Bernard R. Zegarski

Complex CO–potassium interactions on Cu(100): An electron energy loss, thermal desorption, and work function study

A detailed examination of the adsorption states of carbon monoxide on a potassium‐dosed Cu(100) surface is reported. High resolution electron energy loss spectroscopy (EELS) studies on surfaces with a variety of potassium precoverages indicate the presence of at least seven different C–O vibrational modes ranging in frequency from 900 to 2090 cm−1 with as many as five modes observed simultaneously. Thermal desorption spectroscopy (TDS) demonstrates at least five states of CO coadsorbed with potassium with desorption maxima occuring over a range from 120 to 600 K. Low resolution EELS and work function changes are discussed as well. The complexity of the high resolution EELS and TDS measurements precludes models involving only one or two types of potassium–CO interactions. In this system we suggest that potassium influences CO adsorption by, (1) indirectly increasing 2π* backbonding, (2) indirectly changing bonding sites, and (3) effecting a direct interaction of adsorbed CO with one, two, or possibly three...

Selectivity and Copper Chemical Vapor Deposition

The question of selectivity (on metal vs. insulator) in the growth of copper thin films from organometallic precursors is addressed by studying the adsorption of Cu(hfac)(vtms) (where hfac=1, 1,1,5,5,5-hexafluoroacetylacetonate and vtms=vinyltrimethylsilane) on high surface area silica using transmission infrared spectroscopy. No deposition is observed on dehydrated SiO 2 . In the presence of adsorbed, hydrogen bonded OH (OD) groups (from the dissociative adsorption of either water or ethanol-d 6 ), thin film growth is nucleated and selectivity is lost

Rotational excitation in the electron impact ionization of supercooled N2

Electrons of controlled energy have been used to ionize and electronically excite N2 cooled to a translational temperature of <2 °K in a supersonic expansion either of pure N2 or 10% N2/Ar. This source likely provides N2 molecules ’’frozen out’’ in their N′′ = 0 and 1 rotational levels. The rotational state distribution of B 2Σ+uN+2 was determined by monitoring the rotationally resolved emission spectrum. Observation showed that even at high (∼500 eV) impact energies, the N+2 rotational distributions are inconsistent with selection rules (ΔN = ±1) for dipole excitation from N′′ = 0 and 1. For lower electron impact energies the angular momentum content of the excited N+2 ion increases sharply. These observations are rationalized by a model which invokes interactions between the ion and the ejected electron.

Aluminum thin film growth by the thermal decomposition of triethylamine alane

Abstract Triethylamine alane (TEAA) decomposes on an Al(111) single crystal surface at temperatures above ∼310 K to yield pure aluminum thin films, liberating hydrogen and triethylamine into the gas phase. Aluminum deposition is epitaxial and clean (no carbon or nitrogen containing species are observed by Auger electron spectroscopy). The film growth rate is limited by the rate of the recombinative desorption of hydrogen from the surface. These results are compared to similar data from experiments on the surface-mediated thermal decomposition of trimethylamine alane.

Temperature induced reconstruction of model organic surfaces

Abstract The influences of temperature on the structure of hexadecanethiol (C 16 ) and heptadecanethiol (C 17 ) monolayers adsorbed on gold substrates are reported. Infrared Spectroscopy and molecular dynamics simulations show that defects in these layers (i.e. gauche conformations) are concentrated at the chain termini and decrease with decreasing surface temperature. Adsorption band intensity oscillations as a function of chain length show that the chain terminating group is highly oriented. Band splittings observed at low temperature establish that there must be at least two chains per unit cell. The temperature dependence of the spectral band intensities of the polymethylene chains is very similar to that found in bulk hydrocarbon crystals.

Laser induced fluorescence spectrum of gaseous C6H+6

A laser induced fluorescence spectrum of the radical cation, C6H+6, of dimethyl‐diacetylene has been observed in the gas phase. Vibrational structure is clearly resolved, analyzed, and compared with earlier data on C6H+6 from matrix isolation studies. Observations are reported that are relevant to the photodissociation of C6H+6 as well as possible Jahn–Teller distortion of the ? 2E1g and ? 2E1u states.

The fine structure of the B 2Σ+ and a4Σ+ states of CN as determined by molecular anticrossing spectroscopy

The anticrossing between the B 2Σ+, v=11, N=20 and the a4Σ+, N=20 states of CN has been investigated in detail. The width and shape of the anticrossing signal are shown to be dependent upon the fine structure constants of the two states. Computer fits to this line shape have determined the spin–rotation constants of the states, the spin–spin constant of the quartet, the zero field separation, and a firm upper limit to the strength of the perturbation between the states.

Singlet—triplet anticrossings and the electronic isotope shift in D2

Abstract Anticrossings between the 3d 1 Π g and the 3d 3 Π g states of D 2 have been used to determine the relative positions of singlet and triplet levels, and T e , T 0 and the electronic isotope shift for the a 3 Σ state. An ab initio calculation of the a 3 Σ state differs from experiment by only 1 or 2 cm −1 , a difference, however, that exceeds the experimental error estimates.

The influence of electron-withdrawing substituents on the adsorption of CO on copper

Abstract The chemisorption of carbon monoxide on Cu(100) in the presence of either methyl chloride or formic acid results in an increase in the the CO stretching frequency to above the gas-phase value and a simultaneous increase in the heat of adsorption of CO. We explain this behavior qualitatively in terms of the simple Lewis acid/base character of both the surface and the adsorbate.

The activated adsorption of silane on nickel

Abstract The dissociative adsorption of silane (SiH 4 ) on Ni(100) was studied using Auger electron spectroscopy, thermal desorption mass spectroscopy, high resolution electron energy loss spectroscopy, and low-energy electron diffraction. The effects of varying the surface temperature (100–1200 K), the gas temperature (300–600 K), and deuteration (SiD 4 versus SiH 4 ) were examined. Adsorption occurs through an extrinsic precursor state with the reactive sticking coefficient ( S r ) increasing approximately linearly with increasing surface temperature. Raising the gas temperature is also effective at increasing S r . We find no significant change in ( S r when SiD 4 is adsorbed indicating that motion of the central silicon atom is most likely involved in the transition state. At surface temperatures less than 250 K the stable species is a silyl (SiH 3 ) group. The dissociation of this species, the formation of Ni 2 Si thin films, and the dissolution of silicon into bulk nickel are also discussed. Our results are compared to recent studies on the adsorption of CH 4 on nickel and silane on silicon.