Electron emission in vacuum electronics underlies many modern commercial and military applications, including radio frequency generating magnetrons in microwave ovens, electron emitters in electron microscopes and x-ray generators, and power tubes in particle accelerators and satellite communications. Lanthanum sulfide (LaS) has been successfully proved as an advanced electron emitter material, primarily because of its extraordinarily low effective work function (1.05 eV), their high stability in current emissions and their robustness. Recently, high aspect ratio structures such as nanowires have been found to drastically improve the emission efficiency due to the field enhancement at the nano-sized tips. However, LaS has not been utilized to fabricate better nano-sized emitters because of the difficulty to synthesize such single crystalline materials using the conventional sintering, arc discharge technique or physical vapor deposition. The aim of this project is to synthesize LaS nanowires by the metal-nanoparticle-assisted chemical vapor deposition (CVD) based on our previously developed method and to determine their election emission properties under applied electric field. The project will capitalize on the expertise of the synthesis of rare-earth boride nanomaterials in Cheung's group.

Undergraduates who join this project are expected to carry out and learn (a) the synthesis of lanthanum sulfide nanowires by the catalyst-assisted CVD, (b) the characterization of the nanomaterials by scanning electron microscopy (SEM) and x-ray diffractometry, and (c) quantum tunneling theory and measurement of the electron emission characteristics. The students will tabulate the reaction conditions vs. the material's diameter and length to extract the apparent activation energy of the reaction. They will also correlate the field induced emission characteristics with different geometric parameters of the nanowires such as length and diameters. Each student will be mentored daily by a graduate student. The students will learn chemical synthetic skills and vacuum techniques. They will be trained to use the SEM for sample characterization. They will be required to present the research results in a group meeting. Cheung will hold weekly meetings with the students and his daily mentor to discuss project progress.

The discovery of the growth and characterization of chiral nanostructures established a new field in solid state materials research. The ability to control the shape and scale of the nanoobjects allows tailoring of the basic functionality of chiral media, providing promise for applications in a wide variety of technologies, including magnetic storage media, optical filters, tunable electromagnetic resonator structures in the Terahertz region or nano-electromechanical precision actuators. Chiral nanostructures can be fabricated by glancing angle deposition using an extremely oblique angle of incidence for the particle flux and a synchronized substrate motion, for condition that support the growth of helices, posts, chevrons or screws.

Undergraduate students will utilize glancing angle deposition via electron beam evaporation to grow chiral nanostructures from metals (cobalt, aluminum). The growth will be optimized regarding shape, size and crystallinity by a variation of the particle flux angle of incidence, substrate rotation speed and substrate temperature. They will determine the structural characteristics by examining the structures with scanning electron microscopy and x-ray diffraction.

Human mucin MUC1 is a well-characterized biomarker for the diagnosis of various ductal adenocarcinomas such as pancreatic cancer. While various biosensing platforms have been developed for the detection of MUC1, a simple colorimetric biosensor has yet to be realized. Our proposed sensing mechanism is based on gold nanoparticles (GNP) aggregation, which causes color changes that are due to both electronic dipole-dipole coupling between neighboring particles and scattering. Dispersed GNPs having interparticle distances substantially greater than their average particle diameter appear red, whereas the color of the aggregates changes to purple as the interparticle distance drops below the average particle diameter. To date, GNP aggregation-based sensors have been demonstrated for the detection of DNA, proteins and ions. However, studies focused on the detection of MUC1 mucin have not been reported. Thus motivated, this project aims at detecting MUC1 mucin, utilizing an aptamer that specifically targets the underglycosylated variable tandem repeat (VTR) that is commonly present in cancer cells. Of note, each MUC1 mucin has 18 to over 100 VTRs, this unique property allows GNPs to aggregate extensively even at extremely low protein concentrations. Initial studies will utilize synthetic peptide targets with 3-5 repeats of the VTR, successful results from this study will be the first step towards the detection of MUC1 mucin in pancreatic cancer cell lysates.

Undergraduates on this project will (a) learn to synthesize aptamer-modified gold nanoparticles (week 1-3), (b) study the effect of target concentration on sensor behavior (week 4-6), and (c) investigate the effects of ionic strength and sample matrix on sensor performance (week 7-10). Through these studies, the student will receive training and exposure to basic optical techniques and knowledge in nanoparticles and biosensor design. The undergraduates will work closely with a graduate student or postdoctoral researcher in the Lai group. The student must keep and maintain a laboratory notebook, which will be examined regularly by the supervising graduate student or postdoctoral researcher. The student will also be required to participate in the weekly group meeting and submit a written report on their work at the end of the program.

One pulse from a high intensity pulsed laser can be used to directly prepare (without the use of photoresist) two dimensional arrays of dots and/or antidots, where the (anti) dots have different materials properties than the matrix. Rapid local heating at the interference maxima causes significant changes in the materials properties (e.g., the local magnetization of Fe/V films can be increased by a factor of two). The array properties (stripes, dots, antidots and their spacing) can be controlled through angles of incidence and polarizations of the beams.

Undergraduate students will use optical methods to split the 5 ns pulse from an Nd:YAG laser into two-to-four beams, which then interfere on a sample surface. They will study the magnetic properties of these arrays using a variety of experimental techniques, including magnetometers and magneto-optic methods.

These unique materials are the first ever two-dimensional ferroelectrics, formed layer-by-layer into ultrathin crystals ranging from 1 nm to over 1000 nm thick. They exhibit many of the classic properties of ferroelectricity, the electric analog of ferromagnetism. However, their behavior during switching, the reversal of the electric polarization caused by an external electric field, are very different from other ferroelectric materials. We intend to probe the underlying cause of the unique switching properties by studying the distribution and behavior of individual ferroelectric domains, regions of uniform polarization.

Undergraduate participants will probe the domain properties using our special technique of Scanning Pyroelectric Microscopy as part of a coordinated effort to understand the complex behavior of polarization switching in the two-dimensional ferroelectric films. The research group working on ferroelectric polymers consists of Professor Ducharme, distinguished visiting scholar Professor Vladimir Fridkin, a post-doc or two, several graduate students, and several undergraduate students. We collaborate closely with other research groups at UNL and around the world. Our group functions as a highly integrated unit, with each member making essential contributions to the study of these complex materials. The undergraduate students will be expected to work cooperatively with other members of the group and with collaborators, learning from other group members and offering their own results and insights from the laboratory work.

Progress in nanomagnetism is critically important for future technologies such as information processing and storage, medicine, and energy production and conservation. This project involves the study of new types of magnetic clusters, cluster-assembled materials, and multi-component or multi-phase nanostructures. The work builds upon our recent experimental advances in which a variety of novel metal and oxide clusters have been synthesized by physical and chemical methods.

Our cluster-synthesis capabilities enable us to investigate clusters of the 3d magnetic and core-shell structure transition metal (TM) elements and FeCo alloys with diameters as small as 1-3 nm. We will deposit core-shell structures of the form TM-X, where X = Au, C, SiO2, and also cluster-assembled structures TM:X, where the TM cluster is embedded in the co-deposited element X. This project will involve the REU students in fabrication of monodispersed elemental and compound clusters with cluster-beam techniques, and measurements of structure and magnetic properties by x-ray diffraction, electron microscopy, and magnetization.

Magnetic interactions between hard and soft magnetic phases in nanostructured two-phase composites result in permanent magnet materials with significantly enhanced magnetic properties. The development of novel nanostructures via eutectic phase transformations offers the potential to significantly increase the volume fraction of the soft magnetic phase, leading to higher energy products. The objective of this project is to develop microstructural selection maps for ternary Sm-Co-T alloys in the vicinity of the binary Sm-Co eutectic at 8 atomic percent Sm. With this information, alloys can be designed with high Co content with eutectic structures (Figure 2) that avoid formation of primary Co. The microstructural selection maps will be determined for both conventionally processed alloys and after rapid solidification. Rapid solidification processing effectively refines the scale of the soft magnetic phase to the nanostructural level necessary for effective exchange interactions between the hard and soft magnetic phases.

Undergraduate student projects will include determining the solidification microstructure in arc-melted ternary (and higher) alloys using optical and scanning electron microscopy, and phase analysis by x-ray diffractometry, and use this information to construct microstructural selection maps for various Sm-Co-T alloys. Selected compositions will then be rapidly solidified by melt spinning. The resulting ribbons will be characterized using x-ray diffractometry and magnetometry, while the microstructures will be investigated by transmission electron microscopy. Students will conduct all of the analysis except TEM.

This project encompasses the processes of growth, characterization, development and control of a new class of semiconductors based on icosahedral building blocks and epitomized by the semiconductor boron carbide. The University of Nebraska-Lincoln's process of plasma-enhanced chemical vapor deposition has successfully produced a semiconducting form of boron carbide. The object here is a detailed understanding of how growth parameters, structure and electronic properties are intertwined, a necessary objective in order to make use of this rather unique semiconductor. Advanced characterization tools and continual feedback will provide the rapid advances necessary to make headway in this intricate materials problem. From a technological standpoint, understanding and materials development will lead to a wide range of devices enabled by the unique properties of this semiconductor. Two of these, an all solid-state neutron detector and magnetic tunnel junctions using boron carbide as the barrier layer will be developed and tested in depth.

Nebraska boasts a strong program on heterostructures with unique magnetic and magnetotransport properties. The functionality of these nanometric spintronics devices is based on the electric control of the interface magnetization in exchange bias heterosystems using molecular beam epitaxy (MBE) growth of magnetoelectric/ferromagnetic exchange coupled thin films. A major goal is the realization of a spintronics prototype device. This challenging task must be broken down into several steps. An important step on the way toward a working spintronic multilayer device is the growth of pinhole free and epitaxial (111) oriented Cr2O3 thin films of a few nanometer thickness. Recently, our group succeeded in growing these films on an Al2O3 surface by evaporation of metallic Cr and simultaneous O2 inlet into the UHV chamber. In addition to the optimization of the magnetoelectric susceptibility and the antiferromagnetic ordering temperature of Cr2O3 thin films, it is paramount to improve the dielectric properties of the films for spintronic applications. The dielectric characterization can be done by four-point resistance measurements at temperatures between 20 and 470 K.

Undergraduate participants involved in this area will be introduced to the four-point measurement technique and determine the temperature-dependent resistance of the films. In addition, characterization of the magnetic properties of all Cr2O3 films grown by MBE is routinely done by, for example, atomic force microscopy. With the resulting data, the quality of the films from a magnetic and dielectric point of view can be determined. This characterization of each individual Cr2O3 film is an important step for further processing of the films. Additionally, participants will be able to study the impact of magnetoelectric annealing on the antiferromagnetic domain structure of the Cr2O3 films. Recent theoretical considerations predict an unperturbed surface magnetic moment when the films are in a single domain state. Magnetoelectric annealing allows the single domain state to be approached, and, hence, provides a mechanism to tune the surface moment of the film. Magnetoelectric annealing requires the simultaneous presence of electric and magnetic fields when cooling below the Néel temperature. Applying a magnetic field is easily achieved with our new magnet, which is designed to be compatible with the new cryostat. Applying electric fields requires an electrical contact on the films with the help of optically transparent electrodes. Making such contacts and performing magnetic and dielectric characterization after magnetoelectric annealing are well-defined but challenging tasks for an undergraduate student.

Residual stresses are of practical importance in bulk materials and coatings, which critically affects their mechanical integrity and reliability. In the recent years the method of nanoindentation has been effectively used to investigate the local stresses in metallic components of MEMS. With the increasing application of polymers in micro- and nano-mechanical systems it is expected that the unavoidable residual stresses have an enormous effect on their mechanical performance as well. However, unlike metals and alloys the mechanical performance of polymers is strongly affected by their viscoelastic properties. Therefore the present models and methods have to be adapted to the specifics of polymers.

The first task of the undergraduate student will be a construction of a 4-point bending-beam sample holder to be used in an existing high precision nano-mechanical scanning probe along the lines of the assemblies used for metals. With this apparatus the polymer blocks will be held under various defined stresses during the nano-indentation experiments. Afterwards, with the help of the mentor, the student will develop a testing routine of quasi-static as well as dynamic indentation experiments to investigate the time-dependent surface and subsurface responses of the polymers. With this project we expect at least one publication of high interest for nano-mechanical systems manufacturer.

Undergraduate students on this project will learn the fundamentals of scanning probe microscopes (SPM) including atomic force microscopes (AFM) and depth sensing indentation (DSI) instruments for nanoindentation. These techniques are essential tools used today for determining mechanical properties (storage modulus, loss modulus, hardness, etc.) of nanoscale materials. Quantitative measurements and imaging techniques will be emphasized. The students will work with a graduate student mentor on the equipment to perform training of each measurement mode until they are at a level sufficient to use the instrument alone. Then the student will be assigned a material system (e.g,. polymer composite, biomaterial, biological sample, etc.) that they will use as their sample for a small term project. The students will also learn about relevant contact mechanics associated with these probes so that they are aware of assumptions used in the instrumentation for extraction of mechanical properties.