120 research outputs found
Electronic Transport Imaging in a Multiwire SnO2 ChemFET Device
The electronic transport and the sensing performance of an individual SnO2
crossed nanowires device in a three-terminal field effect configuration were
investigated using a combination of macroscopic transport measurements and
Scanning Surface Potential Microscopy (SSPM). The structure of the device was
determined using both Scanning Electron- and Atomic Force Microscopy data. The
SSPM images of two crossed 1D nanostructures, simulating a prototypical
nanowire network sensors, exhibit large dc potential drops at the crossed-wire
junction and at the contacts, identifying them as the primary electroactive
elements in the circuit. The gas sensitivity of this device was comparable to
those of sensors formed by individual homogeneous nanostructures of similar
dimensions. Under ambient conditions, the DC transport measurements were found
to be strongly affected by field-induced surface charges on the nanostructure
and the gate oxide. These charges result in a memory effect in transport
measurements and charge dynamics which are visualized by SSPM. Finally,
scanning probe microscopy is used to measure the current-voltage
characteristics of individual active circuit elements, paving the way to a
detailed understanding of chemical functionality at the level of an individual
electroactive element in an individual nanowire.Comment: 30 pages, 8 figures, accepted to J. Appl. Phy
Growth of Highly Doped P-Type Znte Films by Pulsed Laser ablation in Molecular Nitrogen
Highly p-doped ZnTe films have been grown on semi-insulating GaAs (001) substrates by pulsed-laser ablation (PLA) of a stoichiometric ZnTe target in a high-purity N{sub 2} ambient without the use of any assisting (DC or AC) plasma source. Free hole concentrations in the mid-10{sup 19} cm{sup {minus}3} to > 10{sup 20} cm{sup {minus}3} range were obtained for a range of nitrogen pressures The maximum hole concentration equals the highest hole doping reported to date for any wide band gap II-VI compound. The highest hole mobilities were attained for nitrogen pressures of 50--100 mTorr ({approximately}6.5-13 Pa). Unlike recent experiments in which atomic nitrogen beams, extracted from RF and DC plasma sources, were used to produce p-type doping during molecular beam epitaxy deposition, spectroscopic measurements carried out during PLA of ZnTe in N{sub 2} do not reveal the presence of atomic nitrogen. This suggests that the high hole concentrations in laser ablated ZnTe are produced by a new and different mechanism, possibly energetic beam-induced reactions with excited molecular nitrogen adsorbed on the growing film surface, or transient formation of Zn-N complexes in the energetic ablation plume. This appears to be the first time that any wide band gap (Eg > 2 eV) II-VI compound (or other) semiconductor has been impurity-doped from the gas phase by laser ablation. In combination with the recent discovery that epitaxial ZnSe{sub l-x}S{sub x} films and heterostructures with continuously variable composition can be grown by ablation from a single target of fixed composition, these results appear to open the way to explore PLA growth and doping of compound semiconductors as a possible alternative to molecular beam epitaxy
Nanofabrication with Pulsed Lasers
An overview of pulsed laser-assisted methods for nanofabrication, which are currently developed in our Institute (LP3), is presented. The methods compass a variety of possibilities for material nanostructuring offered by laserâmatter interactions and imply either the nanostructuring of the laser-illuminated surface itself, as in cases of direct laser ablation or laser plasma-assisted treatment of semiconductors to form light-absorbing and light-emitting nano-architectures, as well as periodic nanoarrays, or laser-assisted production of nanoclusters and their controlled growth in gaseous or liquid medium to form nanostructured films or colloidal nanoparticles. Nanomaterials synthesized by laser-assisted methods have a variety of unique properties, not reproducible by any other route, and are of importance for photovoltaics, optoelectronics, biological sensing, imaging and therapeutics
Fluctuation-driven, topology-stabilized order in a correlated nodal semimetal
The interplay between strong electron correlation and band topology is at the
forefront of condensed matter research. As a direct consequence of correlation,
magnetism enriches topological phases and also has promising functional
applications. However, the influence of topology on magnetism remains unclear,
and the main research effort has been limited to ground state magnetic orders.
Here we report a novel order above the magnetic transition temperature in
magnetic Weyl semimetal (WSM) CeAlGe. Such order shows a number of anomalies in
electrical and thermal transport, and neutron scattering measurements. We
attribute this order to the coupling of Weyl fermions and magnetic fluctuations
originating from a three-dimensional Seiberg-Witten monopole, which
qualitatively agrees well with the observations. Our work reveals a prominent
role topology may play in tailoring electron correlation beyond ground state
ordering, and offers a new avenue to investigate emergent electronic properties
in magnetic topological materials.Comment: 32 pages, 15 figure
Laser Interactions for the Synthesis and In Situ Diagnostics of Nanomaterials
Laser interactions have traditionall been at thec center of nanomaterials science, providing highly nonequilibrium growth conditions to enable the syn- thesis of novel new nanoparticles, nanotubes, and nanowires with metastable phases. Simultaneously, lasers provide unique opportunities for the remote char- acterization of nanomaterial size, structure, and composition through tunable laser spectroscopy, scattering, and imaging. Pulsed lasers offer the opportunity, there- fore, to supply the required energy and excitation to both control and understand the growth processes of nanomaterials, providing valuable views of the typically nonequilibrium growth kinetics and intermediates involved. Here we illustrate the key challenges and progress in laser interactions for the synthesis and in situ diagnostics of nanomaterials through recent examples involving primarily carbon nanomaterials, including the pulsed growth of carbon nanotubes and graphene
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Nanoscale Science, Engineering and Technology Research Directions
This report describes important future research directions in nanoscale science, engineering and technology. It was prepared in connection with an anticipated national research initiative on nanotechnology for the twenty-first century. The research directions described are not expected to be inclusive but illustrate the wide range of research opportunities and challenges that could be undertaken through the national laboratories and their major national scientific user facilities with the support of universities and industry
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