639 research outputs found
Scaling Laws for NanoFET Sensors
The sensitive conductance change of semiconductor nanowires and carbon
nanotubes in response to binding of charged molecules provide a novel sensing
modality which is generally denoted as nanoFET sensors. In this paper, we study
the scaling laws of nanoplate FET sensors by simplifying nanoplates as random
resistor networks with molecular receptors sitting on lattice sites.
Nanowire/tube FETs are included as the limiting cases where the device width
goes small. Computer simulations show that the field effect strength exerted by
the binding molecules has significant impact on the scaling behaviors. When the
field effect strength is small, nanoFETs have little size and shape dependence.
In contrast, when the field-effect strength becomes stronger, there exists a
lower detection threshold for charge accumulation FETs and an upper detection
threshold for charge depletion FET sensors. At these thresholds, the nanoFET
devices undergo a transition between low and large sensitivities. These
thresholds may set the detection limits of nanoFET sensors, while could be
eliminated by designing devices with very short source-drain distance and large
width
Multifunctional Devices and Logic Gates With Undoped Silicon Nanowires
We report on the electronic transport properties of multiple-gate devices
fabricated from undoped silicon nanowires. Understanding and control of the
relevant transport mechanisms was achieved by means of local electrostatic
gating and temperature dependent measurements. The roles of the source/drain
contacts and of the silicon channel could be independently evaluated and tuned.
Wrap gates surrounding the silicide-silicon contact interfaces were proved to
be effective in inducing a full suppression of the contact Schottky barriers,
thereby enabling carrier injection down to liquid-helium temperature. By
independently tuning the effective Schottky barrier heights, a variety of
reconfigurable device functionalities could be obtained. In particular, the
same nanowire device could be configured to work as a Schottky barrier
transistor, a Schottky diode or a p-n diode with tunable polarities. This
versatility was eventually exploited to realize a NAND logic gate with gain
well above one.Comment: 6 pages, 5 figure
Coupling of Semiconductor Nanowires with Neurons and Their Interfacial Structure
We report on the compatibility of various nanowires with hippocampal neurons and the structural study of the neuron–nanowire interface. Si, Ge, SiGe, and GaN nanowires are compatible with hippocampal neurons due to their native oxide, but ZnO nanowires are toxic to neuron due to a release of Zn ion. The interfaces of fixed Si nanowire and hippocampal neuron, cross-sectional samples, were prepared by focused ion beam and observed by transmission electron microscopy. The results showed that the processes of neuron were adhered well on the nanowire without cleft
Transport in Silicon Nanowires: Role of Radial Dopant Profile
We consider the electronic transport properties of phosphorus (P) doped
silicon nanowires (SiNWs). By combining ab initio density functional theory
(DFT) calculations with a recursive Green's function method, we calculate the
conductance distribution of up to 200 nm long SiNWs with different
distributions of P dopant impurities. We find that the radial distribution of
the dopants influences the conductance properties significantly: Surface doped
wires have longer mean-free paths and smaller sample-to-sample fluctuations in
the cross-over from ballistic to diffusive transport. These findings can be
quantitatively predicted in terms of the scattering properties of the single
dopant atoms, implying that relatively simple calculations are sufficient in
practical device modelingComment: Submitted to Journal of Computational Electronics, presented in
IWCE-1
Programmable Assembly of DNA-Functionalized Liposomes by DNA
This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Nano, copyright © American Chemical Society after peer review and technical editing by publisher. To access the final edited and published work see http://dx.doi.org/10.1021/nn1030093Bionanotechnology involves the use of biomolecules to control both the structure and property of nanomaterials. One of the most studied examples is DNA-directed assembly of inorganic nanoparticles such as gold nanoparticles (AuNPs). However, systematic studies on DNA-linked soft nanoparticles, such as liposomes, are still lacking. We herein report the programmable assembly and systematic characterization of DNA-linked liposomes as a function of liposome size, charge, fluidity, composition, DNA spacer, linker DNA sequence, and salt concentration for direct comparison to DNA-directed assembly of AuNPs. Similar to the assemblies of AuNPs, sharp melting transitions were observed for liposomes where the first derivative of the melting curve full width at half-maximum (fwhm) is equal to or less than 1 °C for all of the tested liposomes, allowing sequence specific DNA detection. We found that parameters such as liposome size, charge, and fluidity have little effect on the DNA melting temperature. Cryo-TEM studies showed that programmable assemblies can be obtained and that the majority of the liposomes maintained a spherical shape in the assembled state. While liposome and AuNP systems are similar in many aspects, there are also important differences that can be explained by their respective physical properties.University of Waterloo ||
Natural Sciences and Engineering Research Council |
A pH sensor based on electric properties of nanotubes on a glass substrate
We fabricated a pH-sensitive device on a glass substrate based on properties of carbon nanotubes. Nanotubes were immobilized specifically on chemically modified areas on a substrate followed by deposition of metallic source and drain electrodes on the area. Some nanotubes connected the source and drain electrodes. A top gate electrode was fabricated on an insulating layer of silane coupling agent on the nanotube. The device showed properties of ann-type field effect transistor when a potential was applied to the nanotube from the top gate electrode. Before fabrication of the insulating layer, the device showed that thep-type field effect transistor and the current through the source and drain electrodes depend on the buffer pH. The current increases with decreasing pH of the CNT solution. This device, which can detect pH, is applicable for use as a biosensor through modification of the CNT surface
Detecting single viruses and nanoparticles using whispering gallery microlasers
Detection and characterization of individual nano-scale particles, virions,
and pathogens are of paramount importance to human health, homeland security,
diagnostic and environmental monitoring[1]. There is a strong demand for
high-resolution, portable, and cost-effective systems to make label-free
detection and measurement of individual nanoparticles, molecules, and viruses
[2-6]. Here, we report an easily accessible, real-time and label-free detection
method with single nanoparticle resolution that surpasses detection limit of
existing micro- and nano-photonic devices. This is achieved by using an
ultra-narrow linewidth whispering gallery microlaser, whose lasing line
undergoes frequency splitting upon the binding of individual nano-objects. We
demonstrate detection of polystyrene and gold nanoparticles as small as 15 nm
and 10 nm in radius, respectively, and Influenza A virions by monitoring
changes in self-heterodyning beat note of the split lasing modes. Experiments
are performed in both air and aqueous environment. The built-in self-heterodyne
interferometric method achieved in a microlaser provides a self-reference
scheme with extraordinary sensitivity [7,8], and paves the way for detection
and spectroscopy of nano-scale objects using micro- and nano-lasers.Comment: Main Text: 14 pages, 5 figures, 27 references. Supplement: 26 pages,
12 figures, 26 reference
Single Bead Affinity Detection (SINBAD) for the Analysis of Protein-Protein Interactions
We present a miniaturized pull-down method for the detection of protein-protein interactions using standard affinity chromatography reagents. Binding events between different proteins, which are color-coded with quantum dots (QDs), are visualized on single affinity chromatography beads by fluorescence microscopy. The use of QDs for single molecule detection allows the simultaneous analysis of multiple protein-protein binding events and reduces the amount of time and material needed to perform a pull-down experiment
Synthesis and Growth Mechanism of Ni Nanotubes and Nanowires
Highly ordered Ni nanotube and nanowire arrays were fabricated via electrodeposition. The Ni microstructures and the process of the formation were investigated using conventional and high-resolution transmission electron microscope. Herein, we demonstrated the systematic fabrication of Ni nanotube and nanowire arrays and proposed an original growth mechanism. With the different deposition time, nanotubes or nanowires can be obtained. Tubular nanostructures can be obtained at short time, while nanowires take longer time to form. This formation mechanism is applicable to design and synthesize other metal nanostructures and even compound nanostuctures via template-based electrodeposition
Catalyst preparation for CMOS-compatible silicon nanowire synthesis
Metallic contamination was key to the discovery of semiconductor nanowires,
but today it stands in the way of their adoption by the semiconductor industry.
This is because many of the metallic catalysts required for nanowire growth are
not compatible with standard CMOS (complementary metal oxide semiconductor)
fabrication processes. Nanowire synthesis with those metals which are CMOS
compatible, such as aluminium and copper, necessitate temperatures higher than
450 C, which is the maximum temperature allowed in CMOS processing. Here, we
demonstrate that the synthesis temperature of silicon nanowires using copper
based catalysts is limited by catalyst preparation. We show that the
appropriate catalyst can be produced by chemical means at temperatures as low
as 400 C. This is achieved by oxidizing the catalyst precursor, contradicting
the accepted wisdom that oxygen prevents metal-catalyzed nanowire growth. By
simultaneously solving material compatibility and temperature issues, this
catalyst synthesis could represent an important step towards real-world
applications of semiconductor nanowires.Comment: Supplementary video can be downloaded on Nature Nanotechnology
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