Search results for "gaps"

Topological Insulators in Ternary Compounds with a Honeycomb Lattice

2010

One of the most exciting subjects in solid state physics is a single layer of graphite which exhibits a variety of unconventional novel properties. The key feature of its electronic structure are linear dispersive bands which cross in a single point at the Fermi energy. This so-called Dirac cone is closely related to the surface states of the recently discovered topological insulators. The ternary compounds, such as LiAuSe and KHgSb with a honeycomb structure of their Au-Se and Hg-Sb layers feature band inversion very similar to HgTe which is a strong precondition for existence of the topological surface states. In contrast to graphene with two Dirac cones at K and K' points, these material…

Crystal symmetry and pressure effects on the valence band structure ofγ-InSe andε-GaSe: Transport measurements and electronic structure calculations

2005

This paper reports on Hall effect and resistivity measurements under high pressure up to 3--4 GPa in $p$-type $\ensuremath{\gamma}$-indium selenide (InSe) (doped with As, Cd, or Zn) and $\ensuremath{\epsilon}$-gallium selenide (GaSe) (doped with N or Sn). The pressure behavior of the hole concentration and mobility exhibits dramatic differences between the two layered compounds. While the hole concentration and mobility increase moderately and monotonously in $\ensuremath{\epsilon}$-GaSe, a large increase of the hole concentration near 0.8 GPa and a large continuous increase of the hole mobility, which doubled its ambient pressure value by 3.2 GPa, is observed in $\ensuremath{\gamma}$-InSe.…

Effects of pressure and temperature on the dielectric constant of GaS, GaSe, and InSe:  Role of the electronic contribution

1999

In this work we report on direct measurements of the temperature and pressure dependences of the low-frequency dielectric constant along c axis $({\ensuremath{\varepsilon}}_{\ensuremath{\parallel}})$ of GaS, GaSe, and InSe. The temperature dependence of both the ordinary and extraordinary refractive indexes is also presented. A large increase of ${\ensuremath{\varepsilon}}_{\ensuremath{\parallel}}$ under pressure has been observed. In the framework of a rigid ion model, the lattice contribution to ${\ensuremath{\varepsilon}}_{\ensuremath{\parallel}}$ is shown to increase slightly under pressure, due to the change of the angle between the anion-cation bond and the layer plane. Consequently, …

THE LIMITING EFFICIENCY OF FOUR-BAND CELLS REVISITED

2014

The limiting theoretical efficiency of four-band solar cells is revisited. In previous work, researchers have looked at the theoretical efficiency of four band cells where the smallest of the three sub-band gaps is closest to the valence band and the largest closest to the conduction band. In this work, limits are calculated also for other possible band configurations. In multi-band cells, photon selectivity can be assured by adjusting the band widths. The present work shows that previous authors have put too rigid constraints on the band structure to achieve spectral selectivity. Relieving these constraints gives a considerably higher limiting efficiency for cells with band width restricti…

Azido bridged binuclear copper(ii) Schiff base compound: synthesis, structure and electrical properties

2019

An azido bridged dinuclear complex [Cu(L−)(μ1,1N3)]2 (1) was synthesized by a 1 : 1 condensation of N-cyclohexyl-1,3-propanediamine and 5-bromosalicylaldehyde (HL). The complex was subsequently characterized based on elemental analyses, IR, single-crystal X-ray diffraction, a Hirshfeld study, FESEM, ESI-MS, powder XRD and also DFT studies successfully. The X-ray crystal structure of complex 1 revealed that the Cu(II) ion exhibited a definite five-coordinate square pyramidal coordination arrangement with a centro-symmetric μ 1,1-azido bridging in the end-on mode and formed a dimeric structure. The optical direct band gap of complex 1 was estimated to be 2.84 eV. The current–voltage character…

Temperature and Isotopic Mass Dependence of the Direct Band Gap in Semiconductors: LCAO Calculations

2000

Palermo si cura. Pratiche culturali di mutuo soccorso come risposta alle fragilità della città (post)pandemica

2023

In un quadro di riferimento in cui la crisi è globalizzata ma diseguale e in mancanza di un sistema di welfare capace di rispondere alle urgenze dei contesti e dei gruppi sociali più marginalizzati, una risposta ai nuovi bisogni sociali ed individuali è stata offerta da reti solidali e da pratiche di mobilitazione dal basso che svolgono un ruolo di agency territoriale, spesso indipendentemente o in assenza di Istituzioni. Nel contesto palermitano un impegno agito da una pluralità di soggetti culturali già attivi sul territorio, riuniti in un’assemblea pubblica (Palermo si cura), durante il periodo del primo lockdown hanno dato vita ad azioni di mutuo soccorso per rispondere all’emergenza ec…

Comparison between nonparametric and parametric estimate of the conditional intensity function of a seismic space-time point process

2008

A seismic gap can be defined as a segment of an active geologic fault that has not produced seismic events for an unusually long time; gaps are often considered susceptible to future strong earthquakes occurrence and therefore their identification may be useful for predictive purposes. In this paper we try to identify gaps in an area of South Tyrrhenian Sea by comparing the observed seismicity, estimated by nonparametric method, and the theoretical one, described by a particular space-time point process (ETAS model).

Is it still too much time indoor and in domestic places? Women's use of leisure time in Italy

2011

Local banks and credit: from crisis to the new regulatory proposals for the development of lending policies in favour of the real economy

2014

Comparing the credit cooperative banks (CCBs) and banking groups operating in Italy, descriptive analyses show that the CCBs, unlike large banks, despite the economic downturn, have continued to extend credit to customers, but at the cost of a higher incidence of bad credit. This increased credit risk of local banks has been caused by management policy choices, such as the preference to modify the conditions applicable to credit supply and to engage firms in long-term credit relationships rather than initiate credit recovery procedures. An empirical analysis shows that this risk has also been caused by a higher incidence of environmental factors such as the spread of situations of crime and…