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Articles 1 - 30 of 208
Full-Text Articles in Physics
Rational Design Of Super-Alkalis And Their Role In Co2 Activation, Tianshan Zhao, Qian Wang, Puru Jena
Rational Design Of Super-Alkalis And Their Role In Co2 Activation, Tianshan Zhao, Qian Wang, Puru Jena
Physics Publications
Super-alkalis are clusters of atoms. With ionization potentials smaller than those of the alkali atoms, they are playing an increasing role in chemistry as highlighted by recent applications in solar cells as well as in Li-ion batteries. For the past 40 years superalkalis were designed using inorganic elements with the sp orbital character. Here, we show that a large class of superalkalis composed of only simple metal atoms, transition metal complexes as well as organic molecules can be designed by making use of electron counting rules beyond the octet rule. Examples include Al-3(+), Mn(B3N3H6)(2)(+), B9C3H12+, and C5NH6+ which obey the …
B-12(Scn)(12)(-): An Ultrastable Weakly Coordinating Dianion, Hong Fang, Puru Jena
B-12(Scn)(12)(-): An Ultrastable Weakly Coordinating Dianion, Hong Fang, Puru Jena
Physics Publications
Stable dianions that are weakly coordinating with metal ions are not common. In this work, we show that the thiocyanate SCN- anion, known for its detoxification property of cyanide CN- and antidegradation property of perovskite solar cell materials, can also be used to produce a new set of weakly coordinating B-12(SCN)(12)(-) dianion complexes which are potential candidates for the anionic part inside the electrolytes of metal-ion, especially the magnesium-ion-based, batteries.
Metal Chalcogenide Clusters With Closed Electronic Shells And The Electronic Properties Of Alkalis And Halogens, Vikas Chauhan, Arthur C. Reber, Shiv N. Khanna
Metal Chalcogenide Clusters With Closed Electronic Shells And The Electronic Properties Of Alkalis And Halogens, Vikas Chauhan, Arthur C. Reber, Shiv N. Khanna
Physics Publications
Clusters with filled electronic shells and a large gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are generally energetically and chemically stable. Enabling clusters to become electron donors with low ionization energies or electron acceptors with high electron affinities usually requires changing the valence electron count. Here we demonstrate that a metal cluster may be transformed from an electron donor to an acceptor by exchanging ligands while the neutral form of the clusters has closed electronic shells. Our studies on Co6Te8(PEt3),(CO) (m + n = 6) clusters show that Co6Te8(PEt3)(6) has a closed …
Symmetry And Magnetism In Ni9te6 Clusters Ligated By Co Or Phosphine Ligands, Arthur C. Reber, Vikas Chauhan, Shiv N. Khanna
Symmetry And Magnetism In Ni9te6 Clusters Ligated By Co Or Phosphine Ligands, Arthur C. Reber, Vikas Chauhan, Shiv N. Khanna
Physics Publications
The removal of a single ligand from the magnetic Ni9Te6(L)(8) (L = P(CH3)(3), CO) clusters is found to quench the magnetic moment. The reduction in magnetic moment is caused by a geometric deformation of the Ni9Te6 core that breaks the octahedral symmetry of the cluster. This effect is observed in both the CO and phosphine based ligands. The octahedral symmetry bare cluster is also found to have a large magnetic moment. These results highlight the dilemma faced by magnetic ligand protected clusters whose symmetry has been broken: whether to break the spin symmetry as in Hund's rules or to break …
The Effect Of Substituted Benzene Dicarboxylic Acid Linkers On The Optical Band Gap Energy And Magnetic Coupling In Manganese Trimer Metal Organic Frameworks, K. S. Asha, Arthur C. Reber, N. Ahmed, R. Nath, Shiv N. Khanna, Sukhendu Mandal
The Effect Of Substituted Benzene Dicarboxylic Acid Linkers On The Optical Band Gap Energy And Magnetic Coupling In Manganese Trimer Metal Organic Frameworks, K. S. Asha, Arthur C. Reber, N. Ahmed, R. Nath, Shiv N. Khanna, Sukhendu Mandal
Physics Publications
We have systematically studied a series of eight metal-organic frameworks (MOFs) in which the secondary building unit is a manganese trimer cluster, and the linkers are differently substituted benzene dicarboxylic acids (BDC). The optical band gap energy of the compounds vary from 2.62 eV to 3.57 eV, and theoretical studies find that different functional groups result in new states in the conduction band, which lie in the gap and lower the optical band gap energy. The optical absorption between the filled Mn 3d states and the ligands is weak due to minimal overlap of the states, and the measured optical …
Evolution Of The Spin Magnetic Moments And Atomic Valence Of Vanadium In Vcux+, Vagx+, And Vaux+ Clusters (X = 3–14), William H. Blades, Arthur C. Reber, Shiv N. Khanna, Luis López-Sosa, Patrizia Calaminici, Andreas M. Köster
Evolution Of The Spin Magnetic Moments And Atomic Valence Of Vanadium In Vcux+, Vagx+, And Vaux+ Clusters (X = 3–14), William H. Blades, Arthur C. Reber, Shiv N. Khanna, Luis López-Sosa, Patrizia Calaminici, Andreas M. Köster
Physics Publications
The atomic structures, bonding characteristics, spin magnetic moments, and stability of VCUx+, VAgx+, and VAux+ (x = 3-14) clusters were examined using density functional theory. Our studies indicate that the effective valence of vanadium is size-dependent and that at small sizes some of the valence electrons of vanadium are localized on vanadium, while at larger sizes the 3d orbitals of the vanadium participate in metallic bonding eventually quenching the spin magnetic moment. The electronic stability of the clusters may be understood through a split-shell model that partitions the valence electrons in either a delocalized shell or localized on the vanadium …
Tuning The Plasmonic Properties Of Silver Nanopatterns Fabricated By Shadow Nanosphere Lithography, Whitney Ingram, Yizhuo He, Keenan Stone, William M. Dennis, Dexian Ye, Yiping Zhao
Tuning The Plasmonic Properties Of Silver Nanopatterns Fabricated By Shadow Nanosphere Lithography, Whitney Ingram, Yizhuo He, Keenan Stone, William M. Dennis, Dexian Ye, Yiping Zhao
Physics Publications
Regular silver (Ag) nanopatterns, from disconnected nanotriangles to well coupled triangular clusters of nanoparticles, were prepared by shadow nanosphere lithography at different incident angles θ from 0 degrees to 20 degrees with continuous azimuthal rotation. The resulting nanopatterns were consistent with predictions by numerical calculations and Monte Carlo simulations of adatoms with high diffusivity. The visible localized surface plasmon resonance of these nanopatterns was tuned by θ systematically due to the change in size, shape, and arrangement of Ag nanopatterns. These resonances were consistent with finite-difference time-domain simulations using realistic nanopatterns based upon scanning electron micrographs. Such a simple fabrication …
A New Silicon Phase With Direct Band Gap And Novel Optoelectronic Properties, Yaguang Guo, Qian Wang, Yoshiyuki Kawazoe, Puru Jena
A New Silicon Phase With Direct Band Gap And Novel Optoelectronic Properties, Yaguang Guo, Qian Wang, Yoshiyuki Kawazoe, Puru Jena
Physics Publications
Due to the compatibility with the well-developed Si-based semiconductor industry, there is considerable interest in developing silicon structures with direct energy band gaps for effective sunlight harvesting. In this paper, using silicon triangles as the building block, we propose a new silicon allotrope with a direct band gap of 0.61 eV, which is dynamically, thermally and mechanically stable. Symmetry group analysis further suggests that dipole transition at the direct band gap is allowed. In addition, this new allotrope displays large carrier mobility (~104 cm/V · s) at room temperature and a low mass density (1.71 g/cm3), making …
Using Graphene To Control Magnetic Anisotropy And Interaction Between Supported Clusters, Sanjubala Sahoo, M Fhokrul Islam, Shiv N. Khanna
Using Graphene To Control Magnetic Anisotropy And Interaction Between Supported Clusters, Sanjubala Sahoo, M Fhokrul Islam, Shiv N. Khanna
Physics Publications
Stabilization of magnetic order in clusters/nanoparticles at elevated temperatures is a fundamentally challenging problem. The magnetic anisotropy energy (MAE) that prevents the thermal fluctuations of the magnetization direction can be around 1–10 K in free transition metal clusters of around a dozen atoms. Here we demonstrate that a graphene support can lead to an order of magnitude enhancement in the anisotropy of supported species. Our studies show that the MAE of supported Co5 and Co13 clusters on graphene increase by factors of 2.6 and 25, respectively. The enhancement is linked to the splitting of selected electronic orbitals that leads to …
18-Electron Rule Inspired Zintl-Like Ions Composed Of All Transition Metals, Jian Zhou, Santanab Giri, Purusottam Jena
18-Electron Rule Inspired Zintl-Like Ions Composed Of All Transition Metals, Jian Zhou, Santanab Giri, Purusottam Jena
Physics Publications
Zintl phase compounds constitute a unique class of compounds composed of metal cations and covalently bonded multiply charged cluster anions. Potential applications of these materials in solution chemistry and thermoelectric materials have given rise to renewed interest in the search for new Zintl ions. Up to now these ions have been mostly composed of group 13, 14, and 15 post-transition metal elements and no Zintl ions composed of all transition metal elements are known. Using gradient corrected density functional theory we show that the 18-electron rule can be applied to design a new class of Zintl-like ions composed of all …
Potential Of Zro Clusters As Replacement Pd Catalyst, Swayamprabha Behera, Nicholas King, Devleena Samanta, Puru Jena
Potential Of Zro Clusters As Replacement Pd Catalyst, Swayamprabha Behera, Nicholas King, Devleena Samanta, Puru Jena
Physics Publications
Atomic clusters with specific size and composition and mimicking the chemistry of elements in the periodic table are commonly known as superatoms. It has been suggested that superatoms could be used to replace elements that are either scarce or expensive. Based on a photoelectron spectroscopy experiment of negatively charged ions, Castleman and co-workers [Proc. Natl. Acad. Sci. U.S.A.107, 975 (2010)] have recently shown that atoms of Ni, Pd, and Pt which are well known for their catalytic properties, have the same electronic structure as their counterpart isovalent diatomic species, TiO, ZrO, and WC, respectively. Based on this similarity they have …
The Viability Of Aluminum Zintl Anion Moieties Within Magnesium-Aluminum Clusters, Haopeng Wang, Yeon Jae Ko, Xinxing Zhang, Gerd Gantefoer, Hansgeorg Schnoeckel, Bryan W. Eichhorn, Puru Jena, Boggavarapu Kiran, Anil K. Kandalam, Kit H. Bowen Jr.
The Viability Of Aluminum Zintl Anion Moieties Within Magnesium-Aluminum Clusters, Haopeng Wang, Yeon Jae Ko, Xinxing Zhang, Gerd Gantefoer, Hansgeorg Schnoeckel, Bryan W. Eichhorn, Puru Jena, Boggavarapu Kiran, Anil K. Kandalam, Kit H. Bowen Jr.
Physics Publications
Through a synergetic combination of anion photoelectron spectroscopy and density functional theory based calculations, we have investigated the extent to which the aluminum moieties within selected magnesium-aluminum clusters are Zintl anions. Magnesium-aluminum cluster anions were generated in a pulsed arc discharge source. After mass selection, photoelectron spectra of Mg m Al n − (m, n = 1,6; 2,5; 2,12; and 3,11) were measured by a magnetic bottle, electron energy analyzer. Calculations on these four stoichiometries provided geometric structures and full charge analyses for the cluster anions and their neutral cluster counterparts, as well as photodetachment transition energies (stick spectra). Calculations …
Aluminum Zintl Anion Moieties Within Sodium Aluminum Clusters, Haopeng Wang, Xinxing Zhang, Yeon Jae Ko, Andrej Grubisic, Xiang Li, Gerd Gantefoer, Hansgeorg Schnoeckel, Bryan W. Eichhorn, Mal-Soon Lee, Puru Jena, Anil K. Kandalam, Boggavarapu Kiran, Kit H. Bowen Jr.
Aluminum Zintl Anion Moieties Within Sodium Aluminum Clusters, Haopeng Wang, Xinxing Zhang, Yeon Jae Ko, Andrej Grubisic, Xiang Li, Gerd Gantefoer, Hansgeorg Schnoeckel, Bryan W. Eichhorn, Mal-Soon Lee, Puru Jena, Anil K. Kandalam, Boggavarapu Kiran, Kit H. Bowen Jr.
Physics Publications
Through a synergetic combination of anion photoelectron spectroscopy and density functional theory based calculations, we have established that aluminum moieties within selected sodium-aluminum clusters are Zintl anions. Sodium–aluminum cluster anions, Na m Al n −, were generated in a pulsed arc discharge source. After mass selection, their photoelectron spectrawere measured by a magnetic bottle, electron energy analyzer. Calculations on a select sub-set of stoichiometries provided geometric structures and full charge analyses for both cluster anions and their neutral cluster counterparts, as well as photodetachment transition energies (stickspectra), and fragment molecular orbital based correlation diagrams.
Live Cell Interferometry Quantifies Dynamics Of Biomass Partitioning During Cytokinesis, Thomas A. Zangle, Michael A. Teitell, Jason Reed
Live Cell Interferometry Quantifies Dynamics Of Biomass Partitioning During Cytokinesis, Thomas A. Zangle, Michael A. Teitell, Jason Reed
Physics Publications
The equal partitioning of cell mass between daughters is the usual and expected outcome of cytokinesis for self-renewing cells. However, most studies of partitioning during cell division have focused on daughter cell shape symmetry or segregation of chromosomes. Here, we use live cell interferometry (LCI) to quantify the partitioning of daughter cell mass during and following cytokinesis. We use adherent and non-adherent mouse fibroblast and mouse and human lymphocyte cell lines as models and show that, on average, mass asymmetries present at the time of cleavage furrow formation persist through cytokinesis. The addition of multiple cytoskeleton-disrupting agents leads to increased …
Time-Resolved Photoluminescence From Defects In N-Type Gan, Michael A. Reshchikov
Time-Resolved Photoluminescence From Defects In N-Type Gan, Michael A. Reshchikov
Physics Publications
Point defects in GaN were studied with time-resolved photoluminescence (PL). The effects of temperature and excitation intensity on defect-related PL have been investigated theoretically and experimentally. A phenomenological model, based on rate equations, explains the dependence of the PL intensity on excitation intensity, as well as the PL lifetime and its temperature dependence. We demonstrate that time-resolved PL measurements can be used to find the concentrations of free electrons and acceptors contributing to PL in n-type semiconductors.
Surface Diffusion Driven Morphological Instability In Free-Standing Nickel Nanorod Arrays, Ebtihaj Alrashid Jr., Dexian Ye
Surface Diffusion Driven Morphological Instability In Free-Standing Nickel Nanorod Arrays, Ebtihaj Alrashid Jr., Dexian Ye
Physics Publications
Metallic nanostructures are thermodynamically unstable due to the excess of energy of large numbers of surface atoms. Morphological instability, such as Rayleigh breakup, sintering, and coalescence, can be observed at a temperature much lower than the bulk melting point of the metal. We study the morphological and crystalline evolution of well-aligned free-standing nickelnanorod arrays at elevated temperatures up to 600 °C. The as-deposited nickel nanorods are faceted with sharp nanotips, which are deformed at annealing temperatures higher than 400 °C due to strong surface diffusion. A mud-crack like pattern is formed in the samples annealed above 400 °C, leading to …
Lattice Thermal Conductivity In Bulk And Nanosheet Naxcoo2, Denis Demchenko, David B. Ameen
Lattice Thermal Conductivity In Bulk And Nanosheet Naxcoo2, Denis Demchenko, David B. Ameen
Physics Publications
In this paper we present the results of calculations of the lattice thermal conductivity of layered complex metal oxide NaxCoO2 within the Green–Kubo theory. Using NaxCoO2 we identify the two competing mechanisms responsible for the favorable scaling properties of the Green–Kubo method for calculating the lattice thermal conductivity. The artificial correlations of the heat flux fluctuations due to the finite size of the supercells are partially cancelled by the missing long wavelength acoustic phonon modes. We compute the lattice thermoelectric properties of bulk NaxCoO2 with varying stoichiometry, structural defects, and temperature. …
Green Luminescence In Mg-Doped Gan, Michael A. Reshchikov, Denis Demchenko, J. D. Mcnamara, S. Fernández-Garrido, R. Calarco
Green Luminescence In Mg-Doped Gan, Michael A. Reshchikov, Denis Demchenko, J. D. Mcnamara, S. Fernández-Garrido, R. Calarco
Physics Publications
A majority of the point defects in GaN that are responsible for broad photoluminescence (PL) bands remain unidentified. One of them is the green luminescence band (GL2) having a maximum at 2.35 eV which was observed previously in undoped GaN grown by molecular-beam epitaxy in Ga-rich conditions. The same PL band was observed in Mg-doped GaN, also grown in very Ga-rich conditions. The unique properties of the GL2 band allowed us to reliably identify it in different samples. The best candidate for the defect which causes the GL2 band is a nitrogen vacancy (VN). We propose that transitions of electrons …
Temperature Dependence Of Defect-Related Photoluminescence In Iii-V And Ii-Vi Semiconductors, Michael A. Reshchikov
Temperature Dependence Of Defect-Related Photoluminescence In Iii-V And Ii-Vi Semiconductors, Michael A. Reshchikov
Physics Publications
Mechanisms of thermal quenching of photoluminescence (PL) related to defects insemiconductors are analyzed. We conclude that the Schön-Klasens (multi-center) mechanism of the thermal quenching of PL is much more common for defects in III–V and II–VI semiconductorsas compared to the Seitz-Mott (one-center) mechanism. The temperature dependencies of PLare simulated with a phenomenological model. In its simplest version, three types of defects are included: a shallow donor, an acceptor responsible for the PL, and a nonradiative center that has the highest recombination efficiency. The case of abrupt and tunable thermal quenching ofPL is considered in more detail. This phenomenon is predicted …
Time-Resolved Photoluminescence From Defects In N-Type Gan, Michael A. Reshchikov
Time-Resolved Photoluminescence From Defects In N-Type Gan, Michael A. Reshchikov
Physics Publications
Point defects in GaN were studied with time-resolved photoluminescence (PL). The effects of temperature and excitation intensity on defect-related PL have been investigated theoretically and experimentally. A phenomenological model, based on rate equations, explains the dependence of the PL intensity on excitation intensity, as well as the PL lifetime and its temperature dependence. We demonstrate that time-resolved PL measurements can be used to find the concentrations of free electrons and acceptors contributing to PL in n-type semiconductors.
Carbon Defects As Sources Of The Green And Yellow Luminescence Bands In Undoped Gan, Michael A. Reshchikov, Denis Demchenko, A. Usikov, H. Helava, Yu Makarov
Carbon Defects As Sources Of The Green And Yellow Luminescence Bands In Undoped Gan, Michael A. Reshchikov, Denis Demchenko, A. Usikov, H. Helava, Yu Makarov
Physics Publications
In high-purity GaN grown by hydride vapor phase epitaxy, the commonly observed yellow luminescence (YL) band gives way to a green luminescence (GL) band at high excitation intensity. We propose that the GL band with a maximum at 2.4 eV is caused by transitions of electrons from the conduction band to the 0/+ level of the isolated CN defect. The YL band, related to transitions via the −/0 level of the same defect, has a maximum at 2.1 eV and can be observed only for some high-purity samples. However, in less pure GaN samples, where no GL band is observed, …
Aromatic Superhalogens, Brandon Child, Santanab Giri, Scott Gronert, Puru Jena
Aromatic Superhalogens, Brandon Child, Santanab Giri, Scott Gronert, Puru Jena
Physics Publications
No organic molecules with electron affinities near or above those of halogens are known. We show for the first time that aromaticity rules can be used to design molecules with electron affinities far exceeding those of halogen atoms either by tailoring the ligands of cyclopentadienyl or by multiple benzo-annulations of cyclopentadienyl in conjunction with the substitution of CH groups with isoelectronic N atoms. Results based on density functional theory reveal that the electron affinities of some of these organic molecules can reach as high as 5.59 eV, thus opening the door to new class of superhalogens that contain neither a …
Self-Consistent Determination Of Hubbard U For Explaining The Anomalous Magnetism Of The Gd13 Cluster, Kun Tao, Jian Zhou, Qiang Sun, Qian Wang, V. S. Stepanyuk, Puru Jena
Self-Consistent Determination Of Hubbard U For Explaining The Anomalous Magnetism Of The Gd13 Cluster, Kun Tao, Jian Zhou, Qiang Sun, Qian Wang, V. S. Stepanyuk, Puru Jena
Physics Publications
The effective on-site Coulomb interaction (Hubbard U) is an important parameter for studying strongly correlated systems. While U is determined empirically by fitting to bulk values, its value for a cluster with a finite number of atoms remains uncertain. Here, we choose Gd13 as a prototypical example of a strongly correlated cluster. Contrary to the well-known results in transition-metal clusters where magnetic moments of clusters are larger than their bulk, in Gd13 cluster the magnetic moment issmaller than its bulk value. Using density functional theory and the linear response approach, we determine U self-consistently for the cluster and apply …
Tailoring Li Adsorption On Graphene, Jian Zhou, Qiang Sun, Qian Wang, Puru Jena
Tailoring Li Adsorption On Graphene, Jian Zhou, Qiang Sun, Qian Wang, Puru Jena
Physics Publications
The technological potential of functionalized graphene has recently stimulated considerable interest in the study of the adsorption of metal atoms on graphene. However, a complete understanding of the optimal adsorption pattern of metal atoms on a graphene substrate has not been easy because of atomic relaxations at the interface and the interaction between metal atoms. We present a partial particle swarm optimization technique that allows us to efficiently search for the equilibrium geometries of metal atoms adsorbed on a substrate as a function of adatom concentration. Using Li deposition on graphene as an example we show that, contrary to previous …
Life2cl N (N = 4–6) Clusters: Double-Exchange Mediated Molecular Magnets, Kalpataru Pradhan, Purusottam Jena
Life2cl N (N = 4–6) Clusters: Double-Exchange Mediated Molecular Magnets, Kalpataru Pradhan, Purusottam Jena
Physics Publications
A systematic study of LiFe2Cl n (n = 4–6) clusters, based on gradient corrected density functional theory (DFT), shows that the electron contributed by Li can transform antiferromagnetic Fe2Cl n(n = 4 and 6) clusters into ferromagnetic clusters. In Fe2Cl6 (Fe2Cl4) cluster, the Fe atoms in +3 (+2) oxidation states are aligned antiferromagnetically, consistent with the super-exchange model. The extra electron from Li atom creates a charge disproportionation in the LiFe2Cl6(LiFe2Cl4) cluster that mediates the double-exchange interaction between the Fe atoms.Antiferromagnetic to ferromagnetic transition can also be induced by hole doping as seen to be the case with Fe2Cl5 which …
Fine Structure Of The Red Luminescence Band In Undoped Gan, Michael A. Reshchikov, A. Usikov, H. Helava, Yu. Makarov
Fine Structure Of The Red Luminescence Band In Undoped Gan, Michael A. Reshchikov, A. Usikov, H. Helava, Yu. Makarov
Physics Publications
Many point defects in GaN responsible for broad photoluminescence (PL) bands remain unidentified. Their presence in thick GaN layers grown by hydride vapor phase epitaxy (HVPE) detrimentally affects the material quality and may hinder the use of GaN in high-power electronic devices. One of the main PL bands in HVPE-grown GaN is the red luminescence (RL) band with a maximum at 1.8 eV. We observed the fine structure of this band with a zero-phonon line (ZPL) at 2.36 eV, which may help to identify the related defect. The shift of the ZPL with excitation intensity and the temperature-related transformation of …
Green Luminescence In Mg-Doped Gan, Michael A. Reshchikov, Denis Demchenko, J. D. Mcnamara, S. Fernández-Garrido, R. Calarco
Green Luminescence In Mg-Doped Gan, Michael A. Reshchikov, Denis Demchenko, J. D. Mcnamara, S. Fernández-Garrido, R. Calarco
Physics Publications
A majority of the point defects in GaN that are responsible for broad photoluminescence (PL) bands remain unidentified. One of them is the green luminescence band (GL2) having a maximum at 2.35 eV which was observed previously in undoped GaN grown by molecular-beam epitaxy in Ga-rich conditions. The same PL band was observed in Mg-doped GaN, also grown in very Ga-rich conditions. The unique properties of the GL2 band allowed us to reliably identify it in different samples. The best candidate for the defect which causes the GL2 band is a nitrogen vacancy (VN). We propose that transitions of electrons …
Electronic Structure And Magnetic Properties Of Mn And Fe Impurities Near The Gaas (110) Surface, M. R. Mahani, M. Fhokrul Islam, A. Pertsova, C. M. Canali
Electronic Structure And Magnetic Properties Of Mn And Fe Impurities Near The Gaas (110) Surface, M. R. Mahani, M. Fhokrul Islam, A. Pertsova, C. M. Canali
Physics Publications
Combining density functional theory calculations and microscopic tight-binding models, we investigate theoretically the electronic and magnetic properties of individual substitutional transition-metal impurities (Mn and Fe) positioned in the vicinity of the (110) surface of GaAs. For the case of the [Mn2+]0 plus acceptor-hole (h) complex, the results of a tight-binding model including explicitly the impurity delectrons are in good agreement with approaches that treat the spin of the impurity as an effective classical vector. For the case of Fe, where both the neutral isoelectronic [Fe3+]0 and the ionized [Fe2+]− states are relevant to address scanning tunneling microscopy (STM) …
First-Principles Studies On Graphene-Supported Transition Metal Clusters, Sanjubala Sahoo, Markus E. Gruner, Shiv N. Khanna, Peter Entel
First-Principles Studies On Graphene-Supported Transition Metal Clusters, Sanjubala Sahoo, Markus E. Gruner, Shiv N. Khanna, Peter Entel
Physics Publications
Theoretical studies on the structure, stability, and magnetic properties of icosahedral TM13 (TM = Fe, Co, Ni) clusters, deposited on pristine (defect free) and defective graphene sheet as well as graphene flakes, have been carried out within a gradient corrected density functional framework. The defects considered in our study include a carbon vacancy for the graphene sheet and a five-membered and a seven-membered ring structures for graphene flakes (finite graphene chunks). It is observed that the presence of defect in the substrate has a profound influence on the electronic structure and magnetic properties of graphene-transition metal complexes, thereby increasing the …
Temperature Dependence Of Defect-Related Photoluminescence In Iii-V And Ii-Vi Semiconductors, Michael A. Reshchikov
Temperature Dependence Of Defect-Related Photoluminescence In Iii-V And Ii-Vi Semiconductors, Michael A. Reshchikov
Physics Publications
Mechanisms of thermal quenching of photoluminescence (PL) related to defects in semiconductors are analyzed. We conclude that the Schön-Klasens (multi-center) mechanism of the thermal quenching of PL is much more common for defects in III–V and II–VI semiconductors as compared to the Seitz-Mott (one-center) mechanism. The temperature dependencies of PL are simulated with a phenomenological model. In its simplest version, three types of defects are included: a shallow donor, an acceptor responsible for the PL, and a nonradiative center that has the highest recombination efficiency. The case of abrupt and tunable thermal quenching of PL is considered in more detail. …