Papers by Keyword: Density of States (DOS)

Abstract: Gaining control over the various parameters of carbon nanotubes-(CNTs) has always been a challenge for researchers. This is because, each parameter depends on a carbon nanotube's dimensions in addition to its structure and composition. This paper aims to investigate how the thermal dependency of structural parameters -like diameter- affects the density of states (DOS). To accomplish this, the study first reviews the basic theoretical aspects of CNTs, we then present calculations of the energy band structures for armchair carbon nanotubes-(aCNTs), zigzag carbon nanotubes-(zCNTs), and chiral carbon nanotubes-(cCNTs). Finally, the study derives the DOSs to help provide an understanding of the relationship between the radial expansion of the diameter and the DOS for typical zCNTs.

Abstract: The electrical properties of bottom-gate amorphous InSnZnO (a-ITZO) thin-film transistors (TFTs) with different channel thicknesses (TITZO) were investigated. The difference between front- and back-channel interface traps influence on subthreshold swing (S) and turn on voltage (Von) of a-ITZO TFTs was further analyzed using device simulation. Variations of front-channel interface traps (Naf) on S and Von were hardly dependent on TITZO. However, variations of S and Von became larger for thinner TITZO TFT when back-channel interface traps (Nabk) varied; which can be explained by considering screening length. Not only Naf but also Nabk are important factors of S and Von to achieve high performance thinner oxide TFT.

Abstract: The effects of Cr addition on the crystal structure, phase stability and magnetic properties of Ni₈Mn_4-xGa₄Cr_x (x=0, 1 and 2) ferromagnetic shape memory alloys are systematically investigated by ab-initio calculations. The formation energy results indicate that the added Cr preferentially occupies the Mn sites in Ni₂MnGa alloy due to the lowest formation energy. The evaluated Curie temperature decreases with increasing Cr content are derived from the decrease of the total energy difference between the paramagnetic and the ferromagnetic austenite.

Abstract: The effects of Cu addition on the crystal structure, phase stability and magnetic properties of Ni₈Mn_4-xGa₄Cu_x (x=0, 0.5, 1, 1.5 and 2) ferromagnetic shape memory alloys are systematically investigated by first-principles calculations. The formation energy results indicate that the added Cu preferentially occupies the Mn sites in Ni₂MnGa alloy. The formation energy results indicate that ferromagnetic austenite is more stable than the paramagnetic one. The ferromagnetic state becomes instable and paramagnetic state becomes more stable when Mn is gradual substituted by Cu. Furthermore, the electronic density of states gives rise to the difference in the magnetic properties.

Abstract: The crystallographic, magnetic and electronic structures of the magnetic shape memory alloys Ni₂XIn (X=Mn, Fe and Co) are systematically investigated by means of the ab initio calculations within the framework of density functional theory. The equilibrium lattice parameters and the bulk modulus of the austenitic phase in Ni₂XIn are systematically calculated. The formation energy of the L2₁ phase of the Ni₂XIn is estimated, and displays a destabilization tendency if Mn atom is substituted by Fe or Co. Furthermore, the magnetic properties of the Ni₂XIn have been investigated, and the essence of the variation in the magnetic properties with the X atomic number has been illustrated from the view of the electronic density of states.

Abstract: The analytical expression for the density-of-states (DOS) of single-layer graphene interacting with the SiC surface (epitaxial graphene) is obtained. The silicon carbide DOS is described within the scope of the Haldane-Anderson model. It is shown that due to the interaction with the substrate the gap of about 0.01-0.06 eV arises in the epitaxial graphene DOS. The estimation indicates that the electron charge of about (−10-3) e/atom transfers from the substrate to graphene.

Abstract: We compare the effect of hydrogen, nitrogen, and phosphorous passivation on total near interface trap density and mobility of 4H(0001)-SiC/SiO2 structure. The results show that nitrogen and phosphorous passivation decrease total near interface trap density by pushing the energy levels of interface traps away from the conduction band. The density of states (DOS), including interface states (Dit), are calculated for several 4H(0001)-SiC/SiO2 structures using density functional theory (DFT).

Abstract: A computational study using the density fuctional through linear augmented plane wave (LAPW) and gradient generalized approximation (GGA) methods on the electronic properties of cadmium telluride (CdTe) in two modes namely with relativistic effect and non-relativistic effect is presented. Two electronic properties were obtained and compared between the computation with and without the relativistic effects. Firstly, plots of density of states were produced which were for the total CdTe. The total DOS showed that the conduction band was dominated by the states of Te atom, whereas the valence band is dominated by the states of Cd atom. Secondly, the total band structure plot obtained showed that the direct energy band gap, Eg calculated value with relativistic effect was about 1.0 eV while the non-relativistic effect value was 1.8 eV.

Abstract: In this paper, the method for plane wave ultrasoft pseudopotentials of first-principles is adopted to calculate electronic structures of three models including VN crystal, the absence of V atoms and the replacement of V atoms by Si atoms by the VASP software package. On the basis of the optimized VN’s lattice constant, the energy band structures and density of states(DOS) curves of those three models are analyzed. The results show that the 3d electrons of V atoms determine that VN crystal is a conductor. The crystal lack of V atoms forms a peak caused by the empty position near the Fermi level. Its valence band energy level splits and the ability to form bonds reduces to be a metastable phase structure. The formation of solid solution interface due to Si atoms replacing V atoms leads to the peak value of total DOS to decrease, the distribution of electrons to be more diffuse and the ability to form bonds to strengthen.

Abstract: The binding energies, formation energies and DOS (density of state) of several carbides(Fe₃C, Fe₂C, Fe₅C₂, NbC) in Nb micro-alloyed steels are investigated using the first-principle pseudo potential plane-wave method. The results show that the structure type with the strongest alloying ability and the highest structure stability is NbC with fcc structure. After compared the DOS of these different structure types, the results show that the discrepancy in structural stability of carbides can be attributed to the difference in the bonding electron numbers at Feimi level. The less the valence electrons at Feimi level are, the better the structural stability of carbides. Therefore, the theory predicts that the existence form of Nb in medium and high carbon steels are the same as low carbon steels. Nb is still the effective alloying element in medium and high carbon steels.