Jeffrey T. Roberts

Chemical vapour deposition of the oxides of titanium, zirconium and hafnium for use as high-k materials in microelectronic devices. A carbon-free precursor for the synthesis of hafnium dioxide

A brief survey of the precursors used for the chemical vapour deposition of the dioxides of titanium, zirconium and hafnium is presented. The review covers precursors used for the closely related process known as atomic layer chemical vapour deposition (ALCVD or ALD). Precursors delivered by standard carrier gas transport and by direct liquid injection (DLI) methods are included. The complexes fall into four classes based upon the ligands: halides, alkoxides, acetylacetonates (acac) and nitrates. Compounds bearing a mixture of ligand types have also found application in this area. The impact of the ligand on the microstructure of the metal oxide film is greatest at lower temperatures where the deposition rate is limited by the surface reactivity. The first use of anhydrous hafnium nitrate, Hf(NO3)4, to deposit films of hafnium oxide on silicon is reported. The films are characterized by Rutherford backscattering and X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy. Copyright

The reactions of thiophene on Mo(110) and Mo(110)-p(2×2)-S

The reactions of thiophene and 2,5-dideuterothiophene on Mo(110) and Mo(110)-p(2×2)-S have been investigated under ultrahigh vacuum conditions using temperature programmed reaction spectroscopy and Auger electron spectroscopy. Thiophene chemisorbed on Mo(110) decomposes during temperature programmed reaction to yield only gaseous dihydrogen, surface carbon, and surface sulfur. At low thiophene exposures, dihydrogen evolves from Mo(110) in a symmetric peak at 440 K. At saturation exposures, three dihydrogen peaks are detected at 360 K, at 420 K and at 565 K. Multilayers of thiophene desorb at 180 K. Temperature programmed reaction of 2,5-dideuterothiophene demonstrates that at high thiophene coverages, one of the α-C-H bonds (those nearest sulfur) breaks first. No bond breaking selectivity is observed at low thiophene exposures. The Mo(110)-p(2×2)-S surface is less active for thiophene decomposition. Thiophene adsorbed on Mo(110)-p(2×2)-S to low coverages decomposes to surface carbon surface sulfur, and hydrogen at 430 K. At reaction saturation, dihydrogen production is observed at 375 and 570 K. In addition, at moderate and high exposures, chemisorbed thiophene desorbs from Mo(110)-p(2×2)-S. At saturation the desorption temperature of the reversibly chemisorbed state is 215 K. Experiments with 2,5-dideuterothiophene demonstrate no surface selectivity for α-C-H bond breaking reactions on Mo(110)-p(2×2)-S. The decomposition mechanism and energetics of thiophene decomposition are proposed to be dependent on the coverage of thiophene. At low thiophene exposures, the ring is proposed to bond parallel to the surface. All C-H bonds in the parallel geometry are sterically available for activation by the surface, accounting for the lack of selectivity in C-H bond breaking. High thiophene coverages are suggested to result in perpendicularly bound thiophene which undergoes selective α-dehydrogenation to an α)-thiophenyl intermediate. The presence of sulfur leads to a high energy pathway for cleavage of C-H bonds in a thiophene derived intermediate. Carbon-hydrogen bonds survive on the surface up to temperatures of 650 K. Comparison of this study with work on Mo(100) demonstrates that the reaction of thiophene on molybdenum is relatively insensitive to the surface geometric structure.

Spectroscopic identification of surface phenyl thiolate and benzyne on Mo(110)

Chemisorbed phenyl thiolate (C6H5S) and surface benzyne (C6H4) formed during the temperature programmed reaction of benzenethiol on Mo(110) have been characterized using x‐ray photoelectron and high resolution electron energy loss spectroscopies. Electron energy loss spectroscopy demonstrates that at all exposures the S–H bond of benzenethiol breaks upon adsorption at 120 K, while x‐ray photoelectron spectroscopy confirms that the C–S bond is intact. The intermediate formed upon adsorption is assigned as a chemisorbed phenyl thiolate. At high exposures, approximately 40% of the phenyl thiolate reacts by way of hydrogenolysis at 350 K to form gaseous benzene and atomic sulfur, while 60% undergoes dehydrogenation at ≊370 K to form surface benzyne and atomic sulfur. Electron energy loss spectroscopy reveals that surface benzyne is aromatic in nature, and x‐ray photoelectron spectroscopy confirms that the C–S bond is no longer intact. Surface benzyne is unusually stable on the sulfided Mo(110), decomposing at...

SiO2 coating of silver nanoparticles by photoinduced chemical vapor deposition

Gas-phase silver nanoparticles were coated with silicon dioxide (SiO2) by photoinduced chemical vapor deposition (photo-CVD). Silver nanoparticles, produced by inert gas condensation, and a SiO2 precursor, tetraethylorthosilicate (TEOS), were exposed to vacuum ultraviolet (VUV) radiation at atmospheric pressure and varying temperatures. The VUV photons dissociate the TEOS precursor, initiating a chemical reaction that forms SiO2 coatings on the particle surfaces. Coating thicknesses were measured for a variety of operation parameters using tandem differential mobility analysis and transmission electron microscopy. The chemical composition of the particle coatings was analyzed using energy dispersive x-ray spectrometry and Fourier transform infrared spectroscopy. The highest purity films were produced at 300-400 degrees C with low flow rates of additional oxygen. The photo-CVD coating technique was shown to effectively coat nanoparticles and limit core particle agglomeration at concentrations up to 10(7) particles cm(-3).

Low Temperature Chemical Vapor Deposition of ZrO2 on Si(100) Using Anhydrous Zirconium (IV) Nitrate

Anhydrous zirconium(IV) nitrate was used as a volatile, carbon-free precursor for the low pressure chemical vapor deposition of thin ZrO 2 films on silicon (100) substrates. Depositions were performed at substrate temperatures between 300 and 500°C at total reactor pressures between 0.25 and 1.1 Torr. During deposition the N 2 carrier gas (flow rates = 20 or 100 sccm) was diverted through the precursor vessel which was maintained between 80 and 95°C. Under these conditions typical growth rates reached 10.0 nm/min. The polycrystalline films were predominantly monoclinic ZrO 2 with compositions very near the ideal value. Cross-sectional transmission electron microscopy and medium energy ion scattering established that an interfacial layer of SiO 2 separates the silicon substrate from the ZrO 2 . Electrical measurements made on capacitors constructed of 58 nm thick films of ZrO 2 with a platinum top electrode suggest that charge trapping occurs in the Si/ZrO 2 interfacial region.

Aerosol-based fabrication of biocompatible organic-inorganic nanocomposites.

Several novel nanoparticle composites were conveniently obtained by appropriately reacting freshly produced aerosol metal nanoparticles with soluble organic components. A serial reactor consisting of a spark particle generator coupled to a collison atomizer was used to fabricate the new materials, which included nanomagnetosols (comprising iron nanoparticles, the drug ketoprofen, and a Eudragit shell), hybrid nanogels (comprising iron nanoparticles and an N-isopropylacrylamide, NIPAM, gel), and nanoinorganics (gold immobilized silica). A fourth hybrid material, consisting of iron-gold nanoparticles and NIPAM) was obtained via an aerosol into liquid configuration, in which aerosol iron-gold particles were collected into a NIPAM/ethanol solution and then formed into nanogels with NIPAM under ultrasonic treatment. The strategy outlined in this work is potentially generalizable as a new platform for creating biocompatible nanocomposites, using only clinically approved starting materials in a single pass and under low-temperature conditions.

A new sulfate‐mediated reaction: Conversion of acetone to trimethylbenzene in the presence of liquid sulfuric acid

A new heterogeneous reaction, namely the sulfate-mediated conversion of acetone to 4-methyl-3-penten-2-one and trimethylbenzene, is reported. The reaction products were observed in their absorbed states by Fourier transform infrared spectroscopy and in the gas phase by mass spectrometry. In addition, protonated, absorbed acetone was observed under certain conditions. The reaction exhibits a strong concentration and / or temperature dependence, with non-reactive uptake as protonated acetone dominating at low temperatures and sulfate concentrations and reactive uptake occurring above 200 K and 75 wt. % H2SO4. Under conditions where reactive uptake occurs, the steady-state acetone loss probability is roughly 40%. It was not possible in this study to assess the relative effects of temperature and concentration on the reactivity of sulfate toward acetone.

Interaction of HCl with crystalline and amorphous ice: Implications for the mechanisms of ice‐catalyzed reactions

The interaction of HCl with ice under ultrahigh vacuum has been studied using temperature programmed desorption and single reflection Fourier transform infrared spectroscopy. Both amorphous and crystalline ice were investigated. At 120 K, HCl is initially absorbed by ice to form a stoichiometric hydrate phase identified as HCl · 6H2O. Upon completion of the bulk phase, HCl is adsorbed to the surface. This initial HCl adsorption probability on crystalline ice is ≈60% of that on amorphous ice. Furthermore, the adsorption probability on crystalline ice decreases more rapidly with increasing HCl uptake. As a result, HCl · 6H2O is more rapidly formed in amorphous ice. The difference in adsorption probabilities is tentatively attributed to a lower coverage of dangling OH groups at the crystalline ice surface.

Silver deposition on a polymer substrate catalyzed by singly charged monodisperse copper nanoparticles.

Aerosol deposition of singly charged monodisperse copper nanoparticles was used to catalytically activate a polymer substrate for electroless silver deposition. An ambient spark discharge was used to produce aerosol copper nanoparticles, and the particles were electrostatically classified at an equivalent mobility diameter of 10 nm, using a nanodifferential mobility analyzer. Deposition of the copper particles onto the surface of the substrate was enhanced by thermophoresis. The copper-deposited substrate was then immersed in a Ag(I) solution, resulting in the electroless deposition of silver (∼17 μm line width) on the previously deposited copper (∼12 μm line width, using a shadow mask with a 100 μm in width patterned stripe). The arithmetic mean roughness and electrical resistivity of the silver pattern were 44.7 nm and 7.9 μΩ cm, respectively, which showed an enhancement compared to those from the nonclassified copper particles (roughness = 162.2 nm, resistivity = 13.3 μΩ cm), because of a more-uniform copper deposition.

Desulfurization of ethylene sulfide on Mo(100): The roles of ring size and strain in adsorbate reaction selectivity

The reactions, under ultrahigh vacuum, of ethylene sulfide (c-C2H4S) on Mo(110) have been examined, by isothermal reaction spectroscopy, temperature programmed reaction spectroscopy, and X-ray photoelectron spectroscopy, Auger electron spectroscopy, and low energy electron diffraction. The dominant reaction channel (~ 85%) is intramolecular elimination of ethylene sulfide to gaseous ethylene. Approximately 70% of the ethylene formation occurs upon ethylene sulfide adsorption for all crystal temperatures examined (100, 120, and 140 K). At high coverages, small amounts of ethylene are formed at ~ 200 K, produced during the decomposition of chemisorbed ethylene sulfide. A minor reaction channel (~15%) for ethylene sulfide on Mo(110) is complete decomposition to surface carbon, surface sulfur, and gaseous dihydrogen. For high ethylene sulfide coverages, the dihydrogen produced during decomposition evolves at 375, 460, and 575 K. Ethylene sulfide desulfurization results in the deposition of 0.35 monolayer of atomic sulfur at reaction saturation for adsorption temperatures of <140 K, as measured by Auger electron and X-ray photoelectron spectroscopies. The high ring strain in ethylene sulfide is proposed to account for the low reaction barrier leading to ethylene. The ethylene product does not trap on the surface even for temperatures of 100 K, attributed to formation of ethylene via a concerted transition state with a large component of momentum perpendicular to the surface. A scheme for the reaction is proposed, and the reaction is compared to those of other cyclic Sulfides on Mo(110).