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  • 1
    Electronic Resource
    Electronic Resource
    The effect of ultrathin oxides on luminescent silicon nanocrystallites (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 841-843 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of ultrathin oxides on nanocrystallites of luminescent porous silicon is studied using infrared, optical, and Auger spectroscopy. Room-temperature oxidation is performed using H2O2 immersion and UV ozone interactions, producing oxides of ∼5 and ∼10 Å, respectively. The H2O2 oxidized sample is optically active, while the ozone oxidized sample is not active. UV–ozone produces a transverse optical Si–O–Si mode blueshifted by ∼90 cm−1 from bulk oxide, which H2O2 does not produce. Auger Si LVV spectra show an oxidelike signal for UV/ozone samples and a Si-like signal for H2O2 samples. We discuss this in terms of different oxidation behaviors that either preserve or break Si–Si dimers that may be responsible for the optical behavior. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122019
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  • 2
    Electronic Resource
    Electronic Resource
    Re-establishment of photoluminescence in Cu quenched porous silicon by acid treatment (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4130-4132 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: HCl, H3PO4, and H2SO4 baths have been used to re-establish the photoluminescence of porous Si whose initial luminescence had been quenched by immersion in CuCl2. HCl had the fastest effect, with luminescence beginning to reappear after typically a few minutes, while the other acids required typically one to two days for dim luminescence to start reappearing. Auger electron spectroscopy (AES) depth profiling showed that after quenching, the Cu profile typically penetrated 2000 to 3000 A(ring) into the porous Si and that the O concentration was greatly enhanced in this region. After re-establishment of the luminescence by acid treatment, the AES depth profiles showed no Cu, but still had an enhanced O region of similar size and concentration. Photoluminescence emission spectra taken in situ during acid treatment with HCl showed a redshift of about 8% in the peak wavelength as the intensity increased. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359559
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  • 3
    Electronic Resource
    Electronic Resource
    Red to green rainbow photoluminescence from unoxidized silicon nanocrystallites (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 3929-3931 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We prepared luminescent silicon by incorporating H2O2 in the anodizing process. Under UV excitation, our samples appear reddish, orangish, yellowish to greenish as the electrolyte-air interface at the meniscus is approached. Under high current anodization, the emission becomes broad but unstable. The time characteristics of all the emission regions are in the range of 1–10 μs. The results are consistent with a significant reduction of crystallite sizes, and may be explained via novel Si–Si dimer surface states that are induced by quantum confinement. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367313
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  • 4
    Electronic Resource
    Electronic Resource
    Correlation of diffuse scattering with nanocrystallite size in porous silicon using transmission microscopy (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 8050-8053 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We use high resolution cross sectional transmission electron microscopy to image the nanostructure of (100) p-type porous Si. A network of pore tracks subdivide the material into nano-islands and nanocrystallites are resolved throughout the material. With distance from the substrate, electron diffraction develops noncrystalline-like diffuse patterns that dominate the coherent scattering in the topmost luminescent layer. Also, with distance from the substrate, crystalline islands evolve such that their size drops to as small as 1 nm in the topmost luminescence material. Although the topmost luminescent layer is very rich in nanocrystallites, it has the strongest diffuse scattering of all regions. This confirms that diffuse scattering is due to size reduction effects rather than to an amorphous state. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370641
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  • 5
    Electronic Resource
    Electronic Resource
    Oxide and hydrogen capped ultrasmall blue luminescent Si nanoparticles (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 779-781 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We dispersed electrochemical etched silicon into a colloid of ultrasmall ultrabright Si nanoparticles. Direct imaging using transmission electron microscopy shows particles of ∼1 nm in diameter, and infrared and electron photospectroscopy show that they are passivated with hydrogen. Under 350 nm excitation, the luminescence is dominated by an extremely strong blue band at 390 nm. We replace hydrogen by a high-quality ultrathin surface oxide cap by self-limiting oxidation in H2O2. Upon capping, the excitation efficiency drops, but only by a factor of 2, to an efficiency still two-fold larger than that of fluorescein. Although of slightly lower brightness, capped Si particles have superior biocompatability, an important property for biosensing applications. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1306659
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  • 6
    Electronic Resource
    Electronic Resource
    Light-induced conductance resonance in ultrasmall Si nanoparticles (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 1668-1670 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ultrasmall, uniform-size (∼1 nm) Si nanoparticles, dispersed from p-type boron-doped silicon, are reconstituted on a Si substrate. Electronic transport processes are studied by current–voltage spectroscopy at room temperature, using scanning tunneling microscopy, in a two-terminal configuration, under both dark conditions and light illumination. Unlike the dark conditions, we observe, under light irradiation, for negative tip biasing, a regular structure at ∼1.0 eV period. The series is discussed in terms of light-induced hole states that otherwise are highly infrequent in ultrasmall Si particles, under standard low doping. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1308524
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  • 7
    Electronic Resource
    Electronic Resource
    Revival of interband crystalline reflectance from nanocrystallites in porous silicon by immersion plating (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 3483-3485 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We prepared porous silicon for which the UV reflectance (3.3–6 eV) is nearly eliminated, and exhibits no features at the Si interband bulk transitions 3.3, 4.3, and 5.5 eV. Plating with a thin layer of copper is found to cause recovery of the UV bulk-like crystalline reflectance and interband resonances. This provides evidence that the loss of crystalline absorption is reversible and is not due to a permanent loss in the crystalline structure. This may relate to a recent model in which the optical activity of ultra small nanocrystallites is produced by a new Si–Si crystalline configuration (or phase), distinct from but interconnected to the diamond-like configuration by a potential barrier. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124135
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  • 8
    Electronic Resource
    Electronic Resource
    Excitation of size selected nanocrystallites in porous silicon (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 2556-2558 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We prepared silicon that exhibits green-to-red rainbow luminescence along the sample, reflecting gradients in the crystallite size. The excitation has a size-dependent feature, riding a smooth bulklike continuum. For the size-dependent contribution, we measured absorption band edges of 3.75 and 3.0–3.25 eV at the meniscus and opposite end. Excitation in the meniscus, monitored at the edge of the blue emission, isolates ultrasmall sizes, with "excitation coefficients" quadratic with energy, and emission encompassing much of the visible spectrum. Results are discussed in terms of quantum-confinement-induced restructuring of the diamondlike bonds to form radiative Si–Si surface states. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121416
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  • 9
    Electronic Resource
    Electronic Resource
    Ideal anodization of silicon (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 3404-3406 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Silicon has been anodized such that the porous layer is passivated with a homogeneous stretching phase by incorporating H2O2 in the anodization mixture. Fourier transform infrared spectroscopy measurements show that the Si–H stretching mode oriented perpendicular to the surface at ∼2100 cm−1 dominates the spectrum with negligible contribution from the bending modes in the 600–900 cm−1 region. Material analysis using Auger electron spectroscopy shows that the samples have very little impurities, and that the luminescent layer is very thin (5–10 nm). Scanning electron microscopy shows that the surface is smoother with features smaller than those of conventional samples. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119185
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  • 10
    Electronic Resource
    Electronic Resource
    Room temperature oxidation enhancement of porous Si(001) using ultraviolet–ozone exposure (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 5415-5421 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interaction of porous silicon (001) with ozone and ultraviolet (uv) was investigated at room temperature and ambient pressure. The O/Si atomic ratio in oxidized samples, as measured by Auger depth profiling, was similar to those measured from thermally oxidized samples. For long exposure times ((approximately-greater-than)15 min), the O/Si ratio stayed constant throughout the porous layer, indicating full oxidation of the porous structure. Additionally, the carbon concentration decreased significantly in the uv–ozone oxidized layers as compared to the untreated porous layers. Oxide layers up to 400 nm were measured. Fourier transform ir absorption measurements show both an increase in the oxygen concentration and a decrease in hydrogen concentration after oxidation. Photoluminescence data show that this method of oxidation quenches light emission from the porous layer. We believe that uv induced excitation of valence electrons results in higher reactivity and diffusion of oxygen and ozone as well as bond softening. The large volume of voids in the porous structure assist penetration of ozone and atomic oxygen throughout the porous structure while the narrow lateral dimensions of the Si skeleton requires a short diffusion length for full oxidation. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362728
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