Semimetal Compound Research Articles

Effect of substrate temperature on the properties of ZrB2 film on Si(111) deposited by pulsed DC magnetron sputtering

The wurtzite GaN and related nitride films are typically grown on sapphire or SiC substrates. However, large lattice-mismatches between GaN and sapphire or SiC can lead to degradation of quality of grown GaN by 16 and 4%, respectively. ZrB2 is a semi-metal compound and has a hexagonal crystal structure. The a-axis lattice constant of ZrB2 is 3.168 Å, which is almost lattice-matched to GaN. The thickness of ZrB2 film is 228 nm which was prepared on a Si(111) substrate by pulsed DC magnetron sputtering deposition. The effects of substrate temperatures ranging from 400 to 550 °C on the microstructure, resistivity and surface roughness of the deposited ZrB2 films were investigated by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), the four-point probe technique and atomic force microscopy (AFM). XRD analysis revealed that the ZrB2 film had a polycrystalline structure and the preferred orientation was along (001) when the substrate temperature was above 450 °C. The relationship between the average grain size of the ZrB2 film and substrate temperatures ranging from 450 to 550 °C forms a downward parabolic function. The minimum average grain size of the ZrB2 film was 10.6 nm when the substrate temperature was 500 °C. The minimum resistivity of the ZrB2 film was 229 µΩ cm when the substrate temperature was 550 °C. The AFM measurements showed the ZrB2 films to have a uniform morphology with a very low surface roughness value of 0.2 nm. In this work, it was found that a uniform surface morphology and preferred orientation along (001) of the ZrB2 film on Si(111) could be obtained through pulsed DC magnetron sputtering when the substrate temperature was above 450 °C. This mirror-polished ZrB2 buffer layer is a good candidate for GaN film growth on Si(111) wafers.

Ab initio study of structural and electronic properties of ternary alkali-metal-based semimetal compounds

Based on the ab initio calculations, we propose a new class of three dimensional (3D) topological insulators in alkali-metals-based ternary intermetallic compounds X2YZ (X=alkali metals, Y=Ag, Z=Sb) with a highly ideal assumption that the X2YZ compounds would crystallize in a cubic lattice. The band topology of X2YZ is explored by using full-potential linear augmented plane wave method. The results reveal that the topological insulator state of X2YZ can be realized by applying a uniaxial tensile strain of greater than 3% along the [001] direction and the electronic structure exhibits a distinct band-inversion feature. This new X2YZ compounds provide an alternate platform for novel quantum phenomena and multifunctional topological devices.

Mössbauer studies of two-electron centers with negative correlation energy in crystalline and amorphous semiconductors

The results of the study of donor U −-centers of tin and germanium in lead chalcogenides by Mossbauer emission spectroscopy are discussed. The published data regarding the identification of amphoteric U −-centers of tin in glassy binary arsenic and germanium chalcogenides using Mossbauer emission spectroscopy, and in multicomponent chalcogenide glasses using Mossbauer absorption spectroscopy are considered. Published data concerning the identification of two-atom U −-centers of copper in lattices of semimetal copper oxides by Mossbauer emission spectroscopy are analyzed. The published data on the detection of spatial inhomogeneity of the Bose-Einstein condensate in superconducting semiconductors and semimetal compounds, and on the existence of the correlation between the electron density in lattice sites and the superconducting transition temperature are presented. The principal possibility of using Mossbauer U −-centers as a tool for studying the Bose-Einstein condensation of electron pairs during the superconducting phase transition in semiconductors and semimetals is considered.

Electroluminescence of InGaAs/GaAs quantum-size heterostructures with (III, Mn)V and Ni ferromagnetic injectors

Electroluminescence characteristics of light-emitting diodes based on InGaAs/GaAs quantum well heterostructures with an injector layer made of ferromagnetic metal (Ni), semimetal compound (MnSb), or magnetic semiconductor (InMnAs) were comparatively studied. The general feature is electroluminescence quenching as the spacer layer thickness between a quantum well and a magnetic injector decreases. It was found that the temperature dependence of the electroluminescence in diodes with Ni and MnSb is caused by thermal ejection of carriers from the quantum well; in diodes with InMnAs, it is caused by the temperature dependence of the carrier concentration in magnetic semiconductor and thermal ejection of carriers from the quantum well in the high-temperature region.

Supramolecular Aggregation of Inorganic Molecules at Au(111) Electrodes under a Strong Ionic Atmosphere

Neutral inorganic molecules are generally weak in surface adsorption and intermolecular interactions. Self-assembly of such types of molecule would provide valuable information about various interactions. At electrochemical interfaces, the relative strength of these interactions may be modified through control of electrode potential and electrolyte, which may lead to the discovery of new structures and new phenomena. However, studies of this nature are as yet lacking. In this work, we consider the covalent-bound semimetal compound molecules, XCl(3) (X = Sb, Bi), as model systems of neutral inorganic molecules to investigate their self-assembly at electrochemical interfaces under a high ionic atmosphere. To fulfill such investigations, in situ STM and cyclic voltammetry are employed, and comparative experiments are performed on Au(111) in ionic liquids as well as aqueous solutions with high ionic strength. In the room temperature ionic liquid of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF(4)), potential-dependent partial charge transfer between the Au surface and XCl(3) molecules creates a molecule-surface interaction and provides the driving force for adsorption of the molecules. Supramolecular aggregations of adsorbed XCl(3) are promoted through chlorine-based short-range intermolecular correlation under crystallographic constraint, while repulsive Coulombic interactions created between the partially charged aggregations facilitate their long-range ordering. For SbCl(3) molecules, hexagonally arranged 6- or 7-member clusters are formed at 0.08 to -0.2 V (vs Pt), which assemble into a secondary ( radical31 x radical31)R8.9 degrees structure. For BiCl(3) molecules, both the 6-membered hexagonal and 3-membered trigonal clusters are formed in the narrow potential range -0.3 to -0.35 V, and are also arranged into an ordered secondary structure. Comparative studies were performed with SbCl(3) in concentrated aqueous solutions containing 2 M HCl to simulate the strong ionic strength of the ionic liquid. Almost identical 6-/7-member clusters and long-range ( radical31 x radical31)R8.9 degrees structure are observed at -0.1 V, demonstrating the crucial role of strong ionic strength in such supramolecular aggregations. However, such supramolecular structures are modified and eventually destroyed as ionic strength is further increased by addition of NaClO(4) up to 6 M. The destructive changes of the supramolecular structures are attributed to the alteration of ion distribution in the double layer from cation-rich to anion-rich at increasing NaClO(4) concentration. This modifies and eventually breaks the balance of intermolecular and molecule-electrolyte interactions. Finally, the dynamic behavior of the SbCl(3) assembly is investigated down to molecular level. It has been demonstrated that the initial stage of assembly follows a two-dimensional nucleation and growth mechanism and has a potential-dependent rate that is closely related to the surface mobility of the SbCl(3) clusters. There is a probability that clusters can escape from an existing assembly domain or insert into a vacancy in such a domain while they can also relax with central or ring members in a dynamic fashion. These phenomena indirectly reflect the dynamic properties of cations from electrolytes at the interface. The rich information contained in the self-assembly behavior of SbCl(3) and BiCl(3) demonstrates that neutral inorganic molecules can be employed for fundamental studies of a variety of interesting issues, especially the interplay of various interfacial interactions.

Iron-based superconductors

For 22 years ceramic oxides of copper seemed to offer the only way to reach high-temperature superconductivity. Now, a new and unexpected route is being charted: through semimetal compounds of iron.

The pure rotational spectrum of TeSe: Rotational parameters, Born–Oppenheimer breakdown corrections, and hyperfine constants

The characterization of tellurium selenide in its electronic ground state (X0 + ∑ − ) was possible by using LASER-ablation to isolate the diatomic in a pulsed molecular beam and by applying Fourier transform microwave spectroscopy to obtain the pure rotational spectrum. Employing a global multi-isotopologue analysis to transitions of 43 isotopologues of TeSe in seven vibrational states spectroscopic Dunham parameters Y ℓ , m , Born–Oppenheimer breakdown coefficients δ ℓ , m , the equilibrium bond lengths r e, as well as the vibration parameters ω e and ω e x e were obtained for all analysed isotopologues. For low vibrational states, the Morse-potential function describes the TeSe-potential very well and provides an estimate of the maximum dissociation energy for this semi-metal compound. In addition, the isotopologue independent molecular constants U ℓ , m and the corresponding Born–Oppenheimer breakdown coefficients Δ ℓ , m were determined. Quite large coefficients Δ 0 , 1 Te and Δ 0 , 1 Se were necessary for Watson's reference isotopologue independent analysis. This is rationalized by the interaction between the two sublevels of the electronic 3Σ-state. Also the magnetic spin–rotation coupling constants that were achieved for some of the isotopologues reflect this electronic ground state. Field shift effects are found to be negligible.

Hydrogen induced antiferromagnetism in the Kondo semimetal CeNiSn

We have used neutron diffraction and magnetic measurements to investigate the changes in magnetic properties of the Kondo semimetal compound CeNiSn after charging with deuterium gas under moderate conditions. Charging with deuterium led to the formation of the monodeuteride CeNiSnD with filled TiNiSi structure. This compound gives rise to long-range antiferromagnetic ordering below T N=5.1 K. The ordered magnetic moment value equals 1.37(3) μ B per Ce atom, the moments pointing along the [001] direction. No significant ordered magnetic moment on the Ni atoms has been observed by powder neutron diffraction.

Heteroepitaxial growth of group-III nitrides on lattice-matched metal boride ZrB 2 (0 0 0 1) by molecular beam epitaxy

Growth of group-III nitrides was carried out on zirconium diboride (ZrB 2) (0 0 0 1) substrates for the first time. ZrB 2 is a semi-metal compound and have a hexagonal crystal structure. The a-axis lattice constant of ZrB 2 is 3.169 Å, which is almost lattice-matched to GaN and AlN. GaN and AlN were grown on mirror-polished ZrB 2 (0 0 0 1) substrate directly by molecular beam epitaxy using elemental Al and Ga, and radio frequency plasma-excited active nitrogen. Epitaxial growth was confirmed by in situ reflection high-energy electron diffraction observation and X-ray diffraction pole-figure measurement. The surface morphology of 1.4 μm-thick GaN layer was rough. On the other hand, that of 0.9 μm-thick AlN layer was specular.

Epitaxy of Dissimilar Materials

Differences in crystal structure, bonding, and materials properties play important roles in dissimilar materials epitaxy. Emphasis is placed on how these differences affect the growth of dissimilar materials heterostructures. Examples of the growth of elemental metals and semi-metals (AI, Ag, Sb, Bi); metallic and semi-metal compounds (transition-metal group III compounds with CsCI crystal structure, rare-earth group V compounds with NaCl crystal structure, orthorhombic YbSb2, Fe3AI'_xSix with BiF3 crystal structure); magnetic compounds (tetragonal ,-MnAI, hexagonal �­ MnAs); and insulators (rare-earth trifluorides with tysonite crystal struc­ ture, metal fluorides with the CaF2 crystal structure) on compound semi­ conductors are used to demonstrate the issues involved. The use of tem­ plate layers is crucial in controlling the orientation and crystal quality of the epitaxial layers.

Atomic radii in semi-metallic compounds of rocksalt structure

Consideration of the lattice parameters observed for semi-metal compounds of the type MX where M is a rare-earth and X = N, P, As, Sb, S, Se or Te leads to a definition of characteristic radii for the non-metal atoms. For S, Se and Te these are close to the Pauling X 2− radii, whereas for N, P, As, Sb the values are less than the calculated X 3− radii, indicating some degree of electron delocalisation into the metallic conduction band. Using these anion radii, the cation radii in the corresponding actinide semi-metal compounds are calculated. It is concluded that these compounds generally contain Th 4+, U 4+ or U 5+ and Pu 3+ or Pu 4+ionic cores.