Self-assembled multilayer thin films of nanometer-sized gold particles linked with organic dithiols have been prepared on glass, indium tin oxide, and gold substrates. The gold particles within these structures retain their integrity and no sintering occurs as demonstrated by their optical absorbance, ellipsometry, and potential modulated transmission and reflectance spectroscopy. The optical response to electrochemical charge injection into the outermost layer of gold particles is completely different from that of bulk gold electrodes, and it is concluded that the particles have to be regarded as discrete, immobilized quantum-dots.

The formation of self-assembled monolayers (SAMs) of alkanethiols on GaAs was studied using attenuated total reflection Fourier transform infrared spectroscopy. SAMs formed from an ethanol solution containing ammonium hydroxide were more ordered and stable than those obtained by the method previously reported in which surfaces were derivatized from neat molten alkanethiols at elevated temperatures. It is suggested that ammonium hydroxide etches the native surface oxide of GaAs during an initial step followed by the chemisorption of alkanethiols on the chemically reactive surface. The effect of ammonium hydroxide concentrations on the SAM coverage was investigated. Well-ordered layers with close packing were formed when the ammonium hydroxide concentration was 3 vol %. SAMs of alkanethiols with different chain lengths showed that the order increases with increasing chain length (from C12H25SH to C18H37SH).

The origin of chemical anisotropy in the dissolution of single-crystal silicon in alkaline solutions is discussed in terms of the atomic conÐguration of silicon in the pentacoordinated transition state for (100) and ( 111) surfaces. It is proposed that tetravalent silicon, which is bonded in a tetrahedral geometry, is attacked in the etch process by the hydroxide ion, forming a pentacoordinated transition state. Owing to the number of bond angles that are Ðxed by the atomic arrangement at the surface, the energetically favoured trigonal bipyramidal geometry for a pentacoordinated complex is only slightly distorted for the former plane but signiÐcantly distorted for the latter, resulting in a higher activation energy for the dissolution of ( 111) surfaces. The di †erence in the activation energies for the dissolution of Si( 100) and ( 111) surfaces, arising from steric hindrance in the transition state, can be estimated from the activation energy for a pseudo-rotation of a similar system.

A new procedure for the production of smooth and defect-free surfaces in the anisotropic etching of silicon in alkaline solutions is described. It has been found that etching in an ultrasonic bath results in the facilitated detachment of hydrogen bubbles at the surface which is suggested to be one of the causes for surface roughening. In the presence of mild ultrasound radiation a significant improvement in surface finish of the orientation has been observed. The inclusion in the bath of oxygen and/or isopropanol results in root mean square roughness values smaller than 20 nm. The effectiveness of bath additives has been related to changes of the contact angle between the liquid/gas/etching interface. Quantitative determination of roughness and surface imaging have been obtained by atomic force microscopy; dissolution rates were studied by profilometry. Etching under ultrasound conditions and the use of additives does not change the etch kinetics, indicating that additional convection only changes hydrogen bubble detachment.

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