A first-principles DFT+GW study of spin-filter and spin-gapless semiconducting Heusler compounds

Among Heusler compounds, the ones being magnetic semiconductors (also known as spin-filter materials) are widely studied as they offer novel functionalities in spintronic/magnetoelectronic devices. The spin-gapless semiconductors are a special case. They possess a zero or almost-zero energy gap in one of the two spin channels. We employ the $GW$ approximation, which allows an elaborate treatment of the electronic correlations, to simulate the electronic band structure of these materials. Our results suggest that in most cases the use of $GW$ self energy instead of the usual density functionals is important to accurately determine the electronic properties of magnetic semiconductors.Comment: Final version as publishe

The surface adhesion parameter: a measure for wafer bondability

A theory is presented which describes the initial direct wafer bonding process. The effect of surface microroughness on the bondability is studied on the basis of the theory of contact and adhesion of elastic solids. An effective bonding energy, the maximum of which is the specific surface energy of adhesion, is proposed to describe the real binding energy of the bonding interface including the influence of the wafer surface microroughness. Both the effective bonding energy and the real area of contact between rough surfaces depend on a dimensionless surface adhesion parameter, &thetas;. Using the adhesion parameter as a measure, three kinds of wafer contact interfaces can be identified with respect to their bondability; viz. the non-bonding regime (&thetas;>&ap;12), the bonding regime (&thetas;<&ap;1), and the adherence regime (1<&thetas;<12). Experimental data are in agreement with this theor

Formation of liquid menisci in flexible nanochannels

This paper describes the elasto-capillary formation of menisci at the liquid-air interface in nanochannels that are covered with flexible capping membranes. The equilibrium between the capillary pressure in the fluid and the membrane bending results in a very peculiar shape of the meniscus. We present an analytical description of these meniscus hapes and show that the protrusion length of the meniscus along the channel is an accurate measure for the deflection of the nanochannels

Quasiparticle band structure of the almost-gapless transition-metal-based Heusler semiconductors

Transition-metal-based Heusler semiconductors are promising materials for a variety of applications ranging from spintronics to thermoelectricity. Employing the $GW$ approximation within the framework of the FLAPW method, we study the quasi-particle band structure of a number of such compounds being almost gapless semiconductors. We find that in contrast to the \textit{sp}-electron based semiconductors such as Si and GaAs, in these systems the many-body corrections have a minimal effect on the electronic band structure and the energy band gap increases by less than 0.2~eV, which makes the starting point density functional theory (DFT) a good approximation for the description of electronic and optical properties of these materials. Furthermore, the band gap can be tuned either by the variation of the lattice parameter or by the substitution of the \emph{sp}-chemical element

ICT education for development — a case study

Abstract“Information and communication technologies for development (ICT4D)” is a general term that is used to define the applications of ICTs for the socioeconomically disadvantaged groups. In other words, the ICT4D is applying information technologies for poverty reduction purposes. Today the concept is far more evolved from when it started just as the ICT industry. Especially along with the Internet now the possibilities for collaboration have significantly increased. Since information and communication technologies will be shaping the future, the jobs acquired in the ICT industry will be even more valid. On the other hand while the need for professionals is increasing, the number of well trained professionals is not accumulating with the same acceleration rate, due to the high costs and accessibility problems. This paper focuses on a unique and successful project called SPARK (Youth Movement in Informatics). SPARK is a partnership of UNDP, Cisco and Youth for Habitat Association. This project aims to improve the level of information technology expertise among youth using the Cisco NetAcad e-learning platform, while simultaneously encouraging volunteerism. Moreover, SPARK aims to support young people to develop their social capacities and helps them participate in the new information-based global economy through the peer education model on advanced information technology and networking skills. Through the case of SPARK, this paper also emphasizes the importance of the ICT education for development and poverty reduction and illustrates the impact it makes on people’s lives

Elastocapillary filling of deformable nanochannels

The capillary filling speed of wetting liquids of varying viscosity and surface tension in hydrophilic nanochannels with an elastic capping layer has been analyzed. The channels, with a height just below 80 nm, are suspended by a thin flexible membrane that easily deforms due to the negative pressure which develops behind the moving meniscus. In the elastocapillary filling of the channels, two opposite effects compete: the decreased cross channel sections increase the flow resistance, while the Laplace pressure that acts as the driving force becomes more negative due to the increased meniscus curvature. Although the meniscus position shows a square root of time behavior as described by the Washburn relation, the net result of the induced bending of the membranes is a definite increase of the filling speed. We propose a relatively straightforward model for this elastocapillary process and present experimental results of the filling speed of ethanol, water, cyclohexane and acetone that are found to be in good agreement with the presented model, for membrane deflections of up to 80 percent of the original channel height

Spin-correlation effects in a one-dimensional electron gas

The Singwi-Sjolander-Tosi-Land (SSTL) approach is generalized to study the spin-correlation effects in a one-dimensional (1D) electron gas. It is shown that the SSTL approach yields different and interesting results compared with the more widely used Singwi-Tosi-Land-Sjolander (STLS) approach. We find out that the self-consistent field approaches, STLS and SSTL, predict a Bloch transition for 1D electron-gas systems at low electron densities

Short-range correlations in a one-dimensional electron gas

We use the Singwi-Sjolander-Tosi-Land (SSTL) approximation to investigate the short-range correlations in a one-dimensional electron gas. We find out that the SSTL approximation satisfies the compressibility sum rule somewhat better than the more widely used Singwi-Tosi-Land-Sjolander approximation in the case of a one-dimensional electron gas