Z.Q. Liu

The growth behavior of self-standing tungsten tips fabricated by electron-beam-induced deposition using 200keV electrons

Self-standing tungsten tips were fabricated by electron-beam-induced deposition in a 200kV scanning transmission electron microscope to study their growth behavior. By increasing deposition time from 0.2to2400s, the tip growth rate decreases from 5–7nm∕s to zero and the root diameter increases from 2to60–65nm. Tips preferably grow downward at the beginning stage with a saturation length of 80–120nm. Dynamic Monte Carlo simulation was carried out, and 200keV electrons were proved to be more capable to fabricate tip with smaller lateral size and higher ratio than the 20keV electrons.

Features of self-supporting tungsten nanowire deposited with high-energy electrons

The features of self-supporting tungsten nanowire fabricated by electron-beam-induced deposition using 200 keV electrons were investigated. The width of wire first decreases with the increase of the scan speed, then saturates at about 7–10 nm when the scan speed is higher than 10 nm/s. The wire has belt-shipped morphology elongated along the incident beam. The wire parallel to the substrate surface was fabricated at the beam scan speed of 4.0 nm/s, while those with upward and downward features were obtained by changing the scan speed. Nanobelt, nanorod, and nanotip with high aspect ration and small lateral size were fabricated with this method. Considering the forward scattering of electrons and the beam Gaussian profile, a model was developed for the growth of wire using high-energy electrons.

Transmission Electron Microscopy Investigation on the Electron-stimulated Oxidation of Iron Nitrides by 2-MeV Electron Irradiation

An iron nitride sample was irradiated by 2-MeV electrons intermittently for 2100 s with a dose rate of 6.3 × 10 24 e.m. −2 s −1 inside a 3-MV high-voltage transmission electron microscope. The electron-stimulated oxidation of Fe 4 N and Fe 2–3 N was investigated in situ and ex situ using conventional transmission electron microscopy and high-resolution electron microscopy. It was found that both Fe 4 N and Fe 2–3 N nitrides were oxidized by the residual gas in the vacuum chamber to form Fe 3 O 4 oxides. The orientation relationship between Fe 4 N (γ′) and Fe 3 O 4 (o) was (110)γ′//(220)o, [001]γ′//[001]o, and that between Fe 2–3 N (ϵ) and Fe 3 O 4 (o) was (110)ϵ//(−220)o, [1–11]ϵ//[001]o. Crystal lattice deformation from iron nitride to iron oxide took place during the dynamic oxidation process. Structural models were proposed to understand the oxide formation, and the models were confirmed by experimental observations. The irradiation effects of Fe 4 N and Fe 2–3 N crystals were compared. The results show that Fe 4 N is more sensitive than Fe 2–3 N to electron irradiation. These results are important not only for the fabrication of insulating iron oxide film, but also in the field of the surface modification of iron nitride to improve its mechanical properties.

Dynamic Monte Carlo simulation on the electron-beam-induced deposition of carbon, silver, and tungsten supertips.

The process of electron-beam-induced deposition (EBID) was simulated with a dynamic Monte Carlo profile simulator, and the growth of carbon, silver, and tungsten supertips was investigated to study the dependence of material composition on the spatial resolution of EBID. Because light atoms have a smaller scattering angle and a longer mean free path, the carbon supertip has the smallest lateral size and the highest aspect ratio of a bottom tip compared to silver and tungsten supertips. Thus the best spatial resolution of EBID can be achieved on materials of low atomic number. The calculation also indicated a significant contribution of primary electrons to the growth of a supertip in EBID, which is consistent with the experimental observations. These results lead to a more comprehensive understanding of EBID, which is a complex interaction process between electrons and solids.

Nanofabrication of Tungsten Structure by Electron-Beam-Induced Deposition in Scanning Transmission Electron Microscope

In the last two decades has Electron-beam-induced deposition (EBID) been developed as a tool for additive lithography to fabricate three dimensional nanostructures[1]. Compared with other direct write techniques using photons (laser) or focused ion beams[2], the virtue of EBID lies in its potential feature size and low irradiation damage. Recently, nanodot with a diameter of 3.5nm has been successfully deposited using high energy electrons[3]. In the present work, the deposition of self-supporting nanowire and self-standing nano-tip were systematically investigated. Based on these results, the fabrication of three dimensional nanostructures was carried out