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  • 1
    Electronic Resource
    Electronic Resource
    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
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457693
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  • 2
    Electronic Resource
    Electronic Resource
    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
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456399
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  • 3
    Electronic Resource
    Electronic Resource
    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
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461864
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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Synthesis of Ge nanocrystals embedded in a Si host matrix (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 8201-8203 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The synthesis of a composite material consisting of Ge nanoclusters (≥2 nm in diameter) embedded in a Si host matrix is reported. The Ge nanoparticles are produced by pulsed laser ablation and are codeposited in a Si film simultaneously grown by chemical beam epitaxy using disilane. Scanning transmission electron microscopy, combined with energy-dispersive x-ray measurements, show that discrete Ge particles (≥2 nm diameter) are deposited within a polycrystalline Si host matrix. High-resolution transmission electron microscopy reveals that the particles are crystalline with a lattice spacing corresponding to that of Ge. The enhancement of Si deposition rates from silanes in the presence of Ge, previously demonstrated in chemical vapor deposition of Si1−xGex alloys, is shown to facilitate the growth of a Si layer around the Ge nanocrystals. The overall composition of the Ge cluster/Si host composite material is determined by Rutherford backscattering measurements. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357878
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  • 6
    Electronic Resource
    Electronic Resource
    Surface control of luminescence in silicon nanoparticles (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 6429-6433 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The intensity of visible photoluminescence from thin films of silicon nanoparticles is shown to be dependent upon the degree of surface passivation on the nanoparticles, while the emission energy is independent of the specific chemical nature of the passivating species. Nanoparticles are deposited into films using a pulsed laser ablation supersonic expansion source. Surface chemistry is controlled with a variety of postdeposition processing steps, including acid, methanol, and iodine treatments. These steps are then correlated with the visible photoluminescence behavior of the sample and the surface chemistry as characterized by x-ray photoelectron spectroscopy. Surface passivation controls the emission intensity through the elimination of competing nonradiative carrier relaxation pathways. The chemical nature of the passivating species does not determine the emission energy and can be easily changed with no anomalous photoluminescence behavior resulting. All results are consistent with a simple quantum confinement model of emission where particle size determines emission energy and surface passivation determines emission intensity. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363662
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  • 7
    Electronic Resource
    Electronic Resource
    Three-dimensional epitaxy: Thermodynamic stability range of coherent germanium nanocrystallites in silicon (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4132-4136 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study the stability range of coherent Ge quantum dots with an epitaxial Si shell. The critical radius is evaluated as a function of Si shell thickness and Ge nanocrystallite radius by comparing the energy of the system in the coherent and incoherent state. We find that the system is coherent up to a Ge nanocrystallite radius of about 100 A(ring), irrespective of the Si shell thickness. Nanocrystallites of radii larger than 270 A(ring) lose coherency by the generation of perfect dislocation loops. In nanocrystallites of intermediate radii (between 100 and 270 A(ring)), the coherency is lost by the introduction of partial dislocation loops enclosing a stacking fault. As the shell thickness decreases, the critical radius increases. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361777
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  • 8
    Electronic Resource
    Electronic Resource
    Synthesis and processing of silicon nanocrystallites using a pulsed laser ablation supersonic expansion method (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 1821-1823 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the preparation of nanometer sized crystallites of silicon by a pulsed laser ablation supersonic expansion technique. High resolution transmission electron microscopy is used to verify that particles with diameter in the range of ∼3 nm and greater are produced. Glancing angle x-ray diffraction results confirm that the particles formed have the silicon diamond cubic crystal structure. Visible photoluminescence emission from self-supporting thin films of agglomerated nanocrystallites is observed under excitation with ultraviolet light.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111766
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