Synthesis and electrical characterization of intrinsic and in situ doped Si nanowires using a novel precursor

Perchlorinated polysilanes were synthesized by polymerization of tetrachlorosilane under cold plasma conditions with hydrogen as a reducing agent. Subsequent selective cleavage of the resulting polymer yielded oligochlorosilanes SinCl2n+2 (n = 2, 3) from which the octachlorotrisilane (n = 3, Cl8Si3, OCTS) was used as a novel precursor for the synthesis of single-crystalline Si nanowires (NW) by the well-established vapor–liquid–solid (VLS) mechanism. By adding doping agents, specifically BBr3 and PCl3, we achieved highly p- and n-type doped Si-NWs by means of atmospheric-pressure chemical vapor deposition (APCVD). These as grown NWs were investigated by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM), as well as electrical measurements of the NWs integrated in four-terminal and back-gated MOSFET modules. The intrinsic NWs appeared to be highly crystalline, with a preferred growth direction of [111] and a specific resistivity of ρ = 6 kΩ·cm. The doped NWs appeared to be [112] oriented with a specific resistivity of ρ = 198 mΩ·cm for p-type Si-NWs and ρ = 2.7 mΩ·cm for n-doped Si-NWs, revealing excellent dopant activation

Miniaturized Wide-Range Field-Emission Vacuum Gauge

Miniaturized vacuum gauges (MVGs) for the measurement range 5.7x10-7 to 1.1x10-2 mbar were fabricated in a self-aligned approach using focused ion beam (FIB) nanomachining and reactive ion etching (RIE). The MVG consists of two properly insulated electrodes integrated on top of an atomic force microscopy (AFM) tip, forming a coaxial embodiment. The special design enables us to vary the cathode-anode separation and the turn-on voltage changes accordingly. The experiments show that the MVGs operate at low bias potential and demonstrate very good I-P dependence over a wide pressure range

Highly Biaxially Strained Silicene on Au(111)

Many of graphene’s remarkable properties arise from its linear dispersion of the electronic states, forming a Dirac cone at the K points of the Brillouin zone. Silicene, the 2D allotrope of silicon, is also predicted to show a similar electronic band structure, with the addition of a tunable bandgap, induced by spin–orbit coupling. Because of these outstanding electronic properties, silicene is considered as a promising building block for next-generation electronic devices. Recently, it has been shown that silicene grown on Au(111) still possesses a Dirac cone, despite the interaction with the substrate. Here, to fully characterize the structure of this 2D material, we investigate the vibrational spectrum of a monolayer silicene grown on Au(111) by polarized Raman spectroscopy. To enable a detailed ex situ investigation, we passivated the silicene on Au(111) by encapsulating it under few layers hBN or graphene flakes. The observed spectrum is characterized by vibrational modes that are strongly red-shifted with respect to the ones expected for freestanding silicene. By comparing low-energy electron diffraction (LEED) patterns and Raman results with first-principles calculations, we show that the vibrational modes indicate a highly (>7%) biaxially strained silicene phase.This work was funded by the Fonds zur Förderung der Wissenschaftlichen Forschung (FWF), Austria (Project P29244-N27). We also acknowledge financial support by the Ministerio de Economía, Industria y Competitividad (MINECO) under Grant FEDER-MAT2017-90024-P and the Severo Ochoa Centres of Excellence Program under Grant CEX2019-000917-S, and by the Generalitat de Catalunya under Grant 2017 SGR 1506. The project i-LINK action LINKA20047 funded by CSIC is also acknowledged for financial support. R.R. acknowledges useful discussions with Mariusz Krawiec. CzechNanoLab Project LM2018110 funded by MEYS CR is gratefully acknowledged for the financial support of the measurements at CEITEC Nano Research Infrastructure. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan, Grant JPMXP0112101001, JSPS KAKENHI Grant JP20H00354, and the CREST(JPMJCR15F3), JST.Peer reviewe

Direct writing of gold nanostructures with an electron beam: On the way to pure nanostructures by combining optimized deposition with oxygen-plasma treatment

This work presents a highly effective approach for the chemical purification of directly written 2D and 3D gold nanostructures suitable for plasmonics, biomolecule immobilisation, and nanoelectronics. Gold nano- and microstructures can be fabricated by one-step direct-write lithography process using focused electron beam induced deposition (FEBID). Typically, as-deposited gold nanostructures suffer from a low Au content and unacceptably high carbon contamination. We show that the undesirable carbon contamination can be diminished using a two-step process – a combination of optimized deposition followed by appropriate postdeposition cleaning. Starting from the common metal-organic precursor Me2-Au-tfac, it is demonstrated that the Au content in pristine FEBID nanostructures can be increased from 30 atom % to as much as 72 atom %, depending on the sustained electron beam dose. As a second step, oxygen-plasma treatment is established to further enhance the Au content in the structures, while preserving their morphology to a high degree. This two-step process represents a simple, feasible and high-throughput method for direct writing of purer gold nanostructures that can enable their future use for demanding applications

Origin of Anomalous Piezoresistive Effects in VLS Grown Si Nanowires

Although the various effects of strain on silicon are subject of intensive research since the 1950s the physical background of anomalous piezoresistive effects in Si nanowires (NWs) is still under debate. Recent investigations concur in that due to the high surface-to-volume ratio extrinsic surface related effects superimpose the intrinsic piezoresistive properties of nanostructures. To clarify this interplay of piezoresistive effects and stress related surface potential modifications, we explored a particular tensile straining device (TSD) with a monolithic embedded vapor–liquid–solid (VLS) grown Si NW. Integrating the suspended NW in a gate all around (GAA) field effect transistor (FET) configuration with a transparent gate stack enables optical and field modulated electrical characterization under high uniaxial tensile strain applied along the ⟨111⟩ Si NW growth direction. A model based on stress-induced carrier mobility change and surface charge modulation is proposed to interpret the actual piezoresistive behavior of Si NWs. By controlling the nature and density of surface states via passivation the “true” piezoresistance of the NWs is found to be comparable with that of bulk Si. This demonstrates the indispensability of application-specific NW surface conditioning and the modulation capability of Si NWs properties for sensor applications

Gate-Tunable Electron Transport Phenomena in Al–Ge⟨111⟩–Al Nanowire Heterostructures

Electrostatically tunable negative differential resistance (NDR) is demonstrated in monolithic metal–semiconductor–metal (Al–Ge–Al) nanowire (NW) heterostructures integrated in back-gated field-effect transistors (FETs). Unambiguous signatures of NDR even at room temperature are attributed to intervalley electron transfer. At yet higher electric fields, impact ionization leads to an exponential increase of the current in the ⟨111⟩ oriented Ge NW segments. Modulation of the transfer rates, manifested as a large tunability of the peak-to-valley ratio (PVR) and the onset of impact ionization is achieved by the combined influences of electrostatic gating, geometric confinement, and heterojunction shape on hot electron transfer and by electron–electron scattering rates that can be altered by varying the charge carrier concentration in the NW FETs

Fabrication and characterization of a germanium nanowire light emitting diode

International audienceIn this letter we demonstrate the feasibility of a germanium nanowire light emitting diode as a reasonable approach for downscaling of CMOS compatible light sources. We show room-temperature direct bandgap electroluminescence from axial p-n junction nanowire devices. The electron population in the Γ valley, necessary for direct bandgap emission, is achieved by high injection current densities. Carrier temperature is consistently found to be higher than the lattice temperature, indicating inhibited carrier cooling in small diameter wires. Strong polarization of the emission parallel to the nanowire axis is observed and attributed to dielectric contrast phenomena

Silicene Passivation by Few-Layer Graphene

The final publication is available via https://doi.org/10.1021/acsami.8b20751.The stabilization of silicene at ambient conditions is essential for its characterization, future processing, and device integration. Here, we demonstrate insitu encapsulation of silicene on Ag(111) by exfoliated few-layer graphene (FLG)flakes, allowing subsequent Raman analysis under ambient conditions. Raman spectroscopy measurements proved that FLG capping serves as an effective passivation, preventing degradation of silicene for up to 48 h.The acquired data are consistent with former in situ Raman measurements, showing two characteristic peaks, located at 216 and 515 cm−1. Polarization-dependent measurements allowed to identify the two modes as A and E, demonstrating that the symmetry properties of silicene are unaltered by the capping process.Austrian Science Funds (FWF