A5041612415- Carbon Nanotubes in Composites
- Graphene research and applications
- Atmospheric aerosols and clouds
- Atmospheric chemistry and aerosols
- Mechanical and Optical Resonators
- Atmospheric and Environmental Gas Dynamics
- Atmospheric Ozone and Climate
- Boron and Carbon Nanomaterials Research
- Meteorological Phenomena and Simulations
- Air Quality and Health Impacts
- Calibration and Measurement Techniques
- Fullerene Chemistry and Applications
- Silicon Nanostructures and Photoluminescence
- Fire effects on ecosystems
- Air Quality Monitoring and Forecasting
- Molecular Junctions and Nanostructures
- Nanopore and Nanochannel Transport Studies
- Force Microscopy Techniques and Applications
- Quantum and electron transport phenomena
- GaN-based semiconductor devices and materials
- 2D Materials and Applications
- Spacecraft Design and Technology
- Ionosphere and magnetosphere dynamics
- Semiconductor materials and devices
- Nanotechnology research and applications
Cooperative Institute for Research in Environmental Sciences
2015-2025
National Oceanic and Atmospheric Administration
2015-2025
University of Colorado Boulder
2015-2024
University of Colorado System
2024
NOAA Physical Sciences Laboratory
2020-2021
University of California System
2020
NOAA Earth System Research Laboratory
2015-2018
Los Alamos National Laboratory
2011-2018
Center for Integrated Nanotechnologies
2011-2018
Technische Universität Berlin
2003-2012
From resonant Raman scattering on isolated nanotubes we obtained the optical transition energies, radial breathing mode frequency, and intensity of both metallic semiconducting tubes. We unambiguously assigned chiral index (n(1),n(2)) approximately 50 based solely a third-neighbor tight-binding Kataura plot find omega(RBM)=(214.4+/-2) cm(-1) nm/d+(18.7+/-2) cm(-1). In contrast to luminescence experiments observe all chiralities including zigzag The intensities have systematic chiral-angle...
We present a comprehensive study of the chiral-index assignment carbon nanotubes in aqueous suspensions by resonant Raman scattering radial breathing mode. determine energies first optical transition metallic tubes and second semiconducting for more than 50 chiral indices. The is unique does not depend on empirical parameters. systematics so-called branches Kataura plot are discussed; many properties similar members same branch. show how modes observed single spectrum can be easily assigned...
Significance Nonvolcanic stratospheric aerosols account for 20% of the radiative forcing entire atmospheric aerosol system since 1850. The Asian summer monsoon (ASM) effectively pumps pollutants to upper troposphere and lower stratosphere, leading enhanced formation. Our in situ measurements combined with modeling work show that formed within ASM anticyclone is exported Northern Hemispheric stratosphere. On an annual average basis, we estimate ∼15% Hemisphere column surface area originates...
Abstract Australian wildfires burning from December 2019 to January 2020 injected approximately 0.9 Tg of smoke into the stratosphere; this is largest amount observed in satellite era. A comparison numerical simulations observations plume rise suggests that mass contained 2.5% black carbon. Model calculations project a 1 K warming stratosphere Southern Hemisphere midlatitudes for more than 6 months following injection black‐carbon containing smoke. The average global mean clear sky effective...
A light-weight, low-cost optical particle spectrometer for measurements of aerosol number concentrations and size distributions has been designed, constructed, demonstrated. The is suitable use on small, unmanned aerial vehicles (UAVs) in balloon sondes. uses a 405 nm diode laser to count individual particles the range 140–3000 nm. compact data system combines custom electronics with single-board commercial computer. Power consumption 7W at 9–15 V. 3D printing technology was used...
The search for environmentally clean energy sources has spawned a wave of research into the use carbon nanomaterials photovoltaic applications. In particular, using semiconducting single-walled nanotubes undergone dramatic transformations due to availability high quality samples through colloidal separation techniques. This led breakthrough discoveries on how and charge transport occurs in these materials points applications harvesting. We present review relevant photophysics that dictate...
Abstract Thorough understanding of aerosols, clouds, boundary layer structure, and radiation is required to improve the representation Arctic atmosphere in weather forecasting climate models. To develop such understanding, new perspectives are needed provide details on vertical structure spatial variability key atmospheric properties, along with information over difficult-to-reach surfaces as newly forming sea ice. Over last three years, U.S. Department Energy (DOE) has supported various...
The growth of tall, single-walled carbon nanotube (SWNT) forests is often believed to require the use specific feedstocks (e.g., ethanol) or etchants water). Here, on basis mass spectrometry for hydrogen-diluted methane in a microwave plasma-enhanced chemical vapor deposition (PECVD) reactor, we develop purely thermal CVD process SWNT without an etchant gas. thermally grown are found have similar high quality, purity, rate, areal density, diameter, and chirality distribution as PECVD case....
We show by ab initio calculations that the electron-phonon coupling matrix element ${\mathcal{M}}_{e\text{\ensuremath{-}}\mathit{ph}}$ of radial breathing mode in single-walled carbon nanotubes depends strongly on tube chirality. For same diameter strength ${\ensuremath{\mid}{\mathcal{M}}_{e\text{\ensuremath{-}}\mathit{ph}}\ensuremath{\mid}}^{2}$ is up to one order magnitude stronger for zigzag tubes than armchair tubes. $({n}_{1},{n}_{2})$ value...
Raman spectroscopy on the radial breathing mode is a common tool to determine diameter d or chiral indices (n,m) of single-wall carbon nanotubes. In this work we present an alternative technique and based high-energy G– mode. From resonant scattering experiments 14 highly purified single chirality samples obtain diameter, angle, family dependence G+ peak position. Considering theoretical predictions discuss origin these dependences with respect rehybridization orbitals, confinement,...
Abstract. The rapidly warming Arctic is sensitive to perturbations in the surface energy budget, which can be caused by clouds and aerosols. However, interactions between aerosols are poorly quantified Arctic, part due (1) limited observations of vertical structure relative (2) ground-based often being inadequate for assessing aerosol impacts on cloud formation characteristically stratified atmosphere. Here, we present a novel evaluation distributions using almost 3 years' worth tethered...
In situ atmospheric aerosol measurements have been performed from a Manta unmanned aircraft system (UAS) using recently developed miniaturized instruments. Flights were conducted up to an altitude of 3000 m (AMSL) during spring 2015 in Ny-Ålesund, Svalbard, Norway. We use these flights demonstrate practical set instruments that can be deployed onboard small UASs and provide valuable information on ambient aerosol. Measured properties include size-resolved particle number concentrations,...
We analyze the high-energy Raman modes, ${G}^{+}$ and ${G}^{\ensuremath{-}}$, in a pair of one metallic semiconducting nanotubes. By combining Rayleigh scattering with resonance profiles radial breathing mode we show that observed ${G}^{\ensuremath{-}}$ peaks can originate from longitudinal optical phonons different tubes. The peak is tube; it broadened downshifted due to strong electron-phonon coupling nanotube. tube. This result resolves an ongoing debate literature.
Resonance Raman profiles of WS${}_{2}$ nanotubes different diameter are presented. We show that the A excitonic transition energy lies below bulk value and is increasingly redshifted with decreasing nanotubes. The findings attributed to strain effects associated curvature nanotube walls. silent mode, ${B}_{1u}$ disorder enhanced in spectra nanomaterials. discuss development relative intensities mode nearby ${A}_{1g}$ diameter, excitation energy, hydrostatic pressure terms a slight difference...
Accurate representation of atmospheric aerosol properties is a long-standing problem in research. Modern pilotless aerial systems provide new platform for situ measurement. However, small airborne platforms require miniaturized instrumentation due to apparent size, power, and weight limitations. A Portable Optical Particle Spectrometer (POPS) an emerged instrument measure ambient size distribution with high time resolution, designed deployment on unmanned system (UAS) or tethered balloon...
Abstract The radiative effects of wildfires have been traditionally estimated by models using transfer calculations. Assessment model-predicted commonly involves information on observation-based aerosol optical properties. However, lack or incompleteness this for dense plumes generated intense reduces substantially the applicability assessment. Here we introduce a novel method that provides additional observational constraints such assessments widely available ground-based measurements...
A global network of soundings tracked stratospheric water vapor (H2O) and aerosol enhancements for two years after the explosive eruption submarine Hunga volcano in January 2022. Balloon-borne measurements highlight importance rapid transport from tropics to northern hemisphere (NH) midlatitudes sensitivity H2O entry radiative heating near tropical tropopause. Aerosol plumes separated vertically within four months—H2O was initially transported along isentropic levels at 20...
We grow high-density, aligned single wall carbon nanotube mats for use as interconnects in integrated circuits by remote plasma chemical vapor deposition from a Fe–Al2O3 thin film catalyst. carry out extensive Raman characterization of the resulting mats, and find that this catalyst system gives rise to broad range diameters, with no preferential selectivity semiconducting tubes, but at least 1∕3 metallic tubes.
Abstract. This paper presents details of the University Colorado (CU) “Pilatus” unmanned research aircraft, assembled to provide measurements aerosols, radiation and thermodynamics in lower troposphere. aircraft has a wingspan 3.2 m maximum take-off weight 25 kg, it is powered by an electric motor reduce engine exhaust concerns about carburetor icing. It carries instrumentation make broadband up- downwelling shortwave longwave radiation, aerosol particle size distribution, atmospheric...
We observed the lowest optical transitions $({E}_{11}^{S})$ in separated carbon nanotubes by resonant Raman spectroscopy. Radial breathing mode spectra were collected varying excitation energy near-infrared from $1.15\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}1.48\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. From resonance profiles we obtained ${E}_{11}^{S}$ energies of 11 nanotubes, extending experimental Kataura plot. Strong signal tubes with...
Using a macroscopic ensemble of highly-enriched (6,5) single-wall carbon nanotubes, combined with high signal-to-noise ratio, time-dependent differential transmission spectroscopy, we have generated vibrational modes in an ultrawide spectral range (10-3000 cm^{-1}). A total fourteen were clearly resolved and identified, including fundamental A, E1, E2 symmetries their combinational involving two three phonons. Through comparison CW Raman spectra as well calculations based on extended...
We performed tunable resonance Raman spectroscopy on samples highly enriched in the (5,5), (6,6), (7,7), and (8,8) armchair structures of metallic single-wall carbon nanotubes. present excitation profiles (REPs) for both radial breathing mode $G$-band phonons these species. are shown to resolve expected incoming outgoing resonances scattering process. Notably, asymmetric, with higher-energy weaker than resonance. These results comparable asymmetric observed previously semiconducting...
Abstract We analyze the high‐energy Raman modes, G + and – , in a pair of one metallic semiconducting nanotube grown across 100 mm wide slit. By combining resonance profiles radial breathing mode we assign broad peak to nanotube. Considering theoretical predictions show that both peaks, originate from LO phonon. The is longitudinal tube; it broadened downshifted due strong electron‐phonon coupling tube. An asymmetric lineshape agrees with observations asymmetry be an intrinsic feature...
We exploit an energy level crossover effect [Haroz et al., Phys. Rev. B 77, 125405 (2008)] to probe quantum interference in the resonance Raman response from carbon nanotube samples highly enriched single semiconducting chiralities of (8,6), (9,4), and (10,5). UV excitation profiles $G$-band spectra reveal unambiguous signatures between third fourth excitonic states (${E}_{33}$ ${E}_{44}$). Both constructive destructive responses are observed lead anomalous intensity ratios LO TO modes....