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.

SnO 2 hollow nanospheres were synthesized from glucose and SnCl 2 solution under hydrothermal environment and calcinations. The carbon layer was then deposited as a buffer layer via hydrothermally treated glucose solution. The thickness of the SnO 2 shell in the hollow structures could be adjusted by changing the concentration of the SnCl 2 coating solution. The crystalline structure and morphological observation of the as-synthesized hollow structures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The thickness of SnO 2 under 0.1 and 1 M SnCl 2 coating solution was 15 and 60 nm, respectively. It was demonstrated that the electrochemical performance was significantly improved by the hollow structure and strongly affected by the shell thickness of SnO 2 . The hollow structure with 15 nm in SnO 2 thickness exhibited an outstanding reversible capacity of 500 mA hg -1 at 5 C. The extraordinary performance should be associated with the ultrathin SnO 2 shell and the carbon layer, which could accommodate the volume changes and prevent the agglomeration of Sn particles during cycling.

We propose a low cost solution-based approach to synthesize various low dimensional copper telluride (Cu-Te) nanostructures. By precisely controlling different ethylenediamine (EDA) ratios in a reaction solution, we are able to control the phases and morphologies of Cu-Te nanostructures from Te/Cu core-shell nanowires at a low volume fraction of EDA <8%, Cu 3 Te 2 nanowires at the volume fraction of EDA between 8% and 24%, Cu 2 Te nanowires and nanobelts at the volume fraction of EDA between 24% and 48%, to Cu 2 Te/Cu core-shell nanobelts at the volume fraction of EDA over 48%. The formation mechanism is attributed to varied tendency of different coordinative copper complexes. In situ heating XRD results and TEM observations of the Cu 2 Te nanowires reveal the phase transition from hexagonal P3m1, hexagonal P6/mmm to cubic structure at annealing temperatures of 25 C, 500 C to 600 C, respectively. The lack of back gate dependence demonstrates the metallic feature of Te/Cu core-shell nanowire while obvious p-type behavior can be found for Cu 2 Te nanowire with an on/off ratio of $10 4 and the field effect hole mobility of $18 cm 2 V À1 s À1 . These Cu-Te nanostructures exhibit controllable transport behaviors from metallic to semiconducting natures with different EDA volume fractions and have promising applications in electronics such as nonvolatile memory, photodetectors, and solar cells.

In this Letter, the magnetic phase transition and domain wall motion in a single-crystalline Mn(5)Ge(3) nanowire were investigated by temperature-dependent magneto-transport measurements. The ferromagnetic Mn(5)Ge(3) nanowire was fabricated by fully germaniding a single-crystalline Ge nanowire through the solid-state reaction with Mn contacts upon thermal annealing at 450 °C. Temperature-dependent four-probe resistance measurements on the Mn(5)Ge(3) nanowire showed a clear slope change near 300 K accompanied by a magnetic phase transition from ferromagnetism to paramagnetism. The transition temperature was able to be controlled by both axial and radial magnetic fields as the external magnetic field helped maintain the magnetization aligned in the Mn(5)Ge(3) nanowire. Near the magnetic phase transition, the critical behavior in the 1D system was characterized by a power-law relation with a critical exponent of α = 0.07 ± 0.01. Besides, another interesting feature was revealed as a cusp at about 67 K in the first-order derivative of the nanowire resistance, which was attributed to a possible magnetic transition between two noncollinear and collinear ferromagnetic states in the Mn(5)Ge(3) lattice. Furthermore, temperature-dependent magneto-transport measurements demonstrated a hysteretic, symmetric, and stepwise axial magnetoresistance of the Mn(5)Ge(3) nanowire. The interesting features of abrupt jumps indicated the presence of multiple domain walls in the Mn(5)Ge(3) nanowire and the annihilation of domain walls driven by the magnetic field. The Kurkijärvi model was used to describe the domain wall depinning as thermally assisted escape from a single energy barrier, and the fitting on the temperature-dependent depinning magnetic fields yielded an energy barrier of 0.166 eV.

The effects of partial substitution of Ge for Si in cobalt germanosilicide (CoSi(1-x)Ge(x) and Co(2)Si(1-x)Ge(x)) nanowires (NWs) on the electrical transport, magnetic properties, and magnetoresistance (MR) have been investigated. Cobalt germanosilicide NWs were synthesized by a spontaneous chemical vapor transport growth method. The Ge concentration can be selectively controlled from 0 to 15% and 0-50% for CoSi(1-x)Ge(x) and Co(2)Si(1-x)Ge(x) NWs, respectively, by varying the reaction temperature. Electrical measurements showed that the resistivities of CoSi(1-x)Ge(x) NWs are 90, 60, 30, and 23 μΩ-cm for x = 0, 0.01, 0.05, and 0.15, respectively. Therefore, the electrical resistivity of CoSi(1-x)Ge(x) NWs was found to decrease significantly with an increasing Ge concentration, which is believed to be a result of the band gap narrowing. On the other hand, the Co(2)Si(1-x)Ge(x) (x ≤ 0.5) NWs exhibited ferromagnetism at 300 K, which is attributed to the uncoordinated Co atoms on the NW surface and spin-glass behavior at low temperature. The highest MR response of Co(2)Si(1-x)Ge(x) NWs occurred at x = 0.5, where a MR ratio of 11.7% can be obtained at 10-25 K with a magnetic field of 8 T. The enhanced physical properties of cobalt germanosilicide NWs with Ge substitution shall lead to promising application in the fabrication of nanodevices, including spintronics and serving as the gate and interconnect material.