Activation Energy of Surface Diffusion and Terrace Width Dynamics During the Growth of in (4×3) on Si (100) - (2×1) by Femtosecond Pulsed Laser Deposition

The nucleation and growth of indium on a vicinal Si (100) - (2×1) surface at high temperature by femtosecond pulsed laser deposition was investigated by in situ reflection high energy electron diffraction (RHEED). RHEED intensity relaxation was observed for the first ∼2 ML during the growth of In (4×3) by step flow. From the temperature dependence of the rate of relaxation, an activation energy of 1.4±0.2 eV of surface diffusion was determined. The results indicate that indium small clusters diffused to terrace step edges with a diffusion frequency constant of (1.0±0.1) × 1011 s-1. The RHEED specular beam split peak spacing, which is characteristic of a vicinal surface, was analyzed with the growth temperature to obtain the average terrace width. Gradual reduction in the terrace width during growth of In (4×3) was observed with In coverage and is attributed to the detachment of In atoms from terrace edges. At a substrate temperature of 405 °C, the average terrace width decreased from 61±10 Å, which corresponds to the vicinal Si(100) surface, to an equilibrium value of 45±7 Å after deposition of ∼23 ML. Further In coverage showed a transition of the RHEED pattern from (4×3) to (1×1) and the growth of rounded In islands (average height of ∼1 nm and width of ∼25 nm), as examined by ex situ atomic force microscopy. © 2008 American Institute of Physics. [DOI: 10.1063/1.2909923

Atomic Hydrogen Cleaning of InP(100): Electron Yield and Surface Morphology of Negative Electron Affinity Activated Surfaces

Atomic hydrogen cleaning of the InP(100) surface has been investigated using quantitative reflection high-energy electron diffraction. The quantum efficiency of the surface when activated to negative electron affinity was correlated with surface morphology. The electron diffraction patterns showed that hydrogen cleaning is effective in removing surface contaminants, leaving a clean, ordered, and (2×4)-reconstructed surface. After activation to negative electron affinity, a quantum efficiency of ∼6% was produced in response to photoactivation at 632 nm. Secondary electron emission from the hydrogen-cleaned InP(100)-(2×4) surface was measured and correlated to the quantum efficiency. The morphology of the vicinal InP(100) surface was investigated using electron diffraction. The average terrace width and adatom-vacancy density were measured from the (00) specular beam at the out-of-phase condition. With hydrogen cleaning time, there was some reduction in the average terrace width. The surface quality was improved with hydrogen cleaning, as indicated by the increased (00) spot intensity-to-background ratio at the out-of-phase condition, and improved quantum efficiency after activation to negative electron affinity. © 2002 American Institute of Physics. [DOI: 10.1063/1.1429796

Atomic Hydrogen Cleaning of InP(100) for Preparation of a Negative Electron Affinity Photocathode

Atomic hydrogen cleaning is used to clean InP(100) negative electron affinity photocathodes. Reflection high-energy electron diffraction patterns of reconstructed, phosphorus-stabilized, InP(100) surfaces are obtained after cleaning at ∼400 °C. These surfaces produce high quantum efficiency photocathodes (∼8.5%), in response to 632.8 nm light. Without atomic hydrogen cleaning, activation of InP to negative electron affinity requires heating to ∼530 °C. At this high temperature, phosphorus evaporates preferentially and a rough surface is obtained. These surfaces produce low quantum efficiency photocathodes (∼0.1%). The use of reflection high-energy electron diffraction to measure the thickness of the deposited cesium layer during activation by correlating diffraction intensity with photoemission is demonstrated. © 1998 American Institute of Physics

Interpretation of multispectral and infrared thermal surveys of the Suez Canal Zone, Egypt

Remote sensing airborne surveys were conducted, as part of the plan of rehabilitation, of the Suez Canal Zone using I2S multispectral camera and Bendix LN-3 infrared passive scanner. The multispectral camera gives four separate photographs for the same scene in the blue, green, red, and near infrared bands. The scanner was operated in the microwave bands of 8 to 14 microns and the thermal surveying was carried out both at night and in the day time. The surveys, coupled with intensive ground investigations, were utilized in the construction of new geological, structural lineation and drainage maps for the Suez Canal Zone on a scale of approximately 1:20,000, which are superior to the maps made by normal aerial photography. A considerable number of anomalies belonging to various types were revealed through the interpretation of the executed multispectral and infrared thermal surveys

A Pseudospectral Algorithm for Solving Multipantograph Delay Systems on a Semi-Infinite Interval Using Legendre Rational Functions

A new Legendre rational pseudospectral scheme is proposed and developed for solving numerically systems of linear and nonlinear multipantograph equations on a semi-infinite interval. A Legendre rational collocation method based on Legendre rational-Gauss quadrature points is utilized to reduce the solution of such systems to systems of linear and nonlinear algebraic equations. In addition, accurate approximations are achieved by selecting few Legendre rational-Gauss collocation points. The numerical results obtained by this method have been compared with various exact solutions in order to demonstrate the accuracy and efficiency of the proposed method. Indeed, for relatively limited nodes used, the absolute error in our numerical solutions is sufficiently small

From Gapped Excitons to Gapless Triplons in One Dimension

Often, exotic phases appear in the phase diagrams between conventional phases. Their elementary excitations are of particular interest. Here, we consider the example of the ionic Hubbard model in one dimension. This model is a band insulator (BI) for weak interaction and a Mott insulator (MI) for strong interaction. Inbetween, a spontaneously dimerized insulator (SDI) occurs which is governed by energetically low-lying charge and spin degrees of freedom. Applying a systematically controlled version of the continuous unitary transformations (CUTs) we are able to determine the dispersions of the elementary charge and spin excitations and of their most relevant bound states on equal footing. The key idea is to start from an externally dimerized system using the relative weak interdimer coupling as small expansion parameter which finally is set to unity to recover the original model.Comment: 18 pages, 10 figure

Jacobi rational-Gauss collocation method for Lane-Emden equations of astrophysical significance

In this paper, a new spectral collocation method is applied to solve Lane-Emden equations on a semi-infinite domain. The method allows us to overcome difficulty in both the nonlinearity and the singularity inherent in such problems. This Jacobi rational-Gauss method, based on Jacobi rational functions and Gauss quadrature integration, is implemented for the nonlinear Lane-Emden equation. Once we have developed the method, numerical results are provided to demonstrate the method. Physically interesting examples include Lane-Emden equations of both first and second kind. In the examples given, by selecting relatively few Jacobi rational-Gauss collocation points, we are able to get very accurate approximations, and we are thus able to demonstrate the utility of our approach over other analytical or numerical methods. In this way, the numerical examples provided demonstrate the accuracy, efficiency, and versatility of the method

Impact Factors on Subcontractor's Cash Flow Management

Objective: This study aims to define how to maintain and protect the subcontractor firms' cash flow from economic fluctuation through legally sustainable solutions. Methods/Analysis: We conducted a case study in the Eastern Delta Region of Egypt. A questionnaire containing a list of 22 impact factors on subcontractors' cash flow was distributed across multiple subcontractor firms with an 82% response rate. It was designed to explore the factors causing cash flow instability and analyze them using SPSS statistics. Findings: The study finds that inflation, late payments, non-compensation for late payments, poor subcontractor cash flow management, subcontractor firms' inclination to avoid disputes, material price fluctuation, and non-compensation terms, as well as suppliers rejection of payment delays, are the most critical factors of subcontractor cash flow problems. Novelty/Improvement:The study suggests adding three sub-articles to Article 57 in "Tender Law" as legally sustainable solutions to protect and maintain the firm's growth rate from inflation, late payment, and the inclination to avoid disputes. Also, the study recommends that the owner ensure that cash is available before procuring the general contractors, as stated in Egyptian Law 182 of 2018. This study will contribute to establishing a sustainable win-win relationship between subcontractors and general contractors. Doi: 10.28991/CEJ-SP2023-09-08 Full Text: PD