Near field probe microscopy of porous silicon: Observation of spectral shifts in photoluminescence of small particles

Rogers, J. K.; Seiferth, F.; Vaez-Iravani, M.

doi:10.1063/1.113397

Cited by 25 publications

(7 citation statements)

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“…In a series of recent publications, − we have utilized near-field scanning optical microscopy (NSOM) to study the long, flexible, fluorescent fibers observed in thin films produced from aqueous mixtures of the pseudo-isocyanine dye (PIC), 1,1‘-diethyl-2,2‘-cyanine iodide, and the anionic polymer poly(vinyl sulfate) (PVS). NSOM is a new form of scanned-probe microscopy which utilizes light as the imaging mechanism and provides subwavelength spatial resolution in visible-light imaging and spectroscopy experiments on materials surfaces. − We utilized NSOM in our previous publications to directly study the morphological and electronic properties of the PIC/PVS fibers spin-coated onto fused-quartz substrates. In our first publication, we showed that the fluorescent nature of the fibers resulted from the self-assembly of a well-ordered, homogeneous molecular arrangement of PIC within the fibers .…”

Section: Introductionmentioning

confidence: 99%

A Molecular Yarn: Near-Field Optical Studies of Self-Assembled, Flexible, Fluorescent Fibers

et al. 1996

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The formation of flexible molecular fibers via the solution-phase self-assembly of the pseudo-isocyanine dye (PIC) 1,1′-diethyl-2,2′-cyanine, and poly(vinyl sulfate) (PVS) is reported. The physical and electronic properties of these fibers spin-coated into thin films on fused-quartz substrates are studied by fluorescence and topographic imaging with near-field scanning optical microscopy (NSOM) and also by atomic force microscopy (AFM). The scanned-probe images demonstrate that fibers with lengths in the hundred micrometer range, widths of hundreds of nanometers, and thicknesses of a few tens of nanometers are readily formed in aqueous mixtures of PVS and PIC. Unprecedented flexibility in these fibers is exemplified by the formation of numerous curved and looped structures in the spin-coated thin films. A sandwich-like composite structure of alternating anionic PVS and cationic PIC layers is proposed as a model for the assembly of the dye and polymer in these fibers. The alternating layers in this model are held tightly together via the cooperative "cross-linking" of the PVS and PIC layers by electrostatic dye/ polymer interactions, and by hydrophobic van der Waals interactions between the PIC molecules. The intermolecular interactions in the PIC layer result in the formation of a liquid-crystalline-like, well-ordered layer of the PIC which exhibits the spectral characteristics of J-aggregates. The proposed layered structure apparently possesses "reactive" surfaces which link individual fibers into a yarnlike assembly. This cross-linking effect is supported by the presence of continuous circular fibers and by the gel-forming ability of the solutions from which these fibers are grown.

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Section: Introductionmentioning

confidence: 99%

A Molecular Yarn: Near-Field Optical Studies of Self-Assembled, Flexible, Fluorescent Fibers

et al. 1996

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“…These methods are widely applied to study individual NCs of III-V and II-VI semiconductors 3 but have only scarcely been used to study light emission from silicon NCs ͑Si NCs͒. 4,5 Two main difficulties are the low emission rate from the Si NC ͑long radiation lifetime resulting from the indirect transition͒ and the complicated preparation of diluted and well-defined systems of Si NCs. Recently, the Buratto group reported PL studies of dispersed single porous-Si grains.…”

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confidence: 99%

Photoluminescence spectroscopy of single silicon quantum dots

Valenta¹,

Juhasz²,

Linnros³

2002

Applied Physics Letters

175

128

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Photoluminescence (PL) from single silicon quantum dots have been recorded and spectrally resolved at room temperature. The Si nanocrystals (NCs) were fabricated using electron-beam lithography and reactive ion etching resulting in Si nanopillars that were subsequently oxidized to produce luminescent silicon cores. The NCs are organized in a regular matrix which enables repeated observation of a specific single NC. By reflection and PL imaging, the emission is shown to originate from the Si nanopillars. The single-NC PL spectrum has a single band with a width of ∼130 meV. The emission is polarized in arbitrary directions suggestive of geometrical differences in the shape of the nanocrystals. The quantum efficiency of the PL has been found to reach as much as 35% for some nanocrystals. Our experiments support the quantum-confinement model for the PL emission of Si nanocrystals and elucidate the critical role of defect passivation.

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“…In order to separate the topographical effect from the fluorescence signal, the effect of the particle shape must be considered (Rogers et al ., 1995). The effect of the particle shape is important when the electric field distribution in the particle has some obvious feature, for example the whispering gallery mode in a spherical particle.…”

Section: Resultsmentioning

confidence: 99%

Photoluminescence imaging of phosphor particles using near‐field optical microscope with UV light excitation

Nishikawa

Isu

1999

Journal of Microscopy

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SummaryWe have developed ®bre probes suitable for 325 nm UV light excitation and a photoluminescence near-®eld scanning optical microscope (NSOM) and demonstrated the photoluminescence imaging of phosphor BaMgAl 10 O 17 :Eu 2 (BAM) particles. The probe was fabricated by a two-stepetching method that we developed. The probe had a large taper angle at the top of the probe and a small taper angle at the root. The NSOM image was different from the topographical structure but roughly re¯ected the corresponding features of the particles. The inhomogeneity of the photoluminescence intensity between BAM particles was observed in the NSOM image. The photoluminescence intensity with various bandpass ®lters showed differences between the individual particles, which means that they have different spectra.

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Near field probe microscopy of porous silicon: Observation of spectral shifts in photoluminescence of small particles

Cited by 25 publications

References 0 publications

A Molecular Yarn: Near-Field Optical Studies of Self-Assembled, Flexible, Fluorescent Fibers

A Molecular Yarn: Near-Field Optical Studies of Self-Assembled, Flexible, Fluorescent Fibers

Photoluminescence spectroscopy of single silicon quantum dots

Photoluminescence imaging of phosphor particles using near‐field optical microscope with UV light excitation

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