Browsing by Author "KWEI, CM"

Now showing 1 - 19 of 19

ANALYTIC-FUNCTIONS FOR ATOMIC MOMENTUM-DENSITY DISTRIBUTIONS AND COMPTON PROFILES OF K-SHELLS AND L-SHELLS
(1993-05-01)
CHEN, YF
;
KWEI, CM
;
TUNG, CJ
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
An analytical expression involving three parameters was proposed for atomic momentum-density distributions of K and L shells. This expression was based on the superposition of hydrogenic closed-shell momentum densities. Parameters in the expression were determined by requiring four of its moments to be equal to the corresponding Hartree-Fock results. An analytical function for the Compton profiles was then derived using the impulse approximation. Excellent agreement was found between the present results and detailed theoretical computations.
ANALYTICAL REPRESENTATION OF ATOMIC SHELLWISE ELECTRON-DENSITIES AND APPLICATIONS
(1993-03-28)
CHEN, YF
;
KWEI, CM
;
TUNG, CJ
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Analytical expressions of atomic shellwise electron densities have been constructed. Our approach was based on the superposition of Yukawa potentials for the atomic electrostatic potential. The electron density distribution was then established by the Poisson equation. Parameters characterizing the shellwise electrostatic potential and the corresponding electron density distribution were obtained by a fitting procedure utilizing the Hartree-Fock-Slater (HFS) data. These parameters were determined by the atomic number and electron occupation numbers in various states. The accuracy of constructed electron density distributions was tested by comparing their various moments with the corresponding results obtained from other methods. Applications of these atomic shellwise electron densities were made for calculations of the elastic scattering cross section and the mean excitation energy.
ANGULAR-DISTRIBUTION OF ELECTRONS ELASTICALLY BACKSCATTERED FROM NONCRYSTALLINE SOLID-SURFACES
(1995-10-14)
CHEN, YF
;
KWEI, CM
;
SU, P
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In the energy range 100 eV-2 keV, we applied the Monte Carte method to analyse the elastic reflection coefficient and the angular distribution of electrons elastically backscattered from the solid surface of an isotropic and homogeneous medium. Results indicated that elastically backscattered electrons arose substantially from only a few scatterings with a single scattering event contributing to approximately half of these electrons. Thus, neither the multiple scattering model nor the single scattering model is sufficient to describe the angular distribution. To improve these models, we evaluated the contribution from one, two and three scatterings exactly and higher scatterings by the P-1-approximation, an approximate method to solve the Boltzmann transport equation assuming multiple elastic scattering of electrons in the solid. This approach allowed us to derive analytical formulations for the elastic reflection coefficient and the angular distribution of elastically backscattered electrons. Results calculated based on these formulations were in good agreement with those using Monte Carlo simulations and experimental data.
APPLICATION OF THE LOCAL PLASMA APPROXIMATION FOR ATOMIC GENERALIZED OSCILLATOR-STRENGTHS
(1988-08-28)
KWEI, CM
;
LIN, TL
;
TUNG, CJ
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
DEPENDENCE OF ELECTRON-MOBILITY ON DOPED IMPURITIES
(1995-09-01)
CHEN, YF
;
KWEI, CM
;
SU, P
;
TUNG, CJ
;
電子工程學系及電子研究所
The dependence of electron mobility on doped impurities was investigated. Analytical expressions of the momentum relaxation cross section and the electron mobility in n- and p-doped silicon for electron-impurity scatterings have been derived. Our approach involved the application of a screened scattering potential based on a charge density distribution for impurity ions in the semiconductor. This distribution was determined by the variational statistical method. Calculated results showed that ionized acceptor impurities in silicon scattered electron carriers less strongly than did ionized donor impurities. They also showed that majority electron mobility in n-type silicon was less than minority electron mobility in p-type silicon. These were consistent with experimental observations.
DIFFERENTIAL CROSS-SECTIONS FOR PLASMON EXCITATIONS AND REFLECTED ELECTRON-ENERGY-LOSS SPECTRA
(1994-06-15)
TUNG, CJ
;
CHEN, YF
;
KWEI, CM
;
CHOU, TL
;
交大名義發表
Electron differential inverse mean free paths for volume-plasmon excitations and differential probabilities for surface-plasmon excitations have been calculated using dielectric response theory. A model dielectric function which satisfied sum rules and agreed with optical data was established for these calculations. In surface-plasmon calculations, we considered electron-impact emissions of the reflected electron-energy-loss spectroscopy. Formulations were made for obliquely incident electrons with the recoil effect and without the small-scattering-angle assumption. For volume-plasmon excitations, we evaluated corrections due to the exchange and Z1(3) effects. Comparison between calculated results and experimental data extracted from reflected electron-energy-loss spectra showed good agreement. Calculated differential cross sections have been used to solve the transport equation for the angular and energy flux spectra of reflected electrons. Contributions to the spectra from single and plural plasmon excitations were analyzed. It was found that calculated spectra were in good agreement with measured data.
ELECTRON INELASTIC MEAN FREE PATHS FOR PLASMON EXCITATIONS AND INTERBAND-TRANSITIONS
(1993-08-20)
KWEI, CM
;
CHEN, YF
;
TUNG, CJ
;
WANG, JP
;
電子工程學系及電子研究所
Both plasmon excitations and interband transitions are important in the response of valence bands to fast electrons. An extended Drude dielectric function was established to describe such a response in solids of complex band structures. Parameters in this function were determined by a fit of the imaginary part of the function to experimental optical data. The real part of the dielectric function and the energy-loss function were also checked with experimental data to confirm critical-point energies in the interband transitions and plasmon energies in the collective excitations. In addition, sum-rules about the imaginary part of the dielectric function and the energy-loss function, respectively, were applied to assure the accuracy of these functions. Electron inelastic mean free paths in several solids were calculated and compared to available experimental and theoretical data.
ENERGY-LOSS AND RANGE DISTRIBUTIONS OF LOW-ENERGY ELECTRONS IN ALUMINUM
(1983)
KWEI, CM
;
交大名義發表
;
電控工程研究所
;
National Chiao Tung University
;
Institute of Electrical and Control Engineering
ENERGY-LOSS STRAGGLING OF ELECTRONS TRANSMITTED THROUGH CARBON
(1981)
TUNG, CJ
;
KWEI, CM
;
電控工程研究所
;
Institute of Electrical and Control Engineering
INFLUENCE OF MULTIPLE-SCATTERING ON ENERGY-LOSS STRAGGLINGS FOR ELECTRONS
(1984)
KWEI, CM
;
交大名義發表
;
電控工程研究所
;
National Chiao Tung University
;
Institute of Electrical and Control Engineering
INFLUENCE OF SURFACE EXCITATIONS ON ELECTRONS ELASTICALLY BACKSCATTERED FROM COPPER AND SILVER SURFACES
(1994-12-15)
CHEN, YF
;
SU, P
;
KWEI, CM
;
TUNG, CJ
;
電子工程學系及電子研究所
LOCAL-PLASMA APPROXIMATION FOR ATOMIC AND SOLID EXCITATION-SPECTRA
(1985-12-01)
TUNG, CJ
;
KWEI, CM
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
MEAN EXCITATION-ENERGIES OF ATOMS USING THE LOCAL PLASMA APPROXIMATION
(1988-07-14)
TUNG, CJ
;
SHYU, RL
;
KWEI, CM
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
MOMENTUM DEPENDENCE OF GENERALIZED OSCILLATOR-STRENGTHS OF ATOMIC K-SHELLS USING THE LOCAL PLASMA APPROXIMATION
(1990-08-14)
KWEI, CM
;
TUNG, CJ
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
OPTICAL-CONSTANTS MODEL FOR SEMICONDUCTORS AND INSULATORS
(1993-08-15)
CHEN, YF
;
KWEI, CM
;
TUNG, CJ
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The refractive index and the extinction coefficient, i.e., the real and imaginary parts of the complex index of refraction, for semiconductors and insulators are derived as a function of photon energy. These derivations apply f-sum rules and symmetry relations to critical-point transitions from the valence band to the conduction band. Comparison with measured optical data reveals that present formulations are valid over a wide range of photon energies immediately above the band gap to the first ionization threshold for inner shells. The present work shows an improvement and extension over the theory of Forouhi and Bloomer, which applies for a narrow range of photon energies above the absorption edge.
RECONSTRUCTION OF THE SUM-RULE-CONSTRAINED CLASSICAL BINARY-COLLISION MODEL FOR INNER-SHELL IONIZATIONS
(1992-04-01)
KWEI, CM
;
CHEN, YF
;
TUNG, CJ
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Tung has constructed a sum-rule-constrained classical binary-collision model for the estimation of generalized oscillator strengths (GOS's) of the 1s and 2s subshells of atoms. He applied three sum rules to determine the momentum-dependent parameters introduced in the GOS function based on the classical binary-collision model. Several deficiencies have then been found regarding these sum rules that adopted the less accurate hydrogenic model and included the unwanted contribution from discrete excitations. In the present work, we have reconstructed this model by employing improved sum rules obtained from Hartree-Fock-Slater matrix element calculations. The refined model has been successfully applied to estimate ionization generalized oscillator strengths of atomic K and L shells.
STOPPING POWER OF SEMICONDUCTING-III-V COMPOUNDS FOR LOW-ENERGY ELECTRONS
(1986-02-14)
KWEI, CM
;
TUNG, CJ
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
STRAGGLING OF ENERGY-LOSS FOR ELECTRONS TRANSMITTED THROUGH ALUMINUM
(1981)
KWEI, CM
;
交大名義發表
;
電控工程研究所
;
National Chiao Tung University
;
Institute of Electrical and Control Engineering
THE INELASTIC MEAN FREE PATHS OF ELECTRONS IN SEMICONDUCTING III-V-COMPOUNDS
(1988-01-01)
KWEI, CM
;
CHEN, LW
;
交大名義發表
;
電子工程學系及電子研究所
;
National Chiao Tung University