51 research outputs found
Lineshape of the thermopower of quantum dots
Quantum dots are an important model system for thermoelectric phenomena, and
may be used to enhance the thermal-to-electric energy conversion efficiency in
functional materials. It is therefore important to obtain a detailed
understanding of a quantum-dot's thermopower as a function of the Fermi energy.
However, so far it has proven difficult to take effects of co-tunnelling into
account in the interpretation of experimental data. Here we show that a
single-electron tunnelling model, using knowledge of the dot's electrical
conductance which in fact includes all-order co-tunneling effects, predicts the
thermopower of quantum dots as a function of the relevant energy scales, in
very good agreement with experiment.Comment: 10 pages, 5 figure
Correlating the nanostructure and electronic properties of InAs nanowires
The electronic properties and nanostructure of InAs nanowires are correlated
by creating multiple field effect transistors (FETs) on nanowires grown to have
low and high defect density segments. 4.2 K carrier mobilities are ~4X larger
in the nominally defect-free segments of the wire. We also find that dark field
optical intensity is correlated with the mobility, suggesting a simple route
for selecting wires with a low defect density. At low temperatures, FETs
fabricated on high defect density segments of InAs nanowires showed transport
properties consistent with single electron charging, even on devices with low
resistance ohmic contacts. The charging energies obtained suggest quantum dot
formation at defects in the wires. These results reinforce the importance of
controlling the defect density in order to produce high quality electrical and
optical devices using InAs nanowires.Comment: Related papers at http://pettagroup.princeton.ed
From InSb Nanowires to Nanocubes: Looking for the Sweet Spot
High aspect ratios are highly desired to fully exploit the one-dimensional properties of indium antimonide nanowires. Here we systematically investigate the growth mechanisms and find parameters leading to long and thin nanowires. Variation of the V/III ratio and the nanowire density are found to have the same influence on the “local” growth conditions and can control the InSb shape from thin nanowires to nanocubes. We propose that the V/III ratio controls the droplet composition and the radial growth rate and these parameters determine the nanowire shape. A sweet spot is found for nanowire interdistances around 500 nm leading to aspect ratios up to 35. High electron mobilities up to 3.5 × 10^4 cm^2 V^(–1) s^(–1) enable the realization of complex spintronic and topological devices
Carbohydrate-based block copolymer systems : Directed self-assembly for nanolithography applications
Self-assembly of block copolymers (BCPs) provides an attractive nanolithography approach, which looks especially promising for fabrication of regular structures with characteristic sizes below 10 nm. Nevertheless, directed self-assembly (DSA) and pattern transfer for BCPs with such small features remain to be a challenge. Here we demonstrate DSA of the maltoheptaose-block-polystyrene (MH1,2k-b-PS4,5k) BCP system using graphoepitaxy. BCP thin films were self-organized by solvent vapor annealing in tetrahydrofuran (THF) and water into sub-10 nm scale cylinders of the maltoheptaose (MH) block oriented horizontally or perpendicularly to the surface in a polystyrene (PS) matrix. The guiding patterns for graphoepitaxy were made by the electron beam lithography (EBL) and lift-off process with the distance gradually varying between 0 and 200 nm. Atomic force microscopy (AFM) investigation of MH1,2k-b-PS4,5k BCP DSA patterns revealed good ordering of vertical and horizontal cylindrical MH arrays for DSA lines with 150-200 nm separation. Reactive ion etching (RIE) of MH1,2k and PS4,5k thin films in O2 and CF4 plasma showed up to 14 times higher etch rate of MH compared to PS. These results indicate that MH1,2k-b-PS4,5k is a promising BCP for nanolithographic applications below 10 nm
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