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  • 1
    Electronic Resource
    Electronic Resource
    Reactions of cationic silicon clusters with xenon difluoride (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 5568-5577 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Cationic silicon clusters, Si+1–7, were observed to react bimolecularly and exothermically with xenon difluoride in the ion trap of a Fourier transform mass spectrometer. Three ionic products are observed from Si+n@B: SiF+, Si+n−1, and SinF+. Subsequent reactions of these products with xenon difluoride were determined as well. SinF+, n=2–6, react with xenon difluoride to form two ionic products: SiF+ and Si+n−1. SiF+m, m=1–3, react with xenon difluoride to form SiF+m+1 and XeF+. All observed products correspond to mono- or difluorination of the clusters by xenon difluoride; in many cases the reaction was sufficiently exothermic that the fluorinated cluster fragmented immediately to produce either Si+n−1 or SiF+. Based upon the observed trends in the product distributions, the extent of mono- vs difluorination of the clusters was obtained. The amount of monofluorination varies from 100% for SiF+m, m=0–3, to 0% for Si+7. By extrapolation, xenon difluoride should difluorinate bulk silicon exclusively. The reaction rates for the bare clusters differ only slightly among themselves. The monofluorinated silicon clusters, in contrast, have significant variations in reaction rate as a group. Substantially lower reaction rates are observed for Si4F+ and Si6F+; this is believed to derive from the greater thermodynamic stabilities of Si+4 and Si+6.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452529
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  • 2
    Electronic Resource
    Electronic Resource
    Sequential reactions of SiD+2 with SiD4 (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 4429-4439 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The thermal (300 K) reaction of SiD+2 with SiD4 proceeds at greater than the Langevin collision rate (21±3×10−10 cm3/molecule s ). The reaction products SiD+3, Si2D+2, and Si2D+4 are produced in a 54:7:39 ratio. Both silicon isotope exchange and adduct (Si2D+6) formation are 〈1% of the collision rate at silane pressures of 1–4×10−7 Torr. The branching ratio for SiD+3 formation increases with increasing internal energy of SiD+2. Sequential reactions of SiD+3 and Si2D+2 with SiD4 have been previously found to produce terminal species containing five silicon atoms. Si2D+4 reacts with SiD4 only by silicon isotope exchange at 2.0±0.7% of the collision rate (0.20±0.07×10−10 cm3/molecule s ) with no evidence of other reactions (〈0.5% of the collision rate). Reaction of SiD+2 with SiD4 does not lead to unconstrained clustering and particle formation in silane plasmas. High level ab initio calculations on this system are reported by Raghavachari in his companion paper. Energies of the critical intermediates and transition states along the reaction surface are compared quantitatively to the experimental results via phase space calculations. The energies agree to within 6 kcal/mol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462834
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  • 3
    Electronic Resource
    Electronic Resource
    Sequential clustering reactions of SiD+3 with SiD4 and SiH+3 with SiH4: Another case of arrested growth of hydrogenated silicon particles (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 437-451 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Sequential clustering reactions of SiD+3 with SiD4 and SiH+3 with SiH4 are observed in the ion cell of a Fourier transform mass spectrometer. Clustering occurs either by addition of SiD2 or SiH2 accompanied by loss of D2 or H2, or by the formation and stabilization of the bimolecular adducts. All of the clustering reactions are highly inefficient and lead to bottleneck structures at small silicon cluster sizes containing two to four silicon atoms. Rates are measured for both the addition and association products for each step of the reaction. Back reaction rates are monitored via silicon-29 isotope exchange. Ab initio electronic structure calculations of the reaction pathways including intermediates, transition states and products have been performed by Raghavachari and are presented in his companion paper. The overall reaction mechanisms are similar for each reaction step. First an intermediate complex is formed between the ion and neutral which is strongly bound by a bridging deuterium or hydrogen atom.Collisional stabilization of this complex leads to formation of the observed bimolecular adduct products. These bimolecular adducts do not react further with SiD4 (SiH4) on the time scale of our experiments. Elimination of D2 or H2 leading to the SiD2 (SiH2) addition products occurs via a thermoneutral transition state. Sequential growth by addition of SiD2 (SiH2) arrests at Si3D+7 (Si3H+7). Ab initio calculations find that this occurs because Si3D+7 (Si3H+7) assumes a highly stable cyclic structure. Phase space theoretical modeling of the experimentally measured reaction rates is performed to quantitatively test energies of the reaction intermediate complexes and transition states calculated by Raghavachari. Excellent agreement within 0.13 eV is obtained between the phase space and ab initio energies. Phase space derived kinetic isotope effects on the reaction rates of protiated and deuterated species also correspond well with experiment. Reaction rates at typical temperature and pressure conditions in silane plasmas are also calculated. These results strongly suggest that sequential clustering of SiH+3 with SiH4 does not lead to formation of the deleterious hydrogenated silicon dust observed in silane plasmas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458446
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  • 4
    Electronic Resource
    Electronic Resource
    Reactive etching of GaxAs−y by HCl (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4258-4264 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The gas phase reactions of HCl with anionic gallium arsenide clusters, GaxAs−y, containing two to six atoms are presented. Reaction rates and product distributions for the primary, secondary, and tertiary reactions are tabulated. HCl etches GaxAs−y by loss of GaCl to form Gax−1AsyH−. These products are also etched by HCl through loss of GaCl to form Gax−2AsyH−2. Those clusters which do not contain gallium either react to lose AsCl (As2H− and As3H−) or react to abstract H+ and form Cl−(AsH−2). Three gallium-containing clusters (GaAs−4, Ga2AsH−, and GaAs2H−2) react by proton abstraction to form Cl− rather than lose GaCl. Two clusters (Ga3As−2 and Ga2As−3) have an additional reaction pathway open to form two neutrals (GaCl and As2) plus a smaller anionic cluster. Formation of GaCl and As2 mimics the etching of bulk gallium arsenide by HCl at elevated temperatures. Five clusters (GaAs−4, Ga2As−3, GaAs4H−, Ga4As−2, and Ga2As−4) exhibit dual populations that can be differentiated kinetically. There is an inverse correlation between bare cluster reactivity and its initial abundance from laser desorption. The only exception is Ga2As−3 which has ∼50% population of a very reactive species that is the most abundant cluster initially desorbed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455782
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  • 5
    Electronic Resource
    Electronic Resource
    Sequential reactions of SiD0–3+ and Si2D0–6+ with disilane (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 7226-7233 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Sequential reactions of SiD0–3+ and Si2D0–6+ with 10−7–10−6 Torr of disilane are described. The reactions proceed, with few exceptions, by addition of SiD2 with simultaneous loss of SiD4. The growing cluster cations decrease in reactivity with increasing size. For all reaction sequences, a terminal cluster size is reached that contains fewer than nine silicon atoms. Based on our results, we conclude that the reaction of small subsilane or disilane cations with disilane does not lead to gas phase particle formation in disilane plasmas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463548
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  • 6
    Electronic Resource
    Electronic Resource
    How to grow large clusters from SixD+y ions in silane or disilane: Water them! (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 4233-4245 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Growth of large cationic clusters is observed in real time for subsilane and subdisilane cations in the presence of silane/disilane–water mixtures. SiD+0–3 and Si2D+0–6 are created by electron impact in the trapped ion cell of a Fourier transform mass spectrometer and their sequential clustering reactions with 5% water: 95% silane/disilane are monitored for up to 80 s at total pressures of 10−7–10−5 Torr. Formation of SixDyO+z clusters out to at least 450 amu in silane and 650 amu in disilane can be seen on the available experimental time scales. The early portion of the sequence leading to large clusters has been elucidated for silane. Amazingly, of the possible subsilane cations, only SiD+ reacts with silane and water to form increasingly larger cluster sizes. Reactions of the other subsilane cations, SiD+0,2–3, do not continue without apparent limit. Initial growth of SiD+ proceeds in a highly specific fashion involving the formation of two critical doorway ions, Si4D+7 followed by Si4D7O+.The growth pattern then fans out to include numerous alternating and parallel reactions with both SiD4 and D2O. Several general features of the growth reactions are seen. Reactions with SiD4 are noticeably slower than reactions with D2O. Cluster growth by bimolecular reaction with SiD4 and D2O occurs by addition of SiD2 and addition of an oxygen atom, respectively, accompanied by elimination of D2. Loss of additional molecules of D2 sometimes occurs, particularly as clustering proceeds to large sizes. Cluster growth by termolecular attachment of SiD4 or D2O is also seen. This process results in the formation of SixDyO+z complexes with SiD4 and D2O that appear to serve as important intermediates which enhance cluster growth rates as the total pressure is increased. Sequential clustering without apparent limit is only observed for subsilane and subdisilane cations with silane and disilane when water is present. On this basis, it is proposed that low levels of water contamination can provide a key ingredient for the chemistry which leads to the formation of the hydrogenated silicon particles found ubiquitously in silane plasmas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462816
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  • 7
    Electronic Resource
    Electronic Resource
    Sequential clustering reactions of SiD+ with SiD4: Rapid growth to kinetic dead-end structures (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 7360-7372 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Sequential clustering reactions of SiD+ with SiD4 are monitored in the trapped ion cell of a Fourier transform mass spectrometer. At thermal energies, SiD+ initially clusters by rapid addition of silylene accompanied by elimination of D2. This growth sequence halts after reaching the dead-end structure Si4D+7, which grows further only by a slow termolecular process to form Si5D+11. Nonthermal cluster growth reactions are also observed which generally result in elimination of additional D2 molecules as compared to the thermal reactions. Thus the nonthermal product ions are more silicon rich than the thermal product ions. Some of the resulting nonthermal product ions react further with SiD4, but quickly form dead-end structures which cease to react. Both the forward and back reaction probabilities and products have been determined experimentally for each step of the growth sequence. These are used in combination with phase space theory to model the transition state energies involved in the microscopic pathways that have been elucidated by Raghavachari using ab initio electronic structure theory. The excellent quantitative agreement for these energies, to within 0.12 eV, between the experimentally derived values and those calculated by Raghavachari supports the growth pathway found by ab initio calculations. This pathway also shows why further growth of Si4D+7 can only occur by inefficient bimolecular attachment of SiD4. These experimental results strongly indicate that the sequential growth of SiD+ in reactions with SiD4 will not lead to large hydrogenated silicon particles even under the conditions of higher temperatures, pressures, and ion energies found in silane plasmas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461362
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  • 8
    Electronic Resource
    Electronic Resource
    H/D isotope exchange reaction of SiH+3 with SiD4 and SiD+3 with SiH4: Evidence for hydride stripping reaction (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 3270-3276 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have measured the reaction rates and product distributions for SiHxD+3−x reactions with SiH4 and SiD4. The measured reaction rates for SiH+3 and SiD4 (26.1±1.0×10−10 cc/molecule s) and for SiD+3 and SiH4 (23.1±1.0×10−10 cc/molecule s) are greater than the calculated Langevin collision rate (12.3–12.4×10−10 cc/molecule s). Also, the product distribution observed for H/D exchange is nonstatistical. Dual, competing reaction mechanisms are invoked to account for these observations: reaction via formation of an ion-molecule complex and reaction via long-range hydride stripping. Using an expected product distribution calculated from reaction thermochemistries, the relative contributions of the two mechanisms is obtained for each reaction examined. The reaction rate for the ion-molecule complex mechanism is calculated to be at the Langevin collision rate within experimental error. The reaction rate for the stripping mechanism varies from 1–4×10−10 cc/molecule s (10–30% of the Langevin collision rate) for the mixed isotope ions SiH2D+ and SiHD+2 to 12–18×10−10 cc/molecule s (100%–150% of the Langevin collision rate) for the isotopically pure ions SiH+3 and SiD+3. The faster than Langevin reaction rates lower the expected low field mobility of SiH+3 in silane plasmas by 70% to ∼340 cm2 Torr/V s.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458860
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  • 9
    Electronic Resource
    Electronic Resource
    Sequential reactions of bare silicon clusters with SiD4: Constrained heterogeneous nucleation of deuterated silicon particles (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3121-3135 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Bare silicon cluster ions are observed to undergo exothermic sequential clustering reactions with SiD4 at room temperature. Si+1–7 and Si−1–7 are created by laser evaporation and trapped in the ion cell of a Fourier transform mass spectrometer in the presence of SiD4. Clustering reactions are observed only for Si+1–3 and Si+5. Si+4,6,7 and the negatively charged silicon clusters do not react exothermically with SiD4. All of the reactive silicon clusters encounter chemical constraints to rapid growth of increasingly larger SixD+y species. Ab initio electronic structure calculations are used in concert with phase space theory calculations to deduce the structures of the products of the clustering reactions. These structures are found to be closely related to the lowest energy structures of the bare clusters if the degree of deuterium saturation is low. The inertness of unreactive clusters with 2–5 silicon atoms is correlated to unusually stable structures. Larger unreactive clusters with six or more silicon atoms appear to lack the divalent silicon center required to activate the Si–D bonds of SiD4. These findings are related to the phenomenon of hydrogenated silicon particle formation in silane plasmas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456667
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  • 10
    Electronic Resource
    Electronic Resource
    Methyl nitrite as a low pressure chemical ionization reagent (1982)
    s.l. : American Chemical Society
    Analytical chemistry 54 (1982), S. 1245-1247 
    Details
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ac00244a063
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