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A Nowotny chimney-ladder (NCL) chromium germanide (CrGeγ) with varying compositions has been synthesized under high pressure. Crystal structure parameters of the NCL CrGeγ have been calculated by Le Bail refinement based on the superspace group. The refined γ of CrGeγ increases with the synthesis pressure, indicating an increasing Ge content. The NCL CrGeγ phases are ferromagnetic at T = 2 K regardless of their composition, and the magnetic transition temperature (TC) increases when the γ becomes higher. It is noteworthy that CrGe1.763 and CrGe1.774 synthesized at P = 10 and 14 GPa have magnetic transition temperatures of T = 295 and 333 K above room temperature, respectively. Surprisingly, the magnetic transition temperature has changed by ΔTC = 270 K, although the γ values of the raw material and the sample synthesized at P = 14 GPa differ by only Δγ = 0.05, corresponding to an atomic concentration of 0.62 atom %. The synthesis pressure acts as an essential parameter in tuning the composition of the NCL phase. Accordingly, the high-pressure synthesis may significantly control several physical characteristics of NCL phases by utilizing compositional and structural modulation.

Two-dimensional materials are at the forefront of material research in the past decade. Besides graphene, there exist large groups of its heavier analogues, silicon- and germanium-based two-dimensi...

This work presents preparation of nickel germanide (Ni2Ge) thin films by atomic layer deposition (ALD). The films were grown using NiCl2(tmpda) (tmpda = N,N,N',N',-tetramethyl-1,3-propanediamine) and tributylgermanium hydride serving as a new, efficient reducing agent. This is the first time ALD NixGey films are prepared directly upon the combination of two precursors and without any annealing treatment. NixGey is an important contact material for enabling Ge-based transistors and thus circumventing the scaling issues related to current microelectronics. The Ni2Ge process was examined at low temperatures of 160-200 degrees C. Self-limiting, saturative growth with a high growth rate of 0.91 angstrom/cycle was observed at 180 degrees C. The films were thoroughly analyzed in terms of morphology, crystallinity, composition, and resistivity. The Ni2Ge films were pure, with the sum of contaminants being less than 1 at. %. Owing to their high purity, the films exhibited low resistivity, suggesting suitability for contact applications.

Single crystals of the ternary Pr3Co2+xGe7 and Ln3Co2+xGe7–ySny (Ln = Pr, Nd, Sm) adopting a disordered version of the La3Co2Sn7 structure type have been prepared via flux-growth methods and characterized by single crystal X-ray diffraction. The structure consists of two lanthanide crystallographic sites with one occupying a cuboctahedral coordination environment and a second in a trigonal prismatic environment. The structure can also be described as an intergrowth of AuCu3 and CeNiSi2 structure types, and the stability of the germanide analogues requires Sn incorporation and Co site preferences. Magnetic properties of the Pr3Co2+xGe7–ySny series are highlighted with the Sn-substituted Pr3Co2.514(5)Ge6.66(7)Sn0.360(2) orders magnetically near 5.8 K, while the germanide Pr3Co2.3376(5)Ge7.056(7) exhibits magnetic transitions at 5.3 and 9.3 K, arising from the magnetic sublattices with field-dependent magnetization revealing three metamagnetic transitions at 0.46, 0.80, and 2.1 T.

The method of germanium and silicon regeneration from waste germanium lenses and photovoltaic cells was successfully verified with the total yield of germanium of above 97 wt %. The preparation of magnesium germanide, magnesium silicide, and their mixtures in an optimized semiopened reactor was investigated in detail. Obtained products were characterized by dispersive Raman spectroscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) and X-ray diffraction (XRD), which confirmed high conversion, homogeneity, and crystallinity of prepared products. The measured data, together with data obtained from the literature, served as input parameters for a mathematical model. Subsequent hydrolysis of prepared products to obtain germanium and silicon hydrides was observed by Fourier transform infrared spectroscopy (FTIR) and by gas chromatography mass spectrometry (GC/MS). A successful separation of hydrolysis products to individual hydrides was also performed. Magnesium hydrogen pho...

Heterostructures that consist of a germanium antimony telluride matrix and cobalt germanide precipitates can be obtained by straightforward solid-state synthesis including simple annealing and quenching procedures. The microscale precipitates are homogeneously distributed in a matrix with pronounced "herringbone-like" nanostructure associated with very low thermal conductivities. In comparison to the corresponding pure tellurides, the figure of merit (ZT) values of heterostructured materials are remarkably higher. This is mostly due to an increase of the Seebeck coefficient with only little impact on the electrical conductivity. In addition, the phononic part of the thermal conductivity is significantly reduced in some of the materials. As a result, ZT values of ca. 1.9 at 450 °C are achieved. Temperature-dependent changes of the thermoelectric properties are well-understood and correlate with complex phase transitions of the telluride matrix. However, the high ZT values are retained in multiple measurement cycles.

Lithium alloys of group IV elements such as silicon and germanium are attractive candidates for use as anodes in high-energy-density lithium-ion batteries. However, the poor capacity retention arising from volume swing during lithium cycling restricts their widespread application. Herein, we report high reversible capacity and superior rate capability from core-shell structure consisting of germanium nanorods embedded in multiwall carbon nanotubes. To understand how the core-shell structure helps to mitigate volume swings and buffer against mechanical instability, transmission electron microscopy, X-ray diffraction, and in situ (7)Li nuclear magnetic resonance were used to probe the structural rearrangements and phase evolution of various Li-Ge alloy phases during (de)alloying reactions with lithium. The results provide insights into amorphous-to-crystalline transition and lithium germanide alloy phase transformation, which are important reactions controlling performance in this system.

We demonstrate the formation of hollow nickel germanide nanostructures of Ni-Ge core-shell nanoparticles by solid state reactions. The structural evolutions of nickel germanide hollow nanostructures have been investigated in real-time ultrahigh vacuum transmission electron microscopy (UHV-TEM). Annealed above 450 °C, the nonequilibrium interdiffusion of core and shell species occurred at the interface; thus, Ni germanide hollow nanostructures were formed by solid state reactions involving the Kirkendall effect. In addition, the different hollow nanostructures formed from different core diameters of Ni-Ge core-shell nanoparticles have been studied. Also, we propose the mechanism with effects of the size and annealing duration on the solid state reactions based on the Kirkendall effect.

In this study, germanium nanowire junctionless (GeNW-JL) metal-oxide-semiconductor-field-effect-transistors (MOSFETs) exhibited enhanced electrical performance with low source/drain (S/D) contact resistance under the influence of Ar plasma treatment on the contact regions. We found that the transformation of the surface oxide states by Ar plasma treatment affected the S/D contact resistance. With Ar plasma treatment, the germanium dioxide on the GeNW surface was effectively removed and increased oxygen vacancies were formed in the suboxide on the GeNW, whose germanium-enrichment surface was obtained to form a germanide contact at low temperature. After a rapid thermal annealing process, Ni-germanide contacts were formed on the Ar-plasma-treated GeNW surface. Ni-germanide contact resistance was improved by more than an order of magnitude compared to that of the other devices without Ni-germanide contact. Moreover, the peak field effect mobility value of the GeNW-JL MOSFETs was dramatically improved from 15 cm(2)/(V s) to 550 cm(2)/(V s), and the Ion/off ratio was enhanced from 1 × 10 to 3 × 10(3) due to Ar plasma treatment. The Ar plasma treatment process is essential for forming uniform Ni-germanide-contacts with reduced time and low temperature. It is also crucial for increasing mass productivity and lowering the thermal budget without sacrificing the performance of GeNW-JL MOSFETs.

Iron–germanium (Fe–Ge) is a complex alloy system that includes several structurally and compositionally diverse phases that exhibit a range of interesting magnetic properties that can change significantly when reduced to nanoscale dimensions. Fe–Ge nanostructures have been synthesized using chemical and physical deposition methods but have not previously been accessible as solution-synthesized colloidal materials. Here, we show that colloidal Fe–Ge nanostructures can be synthesized via the hot injection of an oleylamine solution of Fe(CO)5 into a solution containing GeI4, oleylamine, oleic acid, and hexamethyldisilazane. This approach effectively merges recent advances in the synthesis of colloidal Ge nanocrystals with methods routinely used to synthesize metal and alloy nanoparticles. At 260 °C, spherical nanocrystals of Ni2In-type Fe3Ge2 form. Heating the solution at 300 °C transforms the spherical Fe3Ge2 nanocrystals into CoGe-type FeGe nanowires. The Fe3Ge2 nanocrystals are ferromagnetic with T c ≈ 26...

We report the controlled growth of single-crystalline ferromagnetic contacts through solid state reaction at nanoscale. Single-crystal Mn(5)Si(3) and Fe(5)Ge(3) contacts were grown within stressed Si and Ge nanowire templates, where oxide-shells were used to exert compressive stress on the silicide or germanide. Compared to polycrystalline silicide and germanide structures observed within bare nanowires, the built-in high strain in the oxide-shelled nanostructures alters the nucleation behavior of the ferromagnetic materials, leading to single crystal growth in the transverse/radial direction. Interestingly, the compressive stress is also found to affect the magnetic anisotropy of the ferromagnetic contacts. In-plane and out-of-plane magnetization were observed in Fe(5)Ge(3) for different crystal orientations, showing distinctly preferred domain orientations. These interesting results display the capability to control both the crystallinity and the magnetic anisotropy of ferromagnetic contacts in engineered nanostructures.

To explore spintronics applications for Ge nanowire heterostructures formed by thermal annealing, it is critical to develop a ferromagnetic germanide with high Curie temperature and take advantage of the high-quality interface between Ge and the formed ferromagnetic germanide. In this work, we report, for the first time, the formation and characterization of Mn(5)Ge(3)/Ge/Mn(5)Ge(3) nanowire transistors, in which the room-temperature ferromagnetic germanide was found through the solid-state reaction between a single-crystalline Ge nanowire and Mn contact pads upon thermal annealing. The atomically clean interface between Mn(5)Ge(3) and Ge with a relatively small lattice mismatch of 10.6% indicates that Mn(5)Ge(3) is a high-quality ferromagnetic contact to Ge. Temperature-dependent I-V measurements on the Mn(5)Ge(3)/Ge/Mn(5)Ge(3) nanowire heterostructure reveal a Schottky barrier height of 0.25 eV for the Mn(5)Ge(3) contact to p-type Ge. The Ge nanowire field-effect transistors built on the Mn(5)Ge(3)/Ge/Mn(5)Ge(3) heterostructure exhibit a high-performance p-type behavior with a current on/off ratio close to 10(5), and a hole mobility of 150-200 cm(2)/(V s). Temperature-dependent resistance of a fully germanided Mn(5)Ge(3) nanowire shows a clear transition behavior near the Curie temperature of Mn(5)Ge(3) at about 300 K. Our findings of the high-quality room-temperature ferromagnetic Mn(5)Ge(3) contact represent a promising step toward electrical spin injection into Ge nanowires and thus the realization of high-efficiency spintronic devices for room-temperature applications.

Semitransparent dark-red or ruby-red moisture- and air-sensitive single crystals of A 10+x[Ge 9] 2[W 1-xNb xO 4] (A = K, Rb; x = 0, 0.35) were obtained by high-temperature solid-state reactions. The crystal structure of the compounds was determined by single-crystal X-ray diffraction experiments. They crystallize in a new structure type (P2 1/c, Z = 4) with a = 13.908(1) A, b = 15.909(1) A, c = 17.383(1) A, and α = 90.050(6)° for K 10.35(1)[Ge 9] 2[W 0.65(1)Nb 0.35(1)O 4]; a = 14.361(3) A, b = 16.356(3) A, c = 17.839(4) A, and α = 90.01(3)° for Rb 10.35(1)[Ge 9] 2[W 0.65(1)Nb 0.35(1)O 4]; a = 13.8979(2) A, b = 15.5390(3) A, c = 17.4007(3) A, and α = 90.188(1)° for K 10[Ge 9] 2WO 4; and a = 14.3230(7) A, b = 15.9060(9) A, c = 17.8634(9) A, and α = 90.078(4)° for Rb 10[Ge 9] 2WO 4. The compounds contain discrete Ge 9 4- Wades nido clusters and WO 4 2- (or NbO 4 3-) anions, which are packed according to a hierarchical atom-to-cluster replacement of the Al 2Cu prototype and are separated by K and Rb cations, respectively. The alkali metal atoms occupy the corresponding tetrahedral sites of the Al 2Cu prototype. The amount of the alkali metal atoms on these diamagnetic compounds corresponds directly to the amount of W substituted by Nb. Thus, the transition metals W and Nb appear with oxidation numbers +6 and +5, respectively, in the vicinity of a [Ge 9] 4- polyanion. The crystals of the mixed salts were further characterized by Raman spectroscopy. The Raman data are in good agreement with the results from the X-ray structural analyses.

We use first principles Density Functional Theory (DFT), cyclic voltammetry (CV), and Raman spectroscopy to investigate the first-cycle electrochemical lithiation of Ge in comparison with Si – both high-capacity anode materials for Li ion batteries. DFT shows a significant difference in the dilute solubility of Li in Si and Ge, despite similarities in their chemical and physical properties. We attribute this difference to electronic, as opposed to elastic, effects. CV and Raman data reveal little dopant dependence in the lithiation onset voltages in Ge, unlike in Si, due to a smaller energy difference between dilute Li insertion in p-type Ge and bulk germanide formation than the corresponding difference in Si. Finally, we show that there is no orientation dependence in lithiation onset voltages in Ge. We conclude that approaches other than microstructuring are needed to fabricate effective electrodes able to take advantage of the higher rate capability of Ge compared to that of Si.

We prepared a new binary lanthanum germanide, LaGe(3), under high-pressure and high-temperature conditions (3-12 GPa, 500-1200 °C). It crystallizes in the BaPb(3) structure (the space group R ̅3m) with lattice constants of a = 6.376(1) Å, c = 22.272(3) Å, and V = 784.1(2) Å(3). We refined the structure using Rietveld analysis from X-ray powder data. The structure is composed of two types of close-packed atom layers. In one layer, every La atom is surrounded solely by Ge atoms with the same distance of 3.188 Å. The other layer contains Ge(3) regular, triangular cluster units with a Ge-Ge distance of 2.634 Å. The electron localization function and crystal orbital Hamilton population calculations suggest that the triangular cluster is composed of three Ge-Ge covalent bonds and that each Ge atom has a lone pair. The temperature dependence of the magnetic susceptibility and electrical conductivity measurements revealed that LaGe(3) is metallic and shows superconductivity at 7.4 K. This critical temperature is highest for the La-Ge system.

Iridium carbides with various stoichiometries were investigated by using the first-principles method. It is found that iridium carbides with the iridium germanide structures usually exhibit a bette...

The structure and electronic properties of cobalt germanide islands were studied by scanning tunneling microscopy (STM). We found that cobalt-rich surfaces (C-surface) and germanium-rich surfaces (G-surface) coexisted in the islands. Scanning tunneling spectroscopy (STS) confirmed that both surfaces displayed metallic characteristics. Structural models are suggested based on the bias-dependent STM images.

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.

We report for the first time the direct deposition of crystalline molybdenum sulfide (MoS2) using a single-source precursor based on tetrakis(diethylaminodithiocarbomato)molybdate(IV) (abbreviated as Mo(Et2NCS2)4). The chemistry of this precursor adsorbed on a range of substrates (silicon, germanium, gold-coated germanium, nickel, etc.) has been studied using in situ X-ray photoelectron spectroscopy. The Mo(Et2NCS2)4 precursor can be evaporated at 300 °C; its vapor adsorbs on most surfaces at room temperature and decomposes by 400 °C to form crystalline MoS2. Using this method, high-quality, basal plane-oriented MoS2 can be grown on nickel by a one-step thermal evaporation process for the first time. Interestingly, choosing elemental substrates which form eutectic alloys with gold favors the elimination of sulfur from the MoS2 film. This results in Mo intermetallic compound formation at the eutectic temperatures of the Au and substrate element. Unpredecented low-temperature growth of tetragonal MoSi2 or o...

Nickel germanide thin films were prepared using nickel−germanium multilayers as reactive precursors. Over the composition range xNi = 0.24−0.42, high-temperature germanides (δ-Ni5Ge2, e-Ni5Ge3, and...

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...

A Monte Carlo simulation study based on the extended-Huckel tight-binding method was carried out to examine the thermodynamic properties of the ThCr 2 Si 2 and CaBe 2 Ge 2 type main group solids. At room temperature, the ThCr 2 Si 2 structure is more stable owing to a less dispersed filled band and a lower Fermi level. Weaker bonding also counts for the larger atomic thermal motion in layers D of the CaBe 2 Ge 2 structure

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.

We report the sequential synthesis of solid-phase manganese germanide seed particles and crystalline Ge nanowires using low-pressure thermal chemical vapor deposition. Mn was deposited on inert substrates from a gas-phase precursor. Mn particles were converted to solid manganese germanide particles upon exposure to germane gas, and these seed particles directed the one-dimensional growth of Ge nanowires. Growth rates for this vapor−solid−solid process approached 200 nm per minute, and the diameter distribution was tightly clustered around 18 nm. This approach to Ge nanowire growth has at least three attractive features: (1) the seed particle is not Au, avoiding the potentially negative influence of Au impurities on electrical properties; (2) the vapor-phase deposition and self-assembly of the seed greatly simplifies the nanowire synthesis process; and (3) the self-assembled seed naturally produces a narrow distribution of nanowire diameters.