1,721,029 research outputs found
Optical transitions and sum rules at clean semiconductor surfaces
No full textThe experimental results of surface differential reflectivity and reflectance anisotropy spectroscopy show that in Si(111)-2 x 1, Ge(Ill)-2 x 1 and GaAs(001)-2 x 4 a sum rule for the imaginary part of the (surface) dielectric function is verified both for the isotropic and anisotropic parts of epsilon(s)". It is shown that the sum rule together with the dependence of the spectra upon oxygen contamination are useful in the interpretation of the optical transitions of the above surfaces. In particular, for the case of GaAs(001)-2 x 4 the above analysis has allowed the distinction between optical transitions associated to true surface states and bulk states modified by the surface near the 3 eV critical point
Differential-reflectance spectroscopy and reflectance-anisotropy spectroscopy on semiconductor surfaces
No full textThe development and the state of the art of surface methods based on the reflection of light are briefly reviewed. A short account is given of the main experimental and theoretical results obtained on semiconductor surfaces over about three decades
The 2 x 1-reconstructed cleavage surface of diamond: A challenging test for experiment and theory
No full textWe have recently measured for the first time - by using Reflectance Anisotropy spectroscopy- the optical gap between dangling-bond states on a single-domain diamond C(111)-2 x 1 surface. The experimental result we have obtained (1.47 +/- 0.02 eV) represents the conclusion of the long-standing effort to determine if this surface is metallic or semiconducting. The large surface gap (even larger for possible excitonic effects) opens a new scientific question: at the moment neither state-of-the-art band calculations have succeeded in obtaining it, nor has its physical origin been explained. (C) 2009 Elsevier Ltd. All rights reserved
Optical gap between dangling-bond states of a single-domain diamond C(111)-2 x 1 by reflectance anisotropy spectroscopy
No full textThe optical gap between dangling- bond states has been measured on a single- domain diamond C( 111)- 2 x 1 surface. The experimental result is 1.47 eV. Such a large surface gap ( even larger if excitonic effects are considered) so far has not been obtained by state- of- the- art band calculations and its physical origin is still not elucidated. The experimental result suggests a strong electron- phonon interaction in this surface. The renormalization of the bare electronic transition energy by electron- phonon interaction provides a clue to solve the apparent disagreement between theory and experiment
Unpinned Schottky-Barrier Formation at Metal-Gap Interfaces - a Representative Iii-V Compound Interface
No full textLSELPRXXerox corp,webster res ctr,webster,ny 14580. univ wisconsin,dept phys,madison,wi 53706. Chiaradia, p, cnr,ist struttura mat,frascati,italy.ISI Document Delivery No.: J673
Initial-Stages of Gap(1 1 0) Oxidation
No full textLSELPRXXerox corp,webster res ctr,webster,ny 14580. univ wisconsin,dept phys,madison,wi 53706. Chiaradia, p, cnr,ist struttura mat,frascati,italy.ISI Document Delivery No.: P756
Confinement effects in pi -bonded chains at group IV semiconductor (111) surfaces
No full textThe degree of 1D character of surface chains at group IV (111)-2 × 1 reconstructed surfaces is established by surface sensitive optical spectroscopy. Optical experiments on a diamond C(111)-2 × 1 surface show that the absorption peak related to dangling-bond transitions exhibits a marked blueshift upon oxygen exposure of the clean surface. Such behaviour is analogous to that observed on a clean Si(111)-2 × 1 surface. For both surfaces the experimental finding is interpreted in terms of quantum confinement of surface electrons in quasi-one-dimensional π-bonded chains, whose length decreases with oxygen uptake. A different behaviour is observed in Ge(111)-2 × 1, where only a very slight blueshift of the surface-state optical transition is detected upon oxidation. The almost negligible blueshift in Ge(111)-2 × 1 is consistent with a significant coupling between the π-bonded chains resulting in a much less pronounced one-dimensional character of Ge(111)-2 × 1 surface electrons compared to diamond and silicon reconstructed surfaces. © 2013 IOP Publishing Ltd
Infrared surface absorption in Si(111)2x1 observed with reflectance anisotropy spectroscopy
No full textOptical transitions between surface states associated with dangling bonds in Si(111)2X1 have been measured by means of reflection anisotropy spectroscopy in the near infrared. The results confirm those previously obtained with other optical techniques (namely surface differential reflectivity and photothermal deflection spectroscopies). The method does not require oxidation of the surface and thus opens the way to studying a number of problems in surface physics, including the temperature dependence of surface transitions in Si(111)2x1 and Ge(111)2x1
Optical properties of bismuth-terminated GaAs(110) surfaces
No full textWe have investigated the room temperature deposition of ultrathin bismuth layers on GaAs(110) surfaces by using Surface Differential Reflectance (SDR) spectroscopy. In SDR spectra measured at the "as grown" surfaces, optical transitions related to the new electronic structure of the overlayer appear at 0.8 eV and 1.35 eV, below the gap of bulk gallium arsenide. Because of their energy position and dependence upon deposited Bi thickness, we interpret them as related to Bi-overlayer and Bi-substrate bonds, respectively. Subsequent annealings of the overlayer at temperatures in the range 200-350 degrees C have not produced any improvement in the quality of the interface, but a new tweak) transition at about 1.1 eV possibly related to Bi crystallites present at the surface. Annealing at T > 350 degrees C produces desorption of the adsorbed bismuth
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