Papers

ICMCTF2008 Session H1-1: Nanotube, Nanowire and Nanoparticle Thin-Films and Coatings

Wednesday, April 30, 2008 8:00 AM in Room Terrace Pavilion

Wednesday Morning

Start	Invited?	Item
8:00 AM		H1-1-1 Preparation and Properties of Muti-Component Nanocrystal Thin Films: Building With Artificial Atoms C.B. Murray (University of Pennsylvania) The synthesis of colloidal nanocrystals (NCs) with controlled crystal shape, structure and surface passivation provides ideal building blocks for the assembly of new thin films and devices. The NCs are "artificials atoms" with tunable electronic, magnetic, and optical properties. This talk will briefly outline some of the current "best practices" in preparation, isolation and characterization of semiconducting quantum dots and magnetic NCs. I will next discuss the organization of monodisperse NCs in to single component superlattices that retain and enhance many of the desirable mesoscopic properties of individual NCs. We will then explore how these novel building blocks can be integrated in to a range of electronic, magnetic and optical devices. The potential to design new materials and devices expands dramatically with the creation binary NC superlattices BNSLs. I will show how we synthesized differently sized PbS, PbSe, CoPt₃, Fe₂O₃, Au, Ag and Pd nanocrystals and then these nanoscale building blocks into a rich array of multi-functional nanocomposites (metamaterials). We have also identified a novel method to direct superlattice formation by control of nanoparticle charging. Although modular nano-assembly approach has already been extended to a wide range of NC systems, we are confident that we have produced only a tiny fraction of the materials that will soon accessible. Devices based on these new multi-component nanoscale assemblies will be discussed along with some new research directions that focus on emergent physical phenomena in the NC assemblies.
8:40 AM		H1-1-3 Matrix Assisted Pulsed Laser Evaporation (MAPLE) for Deposition of Carbon Nanopearls C.N. Hunter (Air Force Research Laboratory); M.H. Check (SOCHE); J. Hu (University of Dayton Research Institute); A.A. Voevodin (Air Force Research Laboratory) Matrix Assisted Pulsed Laser Evaporation (MAPLE) is a thin film deposition technique that can be applied to a wide range of polymeric and biological materials to produce multifunctional nano-composite coatings for several applications, including wear protection, sensor devices, and field emission cathodes. The key feature of the technique is in preparing dispersed nanostructured material liquid solutions, which are cryogenically solidified to produce a laser ablation target for nanostructured material incorporation in the hybrid plasma thin film deposition. The advantage of using MAPLE compared to other laser techniques is that deposition can be accomplished with little or no damage to the transported nanostructured material. The technology was explored for deposition of carbon nanopearls (approximately 150 nm in size) encapsulated in magnetron-sputtered metal (Au) and ceramic (TiN) matrices. The focus was placed on understanding how to control transport and uniformity of nanopearls on the deposition surface. The controlling parameters included laser fluence, repetition rate, solvent material, and background gas composition and pressure. The characteristics of the synthesized carbon/metal and carbon/ceramic composite films were correlated with area fraction of the nanoparticles, degree of dispersion of the nanoparticles and effect of the transport process on the properties of the nanoparticles. Results from electron microscopy, optical profilometry, XRD, Raman spectroscopy, and XPS are discussed.
9:00 AM		H1-1-4 Nanostructures by Glancing Angle Deposition C.M. Zhou (Rensselaer Polytechnic Institute); S.V. Kesapragada (Novellus System Inc.); D. Gall (Rensselaer Polytechnic Institute) The growth dynamics during glancing angle deposition was investigated using periodic Ta nanopillar arrays on patterned substrates. Both the pattern size (100 to 500 nm) and the growth temperature (30 to 900 °C) were varied to study the effect of surface diffusion on the morphological evolution. The former exhibits a direct scaling, indicating that the overall nanopillar morphologies are controlled by geometric shadowing. However, increased adatom diffusion length causes an exacerbated competitive growth mode and, in turn, the breakdown of the regular array morphology. We develop a novel process for the formation of Y-shaped nanorods by exploiting the combination of atomic shadowing effects during GLAD and the spontaneous twinning in fcc metals. <110> oriented Cu nanorods self-organize into branched Y-structures due to stacking fault formation on two oppositely tilted 111-facets, followed by a growth suppression at the developing grain boundary. GLAD has also been extended to fabricate Ta/Si two component nanostructures. By manipulating the sequence of the deposition, that is, by sequential or simultaneous deposition from two sources, complex nanostructures are formed where the two components are stacked vertically, laterally, or in a checker board arrangement. SEM, back scattered imaging, and TEM provide clear compositional and microstructural contrast and show sharp (< 20 nm) vertical and horizontal interfaces. The use of GLAD nanostructures as pressure sensors is demonstrated using arrays of 50-nm-wide Cr zigzag nanosprings and nanorods which exhibit a reversible resistivity change upon loading and unloading.
9:20 AM		H1-1-5 Influence of Effective Activation Energies on CVD Growth of Carbon Nanotubes M.J. Bronikowski (Jet Propulsion Laboratory) Growth of carbon nanotubes (CNTs) by metal-catalyzed thermal chemical vapor deposition (CVD) upon flat silicon substrates is studied as a function of growth temperature. It is found that the CNT growth rate at a given temperature is constant for a certain amount of growth time, after which growth ceases; the product of the growth rate and the growth time gives the ultimate length of the CNTs. Both the growth rate and the growth time are found to depend on the CVD temperature, and this dependence is such that the ultimate CNT length increases as temperature decreases, i.e., longer CNTs can be grown at lower temperatures than at higher temperatures. This surprising and counter-intuitive result reflects the interaction of competing factors affecting the CNT growth: the rate at which carbon is incorporated into growing CNTs vs the rate at which catalytic metal particles become inactive. Both of these rates are found to have an Arrhenius form of temperature dependence, with activation energies of 2.0 and 3.4 eV, respectively, when an Al₂O₃ diffusion barrier layer is used. These energies are interpreted as "effective" activation barriers arising from activation energy contributions from multiple chemical processes. CNT bundles as long as one millimeter have been grown at a temperature of 600°C.
10:00 AM		H1-1-8 Pulsed Laser Deposition of Nanostructured Double Perovskite Magnetic Thin Films and Multilayers Unknown Deepak (Indian Institute of Technology, Roorkee, India); D. Kaur (Indian Institute of Technology, Roorkee, India) Half metallic ferromagnetic oxides with double perovskite structure show a variety of peculiar magnetic and magneto transport properties for spintronics applications. Double perovskites Sr₂FeMoO₆ and Sr₂FeReO₆ have been known as prospective magnetoresistance compounds, which show an appreciable intrinsic tunneling-type magnetoesistance (TMR) at room temperature. The present research is focused on the synthesis and characterization of nanocrystalline thin films and multilayers of Sr₂FeMoO₆ and Sr₂FeWO₆ compounds on LaAlO₃ substrate by pulsed laser deposition technique. The films are nearly epitaxial with predominant a axis orientation. Field Emission Scanning Electron Microscope (FE-SEM) and Atomic Force Microscope (AFM) studies reflects the uniform grain growth with average grain size of 25nm.and with surface roughness of approx. 2-3nm. Magnetization measurements at temperature of 5K shows that Sr₂FeMO₆ is a ferromagnetic and Sr₂FeWO₆ is antiferromagnetic with marked difference in their magnetic moment. The composite films of Sr₂FeMo_xW_1-xO₆ with 0≤x≤1 are fabricated and the influence of varying concentration of x on magnetic properties has been investigated. Further the effect of film thickness on magnetic properties of multilayers has also been investigated.
10:20 AM		H1-1-9 Vertically Aligned Carbon Nanotube Scaffolding for High Aspect Ratio Microelectromechanical Systems D.N. Hutchison, B. Turner, K. Barnett, R.C. Davis (Brigham Young University); R. Vanfleet (BrighamYoung University) We present a novel method to make high aspect ratio structures in a variety of materials by growing patterned vertically-aligned carbon nanotubes (VACNTs) and then filling the space between tubes with various materials by chemical vapor deposition (CVD). The nanotubes are grown from a lithographically patterned 2nm Fe catalyst film. This substrate is heated to 750°C in a tube furnace flowing hydrogen and ethylene, causing multiwalled carbon nanotubes to grow together vertically upward from the surface from the patterned Fe film, at controllable rates of over 100µm/min. It is possible to grow structures up to 1mm tall with vertical sidewalls and feature size of a few microns. Next, this structure can be easily filled in with amorphous carbon by heating to 950°C in ethylene alone, or other materials like Si or metals can be deposited by low-pressure CVD. Even nanotubes deep inside the forest are found to be uniformly coated with the "filler" material. Since the CNTs serve only as scaffolding and constitute a small volume fraction of the structure, the final product mostly consists of this filler material, and the properties of the final product have been found to be similar to a structure made purely out of the filler material. Deep Reactive Ion Etching is usually used to make high aspect ratio structures in Si, but our CNT scaffolding approach is generalizable to other materials and seems faster, cheaper, simpler, and more scalable. To demonstrate the usefulness and flexibility of this approach, we have made a variety of high aspect ratio structures including high-temperature TEM grids (allowing the sample they hold to be annealed) and a simple MEMS mechanism.}
10:40 AM		H1-1-10 Formation of SiC Nanoparticle Using Thermal Annealing of Two Layer C/Si Films on Si Substrate C.K. Chung, C.W. Lai, C.C. Peng, B.H. Wu (National Cheng Kung University, Taiwan) Ion beam sputtering (IBS) system under ultra high vacuum (UHV) was utilized to deposit 2-layer C/Si thin films. Carbon layer thickness was fixed at 100nm and amorphous silicon (a-Si) ranged from 5 nm to 50 nm. Rapid thermal annealing was performed to investigate the formation of SiC nanoparticles (np-SiC) at 600~900°C for 0.5 min. The np-SiC were formed on specific C/Si films at 900 °C and there was no np-SiC appeared at 600°C, 750°C. The decrease of a-Si thickness in C/a-Si structure is favorable for generation of np-SiC at elevated temperature at 900°C. The np-SiC in C/Si thin film were examined by field emission scanning electron microscope (FESEM) for particle characterization, grazing incidence X-ray diffractometer (GIXRD) for phase identification and auger electron spectroscopy (AES) depth profile for the interdiffusion and reaction behavior.
11:00 AM		H1-1-11 Formation and Cathodoluminescence of Single Crystalline Al:ZnO Nanoscrews Synthesized by Thermal Evaporation Y.-H. Lin, C.-C. Lin (National Tsing Hua University, Taiwan); J.-M. Wu (Feng-Chia University, Taiwan); U.-S. Chen, J.-R. Chen (National Tsing Hua University, Taiwan); H.C. Shih (Chinese Culture University, Taiwan) Recently, ZnO is one of the most promising materials for optoelectronic devices due to its wide direct band gap of 3.37 eV and large exciton binding energy of 60 meV at room temperature. In order to replace the most conventional transparent conductive material, indium-tin oxide (ITO), doping Al into ZnO films to form Al:ZnO (AZO) films is a feasible way¹. But the Al:ZnO nanostructures were less discussed on previous references^2,3. This is because that it is still a challenge to dope Al into ZnO nanostructures and avoid the Al sources being oxidized. In this work, the aluminum-doped zinc oxide (Al:ZnO, AZO) nanoscrews were synthesized on the Al powder spread silicon substrates at 500°C through the thermal evaporation by a chemical vapor deposition process. The TEM results show that both the Al:ZnO nanscrews are oriented in the [0001] direction with single crystalline structure. Furthermore, from the cathodoluminescence (CL) spectrum, it reveals that the Al:ZnO nanoscrews exhibit strong luminescence at 380 nm, 490 nm and 764 nm, respectively. ¹M. Chen, Z.L. Pei, X. Wang, C. Sun, L.S. Wen, J. Vac. Sci. Technol. A 19 (2001)963. ²R.C. Wang, C.P. Liu, J.L. Huang, S.J. Chen, Appl. Phys. Lett. 88 (2006) 23111. ³C.L. Hsu, S.J. Chang, H.C. Hung, Y.R. Lin, C.J. Huang, Y.K. Tseng, I.C. Chen, J. Electrochem. Soc. 152 (2005) 378. .