FIRST STAGE OF THE FORMATION OF SILVER THIN FILMS  ON THE As-PASSIVATED Si(111)-(1×1) SURFACE

The As-terminated Si surface has an ideally flat monolayer of As atoms at the outermost layer, showing a nonreconstructed (1×1) symmetry with one extra valence electron on each As atom, and setting a passivation, on the silicon surface, remarkable for its stablity up to temperatures above 600°C and under Ag deposition. Angle-resolved photoelectron spectroscopy (ARUPS) of valence bands in the main Brillouin zone directions of the As–Si(111) surface, and X-ray photoelectron diffraction (XPD), recorded with the LURE synchrotron light, provide the principal results presented in this work. No arsenic diffusion into the metallic overlayer is detected by photoemission, in a wide range of temperatures, proving the stability of the Ag/As–Si(111) interface, and allowing a first study of the structural and electronic properties of this flat interface. The formation of the silver–metal films on the semiconductor surface has been investigated, in particular the growth mode in the one-monolayer range and the building of the semiconductor–metal interface, and the evolution of the film during the silver deposition up to a few monolayers.

Download Full-text

The Effect of Composition on the Properties of Semiconducting Transition Metal Nitrides

MRS Proceedings ◽

10.1557/proc-1040-q09-01 ◽

2007 ◽

Vol 1040 ◽

Author(s):

Maria G. Moreno-Armenta ◽

Reyes-Serrato Armando ◽

Soto H. Gerardo

Keyword(s):

Nitrogen Concentration ◽

Stoichiometric Composition ◽

Full Potential ◽

Transition Metal Nitrides ◽

Conducting Phase ◽

Wide Range ◽

Structural And Electronic Properties ◽

Ideal Stoichiometry ◽

Nitrogen Concentrations ◽

The Stability

AbstractUsing the full potential linearized augmented plane wave (FP-LAPW) method, we investigate the bulk structural and electronic properties in the scandium-, yttrium-, and copper-nitrides over a wide range of nitrogen concentrations. The N atom was gradually incorporated into metal matrix with and without metal vacancies. The ground state properties like densities of states (DOS) and formation energies are determined for each calculated alloy. We have found that the semi-conducting state in copper nitride have a tinny compositional margin. Any deviation of the ideal stoichiometry will produce a metallic character. What is more, the stabilities of the conductive phases are very close to the stability of the semi conducting phase, with a little margin favorable to the conducting phases. The calculations of scandium- and yttrium nitrides show, that for very low nitrogen incorporations, the hexagonal and fcc phases may coexist. However, for high nitrogen concentration the cubic phases are favored. For non-stoichiometric nitrogen content, the materials behave as metal, whereas at stoichiometric composition the DOS becomes zero at Fermi level (EF), confirming in this way the semiconductor character of these nitrides.

Download Full-text

Stability Behavior of a Natural Circulation Loop with End Heat Exchangers

Journal of Heat Transfer ◽

10.1115/1.1924569 ◽

2005 ◽

Vol 127 (7) ◽

pp. 749-759 ◽

Cited By ~ 16

Author(s):

N. M. Rao ◽

B. Maiti ◽

P. K. Das

Keyword(s):

Heat Exchangers ◽

Natural Circulation ◽

Circulation Rate ◽

Finite Element Program ◽

Stability Behavior ◽

Wide Range ◽

Element Program ◽

The Stability ◽

The One ◽

Two Parameters

The present investigation describes the stability behavior of NCL with end heat exchangers. The one-dimensional transient conservation equations of the loop fluid and the two fluid streams of cold end and hot end heat exchangers are solved simultaneously using the finite element program. For the stability analysis the loop response is found for an imposed finite perturbation to the loop circulation rate. Though the stability may depend on the number of parameters, variation of two nondimensional parameters, namely Ch* and GrL, is studied. Selecting the specific combinations of the above two parameters three different cases of stability, namely, stable, neutrally stable, and unstable, are demonstrated. The stability behavior is scanned over a wide range of Ch* and GrL values and the stability envelope is also constructed.

Download Full-text

Comparative Study of The Reactivity of the Tungsten Oxides WO2 And WO3 With Beryllium at Temperatures up to 1273 K

10.20944/preprints201907.0028.v1 ◽

2019 ◽

Author(s):

Martin Köppen

Keyword(s):

Photoelectron Spectroscopy ◽

Gas Turbines ◽

Power Devices ◽

Tungsten Oxides ◽

First Case ◽

Catastrophic Failures ◽

Experimental Step ◽

Valence Bands ◽

The Stability ◽

Tungsten Substrate

Tungsten oxides play a pivotal role in a variety of modern devices e.g. switchable glasses, wastewater treatment and modern gas sensors and metallic tungsten is used as armour material for e.g. gas turbines and future fusion power devices. In the first case you want to keep the oxide as functional material, while in the second case oxides can lead to catastrophic failures and you want avoid oxidation of tungsten. In both cases it is crucial to understand the stability of the tungsten oxides against chemicals. In this study the different reactivity of tungsten oxides towards the highly oxophilic beryllium is studied and compared. Tungsten--(IV)--oxide and tungsten--(VI)--oxide layers are prepared on a tungsten substrate. In the next step a thin film of beryllium is evaporated on the samples. In consecutive steps the sample is heated in steps of 100 K from r.t. to 1273 K. The chemical composition is investigated after each experimental step by high resolution X-ray photoelectron spectroscopy (XPS) of all involved core levels as well as the valence bands. A model is developed to analyse the chemical reactions after each step. In this study, we found the tungsten trioxid is reduced already by beryllium at r.t. and starts to react towards the ternary compounds BeWO_3 and BeWO_4 at temperatures starting from 673 K. However, the tungsten dioxide sample is reduction resistant to tempartures up to 1173 K. In conclusion, we found the WO_2 surface to be much more chemical resistant towards the reduction agent Be than WO_3.

Download Full-text

Dynamics of three dimensional maps

Facta universitatis - series Electronics and Energetics ◽

10.2298/fuee1101105d ◽

2011 ◽

Vol 24 (1) ◽

pp. 105-117

Author(s):

Asma Djerrai ◽

Ilhem Djellit

Keyword(s):

Invariant Manifolds ◽

Three Dimensional ◽

One Dimensional ◽

Research Fields ◽

Numerical Exploration ◽

Wide Range ◽

Planar Maps ◽

The Stability ◽

The One ◽

One Dimensional Maps

Smooth 3D maps have been a focus of study in a wide range of research fields. Their Properties are investigated qualitatively and numerically. These maps show qualitatively interesting types of bifurcations than those exhibited by generic smooth planar maps. We present a theoretical framework for analyzing three-dimensional smooth coupling maps by finding the stability criteria for periodic orbits and characterizing the system behaviors with the tools of nonlinear dynamics relative to bifurcation in the parameter plane, invariant manifolds, critical manifolds, chaotic attractors. We also show by numerical simulation bifurcations that can occur in such maps. By an analytical and numerical exploration we give some properties and characteristics, since this class of three-dimensional dynamics is associated with the properties of one-dimensional maps. There is an interesting passage from the one-dimensional endomorphisms to the three-dimensional endomorphisms.

Download Full-text

Ab-Initio Study of Electronic and Structural Properties for BaSnO3 Compound Using DFT Calculations and FP-LAPW Technique in Wein2k Software

10.21203/rs.3.rs-325590/v1 ◽

2021 ◽

Author(s):

Zubair Ashraf ◽

Daud Rafique ◽

Tahir Mehmood ◽

Daniyal Akbar

Keyword(s):

Electronic Properties ◽

Structural Properties ◽

Experimental Studies ◽

High Mobility ◽

Cubic Phase ◽

Wide Range ◽

Structural And Electronic Properties ◽

High Carrier Mobility ◽

High Carrier ◽

Valence Bands

Abstract (Perovskites Photovoltaic) PPV cells are the hottest topics in solar cells in the recent years, because of the remarkable structural and electronic properties and hence rapid progress in material science. The Challenge associated with high-mobility BaSnO3 films is to grow. It shows high carrier mobility and UV-visible transparency has been attracting more and more attention as a very promising component for the next generation opto-electronics. Here, we demonstrate a Structural and Electronics properties (Sp and Ep), To characterize this compound theoretical calculation have been performed by using first principal method and the results show BaSnO3 is conductor at 0eV i.e. room temperature and gaining energy make more conduction transferring more electrons from conduction to valence bands. BaSnO3 shows 5.78e.v maximum for the conduction. We have studied this compound in ideal cubic phase. At 0° Kelvin calculation are performed to get different properties. No experimental studies have been done on this compound. And it was difficult to accumulate its experimental data. WC-GGA is used for the study of structural properties of BaSnO3. This Correlation potential can also be used for the calculation of the various perovskite. Depending on the cubic (ABX3) composition, perovskites exhibit a wide range of structural and electronic properties, which are optimized for different applications.

Download Full-text

Contributions to Developments of Photoelectron Spectroscopy and X-ray Absorption Fine Structure Applied to Materials Studies

Communications in Physics ◽

10.15625/0868-3166/15826 ◽

2021 ◽

Vol 31 (2) ◽

pp. 113

Author(s):

Nguyen Van Hung

Keyword(s):

Fine Structure ◽

Photoelectron Spectroscopy ◽

Melting Curve ◽

Debye Model ◽

Near Neighbor ◽

X Ray ◽

Absorption Fine ◽

Valence Bands ◽

The One ◽

X Ray Absorption

This work reviews the contributions of author to the developments and applications of Photoelectron Spectroscopy (PES) and X-ray Absorption Fine Structure (XAFS) to materials studies. Focusing on Angle resolved PES (ARPES) the energy distribution is discussed for angle-resolved photoemission from valence bands of single crystals. The important influence of the spectrometer angle of acceptance on the results of X-ray PES (XPS) is investigated in detail. The Plane Density of States (PDOS) is introduced as a new property of the electronic structure. Most meaningful contributions to XAFS consist of the developments of multiple-scattering and anharmonic XAFS theory. Anharmonic correlated Einstein model (ACEM) and anharmonic correlated Debye model (ACDM) have been derived to obtain Debye-Waller factors (DWF) presented in terms of cumulant expansion which describe the thermodynamic properties and anharmonic effects in XAFS of substances contributing to their accurate structural determination. The anharmonic effective potential (AEP) procedure and first shell near neighbor contributions approach have developed to include many-body effects in the one-dimensional model by a simple measure. Based on DWFs a thermodynamic lattice theory has been derived for studying melting curve and eutectic points of binary alloys. Several applications of the derived methods are performed and the good agreement of the calculated results with experiment illustrate the advantages and efficiencies of the achieved developments.

Download Full-text

Effects of Pressure on the Vibrational, Structural and Electronic Properties of C60 Powder and Thin Films

MRS Proceedings ◽

10.1557/proc-695-l3.10.1 ◽

2001 ◽

Vol 695 ◽

Author(s):

S. C. Sharma ◽

B. Ha ◽

J. H. Rhee ◽

Y. Li ◽

D. Singh ◽

...

Keyword(s):

Thin Films ◽

Electronic Properties ◽

Photoelectron Spectroscopy ◽

Structural Phase ◽

X Ray ◽

Significant Difference ◽

Structural And Electronic Properties ◽

Raman Modes ◽

Valence Bands ◽

La Doped

ABSTRACTWe present results from a study of the vibrational, structural, and electronic properties of C60 powder and thin films. Raman spectroscopy and diamond anvil cell have been used to study pressure dependence of the Raman active modes of C60 powder. The material undergoes structural phase transition between 9 and 15 GPa. Some of the Raman modes soften, while others harden with increasing pressure. Thin films of C60 and La-doped C60 have also been studied by using Raman scattering, x-ray diffraction, x-ray photoelectron spectroscopy and uv photoemission spectroscopy. Whereas the powder and La-doped C60 films exhibit fcc crystalline structure, the C60 film appears disordered. Further, we observe a significant difference in the electronic valence bands of the doped and undoped films.

Download Full-text

Use of a Lyophilized Reference Plasma to Compare Coagulation Test Procedures

Thrombosis and Haemostasis ◽

10.1055/s-0038-1651402 ◽

1975 ◽

Vol 34 (02) ◽

pp. 426-444 ◽

Cited By ~ 3

Author(s):

J Kahan ◽

I Nohén

Keyword(s):

Oral Anticoagulant Therapy ◽

Repeated Measurements ◽

Test Procedures ◽

Coagulation Activity ◽

Close Relationship ◽

Measured Activity ◽

Test Materials ◽

The Difference ◽

The Stability ◽

The One

SummaryIn 4 collaborative trials, involving a varying number of hospital laboratories in the Stockholm area, the coagulation activity of different test materials was estimated with the one-stage prothrombin tests routinely used in the laboratories, viz. Normotest, Simplastin-A and Thrombotest. The test materials included different batches of a lyophilized reference plasma, deep-frozen specimens of diluted and undiluted normal plasmas, and fresh and deep-frozen specimens from patients on long-term oral anticoagulant therapy.Although a close relationship was found between different methods, Simplastin-A gave consistently lower values than Normotest, the difference being proportional to the estimated activity. The discrepancy was of about the same magnitude on all the test materials, and was probably due to a divergence between the manufacturers’ procedures used to set “normal percentage activity”, as well as to a varying ratio of measured activity to plasma concentration. The extent of discrepancy may vary with the batch-to-batch variation of thromboplastin reagents.The close agreement between results obtained on different test materials suggests that the investigated reference plasma could be used to calibrate the examined thromboplastin reagents, and to compare the degree of hypocoagulability estimated by the examined PIVKA-insensitive thromboplastin reagents.The assigned coagulation activity of different batches of the reference plasma agreed closely with experimentally obtained values. The stability of supplied batches was satisfactory as judged from the reproducibility of repeated measurements. The variability of test procedures was approximately the same on different test materials.

Download Full-text

Interactions of Ge Atoms with High- ê Oxide Dielectric Surfaces

MRS Proceedings ◽

10.1557/proc-879-z3.23 ◽

2005 ◽

Vol 879 ◽

Cited By ~ 1

Author(s):

Scott K. Stanley ◽

John G. Ekerdt

Keyword(s):

Oxide Layer ◽

Photoelectron Spectroscopy ◽

Chemical Vapor ◽

Temperature Programmed Desorption ◽

Tungsten Filament ◽

X Ray ◽

Dielectric Surfaces ◽

Temperature Programmed ◽

The Stability ◽

Ge Nanocrystals

AbstractGe is deposited on HfO2 surfaces by chemical vapor deposition (CVD) with GeH4. 0.7-1.0 ML GeHx (x = 0-3) is deposited by thermally cracking GeH4 on a hot tungsten filament. Ge oxidation and bonding are studied at 300-1000 K with X-ray photoelectron spectroscopy (XPS). Ge, GeH, GeO, and GeO2 desorption are measured with temperature programmed desorption (TPD) at 400-1000 K. Ge initially reacts with the dielectric forming an oxide layer followed by Ge deposition and formation of nanocrystals in CVD at 870 K. 0.7-1.0 ML GeHx deposited by cracking rapidly forms a contacting oxide layer on HfO2 that is stable from 300-800 K. Ge is fully removed from the HfO2 surface after annealing to 1000 K. These results help explain the stability of Ge nanocrystals in contact with HfO2.

Download Full-text

Performance of Electronic Structure Methods for the Description of Hückel-Möbius Interconversions in Extended π-Systems

10.26434/chemrxiv.10564115 ◽

2019 ◽

Author(s):

Tatiana Woller ◽

Ambar Banerjee ◽

Nitai Sylvetsky ◽

Xavier Deraet ◽

Frank De Proft ◽

...

Keyword(s):

Electronic Structure ◽

Basis Set ◽

Dft Methods ◽

Molecular Switching ◽

Wide Range ◽

Electronic Structure Methods ◽

Explicitly Correlated ◽

Relative Errors ◽

The Stability ◽

Basis Set Expansion

Expanded porphyrins provide a versatile route to molecular switching devices due to their ability to shift between several π-conjugation topologies encoding distinct properties. Taking into account its size and huge conformational flexibility, DFT remains the workhorse for modeling such extended macrocycles. Nevertheless, the stability of Hückel and Möbius conformers depends on a complex interplay of different factors, such as hydrogen bonding, p···p stacking, steric effects, ring strain and electron delocalization. As a consequence, the selection of an exchange-correlation functional for describing the energy profile of topological switches is very difficult. For these reasons, we have examined the performance of a variety of wavefunction methods and density functionals for describing the thermochemistry and kinetics of topology interconversions across a wide range of macrocycles. Especially for hexa- and heptaphyrins, the Möbius structures have a pronouncedly stronger degree of static correlation than the Hückel and figure-eight structures, and as a result the relative energies of singly-twisted structures are a challenging test for electronic structure methods. Comparison of limited orbital space full CI calculations with CCSD(T) calculations within the same active spaces shows that post-CCSD(T) correlation contributions to relative energies are very minor. At the same time, relative energies are weakly sensitive to further basis set expansion, as proven by the minor energy differences between MP2/cc-pVDZ and explicitly correlated MP2-F12/cc-pVDZ-F12 calculations. Hence, our CCSD(T) reference values are reasonably well-converged in both 1-particle and n-particle spaces. While conventional MP2 and MP3 yield very poor results, SCS-MP2 and particularly SOS-MP2 and SCS-MP3 agree to better than 1 kcal mol-1 with the CCSD(T) relative energies. Regarding DFT methods, only M06-2X provides relative errors close to chemical accuracy with a RMSD of 1.2 kcal mol-1. While the original DSD-PBEP86 double hybrid performs fairly poorly for these extended p-systems, the errors drop down to 2 kcal mol-1 for the revised revDSD-PBEP86-NL, again showing that same-spin MP2-like correlation has a detrimental impact on performance like the SOS-MP2 results.

Download Full-text