Growth Of Crystalline Thin Films Research Articles

Influence of Vanadium substitution on electronic, thermoelectric and optical response of Cu2O

Cu2O semiconductor attained much research interest due to excellent electronic and optical response. In this work, Vanadium-doped Cu2O compositions were studied for electronic, thermoelectric, and optical response using density functional theory. The thin films were experimentally fabricated using the chemically derived spin coating method. The x-ray diffraction analysis revealed the growth of crystalline thin films with cubic structure having space-group 224-Pn-3m. The scanning electron micrographs exhibit the uniform grain growth with well-defined grain boundaries for pure Cu2O films. Density of states spectra display the maxima for O-2p and Cu-3d while V-3d states occupied the conduction band. The value of the experimental band gap for pure Cu2O is estimated as 2.02 eV and found to decrease with V-doping. The Seebeck coefficient and specific heat are found to increase with the increment in V-doping content due to thermal fluctuations. A steady increase is observed in real epsilon with the increase in energy and dopant concentration.

Preparation and Characterization of Crystalline Silicon by Electrochemical Liquid-Liquid-Solid Crystal Growth in Ionic Liquid.

The electrodeposition at low temperature for the direct growth of crystalline thin films without any templating agent in ionic liquid (IL) is a relatively new electrochemical synthetic strategy. This work studied the role of the deposition temperature, deposition time, and different working electrodes in the electrodeposition of crystalline Si thin films from the byproduct silicon tetrachloride in IL at low temperature. X-ray diffraction (XRD) revealed that the as-deposited Si films were crystalline at the temperature of 80 °C. Scanning electron microscopy (SEM) and Raman spectroscopy further indicated that the crystalline quality of the as-deposited silicon film was relatively the best when the electrodeposition time reached 1 h at the temperature of 100 °C; excessive electrodeposition would yield amorphous silicon on the surface of the as-deposit crystalline Si, which decreased the crystal quality of the Si film. The SEM and XRD, respectively, revealed that the crystal structure of Si yielded on e-InGa was significantly different from that produced on Ga and more impurities existed in the film. Research on the influence of these parameters on crystallinity and morphological characteristics of Si gives better control over the growth of crystalline Si thin films for specific applications.

Dynamics of faceted thin films formation during vapor deposition

In this study, an anisotropic phase-field model was established to simulate the growth of crystalline thin films during vapor deposition. The formation and evolution of characteristic surface with faceted morphologies were demonstrated, in accordance with the regularly obtained microstructure in the actual experiments. In addition, the influences of deposition parameters, such as the deposition rate and the interfacial energy, on the formation mechanism of the characteristic morphology were also illustrated. While a relatively low surface energy of substrate was regarded, the faceted islands were formed, owing to the anisotropic interfacial energy of thin films. In the condition of a high surface energy of substrate, the layered structures of deposited films were produced, which was corresponding to the Frank–van der Merwe growth mode. As various deposition rates were utilized in the numerical simulations, diverse surface morphologies were developed on the basis of the dominant mechanisms, correlating with the adatom diffusion and the deposition kinetics. According to the calculation results, it was observed that a surface character with flattened morphology was generally driven by the adatom diffusion, while the factor of the deposition kinetics was inclined to roughen the surface of thin films. These numerical simulations enhanced the knowledge of thin film growth and facilitated the progress of the vapor deposition technology for advanced applications.

Atomic/Molecular Layer Deposition of s‐Block Metal Carboxylate Coordination Network Thin Films

We present novel atomic/molecular layer deposition (ALD/MLD) processes for the fabrication of crystalline inorganic-organic coordination network thin films with different s-block elements. Terephthalic acid is employed as the organic precursor. Such thin films could enable for example, next-generation battery, sensor and gas-storage technologies. The deposition processes fulfill the basic principles of ALD/MLD-type growth including the sequential self-saturated gas-surface reactions and atomic/molecular-level control for the film thickness, and yield crystalline thin films in a wide deposition temperature range. Structural characterization of the films is performed by grazing incidence X-ray diffraction (GIXRD) and Fourier-transform infrared (FTIR) spectroscopy. The data do not unambiguously prove but also do not rule out the crystal structures previously reported for the corresponding bulk samples. We moreover demonstrate the growth of crystalline thin films of a new terephthalate material with La as the metal component. Upon humidity treatments the Li, Na, K, Ba, and La terephthalate films remain unaffected while the Mg, Ca, and Sr terephthalate films reversibly absorb water molecules forming well-defined crystalline water-derivative phases.

Structure versus electron effects in the growth mode of pentacene on metal-induced Si(111)-3×3 surfaces

The growth of pentacene films on different metal (Ga, Pb, Bi, Ag) induced Si(111)-(square root(3) x square root(3))R30 degrees surfaces is investigated by scanning tunneling microscopy. On surfaces with high atomic surface roughness, such as GaSi-square root(3), beta-PbSi-square root(3), and alpha-BiSi-square root(3), pentacene forms an initial disordered wetting layer followed by the growth of crystalline thin films. The growth behavior is independent of the metallicity of the substrate surface in this regime. On the other hand, on surfaces with low adatom surface roughness, pentacene molecules form self-organized structures without forming a wetting layer. Moreover, the molecular orientation is critically dependent on the surface metallicity. This work reveals that the growth mode of pentacene on solid surfaces is determined by the combined effects of structural and electronic properties of the substrate.

Crystalline Ice Grown on the Surface of the Ferroelectric Polymer Poly(vinylidene fluoride) (70%) and Trifluoroethylene (30%)

Water ice is observed to order at the copolymer ferroelectric poly(vinylidene difluoride-trifluoroethylene) surface. The successful growth of crystalline thin films of water on these polymer surfaces implicates water to polymer dipole interactions. These ice thin films are sufficiently ordered for experimental identification of the wave vector dependence in the electronic band structure of hexagonal ice. The significant band dispersion, of about 1 eV, suggests strong overlap of molecular orbitals between adjacent water molecules in the ice film. The presence of dipole interactions with adsorbate water is consistent with the possibility of water acting as a spectator to surface ferroelectric transitions in this system.

The mechanism of low temperature deposition of crystalline anatase by reactive DC magnetron sputtering

It has been reported that TiO 2 film deposition by direct current (DC) magnetron reactive sputtering can occur according to the mechanism proposed by the theory of charged clusters (TCC). In the current study, the TCC was used to explain the mechanism of low temperature TiO 2 crystalline thin film growth. Highly oriented anatase thin films were deposited on unheated substrates. The degree of crystallinity of the thin film was found to depend on the cluster size and its crystallinity as well as the charging efficiency in the reactor. Larger clusters tend to be crystalline. These produce amorphous (nanocrystalline) films. Smaller clusters tend to be amorphous and adopt the structure of clusters already deposited to produce an ordered crystalline film. Increasing the substrate-to-target distance increased the cluster size. In addition, the charge density decreased as the target to substrate distance was increased. Clusters of <2 and 3 nm in diameter were observed at a substrate-to-target distance of 50 and 250 mm, respectively, which correspondingly produced crystalline and amorphous films. The DC power level did not appear to have a large effect on the cluster size nor did it affect the degree of crystallinity of the resulting thin film. The main factors affecting whether or not a crystalline film is deposited are the cluster size and the charge density in the reactor.

Analysis of Island Dynamics in Epitaxial Growth of Thin Films

This work is concerned with analysis and refinement for a class of island dynamics models for epitaxial growth of crystalline thin films. An island dynamics model consists of evolution equations for step edges (or island boundaries), coupled with a diffusion equation for the adatom density, on an epitaxial surface. The island dynamics model with irreversible aggregation is confirmed to be mathematically ill-posed, with a growth rate that is approximately linear for large wavenumbers. By including a kinetic model for the structure and evolution of step edges, the island dynamics model is made mathematically well-posed. In the limit of small edge Péclet number, the edge kinetics model reduces to a set of boundary conditions, involving line tension and one-dimensional surface diffusion, for the adatom density. Finally, in the infinitely fast terrace diffusion limit, a simplified model ofone-dimensional surface diffusion and kink convection is derived and found to be linearly stable.

Macroscopically ordered thin films of an organic salt grown by low-pressure organic vapor-phase deposition

We demonstrate the process of low-pressure organic vapor-phase deposition (LP-OVPD) for the growth of crystalline thin films of the organic charge-transfer salt 4′-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) on amorphous TiO 2 substrates. LP-OVPD grown films exhibit polycrystallinity with long-range structural ordering limited only by substrate size. Film surface coverage and macroscopic ordering are strongly determined by the preparation of the TiO 2 surface prior to growth. The morphology and ordering of the films are also found to depend on the deposition temperature and the composition of the precursor molecules. These results suggest that LP-OVPD films are of sufficient quality for use in optical waveguide and related photonic devices.

Role of ion beam energy for crystalline growth of thin films

Cubic boron nitride and aluminum nitride films were prepared by nitrogen ion beam bombardment and simultaneous boron or aluminum vapor deposition, and carbon films were prepared by neon ion irradiation during carbon vapor deposition (IVD method). These films were formed by varying the ion beam energy in the range 0.2–20 keV on substrates of silicon crystal wafers. In order to study the relationship between the crystalline growth of the films and the ion beam energies, X-ray diffraction and Raman-scattering analyses were performed for the evaluation of nitride films and carbon films, respectively. The results showed that the peak intensities changed with ion beam energy and the crystalline state of the film was dependent on the energy of the irradiated ions. As a result of a study of the thermal spike effect by ion beam irradiation, the dependence of the crystalline growth of the films on the ion beam energy was demonstrated.