Effects of Interface Disorder on Valley Splitting in SiGe/Si/SiGe Quantum Wells

A sharp potential barrier at the Si/SiGe interface introduces valley splitting (VS), which lifts the 2-fold valley degeneracy in strained SiGe/Si/SiGe quantum wells (QWs). This work examines in detail the effects of Si/SiGe interface disorder on the VS in an atomistic tight binding approach based on statistical sampling. VS is analyzed as a function of electric field, QW thickness, and simulation domain size. Strong electric fields push the electron wavefunctions into the SiGe buffer and introduce significant VS fluctuations from device to device. A Gedankenexperiment with ordered alloys sheds light on the importance of different bonding configurations on VS. We conclude that a single SiGe band offset and effective mass cannot comprehend the complex Si/SiGe interface interactions that dominate VS.Comment: 5 figure

An enhanced finite difference time domain method for two dimensional Maxwell's equations

An efficient finite-difference time-domain (FDTD) algorithm is built to solve the transverse electric 2D Maxwell's equations with inhomogeneous dielectric media where the electric fields are discontinuous across the dielectric interface. The new algorithm is derived based upon the integral version of the Maxwell's equations as well as the relationship between the electric fields across the interface. It is an improvement over the contour-path effective-permittivity algorithm by including some extra terms in the formulas. The scheme is validated in solving the scattering of a dielectric cylinder with exact solution from Mie theory and is then compared with the above contour-path method, the usual staircase and the volume-average method. The numerical results demonstrate that the new algorithm has achieved significant improvement in accuracy over the other methods. Furthermore, the algorithm has a simple structure and can be merged into any existing FDTD software package very easily

Vanadium(v) phenolate complexes for ring opening homo- and co-polymerisation of ε-caprolactone, L-lactide and rac-lactide

The vanadyl complexes [VO(OtBu)L¹ ] (1) and {[VO(OiPr)]₂ (μ-p-L²ᵖ)} (2) {[VO(OR)]₂ (μ-p-L²ᵐ )} (R = iPr 3, tBu 4) have been prepared from [VO(OR)₃ ] (R = nPr, iPr or tBu) and the respective phenol, namely 2,2′-ethylidenebis(4,6-di-tert-butylphenol) (L¹ H₂ ) or α,α,α′,α′-tetra(3,5-di-tert-butyl-2-hydroxyphenyl–p/m-)xylene-para-tetraphenol (L2p/mH₄). For comparative studies, the known complexes [VO(μ-OnPr)L¹]₂ (I), [VOL³ ]₂ (II) (L³H₃ = 2,6-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-4-tert-butylphenol) were prepared. An imido complex {[VCl(Np-tolyl)(NCMe)]₂(μ-p-L²ᵖ)} (5) has been prepared following work-up from [V(Np-tolyl)Cl₃ ], L²ᵖH₄ and Et₃ N. The molecular structures of complexes 1–5 are reported. Complexes 1–5 and I and II have been screened for their ability to ring open polymerise ε-caprolactone, L-lactide or rac-lactide with and without solvent present. The co-polymerization of ε-caprolactone with L-lactide or rac-lactide afforded co-polymers with low lactide content; the reverse addition was ineffective

Enhancement of fundamental mode third harmonic generation efficiency in microfibres

We present a scheme to generate the third harmonic in the fundamental mode using microfibres, by introducing a counter-propagating pump field to partly compensate the phase mismatch and thus enhance the harmonic conversion efficiency

Associations between adjustment disorder and hospital-based infections in the Danish population.

OBJECTIVE:There is some evidence that posttraumatic stress disorder (PTSD) is associated with increased risk of infections, and it is unknown whether adjustment disorder is as well. We assessed the association between adjustment disorder and subsequent infections, and assessed additive interaction with sex. METHODS:The study population included a nationwide cohort of all Danish-born residents of Denmark diagnosed with adjustment disorder between 1995 and 2011, and an age- and sex-matched general population comparison cohort. We compared rates of infections requiring inpatient or outpatient hospitalization in the two cohorts. We fit Cox proportional hazards models to compute adjusted hazard ratios (aHR) for the associations between adjustment disorder and 32 types of infections, and calculated interaction contrasts to assess interaction between adjustment disorder and sex. RESULTS:Adjustment disorder was associated with increased rates of infections overall (n = 19,838 infections, aHR = 1.8, 95% confidence interval = 1.8. 1.9), and increased rates of each individual infection type (aHRs for 30 infections ranged from 1.5 to 2.3), adjusting for baseline psychiatric and somatic comorbidities and marital status. For many infection types (e.g., skin infections, pneumonia), interaction contrasts indicated rate differences were greater among men than women, while for two (urinary tract infections and sexually transmitted infections), rate differences were greater for women. CONCLUSIONS:These findings are consistent with studies examining the relationship between psychological stress and infections, and between PTSD and infections. They may be explained by a combination of the triggering of unhealthy behaviors as well as immune responses to stress