Chi-Chin Wu, U.S. Army Research Laboratory
Cheng-Che Hsu, National Taiwan University
Vasiliki Poenitzsch, Southwest Research Institute
Mohan Sankaran, Case Western Reserve University
Journal of Applied Physics | AIP Publishing
PM01.01: Atmospheric Pressure Plasmas I
Monday AM, November 27, 2017
Sheraton, 3rd Floor, Fairfax B
8:00 AM - *PM01.01.01
Advances in Surface Processing Using Atmospheric Pressure Dielectric Barrier Discharges
Fiorenza Fanelli 1 , Antonia Mallardi 2 , Vincenza Armenise 3 , Gerardo Palazzo 3 , Francesco Fracassi 1 3 Show Abstract
1 , National Research Council (CNR), Institute of Nanotechnology (NANOTEC), Bari Division, Bari Italy, 2 , National Research Council (CNR), Institute for the Chemical Physics Processes (IPCF), Bari Division, Bari Italy, 3 Department of Chemistry, Università degli studi di Bari Aldo Moro, Bari Italy
Atmospheric pressure non-equilibrium plasma technology received enormous attention in surface processing in the last two decades, and still continues nowadays to attract growing interest. In particular, among the different strategies used to obtain non-equilibrium plasma conditions at atmospheric pressure, dielectric barrier discharges (DBDs) have attracted much interest due to their simple design, ease of generation, scalability to large area substrates. Considerable research efforts have been directed to develop a plethora of processes which exploit different DBD electrode geometries for the direct and remote processing of a large variety of materials.
In this contribution, a brief overview of our recent progress in surface engineering and functionalization using DBDs will be presented with particular focus on process optimization. First, the attention will be directed to the surface modification of open-cell polymer foams accomplished by igniting the DBD throughout the entire three-dimensional (3D) porous structure of the material. Examples will include the plasma-enhanced chemical vapor deposition (PECVD) of fluorocarbon coatings and the plasma treatment through chemical grafting of oxygen-containing functional groups and variation of the surface roughness. Then, our studies on the growth and structure of hybrid organic/inorganic nanocomposite coatings using an aerosol-assisted process will be briefly reviewed. In this process the atmospheric plasma, fed with a carrier gas and the aerosol of a dispersion of nanoparticles (NPs) in a liquid organic precursor, allows the deposition of nanocomposite coatings consisting of NPs embedded in the organic component formed through plasma polymerization of the liquid precursor. The deposited coatings show multifunctional behavior due to the combination at the nanoscale level of the specific properties of the organic and inorganic components. Finally, our very recent results on the immobilization of enzymes by overcoating using a plasma-deposited polymer layer will be presented. The proposed immobilization strategy consists of a two-step procedure in which the enzyme is adsorbed on a support and then overcoated by a thin film deposited in a dielectric barrier discharge at atmospheric pressure. The enzyme is expected to be entrapped under the polymer coating that should protect the enzyme from leaching while allowing the passage of substrate and product molecules. Since this approach involves the direct exposure of enzymes to the atmospheric plasma, a comprehensive study of the effects of DBDs on enzymes functionality has been carried out. The most significant outcomes of the aforementioned study will be presented along with preliminary results on coatings permeability to enzymes and small molecules.
8:30 AM - *PM01.01.02
Atmospheric Pressure Plasma Processes for Next Generation Photovoltaic Materials
Davide Mariotti 1 Show Abstract
1 , Ulster University, Newtownabbey United Kingdom
Atmospheric pressure plasmas (APPs) have demonstrated unprecedented versatility for the synthesis and processing of nanoscale structures. APPs have shown the possibility of producing thin films, nanostructured coatings, nanoparticles and other complex materials from a variety of precursors that include solid, liquid and gases (e.g. [1-3]). The synthesis of metallic, metal-oxide and semiconducting materials has been demonstrated covering a wide range of elements in the chemical table. Despite research efforts go back only a decade, the quality of the materials produced by APPs is comparable and in some cases superior to results produced with other methods (e.g. wet chemistry, low-pressure plasmas).
In this context, microplasmas at atmospheric pressure have played a major role and have revealed great opportunities for nanoscale engineering, providing unique avenues for accurately tailoring materials properties. While the scale-up of atmospheric pressure microplasmas has not been fully demonstrated yet, progress has been made also in this direction which suggests the possibility of integrating microplasma processes in the fabrication of application devices .
In this contribution we will first review the capabilities of APP-based materials synthesis, highlighting the wide range of achievable morphologies and chemical compositions . Examples of advanced nanoscale engineering will be provided that include the formation of hybrid organic/inorganic nanocomposite structures for a variety of applications. The possibility of introducing APP-based processes in the fabrication of solar cell devices is then discussed [3, 5, 6]. The focus of our research is on the development of third generation photovoltaic devices and we have so far integrated APP processes for the deposition of a range of metal oxides as selective contacts (i.e. blocking and transport layers) and a range of quantum confined semiconducting nanoparticles as active layers (e.g. [1-3, 7]).
1. M. Macias-Montero, S. Askari, S. Mitra, C. Rocks, C. Ni, V. Švrček, P.A. Connor, P. Maguire, J.T.S. Irvine, D. Mariotti, Nanoscale 8 (2016) 6623.
2. S. Askari, V. Švrček, P. Maguire, D. Mariotti, Advanced Materials 27 (2015) 8011.
3. D. Mariotti, T. Belmonte, J. Benedikt, T. Velusamy, G. Jain, V. Švrček, Plasma Processes and Polymers 13 (2016) 70.
4. A.J. Wagner, D. Mariotti, K.J. Yurchenko, T.K. Das, Physical Review E 80 (2009) 065401R.
5. V. Švrček, M. Kondo, K. Kalia, D. Mariotti, Chemical Physics Letters 478 (2009) 224.
6. V. Švrček, D. Mariotti, Y. Shibata, M. Kondo Journal of Physics D: Applied Physics 43 (2010) 415402.
7. S. Askari, I. Levchenko, K. Ostrikov, P. Maguire, D. Mariotti Applied Physics Letters 104 (2014) 163103
9:00 AM - PM01.01.03
Ethylenediamine as a Doping Agent in the Plasma Synthesis of Doped- ZnO Nanoparticles
Gunisha Jain 1 , Conor Rocks 1 , Paul D. Maguire 1 , Davide Mariotti 1 Show Abstract
1 , University of Ulster, Newtownabby United Kingdom
Atmospheric pressure microplasmas exhibit important characteristics that allow efficient and non-thermal dissociation of molecular gases or other vapour precursors to produce high concentrations of reactive radical species. Atmospheric pressure operating conditions are cheaper, easier and highly desirable in terms of low equipment cost and lower maintenance requirement of the reactors. Here, we have used a non-thermal atmospheric pressure microplasma coupled to a liquid to synthesise surfactant and capping-free nitrogen and nitrogen/carbon doped zinc oxide (ZnO) nanoparticles.
Doping has been considered as an approach to improve ZnO optical response under visible light exposure and to produce p-type ZnO for improved electrical properties. Many methods have been used to synthesize doped ZnO such as sol-gel, MOCVD, microwave plasma, precipitation method etc.
Here, the process is carried out with an atmospheric pressure microplasma generated by a direct current generator. The synthesis setup consists of a nickel capillary tube as cathode, a metallic zinc foil as an anode and zinc precursor, deionised (DI) water as a solvent, ethylenediamine (EDA) as N and N-C doping agents and helium as a background gas. EDA has been used in previous studies as a passivating agent, for controlling morphology and size of the zinc oxide nanoparticles, however here it is used as a doping agent. At lower EDA concentration, N-doping is dominant while at higher EDA concentration, combined N/C-doping is observed. The bandgap of the nanoparticles was determined using Tauc plots and resulted in values within 3.0-3.3 eV. The nanoparticle size, morphology, and crystal structure were analysed using transmission electron microscopy (TEM), X-ray diffraction and other techniques. TEM analysis revealed that the nanoparticle size is reduced as the dopant concentration is increased while the crystallinity was generally preserved and resulted in the basic wurtzite structure. The chemical composition was studied by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS). It was also observed that the hydrophilic nature of ZnO was decreased as doping concentration increased. The atomic concentration of the doped ZnO nanoparticles was evaluated by XPS analysis. The complete band electronic diagram was investigated by XPS and Kelvin probe measurements. The Raman spectrum shows a very strong fluorescence of the doped ZnO. Finally, mechanisms leading to the synthesis of doped ZnO are also proposed and discussed.
9:15 AM - PM01.01.04
Catalyst-Free, Plasma Conversion of Ammonia Borane to h-BN Thin Films at Low Temperature and Atmospheric Pressure
Tianqi Liu 1 , Mohan Sankaran 1 Show Abstract
1 , Case Western Reserve University, Cleveland, Ohio, United States
Hexagonal boron nitride (h-BN) is an insulating, two-dimensional (2D) equivalent of graphene that has importance as an insulating spacer in emerging electronic devices and substrate for the growth of other 2D materials including graphene and tungsten disulfide (WS2). h-BN films are typically produced by sputter deposition or mechanical exfoliation from bulk crystals.1 Recently, chemical vapor deposition (CVD) of h-BN from molecular precursors has been demonstrated which enables better control over the layer thickness or number and is scalable.2-4 However, film nucleation requires a catalytic substrate such as Cu and relatively high temperatures of ~1000 oC. Here, we present a plasma-based approach to convert ammonia borane to h-BN that eliminates the catalytic substrate and lowers the temperature for h-BN formation. The ammonia borane was first prepared as a thin film on silicon or quartz substrates from solution by spin coating or other deposition techniques, then reacted with an atmospheric-pressure dielectric barrier discharge (DBD) formed inside a hot-wall furnace in flowing mixtures of argon (Ar) and hydrogen (H2) gas. The films were characterized by micro Raman spectroscopy and transmission electron microscopy to confirm the nucleation and growth of h-BN. By systematically comparing the plasma process with only thermal treatment, we find that the temperature for h-BN growth can be lowered from ~800 to 650 oC for Ar and to 500 oC for Ar + H2. We propose that plasma species including electrons, Ar ions, and, in particular, atomic hydrogen (H), enhance dehydrogenation reactions that lead to the decomposition of ammonia borane and h-BN nucleation.5,6 These results illustrate the potential of non-equilibrium chemistry afforded by plasmas for the low-temperature growth of h-BN on arbitrary substrates which should be attractive for flexible device applications.
1. C. Mitterer et al., J. Vac. Sci. Techn. A. 7, 2646 (1989).
2. L. Songet al., Nano Lett. 10, 3209 (2010).
3. K. Kim et al., Nano Lett. 12, 161 (2012).
4. Z. Liu et al. Nat. Comm. 10, 2541 (2013).
5. R. Whittell et al., Angew. Chem. Int . Ed. 50, 10288 (2011).
6. S. Frueh et al., Inorg. Chem. 50, 783 (2011).
9:30 AM - PM01.04.05
Development of a Hybrid Plasma-Liquid System for the Production of Nanofluids
Ruairi McGlynn 1 , Supriya Chakrabarti 1 , Darragh Carolan 1 , Paul D. Maguire 1 , Davide Mariotti 1 Show Abstract
1 , Ulster University, Newtownabbey United Kingdom
Direct absorption solar collectors provide a pathway to provide thermal energy without relying on fossil fuels which are becoming scarcer. Traditional working fluids used in solar collectors such as water and ethylene glycol are known to be poor absorbers of solar radiation in the visible light region.1 As such a significant proportion of the incident energy is not absorbed but transmitted through the fluid.2 This makes it essential to tailor the properties of the absorbing fluid to capture this energy. The simplest method of achieving this is to add materials to the base fluid to produce a composite working fluid. Of great interest is the addition of nanoparticles such as gold nanoparticles which are well known to show plasmonic effects with a consequent increase in the absorption of light in the visible region.3 These nanoparticle-laden fluids are often known as nanofluids.
In this work, a hybrid plasma-liquid system has been used to rapidly produce colloidal gold nanoparticles through the reduction of dilute HAuCl4 with no need for reducing agents or surfactants.4, 5 We produced gold nanoparticles of average size 29 nm, which yields a nanofluid with a surface plasmon resonance peak between 520 nm and 580 nm. As this corresponds to the high energy region of the solar irradiance spectra, a very small concentration of nanoparticles can greatly enhance the absorbed energy. The absorption coefficient was used to estimate that a nanofluid volume of 104 cm3 could capture an additional 8.5 W of energy over that of ethylene glycol alone, with a volume concentration of only 5.46 x 10-5 %. Further, the stability of the colloidal solutions has been studied over a period of several weeks.
It is of interest to scale up the synthesis, maintaining or reducing costs and where, differently from other applications, narrow size dispersion is not a critical parameter. The use of the very rapid reactions and low cost of the plasma-liquid system is therefore very attractive. Therefore, progress towards scale up and continuous flow synthesis will be discussed.
1. Otanicar TP, Phelan PE, Golden JS. J Solar Energy 2009, 83, 969
2. ASTM G173-03(2012), ASTM International, West Conshohocken, PA, 2012, www.astm.org.
3. Link S, El-Sayed M,A. J Phys Chem B 1999, 103, 4212.
4. McKenna J, Patel J, Mitra S, Soin N, Švrček V, Maguire P, Mariotti D. Eur.Phys.J.Appl.Phys. 2011, 56, 24020.
5. Patel J, Němcová L, Maguire P, Graham W,G., Mariotti D. Nanotechnology 2013, 24, 245604.
10:15 AM - *PM01.01.06
Opportunities for Open-Air Atmospheric Plasma Deposition of Multi-Functional Films
Reinhold Dauskardt 1 Show Abstract
1 , Stanford University, Stanford, California, United States
Open-air atmospheric plasmas provide opportunities for versatile and low cost materials synthesis and film deposition on large and/or complex shapes in laboratory air and at low temperature. The generally solvent-free process further allows for the simultaneous functionalization of, and deposition on, substrates in a single step. Recent advances in the use of plasma process gasses (primary and carrier) that include inexpensive N2 and compressed air together with the possibility of combining plasmas with spray deposition have further expanded the utility of the deposition technique.
We demonstrate highly efficient deposition methods using single and dual precursors to deposit multilayer organosilicate transparent films on selected polymer, silicon and glass substrates. The films exhibit ~100% transmittance in the visible range and can be tuned to incorporate controlled organic molecular components (-C-C-)n despite the strongly oxidizing environment. Films with impressive adhesion to plastics along with exceptional elastic stiffness to 34 GPa without post-deposition anneal are demonstrated. We also report on the feasibility of using open air atmospheric plasma to deposit various conductive and antireflective bilayer films on both silicon and plastics, including ZnO and blends of TiN/TiO films. We discuss our work controlling the refractive index of TaO and TiO films for antireflective coating layers and make comparisons with traditional fabrication techniques to assess the viability of a TaOx/SiOy anti-reflection bilayer deposited by open air atmospheric plasma.
Finally, we demonstrate a scalable atmospheric plasma process to rapidly deposit and form photoactive perovskite films in open air at linear deposition rates exceeding 2 cm/s. The process uses clean dry air to produce a combination of reactive species, UV and thermal energy to rapidly form the perovskite film after air spraying. The high energy reactive species diffuse through the thin plasma-liquid interface, inducing dissociation and volatilization of solvent molecules, and assisting on the rapid conversion into the perovskite structure. We describe the fast deposition of pinhole-free, robust CH3NH3PbI3 layers with a ten-fold increase in fracture toughness, a key metric for reliability. Completed perovskite devices were further encapsulated with atmospheric plasma deposition of dense silica barrier films. The efficiency of devices increased from 15.0% to 15.7% with improved Voc and FF after depositing the barrier film and showed improved moisture stability by several orders of magnitude, allowing for operation in 85% R.H. environments without degradation.
10:45 AM - PM01.01.07
Tuning Electrode Properties and Surface Contacts for Uniform Deposits Produced by Atmospheric Plasma Dielectric Barrier Discharge Reactors
Chi-Chin Wu 1 , Timothy Jenkins 1 , Rose Pesce-Rodriguez 1 Show Abstract
1 , U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland, United States
Atmospheric non-thermal plasma-enhanced chemical vapor deposition (PECVD) utilizing dielectric barrier discharge (DBD) configurations has attracted much interest for novel chemical synthesis of new materials that would be otherwise difficult or impossible to make via conventional methods. A suitable design on the electrodes and their contact surfaces with the dielectric substrates have detrimental influences on the chemical and physical properties of the deposited material. Using a pulsed AC high voltage power source, different electrode materials including solid thick aluminum, copper wire mesh, and aluminum/copper mesh composite electrodes, were explored to investigate their inter-correlations to the elevation of deposition temperature, load resistance, and the uniformity of the deposited material. Possible effects of non-ideal interfacial conditions between the surfaces of electrode and substrate were also studied with various modified surface thermal conditions. The deposited material was found to be most uniform with desired properties by using the aluminum/copper mesh composite electrodes with flat contacts, no thermal medium at the electrode/substrate interfaces, and sustainable temperature control across the deposition region. Although the experimental conditions of PECVD are often system and application oriented, this work provides insights on technical details on the design for plasma-enhanced chemical synthesis in DBD reactors.
11:00 AM - PM01.01.08
The Development of a Portable Device for Detection of Heavy Metal Ions in Water Using a Microplasma Generation Device Integrated with a Cellphone-Based Spectrometer
Cheng-Che Hsu 1 , Fu-Yu Yang 1 , Ting Kai Yuan 1 , Qi-Ming Jian 1 , Po-Wei Yeh 1 , Fei-hung Huang 1 , Min-Chun Chen 1 , Peng-Kai Kao 1 , Yen-Yu Lin 1 Show Abstract
1 , National Taiwan University, Taipei Taiwan
Funding support: 103-2221-E-002-184-MY3, MOST, Taiwan
This work presents the development of a portable device that integrates a microplasma generation device (MGD) and a cellphone-based spectrometer (CBS) for the detection of heavy metal ions in water solution. The MGD is a needle-to-surface electrode system driven by a homemade high voltage module. This module is powered by a 5-V cellphone charger and supplies a DC voltage up to 3 kV to ignite the plasma. The homemade CBS contains a slit, a grating, and utilizes the cellphone camera for spectra acquisition. The main structure of this device is constructed using a 3D-printer. The width of the slit is 40-50 µm and a 1000 lines/mm grating are used. This CBS is able to perform spectral analysis with the wavelengths from 400 to 700 nm with a full width at half maximum well below 10 nm. The MGD and CBS are integrated such that the optical emission emanating from the plasma can be acquired by the CBS.
With this device, metallic ions in aqueous solutions can be detected by analyzing the plasma emission spectroscopy acquired by the CBS with a sample amount as small as a few μL. This portable device is able to detect multiple metallic elements simulatenously by analyzing the optical emission spectra. For example, 200 ppm-Pb ions and trace Na ions (sub-ppm, existed as the impurity in the chemical used) can be detected. Using the cellphone charger as the power source for the MGD, this portable device can be used to test tens of samples without running out the charger power. At the end of the presentation, I will discuss the limitation and challenges using this device as a general analytical tool for metallic element detection and quantification.
11:15 AM - *PM01.01.09
Graphene Synthesized in Atmospheric Plasmas—Research and Applications
Albert Dato 1 Show Abstract
1 , Harvey Mudd College, Claremont, California, United States
Atmospheric-pressure plasmas can be used to rapidly and continuously synthesize graphene powders that have numerous applications, including composites, lubricants, and energy storage. The gas-phase synthesis process involves sending precursors, such as ethanol and dimethyl ether, into microwave-generated argon plasmas, which results in the formation of graphene that is pure and highly ordered. In this talk, I will first review the substrate-free gas-phase synthesis method of producing graphene. The most recent research into the bottom-up technique will then be presented. Factors affecting the production of graphene, such as gases, precursors, and precursor delivery methods, will be discussed. Additionally, the characteristics and applications of gas-phase-synthesized graphene will be reported. The experimental results elucidate the complex processes occurring in the plasma reactor and demonstrate feasible applications for gas-phase-synthesized graphene.
PM01.02: Atmospheric Pressure Plasmas II
Monday PM, November 27, 2017
Sheraton, 3rd Floor, Fairfax B
1:30 PM - *PM01.02.01
Controlled Co-Deposition of Thin Films and Engineered Nano-Additives for Tailored Plasmonic Response via Atmospheric Pressure Plasma-Assisted Chemical Vapor Deposition
Andres Bujanda 1 , John Demaree 1 , Mark Griep 1 Show Abstract
1 , U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland, United States
Silicon oxide films (SixOy) have been successfully synthesized from organosiloxane precursors via atmospheric pressure plasma-enhanced chemical vapor deposition (AP-PECVD). By incorporating a nebulizer spray head into the AP-PECVD system, it is possible to co-deposit engineered nanoparticles, such as gold nanorods, into the deposited SiO2. This method of co-deposition enables a high degree of control over not only the mechanical and chemical properties of the resulting film, but also control over the location, concentration, and type of nano-additives contained in the film. In addition, it is possible to deposit nanoparticles without protective coatings, such as Si-shells, necessary for conventional integration methodologies. In this study, gold nanorods were successfully incorporated in-situ into AP-PECVD deposited SixOy using a nebulizer spray head. The resulting films were analyzed using ultra violet visible spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and Rutherford backscattering spectrometry.
2:00 PM - PM01.02.02
Copolymerization of Sulfobetaine Methacrylate and Acrylic Acid in Liquid Phase via Atmospheric Pressure Argon Plasma Jet Treatment
Yueh-Han Huang 1 , Meng-Jiy Wang 1 Show Abstract
1 , National Taiwan University of Science and Technology, Taipei Taiwan
Biofouling is a commonly encountered problem for biomaterials such as wound dressing, biosensors, and medical implants, that was potentially avoidable by incorporating anti-fouling layers for the surface modifications for the biomaterials.1 Poly(sulfobetaine methacrylate) (polySBMA) has been proved to show ultra-low fouling to non-specific proteins, cells, and bacterial.2 It is considered that the unique properties of polySBMA can be ascribed to its super hydrophilic nature as well as the balanced charge.3 As a result, polySBMA and its copolymers have been applied in the fields of wound dressing, improving hemocompatibility of biomaterials, and water-oil separation system.1, 4
Free radical polymerization is the most extensively employed method to synthesize polymers that were initiated via radicals resulted from the thermal initiators or photoinitiators. Recently, atmospheric pressure plasma jet (APPJ) in contact with liquids for bio-applications has drawn dramatic attention because APPJ allowed to generate reactive oxygen and nitrogen species (RONS), such as OH radical, NO2 radical, H2O2, and NO3-.5, in the liquid phase during plasma treatment.
In this work, sulfobetaine methacrylate (SBMA) and acrylic acid (AA) were copolymerized in deionized water by using 13.56 MHz radio frequency (RF) APPJ to scan the precursor solution under different applied power and scan numbers to evaluate the effects on polymer structure and composition. The chemical functionalities, composition, and molecular weight were analyzed by Fourier transform infrared spectroscopy (FTIR), 1H-neclear magnetic resonance spectroscopy (1H-NMR), and gel permeation chromatography (GPC), respectively. Moreover, the antifouling ability of the APPJ synthesized poly(SBMA-co-AA) will be evaluated to verify the characteristics of polySBMA.
1. Lalani, R.; Liu, L., Synthesis, characterization, and electrospinning of zwitterionic poly (sulfobetaine methacrylate). Polymer 2011, 52 (23), 5344-5354.
2. Kuo, W.-H.; Wang, M.-J.; Chien, H.-W.; Wei, T.-C.; Lee, C.; Tsai, W.-B., Surface modification with poly (sulfobetaine methacrylate-co-acrylic acid) to reduce fibrinogen adsorption, platelet adhesion, and plasma coagulation. Biomacromolecules 2011, 12 (12), 4348-4356.
3. Chen, S.; Li, L.; Zhao, C.; Zheng, J., Surface hydration: principles and applications toward low-fouling/nonfouling biomaterials. Polymer 2010, 51 (23), 5283-5293.
4. Liu, Q.; Patel, A. A.; Liu, L., Superhydrophilic and underwater superoleophobic poly (sulfobetaine methacrylate)-grafted glass fiber filters for oil–water separation. ACS applied materials & interfaces 2014, 6 (12), 8996-9003.
5. Lukes, P.; Dolezalova, E.; Sisrova, I.; Clupek, M., Aqueous-phase chemistry and bactericidal effects from an air discharge plasma in contact with water: evidence for the formation of peroxynitrite through a pseudo-second-order post-discharge reaction of H2O2 and HNO2. Plasma Sources Science and Technology 2014, 23 (1), 015019.
2:15 PM - PM01.02.03
Studies of the Atmospheric Pressure Plasma Jet Treatments Toward Cell Viability of Mouse L-929 and 3T3 Fibroblasts
Saitong Muneekaew 1 , Alfin Kurniawan 1 , Meng-Jiy Wang 1 Show Abstract
1 Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei Taiwan
Plasma is widely considered to be the fourth state of matter and has been used in biology, medicine, and electronic fields. Recently, the atmospheric pressure plasma jet (APPJ) has drawn increasingly attention due to its efficiency in modulating the viability of different types of cells (1-3). Moreover, APPJ has been reported to induce cytotoxicity of cells including apoptosis, necrosis, and autophagy (4-5). In this regard, the reactive oxygen species (ROS) play a key role in regulating the cell responses induced by APPJ treatment. However, to date, the ROS generated during plasma treatment and detailed mechanism that leads to cytotoxic response remain unclear.
In this work, mouse L-929 fibroblast cells were used as a model cell to study the cellular cytotoxicity after treatment with argon-APPJ for 30 s. The cell number after argon-APPJ treatment was determined by lactate dehydrogenase (LDH) assay. The results indicated that APPJ treatment had no effect on the cell number of L929 fibroblasts following incubation for 1, 2, and 4 h. On the other hand, the argon-APPJ treatment resulted in the decrease of cell density after 6 h of incubation, suggesting that the ROS generated by APPJ might induce signaling pathways involving apoptosis, necrosis, or autophagy for this incubation period. To study the cytotoxic responses in more detail, the 3T3 cells obtained from hypertriploid mouse were used to compare the results obtained for L-929 fibroblasts. Furthermore, flow cytometry was employed to further elucidate the role of toxicity of both cells treated with argon-APPJ.
Monday PM, November 27, 2017
Sheraton, 3rd Floor, Fairfax B
3:00 PM - *PM01.03.01
Metal Oxide Nanosurfaces and Hetero-Interfaces for Solar Harvesting Applications
Sanjay Mathur 1 , Yakup Gonullu 1 , Jennifer Leduc 1 , Thomas Fischer 1 , Myeongwhun Pyeon 1 Show Abstract
1 , University of Cologne, Cologne Germany
Metal oxide nanostructures with hetero-contacts and phase boundaries offer unique platform for designing materials architectures for solar harvesting applications. Besides the size and surface effects, the modulation of electronic behavior due to junction properties leads to modify surface states that promote higher efficiency. The growing possibilities of engineering nanostructures in various compositions (pure, doped, composites, heterostructures) and forms (particles, tubes, wires, films) has intensified the research on the integration of different functional material units in a single architecture to obtain new materials for solar energy harvesting application.
In this work we present the deposition and modification of metal oxides (TiO2, Fe2O3) and their multilayers (Fe2O3/Nd2Sn2O7, TiO2/Fe2O3) for photoelectrochemical (PEC) hydrogen production. The deposition parameters for thin film creation were optimized with respect to the PEC performance of the resulting materials in both alkali solution and simulated seawater. The long-term performances of the metal oxide photoanodes were determined in alkali and seawater electrolyte, as well. The results presented that the multilayered TiO2/Fe2O3 photonanode yielded higher photocurrent density (1.8 mAcm-2 at 1.23 V) with very stable conditions even after 1-week measurement. Not only the heterostructuring of metal oxide, but also their modifications such as patterning, O2 plasma treatment, H2 Plasma treatment was also investigated.
3:30 PM - PM01.03.02
Micro-Nano Conical and Triangular Structures for Perfect Antireflection Surfaces in Solar Photovoltaic and Photoelectrochemical Devices Fabricated via Plasma Etching with Precise Taper Control
Sisir Yalamanchili 1 , Colton Bukowsky 1 , Rebecca Saive 1 , Paul Kempler 1 , Nathan Lewis 1 , Harry Atwater 1 Show Abstract
1 , California Institute of Technology, Pasadena, California, United States
Dry etching of Si via ICPRIE (Inductively coupled plasma reactive ion etching) allows for micro-nano machining of Si under cryogenic conditions using SF6 and O2 etch chemistry. This method is widely used in etching submicron high aspect ratio anisotropic structures for bioelectronics, optoelectronics, and electromechanical systems. Here we present the fabrication of nano-micro conical and triangular structures in Si with precise taper control that achieve perfect antireflection in solar cells and panels, and thus enhancing their efficiencies in a scalable way.
Front surface reflection of glass in solar panels amounts to ~5% of photocurrent loss in all solar panels. We show that utilizing SiO2 periodic nanoconical arrays with optimized parameters can reduce this loss to <1% making the front glass a perfect antireflector. One scalable way to fabricate these structures is to have these structures etched onto a Si substrate and use it to make a polymer template for nanoimprinting. This template can be reused multiple times to imprint SiO2 structures using solgel on glass substrate. We experimentally demonstrate the antireflection effect by imprinting SiO2 structures on glass.
Another major loss of photocurrent in solar cells is due to reflection loss from flat metallic top contacts. One way to overcome this loss is to change the shape of such contacts into triangles such that the tapered sidewalls of a triangle redirects the incoming sunlight onto bare regions of the solar cell. These triangles were previously shown by to enhance the photocurrent by as much as 2 mA/cm2 without any loss in open circuit voltage and fill factor by our group. Here we show that ICPRIE can be utilized to create etched masters for nano imprinting such contacts. One master can be used to prepare multiple polymer templates that can be reused multiple times to deposit triangular Ag contacts.
Finally we also report ordered, high aspect ratio (25:1), tapered Si microwire arrays that exhibit an extremely-low angular (0o to 50o) and spectrally averaged reflectivity of <1% of the incident 400 nm - 1100 nm illumination fabricated via ICPRIE. After isolating the arrays from their substrate with a polymer infill and peel off process, the arrays absorb 89.1% of angular averaged incident illumination (0o to 50o) in the equivalent volume of a 20 micron thick Si planar slab. The absorption is slightly below the 4n2 classical light trapping limit of a 20 micron thick Si slab for most of the solar spectrum, and exceeded the limit at wavelengths near the Si band gap (1050 nm – 1100 nm), reaching 99.5% of the classical light trapping limit between 400 nm - 1100 nm. Due to low lattice defects near the surface, solar cells based on these arrays under optimum surface passivation can reach open circuit voltages > 0.7V and efficiencies >25%. Due to high surface area these arrays are ideal for liquid contacts and they show ~40 mA/cm2 photocurrent when used as photocathodes for H2 evolution.
3:45 PM - *PM01.03.03
Applications of Atmospheric Pressure Plasma Treatments in Photovoltaic Devices
I-Chun Cheng 1 , Cheng-Che Hsu 1 , Jian-Zhang Chen 1 , Zhen-Chun Chen 1 , Chan-Cheng Lin 1 Show Abstract
1 , National Taiwan University, Taipei Taiwan
Atmospheric pressure plasma technologies have received great attention in versatile applications, such as surface modification, rapid thermal annealing, thin-film deposition, bacteria inactivation, and rapid sintering processes. Without the requirement of vacuum environments, they possess potential economic benefits in comparison with low-pressure plasma techniques, which makes them attractive for processing large-area low-cost photovoltaic devices. Here we demonstrate dye-sensitized solar cells and perovskite solar cells with the assistance of atmospheric pressure plasma processes.
In the case of dye-sensitized solar cells, an ultrashort process was developed to lower the thermal budget for the fabrication of carbonaceous counter electrodes. The screen-printed reduce graphene oxide (rGO)-containing precursor film was treated by an N2 atmospheric pressure plasma jet (APPJ) for an ultrashort duration. Strong emission bands from CN violet system were observed in the time-resolved optical emission spectra at the early stage of the treatment, resulting from the strong reaction between the N2 plasma and the ethyl cellulose within the precursor film. The APPJ treatment removes the organic binder rapidly but also introduces defects and oxidic surface groups in the rGO at the same time. The negative impact of the inferior conductivity was mitigated by the improved catalytic activity of APPJ-treated rGO, showing a comparable cell performance to a 15 min furnace calcination at a treatment duration of 11 s.
In the case of perovskite solar cells, a planar-type dielectric barrier discharge apparatus was used to treat the absorber layers of lead halide perovskite solar cells. The cell has a regular planar structure. A compact TiO2 electron transport layer was first solution processed and furnace annealed. Next the perovskite absorber layer was formed by spin-coating a dimethylformamide solution containing CH3NH3I and PbI2, followed by a soft-bake. Prior to the deposition of the spiro-OMeTAD hole transport layer, a surface treatment of the perovskite absorber layer was carried out by dielectric barrier discharge in a nitrogen ambient. Finally, an Ag layer was thermally-evaporated as the cathode. The scanning electron micrographs show that the dielectric barrier discharge treatment can introduce the surface modification and grain growth of the perovskite absorber. But a prolong treatment results in the decomposition of the perovskite thin film with the formation of PbI2. An optimal photoelectric conversion efficiency of ~14.2% ( >30% improvement) was achieved when a 20 s dielectric barrier discharge treatment was performed.
4:15 PM - *PM01.03.04
Photoelectric Conversion Device Using Plasma Processed Semiconducting Single-Walled Carbon Nanotubes and Transition Metal Dichalcogenide
Toshiro Kaneko 1 , Toshiki Akama 1 , Toshiaki Kato 1 Show Abstract
1 , Tohoku University, Sendai Japan
In order to greatly increase the solar cell efficiency, a full use of the solar spectrum is one of the crucial issues, and therefore, development of multi-junction thin-film solar cells is strongly desired. Especially, for fabrication of an infrared solar cell as the bottom cell, single-walled carbon nanotubes (SWNTs) are attracting much interest for photovoltaic energy conversion because of their broad absorption bands including the infrared range (0.2 ~ 1.3 eV). To realize the solar cell with SWNTs [1,2], it is necessary to establish a method for carrier type-, density-, and position-controllable doping into SWNTs. In this study, we have fabricated the p-n junction embedded SWNTs solar cell using SWNTs thin films. We have demonstrated the controllable and stable n-type carrier doping into semiconducting SWNTs thin films by position selective cesium (Cs) encapsulation into SWNTs with a plasma ion irradiation method . Optoelectrical features were also measured and rectifying features can be observed for the p-n junction embedded SWNTs. Furthermore, we fabricated the photoelectric conversion device using SWNTs and transition metal dichalcogenide (TMD) heterojunction, where SWNTs are expected to extract the excitons from TMD. The open circuit voltage and the short circuit current can be clearly obtained with light illumination in these devices. These are the first results showing the photovoltaic power generation using the p-n junction embedded SWNTs thin films solar cell and the SWNTs/TMD heterojunction solar cell.
 R. Hatakeyama, Y. F. Li, T. Y. Kato, and T. Kaneko, Appl. Phys. Lett. 97 (2010) 013104.
 Y. F. Li, S. Kodama, T. Kaneko, and R. Hatakeyama, Appl. Phys. Lett. 101 (2012) 083901.
 T. Kato, E.C. Neyts, Y. Abiko, T. Akama, R. Hatakeyama, and T. Kaneko, J. Phys. Chem. C 119 (2015) 11903.
PM01.04: Poster Session
Monday PM, November 27, 2017
Hynes, Level 1, Hall B
8:00 PM - PM01.04.01
Inner-Wall Surface Treatment of High-Aspect-Ratio Structures Using an Oxygen Plasma for Material Surface Property Design
Shogo Uehara 1 , Peter Wood 1 , Tobin Mcgee 1 Show Abstract
1 OPTO Films Research Laboratory, SAMCO Inc., Sunnyvale, California, United States
Oxygen plasma generates plasma species such as oxygen ions, atomic oxygen and oxygen radicals. Recently, interest has grown in the plasma treatment of three dimensional (3D) structures since it is expected there will be promising applications in the material surface property design of medical polymer tubing and electronics packaging. Eto et al. conducted sterilization of medical plastic tubes using linear dielectric barrier discharge . Chen et al. examined hydrophilization of polytetrafluoroethylene (PTFE) tubes using atmospheric pressure plasma jets . In this research, vacuum plasma treatment of inner-wall surfaces was investigated using aluminum-made structures with lateral deep holes.
Polyetheretherketone (PEEK) and photoresist (Shipley, SPR 3000)-coated silicon coupons (5 mm x 5 mm) were placed at various depths (aspect ratios) inside a straight cave (6 mm x 6 mm square and 96 mm maximum depth) and a straight tube (6 mm x 6 mm square hole and 180 mm deep) to investigate oxygen plasma treatment effects in different hole structures. A SAMCO plasma cleaner PC-300 was used in this study. The surface wettability of PEEK was examined by the water contact angle, and the photoresist ashing rate was measured using a stylus profilometer (Ambios Technology, XP-200).
Generally, samples processed at higher aspect ratios had higher contact angles and lower ashing rates. Even though there is a possibility of oxygen ion and radical inflow from outside of the structures, their effects are relatively negligible at higher aspect ratios due to the short mean free path (less than 1.5 mm) of the ions at 50 – 150 Pa and the short life time of the radicals. Our results indicated that a plasma discharge occurs not only in the plasma chamber but also locally inside the deep holes as hollow-anode plasma, and the high-aspect-ratio structures on the ground electrode works as an anode. It is assumed that the density of the plasma species generated in the local plasma discharge is influenced by the feed gas oxygen flux inside the structures because oxygen molecule supply inside the structures is limited.
At an aspect ratio of 10, higher ashing rates were obtained at higher pressure in the cave structure compared to those in the open tube structure. Although higher pressure is beneficial to increased ion density, there is a trade-off between the ion density and the mean free path of the ions, as seen in plasma etching . Our results indicated that the plasma treatment effects of high-aspect-ratio structures are dependent not only on the density and mean free path of the species in the plasma but also on the geometry of the structures due to complex gas molecule diffusion inside the structures.
 H. Eto, Y. Ono, A. Ogino, and M. Nagatsu. Plasma Processes Polym. 5 269–274 (2008)
 F. Chen, J. Song, S. Huang, S. Xu, G. Xia, D. Yang, W. Xu, J. Sun, and X. Liu. J. Phys. D: Appl. Phys. 49 365202 (2016)
 F. A. Khan and I. Adesida. Appl. Phys. Lett. 75 15 (1999)
8:00 PM - PM01.04.02
Pathway for a Low-Temperature (250°C) Deposition of Thermochromic VO2 without Substrate Bias Voltage
Jiri Houska 1 , David Kolenaty 1 , Jiri Rezek 1 , Jaroslav Vlcek 1 Show Abstract
1 , University of West Bohemia, Plzen Czechia
VO2 is an extremely interesting thermochromic material due to its reversible transition from a low-temperature monoclinic semiconductor to a high-temperature tetragonal metal. High modulation of infrared transmittance and electrical and thermal conductivity makes VO2-based films a suitable candidate for numerous applications, such as smart windows with automatically varied solar transmission. The efforts to prepare such films deal with the following two main challenges: to achieve the correct elemental composition (avoiding e.g. V2O5 or V2O3), and to achieve the crystallinity of VO2 (without limiting the application potential by means such as high deposition temperature (Tdep), rf substrate bias voltage or post-deposition annealing). There is no work reporting a deposition of thermochromic VO2 onto unbiased substrates at Tdep < 400°C.
The subject of this contribution is the preparation of thermochromic VO2 using high-power impulse magnetron sputtering (HiPIMS) with pulsed reactive gas flow control (RGFC) under exceptionally industry-friendly conditions: without any substrate bias voltage, at low Tdep = 300°C in a case of amorphous glass substrates without any interlayer, and at even lower Tdep = 250°C in a case of Si substrates . We show that and how strongly thermochromic VO2 films can be prepared even under these seemingly unfavorable conditions, we explain the ideas behind the synthesis pathway (from the oscillations of the O2 pressure around an optimum critical value through the role of highly ionized fluxes of film-forming particles resulting from sputtering powers up to 5 kWcm-2 to the optimum geometry of the deposition system), and compare the film properties with those achieved under other conditions.
The film characterization is focused on X-ray diffraction, Raman spectroscopy, electrical resistivity, and especially optical properties studied by spectroscopic ellipsometry and spectrophotometry in a wide range from -30 to 100°C. The properties achieved using unbiased amorphous glass substrates at Tdep = 300°C include e.g. transition temperature (Ttr) of around 50°C, extinction coefficient at 550 nm of around 0.50, modulation of the extinction coefficient at 2000 nm between 0.35 (room temperature) and 3.77 (above Ttr) or modulation of the resistivity between 5.3×10-3 Ωm (room temperature) and 1.5×10-5 Ωm (above Ttr). Crystalline (Si) substrates lead to the VO2 crystallinity in a wider range of HiPIMS and RGFC parameters, allowing one not only to further decrease Tdep to 250°C, but also, in parallel, to optimize the elemental composition even further and to achieve an extremely low (for VO2) extinction coefficient at 550 nm of around 0.10.
The results are important for the design of pathways for the preparation of thermochromic films under industry-friendly conditions, and, in turn, dramatically increase the application potential of these films.
 J. Houska et al., Appl. Surf. Sci., in print, dx.doi.org/10.1016/j.apsusc.2016.10.084
8:00 PM - PM01.04.03
Gallium Nitride (GaN) and Indium Gallium Nitride (InGaN) Formation at Room Temperature Using Neutral Beam Enhanced Atomic Layer Deposition
Yoshiyuki Kikuchi 1 , Seiji Samukawa 2 Show Abstract
1 , Tokyo Electron Ltd, Nirasaki Japan, 2 , Tohoku University, Sendai Japan
III-nitride semiconductors such as gallium nitride (GaN) and indium gallium nitride (InGaN) alloy are important materials because InGaN provides tunable band gap (Eg) value from 0.7 eV to 3.4 eV by the In concentration of InxGa(1-x)N. For this reason, InGaN is focused on its application in green light-emitting diodes (LEDs). The In concentration is required to be 0.5 or more to obtain Eg of 2.5 eV or less. However, green LEDs with In-rich InGaN show low efficiency in comparison with red and blue LEDs. This hurdle is caused by difficulty of growth with decent crystalline quality for In-rich InGaN at growth temperatures of 500 – 800 degree Celsius.Recently, in order to reduce growth temperature with high film quality, plasma assisted atomic layer deposition (PA-ALD) was attempted to GaN or InGaN formation. It achieved to form In-rich InGaN at the growth temperature less than 200 degree Celsius. However, there are still film quality problems such as carbon impurity of a few percent and damage layer by UV light irradiation from plasma. During film formation, a byproduct such as hydrocarbon could be reactivated in plasma, so that some carbon was mixed in film. Therefore, neutral beam technique has been developed to chemical vapor deposition with high film quality at low growth temperature by separation of plasma and substrate.
The aim of this work is to demonstrate GaN and In-rich InxGa(1-x)N formation with In concentration of 0.5 or more on sapphire substrate at room temperature using neutral beam enhanced ALD (NBEALD).
The stepwise sequence of NBEALD process is carried out as 1) dose precursors, 2) purge precursors, 3) irradiate nitriding neutral beam (NB), and 4) purge NB. Trimethylgallium (TMG) and trimethylindium (TMI) were used as gallium and indium metal precursors. The nitriding NB was generated by N2/H2 inductively coupled plasma.
First, NBEALD GaN film was formed on sapphire substrate at room temperature. The Eg of NBEALD GaN was 3.4 eV by analyzing spectroscopic ellipsometry and photoluminescence. The measured values correspond reasonably well with the single crystalline GaN data. The crystalline structure was hexagonal wurtzite GaN phase by analysis of grazing incidence X-ray diffraction patterns. The high resolution TEM image revealed the film consisted of polycrystalline with 5 – 10 nm sizes. The carbon impurity was 0.3 percent by measuring secondary ion mass spectrometry. It was smaller than a few percent of PA-ALD GaN. Next, InGaN formation was demonstrated using TMI and TMG mixed gas. In order to control In concentration, TMI/(TMI+TMG) gas ratio was varied. As a result, the In concentration reached 0.5 and more by increasing the TMI/(TMI+TMG) gas ratio. The Eg was investigated with different In concentration of NBEALD InGaNs by analyzing spectroscopic ellipsometry. It was demonstrated that Eg of NBEALD InGaN decreased from 3 eV to 2 eV when the In concentration increased from 0.6 to 0.85 at room temperature growth.
8:00 PM - PM01.04.04
Formation of Aluminum Thin Films by Atomic Layer Deposition with Hydrogen Plasma
Katherine Hansen 1 , Chen Yang 2 Show Abstract
1 Chemistry, Boston University, Boston, Massachusetts, United States, 2 ECE, Boston University, Boston, Massachusetts, United States
Uniform, conformal thin films, especially pure metals, can be utilized in a variety of applications such as semiconductor microelectronics, displays, optical filters, magnetic storage, and catalysis. An ideal method for producing such films would be atomic layer deposition (ALD) where the self-limiting surface reactions of the precursors result in monolayer deposition. Current aluminum ALD processes utilize the precursors of trimethyl aluminum (TMA) as the aluminum source and hydrogen plasma as a reducing agent. However, these methods do not fully separate the two surface reactions, a key advantage of ALD processes losing thickness control. The current aluminum ALD methods either have no cycling at all, or rely on first reacting the TMA with hydrogen in the gas phase producing mainly AlH3 as the actual precursor as well as a carbon contaminant that requires a specialized buffer line to prevent contamination, making the process not feasible in systems without such a line.
To address these limitations and create a more universal process, we present a process where the hydrogen plasma acts as a reducing agent for the precursor trimethylaluminum (TMA) to create aluminum thin films on electron donating substrates. The films properties were analyzed using high resolution transmission electron microscopy, atomic force microscopy, and x-ray photoemission spectroscopy. The growth rate of the deposition was saturated at 0.04511 nm/ cycle as determined by X-ray reflectivity (XRR). Repeating the reaction cycle led to controlled layer-by-layer growth and precise thickness control. The root-mean-square thickness variation of a film deposited in 400 cycles (~18 nm) was found to be 0.1436 nm. ALD films also had good step coverage on high aspect ratio nanowires.
8:00 PM - PM01.04.05
Plasma Polymerized Coatings as Primer to Increase Corrosion Resistance
Yang Zhou 1 , Qixin Zhou 2 , Ali Dhinojwala 1 , Mark Foster 1 Show Abstract
1 Polymer Science, University of Akron, Akron, Ohio, United States, 2 Chemical and Biomolecular Engineering, University of Akron, Akron, Ohio, United States
Plasma polymerized films have potential as corrosion resistance coatings. Compared to conventional polymer coatings, plasma polymerized coatings are highly crosslinked and have good adhesion to substrates. In addition, plasma enhanced chemical vapor deposition (PECVD) is a non-solvent process which can reduce damage to the environment by decreasing the emission of VOCs. While past research has focused on the properties of comparatively thick plasma polymerized (pp) films and of pp films used alone to protect surfaces, we are investigating use of a thin plasma polymerized coating as a primer to increase corrosion resistance. Even a plasma polymerized coating with a thickness on the nanometer scale slows water penetration and increases the adhesion between the metal and a polyurethane (PU) top coat. Also, the plasma polymerized coating replaces the chromium based conversion coating, which is a known health hazard.
Plasma polymerized coatings with the monomer hexamethyldisiloxane (HMDSO) have been recognized as good candidates for protective coatings on metals and other substrates. This monomer has been used due to the flexibility of the Si–O–Si bond in the backbone and for the resistance of polysiloxane films to water permeation. Also, it is believed that chemical bonds are created at the interface between the plasma polymerized coating and the metal surface, enhancing the interfacial adhesion.
Plasma polymerized (pp) HMDSO coatings were deposited on Al substrates in a low pressure, radio frequency powered reactor. The pp-HMDSO coatings are hydrophobic and highly crosslinked. Electrochemical impedance spectroscopy (EIS) measurements showed that using a thin pp-HMDSO coating as a primer under a PU top coat can increase the corrosion resistance by a factor of 10 times over that for a PU top coat directly on the Al coupon. This is consistent with nanoscale characterization with Neutron Reflectivity and Sum Frequency Generation Spectroscopy that shows very slow water penetration through a pp-HMDSO coating.
Pull-off adhesion measurements reveal that while the hydrophobic pp-HMDSO coating adheres well to the metal, it adheres poorly to the top coat. Adhesion to the top coat can be improved either by modifying with nitrogen plasma the surface of the pp-HMDSO coating or by depositing a very thin layer of hydrophilic pp-maleic anhydride (ppMA) on top of the pp-HMDSO layer.
8:00 PM - PM01.04.06
Reduction of Threading Dislocation Density in InN Film Grown with In Situ Surface Reformation by Radio-Frequency Plasma-Excited Molecular Beam Epitaxy
Faizulsalihin Bin Abas 1 , Ryoichi Fujita 1 , Shinichiro Mouri 1 , Tsutomu Araki 1 , Yasushi Nanishi 1 Show Abstract
1 , Ritsumeikan University, Kusatsu Japan
InN which has the smallest direct-bandgap energy and the largest mobility among III nitride semiconductors is expected to be a very promising material for future electronic and optoelectronic devices. Up to present, almost all InN thin films were grown on foreign substrates. As a result, threading dislocation density of the hetero-epitaxial InN layers has been extremely high. These threading dislocations contribute to high residual carrier concentration and cause deterioration of mobility and device performance . Therefore, advanced technologies are indispensable in order to reduce the dislocations and improve the crystalline quality of InN film. Hitherto, nanocolumns growth  and selective-area lateral growth  have been reported as successful methods to reduce threading dislocation in InN. Our group has previously succeeded in growth of InN film with lower density of threading dislocation on micro-facetted InN template wet etched by KOH .
In this presentation, we report an idea of growth of In-polar InN with in-situ surface reformation by radical beam irradiation on MOCVD-grown (0001) GaN/sapphire substrate using radio-frequency plasma-excited molecular beam epitaxy (RF-MBE). After thermal cleaning at 750 °C for 10 min, the growth consists of several steps: (1) growth of a thin GaN layer at 650 °C for 3 min; (2) growth of InN template at 435 °C for 60 min; (3) N radical beam irradiation on the InN template at 435 °C with a plasma power of 200 W for 60 min; (4) finally, re-growth of InN film on the irradiated template at 435 °C for 60 min. Droplet elimination by radical beam irradiation (DERI) method  was utilized in the growth of InN templates and the re-growth of InN films. TEM specimens for cross-sectional observation were prepared by focused ion beam etching and observed with a JEOL2010 TEM operated at 200 kV.
From transmission electron microscopy observation, it was confirmed that the edge dislocations in InN grown on the irradiated InN template bent and merged at several places along the regrowth interface. Moreover, the threading dislocation density reduces by an order of magnitude from about 2×1010 cm-2 to 6×109 cm-2 in some regions. Based on the results, we propose that regrowth of InN on irradiated InN template by radio-frequency plasma-excited molecular beam epitaxy might be an effective way to obtain high-quality InN film. Further work has to be done to understand the driving force of dislocation bending and to achieve further reduction of dislocation density.
This work was supported by JSPS KAKENHI Grant Number JP16H03860, JP16H06415, and JP15H03559.
 X. Q. Wang et al., Appl. Phys. Lett. 90, 1 (2007).
 S. Harui et al., Jpn. J. Appl. Phys. 47, 5330 (2008).
 J. Kamimura et al., Appl. Phys. Lett. 97, 141913 (2010).
 D. Muto et al., Phys. Status Solidi (a) 203, 1691 (2006).
 T. Yamaguchi and Y. Nanishi, Appl. Phys. Express, 2, 051001 (2009).
8:00 PM - PM01.04.07
Plasma Processing of Colloidal Nanocrystal Superlattices—A Strategy for Materials Design
Santosh Shaw 1 , Tiago Silva 2 , Jonathan Bobbitt 1 , Cleber Rodrigues 2 , Fabian Naab 3 , Xinchun Tian 1 , Pratyasha Mohapatra 1 , Julia Chang 1 , Emily Smith 1 , Ludovico Cademartiri 1 Show Abstract
1 , Iowa State University, Ames, Iowa, United States, 2 Institute of Physics, University of São Paulo State–UNESP, Sao Paulo Brazil, 3 Michigan Ion Beam Laboratory, University of Michigan–Ann Arbor, Ann Arbor, Michigan, United States
We will discuss recent work in our laboratory that has focused on the processing of colloidal nanocrystal assemblies by plasmas. Plasmas are exceedingly attractive for this purpouse because (i) they allow for the complete removal of the organic fraction from these arrays, therefore converting them into all-inorganic materials, (ii) their low temperature preserves the nanoscale features of the building blocks, (iii) their chemical makeup allows for the chemical tuning of interfaces into these materials. The combination of the building block design by nanocrystal chemistry with plasma processing is gradually enabling the design of materials with completely controlled microstructure and properties.
We will describe our work to determine the extent and kinetics (and therefore, the rate limiting processes) of ligand removal, the use of non-oxidizing plasmas for the removal of ligands, the comparison with calcination, the use of plasma composition to tune the composition of the particles, and the use of this approach to produce mesoporous materials for catalysis.
8:00 PM - PM01.04.08
Atmospheric-Pressure Plasma Jet Processed PtZn Counter Electrodes for Dye-Sensitized Solar Cells
Chia-Chun Lee 1 , I-Chun Cheng 2 , Cheng-Che Hsu 3 , Jian-Zhang Chen 1 Show Abstract
1 Graduate Institute of Applied Mechanics, National Taiwan University, Taipei city Taiwan, 2 Department of Electrical Engineering and Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei City Taiwan, 3 Department of Chemical Engineering, National Taiwan University, Taipei city Taiwan
We use a nitrogen dc-pulse atmospheric pressure plasma jet (APPJ) to fabricate bimetallic PtZn counter electrodes (CEs) of dye-sensitized solar cells (DSSCs). A mixture solution consisting of chloroplatinic acid and zinc acetate is spun on fluorine-doped tin oxide (FTO) glass substrate and then calcined by APPJ. The efficiency of DSSC increases rapidly with the processing time. Within 15 s processing time, the efficiency is already comparable to that of DSSC with Pt CE calcined by conventional furnace for 15 min. The rapid processing capability of nitrogen dc-pulse APPJ is attributed to the synergetic effect of the reactive plasma species and heat. As indicated by the experimental results of scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), PtZn nanoparticles reduced by nitrogen APPJ are well-distributed on the FTO glass substrates. Electrochemical impedance spectroscopy (EIS) and Tafel measurement indicate low charge transfer resistance (Rct) and high exchange current density (J0) in DSSCs with good efficiency. The best cell efficiency is achieved at an APPJ processing time of 60 s. Our results suggest that nitrogen dc-pulse APPJ is an efficient tool for fabricating bimetallic PtZn nanoparticles on FTO glass substrates that can be used as the CEs of DSSCs.
8:00 PM - PM01.04.09
Improved Performance of a Polyaniline/Reduce Graphene Oxide Supercapacitor by Atmospheric-Pressure-Plasma-Jet Surface Treatment on Carbon Cloth
Hung-Hua Chien 1 , I-Chun Cheng 2 , Cheng-Che Hsu 3 , Jian-Zhang Chen 1 Show Abstract
1 Graduate Institute of Applied Mechanics, National Taiwan University, Taipei City Taiwan, 2 Department of Electrical Engineering and Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei City Taiwan, 3 Department of Chemical Engineering, National Taiwan University, Taipei City Taiwan
We fabricate flexible polyvinyl alcohol (PVA)/sulfuric acid (H2SO4) gel-electrolyte supercapacitor on polyaniline (PANI)/reduced graphene oxide (rGO) nanocomposite coated carbon cloth. Prior to the PANI/rGO coating, carbon cloth is treated by a nitrogen dc-pulse atmospheric pressure plasma jet (APPJ) in scanning mode. The carbon cloth originally exhibits a water contact angle of ~140°; after APPJ treatment, the surface becomes highly hydrophilic and the testing water droplet completely penetrates into the carbon cloth. X-ray photoelectron spectroscopy (XPS) indicates nitrogen doping introduced to the carbon cloth by the nitrogen APPJ treatment. The PANI/rGO supercapacitor made with APPJ-treated carbon cloth shows an excellent specific capacitance of 580.2 F/g (evaluated by cyclic voltammetry under a potential scan rate of 2 mV/s), in comparison to 315.0 F/g without APPJ treatment. Under bending with a bending radius of 0.75 cm, the supercapacitor still possesses a specific capacitance of 511.7 F/g, indicating good supercapacitive functionality under bending condition. After a 1000-cycle cycling stability test, the capacitance retention rate is ~85 %. Our experimental results indicate that nitrogen dc-pulse APPJ treatment on carbon cloth is an efficient method to improve the supercapacitance performance of a flexible PANI/rGO supercapacitor.
8:00 PM - PM01.04.10
Development of a Needle Type Electrostatic Precipitator for Airborne Fine Particle Removal
Ching-Yu Wang 1 , Cheng-Che Hsu 1 Show Abstract
1 Department of Chemical Engineering, National Taiwan University, Taipei Taiwan
A needle type electrostatic precipitator (ESP) operated in air is developed for removing particulates in the air. The ESP consists of a ground electrode and a needle-type electrode with a high radius of curvature driven by high voltage. Particle detection devices are integrated with this ESP. A corona discharge is generated near the high-voltage electrode tip with an applied voltage of 8~20 kV DC with either positive or negative polarities. A fine particulate sensor (PMS3003, Plantower) and a home-made light scattering system are used to monitor the absolute (<1400 ug/m3) and relative particulate concentrations, respectively. The light scattering system allows for monitoring spatially- and temporally-resolved particulate concentration. This ESP has been tested in a 700-cm3 cubic volume and in a tubular system 60 cm in length and 6 cm in diameter. At -11 kV DC, particulate concentration can be reduced from 900 to below 10 ug/m3 within 20 secs in the cubic system. In the tubular system, the particular is removed in the location within 30 cm away from the needle electrode. The particle removing efficiency increases with the applied voltage and no observable difference is observed for different polarities. The ESP driven with high voltage pulses are also tested with the goal of understanding the temporally-resolved particulate concentration change upon on and off of the high voltage.
Funding support: 103-2221-E-002-184-MY3, MOST, Taiwan
8:00 PM - PM01.04.11
The Development of a Cellphone-Based Spectrometer for Acquisition of Plasma Optical Emission Spectroscopy
Qi-Ming Jian 1 , Po-Wei Yeh 1 , Cheng-Che Hsu 1 Show Abstract
1 Department of Chemical Engineering, National Taiwan University, Taipei Taiwan
This work presented the development of a cellphone-based spectrometer (CBS) for acquisition of plasma optical emission. The homemade CBS contains a slit, a grating, and utilizes the camera of a cellphone for spectra acquisition. The main structure of this device, a 5.0×2×7.8 cm3 cuboid, is constructed using a 3D-printer. The width of the slit is 40-50 µm and the grating with 500 and 1000 lines/mm are used. Due to the limitation of the cellphone camera, this CBS is able to perform spectral analysis with the wavelengths from 400 to 700 nm. The full width at half maximum of this CBS is well below 10 nm, which is comparable with commercial compact spectrometers. We then use this CBS to acquire optical emission emanating from plasmas. In a pin-to-water surface microplasma generation device using Na-containing salt solution as the water electrode, the Na emission at 588nm is clearly identified using this CBS. We also used this CBS to acquire optical emission emanating from a dielectric-barrier-discharge-type microplasma generation device ignited in several different ambient. It is shown that the ambient can be clearly discriminated by the emission acquired using this CBS. We will further discuss how to efficiently convert the cellphone imgages to useful spectra, and how the design of the CBS influences the sensitivity of the CBS.
Funding support: 103-2221-E-002-184-MY3, MOST, Taiwan
8:00 PM - PM01.04.13
A Deposition Method of Functionalized Polymeric Multilayers for Fiber Electronics
Jin Yong Lee 1 , Dong-guk Cho 2 , Seunghun Hong 2 , Woong-Ryeol Yu 1 Show Abstract
1 Material Science and Engineering, Seoul National University, Seoul Korea (the Republic of), 2 Physics and Astronomy, Seoul National University, Seoul Korea (the Republic of)
Demands on flexible and soft electronics have increased considerably for wearable devices in these days. For wearable electronics, fiber-based structures are highly desired due to their light-weight, low-cost, and flexibility. With advances in nanotechnology, it has become possible to build electronic devices directly on or within single microfiber with a diameter of tens of microns. However, it is still challenging to impart an electronic function to three-dimensional fiber assemblies with high deformability. To address this, we have developed plasma enhanced chemical vapor deposition (PECVD) system to uniformly deposit thin organic films (for insulation or semi-insulation) on microfibers and their three-dimensional fiber assemblies. PECVD is one of mature technology for in-situ polymerization of organic thin film on the substrate by gas phase reaction. In this research, defect-free insulation films were coated on single microfiber by PECVD system using organosilicon materials such as hexamethyldisiloxane. Controlling process time, microfibers coated by thin insulation films in various thickness were manufactured. As for fibers, wet-spun graphene, CNT-directly-spun, and aluminum fibers were used to investigate the effect of the surface roughness on uniformity and properties of the coated films. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were used to investigate the chemical structure of the thin film, revealing that Si-O and Si-C chemical bondings were formed as expected. The electrical properties of the thin film were measured with a Keithley 4200-SCS. Aluminum fibers with the thin film in sub-micron thick, for example, showed a breakdown voltage of 0.1 MV/cm, demonstrating that the thin film coated on microfibers is an actual insulator. Finally, another organic thin film was also deposited on the microfibers with insulation thin film by changing source gas (e.g., parylene precursors). The multilayer structure was investigated using energy dispersive X-ray spectroscopy analysis and scanning electron microscopy images. To obtain more promising results, the homogeneous deposition on microfibers and the effect of multilayer coating on electrical properties are under investigation and are presented at the conference.
8:00 PM - PM01.04.14
Characteristic of Germanium Metal-Oxide-Semiconductor Capacitors Directly Integrated on Silicon Using Low-Temperature Process
Ghada Dushaq 1 , Mahmoud Rasras 1 , Ammar Nayfeh 1 Show Abstract
1 , Masdar Institute, Abu Dhabi United Arab Emirates
In order to address the high demand for CMOS scaling, in the recent years, novel structures and new materials are being introduced at a rapid pace to the silicon industry. It is very critical for nanoscale devices such as (FinFETs) and nanowire FETs (NW-FETs) to employ channel materials with high electron and hole mobility. Germanium with its high intrinsic electron and hole mobility is considered one of those materials. However, epitaxial growth of Ge on Si is usually performed at a high temperature > 600 C. The high-temperature processes used for direct growth of Ge on Si causes a plethora of problems in the fabricated films, in addition, they are hardly compatible with standard Si technology. Being able to achieve high-quality Ge-on-Si layers at low cost and with a low thermal budget is a main concern in Ge-based devices. Several techniques for fabricating and optimizing the direct growth of Ge on Si have been reported previously. However, temperatures as high as 650 C were used in performing the epitaxial deposition.
The goal of this work is to demonstrate Ge MOS capacitors integrated on Si based on low-temperature growth using RF-PECVD. In addition, the correlation between the electrical and structural properties of the integrated Ge films and its effect on the MOSCAP performance is investigated. To achieve a high-quality Ge layer, a pre-growth cleaning process of Si wafer is performed using diluted hydrofluoric acid (HF) 1:10 solution. After being cleaned, the wafer is loaded immediately to a load lock of an Oxford Instrument System 100 PECVD activated by 13.56 MHz radio frequency signal. The undoped Ge film was grown using the two-step approach. Prior to MOSCAPs fabrication, the Ge/Si wafers were cleaned by dipping the samples into diluted HF (1:10) solution at room ambient, followed by a rinse and drain in deionized water, and subsequently dried by N2. A high-κ dielectric (Al2O3) with a thickness of ~9 nm was deposited by atomic layer deposition (ALD) at a temperature of 300 C. Finally, a 50nm Ti/ 250nm Al film was deposited by e-beam evaporation through a shadow mask to define the gates. The electrical characteristics of 9 nm Al2O3/i-Ge/Si MOSCAPs exhibit n-type (p-channel) behavior and normal high-frequency Capacitance–Voltage (C-V) responses. In addition to C-V measurements, the gate leakage (Ig) vs applied voltage (V) is measured, where the I-V curve indicated a gate leakage current of ~10μA at 1V (1.1MV/cm). The Ge/high-κ interface trap density vs. surface potential is extracted with a peak value of ~ 1x1012 eV-1 cm-2. Study of the post-annealed Ge layers at different temperatures in H2 and N2 gas ambient revealed an improved electrical and transport properties of films treated at T<600 C. In the context of those findings, the low-temperature processing of Ge MOSCAPs on Si is a promising technique for future high-performance p-channel MOSFET devices in a CMOS and 3D design.
8:00 PM - PM01.04.15
Synthesis of Cd-Ag Nanostructures by Nanosecond-Pulsed Discharges in Liquid Nitrogen
Mahmoud Trad 1 , Alexandre Nomine 1 , Jaafar Ghanbaja 1 , Cédric Noël 1 , Hui Ying Yang 3 , Malek Tabbal 2 , Thierry Belmonte 1 Show Abstract
1 , Institut Jean Lamour, CNRS, Université de Lorraine, Nancy France, 3 Pillar of Engineering Product Development, Singapore University of Technology and Design, Singapore Singapore, 2 Department of Physics, American University of Beirut, Beirut Lebanon
Nanomaterials synthesized by plasmas in liquids have many applications in nanoscience . Silver electric contacts incorporating 10 to 15 per cent cadmium or cadmium oxide are useful in many heavy duty electrical applications such as relays, switches and thermostats. The presence of cadmium gives some degree of arc-quenching and improves resistance to material transfer and electric erosion.
Recently, hollow nanostructures of inorganic materials have attracted great research attention because they exhibit a lower density, higher surface area, and distinct optical property, and in most cases, have improved performances . Original cadmium oxide structures can be grown by electrical discharges in liquid nitrogen. Indeed, contrary to other metallic nanoparticles synthesized by the same process, nanoparticles self-assemble to give hollow micrometric cubes that transform into bunches of nanowires when the applied voltage increases.
With a nanosecond-pulsed power generator, discharges are created by applying a pulsed high-voltage (10kV – 500 ns – 3 Hz) between one cadmium and one silver electrode immersed in liquid nitrogen. The structure of the nano-objects thus synthesized, as well as their composition, is analyzed by transmission electron microscopy, micro-EDX analyses and electron-energy loss spectroscopy. As the Cd-Ag exhibits a lot of intermetallic electron phases like AgCd or Ag2Cd3, the composition of nano-objects is a key element to better understand alloying mechanism in this kind of discharge.
The French ANR funding agency is gratefully acknowledged for the financial support to this work within the framework of the CEENEMA project.
 Graham W and Stalder K 2011 Plasmas in liquids and some of their applications in nanoscience J. Phys. D: Appl. Phys. 44 174037.
 Yu H, Wang D and Han MY 2007 Top-down solid-phase fabrication of nanoporous cadmium oxide architectures J. Amer. Chem. Soc. 129 2333.
8:00 PM - PM01.04.16
Enhanced Positive Bias Stress Stability of Polymer Co-Sputtered Indium-Gallium-Zinc Oxide Thin-Film Transistors
Jae Won Na 1 , Mohammad Khojah 2 , Hyun Jae Kim 1 Show Abstract
1 School of Electrical and Electronic Engineering, Yonsei University, Seoul Korea (the Republic of), 2 Department of Electrical Engineering, Columbia University, New York, New York, United States
Amorphous oxide semiconductors (AOSs) have been researched as a promising active layer material for display backplanes due to their superior electrical characteristics compared with conventional amorphous Si. Especially, indium-gallium-zinc (IGZO) based thin film transistors (TFTs) exhibit many advantages in terms of electron mobility, transparency for visible light, and uniformity over large area fabrication. However, IGZO TFTs have critical instability issues against various stress conditions such as illumination, bias, current, and temperature. One of the most critical problems is the instability from the adsorption of ambient oxygen species (O2) on the back channel of IGZO TFTs, because the adsorbed oxygen species (O2) can trap electrons. Therefore, positive shift of threshold voltage (Vth) occurred under positive bias stress (PBS). A number of reports have proposed methods to enhance the stability of IGZO TFTs, including high-pressure annealing, plasma treatment, and UV irradiation on the active layer. However, these methods require additional process steps which add cost and complexity to the TFT fabrication process. Here, we propose a new material, polymer co-sputtered IGZO (P:IGZO) made by RF magnetron co-sputtering process of polymer and IGZO. Without additional complex processes, the P:IGZO TFT showed improved PBS stability compared to conventional IGZO TFT. As a result, positive shifts of the Vth under PBS test of a IGZO TFT and a P:IGZO TFT are 5.83 and 2.97 V, respectively. The PBS test was conducted at VGS = 20 V and VDS =0.1 V for 10,000s in the air. The incorporation of polymer in IGZO did not deteriorate the electrical performances compared to conventional IGZO TFT: mobility, on/off ratio, and subthreshold swing (S.S) maintained similar level from 12.19 to 12.23 cm2/Vs, from 8.77x108 to 8.31x107, and from 0.38 to 0.38, respectively. Consequently, the incorporation of polymer in IGZO could enhance PBS stability without degrading the electrical performances.
8:00 PM - PM01.04.17
Dry Etching of Aluminum Hard Etch Mask in Cl2 Plasma for a Residue Free Polyimide Etch
Shivani Joshi 3 1 , Angel Savov 3 1 , Salman Shafqat 2 , Ronald Dekker 1 3 Show Abstract
3 , Delft University of Technology , Delft Netherlands, 1 , Philips Research, Eindhoven Netherlands, 2 , Eindhoven University of Technology , Eindhoven Netherlands
Polyimides (PI) are thermosetting ring chain polymers comprising of repeating chains of imide monomers. They are used as sacrificial layers, structural layers, isolation layers and as substrate material in flexible/ stretchable electronic circuits due to their outstanding properties such as high thermal stability and mechanical strength. Patterning of the PI can be achieved by using either a resist mask or a hard-etch mask. The plasma chemistry used for the etching of PI consists of oxygen radicals which break the unsaturated groups within the chemical structure of the polyimide. Since resist mask gets eroded in the etch chemistry of PI, an alternative of hard etch mask has been adopted in the microfabrication industry. After etching of the polyimide using an Aluminum (Al) metal mask, residues on the etched areas were observed. These residues can lead to micro masking of the underlying layer, cause contamination and also adversely affect the performance of a device. In this paper we investigate the origin/nature of these residues and provide solutions compatible with the microfabrication of PI-based electronics.
To investigate the origin of these residues short loop experiments are prepared. Silicon (6- inch) wafers are coated with 1 µm of plasma enhanced chemical vapor deposited (PECVD) SiO2. The wafers are spin coated with PI (5.2 µm) and cured, next they are sputtered with 200 nm Al. For a proper adhesion of the metal mask (Al) to the PI, the polymer surface is exposed to a short Ar+ ion sputter etch. The Al mask is next patterned by wet etching. Variations in surface treatment of the PI and etching of Al were made in different samples. However, in all the samples the PI is dry etched in O2 plasma for 6 mins. The samples are investigated by means of Scanning Electron Microscopy in combination with X-ray Microanalysis (SEM/EDX). Additionally EDX spectra and element-mappings were recorded using the Oxford Xmax80 EDX system. Raman spectra of the residues were recorded with 514 nm excitation.
Presence of Al in the residues after analysis was detected. The surface roughness of the PI created after Ar+ ion sputtering is speculated to encompass Al inclusions within the roughened PI grooves. The metal inclusions in the grooves do not get etched in the Al wet etch as the PI is hydrophobic in nature, making wetting of the grooves difficult. In order to support this hypothesis, the metal mask is dry etched in a Cl2 chemistry plasma instead of wet etchant. An over etch time of 15% is used to ensure the removal of the entrapped Al in the roughened PI, this does not affect the underlying PI layer. This slight over etch is enough to erode the top layer of the PI and remove the metal inclusions. PI is etched in exactly the same way as in the previous experiments and the surface is inspected in the SEM. SEM analysis showed no presence of residues on the surface, confirming the hypothesis and providing a one-step dry etch solution.
8:00 PM - PM01.04.19
Plasma Synthesis of GaSb Nanocrystals for Bioimaging in the Short Wave Infrared (SWIR)
Necip Uner 1 , Elijah Thimsen 1 Show Abstract
1 , Washington University in St. Louis, Saint Louis, Missouri, United States
Biological tissue exhibits higher transparency and lower scattering in the short wave infrared (SWIR, 1000 to 2000 nm) spectral region when compared to the visible and near infrared. Use of the SWIR for deep tissue imaging has been difficult due to the lack of photoluminescent materials that have high brightness and high quantum efficiency in that spectral region. Photophysics in the SWIR are different when compared to the visible and near infrared. Energetic coupling to overtones of molecular vibrational modes (e.g. O-H or C-H) in surface ligands and the surrounding matrix open facile nonradiative recombination pathways for excitons. Quantum dots of e.g. PbS(e) and InAs have demonstrated the highest quantum efficiency in the SWIR, but only approximately 10%. These materials require strong quantum confinement to shift the bandgap into the SWIR. In such a confined state, the exciton has a strong interaction with the nanocrystal surface, which exacerbates vibrational quenching by ligands and the surrounding matrix. Since the energy transfer is strongly distance-dependent, the hypothesis is that vibrational quenching can be ameliorated by using nanocrystal emitters that are not so strongly confined. GaSb is a semiconductor that has a direct bandgap in the bulk of 0.75 eV (1660 nm) and a Bohr exciton radius of approximately 10 nm. Nanocrystals of GaSb could be used for photoluminescence in the SWIR with little or no quantum confinement, thereby potentially alleviating vibrational quenching. Moreover, GaSb nanocrystals may have higher brightness when compared to PbS(e) and InAs, since larger nanocrystal size can be used while maintaining emission in the SWIR, therefore resulting in a higher molar absorptivity on a per particle basis. Furthermore, a synthesis for high quality, free standing, photoluminescent GaSb nanocrystals has, to our knowledge, not been published. In this work, we present a gas-phase method that employs low temperature plasma to synthesize free standing GaSb nanocrystals. We report on the size distribution, controlled in the range from 5 to 30 nm diameter, as well as characterization of photoluminescence.
8:00 PM - PM01.04.20
Investigated the Hydrophobic Recovery of RGP Contact Lens Treated with Argon Surface Plasma by Storing in the Different Environment
Wen-Pin Lin 1 , Yi-Zeng Sun 1 , Meng-Jiy Wang 1 Show Abstract
1 Chemical Engineering, National Taiwan University of Science and Technology, Taipei Taiwan
Rigid gas permeable (RGP) contact lenses are composed mainly of silicone methacrylate (SMA) or fluorosilicone acrylate (FSA), and polymethyl methacrylate (PMMA). RGP contact lens can correct different degree of ametropia in an effective manner. Orthokeratology lens (OK lens) is one type of RGP contact lens with reverse geometric design and can specifically reduce myopia without requiring surgery. The correction of myopia in children with OK lens allows to improve the visual acuity satisfactory and to delay the increase of myopia .
The surface of RGP contact lens is generally hydrophobic that tear cannot complete spread over the surface of lens during blinks that resulted in discomfort [2-3]. Low temperature plasma is one of the most commonly applied methods to increase the surface hydrophilicity of lens. However, plasma treated lens suffer usually from aging effects that the hydrophobicity recovered within certain period of time . In addition, the regulation from 3- and 9-o'clock staining from contact lens set the requirements RGP material to be clean with well wetting surface . The deposition lipids on RGP contact lenses can be due to the equilibrium of surface hydrophobicity and hydrophilicity of materials .
In this study, the wettability on the contact lens treated by argon plasma was investigated by water contact angle measurements to optimize the storage conditions (temperature and environment) and plasma treatment parameters (power, flow rate, pressure as well as treatment time). Additionally, the influences of storage time on lens surface wettability were evaluated for 30 days. The correlations between hydrophobicity recovery and the plasma parameters showed that optimized plasma treatment and would be 80 W argon plasma with 120 seconds treatment time, by using 10 sccm flow rate under 100 mTorr.
 Shin, H.S., et al., Surface Modification of Rigid Gas Permeable RGP contact lens Treated by Using a Low-Temperature Plasma in Air. Journal of the Korean Physical Society, 55(6): p. 2436-2440, (2009).
 Rankin BF, Trager SF. Wetting of contact lenses. Am J Optom Arch Acad Optom, 47(9): p. 698 –702, (1970).
 Seidner L, Sharp MS. Surface deposits with gas permeable lenses. CL Forum. 9(Oct): p. 55 – 65, (1984).
 Lebow K. Peripheral corneal staining. In: Silbert JA, ed. Anterior Segment Complications of RGP contact lens Wear. New York: Churchill Livingstone, p. 59–90, (1994)
 Bontempo, A.R. and J. Rapp, Lipid deposits on hydrophilic and rigid gas permeable contact lenses. Clao j, 20(4): p. 242-5, (1994).
8:00 PM - PM01.04.21
The Development of a Portable High Voltage Module for Microplasma Generation Devices
Ting Kai Yuan 1 , Cheng-Che Hsu 1 Show Abstract
1 , National Taiwan University, Taipei Taiwan
This work presents the development of portable high voltage modules for the use in driving microplasma generation devices. The high voltage module consists of a DC power source, an oscillating circuit connecting to a transformer with high turns ratio, and followed by a voltage doubler circuit to provide DC upto 3 kV. Modules driven with 5- and 9-V DC sources use transformers with turns ration of 280 and 170, respectively, are developed. These two modules are tested by driving pin-to-surface microplasma generation devices. We characterize and compare the plasma driven by both modules by analyzing plasma optical emission, I-V characteristics, and visual appearance. The microplasmas show self-pulsing characteristics when driven by both modules. With 5-V source module using a commercial 5-V cellphone charger as the source, the plasma can be continuously sustained for tens of minutes, which clearly shows the capability using this module for portable microplasma generation devices.
funding support: 103-2221-E-002-184-MY3, MOST, Taiwan
8:00 PM - PM01.04.22
The Design and Development of a Portable Microplasma Generation Device for Detection of Metallic Ions in Aqueous Solutions
Fu-Yu Yang 1 , Cheng-Che Hsu 1 Show Abstract
1 Chemical Engineering, National Taiwan University, Taipei Taiwan
funding support: 103-2221-E-002-184-MY3, MOST, Taiwan
This work presents a simple setup and portable microplasma generation device (MGD) for the detection of metallic ions by optical emission spectrometry. Several devices with different electrode setups have been tested. The first design, features with its simple setup, is a needle-to-water surface electrode system. The second design, with the addition of a capillary tube around the needle electrodeon in the above design , allows for a better confinement of the discharge area and minimization the ambient air interference in the optical emission. The third design uses copper and porous medium soaked with test solution as the electrodes. The plasma can be ignited in ambient air by a homemade high voltage module, which supplied a DC voltage up to 3 kV. With this device, metallic ions in aqueous solutions can be detected by analyzing the plasma emission spectroscopy with a sample amount as small as a few μL. The above designed electrode sets allow for the detection of 200 ppm-Pb ions and trace Na ions (sub-ppm, existed as the impurity in the chemical used). How electrode system design influences the plasma behavior and the detection limit are examined with the goal of quantification of salt solution concentration.
Chi-Chin Wu, U.S. Army Research Laboratory
Cheng-Che Hsu, National Taiwan University
Vasiliki Poenitzsch, Southwest Research Institute
Mohan Sankaran, Case Western Reserve University
Journal of Applied Physics | AIP Publishing
PM01.05: Plasma Processing and Materials
Tuesday AM, November 28, 2017
Sheraton, 3rd Floor, Fairfax B
8:15 AM - *PM01.05.01
Low Temperature Plasmas as Processors of Matter
Elijah Thimsen 1 Show Abstract
1 , Washington University in St. Louis, St. Louis, Missouri, United States
Low temperature plasma (LTP) presents a tremendous opportunity for producing novel configurations of matter. The opportunity stems from the violation of a very simple, yet critical assumption that is made in nearly all of thermodynamics and traditional statistical mechanics: local thermal equilibrium. If one assumes that a system is in local thermal equilibrium, i.e. that the temperatures of different phases and degrees of freedom are nominally the same at the microscopic level, then prediction is possible using the framework of equilibrium thermodynamics. The assumption is reasonable for most conventional material syntheses reactors based on hot-wall, cold-wall, solution phase, flames, and even electrical arcs. However, in low temperature plasma, the assumption is violated to a significant extent. The neutral gas temperature in LTP is often on the order of several hundred Kelvin, while the electrons are extremely hot, with tempearture on the order of ten thousand Kelvin. There is no established thermodynamics framework to describe this reality, and therefore, the limits of LTP for producing novel configurations of matter are unknown. Since the theoretical limits are unknown, it is a time of tremendous opportunity for experimental discovery in the use of LTPs to synthesize novel materials. The interactions at the boundary of an open system that contains an LTP make it possible to alter the configuration of matter that flows through, such that the outlet state is further from equilibrium than the inlet state. Decreases in specific entropy and increases in specific energy are allowed, and may in fact be required if certain conditions are met. In this presentation, I will discuss illustrative examples from our recent work, as well as the works of others, and outline the opportunities and challenges that lay ahead for processing matter into novel configurations using LTP.
8:45 AM - PM01.05.02
Plasma Polymerization of Sacrificial Thin Films in an Inductive Parallel Plate Reactor
Mustafa Karaman 1 , Yunus Yartasi 1 Show Abstract
1 Chemical Engineering, Selçuk University, Konya Turkey
Sacrificial thin films are important types of materials that are required in production of microelectromechanical, microfluidics and optical systems. In order to produce such end products, as-deposited sacrificial film has to be removed to leave behind empty space on the substrate surface. Conventional methods of removal of sacrificial layers require the use of solutions or etchants. Recently, heat-decomposing sacrificial materials have been proposed as an alternative to conventional ones. Poly(cyclohexyl methacrylate) (PCHMA) is a desired sacrificial polymer for many applications because of its hydrophobicity and clean decomposition properties. Although thin films of PCHMA can be formed on different surfaces using either solution based or vapor based techniques, the desired technique should allow for rapid coatings with a high degree of retention of chemical functional groups and the method should be applicable for fragile and geometrically complex substrates. The solvents used in solution based methods are not compatible for most of the fragile substrates and it causes major environmental problems. Plasma enhanced chemical vapor deposition (PECVD) method, on the other hand,is a dry technique that can produce well defined defect free polymeric films on many different substrates with low energy inputs.
In this study thin films of PCHMA were deposited on silicon wafer substrates in an inductive parallel plate PECVD reactor. The 13.56 Mhz radio frequency (RF) plasma was inductively coupled into the reactor by a planar-coil antenna through a quartz window. The reactor was 16 cm in diameter and 15 cm in height. Pressure in the reactor was controlled downstream and maintained at 0.3 torr. The desired substrate temperature was achieved using water cooling. Monomer CHMA was vaporized in jar and metered in to the reactor using a needle valve. The effects of plasma power and substrate temperature on the deposition rate, chemical and morphological properties of deposited films were investigated. In-situ measurement of film deposition rates was achieved using a laser interferometer. High deposition rates (40 nm/min.) were obtained at low plasma powers. FTIR and XPS analyses of the deposits indicated very high retention of functional groups at low applied plasma powers. The as-deposited polymer was found to decompose cleanly upon thermal annealing. The onset of thermal decomposition was at 230°C.
9:00 AM - *PM01.05.03
Plasma Techniques for Incorporation of Biofunctionalities and Plasma Assisted Copolymerization
Meng-Jiy Wang 1 Show Abstract
1 , National Taiwan University of Science and Technology, Taipei Taiwan
Plasma techniques have been applied in surface modification for versatile biological applications including self-cleaning surface, antibacterial filter, and biomaterials. In this study we reported the employment of both low pressure plasma and atmospheric pressure plasma for the deposition of functional thin films and the assisted plasma polymerizations. The plasma deposited thin films containing amine, carboxylic, or ethylene oxide functional characteristics were applied specifically in supporting the proliferation of mammalian cells and enhancement of the fouling resistance. In addition, the mechanism of reactions of the plasma polymerization will be elucidated. For example, that factors that modulated the precursors with similar structure but different saturation degree which result in significant different deposition kinetics will be interpreted. For example, the multilayered plasma polymers with alternative functionalities which showed beneficial qualities due to the charge transfer characteristics will be discussed in detail.
Beside the low pressure plasma, the studies by using atmospheric pressure plasma jet (APPJ) which was applied to deposit inorganic thin films and to assist the polymer grafting will also be discussed. The APPJ allowed depositing thin films containing SiOx and amine functionalities which proved to promote the biocompatibility of various substrates. In addition, APPJ was also applied to graft environmentally responsive polymer on cellulose membrane in a much effective manner that both advantageous characteristics of cellulose and the responsive polymer were clearly revealed.
9:30 AM - *PM01.05.04
Surface Engineering with Plasmas—Processes for the Atomic to Micron Scale
Frank Papa 1 , Victor Bellido-Gonzales 2 , Oihane Hernandez 2 , Joseph Brindley 2 , Dermot Monaghan 3 , Steven Stanley 3 , Ivan Fernandez 4 Show Abstract
1 , Gencoa USA, Akron, Ohio, United States, 2 Research and Development, Gencoa Ltd, Liverpool United Kingdom, 3 , Gencoa Ltd, Liverpool United Kingdom, 4 , Nano4Energy, Madrid Spain
Plasma based technologies are a key to unlocking the potential of surface engineering. Two critical issues are the functionalization of a surface and control over the coating properties which are to be deposited. Enabling technologies need to match the scale of the surface engineering from the atomic to the micron range and need to be eventually scalable to production environments. Plasma sources and magnetron sputtering are two of these enabling technologies. Anode layer and other types of plasma deposition sources can be used for surface functionalization as well as for processes such as Plasma Enhanced ALD and high rate plasma polymerization. By combining plasma source and magnetron technologies coatings can be “functionalized” in order to improve their stimuli induced reactivity and properties (biomedical applications). High Power Impulse Magnetron Sputtering (HIPIMS) in combination with magnetic control of plasmas allows for control over plasma interactions with the substrate, ionization levels and ion energies as well as “self-biasing” of the substrate. By manipulation of these variables, coatings such as hard non-hydrogenated Diamond Like Carbon (DLC) can be deposited on insulating substrates such as glass and polymers. Several examples of processing techniques for current surface engineering applications from the angstrom to micron scale will be discussed as well as the importance of environmental monitoring of the vacuum itself during processing.
10:30 AM - *PM01.05.05
The New Frontier in Plasma Processing of Functionally Enhanced Complex Material Systems
Jane Chang 1 Show Abstract
1 Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, California, United States
The introduction of new and functionally improved materials into silicon based integrated circuits is a major driver to enable the continued down-scaling of circuit density and performance enhancement in analog, logic, and memory devices. The top-down plasma enhanced reactive ion etching has enabled the advances in integrated circuits over the past five decades; however, as more etch-resistive materials are being introduced into these devices with more complex structures and smaller features, atomic level control and precision is needed in selective removal of these materials. These challenges point to the growing needs of identifying and developing viable etch chemicals and processes that are more effective in patterning complex materials and material systems such as multiferroics, magnetic materials and phase change materials.
In this talk, a generalized approach based on combined thermodynamic assessment and kinetic validation is presented to identify and validate the efficacy of various plasma chemistries. Specifically, potential reactions between the dominant vapor phase/condensed species at the surface are considered at various temperatures and reactant partial pressures. The volatility of etch product was determined to aid the selection of viable etch chemistry leading to improved etch rate of reactive ion etching process. Based on the thermodynamic screening, viable chemistries are tested experimentally to corroborate the theoretical prediction. Some of the above mentioned material systems such as magnetic materials used in non-volatile memory devices are used as examples to demonstrate the broad applicability of this approach.
11:00 AM - PM01.05.06
In Situ Nanoscale Characterization of Water Penetration through Plasma Polymerized Coatings
Yang Zhou 1 , Ali Dhinojwala 1 , Mark Foster 1 Show Abstract
1 Department of Polymer Science, University of Akron, Akron, Ohio, United States
Plasma enhanced chemical vapor deposition (PECVD) is a versatile technique to deposit plasma polymerized thin films on various substrates without volatile organic solvents for a wide range of applications including protection of metal against corrosion. Penetration of water to the metal/coating interface is often the first step in the corrosion of coated surfaces. While past research has focused on macroscopic corrosion phenomena, understanding on the nanoscale of some fundamental aspects of the corrosion process at the metal interface is lacking. Gaining nanoscale information on the movement of water and structure of water at the interface are important to understand and design new protective coatings and also predict corrosion failure in a short time. Off specular X-ray measurements have been used to show that the plasma polymerized coatings are conformal to an underlying Al metal substrate with its native oxide, consistent with good coverage of the substrate and minimization of void space at the interface. Neutron reflectivity (NR) and infrared-visible sum frequency generation spectroscopy (SFG) have been used to characterize the water penetration through two plasma polymerized coatings on the nanoscale.
NR can determine the depth profile of a substance near an interface with a resolution of 1-2 nm. To simulate a practical corrosion process, an in situ experiment in which the sample is in the presence of water or water vapor has been used. By replacing H2O with deuterium oxide, D2O, the contrast has been enhanced. X-ray reflectometry (XR) measurements provide complementary information about interfacial roughnesses and changes in thickness upon exposure to water. Such measurements have revealed that the hydrophobic plasma polymerized hexamethyldisiloxane (pp-HDMSO) coating can prevent water penetration, while a hydrophilic plasma polymerized maleic anhydride (pp-MA) coating absorbs water and swells to approximately 1.5 times the dry coating thickness.
SFG measurements have directly probed the water between the coating and a sapphire substrate mimicking the native oxide on Al. These measurement have also shown that a pp-HMDSO coating prevents water penetration to the coating/sapphire interface over the time scales probed. They also reveal the hydrogen-bonded water network that forms at the interface when water penetrates through the pp-MA coating.
11:15 AM - PM01.05.07
Laser Shock Peening of Additively Manufactured Structures
James Nygaard 1 , Adriaan Spierings 2 , Olha Sereda 3 , Massoud Dadras 3 , Kaushik Vaideeswaran 3 Show Abstract
1 , Rutherford Appleton Laboratory, Harwell, Oxford, United Kingdom, 2 , Inspire AG, Swiss Academy of Engineering Sciences, St. Gallen Switzerland, 3 , Centre Suisse d' Electronique et de Microtechnique, Neuchâtel Switzerland
Laser shock peening is a novel surface treatment that can offer improved material performance through the introduction of compressive residual stress, strain hardening and densification of surface material at depths approaching 2mm. The treatment of additively manufactured components using laser shock peening is particularly promising due to the unique flexibility of this laser technique which can help to mitigate tensile stresses developed during the 3D build process and reduce the high levels of porosity often present in poorly consolidated metal powder products.
Commissioning of a new laser shock peening platform has taken place at the Rutherford Appleton Laboratory's Central Laser Facility based on our diode-pumped and cryogenic gas-cooled laser architecture DiPOLE . Nanosecond pulses of infra-red laser light at 10J impinge on the target surface creating energetic plasma shockwaves that penetrate deep into the material surface. Study of this plasma reveals the relationship between individual laser parameters and the resulting shockwave, which can be amplified using confinement methods and ablative coatings to enhance the energy absorption and minimise surface distortion.
A systematic parametric study has been conducted across a range of metallic targets, including selective laser melted 316L stainless steel and wire arc additively manufactured titanium grade Ti6Al4V. Subsurface defects are examined in additively manufactured samples treated with laser shock peening and these results are compared with other consolidation processes such as hot isostatic pressing. Residual stress data is presented, along with microhardness changes and detailed microstructural characterisation of the processed material. Future ideas for optimisation of the laser shock peening technique are discussed that may lead to further improvements in component quality when paired with in-line automated process routes.
 Saumyabrata Banerjee, Klaus Ertel, Paul D. Mason, P. Jonathan Phillips, Mariastefania De Vido, Jodie M. Smith, Thomas J. Butcher, Cristina HernandezGomez, R. Justin S. Greenhalgh, and John L. Collier, “DiPOLE: a 10 J, 10 Hz cryogenic gas cooled multi-slab nanosecond Yb:YAG laser”, Optics Express 23, 15, 2015
11:30 AM - *PM01.05.08
Electron Beam Generated Plasmas—Ultra Cold Sources for Atomic Layer Processing
Scott Walton 1 Show Abstract
1 , U.S. Naval Research Laboratory, Washington, District of Columbia, United States
The advantages of plasma-based materials processing techniques are numerous. The capability to rapidly modify large areas (> 103 cm2) with precision down to a fraction of a micron is one reason plasmas are widely used in the materials and surface engineering communities. With the rapidly evolving demand for new materials and single nanometer-scale architectures across a variety of applications, processing schemes capable of atomic layer precision are a growing requirement. In this respect, some of the limitations of conventional plasma sources are becoming apparent. The lack of control over the flux of species and energy deposition at the surface are examples.
The Naval Research Laboratory (NRL) has developed a processing system based on an electron beam-generated plasma. Unlike conventional discharges produced by electric fields (DC, RF, microwave, etc.), ionization is driven by a high-energy (~ keV) electron beam, an approach that can overcome many of the problems associated with conventional plasma processing systems. Species production via high energy beams, for example, is greatly simplified in comparison to discharges. Importantly, high plasma densities (1010- 1011 cm-3) can be produced in beam-driven plasmas, while the electron temperature typically remains between 0.3 and 1.0 eV. Accordingly, a large but tunable flux of ions can be delivered to substrate surfaces with kinetic energies in the range of 1 to 5 eV, a value comparable to the bond strength in most materials. This provides the potential for engineering both the surface morphology and chemistry with monolayer precision.
An overview of NRL’s research efforts in developing this technology will be presented, with a focus on source development, plasma characterizations, and materials processing. Particular attention will be paid to the unique features and “knobs” available in the system that enable processing with atomic layer precision. Examples will include the processing of graphene and select semiconductor materials, where we take advantage of the unique attributes of electron beam generated plasmas to engineer the surface properties of these materials for applications ranging from sensing to electronics. This work is supported by the Naval Research Laboratory base program.
PM01.06: Plasma Sources and Thin Films
Tuesday PM, November 28, 2017
Sheraton, 3rd Floor, Fairfax B
1:30 PM - *PM01.06.01
Non-Conventional Plasma Sources for Ionized PVD, Hybrid Processes, Plasma Catalysis and Plasma in Liquids
Hana Barankova 1 , Ladislav Bardos 1 Show Abstract
1 , Uppsala University, Uppsala Sweden
Non-equilibrium plasma sources used for film deposition, in surface treatment or for plasma-chemical reactions need to provide stable and reproducible processes in order to achieve desirable properties of films, surfaces and reaction products. High and even tunable activation degree in the plasma is required. Very efficient plasma sources that can be used directly for PVD, PE CVD or for hybrid combination of PVD and PE CVD are hollow cathodes. The paper gives a picture of the development of hollow cathode based plasma sources both for reduced and atmospheric pressures. The linear hollow cathodes in several arrangements for generation of plasma over large areas and suitable for further scale-up are presented. Examples of surface processing and coating by PVD, both by the Hollow Cathode Discharge and Hollow Cathode Arc, are given. A new type of planar magnetron in which the target is coupled with the hollow cathode magnetized by the magnetic field of the magnetron is introduced. Detailed principles of such arrangements are explained. Concepts of Fused Hollow Cathode (FHC), Microwave Antenna (MWA) and Hybrid Hollow Electrode Activated Discharge (H-HEAD) cold atmospheric plasma sources are discussed. A non-equilibrium atmospheric plasma source utilizing the Fused Hollow Cathode can be used for gas conversion and for surface treatment at ambient atmosphere. The plasma source with a coaxial geometry based on the Fused Hollow Cathode (FHC) geometry was used for generation of plasma inside water and ethanol-water mixtures.
2:00 PM - PM01.06.02
Characterization and Enhancement of IR Optical and Tribological Properties of DLC Films Synthesized by RF-PECVD
Vahit Eren Taburoglu 1 , Ilker Yildiz 1 , Ahmet Macit Ozenbas 1 Show Abstract
1 , Orta Dogu Teknik University, Ankara Turkey
This study analyzes the hydrogenated amorphous diamond like carbon (a-DLC) films coated on aluminum substrates by the technique of plasma enhanced chemical vapor deposition (PECVD). In order to obtain the targeted results in terms of optical reflectivity, hardness, elasticity and durability of the film, one should use a well thought combination of thickness, hydrogen content and RF power in design and production stages. Frictional effects, recovery power (ratio of hardness ([H] to Young’s modulus [E]; namely H/E) and restoration power are studied under a continuous predetermined scratching attack to decide on optimum initial coating conditions.
Interferometer measurements showed that increasing thickness increases tension which is due to intrinsic compressive stress and if this tension overwhelms the adhesion force of the film, it can be destructed easily. Furthermore, increasing hydrogen content has the reverse effects on intrinsic compressive stress and decreases it, and but this decrease can also be detrimental to the film. Experiments also show that too much energy (an output of high RF Power in our case) reduces hydrogen content, intrinsic compressive stress and resultantly can also harm on and reduce the life of the film. Reflectance is directly dependent on the film thickness and refractive index. Characterization works show that 2500 nm film thickness and 150 cm3/s H2 flowrates are ideal for maximum reflectance in our case.
Experiments also show that thickness of 2500 nm is ideal for hardness, elasticity and the recovery power (H/E) in our case. Furthermore increasing hydrogen content decreases both hardness and elasticity together, on the other hand the recovery power is not decreased, on the contrary it increases from 0.14 - 0.15 to 0.16. Frictional analysis proves that increasing only thickness adds nothing to friction coefficient and restoration power but avoids having contact with the aluminum surface. Moreover we observed that as the hydrogen content decreases, the total destruction length elongates, so this makes the film more robust.
XPS results show that sp3/sp2 distribution is not uniform throughout the films. On the other hand, it seems that there is a positive correlation between hydrogen content and sp3 fractions. Though non-uniformity, results show that increase in RF power may result a slight increase in sp3 content.
Lastly environmental tests show that since any increase in film thickness also increases total amount of tension, it also decreases the durability of the film considering rated temperature changes. Furthermore, we observed that elasticity is decreased with increasing hydrogen content, hence this decrease in elasticity is another reason to fail in a relatively harsh and unstable environment. Moreover too low or high RF powers cause the similar results with high hydrogen content and make the film more vulnerable to severe environmental conditions.
2:15 PM - PM01.06.03
Chemical Processing of Metal Thin Films by Plasma Assisted Vapor Phase Methods
Lisa Czympiel 1 , Sanjay Mathur 1 , Jennifer Leduc 1 , Alexander Sasinska 1 Show Abstract
1 , University of Cologne, Cologne Germany
Chemical processing of materials has played a crucial role in the development of nanomaterials science and engineering particularly due to the intimate relationship between molecular precursors and composition, microstructure and properties of the resulting materials. Moreover, the potential of precursor-based materials synthesis lies not only in their relatively low decomposition temperature but also more importantly in the application of chemical principles that allow controlling the decomposition mechanism through judicious choice of ligands and co-ligands, for instance to manifest Janus-type reactivity by combining both reactive and stable coordination sites in a single molecular species. Multidentate chelating ligands are especially suited to stabilize metal ions and over the past decade, we have developed a precursor library for the chemical synthesis of nanomaterials.
In recent years the interest in precursors for the formation of metallic films has substantially increased. This work presents the deposition of metallic nickel, cobalt, copper and palladium thin films by plasma assisted Chemical Vapor Deposition (PECVD) and plasma assisted Atomic Layer Deposition (ALD) from air stable and volatile precursors. The new ligand design with its bi- or tridentate bonding to the metal center ensures long-term stability under ambient conditions. Clean and intact thermal evaporation combined with TG/DTA measurements confirmed high volatility and suitability in gas phase processes. The precursors were activated by remote reactive plasma to deposit metallic films which was in the case of Ni, Co and Cu films followed by a subsequent hydrogen plasma treatment of the as-deposited films enhancing film quality and purity through a recrystallization process. XRD and XPS measurements showed a preferential orientation (111) in as prepared films and a low percentage of impurity atoms whereas SEM and AFM imaging revealed smooth and pinhole-free films indicating a successful ALD process. In a detailed study the binding interaction of the first monolayer of the precursor with the surface functional groups of the substrate was investigated by detailed XPS studies to elucidate the chemisorption mechanism. This study highlights the versatile application of plasma activation in gas phase processing methods and its great potential for the formation of metallic thin films on various substrate materials exhibiting also complex surface geometries.
3:00 PM - PM01.06.04
Development of Extended Structure Zone Diagrams for HiPIMS-Deposited Transition Metal-Aluminum-Oxynitride Systems
Lars Banko 1 , Dario Grochla 1 , Stefan Ries 2 , Peter Awakowicz 2 3 , Alfred Ludwig 1 4 Show Abstract
1 Materials Institute, Ruhr-Universität Bochum, Bochum Germany, 2 Institute for Electrical Engineering and Plasma Technology, Ruhr-Universität Bochum, Bochum Germany, 3 Research Department Plasmas with Complex Interactions, Ruhr-Universität Bochum, Bochum Germany, 4 Materials Research Department, Ruhr-Universität Bochum, Bochum Germany
An approach for the development of extended structure zone diagrams is outlined on the example of transition metal (TM) TM-Al-O-N systems. Materials properties such as Young’s modulus, hardness and stress are added to the structure zones to provide criteria for process parameter selection in high power impulse magnetron sputter deposition (HiPIMS).
Al-Cr-O-N materials libraries with a binary composition spread of Al und Cr were deposited in a combinatorial sputter chamber using HiPIMS. An in-house developed step heater was used to deposit 5 binary materials libraries at 5 discrete substrate temperatures (200, 400, 600, 800, 1000°C) in a single deposition. Time- and space-resolved plasma diagnostics were applied to characterize ion energy, ion flux and electron density at sites corresponding to different compositions. Without additional bias, maximum ion energies of 70 eV were measured. The mean ion energy was found to vary between 4.5 and 9 eV, depending on the peak power density of the HiPIMS discharge. Large data sets were created by high-throughput characterization and analyzed to study the effect of composition, temperature, different process parameters and resulting plasma properties on the materials properties. The structure was analyzed regarding phase evolution and texture by XRD and synchrotron diffraction. Micro-cantilever stress sensors were applied to evaluate intrinsic and thermal stresses. The results of this investigation clearly show the influence of plasma properties and growth conditions on nanostructure and morphology and thereby on mechanical properties like residual stress and hardness. Conclusions towards the development of plasma-based extended structure zone diagrams will be drawn.
This work was supported by Deutsche Forschungsgemeinschaft within the Collaborative Research Center SFB-TR 87/2 “Pulsed high power plasmas for the synthesis of nanostructured functional layers.”
3:15 PM - PM01.06.05
Thermoelectric Properties of Platinum Thin Film Grown with Plasma Enhanced Atomic Layer Deposition
Hyo Jin Kim 1 , J Provine 1 , Kirsten Kaplan 1 , Martin Winterkorn 1 , Timothy English 1 , Thomas Kenny 1 Show Abstract
1 Mechanical Engineering, Stanford University, Stanford, California, United States
Bulk platinum has excellent thermal and electric properties that make it an attractive material for temperature and other sensing applications. As ultra-thin films are also required in many applications, there is an unmet need for fabrication methods capable of thermoelectrically stable, ultra-thin platinum films. Platinum thin films can be deposited with traditional thermal Atomic Layer Deposition (t-ALD) and Plasma Enhanced Atomic Layer Deposition (PEALD). PEALD has been shown to address the limitations of t-ALD by shortening the nucleation phase and allowing the process to be less substrate dependent. In this work, 13-14 nm thick platinum films were deposited using PEALD on four different oxide seed layers: Al2O3, TiO2, ZrO2 and SiO2. These seed layers were also deposited with PEALD. The PEALD was performed on an Ultratech/Cambridge Nanotech Fiji system. We compared the nucleation delays, resistivity, temperature coefficient of resistance (TCR), and electrical stability of the platinum thin films formed on each seed layer. The platinum films grown on the three metal oxides have electrical resistivity, TCR, and electrical stability values ranging from 16.6 – 18.1 μΩcm, 2.13*10-3 – 2.31*10-3 1/oC and 4.6 – 5.5 ppm, respectively. Moreover, the full wafer sheet resistances of platinum on these oxides have standard deviations ranging from 0.58 to 0.67. These results indicate that Al2O3, TiO2, and ZrO2 seed layers all yield similar platinum material properties at the wafer-scale in a process compatible with batch fabrication. Thus, the seed layer can be selected to most appropriately fit the application and other fabrication steps. In contrast, platinum grown on the PEALD SiO2 seed layer had pinholes even after 250 cycles, which is not the case for any of the metal oxide seed layers. The presence of these pinholes indicates significantly more nucleation delay on SiO2 than the other oxide seed layers. Additionally, the poor adhesion between platinum and SiO2 prevents integration of this oxide into batch fabrication processes.
3:30 PM - PM01.06.06
Plasma Assisted Low Temperature Electron Beam Deposition of NiO Thin Films for Electro-Optic Applications
M. Burak Cosar 1 , Kerem Cagatay Icli 1 , Ahmet Macit Ozenbas 1 Show Abstract
1 , Orta Dogu Teknik University, Ankara Turkey
This study aims to create high quality nickel oxide (NiO) thin films at low temperature which supply advantage in coating on temperature sensitive substrates. Nickel oxide chunks are evaporated using electron beam source at around 300 nm thicknesses. Depositions are performed at different experimental conditions: oxygen amount, deposition temperature, deposition rate, and plasma assistance. Deposited films are analyzed regarding to structural, optical and electrical aspects. Crystallinity of thin films is determined using X-ray diffraction and highly qualified morphology is observed through scanning electron microscopy (SEM) images. X-ray diffraction and X-ray photoelectron spectroscopy results reveal that the phase formed is nickel oxide with preferred orientation of (111). Non-stoichiometry of NiO thin films increases with increasing oxygen rate and plasma assistance leads to stoichiometric NiO films. Needle, spherical and cuboidal particle formations are seen in SEM images. Grain size, lattice parameter and grain morphology are used to explain the change in optical and electrical properties. Electrical properties for thin films are analyzed using Hall Effect and Ultraviolet photoelectron spectroscopy data. Mobility of the films increases with oxygen flow rate because of enhanced grain size revealed by XRD calculations and SEM images. Plasma assistance dramatically lowers the resistivity to 152 ohm.cm compared to non assisted films possessing on the order of megaohm.cm resistivities. Although this sample has low mobility (0.18 cm2/(V.s)), sheet carrier concentration is too high (1.09E+13 cm-1). This condition is related to denser films with higher crystallinity, which was detected from refractive index spectrum and confirmed by SEM analysis. Transmittance and reflectance measurements are performed to observe the optical properties. Band gap and refractive index are also calculated from these measurements. Absorption at 400-600 nm was observed and it is detected that high oxygen, high deposition temperature and low deposition rate minimizes the absorption. Although low oxygen samples suffer from absorption, it is found that low oxygen samples have higher transmittance at longer wavelengths due to the nature of low optical scattering. Optical band gaps which are found using the tauc plots increase with oxygen amount, temperature and deposition rate. Band structure of the films was investigated by ultraviolet photoelectron spectroscopy measurements. It was seen that Fermi level and valence band minima of the films highly depend on oxygen flow rate and can be engineered by manipulating the flow rate of oxygen and deposition conditions. Valence band edge of the films vary between -5.24 eV and -5.5 eV, which is quite suitable for most organic and metalorganic perovskite based solar devices. These films can also be deposited on flexible substrates due to low temperature deposition conditions.
3:45 PM - *PM01.06.07
Coatings Formed from the Deposition of Metastable Plasma-Activated Adducts versus Impulse Conditions
Michael Miller 1 , Kent Coulter 1 , Ronghua Wei 1 , Vasiliki Poenitzsch 1 Show Abstract
1 , Southwest Research Institute, San Antonio, Texas, United States
Plasma Immersion Ion Deposition (PIID) is a scalable technology being utilized to deposit robust coatings on a wide range of substrates and large structures; for example, we have developed a variant of this technology to coat the internal surface of long (25 m) cylindrical structures. At the heart of PIID lies the confluence of several adjustable parameters which may be used advantageously to achieve a coating with desirable properties. Key among these process parameters are the impulse power waveform (i.e., DC pulse sequence) providing the excitation source for the plasma, the chemical precursors selected for the process, and the corresponding fragment species yielded by the effect of the impulse conditions. The precursor flow rate and pulse sequence of the plasma-generating power source is preferably selected to adjust the population of molecular fragment species derived from the chemical precursors. Such fragments may have a relatively broad range of thermochemical stabilities and lifetimes. In particular, we have found that, through control of impulse conditions and the stoichiometric ratio of the precursors during the coating process, certain fragment species combine to form unique, metastable adducts in the plasma phase.
The derived adducts, which are not accessible by conventional gas-phase or solution synthetic approaches, provide new pathways to engineer coatings with tailored properties. Our interest is focused on the need to control surface energy (critical surface tensions) for inhibiting the nucleation and growth of various kinds of deposits. Furthermore, precursor selections and molar proportions are being guided by developing an understanding of the gas-phase ion chemistries using first-principles and semi-empirical computational methods.
Chi-Chin Wu, U.S. Army Research Laboratory
Cheng-Che Hsu, National Taiwan University
Vasiliki Poenitzsch, Southwest Research Institute
Mohan Sankaran, Case Western Reserve University
Journal of Applied Physics | AIP Publishing
Wednesday AM, November 29, 2017
Sheraton, 3rd Floor, Fairfax B
8:45 AM - *PM01.07.01
Nonthermal Plasmas for Crystalline Nanomaterials
Rebecca Anthony 1 Show Abstract
1 , Michigan State University, East Lansing, Michigan, United States
Among the many synthesis methods for semiconductor nanocrystals, nonthermal plasmas are becoming increasingly popular, particularly for synthesis of otherwise hard-to-grow materials such as Group IV elemental crystals with high melting points. Recent developments have also shown the ability to modify these reactors into multi-stage processing tools which allow core/shell growth, molecular surface attachment, and more. Low-pressure radiofrequency (RF) reactors work by dissociating vapor-phase precursors - the fragments cluster and grow in the plasma environment, forming nanoparticles with tunable properties. These syntheses are enabled via the high-energy electrons in the plasma, and yet the neutral gas species and ions remain near room temperature, making this an overall low-temperature process. These low-temperature, solvent-free reactors offer high-quality nanocrystal growth, scalability, and tunable parameters for adjusting nanoparticle surface, structural, and optoelectronic properties. The resulting vapor-phase nanoparticles can be collected as powders or inertially impacted directly into thin films for device fabrication, adding to versatility of this process.
In this work, we exploit the non-equilibrium of plasmas reactors for synthesis and modification of nanocrystals. While nanocrystals immersed in the plasma experience spikes in temperature well in excess of room temperature, the gas species in the reactor are cool and the nanocrystals accommodate to room temperature before they exit the reactor, meaning they can be directly deployed onto device substrates regardless of thermal tolerance. Thus, synthesizing optically functional nanocrystals using plasmas opens the door to direct incorporation of these materials into arbitrary device architectures including stretchable and bendable devices. Along this line, we discuss the tunable properties of silicon nanocrystals based on plasma parameters, including growth of silicon nitride shells around silicon nanocrystal cores using a multi-stage plasma reactor. We also discuss formation of other optically active nanomaterials, including freestanding GaN nanocrystals. These nanocrystals have tunable size based on reactor parameters, and excellent crystal quality. Finally, we will discuss future directions in expanding the range of optoelectronically functional nanomaterials that can be made using nonthermal plasmas, highlighting ongoing applications of these materials in stretchable layers, as optical emitters, and as sensitizers for pollutant photodegradation.
9:15 AM - PM01.07.02
Microwave-Assisted Hydrothermal Synthesis and Manufacturing of TiO2 Nano-Array Integrated Catalytic Converters
Xingxu Lu 2 1 , Son Hoang 2 1 , Wenxiang Tang 2 1 , Shoucheng Du 2 1 , Wei Zhong 1 , Steven Suib 3 1 , Pu-Xian Gao 2 1 Show Abstract
2 Department of Materials Science and Engineering, University of Connecticut, Storrs, Connecticut, United States, 1 Institute of Materials Science, University of Connecticut, Storrs, Connecticut, United States, 3 Department of Chemistry, University of Connecticut, Storrs, Connecticut, United States
One-dimensional nano-array based monolithic catalysts have been proved to show advantages in terms of enhanced materials utilization efficiency, good thermal stability and mechanical robustness as well as tunable structures and catalytic performance. (1-4) In this work, we report a facile microwave-assisted hydrothermal method for the synthesis and manufacturing of TiO2 nano-arrays onto channeled honeycomb monolithic substrates as high-performance autocatalysts with prominent mechanical and hydrothermal stability. A two-step sustained-release microwave-assisted reaction strategy was employed to achieve the heterogeneous growth of TiO2 nano-arrays at low temperature and pressure. Using TiCl3 as the titanium source, H2O2 as an oxidizer to promote the oxidation of Ti3+, and hydrochloride acid to control the hydrolysis rate in solution, a growth rate of 42nm/min was achieved. This approach provides a new pathway for low-temperature scalable synthesis and manufacturing of both lab scale and field-size TiO2 nano-array integrated catalytic reactors with decent production rates and enhanced material utilization efficiency. With 50g/ft3 Pt loading, the TiO2 nano-array integrated monoliths have been demonstrated with excellent low light-off temperatures for CO and HCs as low as below 150 oC under simulated exhaust gas condition. After sonication in water for 4 hours and hydrothermal aging at 700 oC for 100 hours, no significant changes of the light-off temperatures were observed on the sonicated samples, and a small increase of ~40 oC was observed on the hydrothermally aged samples in comparison with the fresh samples. This new type of robust and efficient nano-array integrated catalytic converters could be a promising candidate device for low-temperature auto-emission control applications.
1. S. Wang et al., Catalysis Today 258, Part 2, 549 (12/1/, 2015).
2. Z. Ren et al., Catalysis Today 258, 441 (2015).
3. Z. Ren et al., Angewandte Chemie International Edition 53, 7223 (2014).
4. Y. Guo et al., Nano Energy 2, 873 (2013).
9:30 AM - PM01.07.03
Self-Organized Multilayered Graphene-Boron Doped Diamond Hybrid Nanowalls for High Performance Field Electron Emission Devices
Sankaran K. J. 1 2 , Mateusz Ficek 3 , C. J. Yeh 4 , K. Srinivasu 4 , Kalpataru Panda 5 , Jeong Young Park 5 , Robert Bogdanowicz 3 , I-Nan Lin 6 , Ken Haenen 1 2 Show Abstract
1 Institute for Materials Research (IMO), Hasselt University, Diepenbeek, Belgium, Diepenbeek Belgium, 2 IMOMEC, imec, Diepenbeek Belgium, 3 Department of Metrology and Optoelectronics, Faculty of Electronics, Telecommunications and Informatics, Gdansk University of Technology, Gdansk Poland, 4 Department of Engineering and System Science, National Tsing Hua University, Hsinchu Taiwan, 5 Center for Nanomaterials and Chemical Reactions, Institute for Basic Science (IBS), Daejeon Korea (the Republic of), 6 Department of Physics, Tamkang University, Tamsui Taiwan
Electron emission sources are ubiquitous in modern society and play a significant role in information displays. Carbon-based cold cathode materials like carbon nanotubes, carbon nanowalls, graphene and diamond thin films, owning a low turn-on voltage and a high emission current are strongly anticipated for applications in field electron emission (FEE) based devices such as flat panel displays, electron microscopes, vacuum microelectronic devices and X-ray sources. Even though many field electron emitters emit electrons proficiently, many struggle with temporal stability of the current at high electric fields corresponding to operative conditions. Therefore, the fabrication of a stable and extended life-time cold cathode emitter is the foremost challenge for device applications.
Nano-carbon hybrid structures that integrate two carbon allotropes generate much attention not only owing to their outstanding individual properties but also because of their synergistic electronic behavior, predominantly when combining sp2 and sp3 bonds, like “graphene-diamond hybrids”. The current work focuses on the highly reproducible microwave plasma enhanced chemical vapor deposition of highly conductive self-organized multilayered graphene (MLG)-boron doped diamond (BDD) hybrid nanowalls. The hybrid nanowalls growth mechanism involves the joint chemistry of many species, such as CN-, HyCNHx, BH-x, and CH+x radicals in the growth plasma. The incorporation of boron into these nanowalls is examined by C1s X-ray photoemission spectroscopy and morphology of these nanowalls is revealed using field-emission scanning electron microscopy and transmission electron microscopy (TEM). The electron diffraction pattern and the Raman spectroscopy display the coexistence of sp3 diamond and sp2 MLG phases in the hybrid nanowalls. In addition, the microstructure investigation, carried out by high-resolution TEM with Fourier transformed pattern, indicates diamond grains are encased by grain boundaries of approximately tens of layers of MLG with good crystallinity. The obtained samples achieved high conductivity values of 2.8 × 103 S/cm with a carrier concentration of 6.2 × 1016 cm-3 and mobility of ~100 cm2/V s. Peak force-controlled tunneling atomic force microscopy measurements revealed that grain boundaries are the prominent emission sites as compared to the grains. Interestingly, this specific feature of high conducting MLG-BDD hybrid nanowalls demonstrates a high efficiency in field emission with low turn-on field of 2.4 V/μm, high FEE current density of 4.2 mA/cm2 (at 4.0 V/μm) and a high FEE stability of 700 min. The simple fabrication process of these MLG-BDD hybrid nanowalls may have great potential for cathode applications such as field emission and microplasma display devices.
K. J. Sankaran is a Postdoctoral Fellow of the Research Foundation-Flanders (FWO).
10:15 AM - PM01.07.04
Towards Understanding of Arc-Based Synthesis of Carbon Nanotubes
Y Raitses 1 , Yao-Wen Yeh 2 , Vlad Vekselman 1 , Michael Keidar 3 , Alexander Khrabryi 1 , Shurik Yatom 1 , Alexandros Gerakis 1 , Igor Kaganovich 1 , Predrag Krstic 5 6 , Longtao Han 4 , Bruce Koel 7 , Brentley Stratton 1 Show Abstract
1 Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey, United States, 2 Princeton Institute for Science and Technology of Materials (PRISM), Princeton University, Princeton, New Jersey, United States, 3 Mechanical and Aerospace Engineering, The George Washington University, Washington, District of Columbia, United States, 5 , Theoretik, LLC, New York City, New York, United States, 6 Institute for Advanced Computational Science, SUNY at Stony Brook, Stony Brook, New York, United States, 4 Department of Material Science and Engineering, SUNY at Stony Brook, Stony Brook, New York, United States, 7 Chemical and Bio Engineering, Princeton University, Princeton, New Jersey, United States
We report on studies of arc-based synthesis of carbon nanomaterials. Applying a set of the developed in situ diagnostics of plasma and nanoparticles, our synthesis experiments revealed that the carbon arc forms a highly inhomogeneous plasma consisting of distinguishable regions with . Experimental and modeling results demonstrate that different steps of the synthesis process, including generation of a feedstock of atomic and molecular species and ions, formation of larger molecules and clusters, growth of nanotubes, and agglomeration of nanoparticles in large particles and bundles occur in different regions of the arc discharge. Plasma effects on the growth of nanotubes will be discussed.
This work was supported by U.S. Department of Energy, Office of Science, Basic Sciences, Materials Sciences and Engineering Division.
10:30 AM - PM01.07.05
Nanodiamonds Formation from Ferrocene Precursor by Atmospheric Pressure Microplasmas
Bruno Alessi 1 , Manuel Macias-Montero 1 , Paul D. Maguire 1 , Davide Mariotti 1 Show Abstract
1 , University of Ulster, Newtownabbey United Kingdom
Carbon allotropes are nowadays important for multiple purposes. Forthcoming technology will adopt carbon nanotubes and graphene because of the unique combination of material properties they possess, either for the mechanical strength or optoelectronic behaviour. Diamonds are known for their superlative physical qualities such as the extreme hardness and thermal conductivity as well as for the high refractive index. Graphite is the most stable form of C for bulk samples, however it is established that diamond phase is more stable for particles nucleated below 3 nm because of the contribution of surface energy . Nevertheless, most synthesis processes for nanodiamonds use extreme conditions in terms of pressure and/or temperature such as detonation of carbon containing explosives or high temperature plasma-enhanced chemical vapour deposition.
Atmospheric pressure micro-plasmas made recently their appearance as valuable tools for nanomaterial synthesis . They offer at the same time a cheap alternative to low pressure plasmas and some unique peculiarities. For example, the non-thermal character makes them suitable for treating temperature sensitive materials, and the high densities of energetic electrons allows activating chemical reactions which would otherwise be hard to achieve. Moreover, the high degree of collisionality due to the ion-neutral interactions is responsible for the selective heating of particles surface inside the plasma, allowing achieving higher nanoparticle temperatures. In this work, ultra-small nanodiamonds have been produced with a gas phase atmospheric pressure microplasma using a metalorganic precursor, ferrocene, usually known for its ability to catalyse the formation of carbon nanotubes in chemical vapour deposition processes. The mean diameter of the synthesized nanodiamonds is 2 nm with a small size dispersion (0.4 nm). Transmission electron diffraction analysis reveals the presence of distinct phases of diamond, either cubic, hexagonal or the FCC, the latter showing an expanded lattice constant. In addition, the nanodiamonds are mostly spherical and well separated. Optical emission spectroscopy of the plasma process confirms the presence of C2 and CH moieties, which have been proposed to act as seeds for nanodiamond nucleation.
With respect to previous studies, nanodiamonds produced here are smaller and the process seems to have a higher throughput. The successful production of phase pure ultrasmall nanodiamonds could have straightforward applications as biomarkers and drug delivery vectors, given their optical properties and non-toxicity to human cells. Furthermore, there is an enormous interest in understanding the nucleation dynamics as well as the phase stability of C allotropes at the nanometre scale.
 Badziag, P., Verwoerd, W. S., Ellis, W. P. and Greiner, N. R., Nature 343, 244-245 (1990)
 Mariotti, Davide, and R. Mohan Sankaran., Journal of Physics D: Applied Physics 43.32 (2010): 323001
10:45 AM - *PM01.07.06
Processing Refractory Materials with Low-Temperature Plasmas
Lorenzo Mangolini 1 , Alejandro Alvarez 1 , Devin Coleman 1 Show Abstract
1 , University of California, Riverside, Riverside, California, United States
Low temperature plasmas have been successfully utilized for the synthesis and processing of nanoparticles composed of a broad range of materials. In this talk we focus on RF continuous flow plasmas operated in tube reactors and run in a low-to-mid pressure regime (1-10 Torr range). We first discuss how the interaction between the particles and a plasma produced in such configuration can lead to substantial nanoparticle heating. This has been experimentally verified by (a) measuring the rate of crystallization of amorphous silicon particles exposed to a non-thermal plasma  and (b) monitoring the surface termination of silicon nanoparticles produced in a non-thermal plasma using silane as precursor. Both studies provide experimental confirmation that the nanoparticle temperature can exceed 1000K even at moderate input power levels.
We then discuss how to leverage the intense heating to produce nanoparticles of materials that are considered difficult to process. Sub-10 nm beta-silicon carbide nanoparticles can be easily produced by nucleating silicon particles in a first plasma and by aerodynamically dragging the particles to a second discharge to which methane is added. Simple calculations based on the rate of carbon diffusion in silicon suggest that for carbonization to take place in the short span corresponding to the residence time in the plasma (around 100 msec) the particle temperature must well exceed a temperature of 1000K . The use of such particles as inclusion in bulk thermoelectric materials will be briefly described.
Finally, we discuss the synthesis and processing of titanium nitride nanoparticles using low-temperature plasmas. We have demonstrated that <10 nm TiN particles with near perfect stoichiometry can be obtained starting using titanium tetrachloride and ammonia as precursor couple . A combination of in-situ FTIR and optical emission spectroscopy indicate the atomic nitrogen density is the main factor controlling the stoichiometry of the particles. Stoichiometry affects the degree of oxidation of the particles, which in turns control their plasmonic response in the visible range. A two-steps plasma process will be described in which titanium nitride nanoparticles are coated in-flight with a silicon nitride shell. This approach effectively prevents oxidation of the TiN particles, leading to a large improvement in their plasmonic response.
1. Lopez, T. and L. Mangolini, Journal of Vacuum Science & Technology B, 2014. 32(6): p. 061802.
2. Lopez, T. and L. Mangolini, Journal of Vacuum Science & Technology B, 2016. 34(4): p. 041206.
3. Coleman, D., T. Lopez, O. Yasar-Inceoglu, and L. Mangolini, Journal of Applied Physics, 2015. 117(19): p. 193301.
4. Alvarez Barragan, A., N.V. Ilawe, L. Zhong, B.M. Wong, and L. Mangolini, The Journal of Physical Chemistry C, 2017. 121(4): p. 2316-2322.