Microwires Research Articles

Three‐Dimensional Kelvin Probe Microscopy for Characterizing In‐Plane Piezoelectric Potential of Laterally Deflected ZnO Micro‐/Nanowires

AbstractPotential characterization of deflected piezoelectric nanowires (NWs) is of great interest for current development of electromechanical nanogenerators that harvest ambient mechanical energy. In this paper, a Kelvin probe microscopy (KPM) technique hybridizing scanning KPM (SKPM) with atomic force microscope (AFM) surface‐approach spectroscopy methods for characterizing in‐plane piezoelectric potential of ZnO microwires (MWs) is presented. This technique decouples the scanning motion of the AFM tip from sample topography, and thus effectively eliminates artifacts induced by high topographical variations along the edges of MWs/NWs which make characterization by conventional SKPM inappropriate or impossible. By virtue of the topography/tip motion decoupling approach, the electrical potential can also be mapped in a three‐dimensional (3D) spatial volume above the sample surface. Therefore, this technique is named 3DKPM. Through 3DKPM mapping, the piezopotential generated by a laterally deflected ZnO MW was determined by extracting the potential asymmetry from opposite sides of the MW. The measurement results agree well with theoretical predictions. Integrating an external bias to the MW sample allowed direct observation of piezopotential and carrier concentration coupling phenomenon in ZnO, opening a door toward quantitative microscopic investigation of the piezotronic effect. With further positioning refinements, 3DKPM could become a powerful technique for the characterization of piezoelectric potential and related effects in micro/nanostructures of high topographical variations, as well as development of MW/NW‐based piezoelectric nanodevices.

Carburization of Si Microwires by Chemical Vapour Deposition

We report the elaboration of silicon carbide (SiC) nanostructures thanks to the carburization of silicon microwires (MWs) under methane at high temperature. The produced SiC nanostructures display a tubular shape and are polycrystalline. The as-prepared silicon carbide microtubes (MTs) were characterized and studied by scanning electron microscopy (SEM), dual focused ion beam-scanning electron microscope (FIB-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. The formation of microtubes can be explained by the out-diffusion of Si through the SiC during the carburization process.

Growth of SiC Microwires through Si Microwires Carburization

Silicon microwires (MWs) previously synthesized using the VLS method with gold catalyst are being carburized at 1100°C under methane aiming to their conversion to SiC. SEM, TEM as well as XPS and Raman spectroscopy were used for structural and morphological characterization. After carburization achievement, SiC is found to be polycrystalline with a high density of stacking faults associated to an increase of surface roughness. Directions for the carburization process optimization are given.

A waferscale Si wire solar cell using radial and bulk p–n junctions

Silicon nanowires (NWs) and microwires (MWs) are cost-effectively integrated on a 4-inchwafer using metal-assisted electroless etching for solar cell applications. MWs areperiodically positioned using low-level optical patterning in between a dense array of NWs.A spin-on-doping technique is found to be effective for the formation of heavily doped, thinn-type shells of MWs in which the radial doping profile is easily delineated by low voltagescanning electron microscopy. Controlled tapering of the NWs results in additional opticalenhancement via optimization of the tradeoff between increased light trapping (by agraded-refractive-index) and increased reflectance (by decreasing areal density ofNWs). Compared to single NW (or MW) arrayed cells, the co-integrated solar cellsdemonstrate improved photovoltaic characteristics, i.e. a short circuit current of20.59 mA cm − 2 and a cell conversionefficiency of ∼ 7.19% at AM 1.5G illumination.

Formation and optical properties of ZnO:ZnFe2O4 superlattice microwires

Pure ZnO hexagonal microwires and Fe(III)-doped ZnO microwires (MWs) with a novel rectangular cross section were synthesized in a confined chamber by a convenient one-step thermal evaporation method. An oriented attachment mechanism is consistent with a vapor-solid growth process. Photoluminescence (PL) and Raman spectroscopy of the Fe(III)-doped ZnO MWs and in situ spectral mappings indicate a quasi-periodic distribution of Fe(III) along a one-dimensional (1-D) superlattice ZnO:ZnFe2O4 wire, while PL mapping shows the presence of optical multicavities and related multimodes. The PL spectra at room temperature show weak near-edge doublets (376 nm and 383 nm) and a broad band (450–650 nm) composed of strong discrete lines, due to a 1-D photonic crystal structure. Such a 1-D coupled optical cavity material may find many applications in future photonic and spintronic devices.

Magnetosensors based on semiconductor microwires

Some aspects of the technology of semiconductor and semimetal microwires (MW) with glass coating are described. Two types of MW magnetosensing elements (magnetoresistive and galvanomagnetorecombination) are proposed and obtained on the basis of Ge, Bi, InSb and their alloys. Such MW magnetoelements with various constructive variants allowed us to use them for the design and fabrication of new magnetosensors and transducers. The design and the characteristics of some MW magnetosensors, enabling the measurement of turn angles, small and large displacements, and electric charges, are analyzed.