Use of thin film of a Co<Subscript>15</Subscript>Ti<Subscript>40</Subscript>N<Subscript>35</Subscript> alloy for CVD catalytic growth of carbon nanotubes

It is shown that multiwalled carbon nanotubes can be grown on the catalytic surface of a Co–Ti–N alloy with low (~10 at %) cobalt content by the conventional method of chemical deposition from acetylene. Adding nitrogen to the composition of the Co–Ti contributes the formation of the TiN compound and extrusion of Co onto the surface where it makes a catalytic effect for CNT growth. It was found that the tubes begin growth at a temperature of 400°C. It is shown by studies using Raman spectroscopy that the quality of CNT improves with increasing temperature.     

Physical Properties of Sn<Subscript>96.5</Subscript>Ag<Subscript>3.5</Subscript>-Based Solders with Additions of Bi,Ge, and In

The melting temperature, electrical resistivity, surface tension, and density of the (Sn_0.965Ag_0.035)_95.17Bi_4.83, (Sn_0.965Ag_0.035)_95.17Bi_4.73Ge_0.1, and (Sn_0.965Ag_0.035)₉₄-Bi₂In₄ alloys have been studied in comparison with the Sn₆₀Pb₄₀ and Sn_96.5Ag_3.5 binary alloys (all wt.%). The electrical conductivity of the solid alloys based on Sn_96.5Ag_3.5 is comparable to that of the Sn₆₀Pb₄₀ alloy. The wetting behavior on Cu and Ni surfaces has been investigated in a wide temperature interval. It is established that the addition of Bi to Sn_96.5Ag_3.5 decreases the surface tension and improves the wetting properties of the alloy. The addition of a small quantity of Ge to the Sn-Ag-Bi alloy did not improve the wetting behavior on either Cu or Ni surfaces. The wetting ability of the (Sn_0.965Ag_0.035)₉₄Bi₂In₄ alloy was slightly worse as compared with (Sn_0.965Ag_0.035)_95.17Bi_4.83.     

Formation of Intermetallic Compounds Between Liquid Sn and Various CuNi<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Metallizations

Interfacial reactions between liquid Sn and various Cu-Ni alloy metallizations as well as the subsequent phase transformations during the cooling were investigated with an emphasis on the microstructures of the reaction zones. It was found that the extent of the microstructurally complex reaction layer (during reflow at 240°C) does not depend linearly on the Ni content of the alloy metallization. On the contrary, when Cu is alloyed with Ni, the rate of thickness change of the total reaction layer first increases and reaches a maximum at a composition of about 10 at.% Ni. The reaction layer is composed of a relatively uniform continuous (Cu,Ni)₆Sn₅ reaction layer (a uniphase layer) next to the NiCu metallizations and is followed by the two-phase solidification structures between the single-phase layer and Sn matrix. The thickness of the two-phase layer, where the intermetallic tubes and fibers have grown from the continuous interfacial (Cu,Ni)₆Sn₅ layer, varies with the Ni-to-Cu ratio of the alloy metallization. In order to explain the formation mechanism of the reaction layers and their observed kinetics, the phase equilibria in the Sn-rich side of the SnCuNi system at 240°C were evaluated thermodynamically utilizing the available data, and the results of the Sn/Cu _x Ni_1−x diffusion couple experiments. With the help of the assessed data, one can also evaluate the minimum Cu content of Sn-(Ag)-Cu solder, at which (Ni,Cu)₃Sn₄ transforms into (Cu,Ni)₆Sn₅, as a function of temperature and the composition of the liquid solders.     

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 and Thermal Conductivity and Conduction Mechanism of Ge<Subscript>2</Subscript>Sb<Subscript>2</Subscript>Te<Subscript>5</Subscript> Alloy

Ge₂Sb₂Te₅ alloy has drawn much attention due to its application in phase-change random-access memory and potential as a thermoelectric material. Electrical and thermal conductivity are important material properties in both applications. The aim of this work is to investigate the temperature dependence of the electrical and thermal conductivity of Ge₂Sb₂Te₅ alloy and discuss the thermal conduction mechanism. The electrical resistivity and thermal conductivity of Ge₂Sb₂Te₅ alloy were measured from room temperature to 823 K by four-terminal and hot-strip method, respectively. With increasing temperature, the electrical resistivity increased while the thermal conductivity first decreased up to about 600 K then increased. The electronic component of the thermal conductivity was calculated from the Wiedemann–Franz law using the resistivity results. At room temperature, Ge₂Sb₂Te₅ alloy has large electronic thermal conductivity and low lattice thermal conductivity. Bipolar diffusion contributes more to the thermal conductivity with increasing temperature. The special crystallographic structure of Ge₂Sb₂Te₅ alloy accounts for the thermal conduction mechanism.     

Thermoelectric properties of Bi<Subscript>0.5</Subscript>Sb<Subscript>1.5</Subscript>Te<Subscript>3</Subscript> ribbons prepared by melt spinning

The results of studying the thermoelectric properties of p-type Bi_0.5Sb_1.5Te₃ alloy samples prepared by melt spinning quenching are presented. The material after melt spinning is shaped as thin ribbons and has a quasi-amorphous structure. The thermoelectric properties (thermoelectric power and electrical resistance) and crystallization processes of as-prepared melt-spun ribbons are studied at 300–800 K for the first time. The stability range of the initial state, the crystallization-onset temperature, and the effect of thermal annealing on the thermoelectric-power factor of the alloy are determined.     

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.     

Study of Critical Behavior in Amorphous Fe<Subscript>85</Subscript>Sn<Subscript>5</Subscript>Zr<Subscript>10</Subscript> Alloy Ribbon

We have investigated the critical behavior in amorphous Fe₈₅Sn₅Zr₁₀ alloy ribbon prepared using a single-roller melt-spinning method. This alloy shows a second-order magnetic transition from paramagnetic to ferromagnetic (FM) state at the Curie temperature T _C (～306 K). To obtain more information on the features of the magnetic transition, a detailed critical exponent study was carried out using isothermal magnetization M (H, T) data in the vicinity of the T _C. Modified Arrott plot, Kouvel–Fisher plot, Widom’s scaling relation and critical isotherm analysis techniques were used to investigate the critical behavior of this alloy system around its phase transition point. The values of critical exponents determined using the above methods are self-consistent. The estimated critical exponents are fairly close to the theoretical prediction of the three-dimensional (3D) Heisenberg model, implying that short-range FM interactions dominate the critical behavior in amorphous Fe₈₅Sn₅Zr₁₀ alloy ribbon.     

Optical and structural properties of Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> thin films obtained by pulsed laser deposition in a H<Subscript>2</Subscript>S atmosphere with subsequent annealing in a N<Subscript>2</Subscript> atmosphere

The structural and optical properties of Cu₂ZnSnS₄ thin-film layers formed by reactive pulsed laser deposition in a H₂S atmosphere at room temperature with the use of a Cu metal target and a Zn–Sn alloy target are studied in relation to the parameters of annealing in a N₂ atmosphere.     

Carbon Fiber–Bismaleimide Composites Filled with Nickel‐Coated Single‐Walled Carbon Nanotubes for Lightning‐Strike Protection

Multifunctional carbon fiber composites are imperative for next‐generation lightweight aircraft structures. However, lightning‐strike protection is a feature that is lacking in many modern carbon fiber high‐temperature polymer systems, due to their high electrical resistivity. This work presents a study on processing, materials optimization, and property development of high‐temperature bismaleimide (BMI)–carbon fiber composites filled with nickel‐coated single‐walled carbon nanotubes (Ni‐SWNTs) based on three key factors: i) dispersion of Ni‐SWNTs, ii) their surface coverage on the carbon plies and, iii) the composite surface resistivity. Atomic force microscopy analysis revealed that coating purified SWNTs with nickel enabled improved dispersion which resulted in uniform surface coverage on the carbon plies. The electrical resistivity of the baseline composite system was reduced by ten orders of magnitude by the addition of 4 wt% Ni‐SWNTs (calculated with respect to the weight of a single carbon ply). Ni‐SWNT–filled composites showed a reduced amount of damage to simulated lightning strike compared to their unfilled counterparts, as indicated by the minimal carbon fiber pull‐out.     

Thermoelectric Properties of the Pseudobinary Alloy (Ag<Subscript>0.365</Subscript>Sb<Subscript>0.558</Subscript>Te)<Subscript>0.975</Subscript>(GeTe)<Subscript>0.025</Subscript> Prepared by Spark Plasma Sintering

Ag-Sb-Te-Ge-based alloys have received great attention in recent years. In the present work we prepared the pseudobinary alloy (Ag_0.365Sb_0.558Te)_0.975 (GeTe)_0.025 using spark plasma sintering and evaluated its thermoelectric (TE) properties over the temperature range from 318 K to 551 K. Rietveld analysis revealed that about 1.3 at.% Ge atoms occupy the Sb sites and that the alloy exhibits the same crystal structure as AgSbTe₂. By using back-scattered electron imaging, we observed two instead of one phase in the sample. The small white AgSbTe₂ chunks embedded in the matrix can substantially scatter phonons. Compared with the transport properties of Ag_0.365Sb_0.558Te, we obtained a slightly increased Seebeck coefficient and reduced thermal conductivity without sacrificing electrical conductivity. The highest TE figure of merit, ZT, was 0.69 at 551 K, whereas that of the ternary alloy Ag_0.365Sb_0.558Te was 0.61 at the corresponding temperature, suggesting that (Ag_0.365Sb_0.558Te)_0.975(GeTe)_0.025 has the potential to improve TE performance with optimization of its chemical composition.     

Composites Based on Core–Shell Structured HBCuPc@CNTs-Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> and Polyarylene Ether Nitriles with Excellent Dielectric and Mechanical Properties

Core–shell structured magnetic carbon nanotubes (CNTs-Fe₃O₄) coated with hyperbranched copper phthalocyanine (HBCuPc) (HBCuPc@CNTs-Fe₃O₄) hybrids were prepared by the solvent-thermal method. The results indicated that the HBCuPc molecules were decorated on the surface of CNTs-Fe₃O₄ through coordination behavior of phthalocyanines, and the CNTs-Fe₃O₄ core was completely coaxial wrapped by a functional intermediate HBCuPc shell. Then, polymer-based composites with a relatively high dielectric constant and low dielectric loss were fabricated by using core–shell structured HBCuPc@CNTs-Fe₃O₄ hybrids as fillers and polyarylene ether nitriles (PEN) as the polymer matrix. The cross-sectional scanning electron microscopy (SEM) images of composites showed that there is almost no agglomeration and internal delamination. In addition, the rheological analysis reveals that the core–shell structured HBCuPc@CNTs-Fe₃O₄ hybrids present better dispersion and stronger interface adhesion with the PEN matrix than CNTs-Fe₃O₄, thus resulting in significant improvement of the mechanical, thermal and dielectric properties of polymer-based composites.     

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.     

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.     

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.     

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.     

Metalorganic Vapor-Phase Epitaxy Growth Parameters for Two-Dimensional MoS<Subscript>2</Subscript>

The influence of the main growth parameters on the growth mechanism and film formation processes during metalorganic vapor-phase epitaxy (MOVPE) of two-dimensional MoS₂ on sapphire (0001) have been investigated. Deposition was performed using molybdenum hexacarbonyl and di-tert-butyl sulfide as metalorganic precursors in a horizontal hot-wall MOVPE reactor from AIXTRON. The structural properties of the MoS₂ films were analyzed by atomic force microscopy, scanning electron microscopy, and Raman spectroscopy. It was found that a substrate prebake step prior to growth reduced the nucleation density of the polycrystalline film. Simultaneously, the size of the MoS₂ domains increased and the formation of parasitic carbonaceous film was suppressed. Additionally, the influence of growth parameters such as reactor pressure and surface temperature is discussed. An upper limit for these parameters was found, beyond which strong parasitic deposition or incorporation of carbon into MoS₂ took place. This carbon contamination became significant at reactor pressure above 100 hPa and temperature above 900°C.     

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.     

Photoluminescence and composition of amorphous As<Subscript>2</Subscript>Se<Subscript>3</Subscript> films modified with Er(<Emphasis Type="Italic">thd</Emphasis>)<Subscript>3</Subscript> complex compound

The photoluminescence and composition of amorphous As₂Se₃ films modified with an Er(thd)₃ complex compound have been studied. A band centered at 1.54 μm, characteristic of photoluminescence from Er embedded in amorphous matrices, has been revealed at room temperature. The composition of thin amorphous As₂Se₃ films modified with an Er(thd)₃ complex compound has been examined by methods of nuclear microanalysis: Rutherford backscattering and nuclear resonant reactions. Dependences of the concentrations of Er ions, oxygen, and carbon on the growth conditions of the films are obtained. It is shown that the Er concentration in a thin film varies nonlinearly as the relative concentration of the starting complex compound increases. In addition, the increase in the Er content of a film is accompanied by a simultaneous rise in the content of such light elements as oxygen and carbon. Comparative analysis of the nuclear microanalysis data and IR spectra demonstrates that, in modification of As₂Se₃ with the Er(thd)₃ complex compound by the given method, the nearest environment of Er in the complex compound is partly preserved.