Photodetector devices based on PIN and barrier structures of the mid-wave IR range of the spectrum

Multilayer structures based on the antimonide group materials with absorber layers InSb or AlxIn1-XSb, and XBn-structures with AlxIn1-XSb barrier layer (InSb/AlxIn1-XSb/InSb), designed for the manufacture of advanced photosensitive devices detecting radiation in the medium-wave infrared (IR) range (MWIR), have been developed and investigated. Various topology photosensitive elements (PSE) with absorbing layers InSb or AlxIn1-XSb were fabricated on the basis of MBE-grown p–i–n and barrier structures. It is shown that wideband ternary al-loys AlxIn1-XSb are considered as an alternative to the narrowband binary compound InSb, since, due to wide-band material properties, photodiodes based on AlxIn1-XSb have lower dark currents, and, consequently, noise. The average values of detectivity D* and noise-equivalent temperature difference (NETD) have been measured for various topology photodetectors, so D* was more than 1011 cmW-1Hz1/2 in p–i–n-structures, and D* exceed of 1012 cmW-1Hz1/2 in barrier structures.

Phase equilibrium diagram of the Hf-Fe-Sn system at 1070 K

Experimental studies of the phase equilibrium diagram of the Hf-Fe-Sn ternary system at 1070 K were performed by X-ray powder diffractometry, scanning electron microscopy and electron probe microanalysis techniques in the whole concentration range. At annealing temperature four ternary compounds are realized: Hf6FeSn2 (K2UF6 structure type, space group P-62m), Hf1.8Fe5Sn3.8 (Hf1.82Fe5Sn3.82 structure type, space group Cmmm), Hf3Fe4Sn4 (Zr3Fe4Sn4 structure type, space group Pnma), and Hf9Fe3.7Sn10.3 (Hf9Fe4Sn10 structure type, space group Cmc21). An existence of the Hf1-xFe2+x-ySny solid solution formed by substitution of the iron atoms by tin in the Hf1-xFe2+x (MgZn2-type) binary compound up to 19 at. % Sn was found. Solubility of Fe in the Hf5Sn3 binary (Mn5Si3-type) extends up to 10 at. % (a=0.8363(2)-0.8324(4), c=0.5726(1)-0.5686(4) nm).

The Role of Different Alkali Metals in the A15Tl27 Type Structure and the Synthesis and X-ray Structure Analysis of a New Substitutional Variant Cs14.53Tl28.4

Alkali metal thallides have been known since the report of E. Zintl on NaTl in 1932. Subsequently, binary and ternary thallides of alkali metals have been characterized. At an alkali metal proportion of approximately 33% (A:Tl~1:2, A = alkali metal), three different unique type structures are reported: K49Tl108, Rb17Tl41 and A15Tl27 (A = Rb, Cs). Whereas Rb17Tl41 and K49Tl108 feature a three-dimensional sublattice of Tl atoms, the A15Tl27 structure type includes isolated Tl11 clusters as well as two-dimensional Tl-layers. This unique arrangement is only known so far when the heavier alkali metals Rb and Cs are included. In our contribution, we present single-crystal X-ray structure analyses of new ternary and quaternary compounds of the A15Tl27 type structure, which include different amounts of potassium. The crystal structures allow for the discussion of the favored alkali metal for each of the four Wyckoff positions and clearly demonstrate alkali metal dependent site preferences. Thereby, the compound Cs2.27K12.73Tl27 unambiguously proves the possibility of a potassium-rich A15Tl27 phase, even though a small amount of cesium appears to be needed for the stabilization of the latter structure type. Furthermore, we also present two compounds that show an embedding of Tl instead of alkali metal into the two-dimensional substructure, being equivalent to the formal oxidation of the latter. Cs14.53Tl28.4 represents the binary compound with the so far largest proportion of incorporated Tl in the structure type A15Tl27.

Crystal structure of new ternary disilicide of platinum and erbium

Crystal structure of the ternary compound ErPtSi2 (diffractometer HZG-4a, CuK-radiation, structure type YIrGe2, Pearson symbol oI32, space group Immm, a=4.19395(6) Å, b=8.41465(13) Å, c=15.85404(19) Å, RB=0.0639, Rp=0.0424, and 2=1.11) was studied by X-ray powder diffraction method. Intermetallide ErPtSi2 is the first representative of YIrGe2 structure type in R–Pt–Si systems. Crystal structures of ternary compounds in the system Er–Pt–Si were analyzed and the structural relationships between them were established according to the systematics of the nearest coordination environment around the less electronegative Er atoms. Compounds, found in the system, were divided into two main types based on the nearest coordination environment, namely on the derivatives of hexagonal and pentagonal prisms with different amounts of additional atoms. These polyhedra exist both alone and in the combination with each other and with cubooctahedra in the structures of the different ternary silicides of erbium. Such a relatively small coordination environment of rare-earth metal atoms can be explained by the structural peculiarities of the ErPt3 binary compound. The coordination polyhedra of the smallest atoms are trigonal prisms with different amounts of additional atoms or cubooctahedra.

Qualitative analysis of Phytochemical studies on Sargassum wightii and Padina gymnospora

In recent years, the secondary metabolites are extensively investigated as a supply of healthful agents. The sample for the study constitutes Sargassum wightii and Padina gymnospora and it was collected from the Mandapam coast, Rameswaram, TamilNadu, India. Sargassum wightii is belonging to the family Sargassum wightii and Padina gymnospora belonging to the family Dictyotaceae are 2 brown seaweeds better-known for varied biological activities like bactericide, antiviral, inhibitor, opposed cancer, medicine, etc. Five totally different extracts of Sargassum wightii and Padina gymnospora were subjected to phytochemical analysis of secondary metabolites of qualitatively phytochemical screening tests of twelve different chemical compounds (alkaloids, terpenoids, steroids, tannins, saponins, flavonoids, phenols, coumarins, proteins, sugars, quinones, and glycosides). Among the solvent extracts of alga Sargassum wightii and Padina gymnospora showed the utmost presence of saponins, carbohydrates, proteins, and quinines in 3 completely different extracts (ethanol, methanol, water) except solvent and chloroform. So the present study on extractive values of methyl alcohol extract and the binary compound extract was most in each the seaweeds, however, were significantly a lot of in P. gymnopora than S. wightii. Considering their therapeutic uses, like alternative healthful plants there’s a requirement to try pharmacognostic studies of those 2 seaweeds. KEYWORDS: Seaweeds, Coumarins, Phytochemicals, Sargassum wightii and Padina gymnospora

Synthesis and Characterization of Copper Selenide and Tin Selenide Powders by Mechanical Alloying Method

This paper reports on the synthesis of copper selenide (CuSe) and tin selenide (SnSe) powders by high energy planetary ball milling, starting from elemental powders. Synthesis time and milling speed have been optimized to produce single phase CuSe and SnSe materials. The structural, compositional, morphological and optical properties of the synthesized samples have been analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM), Field Emission Scanning Electron Microscopy (FESEM) and UV-Vis. The low-temperature phase selection of the binary compound in this system is seen as a direct consequence of the thermodynamic facilitation, coupled with the capability of mechano-chemical synthesis to aid in overcoming kinetic constraints.

First principles study of the structural, electronic, optical and thermodynamic properties of cubic quaternary Al x In1−x P y Bi1−y alloys

The non-relativistic full potential linearized augmented plane wave (FP LAPW) method was applied to investigate the structural, electronic, optical and thermodynamic properties of (ZB)-AlP, AlBi, InP and InBi compounds and their ternary Al x In1−x P, Al x In1−x Bi, AlP x Bi1−x and InP x Bi1−x and the ordered Al x In1−x P y Bi1−y quaternary alloys. For the exchange-correlation potential, the LDA, GGA and WC-GGA have been used to calculate structural parameters. The TB-mBJ approximation was used to compute the band structures. Our results for binary compound agree well with available data found in literature. The lattice constants and the bulk modulus versus compositions x and y deviate from the linearity. All quaternary alloys are semiconductors with direct band gap with the exception for Al0.25In0.75P0.25Bi0.75 and Al0.25In0.75P0.50Bi0.50, which exhibit a half metallic character (the band gap tends to zero). Furthermore, the optical properties such as the dielectric constants, refractive index, absorption, reflectivity and the energy loss have been calculated and analysed in the energy range varying from 0 to 14 eV. At the end, we have investigated some thermodynamic properties, where the lattice constants, the Debye temperature θ D, the heat capacity C V and the entropy S were carried out, plotted and discussed.

Discovery of $${\hat{\boldsymbol{C}}}_2$$ rotation anomaly in topological crystalline insulator SrPb

Topological crystalline insulators (TCIs) are insulating electronic states with nontrivial topology protected by crystalline symmetries. Recently, theory has proposed new classes of TCIs protected by rotation symmetries $$\hat C_n$$ C ̂ n , which have surface rotation anomaly evading the fermion doubling theorem, i.e., n instead of 2n Dirac cones on the surface preserving the rotation symmetry. Here, we report the first realization of the $$\hat C_2$$ C ̂ 2 rotation anomaly in a binary compound SrPb. Our first-principles calculations reveal two massless Dirac fermions protected by the combination of time-reversal symmetry $$\hat T$$ T ̂ and $$\hat C_{2y}$$ C ̂ 2 y on the (010) surface. Using angle-resolved photoemission spectroscopy, we identify two Dirac surface states inside the bulk band gap of SrPb, confirming the $$\hat C_2$$ C ̂ 2 rotation anomaly in the new classes of TCIs. The findings enrich the classification of topological phases, which pave the way for exploring exotic behavior of the new classes of TCIs.

Interaction of Components in the Lu-Ag-Si System at 500 ºC

Isothermal section of the Lu-Ag-Si system at 500ºC was studied by means of X-ray powder diffraction, microstructure and EDX-analyses in the whole concentration range. The existence of earlier reported binary compounds LuAg4, LuAg2, LuAg and LuSi2, LuSi, Lu5Si3, Lu5Si4 was confirmed. New binary compound Lu3Si5 (own str. type) was found. Almost none of the binary silicides dissolve more than 5 at.% of third component. The exception is the existence of the substitution type solid solutions based on LuAg2 (MoSi2-type structure), which dissolves up to 20 at.% Si, as well as on Lu5Si3 (Mn5Si3-type structure), which dissolves up to 15 at.% Ag. The crystal structure of the LuSi compound was redetermined by X-ray single crystal diffraction (TlI-type, space group Cmcm, a = 4.1493(3), b = 10.2641(7), c = 3.7518(2) Å, R = 0.0173, wR = 0.0415 for 173 independent reflections). No ternary compound is observed in the Lu-Ag-Si system.