Search

Silicides and germanides are compounds consisting of a metal and silicon or germanium. In the microelectronics industry, silicides are the material of choice for contacting silicon based devices (over the years, CoSi2, C54-TiSi2, and NiSi have been adopted), while germanides are considered as a top candidate for contacting future germanium based electronics. Since also strain engineering through the use of Si1−xGex in the source/drain/gate regions of MOSFET devices is an important technique for improving device characteristics in modern Si-based microelectronics industry, a profound understanding of the formation of silicide/germanide contacts to silicon and germanium is of utmost importance. The crystallographic texture of these films, which is defined as the statistical distribution of the orientation of the grains in the film, has been the subject of scientific studies since the 1970s. Different types of texture like epitaxy, axiotaxy, fiber, or combinations thereof have been observed in such films. In...

The intermetallic compounds Ln6Co5Ge1.80Al2.20 (Ln: Pr, Nd) are prepared by reactions of Ge and Al in a reactive Ln/Co flux (alumina crucible, 950 °C, 12 h, annealing at 650 °C for 84 h).

Ba1.9Ca2.4Mg9.7Si7 was grown as large crystals from the reaction of silicon with barium and calcium in Mg/Al flux. This compound is a charge-balanced Zintl phase with the Zr2Fe12P7 structure type in hexagonal space group P6 (a = 11.196(2) A, c = 4.4595(9) A); barium occupies the Zr sites, the lighter alkaline earths (Mg, Ca) mix on the Fe sites, and silicon occupies the phosphorus sites. An isostructural germanide (Ba1.2Sr0.9Mg11.9Ge7, a = 11.064(1) A, c = 4.3709(6) A)) was similarly synthesized from reactions of germanium with barium and strontium in Mg/Al flux. Density of states calculations indicate these phases are semimetals, in agreement with their charge-balanced nature. Measurements of electrical resistivity, thermal conductivity, and Seebeck coefficient were carried out from 300–1000 K to investigate the thermoelectric properties of Ba1.9Ca2.4Mg9.7Si7. This compound is an n-type semimetal with low thermal conductivity (2 W/(m·K)), moderate Seebeck coefficient (−200 μV/K at 900 K), and a thermoel...

The title compound is synthesized from the elements at 13 GPa and 1100 °C and characterized by single crystal XRD, magnetic measurements, and DFT band structure calculations.

The surge in advancing the materials science of solid-state reactions for nanoscale contacts to advanced semiconductor devices necessitates a comprehensive dissemination and discussion on recent progress. The objective of this work is to review the notable developments in compound and alloy contact formation to nanoscale nanowire channels made of germanium, silicon, and their heterostructures, and to develop a unifying framework for understanding the significantly distinct reaction behaviors from those commonly observed in bulk. The Ni-based compound and alloy contacts are used as a platform to highlight the size-relevant, thermodynamic, and kinetic differences, and their key material, reaction, and electronic parameters and properties are summarized. Special attention is given to the interplay between the compound/alloy contact structure and the resultant electronic properties.

The title compound is prepared from a stoichiometric mixture of the elements (sealed Nb ampule, 1080 °C, 5 h and 750 °C, 2 d) and characterized by single crystal XRD and TB-LMTO computations.

Eu1.32Ca0.68Ge2Pb (I) and Sr0.42Eu1.58Ge2Pb (II) are synthesized from mixtures of the elements by Pb flux reactions (800 °C, 5 h).

Semitransparent dark-red or ruby-red single crystals of K10.35Ge18W0.65Nb0.35 O4, Rb10.35Ge18W0.65Nb0.35 O4, K10Ge18WO4, and Rb10Ge18WO4 are synthesized by solid state reactions using K, Rb, Ge, W, WO3, K2WO4, Rb2WO4, GeO2 and HgO as starting materials (Nb crucible, 800 °C, 120 h).

The title compounds are prepared by reaction of “ZrCuGe” or “HfCuGe” precursors (obtained by arc melting of the elements) with As at 800 °C for two weeks.

The new title compounds are obtained from melts of the elements and characterized by single crystal XRD and FP-LAPW band structure calculations.

LiCa7Ge3H3 (I) and LiCa11Ge3OH4 (II) are prepared by the reaction of Ge and CaH2 in a Ca/Li flux (1323 K, 2 h; 50% yield for (I) and 20% yield for (II)).

The title compound is obtained from a mixture of BaGe2 and Ge under high-pressure/high-temperature conditions (Kawai type multi-anvil press, 10 GPa, 1200 °C).

The title compound is synthesized from a stoichiometric mixture of La and Ge (10 GPa, 850 °C, 1 h).

Large single crystals of Eu2AuGe3 are prepared in high yield from the elements in liquid indium (1000 °C, 5 h).

Investigations made by susceptibility measurements and neutron diffraction experiments have been performed on the ternary germanide TbMn 6 Ge 6 of HfFe 6 Ge 6 -type structure ( P6/mmm ). TbMn 6 Ge 6 orders ferrimagnetically at T c ≈ 427 K but an antiferromagnetic state occurs below about 410 K. Neutron diffraction study shows that both rare earth and manganese sublattices order simultaneously at room temperature. Over the whole 2–300 K temperature range the magnetic structure is a flat spiral consisting of ferromagnetic (001) sheets (with the moments in the layers) of Mn and Tb atoms respectively stacked along the c axis in the sequence Mn1TbMn2Mn1TbMn2. At 2 K, according to the modulation vector k = (0, 0, ∼0.125), the magnetic moments change their orientation by about 45° within the basal plane on going from one Tb sheet to another, while one observes a spiral turn angle θ 1 ≈ 31° between adjacent Mn1TbMn2 layers and θ 2 ≈ 14° between Mn2Mn1 layers, i.e. a repeat distance of about 65 A. The moment values are μ Tb = 8.43(27) μ B and μ Mn = 1.84(18) μ B . The magnetic behaviour of TbMn 6 Ge 6 is similar to that observed for DyMn 6 Ge 6 above 100 K. In the latter case our refinements lead us to propose a new arrangement for the helimagnetic structure previously published, with a Dy magnetic moment corrected to about 9 μ B at 2 K. The results confirm the interplay between the magnetic coupling and the unit cell volume observed in GdMn 6 Ge 6 . A discussion and some comparisons with the parent RMn 6 Sn 6 compounds are given in conclusion.

The crystal structure of a new ternary germanide, ErNi 3 Ge 2 , formed by a peritectoid reaction at about 1170 K has been determined by X-ray powder diffraction using the Rietveld method ( 783 reflections, space group P 6 , Z=6, a=17.9662(2), c=3.79410(5) A , R I =5.93, R wp =13.15, R exp =7.40% ). The compound represents a new structure type. The relationships between ErNi 3 Ge 2 and CaCu 5 , YNi 5 Si 3 and CeGa 2 Al 2 types are discussed.

New ternary silicides have been discovered with the general formula R4T13X9, where R is a rare earth or uranium, T is rhodium or iridium and X is silicon or germanium. The crystal structure has been solved on a single crystal. The symmetry is orthorhombic with space group Pnmm. The lattice constants for Er4Ir13Si9 are a = 18.848(3) A , b = 10.918(2) A and c = 3.9153(5) A . The formation of the various members of this new family is in competition with that of the well-known ternary silicides RT3X2. Their existence as a function of the various elements (rare earth and transition metals) is discussed. The magnetic properties of the iridium-based compounds are presented. All the samples containing a paramagnetic rare earth are magnetically ordered at low temperature. U4Ir13Si9 and U4Ir13Ge9 exhibit two ordering transition temperatures: 18 and 6.4. K for the silicide and 25 and 7 K for the germanide.

The crystal structure of the uranium germanide U5Ge4 was determined and refined from single crystal X-ray diffraction data to R = 0.043, Rw = 0.054. U5Ge4 crystallizes in the hexagonal Ti5Ga4 (P63/mcm) structure type (filled up Mn5Si3 type) with the following lattice parameters: a = 8.744(4) A and c = 5.863(2) A . Investigation of neighbouring compositions, using X-ray powder diffraction refinements and microprobe analysis, revealed that the binary compound U5Ge4 is in equilibrium with the other binary UGe (ThIn type) and U metal dissolving 3% of germanium, whatever the annealing temperature in the range of 1000–1300°C. These results rule out the existence of the binary compositions U5Ge3 and U7Ge, which were previously reported. Magnetic measurements on an annealed polycrystalline powder sample of U5Ge4 indicate nearly temperature independent paramagnetic behaviour down to 2 K.

Novel ternary ytterbium-zinc-silicides and germanides have been synthesized using pure zinc metal as a flux-solvent. The new compounds, YbZn 2 Si 2 and YbZn 2 Ge 2 crystallize with the BaAl 4 or ThCr 2 Si 2 -type. Yb(Zn,Si) 2 and Yb(Zn,Si) 2− x crystallize with the ThSi 2 and the GdSi 2− x type, respectively. Crystal properties were characterized using X-ray single crystal analysis via Gandolfi and Weissenberg film techniques, by flat specimen X-ray powder diffractometry and in some cases by automatic four circle X-ray single crystal diffractometry. Depending on the heating and cooling program in the synthesis, various lattice parameter values were obtained suggesting the existence of homogeneity regions. Both the Yb-Zn-silicides and the germanide show a temperature independent Pauli-type paramagnetic behaviour down to liquid He temperature consistent with the XAS-measurements revealing an Yb 2+ ground state.

Syntheses of the so-called “suboxide” phases Ba21T2O5 (T = Ge, Si, Ga, In, Tl) are achieved only in the presence of hydrogen. The heavy-atom structure of Ba21Ge2O5H24 at room temperature was redetermined by single-crystal X-ray diffraction and found to be primitive trigonal symmetry (P3121 (No. 152), Z = 6, a = 14.4227(5) A, c = 35.332(3) A) instead of the previously refined cubic (Fd3m) result. The change greatly improves the heavy-atom parameters. Twenty-four independent deuterium atoms have also been located by time-of-flight neutron diffraction. The structure contains Ba2+ cations, and three different types of monatomic anions, corresponding to the oxidation states (Ba+2)21(Ge-4)2(O-2)5(H-)24. The deuterium atoms occupy tetrahedral, square-pyramidal, and octahedral barium interstices while the oxide anions lie in nearly regular octahedral barium polyhedra. The germanide anions are surrounded by 12 barium atoms in a distorted icosahedral configuration. Property measurements show that Ba21Ge2O5H24 is d...

The crystallographic structure of the binary uranium germanide U 3 Ge 5 was determined from single crystal X-ray diffraction data to R ( F )=0.076 and R ω =0.085. U 3 Ge 5 crystallizes with the hexagonal AlB 2 structure type ( P6/mmm ) with the following lattice parameters: a =3.954(1) A, c =4.125(1) A. A partial occupation of the germanium site leads to the effective composition UGe 1.57 and the observation of weak superlattice reflections indicates some ordering of the germanium vacancies which could not be resolved. Magnetic susceptibility measurements on an annealed polycrystalline sample revealed ferromagnetic ordering below T c =94 K, which was previously claimed for the composition U 3 Ge 4 . The magnetic structure was determined from neutron powder diffraction data collected on the G4-1 powder diffractometer at LLB Saclay. The structure is ferromagnetic ( R m =0.02) with the uranium moments at 1.4 K: M U =2.28(4) μ B , described by a main component along the c -axis of the hexagonal subcell M z =1.80(4) μ B and an in-plane component: M x,y =1.40(5) μ B .

The germanide Yb2Ru3Ge4 was synthesized from the elements using the Bridgman crystal growth technique. The monoclinic Hf2Ru3Si4 type structure was investigated by X-ray powder and single crystal diffraction: C2/c, Z=8, a=1993.0(3) pm, b=550.69(8) pm, c=1388.0(2) pm, β=128.383(9)°, wR2=0.0569, 2047 F2 values, and 84 variables. Yb2Ru3Ge4 contains two crystallographically independent ytterbium sites with coordination numbers of 18 and 17 for Yb1 and Yb2, respectively. Each ytterbium atom has three ytterbium neighbors at Yb–Yb distances ranging from 345 to 368 pm. The shortest interatomic distances occur for the Ru–Ge contacts. The three crystallographically independent ruthenium sites have between five and six germanium neighbors in distorted trigonal bipyramidal (Ru1Ge5) or octahedral (Ru2Ge6 and Ru3Ge6) coordination at Ru–Ge distances ranging from 245 to 279 pm. The Ru2 atoms form zig-zag chains running parallel to the b-axis at Ru2–Ru2 of 284 pm. The RuGe5 and RuGe6 units are condensed via common edges and faces leading to a complex three-dimensional [Ru3Ge4] network.

Formation and crystal structure of the binary germanide Eu3Ge5 were investigated in detail. The compound forms peritectically at 10081C and does not undergo any phase transition down to room temperature. The crystal structure was determined first from X-ray powder diffraction data and was later confirmed by single-crystal X-ray diffraction: structure type Pu3Pd5, space group Cmcm (no. 63), a ¼ 9:7675ð4Þ ˚

The Tb 4 Zn 5 Ge 6 phase was prepared by arc melting in an argon atmosphere and then annealed at 670 K for 400 h. The structure of orthorhombic Tb 4 Zn 5 Ge 6 was determined by single-crystal X-ray diffraction ( Cmc 2 1 , Z = 4, a = 4.2330(10) A, b = 18.576(4) A, c = 15.275(3) A, R 1 = 0.0272 and wR 2 = 0.1076). The structure is isostructural to Gd 4 Zn 5 Ge 6 and composed of edge- and corner-sharing ZnGe 4 tetrahedra, Tb-atoms forms trigonal prisms filled by Ge-atom.

The ternary germanide Tb4FeGe8 was obtained from Ga flux reactions. The crystal structure studied with single-crystal X-ray diffraction revealed the existence of an orthorhombic average substructure (Cmcm, Z=1) with cell parameters a = 4.1118(14) A, b=15.844(5) A, and c=3.9885(15) A. The refinement [I > 2sigma(I)] converged to final residuals R1/wR2 = 0.0363/0.0893. The average structure (CeNiSi2-type) consists of a 3D [Fe1/4Ge2] framework where Ge atoms form a square net and Fe atoms reside alternatively above and below it with only 1/4 occupation probability. X-ray and electron diffraction studies showed a modulation in the Ge net. The modulated structure was refined based on a 4-fold monoclinic supercell (P2(1)/n) with parameters a = 5.7315(11) A, b = 15.842(3) A, c = 11.438(2) A, and beta = 91.724(4) degrees with R1/wR2 = 0.0643/0.1735 and uncovered a severe distortion of the Ge square net. The Ge atoms are displaced to form an array of cis-trans chains. The Ge-Ge distances within these chains are distinctively bonding, whereas those between the chains are nonbonding. Results of the electronic structure calculations and magnetic measurements are also reported. The structural distortions found in Tb4FeGe8 cast a doubt onto the correctness of many of the reported REM1-xGe2 disordered compounds and call for reinvestigation.

A new germanide, SrGe6-δ (δ ≅ 0.5), was synthesized by the reaction of Sr and Ge mixtures under a pressure of 5 GPa at 1200 °C. It crystallized in the orthorhombic space group Cmcm (No. 63) with a = 4.0981(6) A, b = 11.159(1) A, c = 12.6825(8) A, V = 580.0(1) A3, and Z = 4. SrGe6-δ is composed of a Ge covalent network having a cagelike structure and Sr atoms situated in the cages. Each Ge atom is coordinated by four neighboring Ge atoms. The coordination polyhedra are fairly distorted from an ideal tetrahedron, and the Ge network contains vacancies and disordering. The resistivity shows metallic behavior down to 2 K, and the positive thermoelectric power indicates the dominant carriers to be holes.

The crystal structure of the ternary intermetallic compounds U3Ni6Si2 and U3Ni6Ge2 have been determined from single crystal X-ray diffraction data. They crystallize in the cubic system, with the lattice parameters a=8.647(2) and 8.7942(3) A, respectively. U, Ni, and (Si, Ge) atoms occupy 12e, 24h and 8c Wyckoff positions of space group Im 3 m. They are ternary ordered variants of the Ce3Ag8 structure type. Interestingly, uranium atoms form regular U6 octahedral clusters, with U–U distances lower (3.31 A) and at the vicinity (3.45 A) of the Hill limit. For the germanide, a significant electron density is present at the center of the octahedral void formed by the uranium atoms, which may be due either to carbon or to oxygen atoms, due to contamination during crystal growth. None of the compounds order magnetically at low temperature.

A new cerium germanide, CeGe 3 was prepared by the reaction of a stoichiometric mixture of CeGe 2 and Ge under a pressure of 5 GPa at 1600 °C. It crystallized in a cubic unit cell with a = 4.354 (4) A, and was isotypic with CeSn 3 and CePb 3 having the Cu 3 Au structure. It showed a Curie-Weiss paramagnetic behavior from room temperature to 20 K with a Curie constant C of 0.0495 emu mol - 1 .K. The effective magnetic moment of 0.63 μ B , which was much smaller than the theoretical values of 2.54 μg for Ce3 + (4f 1 ) ions, was observed. This compound showed a metallic behavior with the resistivity of 130 and 7 μΩ.cm at room temperature and 2K, respectively.

The crystal structure of the new ternary germanide YbFeGe, space group C2/m (N12), a =10.607(6) A, b =3.904(2) A, c =6.715(3) A, β =127.58(1)°, Z =4, V =220.35 A, ρ =9.088 g cm −3 , μ =61.67 mm −1 was refined to R =0.0313, wR2 =0.0705 from single crystal X-ray diffraction data. This is the first representative of a new structure type (str. type) of intermetallic compounds. The formation and crystal structure for this compound were confirmed from X-ray powder diffraction: a =10.5755(5) A, b =3.9034(3) A, c =6.7117(4) A, β =127.68°. An isotypic YbMnGe compound was observed: YbFeGe str. type, C2/m space group (sp. gr.), a =10.5966(4) A, b =3.9014(2) A, c =6.7782(3) A, β =127.42°. The crystal structures for the YbCoGe compound (TiNiSi str. type, Pnma sp. gr., a =6.7168(4) A, b =4.0392(2) A, c =7.2684(4) A) and YbMn 2 Ge 2 compound (CeGa 2 Al 2 str. type, I4/mmm sp. gr., a =4.0334(5) A, c =10.0334(7) A) are reported for the first time.

The Zintl-phase LiGe has recently been shown to undergo a transformation at elevated temperature and pressure to a metastable modification, which differs markedly from the normal-pressure form in the bonding between the Ge atoms. In the normal form the Ge net is exclusively three-connected, but in the high pressure (HP) form there is a mixture of Ge environments. One-third are approximately tetrahedrally four-connected, while the remainder have two short bonds (to the four-connected atoms) and two longer contacts (to other atoms of the same type), arranged in a distorted square plane. Whether or not the longer contacts are ignored, the HP form no longer obeys the electron-counting principles of Zintl or Klemm. In this paper they examine the bonding between the planar four-coordinated atoms and discuss the way the deviation from the Zintl counting rules can be seen to be consistent with the observed structure.

Two parent alloys with compositions Mn11Ge8 and Mn3Ge2 were prepared by melting at 1273 K for 3.6 × 103 s (1 h) in an argon atmosphere. The alloys were then annealed at 953 K for 9.0 × 105 s (250 h) in an evacuated quartz tube. The annealed Mn11Ge8 alloy is not single phase but a two-phase with free germanium. In order to establish the composition of the most germanium-rich germanide, using the two parent alloys, sintered MnGex with the compositions in the range 0.664 ⩽ x ⩽ 0.753 were prepared by a powder metallurgical technique. The apparent density, resistivity and magnetization of MnGex changed drastically over the very narrow range 0.700 ⩽ x ⩽ 0.706. From the results of X-ray integrated diffraction intensity measurements and quantitative analyses by means of electron probe micro-analysis and pycnometric density, it is confirmed that the most germanium-rich germanide of manganese is a line compound Mn44Ge31.