Symposium Organizers
Thomas Zac Ward, Oak Ridge National Laboratory
Kirk Bevan, McGill University
Shriram Ramanathan, Purdue University
Marie-Lise Tremblay, Hydro Quebec
Symposium Support
MDC Vacuum Products, LLC
EM09.01: Solid-Liquid Devices I
Session Chairs
Monday PM, November 27, 2017
Hynes, Level 1, Room 105
9:00 AM - *EM09.01.01
Electrolyte-Gate-Control of Ferromagnetism in Epitaxial La1-xSrxCoO3 Thin Films
Jeffery Walter 1 , Biqiong Yu 1 , Guichuan Yu 1 , Alexander Grutter 2 , Brian Kirby 2 , Julie Borchers 2 , Z Zhang 3 , Hua Zhou 3 , John Freeland 3 , Timothy Charlton 4 , Haile Ambaye 4 , Michael Fitzsimmons 4 , Helin Wang 1 , Bing Luo 1 , C. Daniel Frisbie 1 , Martin Greven 1 , Chris Leighton 1
1 , University of Minnesota, Minneapolis, Minnesota, United States, 2 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 3 , Argonne National Laboratory, Argonne, Illinois, United States, 4 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractRecently, electrolyte gating techniques employing ionic liquids have proven remarkably effective in tuning large carrier densities at the surface of a variety of solid materials. These materials include organic conductors, semiconductors, 2D materials, binary oxides, transition metal oxides, perovskites, and other complex oxides. In essence these electrolytes enable electric double layer transistor operation, the large specific capacitances (10’s of mF/cm2) generating electron/hole densities up to 1014 - 1015 cm-2, i.e., significant fractions of an electron/hole per unit cell in most materials. Notable successes include discovery of superconductivity in KTaO3, tuning over a dome of superconductivity in YBa2Cu3O7-d, and electrical control of the insulator-metal transition in VO2, although many open questions remain. Uncertainties include the true doping mechanism (i.e., electrostatic vs. electrochemical (e.g., redox-based)), the relation between 2D surface and bulk chemical doping, the role of electrostatic disorder, the need for in operando characterization, and the universality of the approach. In this talk we will review the application of electrolyte gating using ionic liquids and ionic gels (or ion gels), the latter enabling simple processing of solid-state devices. [1-3] We focus on ultrathin epitaxial films of the perovskite La1-xSrxCoO3, seeking gate-control of ferromagnetism. Our findings first clarify the issue of charge carrier vs. oxygen defect creation, transport measurements revealing a dramatic asymmetry with respect to bias polarity, with important implications for n-type oxides such as SrTiO3 and VO2. [4] We then report on the development of in operando probes of ion-gel/La1-xSrxCoO3 devices, using hard X-ray synchrotron diffraction and Polarized Neutron Reflectometry (PNR). These provide direct evidence of oxygen vacancy creation at positive bias, vs. electrostatic hole accumulation at negative bias. Gate-control over resistivity, magnetoresistance, magnetization, and Curie temperature is thus demonstrated under hole accumulation, including gate-induced ferromagnetism directly verified by in situ PNR. These results are discussed in terms of recently developed theory for electrolyte-gate-induced percolation [5].
[1] S. Wang, M.-J. Ha, M. Manno, C.D. Frisbie and C. Leighton, Nat. Commun. 3, 1210 (2012).
[2] W. Xie, S. Wang, X. Zhang, C. Leighton and C.D. Frisbie, Phys. Rev. Lett. 113, 246602 (2014).
[3] W. Xie, X. Zhang, C. Leighton and C.D. Frisbie, Adv. Electron. Mater. 3, 1600369 (2017).
[4] J. Walter, H. Wang, B. Luo and C. Leighton, ACS Nano 10, 7799 (2016).
[5] P. Orth, R. Fernandes, J. Walter, C. Leighton and B. Shklovskii, Phys. Rev. Lett. 118, 106801 (2017).
EM09.03: Poster Session: Solid-Liquid Interfaces
Session Chairs
Kirk Bevan
Shriram Ramanathan
Tuesday AM, November 28, 2017
Hynes, Level 1, Hall B
9:00 AM - *EM09.04.01
Interfaces between Photoabsorbers and Water—Condensed Matter Physics Meets Electrochemistry
Giulia Galli 1
1 , University of Chicago, Chicago, Illinois, United States
Show AbstractWe describe first principles simulations and electronic structure calculations aimed at characterizing interfaces between photoabsorbers and water, with focus on transition meta oxides, and water. One of the main objectives is to identify descriptors for the optimization of interfacial properties for water photocatalysis.
EM09.01: Solid-Liquid Devices I
Session Chairs
Monday PM, November 27, 2017
Hynes, Level 1, Room 105
9:30 AM - *EM09.01.02
Enhancement Factors of Electrochemical Conductance Modulation in Ionic Liquid Gating on Correlated Oxide Micro/Nanostructures
Hidekazu Tanaka 1
1 Osaka University, ISIR-Sanken, Ibaraki, Osaka, Japan
Show AbstractThe electric-field effect with ionic liquid electrolytes for transition-metal oxides has been widely used because of the enormous carrier doping and capabilities, and the liquid gate-induced redox reactions revealed by recent investigations have highlighted the complex nature of the electric-field effect.
The gate-induced conductance modulation of perovskite manganite (La,Pr,Ca)MnO3, spinel ferrite (Fe,Zn)3O4, VO2, perovskite nickelate (RNiO3) are presented to demonstrate the dual contributions of volatile and non-volatile field effects arising from electronic static doping and electrochemical reactions, using electric double layer liquid gate transistor (EDLT) with micro/nano-patterned films. Controlling factors of operation atmosphere and temperature, threshold voltage (Vg), chemical composition in material such as Fe/Zn ratio in (Fe,Zn)3O4 and R=Nd, Sm, Eu in RNiO3, will be discussed to enhance electrochemical modulation in ionic liquid gating for high-performance oxide field-effect devices. As one of examples, SmNiO3 film EDLT showed the substantial non-volatile conductivity changes. At 400 K, after applying a +2.5 V for 25 sec, the resistance increased to about 2 times. Above at +3.0 V application for 25 sec, the resistance became to ~103 times. XPS results showed that the reduction of Ni3+ and increase of Ni2+ under positive Vg, that is, the positive bias application lead to the extraction of oxygen ion from SmNiO3 channel, and result in the increase of the resistance.
References. H. Tanaka et al, Sci. Rep. 4 (2014) 5818, Appl. Phys. Exp. 8 (2015) 073201, Sci. Rep. 5 (2015) 17080, APL Mater. 5 (2017) 042303
Acknowledgments: This work was supported by Dr. A. N. Hattori, Mr. D. Kawamoto, Mr. K. Hayashi, Dr. Kanki in Osaka University, Japan and Dr. F. Zuo, S. Yifei, Z. Zhang, R. Koushik, Prof. S. Ramanathan in Purdue University, USA.
EM09.03: Poster Session: Solid-Liquid Interfaces
Session Chairs
Kirk Bevan
Shriram Ramanathan
Tuesday AM, November 28, 2017
Hynes, Level 1, Hall B
9:30 AM - EM09.04.02
Probing Water-Oxidation Interfaces by Operando Optical and X-Ray Spectroscopy
Georges Siddiqi 1 2 , Qianhong Zhu 1 2 , Zhenhua Pan 1 2 , Ethan Crumlin 3 , Shu Hu 1 2
1 Chemical Engineering, Yale Univ, New Haven, Connecticut, United States, 2 Energy Sciences Institute, Yale University, West Haven, Connecticut, United States, 3 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractA photoelectrochemical water-splitting device, driven by light-absorbing semiconductors, takes sunlight and produce H2 and O2 from water. Further scaling down these electrode-based devices essentially to nanoscale leads to a suspension of particle-based photocatalysts, which splits water in a cost effective fashion. Recent breakthroughs in protective coatings enable these otherwise unstable materials to oxidize water efficiently and stably in strongly acidic and basic electrolytes. With protective coatings as a general stabilization strategy, several water-splitting devices of 10%-16% solar-to-hydrogen (STH) efficiencies have been demonstrated; and with photon management, 20% STH demonstrations are well on its way. Particularly, 100s-of-nm thick amorphous TiO2 coatings grown by atomic-layer deposition allows for non-tunneling transport of hole charges. However, the physical models of protected solid/liquid interfaces require further interpretation.
I will mainly present our understanding of photochemical processes at solid/liquid interfaces, particularly using electrostatic and dynamic spectroscopy techniques under operando conditions. Operando spectroscopic techniques based on 1) pump-probe optical absorption and fluorescence and 2) x-ray photo-electron emission are complementary. Synchrotron, ambient-pressure x-ray photoelectron spectroscopy (AP-XPS) presents vast opportunities for understanding electrostatic energetics of protected electrode/electrolyte interfaces. Furthermore, stabilized semiconductor/liquid interfaces allows for optical excitation at femtosecond resolution, and the following optical spectroscopy using probe molecules is able to track photochemical dynamics. Particularly, the rates of charge transfer and selectivity of catalytic pathways at water-oxidation interfaces can be characterized at high energy and temporal resolution. This promise the development of cost-effective particle-based photocatalysts.
9:45 AM - EM09.04.03
The Beneficial Role of Diiodine on Interface Recombination Kinetics in P-Type Dye Sensitized Solar Cells
Taylor Moot 1 , Aaron Taggart 1 , Shannon McCullough 1 , Rene Lopez 1 , James Cahoon 1
1 , University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States
Show AbstractTandem dye-sensitized solar cells (DSSCs) can theoretically use n-type and p-type cells connected in series to substantially boost efficiency compared to a single-cell devices. However, n-type DSSCs outperform their counterpart p-type DSSCs by at least a factor of five in power conversion efficiency. To alleviate this mismatch, significant work has gone into designing new semiconductors and chromophores for p-DSSCs. Despite improvements, the overall device performance still limits the performance of tandem cells. This highlights the need to redesign the p-type DSSC by focusing on the electrolyte, and subsequently the role of semiconductor/liquid interface for controlling charge injection and recombination.
Here, we focus on understanding the commonly used an I-/I3- electrolyte and the role of I2, an electron scavenger, on p-type DSSC device performance. Upon changing the equilibrium concentration of I2 from 10-8 to 10-4, a four-fold increase in overall power conversion efficiency is achieved. This improvement in device performance comes from an almost three time increase in photocurrent and an increase in fill factor from 34% to 51%, reaching up to 80% of the theoretical maximum. The λmax of the P1 chromophore shifts with increasing I2 concentration, suggesting that the local environment of the chromophore, and consequently the interface, changes. We propose that I2 enables efficient dye regeneration, thereby turning off major recombination pathways from the chromophore to the semiconductor. Furthermore, this suggests that an aqueous electrolyte would be advantageous for p-DSSCs as the I-/I3- equilibrium constant in water is much lower than in acetonitrile, where a standard 1.0M LiI, 0.1M I2 aqueous electrolyte has an equilibrium I2 concentration of 10-4. Fabricated aqueous p-DSSCs reached fill factors of 50% and similar relative improvements in photocurrent. Simply changing the concentration of I2 in the electrolyte allows for more efficient charge separation at the semiconductor-chromophore-electrolyte interface, which minimizes two of the most problematic device performance metrics in p-type DSSCs, low photocurrent and low fill factor.
EM09.01: Solid-Liquid Devices I
Session Chairs
Monday PM, November 27, 2017
Hynes, Level 1, Room 105
EM09.03: Poster Session: Solid-Liquid Interfaces
Session Chairs
Kirk Bevan
Shriram Ramanathan
Tuesday AM, November 28, 2017
Hynes, Level 1, Hall B
EM09.01: Solid-Liquid Devices I
Session Chairs
Monday PM, November 27, 2017
Hynes, Level 1, Room 105
10:30 AM - *EM09.01.03
Electric Field Gating and Ion Intercalation via Ionic Liquids Biasing for Controlled Transport in Electronic Devices
Philip Rack 1 2
1 Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, 2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractThe electric double layer induced at the interface of an ionic liquid (IL)/solid interface can induce a significant electric field which can be used to induce charged carriers in an electronic device or move ions in and out of a lattice. To this end we engineered a variety of devices to investigate both electric field gating and ion intercalation and extraction in transition metal oxide and dichalcogenide materials. Initially compare the field effect transistor properties of an amorphous indium gallium zinc oxide thin film transistor fabricated with a dual bottom gate (100 nm thick SiO2 dielectric) and side gate IL ([hmim][Tf2N]) gate. Next we will show how IL biasing was used to gate and tune the oxygen vacancy concentration and subsequently the device characteristics in a-IGZO which served as a room-temperature activation process. Furthermore, we have correlated the IL structure at the interface via in situ atomic force microscopy to the observed channel transconductance and studied how asymmetric gate/channel sizes affects the field effect transistor characteristics. We will also compare device characteristics for few and single layer WSe2 devices. Finally we will illustrate extraction and intercalation of oxygen and lithium ions via IL biasing in exfoliated MoO3 crystals and compare the tunable transport properties of the MoO3.
EM09.03: Poster Session: Solid-Liquid Interfaces
Session Chairs
Kirk Bevan
Shriram Ramanathan
Tuesday AM, November 28, 2017
Hynes, Level 1, Hall B
10:30 AM - *EM09.04.04
Probing the Electrochemical Double Layer (EDL) and Electrode Interfacial Properties at the Solid/Liquid Interface Using Ambient Pressure XPS
Ethan Crumlin 1 2
1 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Joint Center for Energy Storage Research, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractInterfaces play an important role in nearly all aspects of life, and are essential for electrochemistry. Electrochemical systems ranging from high temperature solid oxide fuel cells (SOFC) to batteries to capacitors have a wide range of important interfaces between solids, liquids, and gases which play a pivotal role in how energy is stored, transferred, and/or converted. This talk will focus on our use of ambient pressure XPS (APXPS) to directly probe the solid/liquid electrochemical interface. In particular, I will discuss how we were able to probe the potential drop within the electrochemical double layer (EDL) as well as the potential of zero charge under polarization conditions. This unique approach was accomplished by measuring spectral changes observed in both the electrolyte (water) and a neutral spectator probing molecule (pyrazine). By combining these experiments with numerical simulations provided the ability to discern the shape of the electrochemical double layer profile as a function of both electrolyte concentration and applied potentials. Extending beyond the EDL, I will highlight some of our recent investigations into both the oxygen evolution reaction on a platinum electrode as well as a magnesium electrode in a non-aqueous electrolyte. Information gained from these studies will aid in the guided design and control of future electrochemical interfaces.
EM09.01: Solid-Liquid Devices I
Session Chairs
Monday PM, November 27, 2017
Hynes, Level 1, Room 105
11:00 AM - EM09.01.04
Electric-Field-Induced Phase Transition in VO2 Thin Film Using All-Solid-State 3-Terminal Proton Transistor
Minguk Jo 1 , Hyeon Jun Lee 2 , Chadol Oh 1 , Ji Young Jo 2 , Junwoo Son 1
1 Material Science and Engineering, Pohang University of Science and Technology, Pohang Korea (the Republic of), 2 Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of)
Show AbstractElectric-field-induced insulator-to-metal transition (IMT) is a core technology for developing novel electronic devices, as well as a powerful tool to reversibly monitor the stability of competing phases in correlated oxide systems. Recently, ionic liquid (IL) gating has been utilized to electrostatically produce a huge amount of carrier density more than 1014 cm-2 at the surface of correlated oxide channel in a field-effect transistor geometry. Despite the great potential of IL gating to induce a large amount of carriers by electrostatic doping, this mechanism has been controversial due to the possible electrochemical doping at the interface and the slow switching speed was also limiting for the device application.
In this presentation, we demonstrate electric-field-induced reversible phase transition in VO2 epitaxial thin film using all-solid-state 3-terminal ionic transistor. To modulate electronic phase in VO2 thin films at room temperature, proton-containing porous silica was utilized to supply sufficient protons into 10-nm-thick epitaxial VO2 channel by gate voltage. When a positive bias is applied, sheet resistance (Rs) of VO2 (Rs = 1.0 × 106 Ω) initially decreases, and the channel converted to a protonated metallic state (Rs = 2.9 × 103 Ω). Interestingly, further gate bias increases Rs again and thus a fully protonated insulating state (Rs ≥ 2.4 × 107 Ω) can be stabilized by gate bias. In-situ synchrotron X-ray scattering and SIMS data represent that supplied protons in VO2 film are responsible for this structural and electronic modulation of the channel in correlated materials. These findings provide a novel method to reversibly control electronic states of correlated-electron oxides by protonation, which can be further applicable for novel electronic devices.
EM09.03: Poster Session: Solid-Liquid Interfaces
Session Chairs
Kirk Bevan
Shriram Ramanathan
Tuesday AM, November 28, 2017
Hynes, Level 1, Hall B
11:00 AM - EM09.04.05
Carbon Electrodes in Room Temperature Ionic Liquids—Effect of IL Type, Electrode Microstructure and Surface Chemistry on Interfacial Capacitance
Kirti Bhardwaj 1 , Greg Swain 1
1 , Michigan State University, East Lansing, Michigan, United States
Show AbstractThe properties of room temperature ionic liquids (RTILs) and the structure of the electrified interfaces they form with carbon electrodes has been the subject of both fundamental and applied research, particularly in the field of energy storage devices like supercapacitors. RTILs have great potential to replace conventional organic solvent/electrolyte systems because of their environmentally-benign characteristics (non-volatility, non-toxicity) and excellent thermal and electrochemical stability. The physicochemical properties of RTILs can be flexibly tuned through selection of the component ions. Research is needed to better understand the structure of electrified interfaces formed in these novel media at carbon electrodes of different surface chemistry and microstructure. Traditional models of the electrochemical double layer based on the dilute-solution approximation may not be applicable to RTILs because of the absence of solvent, the high concentration of ions, strong interionic columbic forces, and electrostatic and hydrophobic interactions of charged ions with the electrode surface.
In this presentation, electrochemical investigations of the capacitance of carbon electrodes as a function of potential, the RTIL type, carbon electrode type and surface chemistry will be reported on. 1-alkyl-3-methylimidazolium-based RTILs were studied at boron-doped-diamond and nitrogen-incorporated tetrahedral amorphous carbon thin-film electrodes. Comparison measurements were made using glassy carbon. Cyclic voltammetry and electrochemical impedance spectroscopy were used to measure the interfacial capacitance.
EM09.01: Solid-Liquid Devices I
Session Chairs
Monday PM, November 27, 2017
Hynes, Level 1, Room 105
11:15 AM - EM09.01.05
Electrochemical Gating-Induced Hydrogenation in VO2 Nano-Patterned Devices
Hidekazu Tanaka 1 , Teruo Kanki 1 , Keita Muraoka 1 , Yifei Sun 2 , Shriram Ramanathan 2
1 ISIR-Sanken, Osaka University, Ibaraki, Osaka, Japan, 2 , Purdue University, West Lafayette, Indiana, United States
Show AbstractThe transport characteristics of transition metal oxides are sensitive to redox reactions because the valence numbers of the transition metal ions and therefore orbital structure are easily changed. We report drastic modulation of the transport properties in vanadium dioxide (VO2) nanowires by electric field-induced hydrogenation at room temperature using nanogaps, separated by humid air in field-effect transistors with planer-type gates (PG-FET), and discuss their origin in comparison with VO2 films hydrogenated by spillover method with Pt catalyst.
In a VO2 nanowire channel (wire width=500nm) in PG-FET, the non-volatile and reversible resistance reduction was found by applying a positive gate bias (VG) at 300K under a humidity of 50%. The channel resistance slowly continued to drop down to 75% to initial resistance during the application of VG=+100V. Moreover, application of VG= +100V to VO2 channel sometime caused to increase channel resistance as opposite tendency. We also observed increase of electrical resistance in high mobility epitaxial VO2 film deposited on TiO2 (001) substrate by hydrogenation whereas decrease of electrical resistance in low mobility VO2 film on Al2O3 (0001) substrate by spillover method with Pt catalyst. It is considered that heavily doped HxVO2 state in former case exhibited Mott insulting behavior whereas lightly doped one in latter case stabilized metallic state. In a VO2 nanowire channel in PG-FET, the different behavior of decrease/increase in electrical resistance against bias voltage will be explained from the point of view on Mott metal-insulator transition of H1-xVO2 system via electrochemical gating-induced hydrogenation. These results show that air nanogaps can operate as an electrochemical reaction field, even in a gaseous atmosphere at room temperature.
EM09.03: Poster Session: Solid-Liquid Interfaces
Session Chairs
Kirk Bevan
Shriram Ramanathan
Tuesday AM, November 28, 2017
Hynes, Level 1, Hall B
11:15 AM - EM09.04.06
Electron Transportation of Carbon Nanotube-Based Film in Liquid Medium
Quan Zhang 1 , Guoan Cheng 1 , Ruiting Zheng 1 , Xiaoling Wu 1
1 , Laboratory of Nanomaterial and technology, College of Nuclear Science and Technology, Beijing Normal University, Beijing China
Show AbstractIn carbon nanotube-based assemblies, carbon nanotube network directly influences their electrical conductivity. In this work, we explored that electron transportation characteristic of carbon nanotube-based film immersed in different liquid medium. For the ordered film composed of pristine carbon nanotubes, as the film was immersed in the liquid, a distinct change of the film resistance occurred. And this change gradually disappeared with the liquid evaporating out of the film, when it was drawn out of the liquid. Molecular dynamics simulation confirms that the molecules of liquid with high wettability can infiltrates into junctions of carbon nanotubes network due to capillarity. The reduced contact area (even breaking) of the junctions interrupts the electron transportation path and thus increases the resistance of the film. A series of measurements illuminate that the variation of the film resistance is dominated by the interface tension between the film and the immersed liquid. Comparing with the ordered film, random orientation of the carbon nanotubes in the film reduced response degree. In addition, the surface modification could efficiently change the wettability of carbon nanotubes with different liquid. Based on this phenomenon, the response range of the film was tuned by the treatment of constituent carbon nanotube. Such an ability to sensitive and repeatable resistance change of carbon nanotube film with liquid immersion could have important implications in the measurement of liquid surface tension, liquid sensors, and material in solution detection.
11:30 AM - EM09.04.07
In Operando X-Ray Diffraction and EIS on NCA Battery Cathodes
Donata Passarello 1 , Christopher Takacs 1 , Hans-Georg Steinrueck 1 , Michael Toney 1
1 Materials Science Division, Stanford Synchrotron Radiation Lightsource, Menlo Park, California, United States
Show AbstractSignificant efforts have been devoted to fundamental and commercial research and development of layered oxide cathodes for lithium ion batteries (LIB) with small structural deformation upon lithium intercalation and de-intercalation. Towards this end, there is a need to couple modern electroanalytical techniques with advanced structural characterization methods. Here I discuss current progress to complement electrochemical impedance spectroscopy (EIS) with in operando x-ray methods, focusing on correlating time-dependent measurements in order to add structural information to the commonly used equivalent circuit models. EIS is widely used as a measure of kinetics and interface properties in a wide variety of systems. In a battery system, correlating the impedance parameters to the cycling efficiency of the cell, helps predicting the likelihood of battery failures. While EIS is a very powerful analysis tool, the interpretation of the data is non-trivial, as they can`t be fit by a unique model. In this study, we investigate the structural behavior of LiNi0.80Co0.15Al0.05O2 (NCA) cathode material, of particular interest as it exhibits high structural stability. We track frequency dependent changes in the x-ray diffraction peaks to directly determine the diffusion mechanism of the lithium ions into the cathode material. We aim to gain additional structural information from x-ray diffraction methods in order to unambiguity model the EIS data.
Symposium Organizers
Thomas Zac Ward, Oak Ridge National Laboratory
Kirk Bevan, McGill University
Shriram Ramanathan, Purdue University
Marie-Lise Tremblay, Hydro Quebec
Symposium Support
MDC Vacuum Products, LLC
EM09.04: Solid-Liquid Energy Applications I
Session Chairs
Tuesday AM, November 28, 2017
Hynes, Level 1, Room 105
9:00 AM - *EM09.06.01
Conditions for Metal-Semiconductor Epitaxial Growth via Electrodeposition
Karen Kavanagh 1
1 , Simon Fraser University, Burnaby, British Columbia, Canada
Show AbstractMany metals and alloys grow epitaxially on semiconductors such as Si and GaAs. Simply provide an atomically clean environment, sufficient thermal energy for atomic diffusion, and interfaces will form with the most stable structures. While vacuum and gas flow systems are well known to provide these conditions, aqueous electrodeposition offers another type of clean environment, with sufficient thermal energy for many atomic systems. And despite the obvious abundance of water, metallic epitaxial nucleation and growth is feasible in many cases. Nanoparticles with controlled facets and preferred orientations are feasible on GaAs surfaces with appropriate preparation.[1] Coalesed epitaxial metallic films form with very low angle grain boundaries and grain sizes sensitive to the temperature of the water.[2, 3] This talk will describe continuing attempts to understand the limitations of this process, and how the semiconductor surface preparation, reaction kinetics, electric potentials, and other deposition conditions influence the resulting crystalline perfection. [1] Karin Leistner et al. Nanoscale 2017, 9, 5315–5322; [2] Zhi Liang Bao et al. J. Appl. Phys. 2005, 98, 066103; [3] Nanofabrication Techniques and Principles, Eds. M. Stepanova and S. Dew, Springer, 2012, pg 217-235. Acknowledgements: NSERC
9:30 AM - EM09.06.02
Self-Terminated and Epitaxial Electrodeposition of Fe Nanostructures
Karin Leistner 1 , Kenny Duschek 1 , Mingze Yang 2 , Christine Damm 1 , Andreas Petr 1 , Karen Kavanagh 2 , Kornelius Nielsch 1
1 , IFW Dresden, Dresden Germany, 2 , Simon Fraser University, Burnaby, British Columbia, Canada
Show AbstractFe/FeOx nanoparticles (NPs) with defined shape are highly interesting because of their distinct electronic, catalytic and magnetic properties [1]. Several preparation methods for Fe NPs exist, including chemical reduction of iron hydroxides or iron salts, high temperature chemical synthesis using iron organic precursors, and sputter-gas-aggregation. Electrodeposition would be a competitive room temperature synthesis method, not requiring vacuum techniques or sophisticated reaction steps. The understanding of nucleation and growth mechanisms at the solid/liquid interface already allows the precise control over shape and orientation of electrodeposited Co nanoparticles [2]. In contrast, the electrodeposition of the less noble Fe is more challenging sinceit is always accompanied by hydrogen evolution. In addition, Fe is not stable in acidic electrolytes after the reduction voltage is switched off. We investigated the electrode processes during the nanoscale electrodeposition of Fe on Au/Cr/Si substrates with electrochemical quartz microbalance. The partial current densities of iron ion reduction and hydrogen evolution were separated and the dissolution rate after the deposition step was probed. For a nominal Fe thickness of 2 nm, a NP morphology is achieved. At potentials where hydrogen evolution dominates over iron ion reduction, a self-limiting behavior is observed. This can be explained by an iron hydroxide layer passivating the electrode [3]. These self-limited electrodeposits, in contrast to those deposited at lower overpotentials, exhibit a smoother morphology and do not dissolve in the electrolyte for several tens of seconds.
It is expected that control over the orientation of the Fe nanoparticles is within reach if the substrate induces epitaxial growth. We synthesized aligned Fe/FeOx nanoparticles with long term stability by epitaxial electrodeposition on GaAs(001)[4]. Helium ion microscopy secondary electron images and transmission electron microscopy images revealed that most of our Fe particles are square cuboid in shape with side lengths between 30 and 80 nm and heights of up to 30 nm. The shape and alignment of these nanoparticles agrees with epitaxial cube on cube growth of body centered cubic (bcc) Fe(001) on GaAs(001) with {100} facets. The magnetic characterization by ferromagnetic resonance revealed an in-plane anisotropy as expected for oriented bcc Fe. Results from current investigations of the effects of initiation conditions on the NP properties will be presented. Aligned NPs offer unprecedented routes for the fundamental study of the magnetic and electronic properties of individual nano-objects [5].
[1] J. Pal and T. Pal, Nanoscale 7 (2015) 14159
[2] P. Allongue and F. Maroun, MRS Bull. 35 (2010) 761
[3] R. Wang, et al. , J. Phys. Chem. C 120 (2016) 16228
[4] K. Leistner, M. Yang, et al. , Nanoscale 9, (2017) 5315.
[5] C. Gatel, et al. , J. Magn. Magn. Mater. 428 (2017) 394
9:45 AM - EM09.06.03
Electrochemical Impedance Spectroscopy for Quantitative Interface State Characterization of Planar and Nanostructured Semiconductor-Dielectric Interfaces
Andrew Meng 1 , Kechao Tang 2 1 , Michael Braun 1 , LiangLiang Zhang 1 , Paul McIntyre 1
1 , Stanford University, Stanford, California, United States, 2 , University of California, Berkeley, Berkeley, California, United States
Show AbstractQuantitative interface state characterization of planar oxide/semiconductor interfaces is performed by forming a metal-oxide-semiconductor capacitor on which multifrequency capacitance-voltage and conductance-voltage measurements can be made. However, similar quantitative measurements on nanostructured semiconductors requires conformal gate metal deposition over a known surface area, which can be challenging for large arrays of nanostructures. On the other hand, single nanowire measurements can be accomplished by electron-beam lithographic definition of the gate, but suffer from poor statistical sampling. Single wire capacitance values are also very low, and while interface trap density can be inferred from transistor characteristics, this is an indirect measurement that makes it difficult to extract a trap energy distribution. We demonstrate an alternative method using semiconductor-liquid junctions and electrochemical impedance spectroscopy which has broad applications to quantitative interface state characterization.
Using aqueous KCl solution as a blocking contact to a semiconductor electrode, electrochemical impedance spectroscopy measures the multifrequency capacitance-voltage and conductance-voltage characteristics of planar p-Si (100), planar p-Si0.55Ge0.45 (100), and p-Si crystals with surfaces that are textured to create nanoscale features. The substrates are coated with atomic layer deposited Al2O3 gate dielectrics. Analysis of impedance data obtained from the planar samples produces results that are in good agreement with solid-state multi-frequency C-V and g-V data from the same sample, and result in similar extracted values for density of interface states. The electrochemical impedance spectroscopy gave more reliable results because the use of a blocking electrolyte contact suppressed leakage/shunt currents that were observed in solid state measurements of the MOS capacitors. Electrochemical impedance spectroscopy for quantitative characterization of interface defects shows promise as a tool to better understand the interface properties of semiconductor nanostructures.
10:30 AM - *EM09.06.04
Insights into the Dynamics of Mass and Charge Transfer at the Ionic Liquid/Metal Interface Revealed Using Voltammetry and Scanning Electrochemical Microscopy
Darren Walsh 1
1 , University of Nottingham, Nottingham United Kingdom
Show AbstractRoom-temperature ionic liquids (RTILs) are salts that are liquid below 100 °C. Due to their very low volatilities, and the ability to tune their physicochemical properties by changing the constituent ions, RTILs have been proposed as “designer” solvents that could replace many organic solvents in industrial processes. In addition, as they are thermally and electrochemically stable, RTILs are being proposed for use in devices such as batteries, supercapacitors, and fuel cells. However, the high viscosity of many RTILs presents a challenge when developing RTILs for electrochemical devices; in particular, mass and charge transport are generally significantly slower in RTILs than in conventional media. Understanding the effects of the physicochemical properties of RTILs on transport dynamics is important for the use of these neoteric solvents in next-generation devices. In this presentation, I will describe the use of electroanalytical methods to study transport dynamics in a series of imidazolium-based RTILs.
Our data show that ultramicroelectrode voltammetry of RTILs is very sensitive to experimental parameters such as the voltammetric scan rate, the electrode dimensions and the RTIL viscosity, and steady-state voltammograms can only by recorded under well-defined conditions. Moreover, the ability to record steady-state scanning electrochemical microscopy (SECM) data, which agrees with conventional SECM theory, depends on the RTIL viscosity, the SECM-tip radius, and the tip-approach speed. Steady-state SECM feedback approach curves, which agree with conventional electrochemical theory, can be recorded in RTILs, even when moderately viscous, provided that the experimental parameters are tuned to maintain steady-state diffusion at the SECM tip. Under steady-state conditions, it is possible to extract electrochemical-kinetic data, revealing that the oxidation of the prototypical redox species ferrocene is significantly slower in RTILs than in conventional electrochemical media. When very viscous RTILs are used as the electrolyte for SECM, tip-induced convection inevitably contributes significantly to the analytical signal. However, this effect can be accounted for theoretically using mass-transport equations that include diffusive and convective terms.
Analysis of the mass-transport characteristics of imidazolium-based RTILs also reveals that the Stokes–Einstein equation is not applicable in these systems. Instead, the size of the diffusing species corresponds to the average size of holes (voids) in the liquid, suggesting that a model in which the diffusing species jumps between holes in the liquids is more appropriate than one in which the diffusing species moves through a structureless medium.
11:00 AM - EM09.06.05
Electronically and Spectroscopically Probed Adsorption of Molecular Species at the Interface between Biomedically Relevant Solutions and GaAs Diodes
T. Alkhidir 1 , A. Devarajan 1 , C. Alpha 2 , I. A. H. Farhat 1 , D. L. Gater 1 , Abdel Isakovic 1
1 , Khalifa University (KUST), Abu Dhabi United Arab Emirates, 2 CNF, Cornell University, Ithaca, New York, United States
Show AbstractInterfaces between some biomedically relevant solutions (H2O, D2O, PBS and others) on one side, and as-grown and etched single crystal GaAs samples, and micro-fabricated GaAs Schottky and photodiodes on the other side, have been studied with spectroscopic (FTIR), transport (J-V, C-V) and surface techniques (AFM, SEM) with a dual prupose. We wish to quantify how various molecular species at the interface of GaAs affect the charge transport in (and at the surface of) GaAs diodes, and, in turn, whether functional GaAs diodes, such as Schottky and photodiodes, could be used to control the transport of molecular species at the solution-GaAs interface. Specifically, among the solutions applied to the surface of GaAs were H2O, D2O, PBS (phosphate buffered saline) and others. FTIR results demonstrate the presence of more than a dozen species, such as Ga-O, As-O, Ga-H-Ga, Ga-D, Ga-OH, As-OH and others, in their respective stretching, bending, wagging and other modes. In transport studies, with a moderate bias of the order of +/-1 V, J-V curves obtained for GaAs Schottky and GaAs photodiodes immersed in solutions, show the influence of various spectroscopically identified molecular species, which were either adsorbed onto the GaAs surface, or fully bonded with either Ga or As. This influence manifests itself via shifts in the threshold point of diodes’ J-V curves, and/or modification of the slope of J-V curves, as well as through the presence of hysteretic J-V curves in some instances. These findings demonstrate some level of active participation of the adsorbed and bonded molecular species in electronic and/or ionic transport. An additional control parameter was the surface roughness of GaAs, the influence of which we studied through: (a) pristine, (b) control-etched, and (c) post-fabricated (for diodes) cases. The influence of surface roughness on the adsoprtion, surface bonding and interface transport was studied via AFM and SEM. The nature of the reaction between applied solutions and the GaAs surface was studied with C-V measurements, and the correlation between transport and AFM data on etched surface leads towards identification of possible controllable trapping mechanisms.
We acknowledge the support from A2RE-ADEC and SRC (2011-KJ-2190). A part of the work was conducted at Cornell University Center for Nanofabrication, supported by NSF. A part of the work was conducted at KUST Core Facilities.
11:15 AM - EM09.06.06
Controlling the Electrical Properties of Organic Electronics—A Path Towards Low-Power Printed Electronics
Sean Doris 1 , Adrien Pierre 1 , Robert Street 1
1 , Palo Alto Research Center, Palo Alto, California, United States
Show AbstractOrganic electrochemical transistors (OECTs) have emerged as a promising new class of organic electronics with applications in chemical and biological sensing, bio-interfacing, printed electronics and neuromorphic computing. Their low-voltage operation is particularly important in power-sensitive applications like wearable devices, remote sensing platforms, smart packaging, and other internet-of-things applications. Despite their low-voltage operation, the implementation of reliable low-power circuits based on OECTs is hindered by the lack of methods for easily tuning their threshold voltage. Tuning the threshold voltage of OECTs would allow the power consumption of complementary circuits to be minimized by matching the threshold voltages of the p and n-type transistors. Furthermore, it would allow the noise margin of digital circuits based on OECTs to be optimized, thus improving device reliability. This presentation will show that the threshold voltage of OECTs can be varied by ~0.8 V, and how this tunability enables their integration in low-power printed electronics. We will also show how the approach can be extended to create OECTs with dynamic threshold voltages that are sensitive to environmental stimuli, which opens new opportunities in chemical and biological sensing and control.
11:30 AM - EM09.06.07
The Nanoscale Structure of the Electrolyte-Metal Oxide Interface
Hans-Georg Steinrueck 1 , Chuntian Cao 1 3 , Yuchi Tsao 2 , Christopher Takacs 1 , Oleg Konovalov 4 , Jenel Vatamanu 5 , Oleg Borodin 5 , Michael Toney 1
1 , Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California, United States, 3 Department of Materials Science and Engineering, Stanford University, Stanford, California, United States, 2 Department of Chemistry, Stanford University, Stanford, California, United States, 4 , ESRF, Grenoble France, 5 Electrochemistry Branch, Sensor and Electron Devices Directorate, U.S. Army Research Laboratory, Adelphi, Maryland, United States
Show AbstractThere are still open scientific questions as to the basic structural motifs of the electrolyte/electrode interface, especially the structure of the electrolyte, which is essential to the operation of LIBs. In particular, the arrangement of the electrolyte molecules directly at the electrode interface is expected to govern the ion transport during charge/discharge, as well as affect the origin and properties of the solid electrolyte interphase layer (SEI). While there have been theoretical efforts to shed light these issues, molecular resolution experimental studies of the electrolyte/electrode interface with particular focus in the ordering of the electrolyte are still missing. Such experimental evidence is extremely important to test the simulations and to gain insight into systems under realistic conditions.
In the present study, we have explored, via surface sensitive resolution X-ray reflectivity (XRR), the structure of Lithium hexafluorophosphate (LiPF6) in a non-aqueous solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) with a weight ratio of 1:1 at the solid-liquid sapphire (001) interface. Our results for various salt-concentrations show distinct layering of the electrolyte molecules at the surface, which decays into the bulk with a characteristic decay length of about one molecular layer after which bulk properties are reached. The XRR fit-derived surface normal electron density profile is in good agreement with the one obtained from complementary molecular dynamics simulations. When increasing the salt concentration, we observe an increase in the layering periodicity, which we speculate to be caused by a reorientation of the solvent molecules in the presence of the ions and formation of the larger Li-solvent complexes. This indicates that the solid interface not only gives rise to liquid layering but also determines the orientation of the electrolyte molecules and ions near the surface. We discuss the implications of our results to lithium ion batteries, in particular concerning the relation between interfacial structure and ion transport in and out-of the electrode, which can determine the rate at which a battery can be charged and discharged.
EM09.05: Solid-Liquid Energy Applications II
Session Chairs
Ahmad Islam
Marie-Lise Tremblay
Tuesday PM, November 28, 2017
Hynes, Level 1, Room 105
1:30 PM - *EM09.07.01
Electrical Double Layer in Porous Electrodes—Capacitance, Capacitive Mixing and Electroosomosis
Jianzhong Wu 1
1 , University of California, Riverside, Riverside, California, United States
Show AbstractThis talk presents an overview of our recent theoretical efforts directed at understanding the thermodynamic and transport properties of ionic species in charged micropores based on the classical density functional theory in combination with coarse-grained molecular models and continuous equations to describe ionic distributions, fluid mechanics and reaction kinetics. Illustrative examples will be discussed in the context of experimental strategies to improve electrochemical capacitor performance, to identify optimal operation parameters for capacitive energy extraction with porous electrodes, and to understand the flow effects on ion transport and surface reactions in microchannels.
2:00 PM - EM09.07.02
Probing Local Charge Screening Dynamics and Electrochemical Processes Using Electrochemical Force Microscopy (EcFM)
Liam Collins 1 , Stephen Jesse 1 , Nina Balke 1 , Brian Rodriguez 2 , Sergei Kalinin 1
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , University College Dublin, Dublin Ireland
Show AbstractEnergy technologies of the 21st century require a full understanding of, and precise control over, ion transport and electrochemistry at all length scales – from single atoms to macroscopic devices. Of particular interest are the electrochemical phenomena at solid-liquid interfaces, a key element of classical and flow batteries, supercapacitors, sensors, and biological systems. Ultimately, optimization of these materials/devices requires measurement techniques capable of probing both structural and electrochemical functionalities on the length-scales of the material inhomongenities (e.g. step edge, grain boundary or point defect). While voltage modulated scanning probe microscopy techniques (e.g. Kelvin probe force microscopy, Electrochemical strain microscopy) have found broad applicability for probing reversible and irreversible electrochemistry and transport phenomena in solids, these techniques cannot be directly applied in liquids, due to a non-trivial role of liquid electrolytes. In this presentation, I will illustrate a new approach for electrochemical imaging in-situ. Electrochemical force microscopy (EcFM)[1] is a force-based imaging mode for spatial mapping of electrochemical functionalities with submicron spatial resolution. I will describe how EcFM can be used to measure surface potentials in low molarity solutions, as well as charge screening dynamics and slow faradaic processes in the probe–sample junction. Finally I will demonstrate imaging of electrochemical functionality on model systems using this approach. As such, the work presented herein can lead to a paradigm shift in local electrochemical measurements, from current to force based detection methods.
[1] Collins, Liam, et al. "Probing charge screening dynamics and electrochemical processes at the solid–liquid interface with electrochemical force microscopy." Nature communications 5 (2014).
This research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. (CNMS2012-036 and CNMS2013-339)
2:15 PM - EM09.07.03
Charge Transfer Dynamics in Graphene-Inorganic ‘Hybrids’ with Transition Metal Oxides Using In Situ Raman Spectroelectrochemistry
Sanju Gupta 1 , Sara Carrizosa 1 , N. Dimakis 2
1 , Western Kentucky University, Bowling Green, Kentucky, United States, 2 Physics, The University of Texas–Pan American, Rio Grande Valley, Texas, United States
Show AbstractWe report on the electrochemical assembled two- and three-dimensional graphene variants with nanostructured cobalt oxide (CoO and Co3O4) polymorphs that synthesize hybrids with optimal loading and chemical attachment of cobalt oxides micro/nano particles on the functionalized graphene surface, creating tailored interfaces crucial to electrochemical property enhancement. In-situ Raman spectroscopy integrated with electrochemistry was employed to investigate ion transport and charge transfer dynamics and to determine the concomitant electrochemical tuning of Fermi level. The variation of structural bonding in these hybrids dipped in aqueous alkaline electrolyte (e.g. KOH) with electrochemical biasing was monitored. It is because Raman spectroscopy can detect changes in graphene/metal and graphene/metal oxide bond through various spectral features. Two of the transverse optical phonons and corresponding longitudinal optical (LO) phonons of Co3O4 (and CoO) above 500 cm−1 are observed depending on the surface morphology and particle size as well as carbon-carbon bonding via G and 2D bands at 1590 cm−1 and 2670 cm-1, respectively. Consistent reversible and substantial variations in Raman intensity and band positions of these modes induced by electrode potential point at the fine and continuous tuning, indicative of emptying/depleting or filling of the specific bonding and antibonding states which become electroactive. The results were explained in terms of changes in the electron density of states arising due to alterations in the overlap integral of bonds between the s and p (and d) orbitals of the adjacent carbon and metal oxide atoms. We estimated the extent of variation of the absolute potential of the Fermi level and overlap integral between the nearest-neighbor atoms from modeling the electrochemical potential dependence of Raman intensity thus corroborating the synergistic coupling of graphene and cobalt oxide polymorphs. The interplay of heterogeneous basal and edge plane sites graphene and crystalline spinel cobalt oxides reinforce density of states in the vicinity of Fermi level and efficient interfacial electron transfer. We acknowledge financial support in parts by KY NSF EPSCOR RSP, WKU Research Foundation and Graduate School internal awards.
3:30 PM - *EM09.07.04
Bridging Fundamental Structural and Chemical Basis of Ionic Electrolyte Gating on Oxide Heterostructures
Hua Zhou 1
1 Advanced Photon Source, Argonne National Laboratory, Lemont, Illinois, United States
Show AbstractDue to unique fundamental behaviors of complex oxides, such as the subtle balance between competing electronic and magnetic phases, and their sensitivity to defects and doping, electric fields can be used to craft electronic order, modify chemistry, apply strain, and manipulate spin-orbit couplings (e.g. in the 5d oxides). This presents a promising opportunity to create novel functionalities, in principle, enabling device concepts that go far beyond what conventional semiconductor physics allows (i.e. adopting a scheme that emulates the neuron-circuit in the human brain). In particular, the very high charge density induced by an electric double layer (EDL) formed at an electrochemical solid-liquid interface has recently been used to induce or “gate” exotic phase transitions, therefore electronic ground states of strongly correlated oxides in the interfacial region, via the subtle interplay between electrostatic (electronic phenomena) and chemical redox effects (field-driven ionic motion) depending on field polarity and defect instability. It is highly expected that leveraging ionic electrolyte gating would still be fertile ground for exploration in a broad range of oxides that exhibit novel functionalities.
In this talk, I will present our recent in-situ and real-time X-ray studies to make fundamental understanding of structural and chemical basis (e.g. lattice reconstruction and valence state evolution) and their inherent links during EDL gating on various complex oxide heterostructures, including LaAlO3/SrTiO3 interface, perovskite nickelates/ruthenate/tungstate and underdoped cuprate. The structural behaviors, static and dynamic, in LAO/STO during EDL gating can be reconciled with the synergy of polar reconstruction, electrostriction and surface defects, which are intimately linked with the mechanism responsible for the establishment of 2DEG at this interface. The EDL gating on underdoped cuprate presents evidence for yet another response mechanism, namely, that the strong electric fields can reversibly displace but not knock-off anion atoms inside a unit cell while the overall lattice structure remains unchanged. In contrast, the structural evolution in nickelates/ruthenate/tungstate during EDL gating, respectively, is more consistent with controlling a metal-insulator transition by manipulating oxygen vacancies via redox chemistry. More interesting to note that shuttling oxygen vacancies could lead to emergent controllability on structural motif of complex oxides, such as creating metastable brownmiller-phase and dynamic tuning oxygen octahedral rotation.
4:15 PM - EM09.07.06
Electrolyte-Gated Transistors Based on N-Type Semiconductors Undergoing Several Redox Processes—Correlation of Electrochemical and Device Properties
Tian Lan 1 , Francesca Soavi 2 , Jonathan Sayago 3 , Clara Santato 1
1 , Ecole Polytechnique de Montreal, Montreal, Quebec, Canada, 2 , Università di Bologna, Bologna Italy, 3 , Universidad Nacional Autónoma de México (UNAM), Mexico City Mexico
Show AbstractHigh charge carrier densities can be obtained in thin film transistor channels using electrolytes as gating media [1-2].
PCBM (phenyl-C61-butyric acid methyl ester) is a fullerene derivative, widely investigated in the past decades in organic solar cells and transistors. PCBM is known to give up to six mono-electronic redox processes. Consequently, it is particularly intriguing to explore possible correlations between the redox state [3] in the channel material and the charge carrier transport and device properties in PCBM electrolyte-gated transistors. Our work was driven by questions such as: can the presence of several redox processes be exploited to increase the charge carrier density in the organic films? Is the presence of more than one redox process compatible with the device stability?
Hence, using a combination of Atomic Force Microscopy (AFM), cyclic voltammetry (CV) and transistor characterization in N2 atomsphere at room temperature we studied the doping/de-doping processes in PCBM thin film transistors gated with two ionic liquids, namely [EMIM][TFSI] and [PYR14][TFSI], differing for their cations. The two ionic liquids have wide electrochemical stability windows; the former has higher ionic conductivity and lower viscosity than the latter. Within the interval of electrochemical potential included between 0.5 V and -1.9 V vs carbon (used as both the reference and the counter electrode), three redox process are observed in the cyclic voltammograms obtained with scan rate at differnet scan rates. Three reduction peaks and three oxidation peaks are clearly shown in the voltammograms, in both [EMIM][TFSI] and [PYR14][TFSI]. The study of the evolution of the peak current of the first redox process with the scan rate reveals a different behavior of PCBM films interfaced to [EMIM][TFSI] with respect to [PYR14][TFSI]. In the former case, we observe a dependence of the peak current with the square root of the scan rate, attributable to diffusion-limited electrochemical processes, whereas in the latter case the peak current shows a linear dependence with the rate, attributable to capacitive processes. The inclusion of the second and the third redox processes during the doping of the PCBM channel leads to dramatic changes in the shape of the transfer characteristics; the scan rate of the gate-source potential plays a primary role in establishing the weight of the electronic vs ionic contributions to the electrical response of the transistors.
1. Hong, K., et al., Printed, sub-2 V ZnO Electrolyte Gated Transistors and Inverters on Plastic. Advanced Materials, 2013. 25(25): p. 3413-3418. 2. Tarabella, G., et al., New opportunities for organic electronics and bioelectronics: ions in action. Chemical Science, 2013. 4(4): p. 1395-1409. 3. Francesco Paolucci., et al., Electrochemical detection of C60 in solution is tetrahydrofuran a suitable solvent for fullerene studies? Journal of the electrochemical society, 1999. 146(9): p. 3357-3360.
Symposium Organizers
Thomas Zac Ward, Oak Ridge National Laboratory
Kirk Bevan, McGill University
Shriram Ramanathan, Purdue University
Marie-Lise Tremblay, Hydro Quebec
Symposium Support
MDC Vacuum Products, LLC
EM09.07: Solid-Liquid Energy Applications IV
Session Chairs
Wednesday PM, November 29, 2017
Hynes, Level 1, Room 105
8:15 AM - *PM03.12.01
Influence of Misfit Dislocations on Mechanical Properties of Fine Pearlite
Tomotsugu Shimokawa 1 , Tomoaki Niiyama 1
1 Faculty of Mechanical Engineering, Kanazawa University, Kanazawa, Ishikawa Japan
Show AbstractInfluence of misfit dislocations on mechanical properties of fine pearlite is investigated via uniaxial tensile or compressive deformation tests of multilayered composite models composed of ferrite and cementite phases with the Bagaryatsky relation by using molecular dynamics simulations. The analysis models have various spacing of misfit dislocations.
First, we show the relationship between the misfit dislocation spacing and each component of phase stress in ferrite and cementite under no applied stress. Second, it is found that the misfit dislocation spacing influences tensile and compressive yield stresses and the dominant non-elastic phenomena, i.e. phase stresses and misfit dislocation structures influence the resolved shear stress and the critical resolved shear stress for each slip system, respectively. Therefore, the misfit dislocation spacing has a potential to be a controlling parameter of the resolved stress and the critical resolved stress for non-elastic phenomena. In addition, it has been also found that the flow stresses of the lamellar models are affected by the misfit dislocation density. That is, the misfit dislocation spacing influences the mechanical properties of fine pearlite.
8:45 AM - PM03.12.02
Atomistic Investigation into the Energetics and Structure of Interfaces in Pearlite
Matthew Guziewski 1 , Shawn Coleman 2 , Christopher Weinberger 1
1 , Colorado State University, Fort Collins, Colorado, United States, 2 , U.S. Army Research Office—Materials Science Division, Aberdeen Proving Grounds, Maryland, United States
Show AbstractWhile the behavior of steel has been studied extensively for decades, there are still questions regarding the microstructures it forms. In this talk, atomistics is used to gain further insight into the structure of pearlite. Models were constructed for the commonly proposed orientation relationships between cementite and ferrite, including the Isaichev, the Bagaryatskii and the Pitsch-Petch. Dislocation arrays are observed for all orientation relationships, however the energetics and structure of the interface is shown to vary significantly both between the orientations and between the different interfacial chemistries within each orientation. Additionally, a continuum model is implemented to allow for the quantification of Burgers vector values and stress fields.
9:00 AM - PM03.12.03
Resetting Aged Duplex Stainless Steels to Hinder Interfacial Embrittlement
Jaclyn Cann 1 , Cem Tasan 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractDuplex stainless steels (DSS) are commonly used for components in nuclear power plants, where they are subjected to intense operating conditions, undergoing extensive aging over the long lifetime of power plants. This aging causes embrittlement, a serious problem in this application. The goal of this work is to understand the microstructural evolution that accompanies aging, to study the mechanics of deformation to see the effect of interfaces and grain orientation, and to ultimately create heat treatment strategies to reverse the microstructural effects of aging and to thereby increase the operating life of these components. For this purpose, duplex stainless steel samples were supplied by Électricité de France (EDF) after being aged at 400°C for 300 h, 1000 h, and 10000 h. A recovery heat treatment was applied to some of the 10000 h aged sample to determine its effect on ductility. Tension tests were performed and interrupted at various strain intervals on the original samples as well as on the heat treated 10000 h aged sample. Before the experiment and after each interruption, SE (secondary electron) micrographs and EBSD (electron backscatter diffraction) patterns were taken in the scanning electron microscope (SEM) to observe the microstructural evolution with deformation. It was found that in the 10000 h aged condition, the material is the most brittle and cracks nucleate in the ferrite at the ferrite/austenite grain boundaries. In the heat-treated 10000 h aged case, as well as in the cases where less aging has occurred, cracks initiate in the ferrite at much higher strains. In all cases, the cracks are nucleated in the <100> direction. We also study the spinodal decomposition of the ferrite phase and G-phase via atom probe tomography (APT) and transmission electron microscopy (TEM) to determine its extent as a function of aging and subsequent recovery heat treatment. These results indicate that short recovery heat treatments can have substantial results, recovering much of the initial ductility of duplex stainless steels. This is encouraging as the characterizations of the microstructural changes resulting from aging and from the recovery heat treatments should allow for the design of more optimized heat treatments and potentially of alloys optimized for recoverable properties, both of which would increase the lifetime and efficiency of nuclear power plants.
9:15 AM - PM03.12.04
Sub-Structural Evolution of Interfacial Austenite During Deformation and Resetting
Menglei Jiang 1 , Cem Tasan 1
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractBy introducing metastable austenite between the laths of martensite, the mechanical properties of martensitic steels are improved due to the transformation induced plasticity (TRIP) effect. However, the additional strain hardening capacity gained by the martensitic transformation of metastable austenite is limited, since the austenite is consumed during transformation. Post-deformation resetting treatments provide repeatable restoration of original austenite-martensite multilayered structure, thereby increasing the cumulative ductility of the material. Nevertheless, the interfacial microstructure evolution and transformation mechanisms activated during the mechanically-induced martensitic transformation and follow-up resetting processes were not previously understood. Here in this talk we would like to present the results of a novel multi-scale characterization approach to unravelled: i) the role of interface characteristics, stress and plastic strain in the martensitic transformation process and ii) the role of crystallographic defects, elemental segregation and residual plastic strain in the reversion of austenite phase during resetting process.
EM09.06: Solid-Liquid Energy Applications III
Session Chairs
Kirk Bevan
Marie-Lise Tremblay
Wednesday PM, November 29, 2017
Hynes, Level 1, Room 105
10:00 AM - *PM03.13.01
A Model for the Solid-Liquid Interfacial Free Energy in Alloys
Jeffrey Hoyt 1 , Sumathy Raman 2 , Mark Asta 4 , Ning Ma 3
1 , McMaster University, Hamilton, Ontario, Canada, 2 , ExxonMobil Research and Engineering Company, Annandale, New Jersey, United States, 4 , University of California, Berkeley, Berkeley, California, United States, 3 , ExxonMobil Research and Engineering Company, Ananndale, New Jersey, United States
Show AbstractThe solid-liquid interfacial free energy as a function of temperature and composition is needed to model important processes in alloys such as nucleation from the melt and dendritic solidification. In this work, we propose a model for the interfacial energy that is based only on an extension of the Turnbull relationship and the free energy vs composition, where the latter function is available from various thermodynamic databases. The model, which is based on a phase field description of the interface, will be compared to results from atomistic simulations for several binary alloy systems. The solid-liquid interfacial free energy can be obtained from molecular dynamics simulation by the capillary fluctuation method or Gibbs-Cahn integration and the atomistic results provide a fairly precise test of the proposed model. The extension to multicomponent alloys will be discussed.
10:30 AM - PM03.13.02
Manipulation of Pt3Ni Tetrahexahedral Nanoframes Using a Gas Etching Method
Chenyu Wang 1 , Lihua Zhang 2 , Hongzhou Yang 3 , Jinfong Pan 1 , Yiliang Luan 1 , Shouzhong Zou 4 , Jiye Fang 1
1 , State University of New York at Binghamton, Binghamton, New York, United States, 2 , Brookhaven National Laboratory, Upton, New York, United States, 3 , Miami University, Oxford, Ohio, United States, 4 , American University, Washington, District of Columbia, United States
Show AbstractWe developed a facile and robust method to fabricate Pt3Ni tetrahexahedral nanoframes, in which the Pt-Ni tetrahexahedral precursors were prepared using a colloidal synthesis approach and carbon monoxide was employed as an “etching agent” at elevated temperatures. This protocol adopts the Mond process to preferentially de-alloy nickel component in the <100> direction through carbon monoxide etching of carbon-supported Pt-Ni tetrahexahedral nanocrystals at high temperature. The nanoframes feature well-defined high indexed exposed surfaces, whose formation is attributed to the preferential etching pathway and mild annealing temperature. It was also demonstrated that the local elemental segregations and the compositions in the top atomic layers can be different from the bulk/average compositions. Unlike solution-based etching, this developed protocol shortens the etching time and generates well-defined surface structures. The resultant Pt3Ni alloy tetrahexahedral nanoframes possess an open, stable, and high-indexed microstructure, containing a segregated Pt thin layer strained to the Pt−Ni alloy surfaces. The obtained nanoframes address some of the major challenges for advanced catalysts with high stability and activity.
In addition, through the same reaction the nanoframes can be formed by annealing the carbon black supported precursor in air, a common practice for preparing industrial nanocatalysts, which offers straightforward incorporation of the developed approach in industry to engineer surface structure-controlled Pt−Ni and other Ni-containing porous catalysts.
11:00 AM - PM03.13.04
Using Laser-Induced Thermal Voxels to Pattern Diverse Inorganic Materials at the Solid–Liquid Interface
Lauren Zarzar 1 , Brian Swartzentruber 2 , Brian Donovan 3 , Patrick Hopkins 3 , Bryan Kaehr 2
1 , Penn State University, University Park, Pennsylvania, United States, 2 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 3 , University of Virginia, Charlottesville, Virginia, United States
Show AbstractThe ability to spatially control chemical synthesis for fabrication, integration, and patterning of materials with nano/microscale precision is critical for development of many technologies. I will discuss a fabrication strategy that combines the 3D spatial control inherent to direct laser writing with the flexible chemistry of solvothermal or hydrothermal inorganic materials synthesis [1]. Using the focal volume of a laser as a solvothermal reaction voxel, we explore deposition of a wide variety of metals and oxides at the solid-fluid interface. We demonstrate that this processing method may enable all such materials to be patterned with high precision, resolution, and user-defined registration via direct laser writing techniques.
[1] Zarzar, L. D., et al. (2016). "Using laser-induced thermal voxels to pattern diverse materials at the solid–liquid interface." ACS Applied Materials & Interfaces 8(33): 21134-21139.
11:15 AM - PM03.13.05
Calculating Free Energies of Metal-He Interfaces in the Cu-Nb-He System
Sanket Navale 1 , Michael Demkowicz 2
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Materials Science and Engineering, Texas A & M University, College Station, Texas, United States
Show AbstractEvolution of He-clusters in metals is governed by metal/He interface free energies. We describe an approach to calculate these free energies from atomic models. By computing the capillary pressure of the interface, we determine its free energy using the Young-Laplace equation. We find that the free energies are not only functions of temperature, but also of He pressure and of interface curvature. These findings alter our understanding of how He clusters evolve in metals under irradiation. Our approach is directly applicable to other solid-liquid interfaces, as well.
11:30 AM - PM03.13.06
Wetting and Spreading at the Nanoscale
Emily Brooke 1 , Anna Regoutz 1 , Catriona McGilvery 1 , Eduardo Gutierrez 1 , David Payne 1
1 Department of Materials, Imperial College London, London United Kingdom
Show AbstractThe study of capillary-driven phenomena involving metals has vital and wide-ranging technological importance in areas as diverse as sintering, soldering, or general thin-film fabrication. However, capturing these processes in real time is extremely challenging. Such experiments usually involve, and often require, elevated temperatures and strict control of the environment.
The objective of this study has been to observe, in-situ the interaction between different metallic nanoparticles, typically difficult to achieve, because the solution-based processes often used to synthesise nanoparticles require surfactants that cap the surfaces and therefore hamper direct contact. To overcome this we used a modified inert gas aggregation nanoparticle deposition system to deposit silver and gold nanoparticles directly onto a TEM grid. We found that under the beam of the electron microscope these deposited nanoparticles coalesce upon contact. However, coalescence of two particles with same composition may not be driven by surface diffusion as previously proposed but rather by evaporation-condensation.
In contrast when two dissimilar particles meet the silver wets and engulfs the gold. This is relatively high atomic mobility at room temperature from the nanoparticles, whilst volume diffusion remains very slow. As a consequence, it is possible to form a metastable gold-silver interface with a very low associated interfacial energy that drives spreading. It is also important to note that despite the fact that we are manipulating and observing phenomena at the nanoscale (< 10 nm), it can be described using existing concepts derived from continuous analysis. These results provide new fundamental information on the interaction between metal nanoparticles and have critical technological implications. For example, for the sintering of novel conductive inks and solders our observations suggest that while the combination of two species can promote liquid state sintering and densification (even if they should inter-diffuse in equilibrium), using a single material may result in structural coarsening.
11:45 AM - PM03.13.07
Thermal Stability and Solid State Dewetting of Thin Au Films Deposited on the KCl Whiskers
Ehud Almog 1 , Nimrod Gazit 1 , Gunther Richter 2 , Leonid Klinger 1 , Eugen Rabkin 1
1 , Technion - Israel Institute of Technology, Haifa Israel, 2 , Max Planck Institute for Intelligent Systems, Stuttgart Germany
Show AbstractWe studied the solid state dewetting process of Au thin film deposited on single crystalline KCl whiskers. For this purpose, we fabricated an array of KCl whiskers grown on porous substrates under well-defined humidity and temperature conditions. Single crystalline KCl whiskers with a very high aspect ratio, perfect rectangular shape, and (100) facets orientation were obtained. The whiskers were subsequently coated with thin Au layer using e-beam and thermal evaporators. We used this unique structure and crystallography to study the dewetting processes of Au thin film with the emphasis on the difference between whiskers side facets and corners. After heat treatment at 350oC it was clearly observed that dewetting processes occur much faster at the corners than on the side facets. The unique dewetting morphologies and orientation relationships between Au and KCl at the whiskers corners were studied and compared to the flat KCl (100) substrates.