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The influences of chemical treatment and thermal annealing of AlxGa1−xN (x = 0.20) have been investigated by X-ray photoelectron spectroscopy (XPS). XPS analysis showed that successive chemical treatments and annealing produced changes in the stoichiometry of the AlxGa1−xN surface, with the surface concentration of N increasing and Al and Ga decreasing with increasing temperature. Band bending occurred at the AlxGa1−xN surface, in parallel with the observed changes in stoichiometry. These results are discussed in the context of the creation of surface states via the activation of vacancies and induced by defects. These findings point towards the possibility of selecting and/or engineering the band structure at AlxGa1−xN surfaces through a combination of surface preparation and annealing.

The electronic changes occurring at the surface of a nano-crystalline SnO 2 sensor upon exposure to O 2 and CH 4 at elevated temperature have been investigated by X-ray photoelectron spectroscopy (XPS). Gas exposures and subsequent XPS scanning were conducted at 120 and 250 °C to simulate the working conditions of the sensor. Exposure to O 2 at 120 °C resulted in a 0.2 eV upward band bending while subsequent exposure to CH 4 resulted in a 0.1 eV downward band bending, as expected from oxidising and reducing gases, respectively. Similar changes in surface band bending were observed at 250 °C, although quantitative analysis suggests that oxygen absorption might be enhanced. The results clearly indicate the electronic nature of the gas sensing mechanism when exposed to O 2 and CH 4 and the very high sensitivity of the sensor.

In this work, we present the microscopic characterisation of intimate Cu contacts formed on (100) In0.53Ga0.47As surfaces. Previous I(V) measurements indicate that Cu–In0.53Ga0.47As (100) dots formed ohmic contacts. In the present study, the metal-semiconductor interface is examined by a variety of techniques, including transmission electron (TEM) and atomic force microscopies (AFM), Auger electron spectrometry (AES) and X-ray microanalysis (EDX). The configuration of the three intimate contacts is discussed in terms of the interfacial reactions resulting from the differing deposition conditions.

Soft X-ray photoelectron spectroscopy (SXPS) was performed on Si/Ge(111)-c(2 × 8) heterojunctions. The effect of an ordered ultrathin (one monolayer) ionic dipole layer of ZnSe placed at the interface was studied. The formation of the interface was monitored via the evolution of the valence band edges and the movements of core levels. It was found that the ZnSe intralayer dramatically modified the valence band offset of the Si/Ge (111) junction. The valence band offset was increased by 0.57 ± 0.1 eV due to the presence of the ZnSe intralayer. This intralayer-induced modification of the valence band offset is interpreted in terms of the charge transfer at the interface.

The control of semiconductor interfaces is essential to engineer new material properties for device applications. In this article we have considered the use of ultra-thin (1 monolayer) interfacial Si and Be dipoles layers to modify the band discontinuity present at the GaAs AlGaAs heterojunction. Soft X-ray photoelectron spectroscopy (SXPS) was performed at the Daresbury synchrotron radiation source (SRS) on samples previously grown by molecular beam epitaxy (MBE). Detailed deconvolution of the As 3d core level spectra enabled the valence band modification due to the presence of the interlayers to be extracted. The results of this study indicate the potential of this method to induce large valence band-offset modification (+0.4 eV for Si and −0.52 eV for Be) due to the presence of the dipole layers. The effect of any near interface doping by the Si and Be layers was considered by solving Poisson's equation for these structures. Finally, the technique is compared to other band engineering methods, namely δ-doping and multi quantum barriers (MQB), to assess the potential and viability for use in real devices.

The passivation properties of the Si GaAs(110) interface have been studied using scanning tunnelling microscopy/spectroscopy (STM/STS) and soft X-ray photoemission spectroscopy (SXPS). Silicon has been deposited at room temperature and STM images show the sub-monolayer growth of silicon islands on the GaAs substrate. The electrical properties of these islands together with the clean surface have been investigated using scanning tunnelling spectroscopy (STS). The spectroscopy clearly illustrates the difference in electrical properties between atomically flat regions of GaAs as compared to those containing defects or steps, i.e. where surface band bending occurs. We have investigated the use of sub-monolayer Si coverages to modify the electronic structure of the surface. Height variations of 3–4Aacross Si islands and 2Aacross steps on the GaAs surface have also been observed using the STM. STS spectra, collected simultaneously with the STM image, showed the Si to have semiconducting properties differing from that of crystalline Si and the GaAs substrate. Comparisons between the STM and STS results together with SXPS have provided a correlation between the structural, electrical and chemical nature of the Si/GaAs(110) interface.

The relaxation mechanism of the tensile In x Ga 1 − x As/In(P001) system is presented by means of transmission electron and atomic force microscopies. It is shown that relaxation occurs through a transition from bi- to tri-dimensional growth and defect nucleation. Such non-planar growth evolves to a faceted surface aligned on [11¯0], which promotes the anisotropy on the appearance of defects.

One challenge in the processing of In 53 Ga 47 As/InP(100) heterostructures is the enhancement of the low Schottky barrier heights (Φ b ) typically exhibited by metal-nIn 53 Ga 47 As(100) contacts. Previous studies of the metallisation of chemically etched In 53 Ga 47 As surfaces have reported increases in Φ b if metallisation is performed at 77 K. This study extends this concept to probe the idealised case of the formation of metal contacts (Au-, Cu- and In-) to atomically clean nIn 53 Ga 47 As/InP(/I) at 80 K and room temperature (294 K). The in-situ current-voltage measurements of intimate Au and Cu contacts formed at both temperatures exhibited ohmic characteristics. However, intimate In contacts formed at 80 and 294 K showed diodic behaviour (Φ b 0.45 and 0.30 eV, respectively), with an improvement in the rectification when formed at 80 K. Conversely, In contacts to etched surfaces were ohmic. It is proposed that this behaviour is linked to the alteration of the structure and nature of the interface as a result of the various fabrication techniques. These results indicate the potential to select Φ b on In 53 Ga 47 As via a combination of cryogenic processing and surface preparation.

A study of the growth copnditions and the relaxation processes of mismatched frsol|GaxIn1−xAs / InP structures (x = 0.3 to 0.5) grown by hydride vapour phase epitaxy is presented. Using double crystal X-ray diffraction and photoluminescence spectroscopy results, the bulk composition and the strain of the layers have been determined. Strained was relieved at thicknesses well above the Matthews-Blakeslee critical thickness; however, small residual strain (≈ 10%) always remained. A kinetic model applied to the growth of strained ternary alloys is developed; with the appropriate choice of the activation energy (Δϵ∗ = 1250 cal/mol) and the interaction parameter (ω = 2800 cal/mol), good agreement between experiemental and theoretical results has been obtained.

An X-ray diffraction investigation of strain relief in InGaAs/InP has been performed for In compositions x of 54.3% and 50.8%, corresponding to compressive and tensile strain, respectively. Strain is relieved at thicknesses well above the Matthews-Blakeslee critical thickness, leading to a small residual strain, in common with most III–V materials grown at conventional substrate temperatures. Recent X-ray photoelectron spectroscopy studies indicate that one or two monolayers of InAs may be incorporated at the interface during thermal oxide desorption in an arsenic atmosphere. Such an interfacial strained layer, if present, would lead to a shift in the observed peak position. Hence there is an uncertainty in the strain analysis for thin epilayers in the absence of detailed information about the interfacial structure.

Carbon dioxide injection into an extrusion cooker is able to produce structured extrudates under low-temperature and high-moisture conditions when the release of steam does not contribute. The effect of carbon dioxide injection pressure on the extruder response and the resulting extrudate structure was studied for wheat starch-sucrose mixtures. An increase in gas pressure decreased the pressure gradient in the extruder and the die pressure, although it had a relatively small effect on the specific mechanical energy consumption. The degree of expansion reached a maximum (and the density a minimum) with increasing gas injection pressure for each composition for the extrusion conditions studied.

Epitaxial layers of InxGa1-xAs (x = 0.53±0.04) have been grown on (100)Si substrates misoriented by 3° towards the [011] direction. Films of 3 μ thickness were grown in the temperature range Tg = 200–550°C and their morphological, structural and electrical properties compared. It was found that three distinct growth temperature windows could be identified, the boundaries between the windows being characterized by abrupt changes in all of the properties of the layers. In particular the best quality material, in all respects, was produced in a very narrow growth temperature (Tg) region (265 ⩽ Tg ⩽ 300°C).

Five herbicides commonly used for suppression of weed growth in white clover seed crops were tested for toxicity to white clover ( Trifolium repens ), the nodule-forming bacteria Rhizobium trifolii , and the nitrogen-fixing symbiosis of these organisms. Trials were carried out under bacteriologically-controlled and glasshouse conditions. Overall, paraquat was more toxic to R. trifolii growth than MCPB, followed by bentazone, fusilade and kerb as the least toxic. Bentazone showed the least toxicity to plant growth, nodulation and N 2 fixation under bacteriologically-controlled conditions. All the other herbicides inhibited C 2 H 2 reduction, while nodule number and plant fresh weight were lowered by paraquat. MCPB and kerb. However, when plants grown in soil were treated, kerb showed the least toxicity with fusilade, bentazone and MCPB being intermediate in toxicity. This study also showed that changes in growth medium, nitrogen status and soil moisture content can alter the activity of particular herbicides. Possible toxicity of herbicides to plant growth and N 2 fixation should be considered when using herbicides to control weeds in leguminous crops.

The strong interaction shift and width for the 2p level and the width for the 3d level have been measured for antiprotonic helium atoms. The results are compared with optical model calculations. The possible existence of strongly bound antiproton states in nuclei is discussed.

A full-kinematics measurement of the π − p→ π − p π 0 reaction in the incident π − momentum region from 295 to 450 MeV/ c is presented. The measurement was performed with the OMICRON spectrometer at the CERN synchrocyclotron. An incident-momentum dependent number of π − p→ π − p π 0 events, ranging from 6 to 430 has been extracted from collected data. Differential cross sections are found to be consistent with phase-space distributions. Integrated cross-sections are used to determine the value of the chiral symmetry breaking parameter ξ. The measured value of ξ =0.1 −0.7 +0.5 is obtained in a model-independent way, strongly favouring Weinberg's choice of ξ =0.

Result of cross section measurements for the reaction π − p → π − π + n are presented. They cover a range of incident pion momenta between 295 and 450 MeV/ c . It is the first time that the cross section has been measured so close to threshold. The experiment was performed with Omicron, a large-solid-angle spectrometer, which enables a measurement of the full set of kinematic variables. In the region of overlap there is a good agreement with other experiments. The extracted value for the chiral-symmetry-breaking parameter ξ is seen to be largely extrapolition dependent but the measured value of -0.5±0.8 leaves Weinberg's prediction of ξ =0 the only remaining choice.

Energies and yields of K-series X-rays from pp atoms have been measured with two gas scintillation proportional detectors at target gas densities of 0.25 and 0.92 ρ STP . Values for the strong interaction shift and width of the 1s state obtained from the X-ray spectra are compared with the predictions of a variety of theoretical models. Upper limits for the yield of K-series X-rays from pd atoms have also been obtained.

The yields of K and L series X-rays from pp atoms and of the L series X-rays from pd atoms have been measured at gas densities of 0.25, 0.92, 2.0 and 10.0ρ STP . For pp atoms the strong interaction shift and width for the 1s state and the width of the 2p state have been measured. The results are in good agreement with the predictions of potential models.

In 1950 at a time when parity conservation was almost universally believed, PURCELL and RAMSEY [1] pointed out that such an assumption must be based on experiment and that there was little experimental evidence for the assumption at that time. We further noted that a search for a neutron electric dipole moment would provide such a test since a dipole moment is forbidden under parity symmetry and the test would be particularly sensitive since the neutron has no electric charge and is consequently not accelerated out of the observation region when a strong external electric field is applied.