This paper summarizes some of the essential aspects of silicon-nanowire growth and of their electrical properties. In the first part, a brief description of the different growth techniques is given, though the general focus of this work is on chemical vapor deposition of silicon nanowires. The advantages and disadvantages of the different catalyst materials for silicon-wire growth are discussed at length. Thereafter, in the second part, three thermodynamic aspects of silicon-wire growth via the vapor–liquid–solid mechanism are presented and discussed. These are the expansion of the base of epitaxially grown Si wires, a stability criterion regarding the surface tension of the catalyst droplet, and the consequences of the Gibbs–Thomson effect for the silicon wire growth velocity. The third part is dedicated to the electrical properties of silicon nanowires. First, different silicon nanowire doping techniques are discussed. Attention is then focused on the diameter dependence of dopant ionization and the influence of interface trap states on the charge carrier density in silicon nanowires. It is concluded by a section on charge carrier mobility and mobility measurements.

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Silicon Nanowires: A Review on Aspects of their Growth and their Electrical Properties

2.4. Molecular Beam Epitaxy 366 2.5. Laser Ablation 367 2.6. Silicon Monoxide Evaporation 367 3. Catalyst Materials 368 3.1. Gold as Catalyst 368 3.2. Alternative Catalyst Materials 369 3.2.1. Type-A, Au-like Catalysts 370 3.2.2. Type-B, Low Si Solubility Catalysts 371 3.2.3. Type-C, Silicide Forming Catalysts 371 4. Crystallography 372 5. Heterostructures 373 6. Surface Induced Lowering of the Eutectic Temperature 375

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Growth, thermodynamics, and electrical properties of silicon nanowires.

The exploration of new and efficient energy storage mechanisms through nanostructured electrode design is crucial for the development of high-performance rechargeable batteries. Herein, black phosphorus quantum dots (BPQDs) and Ti3C2 nanosheets (TNSs) are employed as battery and pseudocapacitive components, respectively, to construct BPQD/TNS composite anodes with a novel battery-capacitive dual-model energy storage (DMES) mechanism for lithium-ion and sodium-ion batteries. Specifically, as a battery-type component, BPQDs anchored on the TNSs are endowed with improved conductivity and relieved stress upon cycling, enabling a high-capacity and stable energy storage. Meanwhile, the pseudocapacitive TNS component with further atomic charge polarization induced by POTi interfacial bonds between the two components allows enhanced charge adsorption and efficient interfacial electron transfer, contributing a higher pseudocapacitive value and fast energy storage. The DMES mechanism is evidenced by substantial characterizations of X-ray photoelectron spectroscopy and X-ray absorption fine structure spectroscopy, density functional theory calculations, and kinetics analyses. Consequently, the composite electrode exhibits superior battery performance, especially for lithium storage, such as high capacity (910 mAh g−1 at 100 mA g−1), long cycling stability (2400 cycles with a capacity retention over 100%), and high rate capability, representing the best comprehensive battery performance in BP-based anodes to date.

Black Phosphorus Quantum Dot/Ti3C2 MXene Nanosheet Composites for Efficient Electrochemical Lithium/Sodium‐Ion Storage

High-density ZnO nanowires doped with 4 atom % sulfur (S) and pure ZnO nanowires were grown vertically aligned on a silicon substrate. They were synthesized via chemical vapor deposition of a Zn or Zn/S powder mixture at 500 °C. The S-doped ZnO nanowires usually form bundles. The average diameter of the S-doped ZnO nanowires and ZnO nanowires is 20 and 50 nm, respectively. They consist of single-crystalline wurtzite ZnO crystals with a uniform growth direction of [001]. Elemental mapping reveals that the S doping takes place mainly at the surface of the nanowires with a thickness of a few nanometers. X-ray diffraction data suggest that the incorporation of S would expand the lattice constants of ZnO. The photoluminescence and cathodoluminescence of S-doped ZnO nanowires exhibit a significantly enhanced green emission band that comes from the S-doped surface region of the nanowires.

Vertically Aligned Sulfur-Doped ZnO Nanowires Synthesized via Chemical Vapor Deposition

S-doped ZnO nanostructures such as nanonails and nanowires have been synthesized via a simple one-step catalyst-free thermal evaporation process on a large scale The doping concentration of sulfur into ZnO nanonails and nanowire were 2 atm % and 75 atm %, respectively Studies found that the S-doped ZnO nanonails and nanowires were single-crystalline wurtzite structure and grew along the (001) direction The average diameters of the nanonails and nanowires were 70 and 50 nm, respectively Low-temperature photoluminescence spectra of ZnO samples showed two luminescence peaks in the UV and green emission region, respectively As the concentration of sulfur in the ZnO nanostructures increased, the intensity of the UV emission peak decreased dramatically, and it showed a little blue-shift while the intensity of the green emission increased greatly

Synthesis and optical properties of S-doped ZnO nanostructures: nanonails and nanowires.

The electronic structure and chemical bonding of heavily phosphorus-doped silicon nanowires have been investigated by near edge x-ray absorption fine structure spectroscopy using total electron yield and x-ray fluorescence yield. The results show that the wires are encapsulated within a silicon oxide layer and that the core of the nanowires was crystalline silicon doped with phosphorus. Phosphorus is found to be inside the core of the Si wire as well as at the silicon oxide–core silicon wire interface but not on the surface of the as-prepared nanowire.

Phosphorus-doped silicon nanowires studied by near edge x-ray absorption fine structure spectroscopy

The optical luminescence excited with synchrotron radiation along a preferential orientation of a quartz crystal has been investigated. It is found that the crystal is composed of two distinct regions, only one of which luminesces upon X-ray excitation. This luminescence is generally uniform and exhibits emission bands in the blue (470 nm with a shoulder at 522 nm) and in the UV (340 nm) regions of the spectrum. The branching ratio for the intensity of these bands is sensitive to the excitation energy across the Si K-edge. XANES spectra collected by partial luminescence yield (PLY) suggest that both emission bands originate from the de-excitation of Si atoms in the quartz. The possible defect sites within the crystal structure that could account for the observed luminescence are investigated and discussed. Additional experiments are proposed to verify this assignment of the optical emission bands.

An X-ray excited optical luminescence study of a zoned quartz crystal from an emerald-bearing quartz vein, Hiddenite, North Carolina, USA

As part of an ongoing study of the electronic interactions between solute and solvent molecules, a method for X-ray excited optical luminescence (XEOL) analysis of aqueous solutions was developed at the double-crystal monochromator beamline (DCM) of the Canadian Synchrotron Radiation Facility (CSRF). It was tested using a series of solutions containing lanthanide ions. The samples were contained in a sample holder for liquids with a 3 μm Mylar window separating them from the vacuum (≤3 × 10−6 torr, 1 torr = 133.3224 Pa) in the solid state absorption chamber of the DCM beamline. Terbium, samarium, and dysprosium have 4 intense and narrow luminescence peaks between 450 and 700 nm, well separated from the luminescence peak of the Mylar window between 300 and 425 nm. The intensity of the rare earth (RE3+) luminescence peaks was lower for the solutions than for solid RECl3·6H2O. In part, this was caused by the lower RE3+ concentration in the solutions than in the solid. In addition, the solvent (water) acts as...

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XEOL spectroscopy of lanthanides in aqueous solution

A methodology for the X-ray XANES and EXAFS analyses of aqueous solutions was developed for the Double Crystal Monochromator (DCM) beamline of the Canadian Synchrotron Radiation Facility (CSRF). Th...

Astrid Jürgensen

Papers

Phosphorus-doped silicon nanowires studied by near edge x-ray absorption fine structure spectroscopy

An X-ray excited optical luminescence study of a zoned quartz crystal from an emerald-bearing quartz vein, Hiddenite, North Carolina, USA

XEOL spectroscopy of lanthanides in aqueous solution

X-ray absorption spectroscopy of aqueous solutions in the X-ray energy region from 1800 to 3700 eV