Densely-packed alkyl monolayers similar to those previously reported by Linford et al. 1,2 are formed by the reaction of 1-alkenes with hydrogen-terminated surfaces of both Si(111) and Si(100). The thermal behavior of these monolayers in vacuum has been studied using high-resolution electron energy loss spectroscopy. Both on Si(111) and on Si(100), the monolayers are found to be stable up to about 615 K. Desorption is signaled by a decrease in the intensity of C-H modes, accompanied by the appearance of Si-H modes, which suggests that desorption occurs through β-hydride elimination reactions. Upon further annealing to 785 K, C-H and Si-H modes essentially disappear, and a peak appears at 780 cm -1 , which is attributed to a SiC vibrational mode. This behavior indicates that decomposition of the monolayers has taken place.

The thermal behavior of alkyltrichlorosilane (CH3(CH2)n-1SiCl3) based self-assembled monolayers on the oxidized Si(100) surface has been examined under ultrahigh vacuum conditions for n ) 4, 8, and 18. Using high-resolution electron energy loss spectroscopy and contact angle analysis, it is found that the monolayers are stable in vacuum up to about 740 K independent of chain length. Above 740 K the chains begin to decompose through C-C bond cleavage, resulting in the desorption of hydrocarbon fragments. Following this initial desorption step, methyl groups attached to silicon atoms are observed. The siloxane head groups remain on the surface following decomposition of the monolayers until about 1100 K.

High-resolution electron-energy-loss spectra of octadecanethiol self-assembled monolayers ͑SAM's͒ on Au thin films have been obtained after annealing the sample to various temperatures. Annealing to 375 K results in the appearance of the S-S stretch at 530 cm Ϫ1 , a direct observation of sulfur dimers for alkanethiol SAM's adsorbed on Au. The appearance of dimers following annealing is explained by the presence of an activation barrier to the formation of gauche defects at the S-C bond. ͓S0163-1829͑99͒51016-3͔ RAPID COMMUNICATIONS

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Articles you may be interested inFabrication of quantum dots using multicoated self-assembled monolayer J. Vac. Sci. Technol. A 28, 730 (2010); 10.1116/1.3360923 Passivation of GaAs by octadecanethiol self-assembled monolayers deposited from liquid and vapor phasesThe structure of alkylsiloxane self-assembled monolayers formed on HF-treated Si 3 N 4 has been studied using x-ray photoelectron spectroscopy, high-resolution electron energy-loss spectroscopy, and contact angle analysis. It is shown that the monolayers are similar in quality to those formed on oxidized silicon, despite the fact that upon etching in HF, the Si 3 N 4 surface contains only 0.2 ML of oxygen. In contrast, on NH 4 F-treated Si͑100͒ surfaces with similar quantities of oxygen, high-quality monolayers cannot be formed. We argue that these results point to the importance of a water layer in monolayer formation.