Martyn E. Pemble

Intelligent window coatings: atmospheric pressure chemical vapour deposition of vanadium oxides

Thin films of the vanadium oxides, V2O5, VO2, VOx (x = 2.00–2.50) and V6O13 were prepared on glass substrates by atmospheric pressure chemical vapour deposition (APCVD) of vanadium tetrachloride and water at 400–550 °C. The specific phase deposited was found to be dependent on the substrate temperature and the reagent concentrations. The films were characterised by Raman microscopy, X-ray diffraction (XRD), Rutherford backscattering (RBS), scanning electron microscopy (SEM), energy dispersive analysis by X-rays (EDX), reflectance/transmittance and UV absorption spectroscopy. The VO2 films show by Raman microscopy and reflectance/transmittance spectroscopy, reversible switching behaviour at 68 °C associated with a phase change from monoclinic (MoO2 structure) to tetragonal (TiO2, rutile structure).

Enhanced Raman spectra from species formed by the coadsorption of halide ions and water molecules on silver electrodes

Abstract The enhanced Raman spectra of water molecules and chloride ions coadsorbed at an electrochemically roughened silver electrode are reported. The spectra are discussed in terms of specifically adsorbed chloride ions.

FT-rairs, eels and leed studies of the adsorption of carbon monoxide on Cu(111)

Abstract The adsorption of CO on Cu(111) has been re-investigated using Fourier transform reflection absorption infrared spectroscopy (FT-RAIRS), electron energy loss spectroscopy (EELS) and low energy electron diffraction (LEED). The combination of these techniques has revealed important new information about this system. At 95 K three adsorption stages (1 to 3) can be distinguished, leading to successive ordered overlayer structures (I to III). Stage 1 exists for coverages up to 0.33 and involves linearly bound species only. The sharpest band observed during the course of these experiments, with an intrinsic FWHM of 4.5 cm −1 , is associated with a coverage of 0.33 and an ordered (√3 × √3) R 30 ° structure (I). Stage 2 is associated with the coverage regime 0.33−0.44. In this stage EELS data show tilted, linear CO species are present. No bridged species exist at this point. On the basis of this, we propose a new overlayer structure (II), for θ = 0.44. Increasing the coverage gives stage 3. During this process, the high resolution FT-RAIRS spectra resolved two bands associated with linear CO species. The behaviour of these bands suggests that the final structure (III) is formed in a step-wise manner, with islands of (II) and (III) coexisting in the adlayer. Both linear and bridged species exist in stage 3. The bandshapes suggest significant inhomogeneities in the adlayer are present at the saturation coverage. Finally, the concentration of bridged species is found to be very sensitive to the adsorption temperature.

A systematic study of (NH4)2S passivation (22%, 10%, 5%, or 1%) on the interface properties of the Al2O3/In0.53Ga0.47As/InP system for n-type and p-type In0.53Ga0.47As epitaxial layers

In this work, we present the results of an investigation into the effectiveness of varying ammonium sulphide (NH4)2S concentrations in the passivation of n-type and p-type In0.53Ga0.47As. Samples were degreased and immersed in aqueous (NH4)2S solutions of concentrations 22%, 10%, 5%, or 1% for 20 min at 295 K, immediately prior to atomic layer deposition of Al2O3. Multi-frequency capacitance-voltage (C-V) results on capacitor structures indicate that the lowest frequency dispersion over the bias range examined occurs for n-type and p-type devices treated with the 10%(NH4)2S solution. The deleterious effect on device behavior of increased ambient exposure time after removal from 10%(NH4)2S solution is also presented. Estimations of the interface state defect density (Dit) for the optimum 10%(NH4)2S passivated In0.53Ga0.47As devices extracted using an approximation to the conductance method, and also extracted using the temperature-modified high-low frequency C-V method, indicate that the same defect is pre...

Temperature and frequency dependent electrical characterization of HfO2/InxGa1−xAs interfaces using capacitance-voltage and conductance methods

Electrical properties of metal-oxide-semiconductor capacitors using atomic layer deposited HfO2 on n-type GaAs or InxGa1−xAs (x=0.53, 0.30, 0.15) epitaxial layers were investigated. Capacitance-voltage (CV) measurements indicated large temperature and frequency dispersion at positive gate bias in devices using n-type GaAs and low In content (x=0.30, 0.15) InxGa1−xAs layers, which is significantly reduced for devices using In0.53Ga0.47As. For In0.53Ga0.47As devices, the CV response at negative gate bias is most likely characteristic of an interface state response and may not be indicative of true inversion. The conductance technique on Pd/HfO2/In0.53Ga0.47As/InP shows reductions in interface state densities by In0.53Ga0.47As surface passivation and forming gas annealing (325 °C).

Low temperature electron energy loss spectra of acetylene chemisorbed on metal single-crystal surfaces; Cu(111), Ni(110) and Pd(110)

Vibrational spectra of acetylene chemisorbed on Cu(111), Ni(110) and Pd(110) at 110–120 K were measured using electron energy loss spectroscopy. Loss peaks were assigned to vibrational modes of the non-dissociatively adsorbed molecules with the aid of the corresponding C2D2 spectra. The spectra show that the molecules undergo significant rehybridisation on adsorption. Comparisons are made with the spectra of acetylene adsorbed on a range of other transition metal surfaces at low temperature. Taking into account these and earlier literature results, two distinct patterns of spectra are observed (Type A and Type B) for specular spectra. The Cu(111) spectrum is classified as Type A while the Ni(110) and Pd(110) spectra are classified as Type B. Suggestions are made for the structures of the surface species corresponding to the two spectral types.

The chemisorption of CO on Pd(110) at 110 and 300 K studied by electron energy loss spectroscopy

The vibrational electron energy loss spectrum of CO adsorbed on Pd(110) at both 110 and 300 K has been recorded as a function of CO exposure. At both temperatures the spectra indicate that CO adsorption occurs predominantly in two-fold bridged sites along the rows of metal atoms. At 110 K the surface may be saturated to give a two-fold bridged (2 × 1) CO overlayer of p2mg unit mesh symmetry, yielding a LEED pattern with absences at the (±12hodd, 0) positions along the 〈110〉 azimuth. Near saturation, (θ ≥ 1.0), a weak band due to CO adsrobed in on-top sites is observed. At 300 K, LEED studies show that a c(2 × 2) pattern forms at low exposures ( <1 L), followed by a p(4 × 2) pattern at higher exposures. The latter structure persists up to a dynamic CO pressure of 1 × 10−7 mbar where an incomplete p2mg pattern forms, with residual four-fold periodicity along the rows of metal atoms. EEL spectra corresponding to the p(4 × 2) overlayer indicate that at least two distinct two-fold bridge CO species are present giving rise to νCO loss features separated by only 60 cm−1.

Enhancement of the photonic gap of opal-based three-dimensional gratings

The “semimetallic” photonic band gap formed in a synthetic opal has been increased by depositing a layer (InP or TiO2) with high refractive index on the inner surface of opal voids. Reflectance spectra of the composites (nanolayers assembled within grating voids) are correlated with both the photonic structure of the opal and electronic structure of the semiconductor.

Synthesis and characterisation of two novel titanium isopropoxides stabilised with a chelating alkoxide: their use in the liquid injection MOCVD of titanium dioxide thin films

The new precursors [Ti(OPri)3(OCH2CH2NMe2)] 1 and [Ti(OPri)2(OCH2CH2NMe2)2] 2 have been prepared and characterised. Compound 1 exists in solution at room temperature as a mixture of monomer and dimer(s), however at elevated temperatures the monomer predominates. Compound 2 exists in solution predominantly as a monomeric complex presumably with pseudo-octahedral coordination at the metal centre. Thin films of TiO2 have been deposited at 300-450C by liquid injection MOCVD using both 1 and 2. Analysis of the films by Auger electron spectroscopy failed to detect nitrogen although trace carbon was detected at levels of between 2.9 and 7.7. The potential utility of these modified compounds as precursors to TiO2 is discussed.

In situ H2S passivation of In0.53Ga0.47As∕InP metal-oxide-semiconductor capacitors with atomic-layer deposited HfO2 gate dielectric

We have studied an in situ passivation of In0.53Ga0.47As, based on H2S exposure (50–350°C) following metal organic vapor phase epitaxy growth, prior to atomic layer deposition of HfO2 using Hf[N(CH3)2]4 and H2O precursors. X-ray photoelectron spectroscopy revealed the suppression of As oxide formation in air exposed InGaAs surfaces for all H2S exposure temperatures. Transmission electron microscopy analysis demonstrates a reduction of the interface oxide between the In0.53Ga0.47As epitaxial layer and the amorphous HfO2 resulting from the in situ H2S passivation. The capacitance-voltage and current-voltage behavior of Pd∕HfO2∕In0.53Ga0.47As∕InP structures demonstrates that the electrical characteristics of samples exposed to 50°C H2S at the end of the metal-organic vapor-phase epitaxy In0.53Ga0.47As growth are comparable to those obtained using an ex situ aqueous (NH4)2S passivation.