S.Q. Feng

Ultraviolet-emitting ZnO nanowires synthesized by a physical vapor deposition approach

ZnO nanowires were mass produced using a physical vapor deposition approach. The ZnO nanowire monocrystallites have an average diameter around 60 nm and length up to a few micrometers. The unidirectional growth of the ZnO nanowires was controlled by the conventional vapor-liquid-solid mechanism. Intensive UV light emission peaked around 3.27 eV was observed at room temperature, which was assigned to emission from free exciton under low excitation intensity. The observed room temperature UV emission was ascribed to the decrease in structure defects as compared to bulk ZnO materials, and in particularly to the size effect in the ZnO wires.

Efficient field emission from ZnO nanoneedle arrays

Well-aligned arrays of ZnO nanoneedles were fabricated using a simple vapor phase growth. The diameters of the nanoneedle tips are as small as several nanometers, which is highly in favor of the field emission. Field-emission measurements using the nanoneedle arrays as cathode showed emission current density as high as 2.4 mA/cm2 under the field of 7 V/μm, and a very low turn-on field of 2.4 V/μm. Such a high emission current density is attributed to the high aspect ratio of the nanoneedles. The high emission current density, high stability, and low turn-on field make the ZnO nanoneedle arrays one of the promising candidates for field-emission displays.

Amorphous silica nanowires: Intensive blue light emitters

We report large-scale synthesis of silica nanowires (SiONWs) using an excimer laser ablation method. Silica was produced in the form of amorphous nanowires at a diameter of ∼15 nm and a length up to hundreds micrometers. The SiONWs emit stable and high brightness blue light at energies of 2.65 and 3.0 eV. The intensity of the emission is two orders of magnitude higher than that of porous silicon. The SiONWs may have potential applications in high-resolution optical heads of scanning near-field optical microscope or nanointerconnections in future integrated optical devices.

Nanoscale silicon wires synthesized using simple physical evaporation

We report the large-scale synthesis of silicon nanowires (SiNWs) using a simple but effective approach. High purity SiNWs of uniform diameters around 15 nm were obtained by sublimating a hot-pressed silicon powder target at 1200 °C in a flowing carrier gas environment. The SiNWs emit stable blue light which seems unrelated to quantum confinement, but related to an amorphous overcoating layer of silicon oxide. Our approach can be used, in principle, as a general method for synthesis of other one-dimensional semiconducting, or conducting nanowires.

Growth of amorphous silicon nanowires via a solid–liquid–solid mechanism

Amorphous silicon nanowires (a-SiNW) with an average diameter of ca. 20 nm were synthesized at about 950°C under an Ar/H2 atmosphere on a large area of a (111) Si substrate without supplying any gaseous or liquid Si sources. The Si substrate, deposited with a layer of Ni (ca. 40 nm thick), served itself as a silicon source for the growth of the a-SiNWs. In contrast to the well-known vapor–liquid–solid (VLS) for conventional whisker growth, it was found that growth of the a-SiNWs was controlled by a solid–liquid–solid (SLS) mechanism, which is analogous to the VLS model.

Morphological effects on the field emission of ZnO nanorod arrays

The field-emission properties of ordered ZnO nanorod arrays with different morphologies were investigated in detail. After comparison of three different morphologies, it was found that the morphology of the ZnO nanorods has considerable effect on their field emission properties, especially the turn-on field and the emission current density. Among them, the ZnO nanoneedle arrays have the lowest turn-on field, highest current density, and the largest emission efficiency, which is ascribed to the small emitter radius on the nanoscale. On the other hand, high nanorod density remarkably reduces the local field at the emitters owing to the screening effect, which is related to the density of the emitters. The analysis results could be valuable for the application of field-emission-based devices using ZnO nanorod arrays as cathode materials.

Nano-scale GeO2 wires synthesized by physical evaporation

Abstract Germanium dioxide nanowires (GeONW) have been synthesized by a physical evaporation method. The morphology, structure and chemical composition of the wires were characterized using transmission electron microscopy (TEM) and spectroscopy of energy dispersive X-ray fluorescence (EDX). TEM observations show that the GeONWs have a very high purity and diameter ranging from 15 to 80 nm. EDX analysis reveals that the GeONWs consist of Ge and O elements. Electron diffraction patterns taken on a single GeONW are spotty patterns of single crystals and are well indexed to a GeO 2 single crystal of hexagonal structure.

Synthesis of nano-scale silicon wires by excimer laser ablation at high temperature

We report below synthesis of nano-scale silicon wires by using laser ablation at high temperature. By this approach we have been able to produce silicon nano wires (SiNWs) with a very high yield, a uniform diameter distribution and a high purity. The structure, morphology and chemical composition of the SiNWs have been characterized by using high resolution X-ray diffraction (XRD), high resolution electron microscopy (HREM), as well as spectroscopy of energy dispersive X-ray fluorescence (EDAX). Our results should be of great interest to researchers working on mesoscopic physical phenomena, such as quantum confinement effects related to materials of reduced dimensions and should lead to the development of new applications for nano-scale devices, together with providing a powerful method for synthesis of similar one-dimensional conducting and semi-conducting wire.

The growth mechanism of silicon nanowires and their quantum confinement effect

Abstract Silicon nanowires (SiNWs) with controlled diameters have been synthesized using a physical evaporation method. The growth mechanism of SiNWs is described based on the vapor–liquid–solid (VLS) model, which can well explain much of the morphology of SiNWs. The quantum confinement effect of SiNWs has been studied by photoluminescence (PL) measurements.

Dependence of the silicon nanowire diameter on ambient pressure

Our present work provides a method to control the diameters of the silicon nanowires. As a dominant experimental parameter, the ambient pressure was controlled between 150 and 600 Torr. It is found that the average size of the silicon nanowires increases with increasing ambient pressure. The mean diameter of the silicon nanowires in our study is proportional to the 0.4 power of ambient pressure. Catalytic nanoparticles and the periodic instability of the nanowires suggest a vapor-liquid-solid growth mechanism. For the growth of nanowires, an explanation of the relationship between the mean diameter of the silicon nanowires and the ambient pressure has been proposed.