The growth of high density germanium (Ge) nanostructures (nanowires and nanotowers) and influence of chromium (Cr) doping on its morphology have been investigated. It is observed that in the absence of Cr, Ge nanowires (NWs) are formed whereas the presence of Cr leads to the growth of Ge nanotowers (NTrs), wherein all other experimental parameters were kept constant. Independent of the Cr concentration, the crystal structures of both nanostructures, that is, NWs and NTrs, are identical. Traditional vapor–liquid–solid (VLS) process was used to explain the growth mechanism of the top of the Ge NTr, consisting of a thin nanowire with a gold tip. The bottom of the NTr consists of lateral (111) and (001) planes of polygonal structure; VLS process along with vapor-solid (VS) process accounts for its further growth. The mechanism for the dopant-dependent morphological changes in Ge nanostructures is clarified. The magnetic properties of the NTrs were probed using a superconducting quantum interference device (SQUID). Room-temperature ferromagnetism in Cr-doped Ge nanotowers was discovered. These findings can thus be exploited for controlling the morphology and generating the magnetic ordering in nonmagnetic semiconductors to develop stabilized novel spintronics devices.
The single-electron transistor (SET) has tremendous importance in the microelectronic industry on account of low-power consumption, an ultrasmall size, and a large integration prospect. The key challenge is to resolve the fabrication issues of a SET to realize a mechanically steady device with reproducible and controllable transport characteristics that operate at room temperature. Herein, we report on the realization of robust and well-controlled SET devices with at least two junctions and multijunctions using an advanced nanochain (NC) architecture of germanium nanoparticles rooted by a germanium oxide ropeway. These two-junction and multitunneling-junction (MTJ) SET devices exhibit an ideal Coulomb staircase behavior of single-electron charge transfer at room temperature and obeyed the theoretical path of increasing threshold voltage with the number of tunnel junctions. This Coulomb transistor prospects magnificent rewards of room-temperature operation, periodic Coulomb oscillations, well-controlled threshold voltage and large on/off ratios and have the potential to modernize the random access memory and digital data storage technologies.
The Cr-doped tunable thickness core-shell Ge/GeO nanowires (NWs) were synthesized and characterized using x-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy and magnetization studies. The shell thickness increases with the increase in synthesis temperature. The presence of metallic Cr and Cr in core-shell structure was confirmed from XPS study. The magnetic property is highly sensitive to the core-shell thickness and intriguing room temperature ferromagnetism is realized only in core-shell NWs. The magnetization decreases with an increase in shell thickness and practically ceases to exist when there is no core. These NWs show remarkably high Curie temperature (T > 300 K) with the dominating values of its magnetic remanence (M) and coercivity (H) compared to germanium dilute magnetic semiconductor nanomaterials. We believe that our finding on these Cr-doped Ge/GeO core-shell NWs has the potential to be used as a hard magnet for future spintronic devices, owing to their higher characteristic values of ferromagnetic ordering.
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