ICMCTF2013 Session F1-1: Nanomaterials, Nanofabrication, and Diagnostics

Tuesday, April 30, 2013 2:10 PM in Room Sunrise

Tuesday Afternoon

Time Period TuA Sessions | Abstract Timeline | Topic F Sessions | Time Periods | Topics | ICMCTF2013 Schedule

Start Invited? Item
2:10 PM F1-1-1 The influence of Reaction Temperature and Volume of Oleic Acid to Synthesize SnS Nano Crystals by using Thermal Decomposition Method
BettyYan-Jin Liang (National Cheng Kung University, Taiwan, Republic of China); Sheng-Chang Wang (Southern Taiwan University of Science and Technology, Taiwan); Yu-Min Shen, Jow-Lay Huang (National Cheng Kung University, Taiwan, Republic of China)
We report synthesis of SnS nano crystals and their size variation with the reaction temperature, and volume of the oleic acid (OA) solvent. These nano crystals were synthesized by using a tin precursor, Sn(OA)x prepared by tin oxide (SnO) with different moles of oleic acid, and mixture of sulfur and oleylamine (OLA) were injected into the solution at different temperatures under argon atmosphere. The SnS nano crystals show orthorhombic crystal structure, and the average particle size is increased from 20 nm to 50 nm and lastly to 200 nm with the increase in temperature from 150 °C to 180 °C and to 210 °C. Careful observations indicate a gradual change in the shape of these nano crystals from spherical to sheet like structure with the increase of oleic acid volume (2 – 5 mmol). The tin sulfide (SnS) films will then grew by spin-coating method and subsequently the film will be applied as an absorber for solar cells in future work. The as-prepared SnS samples and films will be characterized using XRD, SEM and TEM to investigate the structure, phase composition, surface morphology and microstructure. The optical properties of SnS films will be studied by using UV-visible spectroscopy.
2:50 PM F1-1-3 Nanoparticle Synthesis via Laser-induced Plasma in Liquid Environment
Tsuyohito Ito (Osaka University, Japan)

The tremendous interest in various nanostructures is stimulated by the multifunctional characteristics of such materials and the possibility to tune their properties controlling the size, morphology, chemical and phase composition, and surface states. Laser ablation in liquid (LAL) has attracted a lot of attention as one of synthetic techniques to prepare new attractive nanomaterials, with the ability to control both product chemistry and morphology in many systems. Recently, a number of novel nanostructures prepared via this approach have been reported, with diverse chemistries and morphologies. Here, we expand the technique, which was normally limited to the ambient pressure (1 atm), to higher (up to subcritical or even supercritical) pressures, in order to study the effect of pressure and prepare novel nanomaterials with unique properties.

The ablated target and liquid medium used in this study were Zn plates and deionized water, respectively. A nanosecond Nd:YAG laser with the wavelength of 532 nm was applied to irradiate Zn targets placed in a high-pressure cell with the inner volume of approximately 20 ml. The repetition pulse rate was 10 Hz, and the laser power was approximately 30 mJ/pulse. No heating, except for locally induced by laser pulses in pressurized water, was applied, while the pressure was varied from 0.1 MPa (1 atm) to ~30 MPa.

X-ray diffraction (XRD) measurements indicated that the resulted nanoparticles were ZnO. Their average size was approximately 10-20 nm depending on medium pressure, which was confirmed by both transmission electron microscopy observations and XRD measurements. The nanoparticles prepared at higher pressures demonstrated smaller sizes and more homogeneous size distribution. Photoluminescence spectroscopy was performed by using a 266-nm pulsed laser as the excitation source. All collected spectra exhibited a relatively sharp emission peak in the UV range and a broad emission band at ~570 nm. With the increase of medium pressure, the position of the former was shifting to narrower wavelengths (higher energies), while the relative intensity of the latter (at ~570 nm) was gradually increasing. Interestingly, a discontinuity in the visible emission enhancement of the product was observed near ~22 MPa, which is believed to be associated with the critical pressure of water (22.1 MPa).

More details on the Zn ablation, as well as the use of other targets/media, will be presented at the conference.
3:30 PM F1-1-5 Bonding of Metallic Nanoparticles
Michael Chandross, Timothy Boyle, Blythe Clark, Ping Lu (Sandia National Laboratories, US)

In order to create novel nanosolders that bond at lower processing temperatures, it is important to understand the fundamentals of bonding between metallic nanoprticles. Next generation solders can potentially avoid issues with processing, reliability and manufacturing that plague conventional solders. We present the results of large scale molecular dynamics simulations aimed at revealing the mechanisms responsible for reactions at nanoscale metallic interfaces. Specifically, we study the bonding of Ag/Ag and Ag/Cu nanoparticles of varying radii at a range of temperatures. The specifics of the bonding process and the stable final states, both above and below the bulk eutectic temperature, will be compared to high resolution experiments conducted with an aberation correct STEM.

3:50 PM F1-1-6 The Preparation of FeS2 Pyrite Nanocrystal Inks for Photovoltaic Thin Film
Su-Ching Hsiao, Kuo-Wei Wu, Sheng-Hsin Huang, Shih-Hsiang Chiu, Lih-Hsin Chou (National Tsing Hua University, Taiwan, Republic of China)
Semiconductor nanocrystals (NCs) are promising building blocks for next generation photovoltaic devices. FeS2 (pyrite) NCs have been considered as a superior semiconducting material for solar energy conversion and photoelectrochemical applications since it possesses an appropriate band gap of ~1 eV and a very high absorption coefficient (α = 5x105 cm-1). These characteristics coupled with the low cost, environmental compatibility, and abundant elements in the crust make pyrite to be a potential candidate for solar cell absorption layer materials in the form of ultrathin films (< 100 nm). NCs coating technique, which requires a well-dispersed NC ink, is simple and low-cost compared with the traditional vacuum processes for depositing pyrite thin films. However, as the surface energy of NCs is significantly higher than that of larger particles, NCs will tend to agglomerate and disable the formation of continuous, smooth ultrathin films.

In this report, well-dispersed, stable pyrite NC inks were successfully produced by beads-milling technique and smooth pyrite thin films less than 50 nm were produced by coating the dispersed pyrite NC inks on various substrates. Such a work has not been reported up to date and will be interesting to the field.

Initially, 50 μm zirconia beads and a surfactant in a solvent were utilized for grinding and dispersing the pyrite NC clusters comprising pyrite NCs with sizes of 10 to 20 nm. The dynamic light scattering (DLS) was used to measure particle size distributions over time during the milling process. The NCs’ size, shape, and dispersive condition after beads milling were observed by transmission electron microscopy (TEM). X-ray diffractometer (XRD) was employed both before and after beads milling process to check any structure and crystallinity changes of pyrite NCs.

Pyrite thin films less than 50 nm were then spin-coated using the well-dispersed NCs inks. In order to obtain high quality pyrite thin films, post annealing treatment at 400 °C were conducted. The grazing incidence XRD (GIXRD) patterns were applied to show the intensity and FWHM of pyrite peaks. The Hall measurements revealed the semiconducting character of the thin films. The photoelectron emission and Tauc plot will be utilized to determine the band diagram of pyrite thin films.

4:10 PM F1-1-7 Morphological and Optical Properties of AlN Nano-islands Prepared by Plasma Enhanced Chemical Vapor Deposition
Zakaria Bouchkour (Université de Limoges - CNRS, France); Elsa Thune (ENSCI-CNRS, France); Cedric Jaoul, Jean-Christophe Orlianges (Université de Limoges - CNRS, France); René Guinebretière (ENSCI-CNRS, France); Pascal Tristant, Christelle Dublanche-Tixier (Université de Limoges - CNRS, France)

With a band gap of 6.1 eV [1], AlN appears to be an ideal material for the development of deep ultraviolet, vacuum UV, and extreme detectors [2] The 6.1 eV band gap permits the visible background to be intrinsically suppressed and the detectors to operate at room temperature. Results of a LED based on aluminium nitride with an emission wavelength of 210 nm (which is the shortest ever reported) have been recently published [3]. The estimated efficiency of this AlN LED is still lower than for commercial LED but it could be greatly improved by the introduction of carrier confinement structure such as quantum dots. With quantum dots, restrictions due to material properties are shifted or lifted [4] and thus AlN nanostructures could be used successfully in the applications previously mentioned.

In this work, ultrathin AlN films were grown by plasma enhanced chemical vapor deposition (PECVD). The precursors used were nitrogen (N2) as plasma source and nitride precursor and trimethylaluminium (TMA) as aluminium precursor diluted in Ar. A particular attention has been paid to control the deposition time using a shutter above the substrate holder. The surface morphology of the films has been observed by AFM (Atomic force microscopy) in tapping mode under ambient atmosphere at room temperature, in order to characterize the size and surface density of nano-islands on the surface. To verify the crystalline development and preferential orientations relative to the substrate, X-ray diffraction measurements are performed. Spectroscopic ellipsometry (SE) measurements were used to determine the optical properties of the samples and to extract the optical band-gap energy (Eg).

The presence of the shutter greatly improved both cristallinity and chemical composition of the films. Deposition at different time allowed proposing a growth mechanism with a favorable time range to obtain isolated nano-islands. The evolution of Eg versus the deposition time showed that the quantum confinement theory was followed.

[1] J. Li, K.B. Nam, M.L. Nakarmi, J.Y. Lin, H.X. Jiang P. Carrier, S.-H. Wei, Appl. Phys. Lett. 83, 5163 (2003)

[2] J. Lia, Z.Y. Fan, R. Dahal, M.L Nakarmi, J.Y. Lin, H.X. Jiangb, App. Phys. Letters 89, 213510 (2006)

[3] Y. Taniyasu, M. Kasu, T. Makimoto, Nature 441 (7091), 325 (2006)

[4] J. Stangl, V. Holy, G. Bauer, Rev. Mod. Phys. 76, 725 (2004)

4:30 PM F1-1-8 Effect of Indium Concentration on Luminescence and Electrical Property of Indium Doped ZnO Nanowires
Sin-Yee Lim (National Cheng Kung University, Taiwan, Republic of China); Ruey-Chi Wang (National University of Kaohsiung, Taiwan); Chuan-Pu Liu, Sanjaya Brahma, Jow-Lay Huang (National Cheng Kung University, Taiwan, Republic of China)

Indium-doped ZnO nanostructures are regarded as promising candidates for transparent conductors, gas sensors, and photodetectors due to their good physical properties. In this work, we report the structure, microstructure, luminescence and electrical property of ZnO nanowires doped with indium (In) and, effect of In concentration on these properties. Indium doped ZnO nanowires have been grown on Si substrate by Chemical Vapor Deposition (CVD) method, at relatively low temperature (550 °C). A thin ZnO layer with (0002) preferred orientation was deposited on the Si substrate as seed layer by sputtering, which facilitates the growth of well-aligned ZnO nanowires. The average diameter and length of these nanowires varies from 50-180 nm and 10-15 μm, respectively. These nanowires are single crystals having (0001) growth direction. Series of experiments were carried out to estimate the possible solubility of In in ZnO. The maximum solubility of In in ZnO, that has been achieved by this growth process is 3.4 at. %. Photoluminescence (PL) study shows both UV emission and visible luminescence. Careful observation indicates a red shift in the UV emission in the PL pattern and the intensity of the green emission is increased with increasing indium content. Effect of indium concentration on the electrical properties of these nano-wires has also been investigated.

4:50 PM F1-1-9 Carbon Monoxide-induced Reduction and Healing of Graphene Oxide
B. Narayanan, S.L. Weeks (Colorado School of Mines, US); B. Macco, J.-W. Weber (Eindhoven University of Technology, Netherlands); M.C.M. van de Sanden (Dutch Institute for Fundamental Energy Research, Netherlands); S. Agarwal, Cristian Ciobanu (Colorado School of Mines, US)

Graphene oxide holds promise as a carbon-based nanomaterial that can be produced inexpensively in large quantities. However, its structural and electrical properties remain far from those of the graphene sheets obtained by mechanical exfoliation or by chemical vapor deposition – unless efficient reduction methods that preserve the integrity of the parent carbon-network structure are found. Here, we use molecular dynamics and density functional theory calculations to show that the oxygen from the main functional groups present on graphene oxide sheets is removed by the reducing action of carbon monoxide; the energy barriers for reduction by CO are very small and easily overcome

at low temperatures. Infrared and Raman spectroscopy experiments confirm the reduction in CO atmosphere, and also reveal a strong tendency for CO to heal vacancies in the carbon network. Our results show that reduced graphene oxide with superior properties can be obtained through reduction in CO atmosphere.

5:10 PM F1-1-10 Studies on the Optoelectronic Characteristics of the V2O5-PtO2 Core-shell Nanowires
Ko-Ying Pan (National Tsing Hua University, Taiwan, Republic of China); Kang-Chi Chen (Chinese Culture University, Taiwan, Republic of China); Han-Chang Shih (National Tsing Hua University, Taiwan, Republic of China)
V2O5-PtO2 core-shell nanowires have been successfully synthesized through a two-step process. Firstly, high-quality V2O5 nanowires were fabricated by thermal evaporation. Secondly, PtO2 layers were deposited on V2O5 nanowires by atomic layer deposition (ALD). SEM photos show abundant and intensive V2O5 and V2O5-PtO2 core-shell nanowires on the silicon substrates. From HRTEM images of V2O5 core-shell nanowires, it is clear that the depositions of PtO2 particles are quite compact on V2O5 nanowires. The diameter of V2O5 nanowires is 196nm, and the diameters are 215 nm and 247nm at different cycles: 50 cycles and 100 cycles, respectively. By XRD, EDS and XPS results, the core-shell nanowires are composed of V2O5 and PtO2. According to the field emission examination at working function (5.3 eV), the field enhancements(β) of V2O5 nanowires, V2O5-PtO2 core-shell nanowires with 50 cycles and 100 cycles are 573, 1089 and 1487. To further investigate the optoelectronic properties of V2O5-PtO2 core-shell nanowires, the tests of Raman spectra and I-V curve were handled as well.
Time Period TuA Sessions | Abstract Timeline | Topic F Sessions | Time Periods | Topics | ICMCTF2013 Schedule