Chang-Kyun Park

Effects of lattice mismatches in ZnO/substrate structures on the orientations of ZnO films and characteristics of SAW devices

Polycrystalline ZnO films are deposited using RF magnetron sputtering on various substrate materials including AlN/Si-(111), sapphire, DLC/Si-(100), SiO2/Si-(100) and Si-(111). The structural parameters of deposited ZnO films, such as texture coefficient (TC) value for (002)-orientation, crystallite size and full-width at half-maximum (FWHM) at ZnO (002)-peak, are compared. Surface acoustic wave (SAW) devices are also fabricated by using a lift-off method, with the configuration of IDT/ZnO/substrate. The frequency response characteristics (including S21) of the fabricated SAW devices are measured and the device parameters, such as insertion losses and side-lobe rejection level, are estimated in terms of the substrate materials. Experimental results indicate that the lattice matching as well as the structural similarity between ZnO and substrate may be essential for determining the SAW device characteristics.

XPS and XRR studies on microstructures and interfaces of DLC films deposited by FCVA method

Diamond-like carbon (DLC) films have been deposited at room temperature using a filtered cathodic vacuum arc technique. The influence of the negative bias voltage applied to the substrate from 0 to −250 V on the sp3 hybridized carbon fraction is studied by Raman spectroscopy, which is also compared with the result obtained from X-ray photoelectron spectroscopy (XPS) for C 1s core peak. Based on the depth profiles for C 1s, Si 2p, and O 1s XPS peaks, the DLC film is modeled as a structure having three different layers, such as surface, bulk, and interface. In addition, the X-ray reflectivity is proposed as a method for estimating the density, surface roughness, and thickness of the layers constituting the DLC film. The estimated thickness of DLC film shows good agreement with the result obtained from the transmission electron microscope measurement.

Electron-emission from nano- and micro-crystalline diamond films: the effects of nitrogen and oxygen additives

Abstract Diamond films are grown on Si substrate by microwave plasma CVD using CH 4 +H 2 (for undoped) and additive N 2 (for nitrogen-incorporated) with/without O 2 as precursors. Crystal structures for grown films, such as micro- and nano-crystalline and surface morphologies are characterized in terms of growth condition by Raman and field-emission SEM, respectively. Cathodoluminescence (CL) spectra are monitored to identify the nitrogen-incorporation in grown diamond films. Relative intensity ratios of nitrogen-related band to band-A (denoted by I N / I A ) are also estimated from the CL characteristics and the influence of additive N 2 and O 2 precursors on the I N / I A ratio is analyzed. For all-grown films, electron-emission characteristics are measured, from which threshold fields for the emission are also estimated. Observed emission properties are correlated with crystal structures and morphologies obtained from grown films by considering the structural transformation from micro- to nano-crystalline as well as the nitrogen-induced defect states.

Cathodoluminescence characteristics of polycrystalline diamond films grown by cyclic deposition method

Polycrystalline diamond films were deposited using a cyclic deposition method where the H2 plasma for etching (tE) and the CH4+H2 plasma for growing (tG) are alternately modulated with various modulation ratios (tE/tG). From the measurement of full width at half maximum and ID/IG intensity ratio obtained from the Raman spectra, it was found that diamond defects and non-diamond carbon phases were reduced a little by adopting the cyclic deposition method. From the cathodoluminescence (CL) characteristics measured for deposited films, the nitrogen-related band (centered at approximately 590 nm) as well as the so-called band-A (centered at approximately 430 nm) were observed. As the cyclic ratio tE/tG increased, the relative intensity ratio of band-A to nitrogen-related band (IA/IN) was found to monotonically decrease. In addition, analysis of X-ray diffraction spectra and scanning electron microscope morphologies showed that CL characteristics of deposited diamond films were closely related to their crystal orientations and morphologies.

Direct growth of carbon nanotubes on a conical tip as a micro-focused x-ray generation source: Effects of various composition ratios of co-sputtered Ni and Co catalysts

In this study, we first present the experimental results that regard the direct growth of CNTs on a conical-type tungsten (W) tip and their electron emission properties, in terms of the catalyst materials such as a nickel (Ni) and a cobalt (Co) as well as their composition ratios. Sharpening of W-tips was done by electrochemical etch and their diameters were controlled to range from 5 mum down to sub-mum. The co-sputtering method using Ni and Co targets was used to deposit the catalyst layers with various composition ratios of Ni and Co metals. The composition ratio of the co-sputtered catalysts was evaluated by using an energy dispersive X-ray spectroscopy (EDS, Oxford). CNTs were grown by inductively coupled plasma-chemical vapor deposition (ICP-CVD).