Vacancy Band Research Articles

Role of organic modifier sorption on retention phenomena in reversed-phase liquid chromatography

Distribution phenomena associated with the elution of solutes of varying retention from reversed-phase chromatographic columns have been examined. For solutes slightly more retained than the organic modifier component of the mobile phase, displacement of a portion of the modifier that has been extracted into the bonded phase resulted. For longer retained solutes, a vacancy band was produced, indicating a net flux of organic solvent into the bonded phase. These effects revealed that the composition of the extracted modifier system could be varied by the addition of a second solvent to the mobile phase, such as occurs in ternary mobile phase systems. Polar group selectivities of solutes could in large part then be rationalized on the basis of specific solute-modifier interactions in the stationary phase. On the basis of these results unusual organic modifiers have been used in ternary mobile phase systems to achieve large selectivity differences.

Vacancy bandwidth in BCC 3He as determined by specific heat

The specific heat data of Greywall are analyzed and shown to imply a vacancy band of nonzero width. Certain limits on the density of the vacancy states are derived and a fit to the data is presented. Disagreement between the vacancy density measurements of Heald and Simmons and the specific heat data are confirmed.

Absorption coefficient measurements for vacuum-deposited Cu-ternary thin films

The absorption coefficients, α, of polycrystalline CuInS2 and CuInSe2 thin films have been determined at room temperature using transmission measurements. For each of these semiconductors, an absorption edge corresponding to the direct band-gapl transition (1.54±0.02 eV for CuInS2 and 1.00±0.02 eV for CuInSe2) is observed in the α vs hν spectrum. In p-type CuInS2 thin films, another edge is evident at lower energies (1.41×1.42 eV) and is attributed to transitions from a copper vacancy band to the conduction band. The effects of annealing on the absorption coefficient spectra of these chalcopyrite materials are presented. An additional absorption region, appears in the CuInSe2 spectra at higher energies (hν∠1.28 eV), and is critically dependent on the Se concentration of the films. This effect is discussed in terms of band structure, film stoichiometry and structural characteristics of the films.