Growth of ultrathin Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> films on quartz substrates

Niobium oxide films have been grown by reactive rf sputtering in a vacuum system and characterized by absorption spectroscopy and X-ray diffraction. The thickness of the (optically transparent) films has been determined as a function of sputtering time by examining interference effects in a plane-parallel layer. The average deposition rate is determined to be 7.4 ± 0.3 Å/min (95% confidence interval).     

Magnetoresistance of La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> films grown on substrates with orthorhombically distorted unit cells

We have studied the structure and magnetoresistance of 40-nm-thick epitaxial La_0.67Ca_0.33MnO₃ (LCMO) films grown by laser deposition on (001)-oriented NdGaO₃ (NGO) substrates. The manganite layers were oriented so that the b axis was perpendicular to the substrate plane and occurred under the action of inhomogeneous biaxial mechanical stresses. The negative magnetoresistance of the LCMO films in the vicinity of the ferromagnetic spin ordering was about 71% (μ₀ H = 1 T). The observed azimuthal anisotropy of the magnetotransport properties of 40-nm-thick LCMO/(001)NGO films can be explained within the framework of a model of anisotropic magnetoresistance taking into account the presence of the preferred orientation of the spontaneous magnetization.     

Properties of AgInSe<Subscript>2</Subscript> films grown by magnetron sputtering

n-Type AgInSe₂ films 0.5 to 0.9 μm thick were grown by dc magnetron sputtering. As targets, we used AgInSe₂ crystals grown by a modified Bridgman process using high-purity precursors. The crystal structure, morphology, electrical conductivity, and Hall coefficient of the films were studied at various temperatures. We determined the optimal growth and annealing temperatures of the films (500 and 250°C, respectively). Using structures based on the films, we obtained the spectral dependences of their photoresponse, established the nature of interband transitions in the films, and evaluated their band gap. The ability to vary electrical and optical properties with no changes in stoichiometry is of interest for concentrated solar power applications.     

Preparation of La<Subscript>2</Subscript>NiMnO<Subscript>6</Subscript> thin films on Pt/TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript>/Si substrates by pulsed laser deposition

Double perovskite La₂NiMnO₆ thin films were prepared on Pt/TiO₂/SiO₂/Si substrates by the pulsed laser deposition process, and the crystal structure and microstructures were investigated. The temperature and the oxygen pressure played the primary roles dominating the crystallization behavior and the morphology of La₂NiMnO₆ thin films. The well crystallized La₂NiMnO₆ thin films could be obtained at 873 and 923 K under all oxygen pressures investigated here, and the fine morphology was obtained under the oxygen pressures equal to or higher than 50 and 100 Pa, respectively, while phase constitution was significantly affected by the oxygen pressure for La₂NiMnO₆ thin films prepared at 1,023 K where the higher oxygen pressure led to the appearance of some secondary phase.     

Microstructural evaluation of thermally fatigued SiC-reinforced Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/ZrO<Subscript>2</Subscript> matrix composites

Using the water-quenching technique, the thermal fatigue behaviour of an alumina/zirconia and platelets- and particulates-SiC reinforced alumina/zirconia matrix composites hot-pressed at 1500 and 1700^∘C has been studied. The addition of 10 wt% SiC either in the form of platelets or particulates can obviously improve the thermal fatigue resistance of alumina/zirconia composites. The damages present after 40 thermal fatigue cycles in the composites was illustrated by the microstructure examinations and EDX.     

Broadband photovoltaic effect of n-type topological insulator Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> films on p-type Si substrates

We report the photovoltaic effects of n-type topological insulator (TI) Bi2Te3 films grown on p-type Si substrates by chemical vapor deposition (CVD).The films containing large nanoplates with a smooth surface formed on p-Si exhibit good p-n diode characteristics under dark and light illumination conditions and display a good photovoltaic effect under the broadband range from ultraviolet (UV) to near infrared (NIR) wavelengths.Under the light illumination with a wavelength of 1,000 nm,a short circuit current (Isc) of 19.2 μA and an open circuit voltage (Voc) of 235 mV are achieved.The maximum fill factor (FF) increases with a decrease in the wavelength or light density,achieving a value of 35.6％ under 600 nm illumination.The photoresponse of the n-Bi2Te3/p-Si device can be effectively switched between the on and off modes in millisecond time scale.These findings are important for both the fundamental understanding and solar cell device applications of TI materials.     

Changes in dewetting behavior of SiO<Subscript>2</Subscript> films on TiO<Subscript>2</Subscript> substrates due to film thickness and crucible choice

The TiO₂/SiO₂ materials system has had renewed interest in recent years due to its photoelectric and photocatalytic properties, and serves as an ideal model system for liquid-phase sintering studies (LPS). In this study, glass SiO₂ films of three different nanoscale thicknesses were deposited onto (001) rutile TiO₂ substrates. The resulting dewet patterns of the glass were found to change depending on the initial film thickness when subjected to identical annealing conditions. In addition, changing the crucible type from Pt to Al₂O₃, caused films of the same thickness to undergo different convection mechanisms and thus developing very different surface patterns. It is proposed that Marangoni convection drove pattern formation when a Pt crucible was used, while the Rayleigh instability was responsible for dewetting when an Al₂O₃ crucible was used.     

Synthesis of anisometric KSr<Subscript>2</Subscript>Nb<Subscript>5</Subscript>O<Subscript>15</Subscript> particles in the SrNb<Subscript>2</Subscript>O<Subscript>6</Subscript>–Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>–KCl system

Anisometric and agglomerate-free template particles are important for fabrication of grain-oriented ceramics. In the present work, preparation of acicular KSr₂Nb₅O₁₅ (KSN) particles was firstly explored in the SrNb₂O₆–Nb₂O₅–KCl system by molten salt synthesis (MSS) method. It was found that the molar ratio of SrNb₂O₆ to Nb₂O₅, the amount of KCl salt and synthesis time could significantly affect the phase structure and morphology of KSN particles. When calcined at 1,150 °C for 6 h with the molar ratio of SrNb₂O₆ to Nb₂O₅ was 1 and the weight ratio of salt to oxide source was 1.50, pure KSN particles with well-developed acicular morphology were successfully obtained in this system. They were agglomerate-free and with proper scale in the size range of 5–30 μm, which made them the ideal templates for fabricating textured ceramics. In addition, some new reaction and growth mechanisms were proposed in this work.     

Structural transformations in thin Ge<Subscript>2</Subscript>Sb<Subscript>2</Subscript>Te<Subscript>5</Subscript> films

Structural transformations in thin Ge₂Sb₂Te₅ films for phase-change memory applications have been studied by differential scanning calorimetry. As-grown, amorphous films have been shown to undergo structural transitions to a cubic and then to a hexagonal phase. A reproducible endothermic peak has been detected, which had not been reported earlier. A mechanism for the underlying process has been proposed.     

Electric resistance of La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> films biaxially strained during growth on lattice-mismatched substrates

We have studied the electric resistance of 20-nm-thick La_0.67Ca_0.33MnO₃ films coherently grown on single crystal substrates with considerable (negative) and almost zero lattice mismatch. The unit cell volume in the growing film depends on the substrate lattice parameter. At T<200 K and μ₀H=0, the resistance of manganite films on (001)LaAlO₃ substrates was several orders of magnitude greater than the value for an analogous film grown on (001)La_0.29Sr_0.71Al_0.65Ta_0.35O₃. The observed decrease in resistance of the elastically strained (biaxial compression) manganite films is related to a superstoichiometric (≈45%) relative concentration of Mn⁴⁺ ions in the film volume.     

Crystallization of amorphous Bi<Subscript>2</Subscript>S<Subscript>3</Subscript> films

The crystallization kinetics of amorphous Bi₂S₃ films have been studied by kinematic electron diffraction. The results have been used to evaluate the activation energies for activation energy and crystal growth.     

Antireflecting coating from Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> and SiO<Subscript>2</Subscript> multilayer films

Sol-gel method is important for depositing antireflective coating that allows control over thickness as well as the index of refraction. Antireflective coatings which are produced from Ta₂O₅ and SiO₂ multi-layer thin films using sol-gel spin coating method are presented. The refractive index and the thickness are controlled by the composition and the concentration of the solution respectively. The thickness, refractive index and extinction coefficient of the films were calculated through transmission and reflection measurement by an NKD analyser. Mechanical properties of the films were checked by the cross tape test and dry sun test at 760 W/m². The result shows that the sample heat treated at 450^∘C for 15 min approaches a reflectance with less than 0.5% at around 840 nm.     

Characterization and electrical properties of semiconducting Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-K<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript> glasses

Semiconducting glasses of the Fe₂O₃-Bi₂O₃-K₂B₄O₇ system were prepared by the press-quenching method and their dc conductivity in the temperature range 223–393 K was measured. The glass transition temperature values (T_g) of the present glasses were larger than those of tellurite glasses. This indicates a higher thermal stability of the glass in the present system. The density for these glasses was consistent with the ionic size, atomic weight and amount of different elements in the glasses. Mössbauer results revealed that the relative fraction of Fe increases with increasing Fe₂O₃ content. Electrical conductivity showed a similar composition dependency as the fraction of Fe. The glasses had conductivities ranging from 10 to 10 Scm at temperatures from 223 to 393 K. Electrical conduction of the glasses was confirmed to be due to non-adiabatic small polaron hopping and the conduction was primarily determined by hopping carrier mobility.     

Properties of CdSe films produced via spray pyrolysis of [Cd((NH<Subscript>2</Subscript>)<Subscript>2</Subscript>CSe)<Subscript>2</Subscript>Cl<Subscript>2</Subscript>]

Data are presented on microwave photoconductivity kinetics in CdSe films prepared via spray pyrolysis of aqueous solutions of thiourea complexes on quartz and glass-ceramic substrates at temperatures from 300 to 600°C. The films were characterized by x-ray diffraction and optical absorption and reflection spectroscopies. Microwave photoconductivity (excitation with 8-ns laser pulses at 337 nm) was measured at 295 K by a resonator method in the 9-and 36-GHz ranges. The results indicate that the photoresponse decay kinetics depend on deposition temperature and incident intensity. In the films deposited below 400°C, the photoresponse decay follows a first-order rate law. At deposition temperatures above 450°C, the photoresponse decay cannot be represented by a first-or second-order rate law at low excitation intensities and approaches second-order kinetics at high intensities (> 10¹⁵ photons/cm² per pulse). Analysis of the photoresponse decay kinetics in terms of the interaction between free and trapped electrons, holes, and ions allowed us to formulate a model for the processes involved and to evaluate the rate constant of electron-hole recombination in CdSe: (4–6) × 10^?11 cm³/s.     

ZrO<Subscript>2</Subscript> thin films on Si substrate

In the advancement of metal–oxide–semiconductor technology, Si-based semiconductor, with SiO₂ as outstanding dielectric, has been dominating microelectronic industry for decades. However, the drastic down-scaling in ultra-large-scale integrated circuitry has made ultrathin SiO₂ (~1.2 nm) unacceptable for many practical reasons. Introduction of ZrO₂ as high-κ dielectrics replacing SiO₂ is undeniably a potential yet formidable solution for the aforementioned problem. The objective of this review is to present the current knowledge of ZrO₂ thin film as gate dielectric on Si, in terms of its material and electrical properties produced by various deposition techniques. One of the techniques being focused is thermal oxidation of sputtered Zr and the mechanisms of transforming the metal into oxide has been extensively reviewed.     

Photoluminescence of Si<Subscript>0.9</Subscript>Ge<Subscript>0.1</Subscript>O<Subscript>2</Subscript> and GeO<Subscript>2</Subscript> films irradiated with silicon ions

We have studied the photoluminescence (PL) of GeO₂ and 90 mol % SiO₂-10 mol % GeO₂ films synthesized by method of RF magnetron sputtering and then irradiated with silicon ions and annealed. The PL of silicon-implanted GeO₂ films, related to the presence of Si nanocrystals (nc-Si), was observed for the first time. It is established that the transformation of the defect centers responsible for the PL in the spectral range 350–600 nm, as well as the formation of nc-Si emitting in the region of 700–800 nm, significantly depend on the matrix type. In particular, the PL intensity at 700–800 nm in 90 mol % SiO₂-10 mol % GeO₂ films is weak. The role of the isovalent substitution of Si and Ge atoms in the transformation of defect centers and the formation of nc-Si is discussed.     

High pressure effect on MoS<Subscript>2</Subscript> and MoSe<Subscript>2</Subscript> single crystals grown by CVT method

Single crystals of MoS₂ and MoSe₂ were grown by chemical vapour transport method using iodine as a transporting agent and characterized by optical microscopy, energy dispersive analysis (EDAX), X-ray powder diffraction (XRD) and Hall mobility at room temperature. The variation of electrical resistance under pressure was monitored in a Bridgman anvil set-up up to 6.5 GPa to identify occurrence of any structural transition. MoS₂ and MoSe₂ do not undergo any structural transitions under pressure.