A. C. H. Huan

Impact of interface structure on Schottky-barrier height for Ni∕ZrO2(001) interfaces

The Schottky-barrier heights for the Ni and ZrO2 interfaces have been determined using the x-ray photoemission method. Depending on the surface treatment of ZrO2, the variation of Schottky-barrier heights at Ni∕ZrO2 interfaces was found as large as 0.76±0.10eV. The p-type Schottky-barrier height for the oxygen-rich (oxygen-deficient) interface was measured to be 2.60eV (3.36eV). First-principles calculations provide a microscopic explanation of such variation, which was attributed to the different interface dipole formed by interfacial Ni–O, Ni–Zr bonds, or oxygen vacancies.

SIMS study of NO, CO adsorption on Cu(100) and Cu(210) surfaces

Abstract The adsorption of NO and CO on Cu(100) and Cu(210) at 110 K and the subsequent desorption/reaction have been studied by static SIMS, and complemented by XPS. After NO and CO coadsorption at 110 K, the major adsorbates are found to be NO 2 , N 2 O 4 , NO, NO 3 , CO, N and O adatoms. The dissociative adsorption of NO to form N and O adatoms is strongly enhanced on the stepped Cu(210) surface. Most of the molecular species desorb by 200 K upon heating the adlayer. On the stepped surface only, the formation of the isocyanate (-NCO) intermediate is observed, and is deduced to form via the reaction of adsorbed CO and N adatoms at step sites. At higher temperatures (200–300 K) the isocyanate intermediate decomposes to a cyanide (-CN) species.

Enhancement or reduction of catalytic dissolution reaction in chemically amplified resists by substrate contaminants

Chemical interaction of resist and substrate at the interface, which modifies the dissolution reaction, has degraded sidewall profile of resist features. Depending on the nature of the residue on the substrate, the bottom pinching (BP) effect and footing are observed, especially for chemically amplified (CA) resists. The BP effect is observed for CA resist on top of organic bottom antireflection coating (BARC). The BP effect is attributed to the acid generated from the underlying organic BARC. With optimization on softbake temperature of BARC, the BP effect is eliminated. On a silicon nitride surface, new chemical information has been obtained which explains footing and BP effects in CA resists. X-ray photoelectron spectroscopy (XPS) measurements indicate that the residual alkaline molecules on the nitride surface play a major role in the formation of footing. It appears that the organic contaminants are not responsible for footing. Less severe footing is observed if the nitride surface is plasma-deposited with a thin oxide cap, which suppresses the surface basicity. However, extended plasma deposition causes resist BP. This is ascribed to the surface acidity of a newly formed oxide cap, which enhances the CA resist development process. Results show that the N (1 s) peak, after extended plasma treatment, has shifted to a higher binding state, which suggests that the nitride surface becomes acidic, causing BP.

Al2O3-incorporation effect on the band structure of Ba0.5Sr0.5TiO3 thin films

The Al2O3-incoporation effect on the crystal structure and band structure of Ba0.5Sr0.5TiO3 thin films on (100) LaAlO3 substrate has been investigated by x-ray diffraction, x-ray photoelectron spectroscopy, and UV-VIS spectrophotometer. The resultant band gaps (Eg) increase with the increase of Al concentration. The shift of the valence-band edge and the core-level spectra with the incorporation of Al indicates that the Al could reduce the oxygen vacancy concentration.

Surface and interface studies of titanium silicide formation

Abstract Secondary ion mass spectrometry (SIMS), Rutherford backscattering spectroscopy (RBS) and X-ray photoelectron spectroscopy (XPS) are used to investigate Ti silicide formation mechanisms on a series of Ti on Si thin-films annealed in ultrahigh vacuum (UHV) at different temperatures and durations. The competition between oxygen diffusion and the silicide formation reaction (the so-called ‘snowplough’ effect) is observed directly, as well as a Tiue5f8Siue5f8O layer. The results from these controlled experiments are compared with those from Ti-silicide films formed under rapid thermal annealing (RTA) conditions in a production furnace, with and without a TiW barrier layer. The TiW layer is shown to act as an effective barrier to silicon and oxygen out-diffusion, as well as the incorporation of ambient gases.

Investigation of tungsten incorporated amorphous carbon film

Metal incorporated carbon films (Me-C:H) were deposited using a new technique with two W screen grids incorporated inside an electron cyclotron resonance chemical vapour deposition (ECR-CVD) chamber. This technique is versatile when applied to the deposition of Me-C:H films as the degree of plasma ionisation, the sputtering rate of the metal grids and the energy of the impinging ions can be independently controlled. In this work, the proposed technique is demonstrated through W-C:H deposition at different flow ratios of CH4 to Ar. A DC bias of 2 330V was applied to the upper and lower grids with either the substrate floating or under direct DC bias. The films were characterised in terms of their conductivity, atomic concentration (RBS), atomic configuration(XPS and XRD), hardness and optical absorption. The resistivities and the optical gaps of the films were noted to decrease drastically upon incorporation of several atomic percentage of W. WC formation is only observed for films deposited with the substrate under direct DC bias. q 1999 Elsevier Science S.A. All rights reserved.

The role of nitrogen in the deposition of polycrystalline diamond films

Abstract The role of nitrogen in the formation of polycrystalline diamond films prepared using a microwave plasma CVD system has been studied using micro-Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy (XPS). Although the nitrogen concentration in the films was too low to be detected by XPS, the Raman spectrum was found to be significantly affected by the nitrogen flow ratio. The intensity of the Raman peak at 1480xa0cm−1 significantly decreases, whereas that of 1190xa0cm−1 peak remains almost unchanged in comparison with the 1350 and 1550xa0cm−1 peaks with increasing nitrogen flow ratio. In contrast, the preferentially (111)-orientated growth and the growth rate were little influenced by the nitrogen flow ratio. These results indicate that nitrogen plays a special role in the formation and structure of the polycrystalline diamond films studied in this report.

Magnetic properties of ultrathin Co films on Si (111)

Abstract Ultrathin cobalt films on clean (7×7) and Au covered Si (111) substrates were prepared by molecular beam epitaxy. The structure was studied by using scanning tunnelling microscopy and low energy electron diffraction. Magnetic properties were determined with the magneto-optic Kerr effect. It was found that Co nucleates in grains that prefer to grow along the bunched step edges of the Si substrate ([112] direction), which induces a strong in-plane uniaxial anisotropy. By introducing Au buffer layers, the magnetic characteristics were improved by preventing the silicide reaction between Si and Co. Moreover, the tendency for step decoration disappears gradually results in the in-plane uniaxial anisotropy reduction.

Gender differences in undergraduate physics examination performance and learning strategies in Singapore

Results of a survey conducted amongst undergraduate physics students in Singapore suggest that female students perform less well in examinations than their male counterparts. The underachievement of many female students appears to be correlated to their less independent learning methods.

Tungsten-carbon thin films deposited using screen grid technique in an electron cyclotron resonance chemical vapour deposition system

A new technique for depositing metal‐carbon(Me‐C:H ) thin films is proposed based on two metal screen grids embedded within an electron cyclotron resonance chemical vapour deposition(ECR‐CVD) system. The grids are negatively biased and supported at adjustable distances above the substrate holder in the deposition chamber. With source gases of methane and argon, sputtering of the metal grids by Ar+ results in the incorporation of metal in the growing carbon films. The amount of metal in the films can be very well controlled over a wide range by varying the bias voltage of the grids, the separation of the grids from the substrate holder and the ratio of CH 4 /Ar. Furthermore, by separately biasing the substrate holder, the properties of the films can be varied resulting in the formation of a great variety of Me‐C:H films with very diVerent mechanical and structural properties. Tungsten incorporated carbon films( W‐C:H ) were deposited using this technique with two tungsten ( W ) grids biased at ’330 V. The fraction of W in the films was controlled by varying the flow ratio of CH 4 /Ar. The films were characterized using Rutherford backscattering and X-ray photoelectron spectroscopy measurements, and also in terms of their conductivity, optical absorption and hardness. The conductivity was found to increase by six orders of magnitude whereas the optical gap decreased by 1.5 eV with an increasing atomic fraction of W in the films from 2% to 8%. WC bonds were not detected, and the W detected was mainly in the form of WO 2 and WO 3 .