No abstract

Studies of the electrodeposition of atomic layers of Se have been prompted by their importance in the formation of II–VI compound semiconductors by electrochemical atomic layer epitaxy (ECALE). ECALE is a method where a compound is formed by the sequential, alternated, electrodeposition of atomic layers of the constituent elements making up a compound. It has been shown that the structure of the first atomic layer is generally the most critical. The present article describes three different methods for forming that first atomic layer. Studies of the structures resulting from those methods have revealed four distinctly different Se structures, all of which can be considered atomic layers, as none is more than a single-Se atom thick. Graphs of coverage versus potential have been obtained for each of the methods, and show distinct plateaus over as much as 0.15 V, indicating the stability of some of the structures. The sequence of structures first involves the formation of a 1/4 coverage (2×2), followed by a (2×√10) at 1/3 coverage, and then a c(2×2) at 1/2 coverage. In addition, Se8 rings were observed to form, much the same as the S8 rings previously observed for S adsorbed on Au surfaces. At coverages near 0.7, these rings begin to coalesce into a nearly complete monolayer of Se atoms, but with systematic absences, which roughly correspond to the initial holes in the Se8 rings. This structure appears to have an average unit cell which can be described as a (3×√10).

Communications self-assembled thin films were fabricated by an electrostatic deposition technique similar to that described by Decher[2]; Rubner [3], and others [9]. The polymer films consist of alternating layers of a cationic poly(p-pyridiniuin vinylene) (PHPyV or Bu-PHPyV) and anionic sulfonated polyaniline (SPANI) or poly(4-styrene sulfonate) (PSS). Films are grown by first initiating ITO-coated glass substrates with positive charges. This initiation is carried out by treating the ITO-coated glass with (3-aminopropyl)triethoxysilane[7] or by depositing a thin film of polypyrrole or polyaniline directly on the substrate[3b]. In the latter case, the thickiicss of the conducting polymer film was limited to keep the total optical density of the resulting substrate below 0.1 in the visible part of the spectrum. The assembly ofthe multilayer polymer film on the cationicsubstrate was carried out by sequentially dipping the substrate into each polymer solution (alternating between anionic and cationic). Dipping time in each solution was 30 minutes. After each dip, the film was rinsed with water (for PSS or SPANI) or THF-acetone (for Bu-PHPyV) or m-cresol-acetonitrile (for PHPyV) and dried under nitrogen flow before the next deposition.The LEDs were fiiiishcd by vacuum depositing an aluminum electrode on top of the organic film. The base pressure of the chamber was mbar and the evaporating pressure was 10-' mbar The thickness of the electrode was ca.1000 a and the area of the electrode was 1 mm2. The I-Vcharacteristics of the devices were measured on an H P 414BB analyzer and the electroluminescent spectra were collected using ail EG & G nionochromator and Electriin 1000 TE CCD camera. The light intensity was detected by a calibrated broad-area silicon photodiode. ahose photocurrent was measured by H P picoampere meters.The electronic absorption spectra weremeasured on an AVIV Spectrophotometer model 14DS (modified Cary-14) and the photoluminescence spectra were taken with a Perkin-Elmer LS-50 Luminescence Spectrometer. The excitation wavelengths used were thc maximum absorption wavelengths in the electronic absorption spectra. PSS is tiansparent at both the excitation and emission wavelengths, while polypyrrole, polyaniline and SPANI have very low optical densities at these wavelengths in the samples prepared here. Photoluminescence quantum yields of Bu-PPyV and Bu-PHPyV were measured in degassed T H F solutions. typically M (based on the monomer repeat unit). The Bu-PH-PyV was made by adding stoichiometric amount methane sulfonic acid to the Bu-PPyV solution. Rhodamine B in ethanol was used as a reference (u, = 1) [11].The excitation wavelengths for the polymer solutions and Rhodamine B were 420 nm and 530 nm. respectively. The photoluminescent quantum yield of Bu-PPyV is greater than 0.9, and the quantum yield of Bu-PHPyV is ca. 0.8. M R 9357415. The authors wish to thank Victor Gruol for assistmce with the XPS measurements, and Andrew Gewirth (University of Illinois) for generous donation of the HOPG substrate. ...

Abstract— Wet chemical treatments have been performed on phosphor particles. ZnO: Zn phosphor was reductively etched with a basic aqueous solution of sodium borohydride. The etch resulted in a two‐fold increase in the cathodoluminescent efficiency without any detected change in particle size or surface composition as detected by Auger electron spectroscopy. The low‐voltage cathodoluminescent characteristics are particularly enhanced. The enhanced efficiency of the phosphor particles may be attributable to a change in surface structure or an increase in the surface coverage of luminescent centers induced by the reductive etch.