12 research outputs found
A Superconducting-Nanowire Three-Terminal Electrothermal Device
Superconducting electronics based
on Josephson junctions are used
to sense and process electronic signals with minimal loss; however,
they are ultrasensitive to magnetic fields, limited in their amplification
capabilities, and difficult to manufacture. We have developed a 3-terminal,
nanowire-based superconducting electrothermal device which has no
Josephson junctions. This device, which we call the nanocryotron,
can be patterned from a single thin film of superconducting material
with conventional electron-beam lithography. The nanocryotron has
a demonstrated gain of >20, can drive impedances of 100 kΩ,
and operates in typical ambient magnetic fields. We have additionally
applied it both as a digital logic element in a half-adder circuit,
and as a digital amplifier for superconducting nanowire single-photon
detectors pulses. The nanocryotron has immediate applications in classical
and quantum communications, photon sensing, and astronomy, and its
input characteristics are suitable for integration with existing superconducting
technologies
Dimensional Tailoring of Hydrothermally Grown Zinc Oxide Nanowire Arrays
Hydrothermally
synthesized ZnO nanowire arrays are critical components
in a range of nanostructured semiconductor devices. The device performance
is governed by relevant nanowire morphological parameters that cannot
be fully controlled during bulk hydrothermal synthesis due to its
transient nature. Here, we maintain homeostatic zinc concentration,
pH, and temperature by employing continuous flow synthesis and demonstrate
independent tailoring of nanowire array dimensions including areal
density, length, and diameter on device-relevant length scales. By
applying diffusion/reaction-limited analysis, we separate the effect
of local diffusive transport from the <i>c</i>-plane surface
reaction rate and identify direct incorporation as the <i>c</i>-plane growth mechanism. Our analysis defines guidelines for precise
and independent control of the nanowire length and diameter by operating
in rate-limiting regimes. We validate its utility by using surface
adsorbents that limit reaction rate to obtain spatially uniform vertical
growth rates across a patterned substrate
Mapping Photoemission and Hot-Electron Emission from Plasmonic Nanoantennas
Understanding plasmon-mediated
electron emission and energy transfer
on the nanometer length scale is critical to controlling light–matter
interactions at nanoscale dimensions. In a high-resolution lithographic
material, electron emission and energy transfer lead to chemical transformations.
In this work, we employ such chemical transformations in two different
high-resolution electron-beam lithography resists, poly(methyl methacrylate)
(PMMA) and hydrogen silsesquioxane (HSQ), to map local electron emission
and energy transfer with nanometer resolution from plasmonic nanoantennas
excited by femtosecond laser pulses. We observe exposure of the electron-beam
resists (both PMMA and HSQ) in regions on the surface of nanoantennas
where the local field is significantly enhanced. Exposure in these
regions is consistent with previously reported optical-field-controlled
electron emission from plasmonic hotspots as well as earlier work
on low-electron-energy scanning probe lithography. For HSQ, in addition
to exposure in hotspots, we observe resist exposure at the centers
of rod-shaped nanoantennas in addition to exposure in plasmonic hotspots.
Optical field enhancement is minimized at the center of nanorods suggesting
that exposure in these regions involves a different mechanism to that
in plasmonic hotspots. Our simulations suggest that exposure at the
center of nanorods results from the emission of hot electrons produced
via plasmon decay in the nanorods. Overall, the results presented
in this work provide a means to map both optical-field-controlled
electron emission and hot-electron transfer from nanoparticles via
chemical transformations produced locally in lithographic materials
Aligned Sub-10-nm Block Copolymer Patterns Templated by Post Arrays
Self-assembly of block copolymer films can generate useful periodic nanopatterns, but the self-assembly needs to be templated to impose long-range order and to control pattern registration with other substrate features. We demonstrate here the fabrication of aligned sub-10-nm line width patterns with a controlled orientation by using lithographically formed post arrays as templates for a 16 kg/mol poly(styrene-block-dimethylsiloxane) (PS-<i>b</i>-PDMS) diblock copolymer. The in-plane orientation of the block copolymer cylinders was controlled by varying the spacing and geometry of the posts, and the results were modeled using 3D self-consistent field theory. This work illustrates how arrays of narrow lines with specific in-plane orientation can be produced, and how the post height and diameter affect the self-assembly
El Compostelano : diario independiente: Ano VIII Número 2236 - 1927 setembro 1
We investigated electron-beam lithography
with an aberration-corrected
scanning transmission electron microscope. We achieved 2 nm isolated
feature size and 5 nm half-pitch in hydrogen silsesquioxane resist.
We also analyzed the resolution limits of this technique by measuring
the point-spread function at 200 keV. Furthermore, we measured the
energy loss in the resist using electron-energy-loss spectroscopy
Efficient Single Photon Detection from 500 nm to 5 μm Wavelength
We report on superconducting nanowire single photon detectors
(SNSPDs)
based on 30 nm wide nanowires with detection efficiency η ∼
2.6–5.5% in the wavelength range λ = 0.5–5 μm.
We compared the sensitivity of 30 nm wide SNSPDs with the sensitivity
of SNSPDs based on wider (85 and 50 nm wide) nanowires for λ
= 0.5–5 μm. The detection efficiency of the detectors
based on the wider nanowires became negligible at shorter wavelengths
than the 30 nm wide SNSPDs. Our 30 nm wide SNSPDs showed 2 orders
of magnitude higher detection efficiency (η ∼ 2%) up
to longer wavelength (λ = 5 μm) than previously reported.
On the basis of our simulations, we expect that by changing the optical
coupling scheme and by integrating the detectors in an optical cavity,
the detection efficiency of our detectors could be increased by a
factor of ∼6
Orientational Preference in Multilayer Block Copolymer Nanomeshes with Respect to Layer-to-Layer Commensurability
We present a combination
of self-consistent field theory simulations
and experimental results to explore the mechanism behind the orientational
preference of second-layer cylinders in nanomeshes formed by two consecutive
steps of the self-assembly of block copolymers (BCPs). Incommensurability
of the top-layer cylinder spacing with that of the bottom-layer features
is found to dictate orientation preference, and this mismatch can
be controlled by either the film height or the nanomesh spacing ratio
via the molecular weight of the polymers used. When the space available
within the film does not accommodate the hexagonal packing of the
parallel orientation, the system will favor orthogonal alignment of
the second-layer cylinders. This behavior is robust: it is consistently
observed in many experimental systems and verified here by the comparison
of free energies of both states obtained from simulations. We also
discuss the impact of substrate selectivity and air–polymer
interface selectivity on these energies and therefore their effect
on the orientational selection
High-Energy Surface and Volume Plasmons in Nanopatterned Sub-10 nm Aluminum Nanostructures
In this work, we use electron energy-loss
spectroscopy to map the
complete plasmonic spectrum of aluminum nanodisks with diameters ranging
from 3 to 120 nm fabricated by high-resolution electron-beam lithography.
Our nanopatterning approach allows us to produce localized surface
plasmon resonances across a wide spectral range spanning 2–8
eV. Electromagnetic simulations using the finite element method support
the existence of dipolar, quadrupolar, and hexapolar surface plasmon
modes as well as centrosymmetric breathing modes depending on the
location of the electron-beam excitation. In addition, we have developed
an approach using nanolithography that is capable of meV control over
the energy and attosecond control over the lifetime of volume plasmons
in these nanodisks. The precise measurement of volume plasmon lifetime
may also provide an opportunity to probe and control the DC electrical
conductivity of highly confined metallic nanostructures. Lastly, we
show the strong influence of the nanodisk boundary in determining
both the energy and lifetime of surface plasmons and volume plasmons
locally across individual aluminum nanodisks, and we have compared
these observations to similar effects produced by scaling the nanodisk
diameter
High-Yield, Ultrafast, Surface Plasmon-Enhanced, Au Nanorod Optical Field Electron Emitter Arrays
Here we demonstrate the design, fabrication, and characterization of ultrafast, surface-plasmon enhanced Au nanorod optical field emitter arrays. We present a quantitative study of electron emission from Au nanorod arrays fabricated by high-resolution electron-beam lithography and excited by 35 fs pulses of 800 nm light. We present accurate models for both the optical field enhancement of Au nanorods within high-density arrays, and electron emission from those nanorods. We have also studied the effects of surface plasmon damping induced by metallic interface layers at the substrate/nanorod interface on near-field enhancement and electron emission. We have identified the peak optical field at which the electron emission mechanism transitions from a 3-photon absorption mechanism to strong-field tunneling emission. Moreover, we have investigated the effects of nanorod array density on nanorod charge yield, including measurement of space-charge effects. The Au nanorod photocathodes presented in this work display 100–1000 times higher conversion efficiency relative to previously reported UV triggered emission from planar Au photocathodes. Consequently, the Au nanorod arrays triggered by ultrafast pulses of 800 nm light in this work may outperform equivalent UV-triggered Au photocathodes, while also offering nanostructuring of the electron pulse produced from such a cathode, which is of interest for X-ray free-electron laser (XFEL) development where nanostructured electron pulses may facilitate more efficient and brighter XFEL radiation
MoS<sub>2</sub> Field-Effect Transistor with Sub-10 nm Channel Length
Atomically
thin molybdenum disulfide (MoS<sub>2</sub>) is an ideal semiconductor
material for field-effect transistors (FETs) with sub-10 nm channel
lengths. The high effective mass and large bandgap of MoS<sub>2</sub> minimize direct source–drain tunneling, while its atomically
thin body maximizes the gate modulation efficiency in ultrashort-channel
transistors. However, no experimental study to date has approached
the sub-10 nm scale due to the multiple challenges related to nanofabrication
at this length scale and the high contact resistance traditionally
observed in MoS<sub>2</sub> transistors. Here, using the semiconducting-to-metallic
phase transition of MoS<sub>2</sub>, we demonstrate sub-10 nm channel-length
transistor fabrication by directed self-assembly patterning of mono-
and trilayer MoS<sub>2</sub>. This is done in a 7.5 nm half-pitch
periodic chain of transistors where semiconducting (2H) MoS<sub>2</sub> channel regions are seamlessly connected to metallic-phase (1T′)
MoS<sub>2</sub> access and contact regions. The resulting 7.5 nm channel-length
MoS<sub>2</sub> FET has a low off-current of 10 pA/μm, an on/off
current ratio of >10<sup>7</sup>, and a subthreshold swing of 120
mV/dec. The experimental results presented in this work, combined
with device transport modeling, reveal the remarkable potential of
2D MoS<sub>2</sub> for future sub-10 nm technology nodes