Richard C. Flagan, Ph.D. - US grants

This research is a combined experimental and theoretical investigation of aerosol reactors for synthesis of high quality powders for ceramic applications. The powders to be studied are silicon nitride and various metal oxides. Size distributions of the powders produced will be measured as a function of gas composition, temperature, residence time, and other relevant variables. Powders will be characterized as to chemical composition and crystallinity by atomic absorption spectroscopy and X-ray diffraction. The suitability of the powders for ceramic application will be evaluated in an ongoing study at another institution. The reactor will be modeled accounting for particle nucleation, particle growth by condensation and coagulation, and aggregate shape change by sintering. Aerosol reactors offer exciting processes for producing powders of unique properties for use in ceramic, optical, electrical, or catalytic applications. This research should help in the design and optimization of such reactors.

A quantum cluster dot is a compact structure in the 5 to 20 um size range where small scale in three dimensions yields discrete electronic states. This research is an interdisplinary, experimental program for the formation and characterization of monodisperse gallium arsenide (G A ) quantum cluster dots. The clusters will be produced in an aerosol reactor by the vapor phase reaction of an organometallic gallium contains vapor with arsine. Particle size and cluster quality will be monitored by in-situ laser induced luminescence spectra. Clusters from the aerosol reactor will be classified into very narrow size ranges required for applications by an electrostatic classifier. Captured particles will be analyzed as to particle morphology, interval defect structure, and carbon contamination using electron microscopy (TEM and STEM), energy dispersive X-ray analysis (EDAX), and electron energy loss spectroscopy (EELS). Exciting new electronic and optical components would result from the incorporation of large numbers of identical quantum cluster dots into solid state structures. Possible applications include semiconductor lasers several orders of magnitude better than conventional diode lasers and new electroluminescent display technology with convenient adjustment of color. However, to achieve such results, the clusters must be produced to very strict size tolerances, typically with size variations not larger than 0.5 um. Otherwise a device averaging the electronic states of many clusters varying in size would lose the distinctness of states inherent in any individual quantum cluster dot.

The atmospheric chemistry and gas-to-particle conversion phenomena of biogenic hydrocarbon systems will be investigated in this research project. The goals of the research are to elucidate the gas-phase photooxidation pathways of key biogenic hydrocarbons, to identify the aerosol-forming capability of these hydrocarbons, to further understanding of gas-to-particle conversion phenomena in atmospheric organic systems, and to evaluate the applicability of nucleation theories to atmospheric species. Outdoor smog chamber experiments will be conducted with isoprene/NOx and beta pinene/NOx mixture over a spectrum of concentration levels. Quantities to be measured include hydrocarbon, O3, NO, NO2 concentrations, aerosol size distributions by differential mobility analyzer, optical particle counter and epiphianiometer, and aerosol molecular composition by GC/MS and FTIR analyses. Aerosol species identified will be studied for nucleation either as single component or binary, with water. Theoretical work will continue on the development of a kinetic theory of nucleation. Analysis of the experimental data will involve a description of gas-phase chemical reaction mechanisms, including the generation of condensable species, the nucleation of these species, either homomolecular or binary, and the diffusion of these and additional species to particles.

Dr. Flagan has proposed to investigate the synthesis of high quality ceramic powders using two approaches: vapor precursor routes in which seed particle are grown by a combination of vapor and cluster deposition, and electrospray to produce fine droplets of liquid precursors. The experimental and modeling research will focus on the densification of agglomerate particles, particle growth by cluster deposition, and scale-up techniques of seeded aerosol reactors and electrosprays. Aerosol formation by vapor deposition and electrospray, sintering of agglomerate, and corresponding scale-up techniques are critical issues for the production of ceramic powders with engineered structures and properties.

Harry Atwater Abstract The acquistion of a quantitative high-resolution video imaging system is proposed. The system will be used in conjunction with existing transmission electron microscopes for (i) atomic-scale imaging of thin films and nanoparticles, (ii) energy-filtered imaging of thin films and nanoparticles, (iii) quantitative electron diffraction nmeasurements,a nd (iv) facilitating the teaching of electron microscopy and microanalyis of materials. ***

Seinfeld 9307603 Gas-to-particle conversion is a ubiquitous process in the atmosphere, understanding the detailed chemistry and physics of which will allow one to predict the effects of primary gaseous and particulate emissions on airborne particulate matter composition and size. This comprehensive research program determine the mechanisms of secondary organic aerosols formation in the atmosphere for a number of important anthropogenic and biogenic hydrocarbons. Experiments in a 1000 liter indoor reactor will be used to probe gas-phase photooxidation mechanisms. A 4 m3 outdoor smog chamber will be used to generate organic aerosols for molecular speciation analysis by gas chromatography/mass spectrometry, while the 60 m3 outdoor smog chamber will be employed to study the integrated gas-phased and gas-to-particle conversion dynamics. Vapor pressures of individual secondary organic aerosol constituents and of the aerosol generated by hydrocarbon photooxidation will be determined with the tandem differential mobility analyzer (TDMA). Information from the individual experiments studies will be integrated in the data analysis phase. Gas-phase photooxidation mechanisms will be formulated and aerosol physics models will be developed based on the concentration dynamics, molecular speciation, and the physical properties deduced from the TDMA studies.

9871850 Atwater This objectives of this project are to develop the synthesis, processing, manipulation and characterization tools to enable and improve novel, emerging silicon nanoparticle memory and logic devices. These devices exploit common approaches for particle synthesis, manipulation, interface passivation and electrical and optical characterization of ordered, passivated arrays of size-classified silicon nanoparticles which are integrated into larger device structures. Device structures to be addressed in this project include: a nonvolatile memory based on discrete charge storage on the nanoparticle floating gate of a field-effect transistor, and a silicon nanoparticle-based implementation for a cellular automata wire/logic gate, in which information is propagated by cell-cell electrostatic interactions rather than by current flow. The nanoparticle engineering and assembly methods developed in this program may enable the first realization of a cellular automata logic gate capable of room temperature operation. Key aspects of the synthesis and processing are engineering of nanoparticle size, shape, dielectric passivation thickness and stoichiometry, and control of nanoparticle position. Control of position is achieved in model device structures using force manipulation by a scanning probe microscope. Another effort is aimed at utilizing fluid and colloidal forces to fabricate ordered linear and planar arrays. Characterization of charge state and morphology at the single particle level is performed using conducting tip atomic force microscopy. %%% The project addresses basic research issues in a topical area of science and engineering having high technological relevance. The research will contribute new knowledge at a fundamental level to important aspects of electronic devices. The basic knowledge and understanding gained from the research is expected to contribute to improving the performance of advanced devices by providing a fundamental understanding and a basis for designing and producing improved materials, and materials combinations. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area. This research grant is made under the Nanotechnology Initiative (NSF 98-20), and is co-funded by the Directorate for Engineering, the Directorate for Computer and Information Science and Engineering, and the Directorate for Mathematical and Physical Sciences. The research team is a university/industry/government lab collaboration between Applied Physics and Chemical Engineering faculty at the California Institute of Technology, and technical staff at Bell Labs/Lucent Technologies and the Jet Propulsion Laboratory.

Recent observations indicate that the air surrounding growing cumulus clouds is sometimes nearly saturated with water vapor. Calculations show that these vapor shrouds or "halos" around clouds can account for a significant increase in the absorption of solar radiation. The purpose of this project is to measure the vapor field around cumulus clouds with high accuracy and resolution and to use the information in calculations of radiative transfer and in assessing the consequences of cloud-environment interactions on cloud microphysics. The specific objectives are as follows:
- To measure the vapor field in and around convective clouds with sufficient detail to characterize the 3-dimensional vapor structure relative to cloud edges;
- To measure concurrently the size distribution, composition, and optical properties of aerosols within the cloud halo;
- To analyze the resulting measurements in order to provide several completely documented cases for use in radiative transfer calculations;
- To carry out radiative transfer analyses including absorption and heating rate calculations for the observed distributions of water vapor, aerosols, and cloud;
- To determine the implications of the radiation analysis for climate modeling.
The measurements will be conducted with the CIRPAS Twin Otter aircraft, equipped with a new instrument called the Fast Water Vapor Monitor developed by Aerodyne Research along with instruments for measuring aerosols, CCN, cloud droplets, and liquid water content. Computer codes with different degrees of complexity will be used for the radiative transfer calculations. The results bear on the question of anomalous cloud absorption, which refers to the discrepancies that have been observed between the observed solar absorption by clouds and the absorption calculated using Mie scattering theory applied to populations of cloud drops. This is a collaborative research project between Cal Tech and Aerodyne Research, Inc. The Aerodyne component of the collaboration is supported by ATM-9910744, Dr. John T. Jayne, PI.

0076486
Atwater

This grant will help develop quantitative electrostatic force scanning probe
microscopy. The project includes modification of a commercial ultrahigh
vacuum scanning probe microscope and development of new electrostatic force
microscopy simulation software. The program comprised both ultrahigh
vacuum electrostatic force microscopy measurements and development and
testing of finite element electrostatic simulation software describing
tip-sample interactions, including van der Waals and electrostatic force
contributions . This will enable more quantitative understanding of
nanometer-scale charge distributions and low mobility electronic
transport. The immediate scientific use for the instrument will be in a
collaborative Caltech/Bell Labs/NASA-JPL multi-investigator research
program aimed at probing charge injection and storage in silicon
nanoparticle structures for nonvolatile memory applications. Information
and software needed to perform quantitative EFM will be disseminated to the
materials research community.

Electrically insulating thin films are critical and ubiquitous components
of electronic devices such as integrated circuits and micromechanical
devices. Trapping of electronic charge, whether by design or as an
unintended effect, is a common characteristic of insulating thin films. It
is desirable to be able to quantitatively measure the extent of and
mechanisms for charge trapping in order to better understand the
performance and reliability of insulating thin films. Scanning probe
microscope techniques such as electrostatic force microscopy have opened a
new vista in the understanding charge trapping in insulators because they
enable measurement at nanometer-scale spatial resolution and total charge
sensitivity down to the single electron level. To date, such electrostatic
force microscopy measurements have been used as a qualitative but not a
quantitative tool for understanding charge trapping in insulators. This
project aims to put the electrostatic force microscopy method on a firm
quantitative foundation, through a combination of measurements and
development of simulation software needed for quantitative
understanding. The results will be applied to characterize charge trapping
in nonvolatile floating gate memory device materials containing
semiconductor nanocrystals. These materials and the devices made with them
are very promising candidates for the next-generation of ultradense,
low-power nonvolatile "flash" memory chips like those now used widely in
portable electronic devices such as wireless telephones, pagers, electronic
cameras and personal digital assistants.

This project supports the deployment of a Twin Otter aircraft and ground-based measurements as part of ACE-Asia (Aerosol Characterization Experiment). A comprehensive instrument package for the Twin Otter will be available for measurements of aerosol physical, chemical, and optical properties, including size distribution, hygroscopic properties (Tandem Differential Mobility Analyzer), size-segregated chemistry, and a novel single particle spectrometer. The objectives of the research flights are to characterize the aerosol in the Asian outflow region and to perform local and column radiative closure studies. In collaboration with a scientist at HKUST (Hong Kong University of Science and Technology), aerosol samples collected by the aircraft and at ground stations in Cheju Island, Korea, and other locations will be analyzed for organic/elemental carbon (EC/OC) and speciated organics via extraction, derivatization, and GC/MS analysis. Modeling studies will be performed in collaboration with Dr. Carmichael (University of Iowa) using a three-dimensional atmospheric chemical transport model which includes gas-phase chemistry, aerosol microphysics, thermodynamics, gas/particle conversion and anthropogenic emissions.

This proposal was submitted in response to the solicitation "Nanoscale Science and Engineering" (NSF 00-119). We propose a joint Caltech/NASA-JPL/Agere Systems research program to develop new materials for Si nanocrystal nonvolatile memories and related nanoscale electronic devices. Under the program:

o New aerosol-based Si nanoparticle and nanowire engineering methods will be developed to enable formation nanoparticle and nanowire arrays with precise control of particle size, particle number and array structure. These methods 'will be compatible with Si ultralarge scale integrated (ULSI) circuit process technology.
o Aerosol-synthesized and colloidally processed silicon nanoparticle and nanowire arrays with novel configurations will be integrated into Si-based metal-oxide-semiconductor (MOS) devices at state-of-the-art device dimensions yielding nanometer-scale memory devices.
o A dielectric heterostructure layered tunnel barrier will be developed to achieve simultaneous ultrafast chargc injection and extremely long charge retention times, which are mutually exclusive for existing conventional dielectric tunnel baffler designs.
o Nanocrystal charging via electrical injection and photoexcited carrier injection will be studied to assess layered tunnel barrier performance and to determine whether quantum size effects on the density of electronic states can be exploited for control of electronic charging energy.

The focal point of the work is a recently demonstrated high-performance aerosol silicon nanocrystal memory device, developed by the present nanoscale interdisciplinary research (NIRT) team under prior NSF support. Silicon nanoparticles comprise the floating gate that is the storage node of a nanocrystal nonvolatile memory. Aerosol synthesis allows control of Si nanocrystal size and shape that are difficult to achieve by other synthesis methods. Uniquely, our team has successfully integrated vapor-synthesized aerosol nanoparticles into a high-performance silicon-based electronic device, fabricated at 0.18 micron design rules on 200 mm substrates by ultraclean processing at state-of-the-au device dimensions. Extensive electrical characterization of transistor subthreshold and turn-on performance, retention time, program-erase cycling, gate and drain disturb characteristics indicated that these devices are high performance memory devices. The Caltech/JPL/Agere NIRT team is unusual in its combination of basic research on new electronic materials developed at Caltech followed by direct materials integration into a flexible, state-of-the-au silicon device process carried out at Caltech and Agere System's fabrication facilities.

This Major Research Instrumentation award supports the acquisition and development of state-of-the art instrumentation for aerosol research. It will enable simultaneous characterization of the chemistry occurring in the gas and condensed phases as secondary aerosol forms and evolves in a laboratory setting. A benchtop instrument for gas chromatography - time-of-flight mass spectrometry (GC-TOF-MS) will be purchased to provide rapid chemical analysis of hydrocarbons and oxygenated volatile organic compounds. A triple quadrupole mass spectrometer will be coupled to an ion chemical ionization front end (TSQ-SICIMS) for real-time analysis of short-lived, reactive compounds. A preparative capillary gas-liquid chromatography (PCGC) instrument will be used to isolate larger quantities of volatile organic compounds for subsequent analysis with a broad array of instruments. Finally, an aerosol trap / concentrator will be developed for use as a front end to the mass spectrometers for rapid analysis of the chemical composition of aerosol.

Studies using these new instruments will provide improved constraints on the mechanisms responsible for production of organic aerosol in Earth's atmosphere. This instrumentation, in combination with the aerosol instrumentation currently available on the Caltech environmental chamber, will enable significant progress in addressing questions such as:
- How important is the formation of low volatility oxidation products in the gas phase to the budget of organic aerosol and how does this chemistry influence the physical properties and environmental effects of atmospheric aerosols?
- How important are aerosol-phase reactions relative to gas-phase oxidation followed by gas-to-particle uptake for determining the chemical composition of the aerosol?
- What are the molecular mechanisms and kinetics of the processes involved in aerosol production?
- What are the most important chemicals leading to aerosol formation (organic acids, oligomers/polymers, etc.) and what are their physicochemical properties (functional groups, molecular mass, stability, volatility, solubility, hygroscopicity, optical absorption, etc.)?
- How do the gas phase and the aerosol composition evolve in the presence of atmospheric oxidants?

Accurate characterization of the chemistry leading to the formation of aerosol in Earth's atmosphere is essential for understanding the interactions of the biosphere and climate as well as for designing appropriate air quality improvement strategies. This aerosol plays a major role in the environment through its deleterious influence on human and animal health and through its impact on visibility in both urban and regional areas. The chemical and physical nature of atmospheric aerosol also determines its light scattering and absorption properties that, in part, control the Earth's radiation field and climate. Finally, the hygroscopicity of the aerosol plays an important role in controlling how efficient an aerosol particle will be for formation of cloud droplets. The instrumentation acquired through this award will provide substantially improved understanding of the nature of the organic chemistry that controls the chemical makeup of atmospheric organic aerosol. The new instrumentation will enhance new and interdisciplinary collaborations of graduate and undergraduate chemists, geochemists, and physicists and their faculty mentors.

CBET-1236909
The proposed research addresses the need to understand workplace exposures to engineered nanoparticles
in two ways: (i) by investigating fundamental mechanisms by which engineered nanoparticles
may become airborne; and (ii) by developing aerosol instruments suitable for routine workplace and
personal monitoring of nanoparticles in the 1-500 nm size range with the ability to follow transient
that may be responsible for most exposure from well-designed nanoparticle synthesis systems.
Controlled laboratory experiments will also be conducted to develop a fundamental understanding
of mechanisms for nanoparticle release to the air, beginning with studies of the aerodynamic
entrainment from nanoparticle-coated surfaces. The long-standing need for suitable instruments
for monitoring workplace exposures will be addressed by creating a small, simple, and low cost
nanoparticle opposed migration aerosol detector (NOMAD) that will enable exposure assessment
with sufficient resolution to estimate lung deposition patterns. The NOMAD performance will be
compared with conventional approaches to exposure monitoring in nanotechnology laboratories, and
provide personal exposure data that is not presently possible.

Intellectual merit: The proposed research will survey sources of airborne nanoparticles using
size resolved instruments with better time response, and broader coverage of the potential size
range than employed in previous studies, thereby enabling detection of transient release events, and
facilitating identification of nanoparticle sources. Subsequent controlled laboratory experiments will
quantify the forces required to entrain nanoparticles from different kinds of surface deposits, and the
extent of agglomeration the airborne nanoparticles that result, thereby laying the groundwork for
a fundamental understanding of potential exposure mechanisms. The new instruments will enable
health effects studies that are clearly needed to understand the risks of nanotechnology, but are
not presently possible due to the cost and complexity of present instruments. With these tools,
continuous exposure data will become a valuable tool in both health effect research and in worker
protection. They will further enable studies of exposures to nanoparticles in the use of consumer
nanotechnology products, and from conventional pollution sources.

Broader impacts: The proposed research will provide new insights into incidental processes
that contribute to the release of engineered nanoparticles into workplace air, and the risks associated
with such releases. The new airborne nanoparticle detectors will enable researchers and industry to
monitor nanoparticle exposures with rigor that is not now possible. Moreover, these new detectors
should become the enabling technology for health effects studies that are clearly needed, but not
presently possible.
Undergraduates will have the opportunity to become involved in the project through Caltech?s
Summer Undergraduate Research Fellowship (SURF). In addition, the Flagan laboratory will recruit
participants from the Minority Undergraduate Research Fellowship (MURF) program as it has in
4 of the last 6 years. We will work with Caltech?s outreach program to invite local area students to
lectures and visits to our laboratory, as well as talk to the students in their schools. Students from
local high schools, particularly those near freeways, will be recruited to undertake science projects
involving measurements of nanoparticles in their home or school environments.
As he has done for 10 years, the PI will continue to co-mentor a First Robotics team at Ramona
Convent Secondary School, a girls high school in Alhambra, CA that has 60% minority enrollment.
This has proven to be a most effective mechanism in stimulating interest in pursuing STEM studies
in college by showing the students that engineering is fun.

Project Abstract
This project proposes the development and demonstration of a label-free sensing instrument based on the integration of an electronically controlled linear swept-frequency semiconductor laser, a high quality factor (Q) optical resonator with covalent surface functionalization, and a microfluidic cell for analyte delivery. It will address a number of key issues that currently prevent this technology from becoming an accessible, affordable, and useful tool. These efforts will develop the optical cavity sensing platform to a point where it is robust and repeatable, and provides sensitivity and cost-effectiveness that are at least an order of magnitude better than any available alternative biomolecular assay instrument.
The proposed system will combine the results of two major recent developments in the field of optical and laser physics: the high-Q optical resonator and the phase-locked electronically controlled swept-frequency semiconductor laser. The high-Q optical resonator is part of a monolithic unit with an integrated optical waveguide, and is fabricated using standard semiconductor lithography-based methods. Optoelectronic swept frequency lasers will be developed at wavelengths relevant for aqueous sensing, and will replace expensive and fragile mechanically-tuned laser sources whose frequency sweeps have limited speed, accuracy and reliability. The resonator will be functionalized using known techniques providing an adaptable and selective surface chemistry. The sensor will include an integrated microfluidic flow cell for precise and low volume delivery of analytes to the resonator surface.
The proposed instrument represents an adaptable and cost-effective platform capable of various sensitive, label-free measurements relevant to the study of biophysics, biomolecular interactions, cell signaling, and a wide range of other life science fields. It will be capable of binding assays, thermodynamic and kinetics measurements, and has the potential for additional impact through integration into existing instruments to replace less sensitive analytical methods. The sensor also has potential applications in point-of-care medical diagnostics, where it can enable early detection of relevant antigens.
The project is inherently multidisciplinary and will develop expertise in and better understanding of the interplay between such diverse fields as semiconductor lasers, optical nanofabrication, high speed electronics, control systems, fiber-optics, microfluidics, biomolecular binding assays, mass transfer, and integrated instrument design. It affords the opportunity for two graduate students and an undergraduate student to take part in a collaborative research effort under the close guidance of the PIs, educating the students in the culture of scientific discovery, alongside engineering and application considerations. The results obtained during the course of the project will be published in leading scientific journals and conferences.

This project is focused on the study of the formation and growth of new particles in the atmosphere. It involves an international collaboration that enables U.S. scientists to work at CERN, the European Organization for Nuclear Research in Switzerland, at the CLOUD (COsmics Leaving Outdoor Droplets) chamber there. The results of this research are expected to have implications that go beyond the atmospheric sciences, to numerous industrial and other natural processes.

The objectives of this research are to: (1) advance measurement methods to make it possible to measure the size distribution of freshly nucleated clusters/particles as a function of time as they exist in the atmosphere in which they are formed in order to map their passage through the Kelvin regime, i.e., from near critical, or even sub-critical cluster sizes through to stable particles; (2) measure and model the multicomponent activation kinetics as low volatility organic compounds and extremely low volatility organic compounds condense on inert and sulfuric acid clusters in the Kelvin size regime, varying the temperature and composition of the atmosphere to probe the underlying mechanisms; (3) measure and model new particle formation, secondary activation, and growth in carefully controlled chamber experiments in order to constrain and parameterize new particle formation under a wide range of atmospheric conditions and for key aerosol precursors.

This project will support the continued membership of Carnegie Mellon University, the California Institute of Technology, and the University of Colorado at Boulder in the CLOUD consortium at CERN to study the chemistry and physics that drive new-particle formation and growth in Earth's atmosphere. CLOUD is a state-of-the-art 26 cubic meter stainless-steel chamber with precise control over temperature and relative humidity. The new research at CLOUD will focus on the study of chemical mechanisms that generate extremely low volatility organic compounds capable of nucleating and condensing onto freshly nucleated particles. Target environments include natural (both forest and marine) and polluted (urban) conditions, as well as cold temperatures characteristic of the free troposphere. <br/><br/>Planned research over the next 3 years, includes studies of: (1) aging of first-generation organic oxidation products under conditions found in the free troposphere; (2) measurement and modeling of key radical intermediates in organic oxidation and also inorganic sulfur, nitrogen, and iodine oxidation, as well as interaction between organic and inorganic systems; (3) measurement and modeling of interactions among vapors and both charged and neutral particles below 10 nm to constrain key microphysical terms; and (4) propagating CLOUD results to atmospheric models, testing their capability to explain field measurements, and understanding the implications of improvements to models for aerosol radiative forcing. In addition to providing the required consortium fee, this project will support shipping and travel to CLOUD experimental campaigns and associated consortium meetings and data workshops. <br/><br/>Both doctoral and postdoctoral students associated with the project (supported by other awards) are integrated into an international collaborative network of students and senior researchers who work with some of the most highly regarded scientists in the study of aerosols and atmospheric chemistry.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.