Subsurface State Research Articles

Fluorescence from (001) surface and sub-surface exciton states in anthracene crystal

We present quasi-simultaneous reflectivity and fluorescence spectra of crystalline anthracene (001) face, with and without gas surface coating. We show the common origin of these spectra and present evidence for the existence of surface exciton states.

ПОВЕРХНОСТНЫЕ ЭЛЕКТРОННЫЕ СОСТОЯНИЯ МОДЕЛИ ОДНОМЕРНОГО ПОЛУБЕСКОНЕЧНОГО КРИСТАЛЛА ТИПА КРОНИГА-ПЕННИ

Using the MO LCAO formalism, exact energy spectrum and wave functions of electrons in the one-dimensional model of a semi-infinite crystal were obtained. The model can be interpreted as a semi-infinite chain composed of two kinds of atoms connected alternately by strong and weak bonds. In addition to Tamm and Shockley surface states, Shockley subsurface states were obtained. It was shown, that the character of the surface state can change depending on its position in the forbidden energy band. Reasons for the occurrence of Shockley surface states are discussed. Results of this paper are compared with those obtained within the framework of Huckel approximation.

Electronic configuration of indium antimonide surfaces

Large signal alternating current field effect experiments previously performed on the {111} A and B “real” surfaces of n and p-type InSb were extended to cleaved {110} and {100} “real” surfaces of n-type InSb. Discrete “fast” states were observed in the energy gap near the valence as well as near the conduction band edge on all surfaces. The discrete state near the conduction band edge exhibited essentially the same density on all surfaces, ~ 4 × 10 11/cm 2, while the state near the valence band edge was found to be 2 to 6 times more dense, increasing in the order: {110} cleaved, {111} A, {100}, and {111} B. All surfaces were found to be p-type; the degree of p-type character correlated directly with the state density near the valence band edge. The present results were found to be consistent with a model according to which the discrete “fast” states near the valence and conduction band edges are acceptor-like, characteristic of the antimony and indium species, respectively. This model was extended to emphasize the importance of sub-surface states. The electrical properties of these surfaces were correlated with their chemical and structural characteristics and were found to be consistent with the Gatos-Lavine model of the dangling bonds on the III–v compound surfaces.

Microfossils from Silurian of England: ABSTRACT

This paper is one of a series dealing with world-wide correlation of Silurian beds utilizing microfossils, chiefly Foraminifera, from acid residues. Extensive collections and several publications cover many of the sequences from North America, from West Texas to the Gaspe Peninsula. To correlate these sequences with sections elsewhere, a world-wide collection of samples has been made, supported by a National Science Foundation grant. The present paper is a report on the specimens recovered from all Silurian carbonate rocks in Great Britain with which correlations are to be made from North America, Norway, Sweden, Austria, Czechoslovakia, and Australia. Preliminary examination of the specimens from the Swedish island of Gotland and Scania show that most of the species from these islands are the same as those from England. A few of the species from England, Norway, and Gotland are identical with those from the Arbuckle Mountains, Oklahoma, Kansas subsurface, and central United States, but most of them are new. Nearly all of the arenaceous Foraminifera belong to the family Saccamminidae. Most are attached forms and have brown tests with abundant iron in the cement. These forms have not been described previously. A few species of Bathysiphon, Hyperammina, and Ammodiscus are the only other genera present. More than 11,000 specimens from England and 3,000 from Gotland have been mounted, providing abundant material for morphologic, evolutionary, and taxonomic study. In many places conodonts and scolecodonts are associated with arenaceous Foraminifera. Extensive studies and publications on these forms in Europe and North America provide a basis for stratigraphic association of all the microfossils. Such knowledge can be utilized to identify and correlate beds in places where only Foraminifera are present, thus providing an additional tool and means for correlation that previously has not existed. End_of_Article - Last_Page 471------------

Subsurface states in one-dimensional crystals

By means of a Green's function method we discuss the energy-spectrum of an electron in a one-dimensional lattice containing only one type of atom, represented as a Dirac δ-function. Limiting the infinite crystal model at one side, we get not only a potential step at the surface, but we assume also that the first n atoms are displaced. We find that the localization of the surface states depends not only on the potential strengths, the lattice constant and the height of the potential barrier at the surface, but also on the different displacements of the n atoms, i.e. on the penetration of the surface potential into the crystal. In the case that the surface potential acts only up to the second crystal cell, we prove the existence of true surface states or Tamm-levels and of “subsurface” states.