Fabrication and field emission property of a Si nanotip array

Surfing Silicon Nanofacets for Cold Cathode Electron Emission Sites

Point sources exhibit low threshold electron emission due to local field enhancement at the tip. In the case of silicon, however, the realization of tip emitters has been hampered by unwanted oxidation, limiting the number of emission sites and the overall current. In contrast to this, here, we report the fascinating low threshold (∼0.67 V μm^-1) cold cathode electron emission from silicon nanofacets (Si-NFs). The ensembles of nanofacets fabricated at different time scales, under low energy ion impacts, yield tunable field emission with a Fowler-Nordheim tunneling field in the range of 0.67-4.75 V μm^-1. The local probe surface microscopy-based tunneling current mapping in conjunction with Kelvin probe force microscopy measurements revealed that the valleys and a part of the sidewalls of the nanofacets contribute more to the field emission process. The observed lowest turn-on field is attributed to the absence of native oxide on the sidewalls of the smallest facets as well as their lowest work function. In addition, first-principle density functional theory-based simulation revealed a crystal orientation-dependent work function of Si, which corroborates well with our experimental observations. The present study demonstrates a novel way to address the origin of the cold cathode electron emission sites from Si-NFs fabricated at room temperature. In principle, the present methodology can be extended to probe the cold cathode electron emission sites from any nanostructured material.

Optimization of a nanotip on a surface for the ultrafast probing of propagating surface plasmons

We theoretically analyze a method for characterizing propagating surface plasmon polaritons (SPPs) on a thin gold film. The SPPs are excited by few-cycle near-infrared pulses using Kretschmann coupling, and a nanotip is used as a local field sensor. This geometry removes the influence of the incident excitation laser from the near fields, and enhances the plasmon electric field strength. Using finite-difference-time-domain studies we show that the geometry can be used to measure SPP waveforms as a function of propagation distance. The effects of the nanotip shape and material on the field enhancement and plasmonic response are discussed.

Fabrication and characterization of well-aligned and ultra-sharp silicon nanotip array

Well-defined, uniform, and large-area nanoscaled tips are of great interest for scanning probe microscopy and high-efficiency field emission. An ultra-sharp nanotip causes higher electrical field and, hence, improves the emission current. In this paper, a large-area and well-aligned ultra-sharp nanotip arrays by reactive ion etching and oxidation techniques are fabricated. The apex of nanotips can be further sharpened to reach 3-nm radius by subsequent oxidation and etching process. A schematic model to explain the formation of nanotip array is proposed. When increasing the etching time, the photoresist on top of the nanotip is also consumed, and the exposed silicon substrate is etched away to form the nanotip. At the end, the photoresist is consumed completely and a nanotip with pyramid-like shape is developed. The field emission property was measured, and the turn-on field and work function of the ultra-sharp nanotip was about 5.37 V/μm and 4.59 eV, respectively. A nanotip with an oxide layer capped on the sidewall is also fabricated in this paper. Comparing to the uncapped nanotip, the oxide-capped sample exhibits stable and excellent field emission property against environmental disturbance.

Silicon rice-straw array emitters and their superior electron field emission

Free standing and vertically aligned silicon rice-straw- like array emitters were fabricated by modified electroless metal deposition (EMD), using HF-H(2)O(2) as an etching solution to reduce the emitter density and to make the emitter end of the formed silicon rice-straw arrays shaper than those formed by conventional EMD. These silicon rice-straw array emitters can be turned on at E(0) = 4.7 V/μm, yielding an EFE (electron field emission) current density of J(e) = 139 μA/cm(2) in an applied field of 12.8 V/μm. According to a simple simulation, the excellent EFE performance of the silicon rice-straw array emitters originates in not only the favorable distribution of emitter arrays, but also the shape of the emitter apexes. The modified-EMD method is easily scaled up without expensive equipment, so silicon rice-straw array emitters are a promising alternative to silicon-based field emitters.

Morphology and wettability control of silicon cone arrays using colloidal lithography

In this paper we present a simple method to fabricate ordered silicon cone arrays with controllable morphologies on a silicon substrate using reactive ion etching with two-dimensional silica colloidal crystals as masks. The etching process and the morphologies of the obtained structure are quantified. Unlike works reported previously, we show that the surface roughness of the obtained silicon cone arrays can be adjusted by controlling the etching duration, which is proved to be of importance in tailoring the behavior of water droplets when being used as antireflection coatings with superhydrophobicity. Moreover, this strategy is compatible with the methods we have established on controlling the arrangement of colloidal spheres, and thus silicon cone arrays with tunable periodicities, different lattice structures, and various patterns can be prepared. The obtained silicon cone arrays with strips can be used as hydrophobic substrates with anisotropic dewetting just like the leaves of rice. It is found that by adjusting the strip width with and without silicon cones, the water droplets can transform from isotropic dewetting to anisotropic dewetting.