615 research outputs found
Controlling the charge transfer flow at the graphene/pyrene-nitrilotriacetic acid interface
The fabrication of highly efficient bio-organic nanoelectronic devices is still a challenge due to the difficulty in interfacing the biomolecular component to the organic counterparts. One of the ways to overcome this bottleneck is to add a self-assembled monolayer (SAM) in between the electrode and the biological material. The addition of a pyrene-nitrilotriacetic acid layer to a graphene metal electrode enhances the charge transfer within the device. Our theoretical calculations and electrochemical results show that the formation of a pyrene-nitrilotriacetic acid SAM enforces a direct electron transfer from graphene to the SAM, while the addition of the Ni2+ cation and imidazole reverses the charge transfer direction, allowing an atomic control of the electron flow, which is essential for a true working device. © 2018 The Royal Society of Chemistry
Exciton mediated one phonon resonant Raman scattering from one-dimensional systems
We use the Kramers-Heisenberg approach to derive a general expression for the
resonant Raman scattering cross section from a one-dimensional (1D) system
explicitly accounting for excitonic effects. The result should prove useful for
analyzing the Raman resonance excitation profile lineshapes for a variety of 1D
systems including carbon nanotubes and semiconductor quantum wires. We apply
this formalism to a simple 1D model system to illustrate the similarities and
differences between the free electron and correlated electron-hole theories.Comment: 10 pages, 6 figure
Chirality dependence of the radial breathing phonon mode density in single wall carbon nanotubes
A mass and spring model is used to calculate the phonon mode dispersion for
single wall carbon nanotubes (SWNTs) of arbitrary chirality. The calculated
dispersions are used to determine the chirality dependence of the radial
breathing phonon mode (RBM) density. Van Hove singularities, usually discussed
in the context of the single particle electronic excitation spectrum, are found
in the RBM density of states with distinct qualitative differences for zig zag,
armchair and chiral SWNTs. The influence the phonon mode density has on the two
phonon resonant Raman scattering cross-section is discussed.Comment: 6 pages, 2 figures, submitted to Phys. Rev.
Tunable Resonant Raman Scattering from Singly Resonant Single Wall Carbon Nanotubes
We perform tunable resonant Raman scattering on 17 semiconducting and 7
metallic singly resonant single wall carbon nanotubes. The measured scattering
cross-section as a function laser energy provides information about a tube's
electronic structure, the lifetime of intermediate states involved in the
scattering process and also energies of zone center optical phonons. Recording
the scattered Raman signal as a function of tube location in the microscope
focal plane allows us to construct two-dimensional spatial maps of singly
resonant tubes. We also describe a spectral nanoscale artifact we have coined
the "nano-slit effect"
100 GHz resonant cavity enhanced Schottky photodiodes
Cataloged from PDF version of article.Resonant cavity enhanced (RCE) photodiodes are promising candidates for applications in optical communications and interconnects where ultrafast high-efficiency detection is desirable. We have designed and fabricated RCE Schottky photodiodes in the (Al, In) GaAs material system for 900-nm wavelength. The observed temporal response with 10-ps pulsewidth was limited
by the measurement setup and a conservative estimation of the bandwidth corresponds to more than 100 GHz. A direct comparison of RCE versus conventional detector performance was performed by high speed measurements under optical excitation at resonant wavelength (895 nm) and at 840 nm where the device functions as a single-pass conventional photodiode. A more than two-fold bandwidth enhancement with the RCE detection scheme was demonstrated
InGaAs-based high-performance p-i-n photodiodes
Cataloged from PDF version of article.In this letter, we have designed, fabricated, and
characterized high-speed and high-efficiency InGaAs-based p-i-n
photodetectors with a resonant cavity enhanced structure. The
devices were fabricated by a microwave-compatible process. By
using a postprocess recess etch, we tuned the resonance wavelength
from 1605 to 1558 nm while keeping the peak efficiencies above
60%. The maximum quantum efficiency was 66% at 1572 nm
which was in good agreement with our theoretical calculations.
The photodiode had a linear response up to 6-mW optical power,
where we obtained 5-mA photocurrent at 3-V reverse bias. The
photodetector had a temporal response of 16 ps at 7-V bias. After
system response deconvolution, the 3-dB bandwidth of the device
was 31 GHz, which corresponds to a bandwidth-efficiency product
of 20 GHz
Design and Optimization of High-Speed Resonant Cavity Enhanced Schottky Photodiodes
Cataloged from PDF version of article.Resonant cavity enhanced (RCE) photodiodes (PD’s)
are promising candidates for applications in optical communications
and interconnects where high-speed high-efficiency photodetection
is desirable. In RCE structures, the electrical properties
of the photodetector remain mostly unchanged; however, the
presence of the microcavity causes wavelength selectivity accompanied
by a drastic increase of the optical field at the resonant
wavelengths. The enhanced optical field allows to maintain a high
efficiency for faster transit-time limited PD’s with thinner absorption
regions. The combination of an RCE detection scheme with
Schottky PD’s allows for the fabrication of high-performance
photodetectors with relatively simple material structures and
fabrication processes. In top-illuminated RCE Schottky PD’s,
a semitransparent Schottky contact can also serve as the top
reflector of the resonant cavity. We present theoretical and
experimental results on spectral and high-speed properties of
GaAs–AlAs–InGaAs RCE Schottky PD’s designed for 900-nm
wavelength
High-Speed High Effiency Large Area Resonant Cavity Enhanced p-I-n Photodiodes for Multimode Fiber Communications
Cataloged from PDF version of article.In this letter, we report AlGaAs–GaAs p-i-n photodiodes
with a 3-dB bandwidth in excess of 10 GHz for devices as
large as 60- m diameter. Resonant cavity enhanced photodetection
is employed to improve quantum efficiency, resulting in more
than 90% peak quantum efficiency at 850 nm
High bandwidth-efficiency solar-blind AlGaN Schottky photodiodes with low dark current
Cataloged from PDF version of article.Al0.38Ga0.62N/GaN heterojunction solar-blind Schottky photodetectors with low dark current, high responsivity, and fast pulse
response were demonstrated. A five-step microwave compatible fabrication process was utilized to fabricate the devices. The solarblind
detectors displayed extremely low dark current values: 30lm diameter devices exhibited leakage current below 3 fA under
reverse bias up to 12V. True solar-blind operation was ensured with a sharp cut-off around 266 nm. Peak responsivity of
147mA/W was measured at 256 nm under 20 V reverse bias. A visible rejection more than 4 orders of magnitude was achieved.
The thermally-limited detectivity of the devices was calculated as 1.8 · 1013 cmHz1/2W 1
. Temporal pulse response measurements
of the solar-blind detectors resulted in fast pulses with high 3-dB bandwidths. The best devices had 53 ps pulse-width and 4.1GHz
bandwidth. A bandwidth-efficiency product of 2.9GHz was achieved with the AlGaN Schottky photodiodes. (C) 2004 Elsevier Ltd. All rights reserve
Digital detection of exosomes by interferometric imaging
Exosomes, which are membranous nanovesicles, are actively released by cells and have been attributed to roles in cell-cell communication, cancer metastasis, and early disease diagnostics. The small size (30–100 nm) along with low refractive index contrast of exosomes makes direct characterization and phenotypical classification very difficult. In this work we present a method based on Single Particle Interferometric Reflectance Imaging Sensor (SP-IRIS) that allows multiplexed phenotyping and digital counting of various populations of individual exosomes (>50 nm) captured on a microarray-based solid phase chip. We demonstrate these characterization concepts using purified exosomes from a HEK 293 cell culture. As a demonstration of clinical utility, we characterize exosomes directly from human cerebrospinal fluid (hCSF). Our interferometric imaging method could capture, from a very small hCSF volume (20 uL), nanoparticles that have a size compatible with exosomes, using antibodies directed against tetraspanins. With this unprecedented capability, we foresee revolutionary implications in the clinical field with improvements in diagnosis and stratification of patients affected by different disorders.This work was supported by Regione Lombardia and Fondazione Cariplo through POR-FESR, project MINER (ID 46875467); Italian Ministry of Health, Ricerca Corrente. This work was partially supported by The Scientific and Technological Research Council of Turkey (grant #113E643). (Regione Lombardia; 46875467 - Fondazione Cariplo through POR-FESR, project MINER; Italian Ministry of Health, Ricerca Corrente; 113E643 - Scientific and Technological Research Council of Turkey)Published versio
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