Positioning of self-assembled Ge islands on stripe-patterned Si (001) substrates

Self-assembled Ge islands were grown on stripe-patterned Si (001) substrates by solid source molecular beam epitaxy. The surface morphology obtained by atomic force microscopy (AFM) and cross-sectional transmission electron microscopy images (TEM) shows that the Ge islands are preferentially grown at the sidewalls of pure Si stripes along [-110] direction at 650o C or along the trenches, whereas most of the Ge islands are formed on the top terrace when the patterned stripes are covered by a strained GeSi buffer layer. Reducing the growth temperature to 600oC results in a nucleation of Ge islands both on the top terrace and at the sidewall of pure Si stripes. A qualitative analysis, based on the growth kinetics, demonstrates that the step structure of the stripes, the external strain field and the local critical wetting layer thickness for the islands formation contribute to the preferential positioning of Ge islands on the stripes.Comment: 10 pages, 7 figures, 1 table, the original paper is in print in J. Appl. Phy

Initial stage of the 2D-3D transition of a strained SiGe layer on a pit-patterned Si(001) template

We investigate the initial stage of the 2D-3D transition of strained Ge layers deposited on pit-patterned Si(001) templates. Within the pits, which assume the shape of inverted, truncated pyramids after optimized growth of a Si buffer layer, the Ge wetting layer develops a complex morphology consisting exclusively of {105} and (001) facets. These results are attributed to a strain-driven step-meandering instability on the facetted side-walls of the pits, and a step-bunching instability at the sharp concave intersections of these facets. Although both instabilities are strain-driven, their coexistence becomes mainly possible by the geometrical restrictions in the pits. It is shown that the morphological transformation of the pit surface into low-energy facets has strong influence on the preferential nucleation of Ge islands at the flat bottom of the pits.Comment: 19 pages, 7 figure

Single-Electron Transistor in Strained Si/SiGe Heterostructures

A split gate technique is used to form a lateral quantum dot in a two-dimensional electron gas of a modulation-doped silicon/silicon-germanium heterostructure. e-beam lithography was employed to produce split gates. By applying negative voltages to these gates the underlying electron gas is depleted and a lateral quantum dot is formed, the size of which can be adjusted by the gate voltage. We observe single-electron operation with Coulomb blockade behavior below 1K. Gate leakage currents are well controlled, indicating that the recently encountered problems with Schottky gates for this type of application are not an inherent limitation of modulation-doped Si/SiGe heterostructures, as had been speculated.Comment: 3 page

Valley splitting of Si/SiGe heterostructures in tilted magnetic fields

We have investigated the valley splitting of two-dimensional electrons in high quality Si/Si$_{1-x}$Ge$_x$ heterostructures under tilted magnetic fields. For all the samples in our study, the valley splitting at filling factor $\nu=3$ ($\Delta_3$) is significantly different before and after the coincidence angle, at which energy levels cross at the Fermi level. On both sides of the coincidence, a linear density dependence of $\Delta_3$ on the electron density was observed, while the slope of these two configurations differs by more than a factor of two. We argue that screening of the Coulomb interaction from the low-lying filled levels, which also explains the observed spin-dependent resistivity, is responsible for the large difference of $\Delta_3$ before and after the coincidence.Comment: REVTEX 4 pages, 4 figure

Inferiority or Even Superiority of Virtual Reality Exposure Therapy in Phobias?—A Systematic Review and Quantitative Meta-Analysis on Randomized Controlled Trials Specifically Comparing the Efficacy of Virtual Reality Exposure to Gold Standard in vivo Exposure in Agoraphobia, Specific Phobia, and Social Phobia

Background: Convincing evidence on Virtual Reality (VR) exposure for phobic anxiety disorders has been reported, however, the benchmark and golden standard for phobia treatment is in vivo exposure. For direct treatment comparisons, the control of confounding variables is essential. Therefore, the comparison of VR and in vivo exposure in studies applying an equivalent amount of exposure in both treatments is necessary. Methods: We conducted a systematic search of reports published until June 2019. Inclusion criteria covered the diagnosis of Specific Phobia, Social Phobia, or Agoraphobia, and a randomized-controlled design with an equivalent amount of exposure in VR and in vivo. We qualitatively reviewed participants' characteristics, materials, and the treatment procedures of all included studies. For quantitative synthesis, we calculated Hedges' g effect sizes for the treatment effects of VR exposure, in vivo exposure, and the comparison of VR to in vivo exposure in all studies and separately for studies on each diagnosis. Results: Nine studies (n = 371) were included, four on Specific Phobia, three on Social Phobia, and two on Agoraphobia. VR and in vivo exposure both showed large, significant effect sizes. The comparison of VR to in vivo exposure revealed a small, but non-significant effect size favoring in vivo (g = −0.20). Specifically, effect sizes for Specific Phobia (g = −0.15) and Agoraphobia (g = −0.01) were non-significant, only for Social Phobia we found a significant effect size favoring in vivo (g = −0.50). Except for Agoraphobia, effect sizes varied across studies from favoring VR to favoring in vivo exposure. Conclusions: We found no evidence that VR exposure is significantly less efficacious than in vivo exposure in Specific Phobia and Agoraphobia. The wide range of study specific effect sizes, especially in Social Phobia, indicates a high potential of VR, but also points to the need for a deeper investigation and empirical examination of relevant working mechanisms. In Social Phobia, a combination of VR exposure with cognitive interventions and the realization of virtual social interactions targeting central fears might be advantageous. Considering the advantages of VR exposure, its dissemination should be emphasized. Improvements in technology and procedures might even yield superior effects in the future

Transient-Enhanced Surface Diffusion on Natural-Oxide-Covered Si(001) Templates during Vacuum Annealing

We report on the transient-enhanced shape transformation of nano-structured Si(001) surfaces upon in vacuo annealing at relatively low temperatures of 900 -950 °C for a few minutes. We find dramatic surface mass transport concomitant with the development of low-energy facets on surfaces that are covered by native oxide. The enhanced surface mass transport ceases after the oxide is completely desorbed, and it is not observed on surfaces where the native oxide had been removed by HF before annealing

Malaria prophylaxis policy for travellers from Europe to the Indian Sub Continent

Analysis of malaria imported into eight European countries from the Indian sub-continent (ISC) (India, Pakistan, Bangladesh and Sri Lanka) led to a consensus statement on the use of chemoprophylaxis within TropNetEurop. The proportion of cases from the ISC in 2004 ranged from 1.4%–4.6% of total imported cases. Plasmodium falciparum cases reported from the eight countries was only 23 (13% of all cases from the region). Total malaria reports between 1999–2004 fell from 317 to 180. The risk of malaria in UK residents visiting the region was > 1 case per 1,000 years exposed. The group recommended non-selective prescribing of chemoprophylaxis for visitors to India, Pakistan, Bangladesh and Sri Lanka should be dropped

The Society for Microelectronics -Annual Report 2003 Spin Relaxation in Si Quantum Wells Suppressed by an Applied Magnetic Field

We investigate spin properties of the two-dimensional electron gas in Si quantum wells defined by SiGe barriers. We find, in contrast to predictions of the classical model of D'yakonov-Perel, a strong anisotropy of spin relaxation and a decrease of the spin relaxation rate with increasing electron mobility. We show that for high electron mobility the cyclotron motion causes an additional modulation of spin-orbit coupling which leads to an effective suppression of spin relaxation rate. In spintronics, the aim is to make use of the spin degrees of freedom in addition to the electronic ones. Therefore, spintronic devices based on spins of carriers in semiconductors appear particularly promising. In such elements carriers can be easily moved by applying external voltages, the well known tool of classical electronics. The utilization of spin properties, however, usually is limited by the fast spin relaxation of conduction electrons. Therefore analysis of the spin relaxation mechanisms and the search for a suitable material and optimum conditions are of primary interest in this field. In III-V compounds the spin relaxation time is below one nanosecond [1]. Silicon based devices, due to much weaker spin-orbit coupling, appear much more promising. 2D Si layers in Si/SiGe structures exhibit a spin relaxation time of the order of a few microseconds by measurements of electron spin resonance (ESR) [2] - The effect of BR coupling on spin, σ, of a conduction electron can be described by an effective magnetic field, B BR . This field is oriented in-plane and perpendicular to electron momentum, ħk. The resulting zero field splitting is given by: The direction of the BR field depends on the direction of electron k-vector, and therefore the spread of k-vectors results in a spread of the BR field. Consequently, the ESR resonance is shifted and broadened. Momentum scattering, described by a rate 1/τ k , causes a modulation of the BR field in time which leads to the so called D'yakonovPerel (DP) spin relaxatio

Interventional Cardiology in Europe 1993

An annual survey on cardiac interventions in Europe is performed by the working group on Coronary Circulation of the European Society of Cardiology with the help of the national societies of cardiology. A questionnaire about cardiac interventions in 1993 was mailed to a representative of the national societies of 35 members of the European Society of Cardiology. The data collection of coronary interventions was delayed by slow backreporting and from 10 of the 35 national members data were missing or grossly incomplete. They were excluded from the analysis. Coronary anglography A total of 756 822 coronary angiograms were reported resulting in an incidence of 1146 ± 1024 per 106 inhabitants, ranging from 24 (Romania) to 3499 (Germany). This represents an increase of 12% compared to 1992. Germany (279 882 cases), France (157 237), the United Kingdom (77 000), Italy (44 934) and Spain (37 591) registered 79% of all the coronary angiograms performed. Percutaneous transluminal coronary angioptasty A total of 183 728 percutaneous transluminal coronary angioplasty cases were reported in 1993, 24% more than in 1992. On average, they accounted for 18 ± 7% (range 8 (Romania) to 35% (Sweden)) of the coronary angiograms. Most of these percutaneous transluminal coronary angioplasties (82%) were confined to a single vessel. In 13% only, percutaneous transluminal coronary angioplasty took place immediately after the diagnostic study. Adjusted per capita, Germany ranks first with 873 percutaneous transluminal coronary angioplasties per 106 inhabitants, followed by France (737), Holland (725), Belgium (713), and Switzerland (665). The European mean of percutaneous transluminal coronary angioplasties per 106 inhabitants was 270 ± 279, representing an increase of 14% compared with 1992. A major in-hospital complication was reported in 3.8% of the patients undergoing percutaneous transluminal coronary angioplasty: 0.6% hospital deaths, 1.5% emergency coronary artery bypass graftings, and 1.7% myocardial infarctions. New devices In 1993 stents were implanted in 6444 patients (3.5% of all percutaneous transluminal coronary angioplasty patients), equally distributed between bail-out situations (53%) and elective procedures. The 14 stent implanting countries showed a mean increase in the incidence of coronary stenting of 53% compared with 1992. Other interventional devices were applied in 7045 cases, i.e. 3.8% of all percutaneous transluminal coronary angioplasty cases. Coronary ultrasound (2194 cases) and coronary angioscopy (380 cases) were performed infrequently. Non-coronary interventions Valvuloplasties were the most frequently performed non-coronary interventions. Six European countries performed more than 300 valvuloplasties each in 1993. Most of them were mitral valvuloplasties in southern countries. Conclusions Although partial backreporting might bias conclusions, several findings of this survey are noteworthy for the participating countries: The number of percutaneous transluminal coronary angioplasties is universally increasing. There is an extremely wide range of coronary angiography and percutaneous transluminal coronary angioplasties performed per population. The most common additional procedure is a stent implantation while other new devices are only rarely applied. Mitral valvuloplasty is the most frequently performed non-coronary intervention. (Eur Heart J 1996; 17: 1318-1328