Thickness-dependent Structure Research Articles

Thickness-dependent structure and properties in zirconium carbide ceramic via orientated deposition

The fine-tuning of controlled structure and property evolution of zirconium carbide (ZrC) ceramic is essential for its functional applications, especially with insufficient understanding of the size effect mechanisms. In this investigation, the physically vapor-deposited ZrC (PVD-ZrC) ceramic was fabricated through magnetron sputtering, with a specific focus on its thickness-dependent growth and evolution of composition, microstructure, growth texture and mechanical properties. As prepared PVD-ZrC presents a hybrid structure characterized by amorphous carbon and nanocrystalline ZrC, with diversity in crystallinity, crystallite size, and growth pattern determined by target power, gas-flow pressure and substrate temperature. Moreover, the PVD-ZrC ceramic deposited by directional deposition, exhibits a structure transition from equiaxed crystals to dense columnar fiber crystals and an isotropy-toward texture. As the thickness increases, the stress gradually shifts towards tensile stress with a weaker fracture toughness. Through the First-principle calculation, it is illustrated that the mechanical properties of bulk polycrystalline ZrC are evidently different from low-dimensional polycrystalline ZrC film. This mechanism of thickness-dependent structure and properties is dominant by the surface effect, size effect, grain boundary effect, and stress effects.

Thickness-dependent structure and properties of SnS2 thin films prepared by atomic layer deposition

Tin disulfide (SnS2) thin films were deposited by a thermal atomic layer deposition (ALD) method at low temperatures. The physical, chemical, and electrical characteristics of SnS2 were investigated as a function of the film thickness. SnS2 exhibited a (001) hexagonal plane peak at 14.9° in the X-ray diffraction (XRD) results and an A1g peak at 311 cm−1 in the Raman spectra. These results demonstrate that SnS2 thin films grown at 150 °C showed a crystalline phase at film thicknesses above 11.2 nm. The crystallinity of the SnS2 thin films was evaluated by a transmission electron microscope (TEM). The X-ray photoelectron spectroscopy (XPS) analysis revealed that SnS2 consisted of Sn4+ and S2− valence states. Both the optical band gap and the transmittance of SnS2 decreased as the film thickness increased. The band gap of SnS2 decreased from 3.0 to 2.4 eV and the transmittance decreased from 85 to 32% at a wavelength of 400 nm. In addition, the resistivity of the thin film SnS2 decreased from 1011 to 106 Ω·cm as the film thickness increased.

Thickness-dependent effects in H2O desorption from glycine/amorphous solid water films

The desorption characteristics of H2O from glycine-on-amorphous solid water (ASW) ultrathin films have been systematically investigated as a function of underlying ASW thickness and the amount of top-deposited glycine using TPD. At the early stages of deposition, substantial amounts of glycine molecules penetrate into the water multilayers and, therefore, thermal destabilization of water layers is detected. Glycine diffusion is governed by the thickness-dependent structure of the ASW as revealed by work function measurements and XPS. For higher glycine coverages, a kinetic restriction of water desorption by the continuous amino acid overlayers is observed independent of the ASW substrate thickness.

Evolution of 2,5-Bis(4-biphenylyl)bithiophene Thin Films and Its Effect on the Weak Epitaxy Growth of ZnPc

Evolution of BP2T films grown at the early stage was investigated using atomic force microscopy (AFM) and X-ray diffraction (XRD). The AFM results demonstrate that the BP2T grown on the SiO2 substrate transformed from a layer by layer growth to island growth when the coverage is higher than 3 ML. The out-of-plane and in-plane X-ray diffraction measurements reveal a phase transition from the thin film phase to the bulk phase suddenly occurs as the growth mode changes. A careful analysis of the structure evolution implies that not only the strain but also the soft matter property of the organic thin films are responsible for the thickness dependent evolution. Moreover, the thickness dependent structure and phase of BP2T films result in different morphologies of ZnPc grown on different layers of BP2T. The ZnPc crystals gradually changed from stripe-like to nanofiber-like, concomitantly with the epitaxy relationships from incommensurate epitaxy to commensurate epitaxy. Conversely, the diversity of ZnPc films also reflects different properties of the BP2T films with different numbers of layer, which cannot be obtained from the AFM or XRD. This study supplies a deeper insight into the thickness evolution of organic thin films and to the weak epitaxy growth.

Light-Emitting Diode of Planar Type Based on Nanocomposites Consisting of Island Au Film and Organic Luminofore Tb(thd)3

Structure, photo-, electroluminescence and electron transport properties of planar nanoscale light-emitting metal-organic device consisting of Au nano-islands and Tb(thd)3 is reported. FTIR and photoluminescence measurements confirm stable vacuum deposition behavior of Tb(thd)3 in a monomeric form. With STM imaging, a thickness-dependent structure of Tb(thd)3 layers was observed and local current-voltage characteristics of organic films were found to be non-linear at voltages exceeding 1.0 V. Electroluminescence from the nanocomposite was observed at voltages 15–30 V, showing the emission features both of Tb(thd)3 and Au nano-islands. The results can be useful for design of planar light-emitting devices with controllable spectral characteristics.

FTIR spectroscopic and STM studies of vacuum deposited aluminium (III) 8-hydroxyquinoline thin films

FTIR spectroscopy and scanning tunneling microscopy (STM) were used to study the molecular organization and morphology of vacuum deposited (VD) thin films of tris (8-hydroxyquinoline) aluminum (Alq3) from metal-organic planar light-emitting nanocomposites consisting of gold island films and VD Alq3 film. It was found that thermal evaporation in vacuum does not cause dissociation of Alq3, and that the obtained films are essentially amorphous. Reflection-absorption (RA) IR spectra show predominantly perpendicular orientation of quinoline groups of Alq3 molecules in the films towards the substrate. With the STM method, a thickness-dependent structure of the films was found and the first near-surface layers of Alq3 films were characterized. It has been revealed that VD deposited Alq3 films of small thickness (5–15 nm) consist of molecular domains with a particular orientation along the Au[112] direction.

Characterisation of Au films on Si( [formula omitted]) [formula omitted]-Au by photoemission and optical second-harmonic generation

Synchrotron radiation photoemission in combination with optical second-harmonic generation (SHG) is used to study the growth of thin Au films on the 3 × 3 -Au-reconstructed Si(1 1 1) surface. The Si2p and Au4f core level spectra show the formation of a surface compound that has stabilized to a constant level at 5-monolayer coverage. Valence band spectra show thickness-dependent structures interpreted as quantization effects in the direction perpendicular to the surface. This is supported by optical SHG experiments showing oscillations in the signal with film thickness due to the shift of the quantized levels. The oscillating second-harmonic signal depends on the azimuthal sample orientation and thus originates from a film with crystalline order. From the thickness dependence of the second-harmonic signal in combination with the photoemission results it is concluded that the Au film is well-ordered below a thin reacted surface layer.

Thickness-dependent oscillation of the magneto-optical properties of Au-sandwiched (001) Fe films.

Au-sandwiched bcc (001) Fe wedges were produced by the molecular beam epitaxy method (0--20 \AA{}). The polar Kerr rotation and Kerr ellipticity spectra (1.5--5 eV) were measured as a function of the Fe thickness d. In both kinds of spectra new peaks appear. The complex Kerr rotation oscillates as a function of the film thickness. More than four oscillations could be clearly observed in the measured thickness range. Magneto-optical transitions from the ${\mathrm{\ensuremath{\Delta}}}_{5}$ band to quantum-well states (QWS's) in the ${\mathrm{\ensuremath{\Delta}}}_{1}$ majority-spin band change the intrinsic dielectric properties. The oscillation period and transition energies are in agreement with theory. Thickness-dependent structures below 2.5 eV strongly suggest the occurrence of partially confined QWS's around ${\mathit{E}}_{\mathit{F}}$ or QWS's in the ${\mathrm{\ensuremath{\Delta}}}_{5}$ band.

Dynamical theory of thermal neutron scattering. II.Pendellösungin inelastic peaks

A theory is presented in which the effect of the dynamical theory of diffraction on inelastic one-phonon peaks is taken into account to the first order in neutron-phonon interaction. In this theory, the distorted-wave Born approximation for the neutron-lattice Hamiltonian is used; the inelastic scattering amplitude for a phonon is then shown to be a coherent sum of the inelastic amplitudes due to all the plane-wave components of the Bloch waves that form the neutron wave function in the crystal under the stationary lattice condition. For this purpose, all the plane-wave components of the dynamical theory of the elastic scattering are on equal footing in determining the inelastic amplitude. The result is then a wavelength- and thickness-dependent structure in one-phonon peaks. An experimental configuration is suggested for observing Pendell\"osung effects in one-phonon peaks.