Raymund Wai Man Kwok

Enhanced photocatalytic activity of Ti1−xVxO2 solid solution on the degradation of acetone

Solid solutions of Ti1−xVxO2 (0.00< x ≤0.025) exhibit higher photocatalytic activity than pure TiO2 for the oxidation of acetone. Results from X-ray photoelectron spectrometry, X-ray diffractometry and photoionization detection reveal that the photocatalytic activity of the solid solution increases with increasing V substitution, but decreases with a decrease in the anatase to rutile ratio. The optimum composition in terms of activity is x = 0.015, with an anatase to rutile ratio of 9: 1. Zeta potential measurements indicate that the isoelectric point (in terms of the pH value) is affected by the amount of V substitution. The catalyst with x = 0.015 has the lowest isoelectric point (at pH 5.5). All these results suggest that V substitution may enhance the adsorption of hydroxide ions onto the surface of the catalyst. More hydroxyl radicals can be generated, resulting in a higher photocatalytic activity. The synthesis of the catalyst and the effect of the crystalline form of the catalyst on its activity are also presented.

Copper phthalocyanine film grown by vacuum deposition under magnetic field

Copper phthalocyanine (CuPc) film with good orientation is always required when CuPc is to be used as an electronic functional layer in different device applications. In the present study, a magnetic field (∼6 mT) was applied during the vacuum deposition of CuPc. The CuPc film grown under such a magnetic field showed better orientation and a new stacking behavior as shown by X-ray diffraction study (XRD) and atomic force microscopy (AFM). In addition, the film grown under magnetic field exhibited different absorption characteristics in the UV-visible range. This demonstrates the potential of using magnetic field to optimize the growth of CuPc for various applications.

XPS studies on SiC thin layers formed by ion implantation with a metal vapor vacuum arc ion source

Abstract We have performed XPS studies on SiC thin layers formed by high-dose C+ implantation into Si with a metal vapor vacuum arc ion source. Composition depth profiles of the implanted SiC samples and the change in the chemical state of the silicon and carbon atoms with respect to composition and depth have been obtained. An unexpected double peak feature in the depth profile of the width of the Si 2p signal has been observed and the results are discussed in terms of the damage properties of the implanted SiC layers.

Lowering of work function induced by deposition of ultra-thin rubidium fluoride layer on polycrystalline diamond surface

Ultra-thin rubidium fluoride (RbF) was thermally evaporated onto polycrystalline diamond surface. The role of RbF as a strong dipole layer to lower the surface work function was investigated using ultraviolet photoemission spectroscopy, Kelvin probe and Auger electron spectroscopy. It was found that deposition of sub-monolayer of RbF could greatly reduce the work function of the diamond surface. Also, the ultra-thin RbF overlayer is very sensitive to electron irradiation. The electron irradiation can seriously weaken the effect of RbF as a surface dipole.

Ordering and surface state reduction of GaAs (100) by low energy S+ bombardment

S+ ions with well-controlled kinetic energy were used to bombard n- and p-type GaAs (100) surfaces. 50 eV S+ bombardment formed a maximum of 1.5 monolayers of sulfide on a GaAs (100) surface and did not change the nonordered surface to an ordered surface. After the bombardment, the surface Fermi levels for both sulfur ion-bombarded n- and p-type samples were moved towards the midgap. After the samples were further annealed at 400 °C, the surface Fermi level of n- and p-type samples gave a separation larger than that of the samples after the UV/O3 and HF treatment. A sharp (1×1) low-energy electron diffraction pattern was observed and the sulfide coverage was about one monolayer. Under such well-controlled conditions, effective surface passivation by reducing surface states and formation of an ordered surface structure can be achieved.

SIMS analysis of lead isotope composition in ancient Chinese metallic artefacts

An attempt on the use of secondary ion mass spectroscopy (SIMS) in studying ancient Chinese bronze is reported with an evaluation of the suitability of SIMS for the provenance study of ancient bronze objects. The advantage of using SIMS in the study of the lead isotope ratio is the high sensitivity that enables the examination of small fragments of valuable relics that are often difficult to collect. The application of SIMS in this direction widens the sampling area, which is limited by the use of thermal ionization mass spectroscopy (TIMS). The focus of the study has been placed on the precision of SIMS when compared to TIMS and the effect of sample matrices on the precision. Samples of Chinese bronze artefacts and a standard lead sample (SRM 981) were tested for their lead isotope ratios using both SIMS and TIMS. A comparison of the data obtained using the two techniques showed that SIMS results have a relatively large standard deviation, which was attributed to the non-uniformity of the ancient samples and the single-isotope detection system of the SIMS set-up used. Matrix effects were found to be small among bronze samples of different compositions. Non-conducting samples can also be analysed when a specimen isolation technique is employed. Although SIMS gave higher uncertainties than TIMS, the SIMS technique can be applied easily to differentiate the high radiogenic lead in Shang bronze artefacts from common lead. Copyright

Sulfur passivation of InP (100) by means of low energy sulfur ions

Sulfur ions with well-controlled kinetic energy were used to introduce additional energy for passivating the InP (100) surface. 50 eV S+ bombardment resulted in the formation of a single In–S species on InP surface and assisted the InP (100) surface to form an ordered (1×1) structure. Further annealing removed the damage introduced during the ion bombardment and resulted in a sharp (1×1) low-energy electron diffraction (LEED) pattern. The treatment was extended to repair Ar+ damaged InP (100) surface. When InP (100) samples were damaged by 200 eV Ar+ bombardment followed by 50 eV S+ treatment and annealing, we could obtain an InP surface with (1×1) LEED pattern and with low surface states.

Electron affinity and surface re-ordering of homoepitaxial diamond (100)

The change in electron affinity and the re-ordering of the diamond surface upon annealing of a homoepitaxially grown diamond (100) thin film were investigated by ultraviolet photoemission spectroscopy, low energy electron diffraction (LEED), and Auger electron spectroscopy. When the sample was heated to ~1250° C, the electron affinity of the sample changed from negative to positive and the LEED pattern changed from (2×1/1×2) to (1×1). When the sample was further annealed at ~900° C, the electron affinity and the LEED pattern reverted to negative and (2×1/1×2) respectively. The sample was then heated to ~1100° C, followed by annealing at ~900° C again, and the same phenomenon was observed. These observations were considered to be associated with the disordering/re-ordering behavior of the diamond surface upon annealing.

Surface studies of (111) facets of cBN mini-crystals

Surface analysis techniques, including x-ray photoelectron spectroscopy with small-spot analysis (down to 100 μm 2 ) capabilities, field emission scanning Auger microscopy, electron energy-loss spectroscopy in association with these two techniques and micro-Raman spectroscopy, have been used to collect surface information on specific facets of commercially available submillimetre-sized cubic boron nitride (cBN) crystals. With the freedom of choosing a specific facet with a known orientation relative to the probing beam and detector, it is possible to obtain accurate information on the surface compositional structure of a cBN crystal before and after a surface reaction.

Construction of cross-linked polymer films covalently attached on silicon substrate via a self-assembled monolayer

A new synthetic approach was developed to fabricate cross-linked polymer films covalently attached on a silicon substrate via a self-assembled monolayer (SAM) using a low energy proton beam as the initiator. The widely used silane coupling reagent 3-(mercaptopropyl) trimethoxysilane [HS(CH2)3Si(OCH3)3] was employed as an intermediate SAM to chemically bond the cross-linked polymer film to the silicon substrate. Dotriacontane was selected as a precursor that was spin-coated on the SAM-terminated silicon wafers. The film thickness can be easily controlled by spin-coating precursor solutions of different concentrations. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and contact angle measurements confirmed the formation of SAM on the silicon substrate and the subsequent cross-linkage between the SAM and the upper polymer film formed. The resulting cross-linked polymer films are relatively stable, with all layers covalently attached together so that the whole film could not be removed by rinsing in both organic solvent and even more reactive HF solutions. In particular, the resistance of the cross-linked polymer film towards HF etching can be useful for lithography and device fabrication for polymer based electronics. The capability of using different SAMs to attach various polymer films was also demonstrated.