Porous Si Nanoparticles Research Articles

External quantum efficiency of single porous silicon nanoparticles

We use a combination of single nanoparticle luminescence and scanning force microscopy to determine the quantum efficiency (QE) of single porous Si nanoparticles and to determine the ratio of luminescent nanoparticles deposited on a silica surface to the total nanoparticles. An estimate of the QE of bulk porous Si based on these data compares favorably to the QE measured experimentally. From this we conclude that the 1% QE of bulk porous Si measured experimentally results primarily from a statistical distribution of high QE quantum-confined Si chromophores.

Luminescence Intermittency and Quantum Efficiency of Individual Porous Si Nanoparticles.

ABSTRACTWe have recently observed spectrally resolved vibronic structure and luminescence intermittency from nanometer-size porous silicon nanocrystals. In this study we examine the quantum efficiency of a single nanoparticle and show that emitting nanoparticles do so with near unity quantum efficiency. This result suggests that the emission from porous Si nanoparticles, and thus bulk porous Si, results from a small number of high quantum efficiency emitters. In our previous work we have shown that our nanoparticles contain more than one coupled chromophore. In order to examine these effects more closely we employ several spectroscopy and microscopy techniques including: 1) single-particle spectroscopy, 2) shear-force microscopy, and 3) time-resolved spectroscopy, on a colloidal suspension of size-selected, surface-oxidized nanoparticles. In addition we apply statistical techniques to provide a more complete picture of the coupling between chromophores in a given nanoparticle.

Photoluminescence from Single Porous Silicon Chromophores

AbstractWe spatially isolate and detect the luminescence from individual porous Si nanoparticles at room temperature. Our experiments show a variety of phenomena not previously observed in the emission from porous Si including a distribution of emission wavelengths, resolved vibronic structure, random spectral wandering, luminescence intermittency and irreversible photobleaching. Our results indicate that the emission from porous Si nanoparticles originates from excitons in quantum confined Si, strongly influenced by the surface passivating layer of the Si nanocrystal.

Surface Oxidation and Luminescence Properties of Weblike Agglomeration of Silicon Nanocrystals Produced by a Laser Vaporization−Controlled Condensation Technique

Weblike aggregates of coalesced Si nanocrystals are produced by a laser vaporization−controlled condensation technique. SEM micrographs show particles with ∼10 nm diameter but the Raman shift suggests the presence of particles as small as ∼4 nm. FTIR of the freshly prepared particles shows weak peaks due to the stretching, bending, and rocking vibrations of the Si−O−Si bonds, indicating the presence of a surface oxidized layer, SiOx (x < 2). Further oxidation of the Si core appears to be very slow and inefficient under ambient temperature, but annealing at higher temperatures facilitates the oxidation. The particles show luminescence properties that are similar to those of porous Si and Si nanoparticles produced by other techniques. The nanoparticles do not luminesce unless, by exposure to air, they acquire the SiOx passivated coating. They show a short-lived blue emission characteristic of the SiO2 coating and a biexponential longer-lived red emission. The short lifetime component of the red emission, ab...

Luminescence Properties of Silicon Nanocrystals

AbstractWeblike aggregates of coalesced Si nanocrystals are produced by a laser vaporization -controlled condensation technique. SEM micrographs show particles with ∼ 10 nm diameters but the Raman shift suggests the presence of particles as small as ∼ 4 nm. FTIR of the freshly prepared particles shows weak peaks due to the stretching, bending and rocking vibrations of the Si-O-Si bonds indicating the presence of a surface oxidized layer SiOx (x&lt;2).The particles show luminescence properties that are similar to those of porous Si and Si nanoparticles produced by other techniques. The nanoparticles do not luminesce unless, by exposure to air, they acquire the SiOx passivated coating. They show a short-lived blue emission characteristic of the SiO2 coating and a biexponential longer-lived red emission. The short lifetime component of the red emission, about 12 μs, does not depend on emission wavelength. The longer-lived component has a lifetime that ranges from 90 to over 130 μs (at 300 K), increasing with emission wavelength. The results are consistent with the quantum confinement mechanism as the source of the red photoluminescence.