The optimization of differential reflectometry at surfaces of transparent crystals

The first-order difference in reflectivity of crystals surfaces due to the adsorption of a (sub)monolayer is calculated for crystals transparent to the incident radiation. Conditions are derived for optimizing experimental studies of both strongly and weakly absorbing surfaces and/or adsorbates. The large and small absorption bandwidths involved correspond respectively to (i) electronic transitions to/from surface, interface and adsorbate states, and, (ii) vibrational excitations of adsorbates. The variable parameters are the angle of the incident light beam and the state of the back surface. It is found that the sensitivity varies with angle of incidence, depending on the type of absorbing monolayer

Adsorption of atomic oxygen (N2O) on a clean Si(100) surface and its influence on the surface state density; A comparison with O2

This paper describes a study concerning the interaction of molecular oxygen (O2) and nitrous oxide (N2O) with the clean Si(100) 2 × 1 surface in ultrahigh vacuum at 300 K. Differential reflectometry (DR) in the photon energy range of 1.5¿4.5 eV, Auger electron spectroscopy (AES) and low energy electron diffraction (LEED) have been used to monitor these solid-gas reactions. With this combination of techniques it is possible to make an analysis of the (geometric and electronic) structure and chemical composition of the surface layer. The aim of the present study was to give a description of the geometric nature of the oxygen covered Si(100) surface. For that purpose we have used both molecular (O2) and atomic oxygen (as released by decomposition of N2O) to oxidize the clean Si(100)2 × 1 surface

Ion-implantation induced anomalous surface amorphization in silicon

Spectroscopic ellipsometry (SE), high-depth-resolution Rutherford backscattering (RBS) and channeling have been used to examine the surface damage formed by room temperature N and B implantation into silicon. For the analysis of the SE data we used the conventional method of assuming appropriate optical models and fitting the model parameters (layer thicknesses and volume fraction of the amorphous silicon component in the layers) by linear regression. The dependence of the thickness of the surface-damaged silicon layer (beneath the native oxide layer) on the implantation parameters was determined: the higher the dose, the thicker the disordered layer at the surface. The mechanism of the surface amorphization process is explained in relation to the ion beam induced layer-by-layer amorphization. The results demonstrate the applicability of Spectroscopic ellipsometry with a proper optical model. RBS, as an independent cross-checking method supported the constructed optical model

Long-term change in respiratory function following spinal cord injury.

STUDY DESIGN: Retrospective study. OBJECTIVES: To model the effect of time since injury on longitudinal respiratory function measures in spinal cord injured-individuals and to investigate the effect of patient characteristics. SETTING: A total of 173 people who sustained a spinal cord injury between 1966 and April 2013 and who had previously participated in research or who underwent clinically indicated outpatient respiratory function tests at the Austin Hospital in Melbourne, Australia, were included in the study. At least two measurements over time were available for analysis in 59 patients. METHODS: Longitudinal data analysis was performed using generalised linear regression models to determine changes in respiratory function following spinal cord injury from immediately post injury to many years later. Secondly, we explored whether injury severity, age, gender and body mass index (BMI) at injury altered the time-dependent change in respiratory function. RESULTS: The generalised linear regression model showed no significant change (P=0.276) in respiratory function measured in (forced) vital capacity ((F)VC) after the spinal cord injury. However, significant (P30 kg m(-2).Spinal Cord advance online publication, 12 January 2016; doi:10.1038/sc.2015.233

Comparative investigation of damage induced by diatomic and monoatomic ion implantation in silicon

The damaging effect of mono- and diatomic phosphorus and arsenic ions implanted into silicon was investigated by spectroscopic ellipsometry (SE) and high-depth-resolution Rutherford backscattering and channeling techniques. A comparison was made between the two methods to check the capability of ellipsometry to examine the damage formed by room temperature implantation into silicon. For the analysis of the spectroscopic ellipsometry data we used the conventional method of assuming appropriate optical models and fitting the model parameters (layer thicknesses and volume fractions of the amorphous silicon component in the layers) by linear regression. The depth dependence of the damage was determined by both methods. It was revealed that SE can be used to investigate the radiation damage of semiconductors together with appropriate optical model construction which can be supported or independently checked by the channeling method. However, in case of low level damage (consisting mainly of isolated point defects) ellipsometry can give false results, overestimating the damage using inappropriate dielectric functions. In that case checking by other methods like channeling is desirable

Determination of complex dielectric functions of ion implanted and implanted‐annealed amorphous silicon by spectroscopic ellipsometry

Measuring with a spectroscopic ellipsometer (SE) in the 1.8–4.5 eV photon energy region we determined the complex dielectric function (ϵ = ϵ1 + iϵ2) of different kinds of amorphous silicon prepared by self‐implantation and thermal relaxation (500 °C, 3 h). These measurements show that the complex dielectric function (and thus the complex refractive index) of implanted a‐Si (i‐a‐Si) differs from that of relaxed (annealed) a‐Si (r‐a‐Si). Moreover, its ϵ differs from the ϵ of evaporated a‐Si (e‐a‐Si) found in the handbooks as ϵ for a‐Si. If we use this ϵ to evaluate SE measurements of ion implanted silicon then the fit is very poor. We deduced the optical band gap of these materials using the Davis–Mott plot based on the relation: (ϵ2E2)1/3 ∼ (E− Eg). The results are: 0.85 eV (i‐a‐Si), 1.12 eV (e‐a‐Si), 1.30 eV (r‐a‐Si). We attribute the optical change to annihilation of point defects

Automatic kelvin probe compatible with ultrahigh vacuum

This article describes a new type of in situ ultrahigh‐vacuum compatible kelvin probe based on a voice‐coil driving mechanism. This design exhibits several advantages over conventional mechanical feed‐through and (in situ) piezoelectric devices in regard to the possibility of multiple probe geometry, flexibility of probe geometry, amplitude of oscillation, and pure parallel vibration. Automatic setup and constant spacing features are achieved using a digital‐to‐analog converter (DAC) steered offset potential. The combination of very low driver noise pick‐up and data‐acquisition system (DAS) signal processing techniques results in a work function (wf  ) resolution, under optimal conditions, of <0.1 meV. Due to its high surface sensitivity and compatibility with standard sample cleaning and analysis techniques this design has numerous applications in surface studies, e.g., adsorption kinetics, sample topography and homogeneity, sputter profiles, etc. For semiconductor specimens the high wf resolution makes it eminently suitable for surface photovoltage (SPV) spectroscopy

Periodic limb movements in tetraplegia

Objective: To establish the prevalence of Periodic Limb Movements during Sleep (PLMS) in patients with tetraplegia, controlling for obstructive sleep apnea. To explore whether demographic and injury characteristics affect PLMS. Study Design: Retrospective cohorts. Setting and Participants: One hundred seventy-three participants with acute (12 months) tetraplegia who underwent full overnight diagnostic sleep studies. Interventions and outcome measures: Two hundred sixty-two sleep study recordings were included. A randomly selected subgroup of 21 studies was assessed for PLM during wakefulness. Data were analysed according to the current American Academy of Sleep Medicine guidelines. Results: Of the participants, 41.6% (43(15.7) years and 14.9% female) had a motor and sensory complete lesion. Sleep was poor with both OSA (87.8% with apnea hypopnoea index ≥ 5) and PLMS (58.4% with PLMS per hour PLMSI > 15) highly prevalent. There was no difference in the PLMSI between those with OSA (36.3(39.8)) or without (42.2(37.7), P = 0.42). PLMS were evident during REM and NREM sleep in all of the 153 patients with PLMSI > 15. All 21 participants in the subgroup of studies analysed for the PLM during quiet wakefulness, exhibited limb movements. None of the modelled variables (injury completeness, gender, OSA severity or time since injury) significantly predicted a PLMSI > 15 (P = 0.343). Conclusion: In conclusion, this study confirms the high prevalence of PLM in tetraplegia and the presence of leg movements in NREM and REM sleep along with wakefulness after controlling for OSA. No associations between the presence of PLMS and patient characteristics or injury specific aspects were found

A multi-technique study of altered granitic rock from the Krunkelbach Valley uranium deposit, Southern Germany

Herein, a multi-technique study was performed to reveal the elemental speciation and microphase composition in altered granitic rock collected from the Krunkelbach Valley uranium (U) deposit area near an abandoned U mine, Black Forest, Southern Germany. The former Krunkelbach U mine with 1–2 km surrounding area represents a unique natural analogue site with the rich accumulation of secondary U minerals suitable for radionuclide migration studies from a spent nuclear fuel (SNF) repository. Based on a micro-technique analysis using several synchrotron-based techniques such as X-ray fluorescence analysis, X-ray absorption spectroscopy, powder X-ray diffraction and laboratory-based scanning electron microscopy and Raman spectroscopy, the complex mineral assemblage was identified. While on the surface of granite, heavily altered metazeunerite–metatorbernite (Cu(UO$_{2}$)$_{2}$(AsO$_{4}$)$_{2-x}$(PO$_{4}$)$_{x}$·8H$_{2}$O) microcrystals were found together with diluted coatings similar to cuprosklodowskite (Cu(UO$_{2}$)$_{2}$(SiO$_{3}$OH)$_{2}$·6H$_{2}$O), in the cavities of the rock predominantly well-preserved microcrystals close to metatorbernite (Cu(UO$_{2}$)$_{2}$(PO$_{4}$)$_{2}$·8H$_{2}$O) were identified. The Cu(UO$_{2}$)$_{2}$(AsO$_{4}$)$_{2-x}$(PO$_{4}$)$_{x}$·8H$_{2}$O species exhibit uneven morphology and varies in its elemental composition, depending on the microcrystal part ranging from well-preserved to heavily altered on a scale of ∼200 μm. The microcrystal phase alteration could be presumably attributed to the microcrystal morphology, variations in chemical composition, and geochemical conditions at the site. The occurrence of uranyl-arsenate-phosphate and uranyl-silicate mineralisation on the surface of the same rock indicates the signatures of different geochemical conditions that took place after the oxidative weathering of the primary U- and arsenic (As)-bearing ores. The relevance of uranyl minerals to SNF storage and the potential role of uranyl-arsenate mineral species in the mobilization of U and As into the environment is discussed