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  • American Institute of Physics (AIP)  (14)
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  • 1
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.461362
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  • 2
    Digitale Medien
    Digitale Medien
    Optical and near-infrared spectroscopy of neutral indium phosphide clusters (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 4759-4767 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Spectra are obtained for a wide distribution of sizes and stoichiometries of indium phosphide clusters using photodissociation techniques. These spectra are presented at two different cluster temperatures throughout the spectral range of 0.65 eV (1900 nm) to 2.0 eV (640 nm) for indium phosphide clusters containing from 5 to 14 atoms. Though the spectral behaviors of the clusters are found to be qualitatively similar, significant quantitative differences exist. A Rice–Ramsberger–Kassel–Marcus (RRKM) dissociation model employing significant fitting constraints is found to accurately describe the observed dissociation behaviors at both temperatures. Dissociation energies ranging from 2.0 to 2.4 eV are determined for the In5Py–In9Py clusters using the RRKM model. Experimental evidence suggests that the dissociation process involves loss of a small phosphorus containing moiety such as P1–2 or InP1–2. Results of the RRKM fitting process also clearly indicate that most of these InxPy clusters have nearly uniform absorption cross sections from 0.65 to 2.0 eV. This range extends well below the band gap of bulk InP. This is the first clear evidence of the presence of electronic states in closed shell semiconductor clusters at energies well below the band gap of the bulk material. Select clusters show significant deviations from pure RRKM behavior. Their behavior is consistent with the presence of spectral structure in their absorption cross sections in the energy range of 0.65–2.0 eV.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.457693
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  • 3
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.456667
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  • 4
    Digitale Medien
    Digitale Medien
    Electronic spectroscopy of neutral indium phosphide clusters (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 5884-5885 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Electronic predissociation and two-color resonant two-photon ionization (R2PI) spectroscopic techniques have been successfully applied for the first time to the investigation of a broad distribution of small neutral clusters of the important III–V semiconductor, InP. Both techniques provide intense signals which display marked wavelength dependence with cluster composition. These techniques promise to provide a variety of critical spectroscopic results for the entire series of small InxPy clusters entrained in the molecular beam, and can be extended to permit the study of many other types of clusters.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.456399
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  • 5
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.462834
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  • 6
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.458860
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  • 7
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.463548
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  • 8
    Digitale Medien
    Digitale Medien
    Direct infrared and visible absorption spectroscopy of stoichiometric and nonstoichiometric clusters of indium phosphide (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 4088-4101 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Resonant two-color and one-color photodissociation spectroscopy is performed on neutral InxPy clusters with x+y=5 to 14 atoms. Absorption spectra of 29 different InxPy clusters are obtained for excitation energies between 0.84 and 1.84 eV. The absorption behavior is qualitatively similar for all of these clusters. An optical-gap-like absorption feature is observed at the blue end of the spectra, particularly for clusters which contain an even number of atoms. This feature shifts as a function of cluster size, but has an onset close to the band gap of bulk crystalline InP. Weaker absorptions are observed tailing to the red. A distinct absorption peak is also observed near the bulk InP band band gap for odd-numbered clusters with a stoichiometry of Inx+3Px. An empirical fitting of the low energy absorption tails reveals a correlation between the optical behaviors of these tiny clusters and amorphous semiconductors.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.461864
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  • 9
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.462816
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  • 10
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.458446
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