}^{+2}$ ions at the Zn${}^{+2}$ location in the ZnO lattice. Finally, it appears that the ferromagnetism at room temperature found in these films, is consistent with endogenous defects (oxygen vacancies) and magnetic ions insertion along the same lines.

The following sections are included:

• Introduction

• General Considerations
  • Absorption Coefficient and Photon Penetration Depth
  • Escape Depths of Various Yields
  • Instrumentation

• Applications
  • Ni/Si(100): Evolution of Nickel Silicide Thin Films
    • General Considerations
    • Ni and Si K edge XANES for the Blanket Films
    • Ni and Si L edge XANES for the Blanket Films and Submicron Lines
  • Al Diffusion Through a TiN_x Diffusion Barrier on Si(100)
    • General Considerations
    • Al K edge: TEY
    • Al K edge: FLY
    • Al L edge TEY and FLY
  • Porous Silicon
    • General Considerations
    • Synchrotron Radiation Induced Luminescence
    • XEOL and Optical XAFS at the Si K edge and the Origin of Luminescence from PS
    • XEOL and Optical XAFS at the Si L_3,2 edge
    • A MCMD Study of the Distribution of Luminescence Sites

• Summary

• Acknowledgments

• References

• Appendix: Recent Publications Using Multidetection X-ray Absorption Spectroscopy (MD-XAS) Techniques

There has been recent renewed interest in electrocapillary and electrowetting phenomena given its potential for microfluidic actuation and manipulation. Different approaches, in which a variety of electrode configurations have been adopted, however, have dominated the developments in this field. These different approaches have given rise to rich and varied behavior, which has often led to some overlap and confusion in the literature. In this article, we delineate the different observations and elucidate the relationship between these phenomena by re-stressing classical concepts and examining their limitations. Particular emphasis is placed on the distinction between static and spontaneous electrowetting. In the former, a static change in the liquid–solid macroscopic contact angle results when a dielectric film-coated planar plate electrode is employed. In the latter, a spontaneous thin fron-t-running electrowetting film is pulled out ahead of the macroscopic drop with the use of planar parallel line electrodes. This dynamically evolving electrowetting film advances much faster than the macroscopic drop itself and behaves in a self-similar manner analogous to gravity spreading films.

We present here an analysis of the regularity of minimizers of a variational model for epitaxially strained thin-films. The regularity of energetically-optimal film profiles is studied by extending previous methods and by developing new ideas based on transmission problems. The achieved regularity results relate to both the Stranski-Krastanow and the Volmer-Weber modes, the possibility of different elastic properties between the film and the substrate, and the presence of the surface tensions of all three involved interfaces: film/gas, substrate/gas, and film/substrate. Finally, geometrical conditions are provided for the optimal wetting angle, i.e. the angle formed at the contact point of films with the substrate. In particular, the Young–Dupré law is shown to hold, yielding what appears to be the first analytical validation of such law for a thin-film model in the context of Continuum Mechanics.

Undoped and silver, lithium and cobalt-doped ZnO thin films have been successfully deposited on glass by chemical bath deposition (CBD). The reaction temperature was 50^∘C and the films were annealed at 400^∘C for 4h in a high temperature furnace. UV/VIS spectrum was used to determine optical transmittance, optical band gap ($E_g)$ and absorbance values of Ag:ZnO, Co:ZnO, Li:ZnO and undoped ZnO thin films. Optical band gap ($E_g)$ and absorbance values of undoped ZnO, Ag:ZnO, Co:ZnO and Li:ZnO thin films were found as 0.0158, 0.0064, 0.2638, 0.0956 and 3.24, 3.13, 3.27, 2.96 eV, respectively. Extinction coefficients and refraction indexes of the films were found to be 0.0096, 0.0038, 0.0068, 0.019 (extinction coefficient) and 1.26, 1.14, 1.66, 2.33 (refraction index), respectively. X-ray patterns of undoped ZnO, Ag:ZnO, Co:ZnO and Li:ZnO thin films were confirmed as amorphous.

Deposition of Zinc sulfide (ZnS) thin films on Si (100) and glass substrates has been performed using electron beam evaporation (EBE) method without annealing. Film structure has been analyzed by XRD, while SEM and AFM have been used to explore the films morphology. Raman spectroscopy has been used to confirm film composition. The stoichiometry has been verified by EDX and XPS techniques. XRD patterns indicated that the films possess a polycrystalline cubic structure with orientations along (111) and (220) planes. The crystallinity has been better with film thickness in the 350–1700 nm range while the RMS roughness increases. Optical properties of the grown films were characterized by optical transmittance measurements (UV–Vis). The deduced energy band gap of the films shows a clear reduction from 3.45 eV to 3.36 eV with increasing film thickness. The evolution of refractive index, extinction coefficient, and dielectric constants with thickness has been investigated from transmittance spectra in the 500–1000 nm wavelength range.

The optical constants and thickness of Al-doped ZnO (ZnO:Al(2.5 wt.%)) thin films prepared by high-frequency magnetron sputtering method are determined. ZnO:Al thin films are crystallized in the hexagonal structure from XRD studies. The optical constants and the bandgap of the films under study have been determined. Optical properties (refractive index $n(\lambda )$, absorption coefficient $\alpha (\lambda )$, extinction coefficient $k(\lambda )$, dielectric functions $𝜀(\lambda )$ and optical conductivity $\sigma (\lambda )$) of thin films and thickness $d$ can be determined from the transmission spectrum. The dispersion of the refractive index was explained using a single oscillator model. Single oscillator energy and dispersion energy are obtained from fitting. Optical parameters of the films were determined using the Cauchy, Sellmeier and Wemple models. The increasing value of dispersion parameter for polycrystalline thin films than for single crystals is observed. The fundamental absorption edge position (3.26 eV) in the transmittance spectrum of studied thin films corresponds to the values that are typical for ZnO:Al compound. No significant increase of the bandgap width was revealed by comparing ZnO:Al thin films with the known results of the optical studies of ZnO thin films. Possible reasons of such behavior were analyzed and the influence of bandgap increase on spectral behavior of optical functions are investigated. The material optical parameters such as normalized integrated transmission, zero and high-frequency dielectric constant, density of state effective mass ratio were also calculated.

Zinc oxide $(\mathrm{\text{ZnO}})$, undoped and Al-doped thin films have been synthesized by the ultrasonic spray-assisted chemical vapor deposition (USCVD) system. The films were deposited on glass substrates. The precursor solution was prepared dissolving zinc chloride in distilled water. First, the precursor concentrations were investigated and optimized before studying $\mathrm{\text{Al}}$ doped, after we have studied the $\mathrm{\text{Al}}$-doped influence on $\mathrm{\text{ZnO}}$ films especially optical and electrical properties for use as a transparent conductive oxide (TCO) in solar cell electrodes. The characterizations have been carried out using X-ray diffraction technique, UV-vis spectrophotometry, Hall Effect measurement (ECOPIA), atomic force microscopy (AFM, VEECO Dimension $3100)$ and scanning electron microscopy (SEM). X-ray diffraction (XRD) results showed that $\mathrm{\text{ZnO}}$ and $\mathrm{\text{Al}}$-doped $\mathrm{\text{ZnO (AZO)}}$ films were crystallized in the hexagonal wurtzite structure with $(002)$ orientation. Optical measurements have shown that all films exhibit, along the visible range, high transmittance and that optical band gap depends strongly to $\mathrm{\text{Al}}$-doped concentration. Hall-effect measurement indicates that the highest carrier concentration $(1.2\times {10}^{20}{\text{cm}}^{\mathrm{\text{-3}}})$ and the lowest resistivity $(2.7\times {10}^{-2}\mathrm{\Omega }\text{cm})$ are obtained for the $4\%$ AZO sample. The SEM shows that the microstructures of $\mathrm{\text{ZnO}}$ and $\mathrm{\text{AZO}}$ are homogeneous and the AFM images prove their microcrystallinity with grains orthogonal to the film surface.

This paper presents alternative analysis methodologies to extract the elastic modulus and hardness of the ultra-thin films from nanoindentation load-displacement data, especially when the film thickness is only few hundred nanometers or less. At such film thickness, the conventional analysis methods for nanoindentation usually do not give accurate film properties due to the substrate effect. The new methods are capable to show how to determine the film-only properties and how the substrates affect the nanoindentation measurement, especially for ultra thin films. These methods give accurate results for nanoindentation of various metallic, ceramic and polymeric films. It also reveals the differences between the use of high-resolution nanoindentation set-up and normal nanoindentation set-up on the same films. The relationships between the mechanical properties and film thickness are also discussed.

This paper reports on the fabrication of CuO_x films to be used as hole transporting layer (HTL) in CH₃NH₃PbI₃ perovskite solar cells (PSCs). Ultra-thin CuO_x coatings were grown onto FTO substrates for the first time via aerosol-assisted chemical vapor deposition (AACVD) of copper acetylacetonate in methanol. After incorporating into the PSCs prepared at ambient air, a highest power conversion efficiency (PCE) of 8.26% with HTL and of 3.34% without HTL were achieved. Our work represents an important step in the development of low-cost CVD technique for fabricating ultra-thin metal oxide functional layers in thin film photovoltaics.

Undoped and Mn-doped TiO₂ thin films have been prepared by sol–gel dip-coating technique on glass and silicon substrates. X-ray diffraction studies showed that both TiO₂ and Mn-doped TiO₂ thin films are of anatase phase with (101) as preferential orientation. All films exhibit high transparency ($\sim$80%) over the visible range. The optical bandgap decreases from 3.66eV to 3.52eV due to the extent of electronic states introduced by doping. Infrared transmission spectra showed Ti–O (625cm${}^{-1}$) and Ti–O–Ti (495–436cm${}^{-1}$) bands. Thermal analysis revealed endothermic reactions between 94^∘C and 110^∘C and exothermic reactions between 406^∘C and 443^∘C. The Nyquist plots depicted that equivalent circuit of the films is an $R_{\mathrm{\text{P}}}{C}_{\mathrm{\text{P}}}$ parallel. The resistance $R_{\mathrm{\text{P}}}$ decreases while the capacitance $C_{\mathrm{\text{P}}}$ increases with Mn-doping.

The optical properties of metal-free phtalocyanine (H₂Pc) in thin film form is investigated. X-ray diffractograms of the (H₂Pc) powder show that it has a α-polycrystalline form with a monoclinic structure. The thermal evaporation of (H₂Pc) powder leads to α-polycrystalline films, oriented preferentially to the (001) plane. After annealing at 623 K for two hours, a mixture of α- and β-phases is formed on an amorphous background. The optical properties of (H₂Pc) thin films have been studied using spectrophotometeric measurements of transmittance and reflectance in the range 200–2200 nm for a different film thickness. The refractive index and the absorption index show independence on the film thickness. The refractive index shows anomalous dispersion in the region of the fundamental absorption edge. The absorption measurements show the characteristic splitting of the Q-band and ΔQ is obtained as 0.22 eV. The absorption coefficient in the absorption region reveals indirect transitions. The fundamental and the onset energy gap are determined as 2.74 eV and 1.55 eV, respectively.

We present a review of the recent progresses in solution processing graphene thin films and highlight some of the uses of graphene and graphene thin films in the construction of organic solar cells. We demonstrate a simple phenomenological model to describe the relationship between sheet conductivity and transmittance in graphene films with good agreement to all of the data found in the literature. We show that graphene thin films have been proven useful in the construction and improvement of organic solar cells not only as a replacement electrode, but also as an active acceptor material, or as a counter electrode when integrated into a conducting polymer matrix.