ICMCTF2007 Session TS4P: TS1 Poster Session

Waterweed-like SnO₂ nanowires have been synthesized on the silicon substrate by thermal evaporation of the Sn powders. Waterweed- like SnO₂ nanowires were prepared by a two-step process. At the first step, SnO₂ nanowires with about 50 nm in diameter and more than 100 um in length were grown on the substrate. Afterwards, SnO₂ nanowhiskers were grown on the nanowires as the second step. Because of the product synthesized by the two-step process, nanowhiskers can be grown on nanowires uniformly. X-ray diffraction indicates that the product belongs to the tetragonal structure. Scanning electron microscopy (SEM) reveals the average width of nanowires is 220 nm, and the width of nanowhiskers is 100 nm. High resolution transmission electron microscopy (HR-TEM, JEOL JSM-2100F) and selected-area diffraction (SAD) patterns show the growth direction of nanowires is along the [101] and nanowhiskers is along the {12}. Room temperature photoluminescence shows that waterweed-like SnO₂ nanowires have three prominent emission bands at 562, 620, and 660nm.

[1]Z.R. Dai, Z.W. Pan, and Z.L. Wang, Adv. Funct. Mater. 2003, 13, No. 1, 9-24 [2]M. Law, X.F. Zhang, R. Yu, T. Kuykendall, and P. Yang, small 2005, 1, No. 8-9, 858-865 [3]S.H. Tsai, C.T. Shiu, S.H. Lai, H.C. Shih, Carbon 2002, 40, 1597-1600.

The micro-electromechanical system technology has been receiving much attention in the past decade for its potential applications. One of the obstacles that needs to overcome to achieve the MEMS technology a step further is stiction and meniscus effect by moisture. It is because that as component scales go down to nanometer scale, the surface force represented by meniscus force in humid atmosphere is the dominant factor affecting the microsystem failure.

So far there are plenty of works about hydrophobic film to prevent the effect of moisture for a long time, most of those films could not sustain over long time due to the water penetration through pinholes of film. The motivation of this work is to design the durable hydrophobic film in molecular level based on the fundamental understandings of the tribochemistry and molecular combination.

The design concept is composed of 3 steps. First, chemically bonded stearic acid molecules were introduced by mechanical activation, which induce the exo-electron emission. This process can make a chemical bonding between stearic acid molecule and silicon substrate as strong as conventional self assembled monolayer films. After that, the secondary molecules were added to increase the packing density and mobility of film. Finally, a UV induced polymer net is added on top of combined molecules to prevent loss of molecules through oxidation or evaporation. The thickness of total film should be less than 3nm.

We identify the hydrophobic property of film was not changed after heating at 150deg for 6hr and also immersion in water for 140hr.

Nickel/hydrogenated amorphous carbon (a-C:H) films have been deposited on single crystal silicon, Ni coated Si and stainless steel substrates at room temperature by combining sputter-deposition of metal and microwave plasma-assisted chemical vapor deposition of carbon from argon-methane mixtures of various compositions. The composition of films was investigated by Rutherford backscattering spectroscopy (RBS), nuclear reaction analyses and elastic recoil detection analyses (ERDA). The crystallographic structure of films was determined by X-ray diffraction (XRD) techniques.

The grain size of Ni and Ni₃C and magnitude of residual stresses were determined as functions of the composition of films. The nanohardness and elastic modulus of films were obtained from the load-displacement nanindentation curves. Ball-on-disk tribological tests for films deposited on steel substrates were conducted in room air at room temperature under a load of 1 N with a sliding speed of 5 cm/s. The minimum value of the friction coefficient was 0.25 for films containing about 75 at.% of carbon.

The dielectric properties of Ni/a-C:H films deposited on Ni coated Si substrates were investigated as functions of the frequency and temperature varying from 0.1 Hz to 1 MHz and from - 150°C to 175°C, respectively. For Ni/a-C:H composite films of 360 nm in thickness containing 19 at.% of nickel, the dielectric constant was higher than 300 at a frequency of 1 Hz. The dielectric constant value for these films was observed to decrease from 300 to 200 as the frequency was varied from 1 Hz to 10 kHz. The temperature and frequency effect as well as the nickel content effect on the dielectric properties of Ni/a-C:H films are discussed.