Adsorption and Thermal Reaction of Short-Chain Alcohols on Ge(100)

Abstract

The adsorption and thermal decomposition of alcohols (CH 3 OH, C 2 H 5 OH, and C 4 H 9 OH) on Ge(100) were investigated with temperature-programmed desorption and Xray photoelectron spectra. At 105 K, CH 3 OH adsorbs both molecularly and dissociatively on Ge(100). Chemisorbed CH 3 OH molecules dissociate to form surface CH 3 O and hydrogen in a temperature range 150−300 K. Surface CH 3 O can dehydrogenate to yield CH 2 O as two desorption features, which depend on coverage. At small coverage, surface CH 3 O undergoes mainly α-hydrogen elimination to desorb CH 2 O at 490 K. At large coverage, another desorption of CH 2 O occurs predominantly at 525 K, which is initiated by a recombinative desorption of CH 3 OH. A calculation with density functional theory at the B3LYP/6-311+G** level shows that the dissociation of the O−H bond has a much smaller barrier (<40 kJ/mol) than those for C−O bond cleavage (>150 kJ/mol). Desorption of CH 2 O results from the moderate barriers (∼110 kJ/mol) for cleavage of the C−H bond of surface CH 3 O and weak adsorption energy of CH 2 O (−56 kJ/mol). The recombination of surface CH 3 O with H occurs at large coverage with an energy barrier 127−140 kJ/mol. Similarly to CH 3 OH, C 2 H 5 OH and C 4 H 9 OH undergo the mechanism of thermal reactions through formation of alkoxyl intermediates. The longer-chain alkoxyl decomposes to desorb aldehyde at lower temperature because the interaction of its alkoxyl chain with the surface is stronger. On annealing to ∼570 K, all alkoxyl groups are completely removed from the surface via dehydrogenation and recombination to desorb aldehyde and alcohol, respectively. At a large coverage, the longer-chain alkoxyl undergoes dehydrogenation to a larger extent than recombinative desorption.

Reaction Behaviors of S‐, O‐, and N‐containing Aliphatic Molecules with a Propyl Moiety on Ge(100) Surface

“…In Figure 2b, we observed a single O 1s peak at 530.9 eV, which is assigned to the OÀ H dissociated structure, according to previous research on a Ge(100) surface, where the O 1s peak related to OÀ H dissociated species with a neutral oxygen atom emerges at 530.6-531.5 eV. [12,28,29] Hence, we suggest that 1-propanol reacts with the Ge(100) surface via OÀ H dissociation. As shown in Figure 2e, we resolved the C 1s signal as two distinct peaks at 284.4 and 285.5 eV.…”

Ring-Opening Reaction of Tetrahydrofuran on Ge(100) Surface

“…A previous investigation has reported that the binding energy of the C 1s peak corresponding to molecularly absorbed Ge–OHCH 3 was observed at 286.3 eV because the carbon atom in the methyl group is influenced by the positively charged oxygen atom next to it. 18 Therefore, we assigned the peak at 286.3 eV to C α because of the effect of the adjacent positively charged oxygen atom bonded to this carbon atom. When tetrahydrofuran and diethyl ether molecules are adsorbed on Si(100) via the formation of O dative bonds, the difference in the binding energies between C α and C β was in the range of 1.0–1.5 eV.…”

“… 2 , 13 − 16 The analogous reactions used in organic chemistry are relatively well known on a Si(100) surface, 17 whereas those performed on Ge(100) are limited as a result of the differences in the chemical reactivity and electronic structures between the two surfaces. 15 , 18 …”

Synthesis of Antitumor Fluorinated Pyrimidine Nucleosides

“…Attempts to introduce the pentyloxycarbonyl group directly on an unprotected 5 0deoxy-fluorocytidine led to the development of new reagents, different from the usual 615 pentylchloroformate, able to selectively functionalize the N-4. With this purpose in mind, starting from N-hydroxysuccinimide 143 , a new pentylcarbonate 130 was recently prepared in 98% yield that selectively functionalized the unprotected 5 0 -deoxy-fluorocytidine at N-4, affording capecitabine 63 in 44% yield (Scheme 73).…”