Jong Liang Lin

Iodomethane dissociation on Cu(111): Bonding and chemistry of adsorbed methyl groups

The chemistry of iodomethane on a Cu(111) surface has been studied by a combination of work function measurements, Auger electron spectroscopy, high‐resolution electron energy‐loss spectroscopy, and temperature programmed reaction spectroscopy. Our results show that iodomethane dissociates below 200 K to form iodine atoms and methyl groups, which are stable up to 400 K. At low coverages, the methyl groups bond with Cs symmetry and at high coverages with C3v symmetry. The methyl group stretching frequency on the surface is redshifted by ∼150 cm−1 compared to that of iodomethane. Possible bonding sites as well as reasons for the stretching mode softening and coverage‐dependent orientation of methyl groups are discussed. The surface reactions of methyl groups on Cu(111) are coverage dependent. At low coverages, CH3(a) decomposes at 450 K to evolve methane, ethylene, and propylene. α elimination from methyl groups to produce CH2 and H is the rate‐determining step in forming these products. At higher coverages...

FTIR study of adsorption, thermal reactions and photochemistry of benzene on powdered TiO2

The adsorption, thermal reactions, and photochemistry of benzene on powdered TiO2 have been investigated using Fourier-transform infrared spectroscopy. Benzene is adsorbed with its π electrons interacting with the surface Ti4+ ions, and is stable even when the TiO2 temperature is increased to 400°C. However, it is subject to thermal decomposition to H2O(g), CO(g) and CO2(g) in the presence of O2 and the dissociation occurs below ∽225°C. With the aid of an adsorption study of phenol and iodobenzene, it is found that phenoxy groups are generated on the surface in the photooxidation of benzene on TiO2 and the amount greatly increases in the presence of H2O or O2. Other surface products containing carbonyl or carboxylate groups are produced as well for benzene photoreaction in O2. The present in situ study shows that the products extracted using solvents from TiO2 catalysts after photooxidation of benzene in previous investigations may not reveal the real products formed on the surface during photoillumination processes.

N-doped, porous TiO2 with rutile phase and visible light sensitive photocatalytic activity

Nitrogen-doped, porous rutile has been prepared by hydrothermal reaction of TiN in nitric acid, with the nitrogen atoms present in the interstitial sites and in the form of adsorbed nitrate ions. The N-rutile powder exhibits outstanding photocatalytic activity toward degradation of adsorbed methylene blue under visible light irradiation.

CH vibrational mode-softening in alkyl groups bound to Cu(111)

Abstract The surface vibrations of C 1 C 3 alkyl groups bound to a Cu(111) surface have been studied by high resolution electron energy loss spectroscopy. The alkyl groups were generated by the dissociative adsorption of alkyl iodides and bromides. All of the adsorbed alkyls show CH stretching mode-softening, and isotope labelling studies indicate that the softened CH bonds are those at the α-carbon (the one bonded to the surface). Our results suggest that charge donation from the metal to the antibonding orbital of the alkyl groups is the cause of the CH stretching mode-softening.

Thermal and electron‐stimulated chemistry of Fomblin–Zdol lubricant on a magnetic disk

The thermal and electron‐induced decomposition of Fomblin–Zdol lubricant on a rigid magnetic disk with a hard carbon overcoat are studied by temperature‐programmed reaction/desorption spectroscopy and electron stimulated desorption. The thermal spectroscopy shows two desorption features peaked at 640 and 700 K resulting from decomposition of the Fomblin–Zdol molecules. The threshold temperature for dissociation of the Fomblin–Zdol molecule is at 500–550 K in accordance with the known thermal stability of the free molecule. HF originating from thermal reactions with either surface OH or surface CH groups is a prominent desorption product. Electron impact also causes Fomblin–Zdol dissociation. Two efficient mechanisms for electron impact dissociation have been resolved separately above and below the ionization threshold of ∼14 eV. The low‐energy process is likely due to the formation of negative ions followed by dissociation (dissociative electron attachment) and has a cross section of ∼2×10−16 cm2. These results show that Fomblin–Zdol as a lubricant on a magnetic disk is inherently unstable thermally and in the presence of triboelectrons.

Adsorption and photochemistry of CH3CN and CH3CONH2 on powdered TiO2

The adsorption and photochemistry of acetonitrile and acetamide on TiO2 have been studied by Fourier-transform infrared spectroscopy (FTIR). Adsorbed CH3CN, CH3CONH2, η2(N,O)-CH3CONH are formed after CH3CN adsorption on TiO2. The last two species are due to surface hydroxy groups attacking the electron-deficient carbon in the cyano group of the adsorbed acetonitrile. UV exposure causes decomposition of CH3CN(a) to CH2CN(a) and decomposition of CH3CONH2(a) and η2(N,O)-CH3CONH(a) to CH3COO(a), HCOO(a), NCO(a) and CN-containing species on the surface.

Interaction of hydrazine and ammonia with TiO2

Adsorption and reaction of N2H4 and NH3 on powdered TiO2 have been studied by Fourier-transformed infrared spectroscopy. N2H4 decomposes on the surface to form NH3 and surface hydroxy groups at temperatures higher than ∽150°C. Based on these findings, a N2H4 reaction pathway on TiO2 is established to be N2H4→2NH2→NH+NH3 and NH+O(l)→N+OH(ads). NH3 decomposes on the surface and forms adsorbed azide N3(ads) species at temperatures higher than ∽350°C. Photooxidation of NH3 and ND3 is investigated as well and the mechanism is discussed in terms of the NH2 reaction pathway and recent reports for the reactions between NHx and NOx (x=1–2) in the gas phase.

FTIR study of interactions of ethyl iodide with powdered TiO2

The adsorption, thermal reactions, and photochemistry of C2H5I have been studied on TiO2 by Fourier-transformed infrared spectroscopy. C2H5I is adsorbed on TiO2 and remains intact at 35°C. However, it decomposes to form C2H5O(a) at temperatures below 200°C in vacuum. It is found that this decomposition process is enhanced by the presence of isolated surface hydroxy groups. In the study of the thermal reaction of C2H5I on TiO2 in a closed IR cell without O2, ethylene is the only gas product detected. However in the presence of O2, in addition to ethylene, H2O, CO and CO2 are generated together with surface species probably derived from the adsorption of another product of acetaldehyde. In the photochemistry of C2H5I on TiO2 in forming surface formate and acetate, which are probably produced ia acetaldehyde intermediate, O2 plays an essential role. It is likely that the photoreaction is initiated by O2−, generated from photoelectron capture by adsorbed O2.

Thermal reactions of fluorocarbon and hydrofluorocarbon species on Si(100)‐(2×1)–CF3I, CF3CH2I, and C2F4

The thermal reactions of CF3I, CF3CH2I, and C2F4 are studied by temperature‐programmed reaction/desorption (TPR/D) on a Si(100) surface. CF3I, CF3CH2I dissociate on the surface, whereas C2F4 adsorbs reversibly, without dissociation. Dissociation of the iodine‐containing molecules is probably initiated by the cleavage of the relatively weak C–I bonds. In the case of CF3I, the C–I bond dissociation generates I(a) and CF3(a). I(a) desorbs as atomic I. CF3(a) dissociates in sequence, producing gas phase SiF2 and SiF4 and a carbon deposit on the surface. In the case of CF3CH2I, the C–I bond dissociation generates I(a) and CF3CH2(a). CF3CH2(a) undergoes β–F elimination to form gas phase CF2CH2 as well as further decomposition on the surface. At higher temperatures H2, I, HI, and SiF2 desorb and carbon deposits on the surface.

THERMAL- AND ELECTRON-STIMULATED CHEMISTRY OF A CYCLOTRIPHOSPHAZENE LUBRICANT ON A MAGNETIC DISK WITH A HARD CARBON OVERCOAT

The thermal and electron induced decomposition of a bis(4‐fluorophenoxy)‐tetrakis(3‐tri‐ fluoromethylphenoxy)cyclotriphosphazene(code‐named X‐1P) lubricant on a magnetic disk are studied by temperature‐programmed desorption spectroscopy, electron‐stimulated desorption, and Auger electron spectroscopy. X‐1P decomposes on the surface with a threshold temperature for dissociation at ∼570 K, ∼100 K lower than the thermal decomposition temperature of fluid molecules. Electron impact also damages X‐1P molecules. Depending on the electron energies, dissociative ionization and dissociative electron attachment are both likely mechanisms for the electron‐induced dissociation. The cross section for the dissociative electron attachment by 3 eV electrons is roughly 9×10−18 cm2. For both 8 and 25 eV electrons the cross sections are larger.