Controlled Synthesis, Processing, and Applications of Structural and Functional Nanomaterials: Metal and Seminconductor Nanostructures
Program Organizers: Haitao Zhang, University of North Carolina at Charlotte; Gurpreet Singh, Kansas State University; Kathy Lu, Virginia Tech; Edward Gorzkowski, Naval Research Laboratory ; Jian Shi, Rensselaer Polytechnic Institute; Kejie Zhao, Purdue University ; Michael Naguib, Tulane University

Monday 2:00 PM
September 30, 2019
Room: C123
Location: Oregon Convention Center

Session Chair: Jian Shi, Rensselaer Polytechnic Institute; Haitao Zhang, University of North Carolina at Charlotte

2:00 PM  Invited
Synthesis and Processing of Quantum Dots for Improved Photoluminescence Quantum Yields: Greg Herman1; 1Oregon State University
    Copper indium diselenide (CIS) is a promising cadmium- or lead-free material for quantum dots. We have recently demonstrated that integrated microwave-based continuous flow methods provide an inexpensive route for the production of uniform quantum dots, including CIS. We will discuss the approach and optimization of the process to obtain high quality CIS quantum dots. An issue that remains is that improvements in CIS photoluminescence is necessary for wide range adaptation in consumer products. We will discuss CIS post-treatment using organic super acids. We have found that passivating the CIS cores with the nonoxidizing organic superacid, bis(trifluoromethane) sulfominide (TFSI) significantly enhanced photoluminescence quantum yields (PLQY). Improvements in PLQY remain even after growth of a zinc sulfide shell. We will discuss characterization of the CIS quantum dots and the reasons for the observed improvement PLQY.

2:30 PM  Invited
Assembly and Integration of Multisegment Nanowires for Electronics and Sensor Applications: Zhiyong Gu1; 1University of Massachusetts Lowell
    Nanowires have been explored for many potential applications, including nanoelectronics, nanophotonics, sensors/biosensors, energy conversion and storage, and nanomedicine. While processing them, assembly and integration of individual nanowire components into functional electronics or devices remain critical steps. A variety of methods have been studied for the assembly of nanowires, such as molecular interactions (e.g., surface tension, hydrophobic force, electrostatic force), molecular linkers (e.g., antibody-antigen), or external forces (e.g., electrical, magnetic, or dielectrophoretic force). In this presentation, I will discuss several fundamental issues in the assembly and integration of multisegmented nanowires into functional electronics or systems. First, I will review several techniques on how to effectively assemble and integrate nanowires. Then, I will discuss the oxidation effect and how to mitigate or solve this problem. Finally, I will show nano-joint formation and large-scale nanowire assembly and soldering, including atomic diffusion, intermetallic formation, and void formation.

3:00 PM  Cancelled
A Novel Synthesis Method for Independent Control of Grain Size, Dispersion and Phase Composition of Thin Films: Paul Rasmussen1; Rohit Sarkar1; Jagannathan Rajagopalan1; 1Arizona State University
    Controlling the micro/nanostructure of thin films is essential to tailoring their mechanical properties. Here, we describe a new process to synthesize thin films with exceptional microstructural control via systematic, in-situ deposition of crystalline seeds into amorphous precursor films. When the amorphous films are subsequently crystallized by annealing, the seeds act as preferential nucleation sites and enables independent control of the grain size, dispersion and spatial distribution. Moreover, by appropriately choosing the seed element, the phase composition of the films can also be systematically varied. We demonstrate the viability of this method by synthesizing NiTi films with highly controlled microstructures composed of pure austenite or pure martensite phase using Cr and Ti seeds, respectively. In addition to controlling the microstructure and phase composition, this method also facilitates crystallization at lower temperatures, which can potentially reduce precipitate formation and, thus, enhance the mechanical properties of NiTi films.

3:20 PM Break

3:40 PM  Cancelled
Synthesis of Metallic Films with Precisely Tailored Multimodal Architectures: Rohit Berlia1; Jagannathan Rajagopalan1; 1Arizona State University
    Materials with heterogeneous microstructures have been shown to exhibit a superior combination of strength and toughness compared to homogeneous nanostructured or coarse-grained materials. However, only limited progress has been made in controlling the microstructure of such materials. Here we report a novel technique to synthesize metallic films with highly tailored multimodal microstructures using magnetron sputtering. This technique enabled us to precisely control the volume fraction, spatial arrangement and connectivity of the two sets of grains. Using this technique, we synthesized bimodal films of pure elements like Copper, Aluminum and Iron where the mean size of smaller grains is around 40-250 nm while larger grains have mean sizes exceeding 5 Ám. The microstructure of these films was characterized by a combination of XRD, EBSD and TEM to reveal the grain size dispersion, texture and orientation distribution. Mechanical properties were also measured using custom made MEMS tensile testing stage.

4:00 PM  
Phase-field Modeling of Self-organization in Physical Vapor-deposited Alloy Films with Coherent Elastic Misfit: Rahul Raghavan1; Kumar Ankit1; 1School for Engineering of Matter, Transport and Energy, Arizona State University
    Elastic interactions arising from a difference of lattice spacing between two coherent phases have a strong influence on the phase separation behavior of alloys. It is known that these elastic interactions may accelerate, slow down or even stop the phase separation process. However, our understanding of the role of misfit strains in modulating the phase-separated morphologies in vapor deposited films is currently limited. Here, we develop a phase-field model which incorporates the multiphysics of interface capillarity and coherency strains to computationally simulate the nanostructural evolution in vapor deposited films. We analyze the influence of lattice mismatch, deposition rate, and temperature on the film morphology. Insights gained from our computations will demonstrate the model's viability in predicting experimentally observed morphologies and supplement our understanding of the competing nature of phase separation and lattice strains.

4:20 PM  Cancelled
In-situ Synthesis of CdS Nanowire Photosensor for Chemiluminescent Immunoassays: Jae-Chul Pyun1; 1Yonsei University
    A hypersensitive CdS nanowire (NW) photosensor was fabricated by an in-situ synthesis process that involved the direct synthesis of CdS NWs on an interdigitated electrode (IDE). Analysis of the photoresponse properties showed that the newly synthesized photosensor had enhanced sensitivity and a highly reproducible photoresponse compared to photosensors prepared from CdS NW suspensions. The NW photosensor was applied to measure the chemiluminescence of luminol, and the sensitivity was compared to a commercial photosensing system. Finally, the feasibility of the CdS NW photosensor for the application to the medical diagnosis of the human hepatitis B surface antigen (hHBsAg) was demonstrated using a lateral-flow immunoassay with a chemiluminescent signal band.

4:50 PM  
Boron Nitride Nanotubes with High Purity for Thermal Management: Mahmoud Amin1; David Kranbuehl1; Hannes Schniepp1; 1The College of William & Mary
    Boron nitride nanotubes (BNNTs) feature outstanding thermal conductivity and are, therefore, an excellent candidate for thermal interface materials (TIM). Since BNNTs are also electrically insulating, they are especially suitable for TIM applications in microelectronics. We have recently developed the first method to completely remove h-BN impurities from BNNTs without doing damage to the tubes, which we demonstrate using characterization techniques based on X-ray diffraction and Raman spectroscopy. Furthermore, our procedure has an extremely high yield, virtually not losing any material. Using our purified, high-quality BNNTs we make polymer nanocomposites with significantly enhanced thermal conductivity and mechanical performance. We developed several processing methods for BNNT/polymer nanocomposites and found that they have a dramatic impact on the observed thermal and structural properties.

5:10 PM  
Synthesis of PbSe Colloidal Quantum Dots Using a Batch Microwave Reactor: Tyler Mccrea1; Stebby John1; Derek Dardzinski1; Erik Wislinsky1; Joseph Bergevin1; Haori Yang1; Gregory Herman1; 1Oregon State University
    PbSe quantum dots (QDs) have been shown to exhibit tunable electronic properties if the diameter is kept below the material’s Bohr radius of 46 nm. Controlling the QD size using synthetic parameters provides a means to tune the electronic and optical properties, and allows further control over impact ionization and carrier multiplication within electronic devices. Our research focuses on the synthesis and characterization of PbSe QDs using a batch microwave reactor. We have used high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, UV-Vis-NIR spectroscopy, and X-ray diffraction to characterize the synthesized PbSe QDs. In this paper, we provide details on our unique synthetic approach for PbSe QDs and how we can precisely control the particle size and their size distributions.