Size-dependent oxygen-related electronic states in silicon nanocrystals

Silicon nanocrystals embedded in SiO2 were isolated with a selective etching procedure, and the isolated nanocrystals' excitonic emission energy was studied during controlled oxidation. Nanocrystals having initial diameters, d(0), of similar to 2.9-3.4 nm showed a photoluminescence (PL) blueshift upon oxidatively induced size reduction, as expected from models of quantum confinement. Oxidation of smaller Si nanocrystals (d(0)similar to 2.5-2.8 nm) also initially resulted in a PL blueshift, but a redshift in the PL was then observed after growth of similar to 0.3 monolayers of native oxide. This decrease in excitonic emission energy during oxidation is consistent with the theoretically predicted formation of an oxygen-related excitonic recombination state

Spectral tuning of plasmon-enhanced silicon quantum dot luminescence

In the presence of nanoscale silver island arrays, silicon quantum dots exhibit up to sevenfold luminescence enhancements at emission frequencies that correspond to the collective dipole plasmon resonance frequency of the Ag island array. Using electron-beam lithography to alter the pitch and particle diameter, this wavelength-selective enhancement can be varied as the metal array resonance wavelength is tuned from 600 to 900 nm. The luminescence intensity enhancement upon coupling is attributed to an increase in the radiative decay rate of the silicon quantum dots

Phosphine Functionalization of GaAs(111)A Surfaces

Phosphorus-functionalized GaAs surfaces have been prepared by exposure of Cl-terminated GaAs(111)A surfaces to triethylphosphine (PEt3) or trichlorophosphine (PCl3), or by the direct functionalization of the native-oxide terminated GaAs(111)A surface with PCl3. The presence of phosphorus on each functionalized surface was confirmed by X-ray photoelectron spectroscopy. High-resolution, soft X-ray photoelectron spectroscopy was used to evaluate the As and Ga 3d regions of such surfaces. On PEt3 treated surfaces, the Ga 3d spectra exhibited a bulk Ga peak as well as peaks that were shifted to 0.35, 0.92 and 1.86 eV higher binding energy. These peaks were assigned to residual Cl-terminated Ga surface sites, surficial Ga2O and surficial Ga2O3, respectively. For PCl3-treated surfaces, the Ga 3d spectra displayed peaks ascribable to bulk Ga(As), Ga2O, and Ga2O3, as well as a peak shifted 0.30 eV to higher binding energy relative to the bulk signal. A peak corresponding to Ga(OH)3, observed on the Cl-terminated surface, was absent from all of the phosphine-functionalized surfaces. After reaction of the Cl-terminated GaAs(111)A surface with PCl3 or PEt3, the As 3d spectral region was free of As oxides and As0. Although native oxide-terminated GaAs surfaces were free of As oxides after reaction with PCl3, such surfaces contained detectable amounts of As0. Photoluminescence measurements indicted that phosphine-functionalized surfaces prepared from Cl-terminated GaAs(111)A surfaces had better electrical properties than the native-oxide capped GaAs(111)A surface, while the native-oxide covered surface treated with PCl3 showed no enhancement in PL intensity

Enhanced Radiative Emission Rate and Quantum Efficiency in Coupled Silicon Nanocrystal-Nanostructured Gold Emitters

We report local-field-enhanced light emission from silicon nanocrystals close to a film of nanoporous gold. We resolve photoluminescence as the gold−Si nanocrystal separation distance is varied between 0 and 20 nm and observe a fourfold luminescence intensity enhancement concomitant with increases in the coupled silicon nanocrystal/nanoporous gold absorbance cross section and radiative decay rate. A detailed analysis of the luminescence data indicated a local-field-enhanced quantum efficiency of 58% for the Si nanocrystals coupled to the nanoporous gold layer

Single‐molecule tracking in live Vibrio cholerae reveals that ToxR recruits the membrane‐bound virulence regulator TcpP to the toxT promoter

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110815/1/mmi12834.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/110815/2/mmi12834-sup-0001-si.pd

Extending the tools of single‐molecule fluorescence imaging to problems in microbiology

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/92099/1/j.1365-2958.2012.08089.x.pd

Addressing the Requirements of High‐Sensitivity Single‐Molecule Imaging of Low‐Copy‐Number Proteins in Bacteria

Single‐molecule fluorescence super‐resolution imaging and tracking provide nanometer‐scale information about subcellular protein positions and dynamics. These single‐molecule imaging experiments can be very powerful, but they are best suited to high‐copy number proteins where many measurements can be made sequentially in each cell. We describe artifacts associated with the challenge of imaging a protein expressed in only a few copies per cell. We image live Bacillus subtilis in a fluorescence microscope, and demonstrate that under standard single‐molecule imaging conditions, unlabeled B. subtilis cells display punctate red fluorescent spots indistinguishable from the few PAmCherry fluorescent protein single molecules under investigation. All Bacillus species investigated were strongly affected by this artifact, whereas we did not find a significant number of these background sources in two other species we investigated, Enterococcus faecalis and Escherichia coli. With single‐molecule resolution, we characterize the number, spatial distribution, and intensities of these impurity spots.Bright spots: A single‐molecule‐like fluorescent background signal is reported in Bacillus subtilis cells, and the density and fluorescence intensity of these spots are quantified in several Bacillus species and other Gram‐negative and Gram‐positive organisms.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/144710/1/cphc201600035_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/144710/2/cphc201600035.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/144710/3/cphc201600035-sup-0001-misc_information.pd

Chip-scale photonics with plasmonic components

In this talk we will describe recent opportunities presented by plasmonics for chip-scale integration of photonic and electronic devices, including i)design of metal-insulator-metal plasmon waveguides that optimize the trade-off between mode localization and propagation loss in the visible and near-infrared ii) on-chip Si CMOS compatible light near-infrared light sources for coupling into plasmonic networks iii) plasmon-enhanced emission from quantum dots, and iv) opportunities for active plasmonic devices based on electro-optic and all-optical modulation of plasmon propagation