2017 Symposium on Functional Nanomaterials: Emerging Nanomaterials and Nanotechnology: Low Dimensional Nanomaterials
Sponsored by: TMS Functional Materials Division, TMS: Nanomaterials Committee
Program Organizers: Jiyoung Kim, University of Texas; Stephen McDonnell, University of Virginia; Chang-Yong Nam, Brookhaven National Laboratory; V. U. Unnikrishnan, The University of Alabama; Nitin Chopra, The University of Alabama

Wednesday 2:00 PM
March 1, 2017
Room: Pacific 26
Location: Marriott Marquis Hotel

Session Chair: Nitin Chopra, University of Alabama; Jiyoung Kim, University of Texas at Dallas

2:00 PM  Invited
Ultrathin Organic-inorganic Hybrid Dielectric Engineering on 2D MoS2 Using Molecular Atomic Layer Deposition: Lanxia Cheng1; Jaebeom Lee1; Hui Zhu1; Arul Vigneswar Ravichandran1; Qiaoxiao Wang1; Zifan Che1; Antonio Lucero1; Moon Kim1; Robert Wallace1; Luigi Colombo2; Jiyoung Kim1; 1University of Texas Dallas; 2Texas Instruments
    Successful realization of 2D-based devices requires ultrathin and pinhole free dielectric films. With reactive ozone species, we deposited thin uniform Al2O3 by atomic layer deposition (ALD) and low-k organic and inorganic OTS-Al hybrid dielectric films on MoS2 by molecular ALD (MALD). In addition to the excellent film uniformity and conformity as revealed by AFM images, the interfacial chemical composition and lattice structure characterization using XPS, Raman, HR-TEM also show a undetectable interfacial oxidation states and lattice disorder to the MoS2 surface, owing to its enhanced surface hydrophilicity and better chemical stability towards ozone exposure. The electrical results of MoS2 devices suggest that these films have promising dielectric properties, such as low leakage current (~10-5 A/cm2) and minimal doping effects. Both ALD and MALD processes are common processes in the semiconductor industry, and their application to deposition of dielectric films on 2D materials can be easily scaled to a production environment.

2:30 PM  
Effect of Substrate-film Interface in Mid-IR Photothermal Response of PLD Grown MoS<2>: Ankur Goswami1; Soupitak Pal1; 1University of California Santa Barbara
    Mid-IR (7 to 8.2μm) photothermal response of molybdenum sulphide (MoS2) thin film (~20 layers) has been studied for potential application in uncooled bolometer. The present study involves the growth of MoS<2> films on crystalline (sapphire and silicon) and amorphous (Si/SiO<2> and Si/SiN) by pulsed laser deposition. We observe MoS<2> film grown on sapphire, similar hcp structure, develops layered structure with semi-coherent interface formation through subtle misfit dislocations. Layer growth morphology is disrupted by growth-twin formation when it grows on silicon (diamond cubic) due to the incoherent interface. Interface engineering of the MoS<2> film by employing different substrate selection leads to a remarkable change of ~ 5.2 % in the sensitivity value for the film grown on Si substrate, compared to film grown on other substrates.

2:50 PM  
Scanning Photocurrent Microscopy of Epitaxial Graphene Heterostructures: Bobby Barker1; Venkata Surya Chava1; MVS Chandrashekhar1; Andrew Greytak1; 1University of South Carolina
    Graphene layers grown epitaxially on SiC substrates are attractive for a variety of sensing and optoelectronic applications because the epitaxial graphene (EG) acts as a transparent, conductive, and chemically responsive layer that is mated to a wide-bandgap semiconductor with large breakdown voltage. Recent advances in control of epitaxial growth and doping of SiC epilayers have increased the range of electronic device architectures that are accessible with this system. Scanning photocurrent microscopy is an essential tool for measuring characteristic charge transport lengthscales and determining the influence of defect structures on performance in emerging epitaxial graphene-based optoelectronic devices. This talk will describe SPCM measurements on a recently-developed EG-SiC bipolar phototransistor with high responsivity toward ultraviolet radiation.

3:10 PM  
Microwave Imaging of Plasma Etched CVD Graphene Using Scanning Microwave Microscope: Kathleen Brockdorf1; Joshua Myers1; Zhonghang Ji1; Hong Huang1; Nick Engel1; Yan Zhuang1; 1Wright State University
    Graphene is an excellent candidate for radio-frequency (RF), microwave (MW), and terahertz (THz) applications. However, micro-processing induced defects have a significant impact on the devices’ performance at RF/MW/THz. Understanding the defects-electrical property correlation of graphene at RF/MW/THz becomes indispensable. This work presents a systematic characterization of micro-patterned graphene using a scanning microwave microscope (SMM). Conductivity mapping of single atomic layered graphene sheet has been recorded at various RF/MW frequencies with a spatial resolution of better than 30nm. By correlating the SMM image contrast recorded at half- and quarter- wavelength resonances, it turns out that the local electrical conductivity of the graphene is significantly reduced due to the micro-processing induced structural imperfection. The results are in very good agreement with Raman measurements. This work demonstrates for the first time that SMM is capable in detecting and examining defects and its impact on the electrical property of single layered graphene.

3:30 PM  
Carbon Nanotube Coated Conductors: Terry Holesinger1; 1Los Alamos National Laboratory
    The development of industrially-scalable processes for aligning very thick coatings of carbon nanotubes (CNTs) on a suitable wire former is a key step for multi-functional CNT composite coated conductors. Aligned CNT coatings up to 100 microns thick have been prepared by conventional solution coating and wire drawing. We have successfully produced wires that display some of the lowest reported resistivity values for CNT coatings. For our best result, an overall wire resistivity was measured to be 2.12 micro-Ohm-cm with a CNT coating resistivity of 5.5 micro-Ohm-cm. In terms of conductivity, the composite wire and CNT coating values were 46 and 18 MS/m, respectively. Electron microscopy has been extensively used to identify and eliminate current limiting defects. Prospects for scale-up and application development will be discussed.

3:50 PM Break

4:10 PM  
Highly Aligned Electronic-type Purified Semiconducting Carbon Nanotube Array Field Effect Transistors with Current Density That Exceeds Silicon and Gallium Arsenide: Gerald Brady1; Austin Way1; Yongho Joo1; Katherine Jinkins1; Harold Evensen2; Padma Gopalan1; Michael Arnold1; 1University of Wisconsin-Madison; 2University of Wisconsin-Platteville
    Aligned arrays of semiconducting carbon nanotubes (CNTs) promise to outperform conventional semiconductors in short-channel, aggressively scaled field effect transistors (FETs). However, constraints in CNT sorting, processing, alignment, and contacts have severely limited performance. Here, we report nearly ballistic CNT array FETs at a density of ~50 CNTs µm-1, created via exceptional electronic-type CNT sorting using polyfluorene derivatives, assembly and alignment via floating evaporative self-assembly, and post-deposition treatment to remove adsorbates. The on-state conductance reaches 0.46 of the quantum conductance per CNT, and the total conductance reaches 1.7 mS µm-1, which is 7x higher than previous state-of-the-art CNT FETs. The saturated on-state current density reaches 900 µA µm-1 and is similar to or exceeds that of Si and GaAs FETs, for the first time, when compared at equivalent length-scales. Gopalan and Arnold et al. Langmuir (2014); ACS Nano (2014); Submitted (2016).

4:30 PM  
Synthesis of Pd Nanoparticles on Graphene Oxide Supports by X-ray Irradiation: Dustin Clifford1; Jessika Rojas1; Carlos Castano1; 1Virginia Commonwealth University
    A novel synthetic approach for generating Pd nanoparticles onto graphene oxide (GrO) supports has been performed that relies on benign and cost effective solvents and replaces thermal input and harsh reductants for X-ray irradiation (> 4 kW). The cubic Pd phase was confirmed by XRD and SAED with absence of PdO and PdO2. Precursor solutions containing Pd2+/GrO (aq.) were irradiated by X-rays for 2 and 3 hours producing Pd nanoparticles possessing average diameters below 10 nm. The monodisperse Pd nanoparticles on GrO supports have functionality toward catalysis such as coupling reactions performed via flow chemistry. Detailed characterization including XPS, XRD and SAED and catalytic properties of the supported Pd nanoparticle system will be discussed along with the “clean chemistry” benefits of using X-ray synthesis.

4:50 PM  
Synthesis and Interface Boundary Characteristics of Gold/Cobalt Janus Nanoparticles: Kyungah Seo1; Olivia Graeve1; 1University of California, San Diego
    Janus particles are well known to have unique physical/chemical properties and directionality within a single particle because of their asymmetry. In particular, magnetic Janus particles are very promising for reliable control of particle rotation and directional movement using external magnetic fields. In this study, plasmonic/magnetic (Au/Co) bimetallic Janus nanoparticles were prepared to determine the effect of surface stability and atomic diffusion on the interface between gold and cobalt. The particles were synthesized by growing Co over the pre-synthesized Au seeds via thermal decomposition of Co2(CO)8. The particles were prepared in several different solutions of varying polarity, including 1-octadecene, diphenyl ether, and benzyl ether, and using various amounts of surfactant/reducing agents to study the effect of cobalt growth on the gold seeds. Transmission electron microscopy, X-ray diffraction, and dynamic light scattering were performed to characterize the sizes, shapes, and morphologies of the synthesized particles.

5:10 PM  
On Effects of Geometric Nonlinearity and Mechanical Anisotropy in Strain-engineered Helical Nanoribbons: Zi Chen1; Shicheng Huang1; Ian Trase1; Lina Zhang1; Nan Hu1; 1Dartmouth College
    Fabrication and synthesis of helical nanoribbons have received increasing attention because of the broad applications of helical nanostructures in nano-elecromechanical/micro-electromechanical systems (NEMS/MEMS), sensors, active materials, drug delivery, etc. In this paper, we study the mechanical principles used in designing strained helical nanoribbons, and propose the use of a full threedimensional finite element method to simulate the coexistence of both left- and right-handed segments in the same strained nanoribbon that mimics the shape of plant tendrils. We also design tabletop demonstrations to showcase how the pre-programed distribution of mismatch strains can result in helical ribbons that have different chiralities, helix angle, and radius in the same ribbon. This work can both help understand the large deformation behaviours of such nanostructures and assist in the design of helical nanostructures for engineering applications.

5:30 PM  
Electrochemical Actuation of Dealloyed Bulk Nanoporous Nickel: Chuan Cheng1; Jörg Weissmüller2; 1Technische Universität Hamburg-Harburg ; 2Technische Universität Hamburg-Harburg
    Electrodes composed of nanoporous structured metals can exhibit reversible dimension change during cyclic potential triggering, due to the surface charge induced strain. An example was nanoporous platinum [1]. Our recent research in nanoporous nickel foils indicated nickel was a promising candidate as electrochemical actuators due to the low-cost and high pseudocapacitance for surface charge storage [2,3]. Other than foils whose thicknesses were restricted by template-based synthesis method, in this presentation, bulk nanoporous nickel with mm-scale in each dimension has been synthesized by dealloying of Ni-Mn alloy. Reversible and sustainable strain up to 1% was found. This work brings a step forward for commercializing metallic-based electrochemical actuators. [1] J. Weissmüller, R. N. Viswanath, D. Kramer, P. Zimmer, R. Würschum, H. Gleiter, Science 2003, 300, 312. [2] C. Cheng, A. H. W. Ngan, ACS Nano 2015, 9, 3984. [3] C. Cheng, J. Weissmüller, A. H. W. Ngan, Adv. Mater. 2016, 10.1002/adma.201600286.