Structure Of Amorphous Thin Films Research Articles

Ultrawide bandgap high near ultraviolet transparency amorphous Sn–Al co-doped ZnO thin films

Transparent amorphous Sn–Al co-doped ZnO thin films (a-SAZO) were prepared by sol-gel spin-coating technique. Sn was inserted with a constant concentration of 2 at.%, and Al was inserted with different concentrations of 1, 2, 3, 4, and 5 at.%. X-ray diffraction patterns indicate that the samples are amorphous. UV-visible spectrometry shows that a-SAZO thin films are a combination of two different amorphous phases; the dominant amorphous phase tends to simulate the amorphous feature and the ultrawide bandgap of the glass substrate, whereas the minor amorphous phase tends to take its proper amorphization and bandgap. The appearance of the dominant amorphous phase is due to the effect of the amorphous glass substrate leading to high near ultraviolet transparency and ultrawide bandgap in the range of 4.00–4.03 eV. The minor amorphous phase shows very low near ultraviolet transparency and bandgap from 3.08 to 3.16 eV. Thus, the control of the amorphous structure of thin films allows attaining the desired near ultraviolet transparency and bandgap. The lowest resistivity was found 6.71×10−3Ω cm for Sn 2 at.% - Al 5 at.% concentration. Amorphous tin-aluminum zinc oxide (a-SAZO) with low resistivity can alternate amorphous indium-gallium zinc oxide (a-IGZO).

Hard x-ray methods for studying the structure of amorphous thin films and bulk glassy oxides

High-energy photon diffraction minimizes many of the corrections associated with laboratory x-ray diffractometers, and enables structure factor measurements to be made over a wide range of momentum transfers. The method edges us closer toward an ideal experiment, in which coordination numbers can be extracted without knowledge of the sample density. Three case studies are presented that demonstrate new hard x-ray methods for studying the structure of glassy and amorphous materials. First, the methodology and analysis of high-energy grazing incidence on thin films is discussed for the case of amorphous In2O3. The connectivity of irregular InO6 polyhedra are shown to exist in face-, edge- and corner-shared configurations in the approximate ratio of 1:2:3. Secondly, the technique of high-energy small and wide angle scattering has been carried out on laser heated and aerodynamically levitated samples of silica-rich barium silicate (20BaO:80SiO2), from the single phase melt at 1500 oC to the phase separated glass at room temperature. Based on Ba–O coordination numbers of 6 to 7, it is argued that the although the potential of Ba is ionic, it is weak enough to cause the liquid–liquid immiscibility to become metastable. Lastly, high-energy small and wide angle scattering has also been applied to high water content (up to 12 wt.%) samples of hydrous SiO2 glass quenched from 1500 oC at 4 GPa. An increase of Si1–O2 correlations at 4.3 Å is found to be consistent with an increase in the population of three-membered SiO4 rings at the expense of larger rings.

Morphological and optical properties induced by ultraviolet radiation of a thiadiazole derivative

CThB amorphous thin films were synthesized by thermal evaporation technique. The amorphous structure of thin films was investigated by X-ray diffraction technique (XRD). The surface morphology of CThB thin films were analyzed by atomic force microscopy (AFM). The optical constants such as refractive index, n, the absorption index, k, and the absorption coefficient, α for as-deposited and UV—irradiated thin films were determined by spectrophotometric measurements of transmittance (T) and reflectance (R) at normal light incidence of wavelength in range (200–2500) nm. The absorption spectrum of CThB shows two absorption bands in UV region of spectra ascribed to n → π* orbital molecular transition. The results denote that UV—irradiation has no effect on the type of electron transition. Optical measurement of CThB as—deposited and UV- irradiated thin films showed normal dispersion of refractive index, n at λ > 750 nm and anomalous dispersion at λ < 750 nm. Some of dispersion parameters such as the high-frequency dielectric constant (e∞), the lattice dielectric constant (eL), the dispersion energy (Ed), the oscillator energy (Eo) and ratio of the free charge carrier concentrate to effective mass (N/m*) were calculated. The optical functions as the real (e1), imaginary (e2) parts of the dielectric constant were estimated and their response to UV—irradiation was discussed. The effect of UV—irradiation on optical energy gap $${E}_{g}^{\text{ind}}$$ with respect of exposure time was estimated. The value of the band gap was found to be 2.5 eV. The width of the localized states was found to be 0.3 eV and was increased upon irradiation.

Infrared phonon modes and local structure of amorphous and crystalline LaLuO3 thin films

The infrared phonon modes and local structure of amorphous and crystalline LaLuO3 thin films were studied by infrared spectroscopy and X-ray absorption fine structure (XAFS). The infrared spectroscopy shows that the crystalline thin film keeps the main infrared phonon modes and preserves the static dielectric constant as crystal bulk sample. But the infrared phonon modes of amorphous thin film reduce and cause the static dielectric constant to decrease. The result is closely related to the local structure as revealed by XAFS. The crystalline thin film has the similar local structure as crystal bulk sample, while the amorphous thin film presents obvious change. The different local structure of the amorphous thin film results in the change of phonon modes and static dielectric constant.

Electronic and atomic structure of amorphous thin films with high-resolution XPS: Examples of applications & limitations

The use of high resolution X-ray photoelectron spectroscopy to study chalcogenide glass thin films is analyzed. It is shown that the method is an effective tool to explore different chemical environments in the films and control chemical composition of the surface. Examples of the method applications such as kinetics study of induced silver dissolution in the thin films and investigation of oxidation on the surface of the thin film are presented. Limitations of the method are shown on the example of photoinduced structural transformations in chalcogenide glass thin films.

Electrochemical capacitive properties of spray-pyrolyzed copper-ferrite thin films

Abstract We report on the synthesis of copper-ferrite (CuFe 2 O 4 ) thin films with tiny grain size (150 A) by a spray-pyrolysis method, which may be suitable for supercapacitor applications. The films show specific capacitance (SC) value of 4 F/g, and their redox reaction active sites are investigated by calculating inner and outer charges. Densely compact surface morphology and calculated results, i.e., total charge and redox active sites show that the degree of ion diffusion into CuFe 2 O 4 matrix is dependent on the porous and amorphous structure of thin films.

Adsorbate-induced changes in the structure of amorphous thin films of ice

The effect of adsorption of thiophene on the infrared spectra of thin amorphous ice films deposited on Pt(111) is studied using reflection-absorption infrared spectroscopy (RAIRS). The changes within the RAIR spectra in the range of the O–H-stretching band system upon adsorption depend on the structure of the ice films and the temperature at which the thiophene is deposited. Preferred binding at the ice surface to sites that are most likely identical with dangling-H groups occurs only if adsorbate mobility is sufficiently high. Otherwise, random film growth is observed, i.e., formation of multilayer islands before the first layer of thiophene on ice is completed. The adsorbate-induced changes within the O–H-stretching band system of the ice films are different for these two situations. Binding to dangling-H sites is shown to influence more than the uppermost layer of the ice, whereas random deposition has an effect only on surface vibrational modes. PACS Nos.: 68.43Fg, 62.35Ja

The structural characterization of amorphous thin films and coatings in their as-deposited state using x-rays at shallow angles of incidence

We demonstrate the method of x-ray diffraction at shallow angles of incidence, using the intrinsically highly collimated x-ray beam generated by a synchrotron source, to study the atomic-scale structure of amorphous thin films and coatings in their as-deposited (i.e., on-substrate) state. As the incident angle is decreased, scattering from the film/coating can be isolated as contributions from the substrate are reduced. Systems studied include chemical vapor deposition (CVD) diamond films deposited onto both silicon and steel substrates, where evidence of an interfacial region between the film and silicon wafer has been observed, but we focus on a range of amorphous films/coatings (mixed TiO2 : SiO2 sol-gel spun films, hydrogenated carbon films and “glassy” carbon coatings, silicon: germanium semiconducting films and alumina coatings). The data are used both to comment upon the systems studied and to elucidate the potential, and the limitations, of the experimental method.

From amorphous to nanocrystalline germanium— the role of twinning studied by high resolution electron microscopy

The structure of amorphous thin films of germanium obtained by physical vapor deposition at temperatures well below one half of the melting temperature has been studies by high resolution electron microscopy. Crystallization of the films was achieved during deposition by appropriate heating of the substrate or after deposition by annealing at elevated temperature, respectively. Therewith, very small crystallites extending from nearly 3 to about 25 nm in size are formed, at which twinning is frequently observed. In particular, multiply-twinned structures with five-fold twin junctions occur at various stages of the crystallization. The temperature at which the crystallization starts can be markedly lowered, and the crystallinity of the films obtained can be substantially increased by capping the crystalline substrates with amorphous carbon layers. A combination of substrate capping and post-deposition annealing leads to almost completely crystalline films which exhibit a heavily twinned structure.

An in situ x-ray diffraction method for the structure of amorphous thin films using shallow angles of incidence

A technique for the structural characterization of thin amorphous films employing synchrotron radiation parallel beam x-ray optics at grazing angles of incidence is detailed. At incident angles near to the critical angle for total external reflection, sampling of specimens may be achieved via the evanescent mode. The parallel beam geometry allows the use of a technique in which a 2θ detector, incorporating a parallel plate collimator, scans diffraction data for a given incident angle. For a specified wavelength, the incident angle chosen will determine the penetration of the radiation into the sample (∼10–1000 Å). The data must be corrected for significant peak shifting resulting from x-ray refraction, as well as for the effects associated with conventional θ:2θ scans. Preliminary data resulting from the first application of this technique to amorphous hydrogenated silicon:carbon thin films, deposited onto crystalline silicon substrates, will be presented and discussed. Conventional θ:2θ powder diffraction data will also be presented as a comparative standard.

Structural and electrical properties of lithio-borate solid electrolyte thin films

The effect of deposition conditions on the growth structure of amorphous thin films of lithio-borate solid electrolyte was investigated by means of infrared absorption and complex impedance spectroscopies. Thin films of vitreous solid electrolyte in the alkali-oxide/borate-oxide system were grown by vacuum quasi-flash evaporation. The complex impedance measurements of the thin solid films in the sandwich geometry show a high ionic conductivity. Incorporation of lithium salt dopant has been also studied. The structure was determined using infrared absorption spectra which are sensitive to deposition conditions and to the amount of lithium incorporated.

Structure of amorphous thin films of WO 3 and MoO 3

Short range and medium range order of WO3 and MoO3 thin films have been investigated. The amorphous structure of these thin films has closely related topology. It is found that there is a temperature range where these materials form microcrystalline state of WO3 and MoO3. X-ray diffraction and Raman scattering data show that the structure of MoO3 microcrystals is different from the structure of bulk MoO3.

Structural investigations of amorphous transition element films

Abstract A randomly connected array of slightly irregular tetrahedra is shown to be highly successful in representing the structure of amorphous thin films of the transition metals. A notable feature of the present model is that it can also be used to represent the liquid state. The latter result is achieved without any modification of the actual model building technique, and requires only an intro- duction of simple thermal fluctuations and a reduction in regularity of the tetrahedra composing the model. Representation of the amorphous solid structure by a totally random or microcrystalline model is also considered, the latter being unsuccessful even when interfacial effects were taken into account.