Projected surface energy bands, Shockley surface states, stability and bonding in transition metal aluminides: The example of β′-CoAl

1983 ◽  
Vol 33 (3) ◽  
pp. 341-349
Author(s):  
M. Tomášek ◽  
Š. Pick
Keyword(s):  
Transition Metal ◽  
Surface Energy ◽  
Surface States ◽  
Energy Bands ◽  
Metal Aluminides

Projected surface energy bands, Shockley surface states and stability of ordered substitutional alloys with CsCl structure: The example of β'-CuZn

1981 ◽  
Vol 46 (6) ◽  
pp. 1301-1317 ◽  
Author(s):  
Mojmír Tomášek ◽  
Štěpán Pick
Keyword(s):  
Surface Energy ◽  
Chemical Bonding ◽  
Surface States ◽  
Qualitative Theory ◽  
Energy Bands ◽  
Cscl Structure ◽  
Substitutional Alloys

Qualitative theory of Shockley surface states is applied to β'-CuZn with the aim to analyse the character and location of its hybridizational gaps and to draw general conclusions on other ordered substitutional alloys with CsCl structure as well. The results are used to propose the role which hybridizational gaps and chemical bonding can play in order-disorder phenomena of such alloys. Some special questions of relevance to these phenomena are also qualitatively discussed.

Electron energy loss near edge structures of intermetallic alloys and grain boundaries in NiAl

1996 ◽  
Vol 54 ◽  
pp. 522-523
Author(s):  
G.A. Botton ◽  
C.J. Humphreys
Keyword(s):  
High Temperature ◽  
Transition Metal ◽  
Energy Loss ◽  
Grain Boundaries ◽  
Industrial Applications ◽  
Edge Structure ◽  
Structural Applications ◽  
Yield Behaviour ◽  
Late Transition ◽  
Metal Aluminides

Transition metal aluminides are of great potential interest for high temperature structural applications. Although these materials exhibit good mechanical properties at high temperature, their use in industrial applications is often limited by their intrinsic room temperature brittleness. Whilst this particular yield behaviour is directly related to the defect structure, the properties of the defects (in particular the mobility of dislocations and the slip system on which these dislocations move) are ultimately determined by the electronic structure and bonding in these materials. The lack of ductility has been attributed, at least in part, to the mixed bonding character (metallic and covalent) as inferred from ab-initio calculations. In this work, we analyse energy loss spectra and discuss the features of the near edge structure in terms of the relevant electronic states in order to compare the predictions on bonding directly with spectroscopic experiments. In this process, we compare spectra of late transition metal (TM) to early TM aluminides (FeAl and TiAl) to assess whether differences in bonding can also be detected. This information is then discussed in terms of bonding changes at grain boundaries in NiAl.

scholarly journals First-principle investigations of structural and electronic properties of TMAl (TM = Fe, Co, and Ni) transition metal aluminides

2015 ◽  
Vol 33 (2) ◽  
pp. 251-258
Author(s):  
Bendouma Doumi ◽  
Allel Mokaddem ◽  
Mustapha Ishak-Boushaki ◽  
Miloud Boutaleb ◽  
Abdelkader Tadjer
Keyword(s):  
Transition Metal ◽  
Electronic Properties ◽  
Density Functional ◽  
First Principle ◽  
Generalized Gradient ◽  
Metallic Behavior ◽  
Plane Wave Method ◽  
Structural And Electronic Properties ◽  
The Difference ◽  
Metal Aluminides

AbstractIn the present work, we have investigated the structural and electronic properties of TMAl (TM = Fe, Co, and Ni) transition metal aluminides in the B2 structure, using first-principle calculations of the density functional theory (DFT) based on the linearized augmented plane wave method (FP-LAPW) as implemented in the WIEN2k code, in which the energy of exchange and correlation are treated by the generalized gradient approximation (GGA), proposed in 1996 by Perdew, Burke and Ernzerhof (PBE). The ground state properties have been calculated and compared with other calculations, and the electronic structures of all FeAl, CoAl, and NiAl compounds exhibited a metallic behavior. It was depicted that the density of states is characterized by the large hybridization between the s-p (Al) and 3d (Fe, Co, and Ni) states, which creates the pseudogap in the region of anti-bonding states. Moreover, the band structures of FeAl, CoAl, and NiAl are similar to each other and the difference between them is in the energy level of each band relative to the Fermi level.

Valence-Mending Passivation of Si(100) Surface: Principle, Practice and Application

2015 ◽  
Vol 242 ◽  
pp. 51-60 ◽  
Author(s):  
Meng Tao
Keyword(s):  
Transition Metal ◽  
Schottky Barrier Height ◽  
New Records ◽  
Transition Metal Dichalcogenides ◽  
Surface States ◽  
Atomic Layer ◽  
Schottky Barriers ◽  
Photovoltaic Devices ◽  
Dangling Bonds ◽  
Metal Dichalcogenides

Surface states have hindered and degraded many semiconductor devices since the Bardeen era. Surface states originate from dangling bonds on the surface. This paper discusses a generic solution to surface states, i.e. valence-mending passivation. For the Si (100) surface, a single atomic layer of valence-mending sulfur, selenium or tellurium can terminate ~99% of the dangling bonds, while group VII fluorine or chlorine can terminate the remaining 1%. Valence-mending passivation of Si (100) has been demonstrated using CVD, MBE and solution passivation. The keys to valence-mending passivation include an atomically-clean Si (100) surface for passivation and precisely one monolayer of valence-mending atoms on the surface. The passivated surface exhibits unprecedented properties. Electronically the Schottky barrier height between various metals and valence-mended Si (100) now follows more closely the Mott-Schottky theory. With metals of extreme workfunctions, new records for low and high Schottky barriers are created on Si (100). The highest barrier so far is 1.14 eV, i.e. a larger-than-bandgap barrier, and the lowest barrier is below 0.08 eV and potentially negative. Chemically silicidation between metal and valence-mended Si (100) is suppressed up to 500 °C, and the thermally-stable record Schottky barriers enable their applications in nanoelectronic, optoelectronic and photovoltaic devices. Another application is transition metal dichalcogenides. Valence-mended Si (100) is an ideal starting surface for growth of dichalcogenides, as it provides only van der Waals bonding to the dichalcogenide.

Site-occupation tendencies for ternary additions (Fe, Co, Ni) in β-phase transition-metal aluminides

1995 ◽  
Vol 51 (13) ◽  
pp. 8102-8106 ◽  
Author(s):  
Mahalingam Balasubramanian ◽  
Douglas M. Pease ◽  
Joseph I. Budnick ◽  
Tariq Manzur ◽  
Dale L. Brewe
Keyword(s):  
Phase Transition ◽  
Transition Metal ◽  
Site Occupation ◽  
Β Phase ◽  
Ternary Additions ◽  
Metal Aluminides

scholarly journals Superconductivity enhancement in phase-engineered molybdenum carbide/disulfide vertical heterostructures

2020 ◽  
Vol 117 (33) ◽  
pp. 19685-19693
Author(s):  
Fu Zhang ◽  
Wenkai Zheng ◽  
Yanfu Lu ◽  
Lavish Pabbi ◽  
Kazunori Fujisawa ◽  
...  
Keyword(s):  
Transition Metal ◽  
Density Functional ◽  
Molybdenum Carbide ◽  
High Temperature Superconductivity ◽  
Surface States ◽  
Molybdenum Sulfide ◽  
Transition Metal Carbide ◽  
Metal Carbide ◽  
Moire Patterns ◽  
Moiré Patterns

Stacking layers of atomically thin transition-metal carbides and two-dimensional (2D) semiconducting transition-metal dichalcogenides, could lead to nontrivial superconductivity and other unprecedented phenomena yet to be studied. In this work, superconducting α-phase thin molybdenum carbide flakes were first synthesized, and a subsequent sulfurization treatment induced the formation of vertical heterolayer systems consisting of different phases of molybdenum carbide—ranging from α to γ′ and γ phases—in conjunction with molybdenum sulfide layers. These transition-metal carbide/disulfide heterostructures exhibited critical superconducting temperatures as high as 6 K, higher than that of the starting single-phased α-Mo2C (4 K). We analyzed possible interface configurations to explain the observed moiré patterns resulting from the vertical heterostacks. Our density-functional theory (DFT) calculations indicate that epitaxial strain and moiré patterns lead to a higher interfacial density of states, which favors superconductivity. Such engineered heterostructures might allow the coupling of superconductivity to the topologically nontrivial surface states featured by transition-metal carbide phases composing these heterostructures potentially leading to unconventional superconductivity. Moreover, we envisage that our approach could also be generalized to other metal carbide and nitride systems that could exhibit high-temperature superconductivity.

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