Summer 2007 SUNRISE Projects

Introduction of New Materials and Structural Challenges to Improve MOSFET Performance

Zohrab Basmajian Glendale CC
Faculty Mentor: Dr. Roger Lake
Laboratory for Terascale and Terahertz Electronics
Department of Electrical Engineering,
University of California, Riverside

In the Laboratory for Terascale and Terahertz Electronics (LATTE), we examine electron transport in different CNT structures. We also develop and model CNTFET using heterogeneous components such as metals, peptides, and biological (DNA/PNA) linkers. The motivation of this research is to build devices with high functionality and invent new information processing structures, materials, and architectures that extend the CMOS technology platform. In order to calculate electron transport through CNT molecular interfaces, we use DFT coupled with NEGF theory. FIREBALL is used to generate matrix elements used in NEGF algorithm. Generating matrix elements takes a couple days depending on single or double precision. I use FIREBALL for three different runs. The first run calculates the band structure energy and solution to one electron Schrödinger equation. The second run calculates the potential difference between repulsive ions and electrons, and the third run uses exchange correlation method, and recomputes Hamiltonian and overlap matrixes. It is important to be converged otherwise I must run FIREBALL again with different Bmix factor and Fermi temperature. When an electron gains enough energy and transfers out, it leaves a hole in the strain of CNT. By applying bios voltage, this hole moves around. As a result, in order to find the probability of an electron being on some layer at some specified energy, I use green blob, which calculates resonant transmission and 3D electron density of states. The advantage of this method with respect to self-assembly is simplified circuit topology.

Baking a Pie in Oven: Changing Magnetic Properties
on Single-Sized Quantum Dots by
Doping with Transition Metals

Zorigt Bazarragchaa UC Berkeley
Mentors: Qichun Zhang2, Phingyun Feng3, Ward Beyermann4, Maurizio Biasini
University of California, Riverside

Imagine making your own synthetic crystalline material that has exactly the magnetic properties you desire. This can be possible with quantum dot crystals, because enriching (doping) a basic plain crystal with non-toxic transition metals can greatly change the magnetic properties from diamagnetic to paramagnetic or ferromagnetic at different temperatures. These new materials could be potentially used for Spintronics. There are basic steps to make the crystals, which is surprisingly similar to baking a pie at your home! My ingredients are PPh4Br 42 mg, Thiourea 49 mg, Cd(SPh)2 189 mg, CH3CN 2.570 g, and then add the choice of metal-salt, such as Co(CH3COO)2, to make my “crystal pie” have a distinctive flavor (enriching the crystals with transition metal). After well mixing the chemicals, put the samples in the hot-oven for about from 3 to 5 days at 110oC, 130oC, or 150oC degrees depending on what kind of crystals I wish to synthesize. This is the same as when you make your apple pie and then bake it in oven for certain hours depending on how crispier crust you want. Like a delicious pie, my results are always rewarding. From my results, I discover new ways to get better and more pure crystals by understanding better about how much chemicals to mix and how long to keep them in the oven at what temperature. The early results lead us to believe that by doping with different transition metals we can change the physical properties of mere solid crystals, or make a better pie. The promising future application for this kind of materials is manufacturing devices in semiconductor industry.

Using Scanning Tunneling Microscopy to Analyze Si/Ge Nanostructures at The Quantum Level

Bert Brumell UC Riverside
Mentors: Jianlin Liu, and Yan Zhu
Department of Electrical Engineering
University of California, Riverside

The ability to analyze surface structure and roughness at the quantum level has always been a challenge for many scientists and engineers in nanotechnology. The importance of being able to see this at the quantum level has many profound applications in the study of nanotechnology. Scanning tunneling microscopy is a relatively powerful method of approach in the study of nanostructures. By using an STM, this research looks into silicon and germanium nanostructures at the quantum level, allowing the characterization of the lattice structure as well as its molecular configuration. The successful research allows us to better understand nanostructures and their device performance.

Thermal Transport in Carbon Nanotube Composites

Wenjun Chen Mt. SAC
Mentor: Professor Alexander A. Balandin
Nano-Device Laboratory
Department of Electrical Engineering
University of California – Riverside

Carbon nanotube (CNT) composites have been proposed as the thermal interface materials for heat spreading from electronic and optoelectronic devices and circuits. The proposed applications of the carbon nanotube composites for thermal management require accurate knowledge of thermal conductivity in such composites as a function of the carbon nanotube filler content. At the same time the mechanism of heat conduction in carbon nanotube composites is very interesting from the fundamental science point of view since carbon nanotubes are unique in the family of nanostructured materials. Moreover there is significant discrepancy in the thermal conductivity data for carbon nanotube composites reported in literature, particularly for small filler fractions. In this project I have measured thermal conductivity K in a set of epoxy-based carbon nanotube composites with small filler fraction. The measurements have been carried out at room temperature using the transient “hot wire” technique. For comparison, the thermal conductivity of the pure epoxy, which was used for the composite fabrication, has also been studied. The measured value of the thermal conductivity for the pure epoxy is 0.24 W/mK. Addition of 0.05% of the multi-wall carbon nanotubes (MWCNT) changes its value to 0.25 W/mK. Addition of the single-wall carbon nanotubes (SWCNT) in the filler content range 0.004% to 0.5% did not produce measurable change in the thermal conductivity value as compared to pure epoxy. The results of my measurements using the transient “hot wire” technique are in good agreement with the data obtained by other techniques as reported in literature. At the same time, the fact that the thermal conductivity in the 0.5% SWCNT was the same as in pure epoxy requires further investigation.

Electro Deposition of FePd Alloy Thin Films and Nanowires

Pilar Davila University of Redlands
Mentors:Sandra Hernández and N. Myung
Department of Chemical and Environmental Engineering
Center for Nanoscale Science and Engineering
University of California, Riverside CA. 92521, USA

Magnetic recording is a process which is currently performed horizontally. If the technique of magnetic recording could be changed to being performed vertically this would allow an increase in memory storage in computers, zip drives, laptops, etc. Because FePd alloys have unique magnetic and material properties, they are receiving much interest and have become the focus of much research. Magneto-restriction has also been found to be exhibited by FePd alloys due to martensitic transformation when induced by a magnetic field1. This makes FePd alloy a good candidate for magnetically driven sensors and actuators2. In this work, FePd thin films and nanowires were electrodeposited from ammonium citrate baths onto stainless steel electrodes (thin film) or polycarbonate or alumina templates (nanowires of 30nm or 200nm width respectively), at various conditions such as current density and bath composition. The effects of the various deposition conditions on the nanowires, as well as the thin films were systematically analyzed by Atomic Absorption Spectrometer and by XRD. The concentrations of iron as well as the pH of the baths were kept constant at 0.02 M and 9.00, accordingly, while the concentration of palladium in the bath was varied from 0.00025 to 0.008 M. The current density was varied at 5 and 10 mA/cm2. Flaking and cracks showed stress in the thin films deposited in high Pd content. Thin films with Fe: Pd composition of 48: 52 have been made yet the deposition of a film and growth of a nanowire of composition of 50: 50 is required for magnetic recording where as the deposition of 20% Fe is ideal for actuation. Annealing and XRD are to be done to analyze and observe the magnetic properties of the alloy and to test the ability for usage as an actuator and for magnetic recording when contacted with a current.

Surface Dynamics of Aniline on Cu(111): Molecular Pinwheels

Jacob Good UC Riverside
Mentors: R. Fawcett, L. Bartels
Department of Chemistry
University of California, Riverside

Scanning tunneling microscopy of aniline at 77 K adsorbed on a Cu(111) surface in an ultra-high vacuum reveals that at a low coverage, most of the aniline molecules diffuse across the surface while a smaller number interact with the surface in a manner that causes them to spin around a fixed anchor, which is most likely a linkage between the substrate and the amine group. This behavior is remarkably similar to that of thiolphenols and halosubstituted thiolphenols studied by the Bartels Group in the past. We will attempt to replicate the dehydrogenation of the thiol group observed in the past with the amine group using electrons injected by the STM tip and cause the aniline molecules to bind more strongly with the Cu(111) substrate. Higher coverages of aniline will be scanned to see if any novel effects, such as a self-assembling film, arise from the intermolecular forces between the anilines when they are more densely packed.

Zeolite Hybrid Coatings on Metal Alloys for Chemical Resistance, Hydrophilicity, and Microbiocidal Activity

Sean Guthrie1
Mentors: Derek Beving2 and Yushan Yan2
Department of Biology
University of Redlands, Redlands, CA 92374.
2Department of Chemical and Environmental Engineering,
University of California, Riverside, CA 92521.

Polycrystalline zeolite membranes, films, and coatings have been demonstrated to be useful in membrane separations, membrane reactors, sensors, adsorption, catalysis, low-k dielectrics, corrosion-resistant coatings, hydrophilic coatings, antimicrobial coatings, heat pumps, and thermoelectrics. For these applications pure phase zeolites are used and their application is dependent on the type of zeolite and their silicon-to-aluminum ratio. High-silica-zeolites (HSZ) are chemically resistant, thermally stable and have surface hydrophobicity. Low-silica-zeolites (LSZ) are hydrophilic, have a large ion exchange capacity and are not significantly chemically resistant. The development of a hydrophilic and ion exchangeable zeolite coating that is chemically and thermally stable is very desirable. We have developed a method to generate zeolite hybrid coatings of tunable thickness incorporating desirable features from both HSZ and LSZ species. The hybrid coating is a purely crystalline, mixed zeolite composite coating made from low-silica zeolite (zeolite Y) seed crystals imbedded in a matrix of high-silica zeolite (MFI). The LSZ-HSZ zeolite hybrid coatings functionally demonstrate features characteristically limited to pure LSZ (zeolite Y) and HSZ (MFI) coatings. The mixed zeolite phase of the hybrid coatings were confirmed by XRD and SEM. Hydrophilicity was determined by contact angle measurements. The hybrid coatings were shown to be extremely chemically resistant, readily silver ion exchangeable and microbiocidal. This zeolite hybrid coating has great utility and its function and application can be easily tuned by changing the zeolite species used to generate it.

Single-Walled Carbon Nanotubes as Substrates for the Growth of Neurons

Michael C. Hara Cal Poly Pomona
Mentors: Erik Malarkey and Vladimir Parpura
Summer Undergraduate Nanoscale Research Institute for Science and Engineering
Department of Cell Biology and Neuroscience
University of California, Riverside 92521

We have investigated the morphology of cultured neurons using different conductive singlewalled carbon nanotube (SWNT) substrates. Biocompatible SWNTs are hypothesized to foster the outgrowth of neuronal processes along with the growth of neurite branches. With a better understanding of how nanotube conductance could nurture neuron viability and neurite outgrowth, clinical research may develop important medical applications; neural prostheses studies could benefit from this work. Rat hippocampal cells have been placed on coverslips coated with SWNT-COOH scaffolding – nanotubes with functional carboxy group. The substrates displayed different conductivities of approximately 200, 00 and 1,400 S/cm. The resulting neuronal morphologies were determined by fluorescence microscopy imaging utilizing calcein AM, a dye that accumulates in live cells. We discuss how the conductivity of a substrate plays a role in neuronal growth and neurite outgrowth.

Magneto-Optical Kerr Effect Microscope

Artin Megerdichian Glendale CC
Mentor: Dr. Roland Kawakami
Department of Physics
University of California, Riverside

It is possible to change the north and south pole of a magnet if a large external magnetic field is created around the magnet in the opposite direction of the targeted magnet’s magnetization. The Magneto-Optical Kerr Effect Microscope is used to see the change in the direction of the magnetization of a sample due to an external magnetic field. To build this microscope from scratch, we will need lenses with negative and positive focal lengths, polarizers, an objective lens, a beamsplitter, a magnetic sample to look at, a CCD camera to capture the image from the sample, a light source to illuminate the sample, a power supply for the light source, and a magnet to create the external magnetic field around the sample. The procedure has to be done very patiently since there are many factors that determine the observation of a clear image on the screen. The sample is placed on a xyz stage, so we are able to move and have control over it in all the three directions The light source is a blue LED, so we will not get interference patterns on the screen. After placing every piece on the optical table and properly adjusting them so the light gets to the sample, we will be able to see the image of the sample. Moreover, we will create a magnetic field around the sample and try to observe the magnetization changes of our sample on the screen.

Photoconductivity of Sb-doped p-type
ZnO Schottky Contact Ultraviolet Detector

Htet Naing Cal Poly Pomona
Mentors: L. J. Mandalapu, and J. L. Liu
Quantum Structures Laboratory
Department of Electrical Engineering,
University of California, Riverside, CA 92521

Zinc Oxide (ZnO) is a semiconductor that has direct band gap of about 3.38 eV and has potential to make high efficiency ultra fast ultraviolet detectors by fabricating metal-ZnO schottky diode. Very limited number of study has been done on p-type ZnO based devices because there are difficulties growing p-type ZnO. However, it has been shown recently by our group that Sb is a suitable candidate to produce p-type ZnO films grown on Si (100) substrates. In this study under the NSF REU SUNRISE program, performance of Sb-doped p-type ZnO and Ti/Al schottky diode is estimated by photo response measurements. Xe arc lamp is used as a light source and a monochromator varies the wavelength of the light incident on the device from 200 nm to 600 nm after chopping. Photocurrent generated in the device is fed into the home built preamplifier and lock in amplifier before recording. The spectral response of the device is analyzed and studied under no bias as well as under reveres bias voltages of 5, 10, 15, and 20 V. The p-type ZnO schottky device is found to have a very good photo response in the light wavelength between 300 nm and 370 nm. The peak photo response is measured at about 350 nm, which corresponds to the effective band gap of ZnO. There is also a photo response above 400 nm due to the defects in the ZnO film and the factors related to the silicon substrate.

Computer Simulation of the Thermal Boundary Resistance in Semiconductor Heterostructures

David Pereda UC Riverside
Faculty Mentor: Alexander A. Balandin
Nano-Device Laboratory
Department of Electrical Engineering
University of California – Riverside

Gallium Nitride (GaN) and related materials have shown promises for applications in the next generation of the high-power high-frequency transistors and blue lasers. At the same time, performance of GaN-based devices has been limited by self-heating. Thus, accurate modeling of heat diffusion and self-heating effects in AlGaN/GaN heterostructures become crucial for further development of nitride technology.
Accurate modeling and computer simulation of heat transport through interfaces between two different materials is important for thermal design optimization and thermal management of electronic and optoelectronic devices. The goal of this project is to develop a user-friendly computer code, which would allow to simulate the thermal boundary resistance (TBR), also referred to as Kapitza resistance, at the interface between two semiconductor materials. The Kapitza resistance at the boundary between two materials is defined as TBR=DT×A/Q, where A is the area, DT is the temperature difference between two side of the interface and Q is the heat flow.
The theoretical formalism, used in the simulation, is based on the diffuse mismatch model (DMM) [1]. The software tool, under development, is written in MATLAB. The input parameters will be the longitudinal and transverse sound velocities in two materials, which form the interface. The results of the simulation will present TBR value as a function of temperature T in the range T=4K to 400K. The software tool will be used by the Nano-Device laboratory group members for quick estimates of TBR values while interpreting experimental thermal conductivity data. The results obtained with my code will be checked by comparison with data available for several different material systems [2].

[1] E. T. Swartz, R. O. Pohl, “Thermal boundary resistance,” Appl. Phys. Lett. 51, 2200-2202 (1987).

[2] K. Filippov and A.A. Balandin, “The effect of the thermal boundary resistance on self-heating of AlGaN/GaN HFETs,” J. Nitride Semiconductor Research , 8: #4 (2003).

DNA Sequencing and Storage by Length

Lauren K. Quezada Loyola Marymount University
Mentors: Nathaniel G. Portney, Dr. Mihri Ozkan
Electrical Engineering
University of California, Riverside

Our goal is to take a prepared cloned DNA fragment and using a computer based binary algorithm decode this fragment into a known message. We have successfully cultured in a solid agar growth media several colonies of a modified E. coli bacterium and increased yield in a liquid culture broth treated with an antibiotic (Kanamyacin). The plasmid DNA contained inside of these cells was then purified using a plasmid prep kit. Purity of the plasmid was tested by measuring the absorbance ratios of DNA to protein (A260/A280). Since this ratio was 1.7, within the accepted range, the plasmid was deemed sufficiently pure. We optimized the imaging settings for a non-toxic dye and a Typhoon imaging system which uses lasers to measure the florescence of our bands. We could then run 17 inch, 10% manually cast TBE-Urea PAGE gels containing our undigested and digested purified plasmid and various markers. The Stu I digestion of our sample was required in order to extract the 110 bp fragment used for decoding. Following this, a manual sequencing gel (30%, 0.35 mm) was then run with an Alu I partial restriction digestion of our fragment along with a serial dilution series to determine the optimal volume of Alu I to cut the fragment along all possible restriction sites. We then quantified the separation of bands, using a factor of 4 or 8 bp to decode from binary the desired message of UCR. For further work we will attach quantum dots to the backbone of DNA to improve visualization of the DNA bands. With this message in hand, we will have successfully merged biology and computer science in the binary decoding of our fragment.

Synthesis of Multi-Walled Carbon Nanotubes Using Chemical Vapor Deposition

Singh, Parminder Riverside CC
Faculty Mentor – Dr Haddon, Robert C
Center for Nanoscale Science and Engineering
Department of Chemistry and Chemical & Environmental Engineering
University of California, Riverside

Carbon Nanotubes (CNTs), seamless hollow cylindrical structure of carbon, have attracted significant attention ever since their discovery in 1991. Their outstanding properties such as remarkably high tensile strength, great electrical and thermal conductivity make them potentially suitable for a wide range of applications ranging from the semiconductor industry to materials science and biomedicine. However, the synthesis and quality control of CNTs are still a challenge and impede their further application. The aspect ratio and purity of the prepared CNTs alter their properties accordingly therefore it is vital to establish a precise control of these parameters. The primary objective of my research project is to optimize the Chemical Vapor Deposition (CVD) method, currently used in the synthesis of multi-walled carbon nanotubes (MWNTs). The advantage of producing nanotubes through this method is that it can be easily scaled up for producing bulk amount of pure and aligned nanotubes. There are several factors that control the synthesis of MWNTs, which include reaction time, reactor temperature, and the feed rate of the chemical reactants. This summer I have worked on the optimization of these factors to control the diameter and the length of the multi-walled nanotubes produced. For my particular experiment, I used a ferrocene (catalyst) – xylene (carbon source) solution to synthesize nanotubes on quartz substrate. In comparison to the nanotubes produced earlier which had a diameter range of 50 – 150 nm, the tubes produced by using the optimized conditions have a diameter of 20 - 50 nm and measure 300 microns in length.

Binding Energy Between Anthraquinone Molecules on Cu(111)

Urvinee B. Solanki1
Faculty Mentor: Dr. Ludwig Bartels
Research Advisor: Kin Wong
University of California, Riverside

1 Department of Chemical and Materials Engineering, California State Polytechnic University, Pomona

At the nanoscale, physical and chemical properties of materials differ in fundamental ways from the properties of bulk matter. In this research, we examined the binding energy between two anthraquinone molecules on a Cu(111) substrate under low temperatures and pressures. A scanning tunneling microscope (STM) was used to observe anthraquinone molecules on Cu(111) at pressures of approximately 1.0x10-10 torr and temperatures below 120 K. The Cu(111) surface was prepared using repeated sputtering and annealing cycles. Deposition of anthraquinone molecules preceded by backfilling the chamber to a partial pressure of approximately 1.0x10-9 torr and exposing the clean surface to the molecules for approximately 30 seconds. Anthraquinone molecules spontaneously form large hollow honeycomb patterns on a Cu(111) surface. Two molecules of anthraquinone are attracted to each other by hydrogen bonds. After scanning, collecting and analyzing tens of thousands of images, rates of binding two anthraquinone molecules for various temperatures below 120K were obtained. These rates were highly temperature dependent and followed an Arrhenius relationship. This allowed us to find the activation energy for binding two anthraquinone molecules on Cu(111) as a result of the hydrogen bonds. In the future, systematic and meticulous studies of molecules at the nanoscale can reveal novel structures, new properties and innovative processes.

Magnetic Properties of Supertetrahedral Clusters Infused with Magnetic Transition Metals

Katherine L. Weeks University of Redlands
Mentors: QiChun Zhang, Pingyun Feng, Ward Beyermann, Maurizio Biasini
The Departments of Physical Chemistry and Physics
University of California Riverside

Indium-Sulfur clusters are known to have semiconducting properties; this study is specialized towards incorporating magnetic properties into these materials via transition metal doping. To be able to change InS anionic framework from having diamagnetic properties to either paramagnetic or ferromagnetic properties could benefit a variety of applications. These structures could provide a nano-electric material for use in spintronics. Other functions could be used towards semiconductors, photocatalysts, sorption, and ion-conductors. Doping metals (Fe, Co and Mn) are used as structural building units with valence states of +2. Structures that are observed in this study include T4 and T5 clusters; these are molecules with tetrahedral components that unite to form tetrahedral clusters. The size of the clusters are dependent on the number of metal layers, as denoted by T4 has four metal atom layers. Synthesis of these chalcogenide superlattices requires stirring of the reagents in a Teflon-stainless steel autoclave, followed by heating at temperatures of 150-190’C for 6 days. By measuring the magnetization of the clusters on a superconducting quantum interference device (SQUID), with temperature ranging from 300K down to 2K, the relationship of magnetization to the number of transition metal atoms in the structure can be derived. The T4 cluster UCR-1 Mn, displayed anti-ferromagnetic properties. The structure was paramagnetic until it was lowered to about 15K. UCR-1 Co and Fe displayed unusual properties but their exact capabilities have not yet been determined. The ability for a nano-structure to have both an electric conductivity with magnetic properties has been achieved.