Andrew C. Kummel - US grants

This project is in the general area of analytical and surface chemistry and in the subfield of gas-surface reaction dynamics. The research program will investigate the forces between a diatomic molecule and a surface when the molecule is crossing an activation barrier prior to dissociative chemisorption or associative desorption. The anisotropy of the reactive gas-surface potential will be probed as a function of molecular orientation geometry using multiphoton laser ionization spectroscopy to detect the specific states of the products of activated associative recombination. Angle-selected, velocity-selected, polarization spectroscopy will be employed to detect specific chemical events. The results of these experimental studies will provide detailed new insights into how chemical reactions occur on surfaces. In addition they will enable precise testing of theoretical methods of modeling the interaction of molecules with surfaces. Development of reliable methods for constructing potential energy surfaces will in turn facilitate modeling of surface chemical reactions.

This research project, supported in the Analytical and Surface Chemistry Program, addresses questions of the detailed dynamics of gas-surface interactions. The objectives of the research are to develop an understanding of the detailed dynamics of dissociative chemisorption of simple diatomic molecules, and the recombination and desorption of adsorbed atoms from well characterized solid surfaces. Velocity resolved, polarization sensitive multi-photon ionization detection of scattered diatomic molecules and desorbed molecules resulting from atom recombination will be carried out. Novel studies of chemisorption of monoenergetic, aligned reagents will also be pursued. %%% Dissociation of molecules on surfaces, as well as recombination and desorption of molecules from the surface, are the principal elementary processes which underlie a wide range of important technologies, including catalysis, corrosion, and electronic device fabrication. This research project develops and applies state-of-the-art methods to the study of the detailed dynamics of these elementary processes. The information gained from these studies is essential in developing our basic understanding of these critical technologies.

9307259 Kummel This research addresses precise etching of GaAs(100) and Si(100) by an exact integral number of monolayers using saturation dosing of Cl2 followed by laser induced desorption. Molecular chlorine is required because it only absorbs to a coverage of one monolayer on these two surfaces. The critical qualities for the laser induced thermal desorption are (a) uniformity across the sample; (b) complete removal of all etching products; (c) restoration of the surface to a clean well-ordered state. These characteristics will be sought through the use of sequences of nanosecond laser pulses or single microsecond laser pulses rather than the conventional nanosecond single pulse technique. The monolayer peeling technique is critical to the development of quantum well devices because, if successful, it would allow etching to the exact interface between two thin semiconductor layers such as GaAs and AlGaAs. %%% The goal of this study is to devise a method of etching GaAs(100) and Si(100) at room temperature without surface damage and with an ultra-precise atomic level control over etch depth. This proposed technique of monolayer peeling is cyclic etching with chlorine and laser induced thermal desorption. The monolayer peeling technique is critical to the development of advanced electronic and photonic devices and integrated circuits using structures such as compound semiconductor quantum wells, because it would provide the basis for a critical fabrication process, etching to the exact interface between two ultra-thin semiconductor layers such as GaAs and AlGaAs.

9355039 Sinha This proposal requests support for 5 graduate research traineeships in atmospheric chemistry. The research and education program described involves the study of a variety of problems in stratospheric and tropospheric chemistry. In addition to graduate research, a complete graduate education curriculum in environmental science, with an emphasis on the atmosphere, is described. The five individual research programs described are involved in a variety of interdisciplinary and collaborative work. Interactions between these groups foster and excellent environment for learning all aspects of atmospheric chemistry. The collective group meetings and course offerings provide a sound foundation for the proposed training program. Problem solving is emphasized in the educational process. ***

9527814 Kummel This research project is an effort to understand basic halogen chemistry on GaAs, and the correlations between surface chemistry, structure and electronic properties. Additionally, the project includes an activity to apply the results of the chemical passivation study to device fabrication with development of a gate insulator of CaF2 or SrF2 and a halogen passivated, un-pinned GaAs surface. For basic passivation studies an atomic passivation layer will be formed by dosing of F2, Cl2, Br2, I2 with a differentially pumped MBE source and cycling the substrate temperature to remove arsenic halides or gallium polyhalide from the surface. Samples will be characterized in an STM chamber with XPS and STM used to detect the position of the Fermi level within the bandgap. %%% The knowledge and understanding gained from this research project is expected to contribute in a fundamental way to improving the performance of advanced compound semiconductor materials used in computing, information processing, and telecommunications by providing a fundamental understanding and a basis for designing and producing improved layered structures of materials required for advanced devices and circuits. 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 project, supported by the Analytical and Surface Chemistry Program, explores the interaction of halogen molecules with the well characterized Al(111) surface. It is particularly concerned with the abstractive dissociative adsorption which can occur with halogens, especially interhalogen molecules. Professor Kummel and his students at the University of California at San Diego will combine molecular beam scattering and scanning tunneling microscopy methods to probe the detailed dynamics of the interaction of these molecules, with a view to understanding the long range charge transfer process which accompanies dissociative adsorption. Oriented beam methods will also be used to probe the interaction of pendular states of the interhalogens with the low work function aluminum surface. An understanding of the dissociative adsorption of simple, high electron affinity molecules such as chlorine when interacting with low work function metals such as aluminum is the focus of this research project. Probing the dynamics of this interaction using scattering and surface microscopic methods will provide information about the mechanisms of these reactions, which are important in the processing of electronic materials, and in corrosion processes.

This research project addresses the fundamental mechanisms of non-adiabatic gas-surface interactions. With the support of the Analytical and Surface Chemistry Program, Professor Andrew Kummel and his coworkers at UC-San Diego are carrying out detailed experimental studies of the dissociative adsorption of halogen and interhalogen molecules interacting with low work function surfaces such as Al(111). Velocity dependent molecular beams of dihalogens and interhalogens are used to probe the mechanisms of remote dissociative and abstractive chemisorption. Velocity distributions of scattered halogen atoms, coupled with scanning probe microscopic examination of the reacted surface provide the details of energy partitioning and mechanism in these studies. The interaction of oriented interhalogen molecules is also examined. In addition to the fundamental insights obtained concerning non-adiabatic processes at surfaces, information relevant to the dry etching of electronic materials results from this work.

The mechanisms of halogen etching reactions taking place on low work function surfaces is the focus of this research project carried out by Professor Kummel and coworkers at UCSD. Using a combination of molecular beam methods, laser spectroscopic characterization of scattered species, and scanning probe microscopy to characterize the reacted surface, detailed information about halogen based plasma enhanced etching processes is obtained. This fundamental research has broad impact on the development of electronic materials etching processes, as well as providing fundamental insight into the mechanisms of an important class of surface reactions.

This project aims for fundamental understanding of the basic formation and evolution of Ga2O3 on GaAs. Collaborators at Motorola have employed photoluminescence and capacitance-voltage measurements to show that the Ga2O3/GaAs(100) interface is unpinned, but the detailed atomic and electronic structure of the interface is unknown. In order to unpin the Fermi level, the binding of Ga2O3 to GaAs must be sufficiently strong that the clean surface states are pushed into either the conduction or the valence bands and no new pinning states are formed. The approach in this project is to use cross-sectional and in-plane scanning tunneling microscopy (STM) and spectroscopy (STS), to determine chemical bonding and electronic structure at the Ga2O3/GaAs interface. Additionally, the chemistry of the Ga2O3 growth process using O, O2 , and O3 oxidation sources will be investigated.
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The project addresses basic research issues in a topical area of materials science having high potential technological relevance. While thermal oxidation of silicon forms an excellent oxide
along with an electrically passive oxide-semiconductor interface, there is no current commercial
process to form gate oxides on GaAs. This dielectric is highly significant because it could underpin a new MOS-like technology based on GaAs with advantages in both electronics and photonics. The research will contribute basic materials science knowledge at a fundamental level to new capabilities in electronic/photonic devices. A variety of fundamental issues are to be addressed in these investigations. 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.
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This grant supports the purchase of a low temperature scanning tunneling microscope (STM) that will be used for investigations of defects and bonding sites in electronic and sensor materials. The low temperature STM provides a zero drift environment in which isolated molecules do not diffuse. In this quiet, stationary environment, the local electronic structure of single defects or bonding sites can be determined using current-voltage (dI/dV) measurements. The specific systems that will be studied with this instrument include: (a) defects at the semiconductor/gate oxide interface; (b) polysilole-based nanowire sensors; (c) halogen reactions with aluminum; (d) mixed, asymmetric metal phthalocyanine-based chemical sensors; and (e) fabrication of ordered arrays of single macromolecular assemblies. With the advent of commercial software (VASP) for calculating the electronic structures of molecules on surfaces, low temperature STM and STS studies can be directly compared to both simulated STM images and the partial density of states on single atoms. This comparison provides critical insights into the control of electronic structure on surfaces.

This instrument will have impact on a broad audience at the university. (a) The San Diego Fellowship program for entering graduate students: UCSD is donating 3 months of support for 4 entering graduate students. These fellowships will be used to support graduate students to increase the diversity of the chemistry and physics graduate programs. (b) Undergraduate research: Undergraduate students will be involved in the proposed research via the Howard Hughes Undergraduate Enrichment Program (HHUEP) and the UCSD Office of Academic Enrichment. (c) UCSD-TV and webcasts: Lectures that are appropriate for high school and college students will be recorded for both broadcast and webcast by the UCSD-TV education outreach program. (d) Teacher training: The funds support one high school science teacher per summer to work in a research laboratory at UCSD. The teacher will have the opportunity to learn how to use the telemetry system developed at the UCSD National Center for Microscopy and Imaging Research (NCMIR). The NCMIR facilities house an electron microscope that can be remotely controlled via the web, enabling teachers and students to use the SEM directly from their classrooms. (e) Industrial collaborations: The low temperature STM will be used in collaborative research projects that focus on device and sensor development and involve Motorola, Microsense, and IBM.

This project addresses atomic and electronic structures formed by a series of vapor deposited oxides onto antimony based semiconductor alloys, "ABCS" (InAs, GaSb, AlSb, and their alloys); the aim is to achieve understanding of basic mechanisms of Fermi level unpinning of oxide-ternary semiconductor interfaces. Related interfacial chemistry issues need to be sufficiently understood to allow prediction of which oxides are best candidates to form unpinned interfaces on channels and confinement layers in InAs device structures. It is conjectured that to grow an unpinned oxide-ABCS interface, sub-oxide molecules insert into surface dimers, break the surface reconstruction, restore the bulk crystal symmetry, and passivate the oxide/semiconductor interface. Three tasks are envisioned: Task 1: To determine the best combinations of sub-oxides (Al2O, Ga2O, In2O, Tl2O, SiO, GeO, TiO) and "ABCS" surfaces (AlSb, GaSb, InAs or their alloys) for passivation, calculations will be performed on a series of sub-oxides and surfaces. These calculations will ensure that each candidate sub-oxide breaks the dimer reconstruction, unpins the Fermi level, and does not displace dimer atoms. This has been done successfully for Ga2O/GaAs. Task 2: To determine the optimal reconstruction and temperature for deposition of sub-oxide-surface combinations identified in Task 1, combinatorial film growth will be used. Sub-oxides will be vapor deposited onto atomically clean, ordered surfaces. Scanning tunneling microscopy (STM) and spectroscopy (STS) will be employed to determine both the atomic and electronic structure of the surface after deposition and without exposure to air. Deposition will be tested on several surface reconstructions. Task 3: A thick (30 to 100A) layer of an insulating gate oxide compatible with the suboxide developed in Task 1 will be deposited on the best oxide-semiconductor surfaces and capacitance and transconductance measurements will be made to characterize the oxide-semiconductor interface. This work will utilize the expansive knowledge base of the NRL in InAs HEMT processing and InAs/GaAs wafer growth. Additionally, all circuit testing will be done by collaboration with Motorola.
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An important impact of the project is in education and human resource development through the integration of research and education. The multi-disciplinary nature of the research where students work in chemistry, physics, or electrical engineering departments provides broad educational opportunities. Special efforts are made to ensure the diversity of students working on the project through summer program activities. To foster student-industrial relations the PI also directs an industrial interaction day bringing together UCSD graduate students working in materials chemistry, physics, and engineering and recent graduates working in industry (Intel, LSI, IBM, HRL, Agilent, Applied Materials, and Novacrystals). The day consists of talks that are given by students and industrial scientists. Technological relevance to ITR (Information Technology Research) includes wireless communication, remote sensor networks, personal digital assistants, and mm-wave imaging arrays, as well as high frequency (100 GHz) logic, micro air vehicles with sensors and telemetry (for detection of environmental pollutants and chemical/biological warfare agents), and microscopic sensors with local signal processing (either for chemical/biological weapons detection or for subdermal implantation for medical diagnostics). These devices all require high speed, low power logic enabled by the research activities of this project with particular relevance to the ITR goals of delivery of critical information anytime, anywhere and optimization of work efficiency.
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Reactive scattering of small molecules from metal phthalocyanine surfaces is used to probe chemisorption dynamics on model organic surfaces. The distinct roles of organic and metal center on the adsorption dynamics is examined in this research project supported by the Analytical and Surface Chemistry Program. Professor Kummel and his coworkers at the University of California-San Diego use a combination of molecular beam scattering tools and scanning tunneling microscopy to examine the dynamics of small molecule adsorption on these model organic surfaces. Bonding sites are examined using STM and STS, chemisorption mechanism is probed using reactive scattering molecular beam methods, and density functional calculations are carried out to model the experimental results.

Understanding how small molecules adsorb and react on organic and organometallic surfaces is the goal of this research project supported in the Analytical and Surface Chemistry Program. Using a combination of experimental probes, particularly molecular beam scattering and scanning probe microscopy, the detailed dynamics of small molecules interacting with phthalocyanine surfaces are examined. This fundamental information may have applicability in the design of molecule specific sensors and organic molecule electronics.

laboratory mouse; neoplasm /cancer diagnosis; technology /technique development

Technical: This project is to conduct fundamental research on the interfaces between compound semiconductors and oxides. It uses an integrated approach, combining atomic layer deposition (ALD), scanning tunneling microscopy and spectroscopy characterization, and density functional theory (DFT) studies to identify the requirements for forming low interface state density, atomically uniform oxides on high-mobility InGaAs and InAs surfaces. The project includes the following main tasks: Investigation of different methods of chemically termination (H, Cl, and OH) prior to deposition of the first oxide layer on compound semiconductors, and their associated bonding structures and Fermi-level pinning; comparison of interfacial bonding structures and defect sites of oxide-metal-semiconductor vs metal-oxide-semiconductor interfaces; studies of the atomic and electronic structures of oxide interfaces grown from two isoelectronic precursors, HfCl4 and ZrCl4; and DFT modeling assessment of the importance of different bonding aspects to pinning at oxide-semiconductor interfaces (ionic bonds, metal-semiconductor bonds, arsenic-oxygen bonds) and determination of the structural differences between trap and fixed charge states in order to develop a fundamental understanding of these interfaces.
Non-technical: The project addresses basic research issues in a topical area of materials science with high technological relevance. It focuses on compound semiconductors substrates such as InGaAs and InAs, which offer higher mobility (therefore faster device performance) and lower power consumption than silicon. The project is highly interdisciplinary, providing students at all levels with training that bridges chemistry, electrical engineering, physics, and materials science. Students trained in these fields represent a valuable resource in maintaining U.S. predominance in electronics technology. The project also includes a program that allows underrepresented entering PhD students to start their graduate research the summer before they enter graduate school.

The Analytical and Surface Chemistry Program of the Division of Chemistry at NSF supports the research program of Prof. Kummel of the University of California, San Diego (UCSD). Prof. Kummel and his students investigate how explosive molecules absorb onto organic films and change their electrical properties; the change in electrical properties is used to detect the presence of the explosive molecules thereby creating a sensor. The sensors are similar to the transistors which power computers but are made of organic materials instead of silicon because organic materials absorb gases from ambient air. The films developed at UCSD can identify peroxides; peroxide sensing is critical for the detection of improvised explosive devices (IEDs) as well as sterilization of surgical equipment, pharmaceutical supplies, and bio-decontamination. Using an array of organic sensor films, more exotic compounds can be detected including nerve agents and volatile organic compounds which are important in mold sensing. The project provides excellent training opportunities to graduate and undergraduate students in a scientific area of great significance to US national security.

DESCRIPTION (provided by applicant): The field of nanotechnology has excellent potential for developing innovative methods to diagnose cancer and provide improved methods for therapy. To fully exploit this new technology future researchers must receive multi-disciplinary training in cancer research and physical sciences/engineering. The mission of the Center for Cross Training Translational Cancer Researchers in Nanotechnology (CRIN) program is to provide cross-training to predoctoral students, postdoctoral scientists, and physicians in nanoscience, nanotechnology, and other emerging technologies, cancer biology, and translational research. Young scientists will be trained in nanoscience, nanoengineering, mesoscale engineering, and image recognition to cancer research. CRIN will build on existing cancer research programs, through the NCI designated UCSD Comprehensive Cancer Center, and nanotechnology focused research programs, including UCSD's Center of Cancer Nanotechnology Excellence and In vivo Cellular and Molecular Imaging Center. The faculty participants are successful researchers with over $27 million in research funding, and are experienced mentors. The program will support 5 graduate students and 2 post-doctoral fellows for two years each, and will provide new opportunities for training underrepresented minorities in cancer nanotechnology research. The program will include research based cross-training, didactic training, workshops, seminars, journal clubs, and professional development activities. CRIN will also develop outreach activities for clinicians, research scientists, and the community.

The PI's request funding to develop a low power, autonomous solid state sensor for simultaneous measurement of seawater pH and Total Alkalinity. The proposed research involves micro sensor development, electrochemistry, marine chemistry, and electrical engineering. Combination of two ISFET measurement principles will be used for rapid, sequential measurement of pH and Total Alkalinity in order to generate a full thermodynamic description of the CO2 system in the analyte solution.

Broader Impacts:

Making sensors to measure pH and total alkalinity in real time and at the appropriate precision is important to our understanding of ocean acidification. If successful, they plan to commercialize it. Other situations where total weak acid or base concentration in combination with the pH form useful information, this proposed system might be used, like in food industry and for biomedical applications. Two graduate students will be involved in this project.

Technical Description: Atomic layer deposition is a cyclic chemical process that provides sub-nanometer control of layer thickness. The bonding of the first layer is the critical step in providing a low defect interface, which enables nucleation of atomic layer deposition within each unit cell. The project is developing an atomic layer understanding of oxide monolayers deposited on two very different semiconducting materials, gallium nitride and graphene, by combining scanning tunneling microscopy and scanning tunneling spectroscopy. These materials have surfaces with very low chemical reactivity, enabling the fabrication of unique electronics devices; however, these materials lack reactive atoms that can strongly bond to atomic layer deposition precursors. For graphene, the non-reactive surface is functionalized via adsorption of an ordered monolayer of organic coordination complexes while for gallium nitride and order layer of inorganic function groups are deposited. Two techniques are developed with broad applicability: (a) ultra high vacuum cross-sectional Kelvin Probe Force Microscopy to image the electrostatic potentials inside working capacitors and field effect transistors on the nanoscale and (b) contactless ultra high vacuum variable frequency capacitance-voltage for in-situ measurement of gate oxide defects.

Non-technical Description: At present, computer chip speed and performance are limited by the dissipation of heat. Further increases in performance require decreasing in the supply voltage to stabilize heat dissipation per unit area. This research project seeks to develop the monolayer chemistry required for nucleating layer by layer growth of the nanoscale insulators, which will enable lower-power computing or more efficient high power communication. The project includes activities designed to recruit and support under-represented minority PhD students and undergraduate students who are interested in materials science and engineering or materials chemistry.

Abstract Studies have indicated that ablative therapies may augment the host immune system response against tumor antigens by enhancing the local immunogenicity of the ablated tumor as well as distal metastatic sites thereby improving therapy outcomes. The proposed project aims to evaluate the synergy of mechanical HIFU using gas filled silica nanoshells in combination with an immune adjuvant, a TLR7 agonist, which will be conjugated to the surface of silica nanoshells. It is postulated that applying mechanical HIFU to the tumor will condition the tumor tissue environment by exposing tumor antigens without denaturing the proteins and by initiating an inflammatory response. Preliminary studies have shown that the immunostimulatory properties of a TLR7 agonist are enhanced when conjugated to 100nm silica nanoshells. These nanoshell conjugates will be used as an immune adjuvant in order to enhance the antitumor immune response. Combination of HIFU ablative therapy and an immune adjuvant will be investigated in a metastatic colon and breast cancer murine model with the aim to enhance tumor ablation, reduce tumor growth, and to elicit a systemic antitumor immune response. The partnership will be used as a mean to support students underrepresented in science to become young independent scientists. The project will provide many opportunities to promote a learning and collaborative environment for students in research education. This will aid students to develop technical and interpersonal skills which will assist them in fulfilling a successful career.

7. PROJECT SUMMARY/ABSTRACT: This training program seeks to address two issues (1) In spite of all of the research advances in cancer biology and application of these discoveries to the clinic, cancer therapies have had limited success in prolonging life. Engineering approaches have begun to show promise, but there is a dearth of investigators who are trained in both cancer research and engineering/materials science. (2) Current PhD and postdoctoral training in cancer research focuses on preparing trainees to be independent researchers, but it doesn't provide a comprehensive set of skills for young scientists who, when starting their careers in academia, will be working closely with small/startup pharmaceutical or device companies or who may even work in a small firm before reentering academia. There is a synergy in addressing both issues since young scientists with cross training in nanotechnology and cancer biology are well positioned to work in collaboration with or work in small pharmaceutical or medical device companies focused on cancer. The proposed program will provide trainees with a balanced combination of (a) a comprehensive cancer biology, engineering, and entrepreneurship didactic training, (b) laboratory experience dual-mentored by a basic science cancer researcher and clinical/translational cancer faculty, and (c) practical skills learned by having the trainees work with small business entrepreneurs directly and/or prepare and defend research proposals. There will be two training tracks: one for trainees who plan to initially work in startup companies and one for trainees who plan to initially work in academia.