Formation of carbon nanotubes on an amorphous Ni<Subscript>25</Subscript>Ta<Subscript>58</Subscript>N<Subscript>17</Subscript> alloy film by chemical vapor deposition

It is shown that it is possible to grow carbon nanotubes on the surface of an amorphous Ni–Ta–N metal alloy film with a low Ni content (~25 at %) by chemical deposition from acetylene at temperature 400–800°C. It is established that the addition of nitrogen into the Ni–Ta alloy composition is favorable for the formation of tantalum nitride and the expulsion of Ni clusters, which act as a catalyst of the growth of carbon nanotubes, onto the surface. From Raman spectroscopy studies, it is found that, as the temperature of synthesis is raised, the quality of nanotubes is improved.     

CVD-growth of CNT with the use of catalutic Ct–Me–N–O thin films incorporated in the technology

The process of the formation of carbon nanotube arrays on Ct–Me–N catalytic alloys of low nickel content (10–20 at %) by chemical vapor deposition, where Ct is a catalytic metal from the group of Ni, Co, Fe, and Pd, and Me is a transition metal of group IV–VII of the periodic table, was investigated. It is shown that CNT grow effectively when the alloy contains Ti, V, Cr, Zr, Hf, Nb, and Ta. The addition of nitrogen and oxygen to the alloy’s composition gives rise to a buildup of oxynitrides, expelling of the catalyst, and formation of its clusters on the surface. The replacement of metals in the alloy has an effect on the diameter of the CNT. Moreover, the alloy films 10–500 nm thick can be used for the CNT growth, which is responsible for high degree of homogeneity and the repeatability of the process. CNT growth was not observed when the alloy contained W and Re.     

Microstructures and Thermoelectric Properties of an Annealed Ti<Subscript>0.5</Subscript>(Hf<Subscript>0.5</Subscript>Zr<Subscript>0.5</Subscript>)<Subscript>0.5</Subscript>NiSn<Subscript>0.998</Subscript>Sb<Subscript>0.002</Subscript> Ribbon

The thermoelectric half-Heusler compound Ti_0.5(Hf_0.5Zr_0.5)_0.5NiSn_0.998Sb_0.002 was fabricated by spin-casting and subsequent annealing. ZT at room temperature increased with annealing time through an increase in absolute Seebeck coefficients despite a decrease in electrical conductivity. ZT reached 0.10 after annealing at 1050 K for 48 h. In powder x-ray diffraction analysis, each half-Heusler peak was accompanied by a bump at the high-angle side, corresponding to a minor Ti-rich half-Heusler phase. The quantity and Ti composition of the minor phase increased with annealing time, although those of the major half-Heusler phase were almost constant. In transmission electron microscopic analysis, granular domains, several nanometers in size, with atomic ordering or disordering were observed. Thermoelectric properties were␣improved by annealing through the growth of heterogeneous microstructures of the Ti-rich and Ti-poor half-Heusler grains and of the granular domains.     

Adsorption,desorption, and contact and thermal transformation of C<Subscript>60</Subscript> molecules on a Ta(100) surface

The adsorption, desorption, initial film growth, and contact and thermal transformation of C₆₀ molecules on a Ta(100) surface in ultra high vacuum at temperatures from 300 to 2000 K are investigated. It is shown that C₆₀ molecules from the first adsorption layer undergo a significant transformation even at room temperature, forming a loose monolayer. The subsequent growth of fullerite occurs in accordance with the Stranski-Krastanov mechanism and results in the formation of compact islands. The thermal stability ranges of fullerite films on tantalum are determined and it is shown that decomposition occurs in the temperature range 850–950 K mainly due to decomposition of the molecules (induced by the catalytically active surface) rather than thermal desorption.     

Electrical properties of InAs-SiO<Subscript>2</Subscript>-In<Subscript>2</Subscript>O<Subscript>3</Subscript> MIS structures with a modified interface

The effect of composition of the electrolyte used in producing a thin anodic oxide layer at the surface of a semiconductor substrate on the electrical properties of the InAs-SiO₂-In₂O₃ metal-insulator-semiconductor structures is studied. It is shown that introduction of ammonium fluoride into the electrolyte results in the formation of an interface with the density of surface states below 5 × 10¹⁰ cm^?2 eV^?1, the built-in charge (4–5 × 10¹¹ cm^?2, and the maximum relaxation time of the surface potential.     

Crystallization behavior and ferroelectric properties of PbTiO<Subscript>3</Subscript>/Ba<Subscript>0.85</Subscript>Sr<Subscript>0.15</Subscript>TiO<Subscript>3</Subscript>/PbTiO<Subscript>3</Subscript> sandwich thin film on Pt/Ti/SiO<Subscript>2</Subscript>/Si substrates

A PbTiO₃/Ba_0.85Sr_0.15TiO₃/PbTiO₃ (PT/BST15/PT) sandwich thin film has been prepared on Pt/Ti/SiO₂/Si substrates by an improved sol-gel technique. It is found that such films under rapid thermal annealing at 700°C crystallize more favorably with the addition of a PbTiO₃ layer. They possess a pure, perovskite-phase structure with a random orientation. The polarization-electric field (P-E) hysteresis loop and current-voltage (I-V) characteristic curves reveal that a PT/BST15/PT film exhibits good ferroelectricity at room temperature. However, no sharp peak, only a weak maximum, is observed in the curves of the dielectric constant versus temperature. The dielectric constant, loss tangent, leakage current density at 20 kV/cm, remnant polarization, and coercive field of the PT/BST15/PT film are 438, 0.025, 1.3 × 10⁻⁶ Acm⁻², 2.46 μCcm⁻², and 41 kVcm⁻¹, respectively, at 25°C and 10 kHz. The PT/BST15/PT film is a candidate material for high sensitivity elements for uncooled, infrared, focal plane arrays (UFPAs) to be used at near ambient temperature.     

AC Electrical Conductivity of FeIn<Subscript>2</Subscript>Se<Subscript>4</Subscript> Single Crystals

The results obtained in a study of the frequency and temperature dependences of the ac electrical conductivity of FeIn₂Se₄ single crystals are presented. It is found that the law σ ~ f ^S (0.1 ≤ S ≤ 1.0) is obeyed for electrical conductivity in the 295–375 K temperature range at frequencies of 2 × 10⁴–10⁶ Hz. It shown that the frequency dependence of the conductivity in an FeIn₂Se₄ single crystal can be accounted for in terms of the multiplet model, and, consequently, the conductivity in these single crystals is characterized by the band-hopping mechanism.     

Reflectance spectra of <Emphasis Type="Italic">p</Emphasis>-Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>:Sn crystals in a wide IR region

The reflectance spectra of a p-Bi₂Te₃:Sn crystal are recorded in the range 50–7900 cm^–1. The spectra possess features characteristic of charge-carrier plasma oscillations and a contribution of phonons. It is shown that the dielectric function that is used in the context of Drude–Lorentz theory and includes the contributions of hole plasma oscillations and two phonons adequately describes the experimental data obtained at room temperature and at a temperature of T = 78 K.     

Formation of the TiN/CoSi<Subscript>2</Subscript> system by rapid thermal annealing of a Co/Ti/Si structure

An Auger-spectroscopy investigation is conducted into the formation of the TiN/CoSi₂ system by rapid thermal annealing of a Co/Ti/Si structure in a nitrogen atmosphere. Two different directions of temperature gradient under annealing are considered. It is established that TiN/CoSi₂ formation occurs only when the temperature on the coated side of the specimen grows with depth. The influence of different factors is discussed.     

Effect of Rapid Thermal Annealing on Sputtered CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> Thin Films

Calcium copper titanium oxide (CaCu₃Ti₄O₁₂, abbreviated to CCTO) films were deposited on Pt/Ti/SiO₂/Si substrates at room temperature (RT) by radiofrequency magnetron sputtering. As-deposited CCTO films were treated by rapid thermal annealing (RTA) at various temperatures and in various atmospheres. X-ray diffraction patterns and scanning electron microscope (SEM) images demonstrated that the crystalline structures and surface morphologies of CCTO thin films were sensitive to the annealing temperature and ambient atmosphere. Polycrystalline CCTO films could be obtained when the annealing temperature was 700°C in air, and the grain size increased signifi- cantly with annealing in O₂. The 0.8-μm CCTO thin film that was deposited at RT for 2 h and then annealed at 700°C in O₂ exhibited a high dielectric constant (ε′) of 410, a dielectric loss (tan δ) of 0.17 (at 10 kHz), and a leakage current density (J) of 1.28 × 10⁻⁵ A/cm² (at 25 kV/cm).     

Determination of Thermodynamic Parameters in the Cu<Subscript>1.95</Subscript>Ni<Subscript>0.05</Subscript>S Phase-Transition Regions

X-ray diffraction and differential thermal analysis data obtained in the Cu_1.95Ni_0.05S phase-transition region are analyzed. It is established that the low-temperature rhombic α phase in Cu_1.95Ni_0.05S transforms to the hexagonal β phase at temperatures of 370–390 K and to the cubic γ phase at temperatures of 740–765 K according to the scheme \(\alpha \to \mathop {\alpha + \beta }\limits_{370 - 390K} \to \mathop {\alpha + \gamma }\limits_{740 - 765K} \to \gamma \). It is determined (using the temperature dependence of differential thermal analysis) that the transition α → β is accompanied by heat absorption while the transition β → γ is accompanied by heat release. It is found that both transitions are allowed and belong to the reconstructive type. Both transitions are found to occur in a fluctuation volume of ~10^–20 cm³ at temperature rates of 0.11 and 0.08 K^–1. It is demonstrated that the transition α → γ is accompanied by alternation of the structures passing through the intermediate β phase, which is incommensurate with respect to the α and γ phases.     

Investigation of the Dielectric Permittivity and Electrical Conductivity of Ce<Subscript>2</Subscript>S<Subscript>3</Subscript>

The rare-earth semiconductor β-Ce₂S₃ compound samples were synthesized and their dielectric permittivity and electrical conductivity were measured in the temperature range 90–400 K. The energy-band structure has been determined. It is shown that the long-known large electrical parameter spread of semiconductor compounds close in composition to Ce₂S₃ is explained by the structure of impurity donor levels formed by cerium atoms and ions with different ionization degrees.     

Thermoelectric properties of Bi<Subscript>2</Subscript>Te<Subscript>2.4</Subscript>Se<Subscript>0.6</Subscript> solid solutions of different particle-size composition

The thermoelectric properties of n-type Bi₂Te_2.4Se_0.6 solid solution prepared by the vacuum hot pressing of powder mixtures with different particle sizes are investigated. The powders were prepared by the mechanical grinding of ingots and melt spinning. The microstructure and fracture pattern of a sample cleavage surface are analyzed using scanning electron microscopy and optical microscopy. The thermoelectric characteristics (the Seebeck coefficient, electrical conductivity, and thermal conductivity) are measured at room temperature and in the temperature range of 100–700 K.     

Kinetics and mechanisms of Cl<Subscript>2</Subscript> or HCl plasma etching of copper

An investigation by experiment and computer simulation is reported into the kinetics and mechanisms of the interaction between copper and impinging reactive species as the former is etched with a chlorine or a hydrogen chloride plasma. It is established that the manner in which etching proceeds is substantially the same for the two parent gases. There are, however, considerable differences in etch rate that are related to those in the types and stationary concentrations of reactive plasma species and in their fluxes to the surface being processed. Two regimes of etching are identified over the temperature range 373–653 K that differ in the character of the etch-rate-temperature relationship and in the shape of kinetics graphs. In a higher temperature regime, the plasma-etching reaction with copper involves complete removal of etch products from the surface; it proceeds under steady-state conditions and is of first order in terms of the concentration of reactive species in the bulk plasma. This occurs at temperatures above 500–520 K for Cl₂ plasmas and at above 580–600 K for HCl plasmas.     

Self-limiting growth of ZrO<Subscript>2</Subscript> films on a Si(100) substrate using ZrCl<Subscript>4</Subscript> and O<Subscript>2</Subscript> under atmospheric pressure

The ZrO₂ films were deposited onto a Si(100) substrate using an alternate reaction of ZrCl₄ and O₂ under atmospheric pressure. It is found that the growth rate of ZrO₂ film depends on the growth conditions, such as growth temperature, partial pressure of the sources being supplied, and exposure time of the substrate to the gaseous sources. Self-limiting growth of the ZrO₂ was achieved in the range of the growth temperature of 673–923 K. The x-ray diffractogram of the ZrO₂ films showed a typical diffraction pattern assigned to the tetragonal polycrystalline phase. The obtained ZrO₂ films were of smooth and uniform surface. It was found that the [O]/[Zr] ratio of the ZrO₂ films are similar to that of the ZrO₂ bulk.     

Light-enhanced sensitivity of SnO<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript> gas sensors

The effect of emission of red, yellow, green, and blue LEDs on the sensitivity of SnO₂-film gas sensors manufactured by a reactive magnetron sputtering with addition of Sb, In, and catalytic coatings of Pt and Pd to vapors of ethyl and isopropyl spirits, acetone, and benzene is investigated. For the first time, it is shown that all types of emission for all listed reactants increase the sensor sensitivity by 2 to 100 times in the case of small (1–10 ppm) doses of all reactants for the sensors, which are low-sensitive without illumination. It is found that the character of dependence of the sensor sensitivity on the illumination intensity is determined by the type of the catalytic coating, linearly growing in the case of Pd and sharply increasing at the highest intensity in the case of Pt. The nature of this phenomenon is discussed taking into account the vapor adsorption and the conductivity of crystallites in tin-dioxide films.     

Temperature dependence of the band gap of the single-crystal compounds In<Subscript>2</Subscript>S<Subscript>3</Subscript> and AgIn<Subscript>5</Subscript>S<Subscript>8</Subscript>

For the single-crystal compounds In₂S₃ and AgIn₅S₈ produced by chemical gas-transport reactions and the Bridgman method (vertical version), the transmission spectra in the region of the fundamental absorption edge are studied in the temperature range from 20 to 300 K. From the recorded spectra, the band gaps of the In₂S₃ and AgIn₅S₈ single crystals are determined and the temperature dependences of the band gaps are constructed. It is established that, as the temperature is lowered, the band gap increases for both of the compounds. Calculation of the temperature dependences is performed. It is shown that the calculated and experimental values are in agreement with each other.     

Effect of rare-earth impurities on the photoluminescence of Ge<Subscript>2</Subscript>S<Subscript>3</Subscript> glass

The photoluminescence properties of Ge₂S₃ glass doped with rare-earth elements La, Ce, Gd have been studied in the temperature range of 4.2–300 K. It has been shown that these impurities do not form new levels responsible for emission. The variation in the principal parameters of the excitation and emission spectra with the concentration and nature of impurities has been estimated.     

Optimization of pretreatment for liquid-phase deposition of SiO<Subscript>2</Subscript> on ARTON plastic substrate

This study extends our previous work on liquid-phase deposition (LPD) of dense, high-quality, silicon-dioxide (SiO₂) films deposited on Si and GaAs substrates from supersaturated, hexafluorosilicic-acid aqueous at near room temperature. Pretreatment to coat the substrate surface with hydroxyl groups was found to be necessary for rapid and high-quality growth. More recent work has extended the range of LPD SiO₂ to plastic. The current paper studies optimal LPD pretreatment of a plastic (ARTON) substrate. It is shown that treating ARTON plastic, first, by exposure to oxygen plasma, second, by potassium manganese (KMnO₄) etching, and finally, by H₂O₂ etching, provides the plastic surface with rich OH-radical formation. The resulting SiO₂/ARTON film is of good quality and reliability. Deposition rate is up to 659 Å/h, and the refractive index is about 1.44 with growth at 40°C. A growth mechanism for LPD-SiO₂ deposition on plastic is proposed.