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Structural and light-emitting properties of nanoparticles of ZnS:Mn annealed in vacuum at temperatures up to 525 °C are presented. Annealing the 3.5 nm particles at temperatures up to 350 °C caused growth of some particles without substantial change in the luminescence or ZnS lattice. After annealing at 400–525 °C, the high-temperature wurtzite phase of ZnS appeared, accompanied by an increase of the average particle diameter to approximately 100 nm and a rearrangement of the Mn ions. Dramatic increase in cathodoluminescence emission was also observed and is compared to the structural information obtained from electron microscopy, x-ray diffraction, x-ray absorption fine structure, and electron paramagnetic resonance measurements.

Selective area deposition of platinum suicide on exposed silicon areas of n-type, Si(100) substrates patterned with a polyimide resist has been demonstrated by using the thermal decomposition of the molecular precursor, Pt(PF3)4, under chemical beam conditions. Selectivity was studied as a function of precursor partial pressure, substrate temperature and duration of deposition. Selectivity was most easily obtained at a precursor partial pressure of 1.33 × 10−4 Pa, substrate temperature of 250 °C and deposition times ranging from 18 to 30 min. Atomic force microscopy, Auger electron spectroscopy, and X-ray photoelectron spectroscopy analyses of selectively deposited films strongly suggested the complete interdiffusion of Si and Pt. Speculations on possible mechanisms for selectivity are discussed.

Conductive, adherent copper films were deposited selectively on diamond substrates using ligating aminosilane self-assembled films and a Pd-based catalyst. Copper chemical vapor deposition (CVD) was performed at 444-456 K in a cold-walled chamber using 4 x 10 -3 Pa of (hexafluoroacetylacetonato)-copper(I)-trimethylvinylsilane mixed 1 :1 (v/v) with H 2 carrier gas. In the absence of the Pd catalyst, only isolated copper particles deposited on hydrogenated or aminosilane-coated diamond. The Pd catalyst enhanced selectivity for Cu deposition by a factor of 10 3 to 10 4 . Copper patterns with feature sizes to 1 μm were formed by lithographically patterning an aminosilane film on diamond using UV (193 nm) radiation and a contact mask prior to catalyst deposition and copper CVD. The Pd catalyst also enhanced Cu deposition on aminosilane-coated Si(100) and quartz substrates. Treating substrates with octadecylsilane or aminosilane self-assembled films without the bound Pd catalyst reduced copper deposition compared to Si(100) native oxide or hydrogenated diamond surfaces.

Multiwalled carbon nanotubes were grown using chemical vapor deposition inside small apertures having a horizontal gate and a sidewall insulator spacer. Emission currents up to 140 nA per cell at 63 V have been obtained. These arrays have exhibited a gate current as low as 2.5% of the anode current throughout the entire gate voltage range, representing the lowest gate to anode current ratio of gated nanotube emitters reported to date. We attribute this feature to the emitter geometry and method of fabrication. The overall fabrication method required only a few and simple processing steps.

Multiwalled carbon nanotubes were grown using chemical vapor deposition on the tops of blunt vertical silicon posts in cells having a horizontal gate aperture of conventional field emitter design. We obtained over 1 mA total emission current from a single array, or 0.3 μA per cell at 40 V. In addition to the low voltage operation, the most distinctive differences from conventional field emitter arrays include their stability and the lack of catastrophic arcing without any special sample preparation.

The adsorption of CO on Ni(111), ion bombarded with various fluences of 1.0 keV Ar+ ions, has been investigated using photoemission from adsorbed xenon (PAX). After ion bombardment of the Ni(111) surface, various amounts of CO were adsorbed, followed by adsorption of xenon at 85 K. Two pressures of xenon were used in examining the 3d 5 2 peak of xenon: 5 × 10−6 and 7 × 10−10 Torr. PAX data taken at both pressures show that CO selectively adsorbs onto the defect (step) sites created by ion bombardment. In addition, it was found that the amount of CO which could occupy a defect site previously occupied by one Xe atom varied from 10 to 2.5, depending on the ion fluence.

The surface defect density generated by 1.0 keV Ar+ ion bombardment of a Ni(111) crystal at 88 K is studied with photoemission of adsorbed xenon (PAX). The defect sites are distinguished by the position of the Xe 3d5/2 peak. The peak position reflects the local electrostatic potential at the Xe adsorption site that is modified at a defect site from the terrace sites by the electron‐density smoothing process. The PAX spectra of the ion bombarded surfaces have peaks at 669.3 eV from Xe adsorbed at terrace sites, 670.0 eV from Xe at step sites, and 671.0 eV. We ascribe the latter peak to Xe adsorbed at small vacancy islands or kink sites where the Xe atom can experience a larger electrostatic potential perturbation compared to Xe adsorbed at a step site producing the additional 1 eV shift to higher binding energy. The PAX spectra are acquired with two ambient Xe pressures, 7×10−10 and 5×10−6 Torr. At low Xe pressure, the total Xe coverage and step peak intensity rapidly increase with low ion fluence with ini...

A low-voltage, low-capacitance, field emitter array (FEA) electron source has been developed for applications such as field emitter displays, high-voltage switches, and high frequency power amplifiers. The FEA cell has a horizontal gate and a vertical edge emitter made by sandwiching a low-work-function lithium dispenser thin film between two ruthenium films. We measured a low turn-on voltage (several nanoamps at 27 V) and high collected current (16 μA at 62 V) from 1 to 3 cells. Based on chemical beam deposition, the fabrication method allows all the FEA cell dimensions to be independently adjustable. Our FEA has many potential advantages in performance such as low capacitance, low voltage, high transconductance, high current, and resistance to oxidation and to erosion by back-ion bombardment. Furthermore, much lower manufacturing cost should result from the significantly fewer processing steps.

X-ray-diffraction studies of nanometer-sized particles of zinc sulfide show a significant reduction in the zinc-blende-to-wurtzite phase transition temperature, as compared to the bulk value. Five nanoparticle samples were annealed in vacuum at temperatures increasing from room temperature (23 \ifmmode^\circ\else\textdegree\fi{}C) to 500 \ifmmode^\circ\else\textdegree\fi{}C. Post-anneal analyses revealed an increase of crystallite size, accompanied by a partial transformation from the cubic, zinc-blende structure to the hexagonal, wurtzite structure at temperatures as low as 400 \ifmmode^\circ\else\textdegree\fi{}C. This is significantly less than accepted bulk transition temperature of 1020 \ifmmode^\circ\else\textdegree\fi{}C. The particles also show some lattice distortion with decreasing particle size and there is a monotonic reduction in the specific volume of about 2.3% as the particle size decreases from about 240 to about 30 \AA{}.

We have synthesized nanoparticles of ZnS doped with Mn for potential use as cathodoluminescent phosphors in field-emission displays (FEDs). We show that the cathodoluminescent efficiency of particles ⩽100 nm in diameter is within 40% of that of a commercial (micron-sized) phosphor when the electron-beam energy ranges between 500 and 3500 eV. The nanoparticles exhibit less current saturation than larger-sized phosphors, an important feature for use in FEDs. Furthermore, the nanoparticles were annealed at just 535 °C, hundreds of degrees below the processing temperatures of standard phosphors. Finally, we discuss the effect of the particle surface on low-voltage luminous efficiency.

The photochemistry of trimethylindium (TMI) adsorbed on a quartz substrate at 150 K has been studied by time of flight mass spectrometry (TOF/MS) using electron impact ionization and resonance-enhanced multiphoton ionization techniques. Photolysis of adsorbed TM1 at 222 nm results in the deposition of indium metal on the surface and the ejection of neutral and ionic fragments into the gas phase. The gas-phase photofragments observed were the neutral products In(CH 3 ) 2 , InCH 3 , In, and CH 3 and the ions In + , CH 3 + , and In(CH 3 ) +

Laser induced fluorescence has been used to study the desorption dynamics of OH radicals produced by the reaction of NO2 and H2 on Pt(111), under ultrahigh vacuum conditions. We measure an apparent Arrhenius activation energy for desorption that increases from 25 to 38 kcal/mol as the NO2 to H2 ratio in the dosing mixture decreases from 2 to 0.05. Boltzmann‐like rotational energy distributions with relatively high rotational to surface temperature ratios (Tr/Ts =0.69−0.87) are reported for crystal temperatures between 1078 and 1433 K. We have also observed a small but definite dependence of the Tr/Ts ratio on both Ts and the dosing mixture ratio. These results are compared with earlier data from the O2+H2 reaction over Pt(111) and interpreted in terms of O coverage.

Novel X-ray sources and applications may be achieved with a combination of gateable electron micro-sources and tailored electron targets. A simple, broad area X-ray source can be constructed in a biplanar geometry, one side consisting of a low atomic number, X-ray transmissive substrate with an array of emitters, and the other side a simple metallic target. The simple metallic target can be replaced with a composite target in which different areas of the surface are coated with different X-ray emitting metals. The resulting X-ray spectrum will be the composite of spectra of all the irradiated metals. The spectrum is selected with sets of separately gated field emitter arrays, each registered to a respective anode metal. Low voltage electronics control the gate array selections. With the further addition of electron focusing within the tube and an external X-ray detector, the device becomes capable of imaging the composition of the electron target. By augmenting the device with a sample handling capability, whereby the sample is put in the location of the target, this instrument then becomes capable of X-ray compositional analysis in a manner analogous to an electron microprobe or SEM with EDX attachments. Such instruments can be miniaturized and used for automated analysis systems. The potential for low power, automated analysis by small, unmanned, distributed systems could augment the capabilities already present with high power laboratory instrumentation. An important technical issue on which the practicality of these developments depends, is the robustness of gated field emitter sources. Recent progress in this area is described.

The difficult aspect of conformal metal film deposition in narrow, high aspect ratio trenches such as those used in the fabrication of high density metal‐oxide‐semiconductor trench capacitor cells for computer memory technology is addressed. This work demonstrates the proof of principle of highly conformal deposition of a 40 nm Pt film on the surfaces of a 0.5‐μm‐wide, 1.5‐μm‐deep, and 2‐mm‐long array of oxidized silicon trenches, using the thermal decomposition of a molecular precursor under chemical beam conditions. In addition, scanning electron, x‐ray photoelectron, and scanning Auger electron microscopy analyses reveal highly uniform and complete coverage on all surfaces, small metal grain size, and the absence of detectable impurities.

Vertical platinum sidewall structures 50 nm thick and 700 nm tall have been fabricated by Pt deposition from the thermal decomposition of tetrakis‐(trifluorophosphine)‐platinum using an effusive gas source followed by ion‐assisted etching. Scanning electron microscope micrographs show that the sidewalls have high uniformity, very fine grains, and very sharp contours, demonstrating a high degree of conformal deposition. Scanning Auger microscopy confirms the presence of platinum only in the sidewalls. X‐ray photoelectron spectroscopy analysis of the as‐deposited platinum film reveals no detectable impurity and Scotch tape test shows good bonding of the film. The method is suitable to large‐scale processing.

A new field emitter array (FEA) electron source has been developed which includes a hollow cylindrical multi-layer thin-film-edge low work function emitter and a low capacitance horizontal extraction gate. The field emitter is made by sandwiching a low work function lithium thin film between two high work function noble metal thin films to create a lithium dispenser field emitter in each FEA cell. Our fabrication method, based on conformal chemical beam deposition, is self-aligned and consists of very few processing steps compared to conical or pyramidal FEAs. The structure is fundamentally tolerant to back ion-bombardment and insensitive to poisoning as determined by cycling the operating emitter from 10 -8 to 10 -6 Torr of room air for several hours with no significant change in emission current. Using an extraction voltage of 62 volts we measured 16 microamps from 1-3 FEA cells. No special activation is required either for initial turn-on or when taking the FEA out to air and back again to vacuum. We believe this new FEA should be scalable and inexpensive for manufacturing low-cost FEDs. The chemistry, fabrication, and emission characteristics will be discussed in this talk.

We have synthesized oxide and sulfide based nanoparticles doped with Mn for potential use as cathodoluminescent phosphors in field-emission displays. Earlier work ion nanophosphors had raised the question whether it is possible to achieve high efficiency using particles that are less than approximately 1 micrometers in size. Although high photoluminescent efficiency had been achieved in particles as small as 3 nm, high cathodoluminescent efficiency has not been reported in nanoparticles. We show, for the first time, that the cathodoluminescent efficiency of nanoparticles is comparable to that of commercial phosphors especially for electron beam energy ranges between 500 V and 3 kV. For example, the luminescence of ZnS:Mn nanoparticles is within a factor of 2.5 of the commercial product at 650V. And, for the Zn2SiO4:Mn nanophosphor we have indeed exceeded the luminance of the commercial product. We stress the importance of a capping layer on the sulfide-based nanophosphors for improved stability and performance.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Selective chemical vapor deposition (CVD) of conductive, adherent copper films was achieved on single-crystal and polycrystalline diamond substrates modified with a ligating aminosilane and a Pd-based catalyst. Only isolated copper particles deposited on hydrogenated or aminosilane-coated diamond substrates without Pd. The Pd catalyst enhanced selectivity by a factor of 103 to 104. Copper CVD was performed in a cold-walled chamber at 446-456 K and 8x10-3 Pa using hexafluoroacetylacetonate-Cu-trimethylvinylsilane in H2 (1:1). Surfaces were characterized with x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Patterned Cu features were formed by exposing the aminosilane films to patterned ultraviolet (193 nm) radiation prior to Pd-catalyst addition and Cu CVD.

The photochemistry of trimethylindium (TMI) adsorbed on a quartz substrate at 150 K has been studied by time of flight mass spectrometry (TOF/MS) using electron impact ionization and resonance-enhanced multiphoton ionization techniques. Photolysis of adsorbed TM1 at 222 nm results in the deposition of indium metal on the surface and the ejection of neutral and ionic fragments into the gas phase. The gas-phase photofragments observed were the neutral products In(CH 3 ) 2 , InCH 3 , In, and CH 3 and the ions In + , CH 3 + , and In(CH 3 ) +

Examples from this laboratory illustrating laser probing of gaseous products formed in chemical reactions on surfaces are taken from the areas of catalytic reactions, silicon etching, and surface photochemistry. The emphasis will be on the unique advantages of laser diagnostics in these dynamical and mechanistic studies in which the chemical reaction product species undergo no collisions after leaving the surface before detection by the laser. UHV experiments on the catalytic oxidation of H2, D2 and NH3 by N02 and H2 by NO2 used the laser-induced fluorescence (LIF) technique to measure the apparent desorption energies of OH radicals and the rotational energy accommodation of the desorbing OH, OD and NO reaction products. The observed different degrees of "rotational cooling" in the different products will be discussed. In multiphoton ionization mass spectrometry experiments (MPI/MS) spectroscopies of three different MPI processes for the SiF2 radical were studied and two of these were applied to the study of silicon etching by XeF2, F2, and NF3. The only observed gaseous products were SiF4 and the SiF2 radical and their apparent production energies correlated with the case of surface fluorine atom production. In the area of surface photochemistry, an excimer laser was used to photolyze iodobenzene, trimethylgallium, and copper acetylacetonate adsorbed on a cold surface. The time-of-flight (TOF) spectra of the fragments or reaction products were measured by using a mass spectrometer equipped with multiphoton (MPI) or electron (EI) ionization.

We report improved emission performance of microgated carbon nanotube field-emitter arrays. The arrays with 0.1mm2 areas produced anode currents in excess of 1mA (1A∕cm2) and transconductance of up to 174μS (174mS∕cm2) at gate voltages of 75V or less. The carbon nanotubes were grown by dc plasma chemical-vapor deposition, but were not oriented vertically during inspection in the scanning electron microscope. Most of the nanotubes had diameters near 10nm. We suggest that the small tube diameter caused the relatively high emission current and also produced limber tubes, unable to support themselves vertically.

Multiwalled carbon nanotubes (cNTs) in both the gated cNT-on-Si post and the cNT-in-open configurations were used in this study. Large increases in field emission current were observed when operating cNTs in substantial pressures of hydrogen, especially after the nanotubes have been contaminated with oxygen. Emission degradation was likely due to surface contamination with oxygen and was removed by reaction with hydrogen (atoms). Exposure of the emitters to molecular hydrogen or oxygen when the arrays are not emitting has no effect on the emission produced once the gases are removed, suggesting that the nanotubes are inert to the molecular forms of hydrogen and oxygen and that the atomic forms, which are created by electron dissociation, react with surface groups. The requirement for relatively high pressures of hydrogen also suggests that atomic hydrogen was responsible for the large enhancement and regeneration effects. The ability to regenerate emission from contaminated cNT can prolong emitter device lifetimes and save cost.

Field emission from air-exposed silicon and other surfaces typically occurs at energies up to several volts below the Fermi level, and the energies can change substantially during emission. We conclude this behavior results from emission from initial states in a dielectric (oxide) surface coating, and that the energies of these states change relative to the emitter Fermi level due to changing oxide state density and charge density. When emission occurs below the bulk Fermi level, energy is deposited into the emitter. In some cases this energy can be coupled to chemical bonds, creating states in the oxide and improving electron transport. If the power density deposited this way becomes excessive, oxide breakdown and arc initiation can result. Thus preventing excessive emission current at potentials more than 1–2V positive relative to the bulk Fermi level may prevent arc initiation. We propose that might be done by building a second (filter) aperture above each gate aperture in an array, and placing the ape...

We report large increases in field emission current when operating carbon nanotubes in substantial pressures of hydrogen, especially when the nanotubes were contaminated. We have previously demonstrated two different configurations of integrally gated carbon nanotube field emitter arrays (cNTFEAs), CNTs grown inside microfabricated gate apertures with and without silicon posts. Salient features of these in situ grown microgated cNTFEAs include the absence of electrical arcing, low operating voltage, and enhancing effect of some residual ambient gases. Operating both configurations of cNTFEAs without special precleaning in greater than 10−5Torr hydrogen produced orders of magnitude enhancement in emission. For a cNTFEA intentionally degraded by oxygen, the operation in hydrogen resulted in a 340-fold increase in emission current at constant gate voltage. The results suggested a dependence on atomic hydrogen produced from the interaction between emission electrons and molecular hydrogen. The observed emissi...

High density patterns of holes in metalorganic chemical vapor deposition grown GaN films on sapphire have been fabricated by inductively coupled plasma etching using a nickel mask. Pattern transfer from the e-beam lithographically patterned resist to the nickel etch mask was accomplished by ion beam milling. A Cl2–BCl3 inductively coupled plasma was used to anisotropically etch patterns of 200–250-nm-diam holes with 300nm center-to-center spacing through the entire thickness of a 265-nm- and a 300-nm-thick GaN film. This work demonstrates a pattern transfer technique to Ni by ion beam milling and Ni as a durable etch mask under a chlorine environment for high density patterning of GaN films.

We demonstrated the proof of principle for the fabrication of trenches with widths down to 0.1 μm on a silicon substrate using photolithographically prefabricated starting mask structures having a spacing of 0.6 μm. The corresponding trench width of 0.15 μm was achieved using starting mask structures having a spacing of 1.0 μm. Chemical‐beam deposition of metals was used to coat the starting mask structures and to narrow the aperture openings. Metal redeposition by ion‐beam sputtering directed perpendicular to the substrate further narrowed the spacing between the sidewalls of the mask structures. The subsequent chemically assisted ion‐beam etching of the underlying substrate through the constricted mask apertures produced the trenches with greatly reduced widths.

In a manner suitable for large‐scale processing, vertical platinum structures having thicknesses (linewidths) down to 20 nm, heights up to 700 nm, an aspect ratio up to 13, and different geometric shapes have been fabricated on top of a silicon dioxide substrate by Pt deposition from the thermal decomposition of a platinum precursor molecule under gas phase collisionless conditions followed by ion‐assisted etching. Scanning electron microscopy analysis shows that the structures have very small grains, high uniformity, and very sharp contours, demonstrating a high degree of conformal deposition. Scanning Auger microscopy reveals platinum only on the structures. X‐ray diffraction and x‐ray photoelectron spectroscopy analysis of the as‐deposited platinum film show that the platinum film is polycrystalline and has no detectable impurity. Scotch tape test shows good bonding of the film. Mass spectrometric measurements suggest that substantial amounts of stable precursor fragments from partial decomposition of ...

A review of research conducted at the Naval Research Laboratory illustrates the unique advantages of using lasers to probe the newly formed gaseous products from chemical reactions on surfaces. Examples to be discussed are taken from the areas of catalytic reactions, silicon etching, and surface photochemistry. UHV experiments on the catalytic oxidation of H2, D2, and NH3 by 02 and of H2 by NO2 used the laser-induced fluorescence technique to measure the apparent desorption energies of OH radicals and the rotational energy accommodation of the desorbing OH, OD, and NO reaction products. The observed different degrees of "rotational cooling" in the different products are discussed. In multiphoton ionization mass spectrometry (MPI/MS) experiments, spectroscopies of three different MPI processes for the SiF2 radical were studied and two of these were applied to the study of silicon etching by XeF2, F2, and NF3. The only observed gaseous products were SiF4 and the SiF2 radical and their apparent production energies correlated with the ease of surface fluorine atom production. In the area of surface photochemistry, an excimer laser was used to photolyze iodobenzene, trimethylgallium, and trimethylindium adsorbed on a cold surface. The time-of-flight spectra of the fragments or reaction products were measured by using a mass spectrometer equipped with MPI or electron ionization (El).

Thermal decomposition of HCOOH has been studied from 1280 to 2030 K over a broad range of initial concentrations (0.07 to 1.6% in Ar) in a shock tube using a stabilized cw CO laser to monitor CO formation. The observed CO concentration profiles over the whole range of temperature and pressureemployed could be satisfactorily accounted for by the following two-channel molecular decomposition mechanism: HCOOH + M → 1 CO + H 2 O + M HCOOH + M → 2 CO 2 + H 2 O + M 89-1 with the following apparent second order rate constants in the pressure range 0.75–2.8 atm. k 1 = 2.3 x 10 15 exp ( − 50 , 000 ± 1700 / RT ) c c mole − 1 sec − 1 k 2 = 1.5 x 10 16 exp ( − 57 , 000 ± 2800 / RT ) c c mole − 1 sec − 1 The values of these two rate constants were evaluated by the non-linear least squares fitting of the observed CO concentration profiles. The possibility of an alternative decomposition route involving the initial production of H atoms, instead of H2, has also been considered. However, the rate constant evaluated from the kintic modeling of the CO formed at high temperatures cannot satisfactorily account for that observed at lower temperatures.

CO absorption up to υ = 11 was detected in the O(3P) + C2F4 reaction. From time-resolved absorption data, the initial vibrational distribution of the CO formed in the reaction was determined. Energetically, the observed population distribution could only be accounted for by the occurrence of the reaction O3P) + triplet CF2 → CO + F2 (ΔH0 = −89 kcal/mole). A statistical model calculation, based on the assumption of a long-lived CF2O complex, predicts a CO vibrational distribution that agrees closely with the observed one.

The unimolecular decomposition of methyl nitrite in the temperature range 680–955 K and pressure range 0.64 to 2.0 atm has been studied in shock-tube experiments employing real-time absorption of CW CO laser radiation by the NO product. Computer kinetic modeling using a set of 23 reactions shows that NO product is relatively unreactive. Its initial rate of production can be used to yield directly the unimolecular rate constant, which in the fall-off region, can be represented by the second-order rate coefficient in the Arrhenius form: A RRKM model calculation, assuming a loose CH3ONO≠ complex with two degrees of free internal rotation, gives good agreement with the experimental rate constants.

The photolysis mechanisms of trimethylindium (In(CH 3 ) 3 ) adsorbed on a quartz surface at 150 K has been studied by time of flight mass spectrometry (TOF/MS) using electron impact ionization and resonance-enhanced multiphonon ionization techniques. Photolysis of adsorbed TMI at 222 nm results in the deposition of indium metal on the surface and the ejection of neutral and ionic fragments. The gas phase photofragments observed were the neutral products In(CH 3 ) 2 , InCH 3 , In, CH 3 and the ions, In + and InCH 3 + . The neutral product TOF profiles were characterized by different temperatures.

The vibrational energy distributions of the HF and CO formed in flash-initiated SO 2 CHFX 2 (X = Cl, Br) mixtures have been measured by laser emission and laser resonance absorption, respectively. Both excited products are believed to result mainly from the O( 3 P) + CHF reaction, which probably takes place via vibronically excited HFCO intermediates. The observed HF and CO vibrational energy distributions could be satisfactorily accounted for by simple statistical models based on the following simplified mechanism: O( 3 P) + CHF(X 1 A′) → [ 3 HFCO*†] → [ 1 HFCO†] → HF† + CO† + ≈190 kcal/mole → H + F + CO† + ≈54 kcal/mole with about 40% of the reaction occurring via the molecular elimination path and about 60% via the atomic formation path.

CO concentration-time profiles have been measured by using CO laser resonance absorption in shock tube experiments on the reaction of CH3 with O2 in the temperature range from 1150 to 1560 K. Computer kinetic modeling of our profile data yielded k2 = 1.0 x 1014 e−(15,500 ± 1,100)/T cm3mol sec for the CH3 + O2 CH3O + O reaction. An RRKM calculation, which took into consideration branching of the CH3 + O2 reaction into different product channels, revealed that by assuming a loose transition state (allowing two free internal rotations) leading to the CH3O + O product channel, we could account very satisfactorily for our results as well as those reported previously for the reaction. A three-parameter leastsquares fit of a smooth curve covering data from three independent studies gave rise to the expression: k2 = 2.20 x 1034 (T/K)−5.94 exp (–21,300 K/T) cm3mol sec for the temperature range 1150-2300 K.

CO laser emission at 5 μm was detected when SO2 and CFBr3 were flash photolyzed in the vacuum ultraviolet above 165 nm. Over 40 vibrational–rotational transitions ranging from Δv = 2 1 to 14 13, with the exception of those between 8 7 and 11 10, were identified. The CO emission is believed to result from the O + CF reaction: The vibrational population of the CO has been measured by means of a CO laser resonance absorption method. The CO was found to be vibrationally excited to v = 24 with a vibrational temperature of about 1.4 × 104°K. The “surprisal analysis” of the observed CO distribution showed the possible occurrence of a minor process (presumably O + CFBr) that generated vibrationally colder CO. The effects of various additives on the CO emission were also examined. The addition of CO2 to a D2-SO2-CFBr3-He mixture resulted in a simultaneous osciallation at 3.6, 5, and 10.6 μm due to DF, CO, and CO2, respectively. Additionally, the utilization of the O + CFn (n = 1, 2, 3) reactions as F-atom sources for HF-laser operation in flash-initiated systems were demonstrated.

Initial isotopic excitation selectivity in cw CO2 laser pumping of 12CH3F and 13CH3F is retained in upper vibrational states even after ladder climbing collisions. Reaction of these states with atomic bromine samples this non-equilibrium distribution and produces isotopically enriched product, CH2FBr, with projected excellent energy efficiency.

The vibrational energy distribution of the CO formed in the E→V energy transfer reaction: Na(3 2PJ) + CO (X 1Σ+, v=0)→Na(3 2S1/2) + CO (X 1Σ+, v?9) was determined at five temperatures between 486 and 672 K. The electronically excited Na atom was optically pumped by a dye laser operating at 590 nm and the CO vibrational energy distribution measured by means of a cw CO laser operating at 5 μm. The CO was found to have a near Poisson distribution, peaking at v=2, with little temperature effect. The efficiency of the E→V transfer was determined to be ∼35%. These findings are consistent with those predicted by a curve‐crossing model involving an ionic Na+(CO)− complex.

The techniques of laser and electron ionization mass spectrometry have been employed to study the thermal etching of Si(110) by F/sub 2/ and NF/sub 4/ at substrate temperatures between 300 and 1200 K. By two-photon resonance-enhanced ionization of SiF/sub 2/ via the B/sup 1/ tilde B/sub 2/ state, the apparent activation energy for gaseous silicon difluoride production was found to be 8.9 +/- 0.3 and 22.1 +/- 1.7 kcal/mol for F/sub 2/ and NF/sub 3/, respectively. SiF was not detected. An extensive search for SiF/sub 3/ during etching by F/sub 2/ at 1000 K, by means of resonance ionization from 320 to 325 and from 416 to 510 nm, also showed no signs of the species. Both SiF and SiF/sub 3/ are thermochemically unimportant etch products under the conditions employed. In F/sub 2/ etching, SiF/sub 4/ and total silicon fluoride ..sigma.. SiF/sub x//sup +/ signals as measured by electron ionization rose rapidly at lower temperatures and stabilized between 700 and 900 K before rising again. No such behavior was observed for SiF/sub 2/ production from F/sub 2/ or for the products formed in NF/sub 3/ etching. Apparent activation energies for total silicon fluoride and SiF/sub 4/ production are similar. Formore » F/sub 2/, they were found to be about 9 kcal/mol in the low-temperature region, and for NF/sub 3/ both were measured to be about 21 kcal/mol. A proposed reaction mechanism explaining these and related results is discussed.« less

The relaxation of electronically excited I2, ICl and NO2 by CO has been investigated using a dye laser for electronic excitation (in the 590 nm region) and a cw CO laser for measuring the extent of CO product vibrational excitation. The CO molecules formed in these quenching reactions were found to carry very small fractions of electronic energies, in sharp contrast to the results observed in other E → V transfer reactions involving atomic species which carry comparable amounts of electronic energies.

The dynamics of the O(3P)+C3O2→3CO reaction (ΔH° =−115 kcal/mole) has been investigated by means of a CO laser resonance absorption technique. The reaction mixtures consisted of NO2 and C3O2, with He or SF6 dilution. The O(3P) atom was generated by the flash photolysis of the NO2 above 300 nm. The three CO’s formed in the reaction were found to carry vibrationally about 19% of the total available energy, with an apparent near statistical population distribution. The results of an 18O‐labeled experiment, however, indicate that the two CO’s originating from the parent C3O2 molecule are vibrationally much colder (〈Ev〉? 4.2 kcal/mole) than that from the reaction of the O atom with the center C atom (〈Ev〉?15 kcal/mole). This result is attributed to the incomplete randomization of the reaction energy in the dissociating C3O3 complex. Possible reaction mechanisms are presented.

Rotational energy distributions of OD and OH radical reaction products desorbing from a smooth Pt(111) single crystal surface have been measured under closely similar experimental conditions by using the laser‐induced fluorescence technique in conjunction with an UHV apparatus. Over the temperature ranges studied, nearly full rotational energy accommodation was observed for OD with a rotational to surface temperature ratio, Tr/Ts =0.96±0.04, and a somewhat lower ratio of 0.86±0.05 was obtained for OH. For both OD and OH the spin–orbit temperatures were the same as the rotational temperatures and no preference for any lambda‐doublet state was observed.

Rotational energy distributions of the desorbing NO product from the NH3+O2 reaction on a Pt(111) single crystal have been measured using the laser‐induced fluorescence technique in conjunction with an UHV apparatus. Over the surface temperature range 800–1300 K, the rotational temperature of NO was found to remain virtually constant near 400 K.

A cw CO laser has been used to probe the complete CO vibrational energy distributions in the reactions of CH2 radicals with O(3P) and O2 (3∑−g. The CO formed from the reaction with the atom was concluded to be produced via two equally important channels, O + C H 2 → C O + H 2 → C O + 2H , , with an average vibrational energy of 19 kcal/mole, and an approximate vibrational temperature of ≈104K (for v≤12), which is sufficient to account for previously observed CO stimulated emission from O(3P)+CH2. The population inversion derives mainly from the molecular hydrogen elimination channel. In the reaction of CH2 with molecular oxygen, the CO formed is believed to be produced from both a molecular elimination path giving H2O+CO and from two possible atomic or radical production processes, yielding H+CO+OH. We find from analysis of the CO product vibrational energy distribution that 30% of the CO formed is produced via the former path, and 70% is formed from the latter path. This information is important to the detailed kinetic modeling of acetylene and other hydrocarbon combustion systems.

The vibrational distribution of CO produced from the electronic-to-vibrational energy transfer reaction: Na(32P) + CO(X1Σ+, υ=0)→Na(32S) + CO(X1Σ+, υ⩽8) has been determined by means of infrared resonance absorption measurements employing a cw CO laser. A flash-lamp-pumped dye laser is used to excite the ground state Na to the 32P 1 2 and 32P 3 2 states. The CO molecules formed in the reaction were found to be vibrationally excited up to the limits of available electronic energies carried by the excited Na atoms, and the vibrational population exhibits a maximum at υ=2. The efficiency of E→V energy transfer was determined to be 35%. Our present results were found to be consistent with the impulsive (half-collision) and curve-crossing models.

The reactions of CS(X 1Σ+), CS2(X 1Σ+g) and OCS(X 1Σ+) with O(3P) were studied at 298 K by means of a CO laser resonance absorption technique. The CO(ν) population distribution produced from the reaction O(3P) + CS(X 1Σ+) studied in a quartz flash photolysis tube (λ>/ 200 nm) is similar to distributions observed previously for ν> 7. For ν / 300 nm) in which the O(3P) + CS2(X 1Σ+g) reaction is the only one which can occur confirmed that the colder population observed is attributable to this process. The branching ratio for the reaction channel O(3P) + CS2(X 1Σ+g) → CO(X 1Σ+) + S2(3Σ−g) has been measured. We find that 1.4 ± 0.2% of the O + CS2 reaction proceeds through this channel, and that the rate constant for this reaction channel is, k = 3.5 (±0.5) × 1010 cm3/mole s. Isotope labeled experiments using 18O atoms show that the O(3P) + OCS(X 1Σ+) reaction takes place by a direct stripping mechanism, wherein CO(ν) is produced exclusively from the parent OCS molecule. The CO(ν) formed in this reaction carries about 9% of the total available energy.

SiF and SiF 2 radicals, produced in the thermal reaction of F 2 and NF 3 with solid silicon, have been detected by multiphoton ionization mass spectrometry in the 438 and 321 nm wavelength regions, respectively. The reaction pathway to the production of SiF radicals is of minor significance compared with SiF 2 production over a wide range of temperatures and pressures. In both cases it was found that little or no fragmentation of the parent ion occurs upon ionization. MPI/MS is thus shown to be a useful diagnostic tool for studies of fluorine-silicon etching reactions.

Boltzmann‐like rotational energy distributions were obtained for desorbing OH radials formed in the oxidation of hydrogen on a Pt(111) single crystal and polycrystalline Pt foil by using the laser‐induced fluorescence method in conjunction with an UHV apparatus. For an O/H=1 reactant gas mixture, relatively high rotational energy accommodation was indicated by the rotational to surface temperature ratios Tr/Ts of 0.85±0.03 over the temperature range 1227–1479 K for the Pt(111) single crystal, and of 0.86±0.04 over 1283–1475 K for the polycrystalline Pt foil. Tr seemed to be proportional to Ts over these temperature ranges. The lack of noticeable dependence of Tr/Ts on the O/H reactant gas mixture ratio suggests that the rotational energy accommodation is not sensitive to the apparent Pt–OH bond strength.