The self-assembly mechanism of alkanethiol monolayers on the (111) surface of gold was discovered with the use of an ultrahigh-vacuum scanning tunneling microscope. Monolayer formation follows a two-step process that begins with condensation of low-density crystalline islands, characterized by surface-aligned molecular axes, from a lower density lattice-gas phase. At saturation coverage of this phase, the monolayer undergoes a phase transition to a denser phase by realignment of the molecular axes with the surface normal. These studies reveal the important role of molecule-substrate and molecule-molecule interactions in the self-assembly of these technologically important material systems.

Crystalline structures of pristine and hydrated mercaptohexanol selfassembled monolayers on Au (111) The temperature dependence of the atomic composition of the surface of Cu(100) after deposition of submonolayer films of Au AIP Conf.

Crystalline structures of pristine and hydrated mercaptohexanol selfassembled monolayers on Au (111) The temperature dependence of the atomic composition of the surface of Cu(100) after deposition of submonolayer films of Au AIP Conf.

The thermal and electron-induced chemistry of biacetyl (CH 3 COCOCH 3 ) on Ag(111) has been studied using temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy. No thermal decomposition of biacetyl occurs, confirming that Ag(111) is inert with respect to the breaking of C-C, CdO, and C-H bonds. There are five molecular biacetyl desorption peaks in TPDs180, 178, 174, 188, and 215 K. The peak at 180 K is attributed to monolayer adsorption, and its saturation peak area is used to scale other TPD biacetyl peaks. The peak at 188 K is assigned to multilayers and that at 215 K to desorption from defect sites. The peaks at 174 and 188 K are discussed in terms of coverage dependent reorientation and bilayers. Nonthermal excitation pathways by which the surface chemistry of biacetyl may be directed were explored by irradiating 1 ML of biacetyl with 50 eV electrons. During irradiation, CO, CH 3 , ketene (H 2 CdCdO), and C 2 H 6 desorb. After irradiation, five new post-irradiation TPD peaks appear. These are identified as H 2 at 210 K, CH 4 at 235 and 315 K, H 2 CdCdO at 240 K, and reaction-limited CH 3 COCOCH 3 at 440 K. XPS shows C (a) and O (a) remain on the surface after heating to 700 K.

R ep rin ted from H ieJournal o f P h y sic a l C h em istry, 1 9 9 3 ,97. C opyright © 1993 by th e A m erican C hem ical S o ciety an d r e p r in te d b y p e r m issio n o f th e copyright ow ner.Adsorption and Decomposition of CF3I on Clean and Iodine-Precovered A g(lll) Received: December 9, 1992; In Final Form: May 13, 1993 To enhance our understanding of the therm al interactions of fluorocarbons w ith transition-m etal surfaces, C F 3I was adsorbed on clean and iodine-precovered A g ( l l l ) and studied by tem perature-program m ed desorption (TPD ), X -ray photoelectron spectroscopy (X P S), ultraviolet photoelectron spectroscopy (U P S ), and A uger electron spectroscopy (A E S). O n clean A g (l 1 1) a t 105 K, dissociative adsorption dom inates a t low coverages and m olecular adsorption a t high coverages. Dissociation involves C -I bond cleavage; there is no evidence for C -F cleavage, even during TPD . W hile m ultilayer desorption peaks near 118 K, chemisorbed C F 3I desorbs in a sharp peak a t 126 K w ith a high-tem perature shoulder near 145 K. T he only other detectable desorption products are C F 3(g) and 1(g), which desorb a t 300 and 830 K, respectively. In the presence of low coverages of 1(a), less C F 3 and m ore C F 3I desorbs. W hen the surface I/A g ratio is 0.33 ( V 3 X * \ / 3R30° structure), the dissociation channel is completely suppressed. T he influence o f atom ic iodine is discussed in term s o f combined electronic and site blocking effects.