10 research outputs found
Self-Assembled Nanoparticle Drumhead Resonators
The self-assembly of nanoscale structures from
functional nanoparticles has provided a powerful path to
developing devices with emergent properties from the bottomup.
Here we demonstrate that freestanding sheets selfassembled
from various nanoparticles form versatile nanomechanical
resonators in the megahertz frequency range.
Using spatially resolved laser-interferometry to measure
thermal vibrational spectra and image vibration modes, we
show that their dynamic behavior is in excellent agreement
with linear elastic response for prestressed drumheads of
negligible bending stiffness. Fabricated in a simple one-step
drying-mediated process, these resonators are highly robust and their inorganicâorganic hybrid nature offers an extremely low
mass, low stiffness, and the potential to couple the intrinsic functionality of the nanoparticle building blocks to nanomechanical
motion
Self-Assembled Nanoparticle Drumhead Resonators
The self-assembly of nanoscale structures
from functional nanoparticles
has provided a powerful path to developing devices with emergent properties
from the bottom-up. Here we demonstrate that freestanding sheets self-assembled
from various nanoparticles form versatile nanomechanical resonators
in the megahertz frequency range. Using spatially resolved laser-interferometry
to measure thermal vibrational spectra and image vibration modes,
we show that their dynamic behavior is in excellent agreement with
linear elastic response for prestressed drumheads of negligible bending
stiffness. Fabricated in a simple one-step drying-mediated process,
these resonators are highly robust and their inorganicâorganic
hybrid nature offers an extremely low mass, low stiffness, and the
potential to couple the intrinsic functionality of the nanoparticle
building blocks to nanomechanical motion
Frustrated Etching during H/Si(111) Methoxylation Produces Fissured Fluorinated Surfaces, Whereas Direct Fluorination Preserves the Atomically Flat Morphology
Two
solution-based strategies for the preparation of partially
fluorinated Si(111) surfaces from H/Si(111) were investigated using
a combination of scanning tunneling microscopy, X-ray photoemission
spectroscopy, infrared spectroscopy, and kinetic Monte Carlo simulations.
Direct fluorination of H/Si(111) with HF (aq) produced atomically
flat surfaces with 11% fluorination. A two-step reaction that first
methoxylated the surface by reaction in methanol and then converted
the methoxy termination to F termination by reaction in HF (aq) produced
atomically rough, fissured surfaces with 24% fluorination. The atomic-scale
roughness was induced by the methoxylation reaction. Methanol was
shown to react with H/Si(111) surfaces through two parallel mechanisms:
an etching reaction and a methoxylation reaction. The methoxylation
reaction locally inhibited or âfrustratedâ the etching
reaction, leading to the development of a characteristic fissured
morphology. The H and F atoms on the fluorinated surface were imaged
with atomic resolution, and no evidence of the previously proposed
nanopatterning mechanism was observed
Size-Dependent Energy Levels of InSb Quantum Dots Measured by Scanning Tunneling Spectroscopy
The electronic structure of single InSb quantum dots (QDs) with diameters between 3 and 7 nm was investigated using atomic force microscopy (AFM) and scanning tunneling spectroscopy (STS). In this size regime, InSb QDs show strong quantum confinement effects which lead to discrete energy levels on both valence and conduction band states. Decrease of the QD size increases the measured band gap and the spacing between energy levels. Multiplets of equally spaced resonance peaks are observed in the tunneling spectra. There, multiplets originate from degeneracy lifting induced by QD charging. The tunneling spectra of InSb QDs are qualitatively different from those observed in the STS of other IIIâV materials, for example, InAs QDs, with similar band gap energy. Theoretical calculations suggest the electron tunneling occurs through the states connected with <i>L</i>-valley of InSb QDs rather than through states of the Î-valley. This observation calls for better understanding of the role of indirect valleys in strongly quantum-confined IIIâV nanomaterials
Low-Temperature Synthesis of a TiO<sub>2</sub>/Si Heterojunction
The classical SiO<sub>2</sub>/Si
interface, which is the basis
of integrated circuit technology, is prepared by thermal oxidation
followed by high temperature (>800 °C) annealing. Here we
show
that an interface synthesized between titanium dioxide (TiO<sub>2</sub>) and hydrogen-terminated silicon (H:Si) is a highly efficient solar
cell heterojunction that can be prepared under typical laboratory
conditions from a simple organometallic precursor. A thin film of
TiO<sub>2</sub> is grown on the surface of H:Si through a sequence
of vapor deposition of titanium tetraÂ(<i>tert</i>-butoxide)
(<b>1</b>) and heating to 100 °C. The TiO<sub>2</sub> film
serves as a hole-blocking layer in a TiO<sub>2</sub>/Si heterojunction
solar cell. Further heating to 250 °C and then treating with
a dilute solution of <b>1</b> yields a hole surface recombination
velocity of 16 cm/s, which is comparable to the best values reported
for the classical SiO<sub>2</sub>/Si interface. The outstanding performance
of this heterojunction is attributed to SiâOâTi bonding
at the TiO<sub>2</sub>/Si interface, which was probed by angle-resolved
X-ray photoelectron spectroscopy. Attenuated total reflectance Fourier
transform infrared spectroscopy (ATR-FTIR) showed that SiâH
bonds remain even after annealing at 250 °C. The ease and scalability
of the synthetic route employed and the quality of the interface it
provides suggest that this surface chemistry has the potential to
enable fundamentally new, efficient silicon solar cell devices