133,066 research outputs found
Application of Scanning Probe Microscopy to Characterize Physical Properties of Polymer Brushes, Photoactive Polymers and Rare Earth Oxide Nanostructures
A sample stage for characterizing photoactive materials was developed for studies with scanning probe microscopy (SPM). A sample stage was designed that directs light from a solar simulator via a fiber optic cable to illuminate the sample. Current-sensing and photocurrent measurements can be acquired with a conductive tip. The designed photocurrent stage can be used for SPM systems with a tip-mounted scanner. Current-sensing measurements can be taken with or without illumination to measure the current produced from organic photovoltaic (OPV) or photoconductive samples. Topography, lateral force and current-sensing images are acquired simultaneously, providing information of how nanoscale morphology affects the measured current. Particle lithography was used to prepare nanostructures of OPV materials for photoconductive measurements. Nanopillars of polythiophene ranging from ~20 – 80 nm in thickness were grafted from indium tin oxide (ITO) surfaces. Samples were characterized with the photocurrent sample stage to directly test how nanoscale changes in film thickness affect the measured current. Current-voltage measurements indicate the polythiophene nanopillars are photoactive. The nanostructured test platform provided an unprecidented scale and morphology of photoactive brush polymers for dark and photocurrent measurements. Films of polynitrophenylene grafted to Au(111) surfaces via photoredox catalysis were investigated with contact-mode atomic force microscopy (AFM). The parameters of concentration of starting material and duration of sample illumination were studied. Films of increasing thickness were prepared from longer illumination times and higher concentrations of the starting materials. Particle lithography provided an internal standard for film thickness measurements. Rare earth oxide materials were nanopatterned using particle lithography. Precursor salts of rare earth oxide materials located on surfaces surrounding the base of mesospheres. The dried nanorings of salt were heated at 800 oC to produce crystalline materials on two transparent surfaces for further luminescence studies. The nanorings were analyzed for signs of Ostwald ripening or physical changes that may have occurred during the heating process and crystal phase transition
Visual Contact Pressure Estimation for Grippers in the Wild
Sensing contact pressure applied by a gripper can benefit autonomous and
teleoperated robotic manipulation, but adding tactile sensors to a gripper's
surface can be difficult or impractical. If a gripper visibly deforms, contact
pressure can be visually estimated using images from an external camera that
observes the gripper. While researchers have demonstrated this capability in
controlled laboratory settings, prior work has not addressed challenges
associated with visual pressure estimation in the wild, where lighting,
surfaces, and other factors vary widely. We present a model and associated
methods that enable visual pressure estimation under widely varying conditions.
Our model, Visual Pressure Estimation for Robots (ViPER), takes an image from
an eye-in-hand camera as input and outputs an image representing the pressure
applied by a soft gripper. Our key insight is that force/torque sensing can be
used as a weak label to efficiently collect training data in settings where
pressure measurements would be difficult to obtain. When trained on this weakly
labeled data combined with fully labeled data that includes pressure
measurements, ViPER outperforms prior methods, enables precision manipulation
in cluttered settings, and provides accurate estimates for unseen conditions
relevant to in-home use.Comment: Accepted for presentation at the 2023 IEEE/RSJ International
Conference on Intelligent Robots and Systems (IROS 2023
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Edge selective gas detection using Langmuir films of graphene platelets
Recent advances in large-scale production of graphene have led to the availability of solution processable platelets at the commercial scale. Langmuir-Schaefer (L-S) deposition is a scalable process for forming a percolating film of graphene platelets which can be used for electronic gas sensing. Here, we demonstrate the use of this deposition method to produce functional gas sensors, using a chemiresistor structure from commercially-available graphene dispersions. The sensitivity of the devices and repeatability of the electrical response upon gas exposure has been characterized. Raman spectroscopy and Kelvin probe force microscopy (KPFM) show doping of the basal plane using ammonia (n-dopant) and acetone (p-dopant). The resistive signal is increased upon exposure to both gases showing that sensing originates from the change in contact resistance between nanosheets. We demonstrate that Arrhenius fitting of the desorption response potentially allows measurements of the desorption process activation energies for gas molecules adsorbed onto the graphene nanosheets
Force-induced acoustic phonon transport across single-digit nanometre vacuum gaps
Heat transfer between bodies separated by nanoscale vacuum gap distances has
been extensively studied for potential applications in thermal management,
energy conversion and data storage. For vacuum gap distances down to 20 nm,
state-of-the-art experiments demonstrated that heat transport is mediated by
near-field thermal radiation, which can exceed Planck's blackbody limit due to
the tunneling of evanescent electromagnetic waves. However, at sub-10-nm vacuum
gap distances, current measurements are in disagreement on the mechanisms
driving thermal transport. While it has been hypothesized that acoustic phonon
transport across single-digit nanometre vacuum gaps (or acoustic phonon
tunneling) can dominate heat transfer, the underlying physics of this
phenomenon and its experimental demonstration are still unexplored. Here, we
use a custom-built high-vacuum shear force microscope (HV-SFM) to measure heat
transfer between a silicon (Si) tip and a feedback-controlled platinum (Pt)
nanoheater in the near-contact, asperity-contact, and bulk-contact regimes. We
demonstrate that in the near-contact regime (i.e., single-digit nanometre or
smaller vacuum gaps before making asperity contact), heat transfer between Si
and Pt surfaces is dominated by force-induced acoustic phonon transport that
exceeds near-field thermal radiation predictions by up to three orders of
magnitude. The measured thermal conductance shows a gap dependence of
in the near-contact regime, which is consistent with acoustic
phonon transport modelling based on the atomistic Green's function (AGF)
framework. Our work suggests the possibility of engineering heat transfer
across single-digit nanometre vacuum gaps with external force stimuli, which
can make transformative impacts to the development of emerging thermal
management technologies.Comment: 9 pages with 4 figures (Main text), 13 pages with 7 figures
(Methods), and 13 pages with 6 figures and 1 table (Supplementary
Information
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