126 research outputs found
Nanomechanical structures with 91 MHz resonance frequency fabricated by local deposition and dry etching
We report an all-dry, two-step, surface nanoengineering method to fabricate nanomechanical elements without photolithography. It is based on the local deposition through a nanostencil of a well-defined aluminum pattern onto a silicon/silicon-nitride substrate, followed by plasma etching to release the structures. The suspended 100-nm-wide, 2-mum-long, and 300-nm-thick nanolevers and nanobridges have natural resonance frequencies of 50 and 91 MHz, respectively. The fabrication method is scalable to a full wafer and allows for a variety of materials to be structured on arbitrary surfaces, thus opening new types of nanoscale mechanical systems
Resonant exciton transfer in mixed-dimensional heterostructures for overcoming dimensional restrictions in optical processes
Nanomaterials exhibit unique optical phenomena, in particular excitonic
quantum processes occurring at room temperature. The low dimensionality,
however, imposes strict requirements for conventional optical excitation, and
an approach for bypassing such restrictions is desirable. Here we report on
exciton transfer in carbon-nanotube/tungsten-diselenide heterostructures, where
band alignment can be systematically varied. The mixed-dimensional
heterostructures display a pronounced exciton reservoir effect where the
longer-lifetime excitons within the two-dimensional semiconductor are funneled
into carbon nanotubes through diffusion. This new excitation pathway presents
several advantages, including larger absorption areas, broadband spectral
response, and polarization-independent efficiency. When band alignment is
resonant, we observe substantially more efficient excitation via tungsten
diselenide compared to direct excitation of the nanotube. We further
demonstrate simultaneous bright emission from an array of carbon nanotubes with
varied chiralities and orientations. Our findings show the potential of
mixed-dimensional heterostructures and band alignment engineering for energy
harvesting and quantum applications through exciton manipulation.Comment: 9 pages, 4 figure
Room-temperature quantum emission from interface excitons in mixed-dimensional heterostructures
The development of van der Waals heterostructures has introduced
unconventional phenomena that emerge at atomically precise interfaces. For
example, interlayer excitons in two-dimensional transition metal
dichalcogenides show intriguing optical properties at low temperatures. Here we
report on room-temperature observation of interface excitons in
mixed-dimensional heterostructures consisting of two-dimensional tungsten
diselenide and one-dimensional carbon nanotubes. Bright emission peaks
originating from the interface are identified, spanning a broad energy range
within the telecommunication wavelengths. The effect of band alignment is
investigated by systematically varying the nanotube bandgap, and we assign the
new peaks to interface excitons as they only appear in type-II
heterostructures. Room-temperature localization of low-energy interface
excitons is indicated by extended lifetimes as well as small excitation
saturation powers, and photon correlation measurements confirm single-photon
emission. With mixed-dimensional van der Waals heterostructures where band
alignment can be engineered, new opportunities for quantum photonics are
envisioned.Comment: 8 pages, 4 figure
Switching Mechanism in Single-Layer Molybdenum Disulfide Transistors: an Insight into Current Flow across Schottky Barriers
In this article, we study the properties of metal contacts to single-layer
molybdenum disulfide (MoS2) crystals, revealing the nature of switching
mechanism in MoS2 transistors. On investigating transistor behavior as contact
length changes, we find that the contact resistivity for metal/MoS2 junctions
is defined by contact area instead of contact width. The minimum gate dependent
transfer length is ~0.63 {\mu}m in the on-state for metal (Ti) contacted
single-layer MoS2. These results reveal that MoS2 transistors are Schottky
barrier transistors, where the on/off states are switched by the tuning the
Schottky barriers at contacts. The effective barrier heights for source and
drain barriers are primarily controlled by gate and drain biases, respectively.
We discuss the drain induced barrier narrowing effect for short channel
devices, which may reduce the influence of large contact resistance for MoS2
Schottky barrier transistors at the channel length scaling limit.Comment: ACS Nano, ASAP (2013
Effective electro-optical modulation with high extinction ratio by a graphene-silicon microring resonator
Graphene opens up for novel optoelectronic applications thanks to its high
carrier mobility, ultra-large absorption bandwidth, and extremely fast material
response. In particular, the opportunity to control optoelectronic properties
through tuning of Fermi level enables electro-optical modulation,
optical-optical switching, and other optoelectronics applications. However,
achieving a high modulation depth remains a challenge because of the modest
graphene-light interaction in the graphene-silicon devices, typically,
utilizing only a monolayer or few layers of graphene. Here, we comprehensively
study the interaction between graphene and a microring resonator, and its
influence on the optical modulation depth. We demonstrate graphene-silicon
microring devices showing a high modulation depth of 12.5 dB with a relatively
low bias voltage of 8.8 V. On-off electro-optical switching with an extinction
ratio of 3.8 dB is successfully demonstrated by applying a square-waveform with
a 4 V peak-to-peak voltage.Comment: 12 pages, including 7 figure
Lack of significant association of an insertion/deletion polymorphism in the angiotensin converting enzyme (ACE) gene with tropical calcific pancreatitis
BACKGROUND: The genetic basis of tropical calcific pancreatitis (TCP) is different and is explained by mutations in the pancreatic secretory trypsin inhibitor (SPINK1) gene. However, mutated SPINK1 does not account for the disease in all the patients, neither does it explain the phenotypic heterogeneity between TCP and fibro-calculous pancreatic diabetes (FCPD). Recent studies suggest a crucial role for pancreatic renin-angiotensin system during chronic hypoxia in acute pancreatitis and for angiotensin converting enzyme (ACE) inhibitors in reducing pancreatic fibrosis in experimental models. We investigated the association of ACE gene insertion/deletion (I/D) polymorphism in TCP patients using a case-control approach. Since SPINK1 mutations are proposed a modifier role, we also investigated its interaction with the ACE gene variant. METHODS: We analyzed the I/D polymorphism in the ACE gene (g.11417_11704del287) in 171 subjects comprising 91 TCP and 80 FCPD patients and compared the allelic and genotypic frequency in them with 99 healthy ethnically matched control subjects. RESULTS: We found 46% and 21% of TCP patients, 56% and 19.6% of FCPD patients and 54.5% and 19.2% of the healthy controls carrying the I/D and D/D genotypes respectively (P>0.05). No significant difference in the clinical picture was observed between patients with and without the del allele at the ACE in/del polymorphism in both categories. No association was observed with the presence or absence of N34S SPINK1 mutation in these patients. CONCLUSION: We conclude that the ACE insertion/deletion variant does not show any significant association with the pathogenesis, fibrosis and progression of tropical calcific pancreatitis and the fibro-calculous pancreatic diabetes
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