| Laser Pulse Desorption Under STM Tip-Cl Removal from Single Site on Si(100) |
14 OCT 96 |
19 pages |
| Authors:
Z. Dohnalek; I. Lyubinetsky; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
 | The desorption of pairs of chlorine atoms influenced by the tip of a scanning tunneling microscope is achieved at preselected sites on the Cl- saturated Si(100)-(2x1) surface using nanosecond laser pulse irradiation of the tip within the tunneling range. Bright features observed for the empty state topographic images after a laser pulse sequence are interpreted to be due to bare Si-Si dimers formed by laser induced desorption of two Cl ... |
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| FTIR Study of the Oxidation of Porous Silicon |
14 OCT 96 |
32 pages |
| Authors:
D. B. Mawhinney; J. A. Glass Jr.; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The oxidation of hydrogen-terminated porous silicon surfaces produced by electrochemical etching has been studied using transmission FTIR spectroscopy. The surface is passivated to oxidation by surface hydrogen below about 523 K. Above this temperature as hydrogen depletion occurs by H2 evolution, Si surface dangling bond sites, capable of O2 dissociation, are involved in initiating the first stage of oxidation. Two reactions are observed. The first, O insertion into Si-Si back ... |
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| Nickel Induced Defects and their Role in Governing Chlorine Chemistry on the Si(100) Surface |
12 JUN 96 |
38 pages |
| Authors:
Z. Dohnalek; W. Yang; V. A. Ukraintsev; W. J. Choyke; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The effect on chlorine surface chemistry of surface defects (split- off dimers) induced by controlled nickel contamination of Si(100) surfaces has been studied. It is shown that the mechanism of chlorine surface etching changes significantly with the presence of a small amount of split-off dimer defects ( direction. This feature is associated with the Cl bonding on the split-off dimer defects, and is similar to that produced on Si(100) surface ... |
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| Silicon Crystal Heating and Thermocouple Mounting Designs |
12 JUN 96 |
24 pages |
| Authors:
H. Nishino; W. Yang; Z. Dohnalek; V. A. Ukraintsev; W. J. Choyke; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| New mounting methods for a silicon crystal and a thermocouple are described. The sample mounted in this design produced a very uniform temperature distribution when resistively heated. Deviations between the silicon temperature and the mounted thermocouple temperature have been measured. Metal contamination on the surface of the sample mounted with a thermocouple by the new methods was found to be below the detection limit of Auger electron spectroscopy. In addition, ... |
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| Electronic Characterization of Defect Sites on Si(OOl)-(2x1) by STM |
27 FEB 96 |
31 pages |
| Authors:
V. A. Ukraintsev; Z. Dohnalek; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| A study of the defect sites on Si(OOl)-(2x1) was undertaken by employing Comparative Scanning Tunneling Spectroscopy (CSTS). Ni induced defects, the A, B, and C defects, and the A and B steps were studied. The STM tip induced band bending significantly affects tunneling spectra. This is evident from comparison of LDOS and local surface potentials obtained for high (10 Ohm-cm) and low (100 Ohm-cm) doped Si(001) crystals. Decay in the ... |
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| Nanosecond Laser Induced Tunneling and Atom Deposition-An STM application to Nanofabrication |
27 FEB 96 |
57 pages |
| Authors:
V. A. Ukraintsev; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| Nanosecond laser pulses, with 2.33 eV photon energy and about 0.6 MW/ cm2 radiation flux, have been used to initiate a transient increase of tunneling current between the tip and sample surface in an ultrahigh vacuum STM apparatus. As the laser power is increased to about 2.5 MW/cm2, single atom transfer from the tip to a silicon surface occurs. For both polarities the laser induced tunneling current is linear with ... |
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| The Role of Nickel in Si(001) Roughening |
10 MAY 95 |
31 pages |
| Authors:
V. A. Ukraintsev; John T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The role of Ni impurities on the structure of the Si(001)-(2x1) surface has been investigated by statistically comparing STM patterns with Auger spectra. Characteristic reconstructed local structures (split off dimers' and vacancy channels') are observed for different surface concentrations of Ni as measured by Auger electron spectroscopy, and it is shown that the STM image provides a high sensitivity to Ni. For high levels of Ni contamination, long range roughening ... |
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| FTIR Studies of CH3OH On Porous Silicon |
NOV 94 |
9 pages |
| Authors:
John A. Glass Jr.; Edward A. Wovchko; John T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| Fourier transform infrared spectroscopy (FTIR) was used to investigate the reaction of methanol with porous silicon and hydrogen passivated porous silicon. At 300 K methanol adsorbs onto hydrogen free porous silicon by cleavage of the O-H bond. Both of the resulting surface species, Si-H and Si- OCH3, were determined to be stable up to approx. 500 K. Above 500 K the Si-0CH3 moiety decomposes by breakage of the C-O and ... |
|
| An Unexpected Adsorption Site Exclusion Process on Si(100)-(2x1) |
05 AUG 94 |
6 pages |
| Authors:
John T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| STM studies are being carried out on Si(100)-(2x1) single crystal surfaces to understand the statistical site distribution of H atoms and Cl atoms. Procedures for producing the clean Si(100) surface with wide terraces have been devised, and preliminary studies have been carried out using three other measurement techniques. |
|
| Photo and Thermal Excitation of Surface Chemistry on Model Catalyst Surfaces |
28 JUN 94 |
|
| Authors:
John T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
 | This is an overview of 16 publications written in the 36 month period of a contract from ARO. The work falls into three main categories: (1) Oxidation of phosphorus on Mo catalyst surfaces, probing the rate limiting step in the oxidative destruction of organophosphonate compounds. (2) Carbon monoxide and oxygen dissociative chemistry on Mo(110) surfaces, probing the fate of CO and oxygen. CO is an important oxidation product in the ... |
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| Chemical Reactions of Chlorine on a Vicinal Si(100) Surface Studied by ESDIAD |
24 MAR 94 |
27 pages |
| Authors:
Z. Dohnalek; Q. Gao; W. J. Choyke; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The reaction of Cl2 on a vicinal Si(100) surface has been studied by ESDIAD. This type of surface possesses two types of sites: pairs of dangling bonds on Si-Si terrace dimers, and single dangling bonds on the 2-atom layer high steps. The reactivity of these two sites is compared. For low coverages the step dangling bonds are identified as the preferred Cl bonding site after 673K- annealing. Upon higher temperature ... |
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| ESDIAD Study of Step Site Bonding on a Vicinal Si(100) Surface Upon Cl2 Adsorption |
14 FEB 94 |
25 pages |
| Authors:
Z. Dohnalek; Q. Gao; W. J. Choyke; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| Characteristic chlorine bonding sites have been detected on a vicinal Si(100) single crystal surface exposing Si(100) terraces. 7-8 Si atoms in width. These terraces are separated by 2-atom layer height steps. Following annealing to 673 K. three C1+ beams are observed by the electron stimulated desorption ion angular distribution (ESDIAD) method. Two of the C1+ beams originate from silicon-dimer dangling bond sites on the Si(100) terraces. The third C1+ beams ... |
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| Direct Images of Thermal Disorder in the Cl-Si and H-O-Si Chemisorption Bond on Si(100) |
27 OCT 93 |
34 pages |
| Authors:
Q. Gao; Z. Dohnalek; C. C. Cheng; W. J. Choyke; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The electron stimulated desorption ion angular distribution (ESDIAD) technique combined with a digital subtraction method have been employed to generate difference ESDIAD patterns between measurements made at 13 OK and 305K for both adsorbed Cl and OH on Si(100). The difference ESDIAD patterns reveal, in real space, images of the thermally excited vibrational amplitudes of the adsorbates. This permits a qualitative visualization of the potential energy surface associated with an ... |
|
| Selected Bibliography II-Diamond Surface Chemistry |
30 SEP 93 |
226 pages |
| Authors:
Jian Wei; V. S. Smentkowski; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| Key articles related to the surface chemistry of diamond crystals are presented in this 1993 update of an earlier compilation. The listings are arranged chronologically. The review extends up to mid-1993. This review will be useful to workers in the field of diamond film-growth chemistry even though the extensive film-growth literature has no been reviewed. Diamond, Surface Chemistry, Bibliography. |
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| The Adsorption and Surface Reaction of SiC14 on Si(100)-(2X1) |
26 MAY 93 |
30 pages |
| Authors:
Q. Geo; Z. Dohnalek; C. C. Cheng; W. J. Choyke; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The adsorption and surface reaction of SiCl4 on Si(100)-(2x1) have been investigated in the temperature range of 100K-1000K. Adsorption of monolayer SiCl4 and multilayer SiCl4 are observed by temperature programmed desorption (TPD), high resolution electron energy loss spectroscopy (HREELS), and electron stimulated desorption ion angular distribution (ESDIAD). Upon heating to approx. 200K and above, Si-Cl bond scission in adsorbed SiCl4 occurs, depositing SiCl(x) species. Heating to 673K leaves the surface ... |
|
| Thermal Disorder in Adsorbed Cl on Si(100) |
21 MAY 93 |
24 pages |
| Authors:
C. C. Cheng; Q. Gao; Z. Dohnalek; W. J. Choyky; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| Thermal broadening of C1(+) ESDIAD patterns, related to the vibrational motion of the adsorbate, has been investigated by subtraction of patterns measured at different temperatures. In the case of C1 on Si(100), the observed difference pattern between 130 K and 305 K indicates that azimuthally isotropic motion of C1 occurs about the most probable Si-C1 bond direction. Equal distributions from the in-plane and out-of-plane bending motions are observed, correlating with ... |
|
| Surface Chemistry of Hydrogen-Passivated Porous Silicon-Oxidation of Surface Si-H Groups by Acetone |
12 APR 93 |
21 pages |
| Authors:
Ling-Fen Rao; John T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The oxidation of hydrogen-passivated porous silicon by acetone at room temperature has been observed by using transmission infrared spectroscopy. After reaction with liquid acetone, two infrared absorption modes at 2253 cm- 1 and 2200 cm-1 develop, and this is accompanied by loss of absorbance of the Si-H stretch modes at 2142 cm-1, 2110 cm-1 and 2089 cm-1. We postulate that oxidation of the surface silicon hydride species by acetone to ... |
|
| Phosphine Chemistry on Mo(110) and Oxidized Mo(110) |
1993 |
8 pages |
| Authors:
X. Zhang; A. Linsebigler; U. Heiz; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The adsorption and desorption of phosphine and the oxidation of phosphorus on Mo(110) and oxidized Mo(110) have been studied by using Auger electron spectroscopy (AES), temperature-programmed desorption (TPD), and low- energy electron diffraction (LEED). Both molecular desorption and dissociative processes were observed on Mo(110), leaving adsorbed P(a) species in a c(4x1) overlayer structure. The P(a) species do not undergo diffusion into the bulk below 1000 K. On the oxidized Mo(110) ... |
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| Electron Energy Loss Investigation of Hole-Plasmon Excitation Following the In situ Doping of Si(111) by Boron |
28 SEP 92 |
24 pages |
| Authors:
P. J. Chen; J. E. Rowe; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| High resolution electron energy loss spectroscopy (HREELS) measurements have been performed on Si(111) surfaces heavily p-doped by the decomposition of adsorbed decaborane. After thermal decomposition of the decaborane to produce B atoms on the surface, the low energy electron diffraction pattern shows a (square root of 3 x square root of 3) R30 deg periodicity due to the presence of 1/3 monolayer of boron in the second complete layer. The ... |
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| Comparison of Cl2 and Hcl Adsorption on Si(100)-(2x1) |
01 JUN 92 |
23 pages |
| Authors:
Q. Gao; C. C. Cheng; P. J. Chen; W. J. Choyke; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The chemisorption and reaction Of Cl2 and HCl on Si(100)-(2xl) have been studied using a variety of measurement methods. At 1OOK, both Cl2 and HCl dissociatively chemisorb on the dangling bonds of Si(100). At saturation coverage, the surface concentration of Cl is about one Cl atom per Si atom while HCl can produce a Cl coverage only one fourth of that achieved with Cl2. This is the first report of ... |
|
| Hydrocarbon Surface Chemistry on Si(100) |
01 JUN 92 |
33 pages |
| Authors:
C. C. Cheng; P. A. Taylor; R. M. Wallace; H. Gutleben; M. L. Clemen; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The interaction of various hydrocarbon species with the Si(l00) surface has been investigated using several surface science techniques. The efficiency of carbon deposition is related to the efficiency of SiC thin film formation. The hydrocarbon species studied include acetylene (C2H2), ethylene (C2H4), and the adsorbed methyl group (CH3(a)). In the case of the chemisorption of acetylene and ethylene, the pi-bond of the olefinic molecules interacts with the dimer unit (Si2) ... |
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| Atomic Hydrogen--A Reagent for the Extraction of Chemical Species from Silicon Surfaces |
01 JUN 92 |
27 pages |
| Authors:
J. T. Yates Jr.; C. C. Cheng; Q. Gao; M. L. Colaianni; W. J. Choyke; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The surface chemistry of adsorbed halogen atoms on Si(100) has been studied using several surface science methods. It has been found that Cl atoms bond to dangling bonds on symmetric Si2 dimer sites, and that the Si-Cl bond angle is tilted from the normal in the vertical plane containing the Si2 dimer bond. The covalently-bonded halogens Cl, Br, and I have been studied on Si(100) using atomic hydrogen bombardment at ... |
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| The Thermal Dissociation of Decaborane on Si(111)-(7x7) and Doping Effects in the Near Surface Region |
01 MAY 92 |
31 pages |
| Authors:
P. J. Chen; M. L. Colaianni; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The thermal decomposition of decaborane (BlOH14) and its doping effects on Si(lll)-(7x7) has been investigated by surface spectroscopies. Upon adsorption between 100-300 K, molecular decaborane was identified on the surface by HREELS by the absence of Si-H surface species production. The thermal decomposition of adsorbed decaborane molecules involves a preferential removal of hydrogen from the weaker B-H-B linkage. H2 thermal desorption was observed to cover a wide temperature range between ... |
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| Silicon Backbond Strain Effects on NH3 Surface Chemistry - Si(111)-(7x7) Compared to Si(100)-(2x1) |
11 MAR 92 |
25 pages |
| Authors:
P. J. Chen; M. L. Colaianni; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The role of surface structure in controlling NH3 surface chemistry has been investigated by HREELS and TPD on Si(lll)-(7x7) and Si(100)-(2xl). Following the initial NH3 dissociative adsorption producing NH2(a) and H(a), the production of >NH(a) species iS favored on Si(lll)-(7x7) between 300-600 K. This is believed to occur through the insertion of >NH(a) into the backbond of the Si adatom on Si(111)-(7x7) and to be driven by the relief of ... |
|
| Interaction of Atomic Hydrogen with the Surface Methyl Group on Si(100) - Removal of Surface Carbon |
06 MAR 92 |
27 pages |
| Authors:
C. C. Cheng; S. R. Lucas; H. Gutleben; W. J. Choyke; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The interaction of atomic hydrogen with an overlayer derived from methyl Iodide on the Si(100) surface has been studied using Auger electron spectroscopy (AES) and temperature programmed desorption (TPD) mass spectroscopy. Efficient removal of surface iodine by reaction with atomic hydrogen is observed. However, experiments with large exposures of atomic hydrogen also show the depletion of surface carbon. In contrast to the almost non-activated behavior observed for the extraction of ... |
|
| The Activation of Chemical Bonds at Surfaces |
27 JAN 92 |
10 pages |
| Authors:
John T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| Studies of the chemisorption, thermal decomposition, and photo decomposition of small molecules on metal and semiconductor oxide surfaces have been carried out. In addition, new methods for research in surface science have been developed. Chemisorption, Photodesorption, Surface chemistry. |
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| Atomic Hydrogen Driven Halogen Extraction from Si(100) -- Eley-Rideal Surface Kinetics |
12 JUL 91 |
23 pages |
| Authors:
C. C. Cheng; S. R. Lucas; H. Gutleben; W. J. Choyke; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The interaction of atomic hydrogen with halogen-terminated Si(100) surfaces was studied by Auger electron spectroscopy (AES) and temperature programmed desorption (TPD) mass spectroscopy. Efficient removal of surface halogen has been observed when the halogen-terminated S1(100) surface was exposed to atomic hydrogen at a substrate temperature, 630 K. The reaction rate constants for halogen extraction on the S1(100) surface follow the trend kI greater than kBr greater than kCl. In addition, ... |
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| Surface Chemistry of Silicon-The Behavior of Dangling Bonds |
22 APR 91 |
|
| Authors:
J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The role of surface dangling bonds in controlling the surface chemistry of Si(100) and Si(111) has been investigated using surface science methods. The adsorption and decomposition of acetylene on Si(100) has been shown to occur by means of mobile precursor mechanism, leading to a di-sigma chemisorbed ethylenic species occupying Si dimer sites on Si(100). This species decomposes at elevated temperatures to produce adsorbed carbon and hydrogen (800 K) and then ... |
|
| Adsorption and Thermal Behavior of Ethylene on Si(100)-(2x1) |
05 MAR 91 |
|
| Authors:
L. Clemen; R. M. Wallace; P. A. Taylor; M. J. Dresser; W. J. Choyke; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The study of the interaction of hydrocarbons with silicon is of importance in understanding the thermally activated formation of adsorbed carbon on silicon. This is the first step in the formation of silicon carbide thin films by chemical vapor deposition (CVD). Silicon carbide is an important material because of its strength, refractory properties, chemical inertness, resistance to radiation damage and its ability to be used as an electronic material in ... |
|
| Inhibition of Atomic Hydrogen Etching of Si(111) |
04 MAR 91 |
19 pages |
| Authors:
P. J. Chen; M. L. Colaianni; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| Subsurface boron reconstructs the Si(111) surface and alters the electronic character of the surface Si atoms. The interaction of atomic hydrogen with the boron-modified Si(111) - (V3xV3) - R30 surface was studied using temperature programmed desorption (TPD), high resolution electron energy loss spectroscopy (HREELS) and low energy electron diffraction (LEED). In comparison to the Si(111) - (7x7) surface, we observe a significantly reduced hydrogen saturation coverage, measured by TPD and ... |
|
| H-Induced Surface Restructuring on Si(100): Formation of Higher Hydrides |
10 AUG 90 |
21 pages |
| Authors:
C. C. Cheng; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| H-induced surface structures on Si(100) were studied using temperature programmed desorption (TPD) mass spectroscopy and low energy electron diffraction (LEED). It is shown that the (3x1) phase consists of mainly monohydride and dihydride structures, while the (1x1) phase is composed of a mixture of mono-, di-, and trihydride surface species. The trihydride surface species is associated with the phase transition between the (3x1) and (1x1) surface phases, and liberates SiH4 ... |
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| Dissociative Adsorption of Ph3 on Si(111)-(7x7). A High Resolution Electron Energy Loss Spectroscopy Study |
07 AUG 90 |
23 pages |
| Authors:
P. J. Chen; M. L. Colaianni; R. M. Wallace; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| Dissociative adsorption of PH3 on Si(111)-(7x7) has been observed at 80 K. The Si-H species is observed to be produced upon PH3 adsorption. Depending upon the PH3 surface coverage, PH3(a) (minority species) and PH2(a) species are found on the surface. The thermal dissociation of the surface PH2 species occurs between 450 and 500 K, resulting in the capture of hydrogen and phosphorus on the surface. Keywords: Phosphine, Silicon, Doping, Phosphorus, ... |
|
| Ni Impurity Effects on Hydrogen Surface Chemistry and Etching of Si(111) |
21 MAY 90 |
20 pages |
| Authors:
R. M. Wallace; C. C. Cheng; P. A. Taylor; W. J. Choyke; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The effect of impurity Nickel on the etching of Silicon by hydrogen chemisorption is examined in ultrahigh vacuum with Auger electron spectroscopy and temperature programmed desorption methods. It is found that a small surface concentration of Ni inhibits the production of Silane from atomic Hydrogen adsorption on the Si(111)-Ni surface. Keywords: Silane, Hydrogen, SiH4, si(111), Ni, Physical chemistry, Impurities, Metal films, AES. (JG) |
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| Background Effects in ESDIAD Measurements on Si(111)-(7x7) |
21 MAY 90 |
21 pages |
| Authors:
R. M. Wallace; P. A. Taylor; M. J. Dresser; W. J. Choyke; J. T. Yates Jr.; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The background effect in electron stimulated desorption ion angular distribution (ESDIAD) measurements due to soft x-ray production on Si(111)-(7x7) is investigated. We find that the background intensity from a Si(111)-(7x7) surface varies linearly with incident electron beam energy and current density. It is also found that the elimination of the background effect (by subtraction) plays a crucial role in both quantitative and qualitative interpretations of digital ESDIAD measurements on silicon, ... |
|
| The Adsorption and Thermal Decomposition of PH3 on Si(111)-(7x7) |
18 MAY 90 |
42 pages |
| Authors:
P. A. Taylor; R. M. Wallace; W. J. Choyke; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The adsorption of PH3 (Phosphine) on Silicon(111)-(7x7) has been studied by Auger electron spectroscopy and temperature programmed desorption. PH3 was found to exhibit two kinds of behavior on the surface. A small surface coverage of molecularly adsorbed PH3 desorbs without and dissociative surface chemistry. For the majority of the adsorbed, PHx species (3>x>1) dissociation occurs to form P(a) and H(a). At 120 K, PH3 initially adsorbs as the reactive species ... |
|
| An ESDIAD Study of Chemisorbed Hydrogen on Clean and H-Exposed Si(111)- (7x7) |
11 MAY 90 |
37 pages |
| Authors:
R. W. Wallace; P. A. Taylor; W. J. Choyke; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The chemisorption of H on Silicon(111)-(7x7) has been studied by digital ESDIAD and temperature programmed desorption methods. It has been found that residual Hydrogen in the bulk of the Si(111) can be transported to the surface upon annealing to temperatures above approx. 1000 K. The adsorption of atomic H on Si(111)-(7x7) results in a mixture of monohydride and polyhydride species as detected by H(+)ESDIAD. Thermal desorption from the H-saturated surface ... |
|
| PH3 Surface Chemistry on Si(111)-(7x7) A Study by Auger Spectroscopy and Electron Stimulated Desorption Methods |
11 APR 90 |
43 pages |
| Authors:
R. M. Wallace; P. A. Taylor; W. J. Choyke; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The adsorption and decomposition of phosphine hydride on silicon (III)-(7x7) was investigated in ultrahigh vacuum by means of temperature programmed desorption (TPD), low-energy electron diffraction (LEED), Auger electron spectroscopy (AES) and electron stimulated desorption (ESD) methods. Phosphine adsorbs on Si(III)-(7x7) at T=120K with an initial sticking coefficient of S(o) equivalent to 1 through a mobile (extrinsic) precursor state. Some PH3 dissociative adsorption at 120 K is observed. Thermal activation of ... |
|
| Adsorption and Decomposition of Chemisorbed Propylene on the Si(100)- (2x1) Surface: A Laser-Induced Thermal Desorption Study |
22 DEC 89 |
16 pages |
| Authors:
Kumar Sinniah; Michael G. Sherman; John T. Yates Jr.; Kenneth C. Janda; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| Deuterated propylene (C3D6) chemisorption and decomposition on the Si(100)-(2x1) surface has been studied in ultrahigh vacuum by using laser induced thermal desorption (LITD) and temperature programmed desorption techniques (TPD). Propylene was found to adsorb molecularly at 110 K and to remain as an undecomposed molecular adsorbate up to approx. 500 K. As the surface temperature is increased, the propylene can both thermally desorb and decompose. ultimately producing a SiC thin ... |
|
| Thermal Stability of the Carbon-Carbon Bond in Ethylene Adsorbed on Si(100): An Isotopic Mixing Study |
10 AUG 89 |
28 pages |
| Authors:
C. C. Cheng; W. J. Choyke; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The interaction of ethylene with the silicon surface has been studied in ultrahigh vacuum using a variety of surface science techniques to investigate the surface complex produced and the nature of the high temperature SiC thin film growth process on the Si(100) surface. Recent studies have shown that on a perfect Si(100) surface a single ethane molecule adsorbs on a silicon dimmer (Si2) site at saturation coverage and a surface ... |
|
| The Orientation of Chemical Bonds at Surfaces: A Key to Understanding the Structure and Bonding of Surface Species |
22 JUN 89 |
18 pages |
| Authors:
John T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| This work has been concerned with the development and use of the digital ESDIAD method for studying the molecular structure and the dynamics of adsorbates on metal single crystal surfaces. A number of new findings have been made involving the following phenomena: (A) First direct observation of the hindered rotation of a chemisorbed molecule; (B) Observation of hydrogen bonding forces between adsorbates causing hinderance of molecular rotation; (C) structural determination ... |
|
| Thermal Decomposition of Chemisorbed Azomethane on Pd(111) |
Jan 1989 |
5 pages |
| Authors:
LLuke Hanley; Xingcai Guo; Yates; J T Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The adsorption and thermal decomposition of azomethane (CH3N=N CH3) on Pd (111) under ultrahigh-vacuum conditions was studied by temperature programmed desorption and work function measurements. Adsorbed azomethane is stable on the surface until N-N bond scission occurs at 250K. Above 280 K, further decomposition forms H(a) and HCN(a) which subsequently desorb at higher temperatures. No C-N bond dissociation is observed on Pd(111). Thus, both N-N and C-H bond cleavages are ... |
|
| The Dissociative Adsorption of Ammonia on Si(100) |
14 DEC 88 |
19 pages |
| Authors:
P. A. Taylor; R. M. Wallace; W. J. Choyke; M. J. Dresser; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The nature of the NH3 adsorption process on Si(100) at 120 K was studied by isotopic mixing with adsorbed atomic deuterium and thermal desorption spectroscopy. NH3 was found to dissociatively absorb onto Si(100) dimers sites at 120 K as NH2(a) and H(a). The NH2(a) species persist up to about 700 K where two reaction channels become available. The major reaction channel leads to the decomposition of NH2(a) to N(a) and ... |
|
| The Adsorption and Decomposition of NH3 on Si(100) - Detection of the NH2(a) Species |
14 DEC 88 |
70 pages |
| Authors:
M. J. Dresser; P. A. Taylor; R. M. Wallace; W. J. Choyke; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
|
| The dissociative adsorption of NH3 on Si(100)(2x1) has been studied using accurate coverage measurements, temperature programmed desorption, Auger spectroscopy and digital ESDIAD/LEED methods. It has been found that NH2 surface species (amino species) are produced to a saturation coverage of 1 NH2/Si dimer at 120 K. This is accompanied by the production of a Si-H surface species. Digital ESDIAD measurements of the H+ angular distribution from NH2(a) species indicate that ... |
|
| Organic Functional Group Reactivities at Metal Surfaces |
DEC 88 |
6 pages |
| Authors:
John T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
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| This report is a summary of the results of an effort to understand the details of chemical bond activation on atomically clean transition metal single crystal surfaces. Modern experimental methods of surface science were employed and developed in this work. The following general classes of chemical bond activation (elementary reaction steps) have been studied on close packed planes of Ni, Pt, Pd, and Mo: O-H; HC-H; C-C; H(3)C-OH; H(3)-CN; H(3)CN-H(2); ... |
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| A New Mechanism for Hydrogen Desorption from Covalent Surfaces: The Monohydride Phase on Si(100) |
12 AUG 88 |
20 pages |
| Authors:
Kumar Sinniah; Michael G. Sherman; Lisa B. Lewis; W. H. Weinberg; John T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
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| A new mechanism for the thermal desorption of molecular hydrogen from the monohydride phase on Si(100) has been identified. The unusual first-order desorption kinetics that are observed are due to the irreversible excitation of a hydrogen adatom into a delocalized, two-dimensional band state on the surface with an activation energy of 47 kcal/mol. The desorption reaction occurs between this excited hydrogen adatom and a second, localized hydrogen adatom. The mechanism ... |
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| X-Ray Photoelectron Spectroscopy Study of Si-C Film Growth by Chemical Vapor Deposition of Ethylene on Si(100) |
18 JUL 88 |
36 pages |
| Authors:
P. A. Taylor; M. Bozack; W. J. Choyke; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
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| The growth of a thin film of silicon carbide grown by chemical vapor deposition (CVD) of ethylene on Si(100) at 970 K was studied by X-Ray Photoelectron Spectroscopy (XPS). The growth of the film was observed through the behavior of the Si(2p) and C(1s) core levels and their plasmon losses. A 1. 2eV (towards higher binding energy) shift is observed for the Si(p) binding energy between silicon in Si(100) and ... |
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| Construction of Pierced Hemispherical Grids |
29 JAN 88 |
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| Authors:
Patrick A. Taylor; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
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| This report describes an easy way to construct hemispherical grids and a procedure to cut holes of any shape through the grids without distorting the grid itself. The grid material may be either stainless steel or tungsten. The grid is made from a high transparency 100x100 screen mesh woven with 0.001 inch diameter wire. The grids are shaped and spot welded onto stainless steel annular rings. Once attached to the ... |
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| Control of the Surface Reactivity of the Si(100) Surface |
16 FEB 87 |
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| Authors:
John T. Yates Jr.; M. J. Bozack; L. Muelhoff; W. J. Choyke; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
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| Molecular beam methods and temperature programmed desorption have been used to probe the reaction of several hydrocarbons with the Silicon (100) surface at cryogenic temperatures. It has been found that the kinetics of the surface reaction with the C=C bond can be strongly influenced by the production of active surface sites using prebombardment with Ar ions. The chemistry of the adsorbate is also influence by electron bombardment of the adsorbed ... |
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| Si-F Bond Directions on Si(100). A Study by ESDIAD |
05 JAN 87 |
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| Authors:
M. J. Bozack; M. J. Dresser; W. J. Choyke; P. Taylor; J. T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
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| The first observation of ion angular distribution originating from electron stimulated desorption of an adsorbed atomic species on a semiconductor surface (ESDIAD) is described. F+ is emitted from Si(100)-(2 x 1) along 4 azimuths corresponding to the principal crystal axes. The most probable F+ energy is 2.4 eV. The F+ angle, alpha = 36 + or - 5 degrees to the surface normal, corresponds closely to the Si-F surface bond ... |
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| Structure of Molecular Adsorbates on Surfaces |
08 AUG 86 |
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| Authors:
John T. Yates Jr; PITTSBURGH UNIV PA SURFACE SCIENCE CENTER
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| This project had as its primary objective and extension of the ESDIAD (Electron Stimulated Desorption Ion Angular Distribution) method to the study of interesting molecular adsorbates structure on single crystal surfaces. A second objective was to develop a digital ESDIAD apparatus capable of more accurate study of ion angular distributions from the ESDIAD phenomena. The fundamental fact that positive ions are ejected from adsorbates along the fragmentation bond direction was ... |
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