•N+-ion bombardment changes physicochemical properties of the p-GaN(0 0 0 1) surface.•The bombardment modified semiconducting character from the p- into n-type.•Electron affinity of the ...p-GaN(0 0 0 1) surface is increased after the bombardment.•The bombardment increases the band bending at the vacuum/surface interface.
The p-GaN(0 0 0 1) crystal with a relatively low acceptor concentration of 5 × 1016 cm−3 is used in these studies, which are carried out in situ under ultrahigh vacuum (UHV) by ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED). The p-GaN(0 0 0 1)-(1 × 1) surface is achieved by thermal cleaning. N+-ion bombardment by a 200 eV ion beam changes the surface stoichiometry, enriches it with nitrogen, and disorders it. Such modified surface layer inverts its semiconducting character from p- into n-type. The electron affinity for the already cleaned p-GaN surface and that just after bombardment shows a shift from 2.2 eV to 3.2 eV, as well as an increase of band bending at the vacuum/surface interface from 1.4 eV to 2.5 eV. Proper post-bombardment heating of the sample restores the initial atomic order of the modified layer, leaving its n-type semiconducting character unchanged. The results of the measurements are discussed based on two types of surface states concepts.
•Annealing of Mn/p-GaN leads to the incorporation of Mn into GaN subsurface.•Enrichment of GaN subsurface region with Mn significantly alters the valence band.•The valence band maximum of ...p-GaN(0001):Mn is almost located at the Fermi level.•LEED of p-GaN:Mn corresponds to (1 × 1)–(0001) structure with evidences of faceting.
In this paper we report the method of the GaN:Mg electron structure modification by Mn co-doping. Manganese layers were deposited on p-GaN(0001) then subjected for thermal treatment processes in situ under ultrahigh vacuum (UHV) condition resulting in a dissolution of Mn in the subsurface layers. Surface-sensitive techniques such as X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and low energy diffraction (LEED) were employed in this experiment. Mn atoms introduced into the p-GaN show strong doping effect and no band bending at the surface. The valence band maximum is strongly shifted and located almost at the Fermi level (EF). The Ga-3d and N-1 s peaks are shifted by 0.4 eV towards the EF relative to the p-GaN substrate. After Mn incorporation into the p-GaN the LEED patterns revealed (1 × 1)–(0001) structure with evidence of the surface faceting.
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•Oxygen bombardment was used as the oxidation method to form an insulator on the GaN substrate.•Ga2O3 layers on the GaN surface with no evidence of epitaxy were obtained.•Valence band offset of ...1.15eV was measured for the Ga2O3/GaN interface.
Oxygen bombardment is used as the oxidation method to form an insulator on GaN substrate at room temperature. The surface of clean substrate and the Ga2O3/GaN interface are characterized in situ by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and low-energy electron diffraction (LEED). XPS spectra of the Ga 2p core level show a peak shift of ∼1eV from GaO to GaN bonding, demonstrating an oxide formation of Ga2O3. Electron affinity of the clean GaN surface amounts to 3.65eV; the electron affinity of the Ga2O3 on GaN(0001) surface is 3.7eV. Valence band offset (VBO) of the Ga2O3/GaN interface measured using XPS and UPS is 1.15eV. After annealing the system at 500°C the electron affinity and the VBO decrease to the values 3.5 and 0.35eV, respectively.
•Ni/GaN contact was formed at room temperature by Ni vapor deposition onto n-type GaN(0001) surface under ultrahigh vacuum.•The Schottky's barrier height of the contact amounted to 1.20eV.•The WF of ...the Ni film of mean thickness of 1nm equaled to 4.1eV. For thicker layers (≥2nm) it increased to 5.1eV.•Annealing of the contact resulted in Ga diffusion into Ni film and Ni–Ga alloying.
Morphology of Ni/GaN contact formed at room temperature (RT) by Ni vapor deposition onto the (0001)-oriented n-type GaN surface under ultrahigh vacuum, and morphological changes introduced by annealing were studied. Measurements were carried out in situ using XPS, UPS, LEED and STM. The WF of the Ni film of the mean thickness 1nm equaled 4.1eV. For thicker layers (≥2nm), it increased to 5.1eV. The Schottky barrier height of the Ni/GaN(0001) contact formed at RT amounted to 1.20eV. Annealing of the Ni/GaN contact at 650°C resulted in Ga diffusion into the Ni film and Ni–Ga alloying. The dominating alloy phase was Ni3Ga. The alloying was accompanied by coalescence of Ni film grains into 3D islands of a Ni–Ga alloy. Annealing at 800°C enriched the islands with Ga. The Ga-rich phases of NiGa and/or Ni3Ga2 were dominant in the alloy.
The electronic structures of Alq3/Si(100), Alq3/LiBr/Si(100), and Alq3/KCl/Si(100) systems are presented in this report. Their energy level diagrams were prepared and discussed. The formation of the ...LiBr and KCl interfacial layers between an Alq3 film and a Si(100) substrate results in a decrease of the energy barrier at the interface. The studies were carried out in situ in ultrahigh vacuum by ultraviolet photoelectron spectroscopy. Alq3 as well as LiBr and KCl layers were vapour evaporated onto n‐type Si(100) crystal. The electron affinity of clean Si(100) surface was 4.0 eV, and the position of the valence band maximum was 0.7 eV below EF. The energetic distance between the valence band maximum of Si(100) and the highest occupied molecular orbital level were 1.5, 2.6, and 2.2 eV, for the Alq3/Si(100), Alq3/LiBr/Si(100), and Alq3/KCl/Si(100) systems, respectively.
Abstract Objective Herein we have presented the results of treatment of acute liver failure (ALF) patients with the use of the Prometheus FPSA dialysis system. Materials and Methods To January 2009, ...we performed 278 FPSA procedures in 114 patients, including 52 experience and ALF. The patients who underwent the FPSA procedure consisted of 32 women and 20 men of overall mean age of 33 ± 12 years. The causes of ALF were: Wilson's disease (n = 15), unknown origin ALF (n = 11), amanita phalloides intoxication (n = 7), paracetamol intoxication (n = 8), acute hepatitis B virus (HBV)/hepatitis C virus (HCV) infection (n = 7), liver insufficiency after parenchymal resection (n = 2) drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome (n = 1), rabdomyolysis (n = 1), or primary nonfunction (PNF) after orthotopic liver transplantation (OLT) (n = 1). All procedures were performed using the Prometheus 4008H Fresenius Medical Care liver support system. The average number of treatments per patient was 2.41 and the average time for each FPSA treatment was 6.3 hours. The average heparin dose used during the procedure was 750 IU/h. Results After the whole treatment regimen, we observed significant improvements in the biochemical results. The average concentrations improved: serum ammonia (before 249.2 μg/dL versus after 109.7 μg/dL); serum bilirubin (before 21.53 mg/dL versus after 8.81 mg/dL), serum aspartate aminotransferase (AST; before 2456.4 U/L versus after 1068.8 U/L); serum alanine aminotransferase (ALT; before 2958.2 U/L versus after 1595.8 U/L); serum urea (before 58.5 mg/dL versus after 21.1 mg/dL); serum creatinine (before 2.9 mg/dL versus after 1.7 mg/dL); and pH value (before 7.11 versus after 7.32). After Prometheus treatment OLT was performed in 33 patients. Among the 28 who survived (53.8%), 22 underwent OLT and 6 did not have OLT. Among the 24 patients who died (46.2%), 13 were before OLT and 11 after OLT. Conclusion The Prometheus 4008H Fresenius Medical Care Liver support system was useful method of detoxification for patients with ALF, serving as an element of pretransplantation care.
•Ni/p-GaN system was formed at room temperature by Ni vapour deposition onto GaN(0 0 0 1) surface.•Annealing of the system results in uncover of Ni-pGaN interface.•For uncovered interface, surface ...photovoltage is generated by UV and X-ray.•Surface photovoltage caused the appearance of quasi Fermi level.
Surface studies on the Ni films on p-GaN concentrated on photoelectron spectroscopies are presented. We found the surface condition on which the surface photovoltage (SPV) effect, caused by an excitation source, leads to the appearance of a quasi-Fermi level located above the Fermi level of the electron energy analyzer. The energy shifts of core-level lines were also noted due to this. This means that for meta/semiconductor systems some energy shifts of peaks observed do not have to result from a chemical reaction and may be done through SPV effects. The formation of the interface, as well as its physicochemical and structural analysis, were carried out in situ under ultrahigh vacuum. Ni films were vapour deposited onto the Mg-doped GaN, (0 0 0 1)-oriented. X-ray and ultraviolet light sources were applied in photoemission experiments. The low-energy electron diffraction technique was employed for surface structure investigation.
Magnetic structure of almandine Zherebetskyy, D.; Lebernegg, S.; Amthauer, G. ...
Physics and chemistry of minerals,
05/2012, Letnik:
39, Številka:
5
Journal Article
Recenzirano
Odprti dostop
The magnetic structure of almandine has been investigated by electronic structure calculations in the local spin density approximation in order to arrive at a more detailed understanding of the ...magnetic structure and the exchange pathways. The calculations are based on experimentally determined geometrical data of the crystal structure at 100 K. The calculated quadrupole splittings, spin-allowed
d
–
d
transitions and magnetic moment for iron atoms are in reasonable agreement with the respective experimental values obtained by Mössbauer and absorption spectroscopy, and magnetization measurements demonstrating the reliability of the calculations. The spin structure is derived from the calculated coupling constants for the possible exchange pathways. The competing superexchange pathways exist via oxygen bridges between directly neighboured iron ions and via edges of silicon tetrahedra and aluminium octahedra connecting more distant iron dodecahedra. Careful consideration revealed that almandine structure contains two identical interpenetrative sublattices of Fe dodecahedra connected via Al octahedra and Si tetrahedra. The calculations provide the information about ferromagnetic interaction between the iron spins within each sublattice, whereas the coupling between two magnetic sublattices is weakly antiferromagnetic via Al octahedra and Si tetrahedra. This antiferromagnetic interaction of two identical magnetic sublattices is in good agreement with the experiments and explains the Mössbauer spectra of almandine below the Néel temperature. Since almandine belongs to most abundant crystallized silicates that are main constituents of the earth and main components of cosmic dust, these results have scientific importance of studying the universe.
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