M. Alsagri

Bio: M. Alsagri is an academic researcher from King Saud University. The author has contributed to research in topics: Band gap & Electronic structure. The author has an hindex of 3, co-authored 6 publications receiving 37 citations.

Ab Initio Investigation of the Structural and Electronic Properties of HgTe/CdTe Superlattices

Abstract: We carried out first-principle calculations to examine the impact of layer periodicity and strain on the structural and electronic features of HgTe/CdTe superlattices (SLs). The full-potential linearized augmented plane wave methodology is used to determine the electronic characteristics of these CdTe-HgTe heterojunctions. The CdTe and HgTe layers have a strong effect on the emerged fundamental energy gap of the SLs owing to the peculiar quantum confinement effect. The impact of layer thickness changes and strain are indispensable for engineering the energy band gap of HgTe/CdTe SLs. This could lead to an enormous development in the optoelectronic characteristics of these SLs, which may result in their broad applications in electronic devices.

First-principles analysis for the modulation of energy band gap and optical characteristics in HgTe/CdTe superlattices

Abstract: HgTe/CdTe superlattices (SLs), have emerged as unprecedented materials with tremendous functionalities, such as solar photocell devices. We carried out first-principles analyses in the framework of the full-potential linearized augmented plane wave (FP-LAPW) scheme to understand the impact of layer periodicity and strain on HgTe/CdTe superlattices. This technique allows us to describe the electronic and optical features of low dimensional systems, such as CdTe–HgTe heterojunctions. Alteration of the layer thickness and strain is imperative for tailoring the energy band gap of HgTe/CdTe superlattices. Thus, the CdTe and HgTe layers possess an appreciable influence on the induced forbidden gap of SLs because of their distinct quantum confinement characteristics. The electronic structures illustrate that the alteration in HgTe and CdTe layer thickness is pivotal for the overlap or non-overlap of the conduction bands and valence bands. Indeed, these systems can yield a semi-metallic or normal state with significant modification in the optical absorption of HgTe/CdTe SLs with respect to their bulk counterparts. Such SL systems have several advantageous features, involving their tailorable near band edge optical properties. Hence, it is feasible to optimize the requisite characteristics for electronic devices based on these SLs. This may enhance the development of HgTe/CdTe SLs in vast applications envisioned in infrared devices.

Direct Determination of the Chemical Bonding of Individual Impurities in Graphene

Abstract: Using a combination of Z-contrast imaging and atomically resolved electron energy-loss spectroscopy on a scanning transmission electron microscope, we show that the chemical bonding of individual impurity atoms can be deduced experimentally. We find that when a Si atom is bonded with four atoms at a double-vacancy site in graphene, Si 3d orbitals contribute significantly to the bonding, resulting in a planar sp(2) d-like hybridization, whereas threefold coordinated Si in graphene adopts the preferred sp(3) hybridization. The conclusions are confirmed by first-principles calculations and demonstrate that chemical bonding of two-dimensional materials can now be explored at the single impurity level.

C K-edge NEXAFS spectra of graphene with physical and chemical defects

Abstract: Recently, C K-edge Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of graphite (HOPG) surfaces have been measured for the pristine material, and for HOPG treated with either bromine or krypton plasmas (Lippitz et al., Surf. Sci., 2013, 611, L1). Changes of the NEXAFS spectra characteristic for physical (krypton) and/or chemical/physical modifications of the surface (bromine) upon plasma treatment were observed. Their molecular origin, however, remained elusive. In this work we study by density functional theory, the effects of selected point and line defects as well as chemical modifications on NEXAFS carbon K-edge spectra of single graphene layers. For Br-treated surfaces, also Br 3d X-ray Photoelectron Spectra (XPS) are simulated by a cluster approach, to identify possible chemical modifications. We observe that some of the defects related to plasma treatment lead to characteristic changes of NEXAFS spectra, similar to those in experiment. Theory provides possible microscopic origins for these changes.

Infrared detectors: an overview

Abstract: The paper presents progress in infrared (IR) detector technologies during 200 history of their development. Classification of two types of IR detectors (photon detectors and thermal detectors) is done on the basis of their principle of operation. The overview of IR systems and detectors is presented. Also recent progress in different IR technologies is described. Discussion is focused mainly on current and the most rapidly developing detectors: HgCdTe heterostructure photodiodes, quantum well AlGaAs/GaAs photoresistors, and thermal detectors. The outlook for near-future trends in IR technologies is also presented.

Electrochemical properties of NiCoO2 synthesized by hydrothermal method

Abstract: NiCoO2 microspheres were successfully synthesized via an easy hydrothermal method, followed by an annealing process at 350 °C under a nitrogen atmosphere. The X-ray diffraction results show that a single phase NiCoO2 was synthesized. The results of electrochemical measurements show that the NiCoO2 exhibits a high specific capacitance of 760 and 470 F g−1 at current densities of 1 and 16 A g−1, respectively, and the specific capacitance retention is 40.9% after 5000 cycles at the current density of 16 A g−1. This reveals the great potential of NiCoO2 as an electrode material for high-performance supercapacitors.