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  • 1
    Electronic Resource
    Electronic Resource
    Nature of the power-dependent ultrafast relaxation process of photoexcited charge carriers in II-VI semiconductor quantum dots: Effects of particle size, surface, and electronic structure (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 2143-2151 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The power-dependent relaxation dynamics of photoexcited charge carriers in a number of II-VI semiconductor quantum dots have been studied using femtosecond laser spectroscopy. The dynamics are obtained via excitation of the quantum dots with high power 390 nm pulses of 150 fs duration, and probing of the photoexcited species by monitoring the change in absorption at 790 nm as a function of time. Particles with vastly differing surfaces, sizes, electronic structures, and solvents all show a fast 1.5–4 picosecond decay component which grows in with power, a 17 ps (CdSe) or 50 ps (CdS and Cd0.5Zn0.5S) decay component, and some transient absorption persisting beyond 600 ps. The power-dependent component for CdSe quantum dots in glass has a 1.5 ps decay time constant, while for the liquid dispersed CdS and Cd0.5Zn0.5S quantum dots it has 2–4 ps decay time constants. This variation in the time constant is due to its power dependence, the time constant decreases with increasing power. It is also shown that the power-dependent decay is only weakly dependent on surface, size, and electronic structure. With the assistance of a power-dependent nanosecond fluorescence study, we have assigned the power-dependent decay primarily to exciton–exciton annihilation. This decay mechanism becomes dominant under high intensity excitation where multiple photoexcited charge carriers are created in each quantum dot, leading to trap state saturation and an accumulation of band edge excitons. Auger recombination may also play an important role at very high excitation intensities. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475593
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  • 2
    Electronic Resource
    Electronic Resource
    Femtosecond study of photo-induced electron dynamics in AgI and core/shell structured AgI/Ag2S and AgBr/Ag2S colloidal nanoparticles (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 3119-3126 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Direct measurements of the dynamics of photoinduced electrons in AgI, AgI/Ag2S, and AgBr/Ag2S semiconductor colloidal nanoparticles have been performed using femtosecond pump–probe laser spectroscopy. In AgI the transient absorption signal features a laser pulsewidth limited rise followed by a double exponential decay with time constants of 2.5 ps and 〉0.5 ns. The decay dynamics were found to be independent of pump power, indicating that the decays are not second order kinetic processes. The dynamics were also independent of the probe wavelengths, suggesting that the absorption spectrum of the photogenerated electrons is fully developed within ∼150 fs. The fast 2.5 ps decay is attributed to trapping and nonradiative electron–hole recombination mediated by a high density of trap states while the slow decay is attributed to reaction of deep trapped electrons with silver ions to form Ag atoms. For core/shell structured cocolloids of AgI/Ag2S, similar decay dynamics were observed. The only interesting difference is that the fast decay becomes faster with increasing concentration of Ag2S. This is due to direct excitation of Ag2S, which has a faster initial decay (800 fs) than in AgI. This is supported by the results of AgBr/Ag2S for which the same 800 fs decay was observed while no signal was observed for AgBr colloids alone, indicating clearly that the signal is from Ag2S. These findings on the early time dynamics of photo-induced excitons in AgI, AgI/Ag2S, and AgBr/Ag2S are important in better understanding the photographic process involving silver halides. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475709
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  • 3
    Electronic Resource
    Electronic Resource
    Methodology for Measuring the Critical Aggregate Concentration of Nonprobe Molecules (1994)
    s.l. : American Chemical Society
    Langmuir 10 (1994), S. 2814-2816 
    Details
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/la00020a051
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  • 4
    Electronic Resource
    Electronic Resource
    Decumbensine and epi-α-Decumbensine: Two New Alkaloids Isolated from Corydalis decumbens (1988)
    s.l. : American Chemical Society
    Journal of natural products 51 (1988), S. 1241-1242 
    Details
    ISSN: 1520-6025
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/np50060a031
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  • 5
    Electronic Resource
    Electronic Resource
    A highly sensitive photoacoustic spectrometer for near infrared overtone (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1975-1980 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: By optimizing the size of a photoacoustic cell for decreasing acoustic loss and noise, and using a proper multipass arrangement for increasing light power in the cell and optical coupling to the acoustic wave, a high-resolution external laser photoacoustic spectrometer with a detection sensitivity of 6.35×10−9 cm−1 (1:1 signal to noise level) has been developed. Using this apparatus, the high quality Doppler-limited overtone spectra of AsH3 (600) and H2Se (60) have been observed at room temperature in the wave number regions 11 500–11 650 and 12 600–12 925 cm−1, respectively. Results are presented which highlight the applicability of this apparatus to the spectroscopy of weak optical transitions. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150564
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  • 6
    Electronic Resource
    Electronic Resource
    Vibrational relaxation of M(CO)6 (M=Cr, Mo, W): Effect of metal mass on vibrational cooling dynamics and non-Boltzmann internal energy distributions (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 7595-7601 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrational relaxation dynamics following the dissociation of C≡O from M(CO)6 (M=Cr, Mo, W) have been studied with picosecond transient absorption spectroscopy. After dissociation of C≡O, the pentacarbonyl species forms a complex with a solvent molecule. The cooling of these solvated pentacarbonyl complexes was monitored from 1 ps to 1 ns and different rates for vibrational relaxation were found for each of these three compounds. The W(CO)5⋅S (S=cyclohexane) vibrationally relaxes in 35 ps, whereas Mo(CO)5⋅S relaxes twice as quickly, 18 ps. This result is surprising because the higher density of states in W(CO)5⋅S would be expected to lead to faster cooling of the hot solvated complex. The primary cooling of Cr(CO)5⋅S is completed in 18 ps just as in Mo(CO)5⋅S, but a slower cooling of approximately 150 ps is also present. This component is assigned to vibrational relaxation of the C≡O stretching mode. From comparisons with other studies, it appears that the existence of this slower cooling component is present only in first row transition metal carbonyls.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465689
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  • 7
    Electronic Resource
    Electronic Resource
    Characteristic Spherulitic Microstructure in Partial-Melt-Processed YBa2Cu3Ox/HfO2 (2000)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 83 (2000), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The microstructure of partial-melt-processed YBa2Cu3Ox/HfO2 has been studied by transmission electron microscopy. A characteristic spherulitic microstructure is formed in the system. A model for the growth mechanism has been proposed. The critical heterogeneous nucleation of the YBa2Cu3Ox phase appears to occur from the melt in an epitaxially controlled manner on CuO particles. Subsequent growth of YBa2Cu3Ox platelets from the nucleus region is repeatedly interrupted by the nucleation of hafnium-rich phases in the liquid at the solid/liquid interface in a manner that again appears to be epitaxially controlled and that promotes the splay of the c orientation of the YBaCuO grain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01365.x
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  • 8
    Electronic Resource
    Electronic Resource
    A ZrO2 (3Y) Matrix Composite Toughened with Fe3Al Intermetallic (2005)
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Near fully dense ZrO2(3Y)/Fe3Al composites with significantly improved fracture toughness were synthesized by hot-press sintering at 1350°C. High fracture toughness and bending-strength values, 36 MPa·m1/2 and 1321 MPa, respectively, were achieved in 40 vol% Fe3Al composite ceramics, whereas those same values for ZrO2(3Y) alone were 10 MPa·m1/2 and 988 MPa, respectively. Microscopic observation of the crack path revealed that Fe3Al particle uniformly dispersed in the matrix have obvious crack-bridging effect. Improved thermal-shock resistance was also obtained, which was attributed to higher toughness, thermal conductivity, and lower Young's modulus by adding of Fe3Al particles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00038.x
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  • 9
    Electronic Resource
    Electronic Resource
    Purification of L-Aspartase by Gene Fusion (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 799 (1996), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1996.tb33237.x
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  • 10
    Electronic Resource
    Electronic Resource
    The Design, Synthesis, and Activity of a Ribozyme That Specially Cleaves Rat 28S rRNA (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 750 (1995), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1995.tb19919.x
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