bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Emerging Neuromorphic Devices for Carbon Nanotubes and Related Low-Dimensional Materials
Authors: Hersam Mark C.
Published: February 2020

The exponentially improving performance of conventional digital computers has slowed in recent years due to the speed and power consumption issues that are largely attributable to the von Neumann bottleneck (i.e., the need to transfer data between spatially separate processor and memory blocks). In contrast, neuromorphic (i.e., brain-like) computing aims to circumvent the limitations of von Neumann architectures by spatially co-locating processor and memory blocks or even combining logic and data storage functions within the same device. In addition to reducing power consumption in conventional computing, neuromorphic devices also provide efficient architectures for emerging applications such as image recognition, machine learning, and artificial intelligence. With this motivation in mind, this talk will explore the opportunities for carbon nanotubes and related low-dimensional materials in neuromorphic devices. For example, by combining p-type semiconducting carbon nanotubes with n-type two-dimensional transition metal dichalcogenides, gate-tunable diodes have been realized, which show anti-ambipolar transfer characteristics that are suitable for artificial neurons, competitive learning, and spiking circuits [1]. In addition, by exploiting field-driven defect motion mediated by grain boundaries in monolayer MoS2, gate-tunable memristive phenomena have been achieved, which enable hybrid memristor/transistor devices (i.e., "memtransistors") that concurrently provide logic and data storage functions [2]. The planar geometry of memtransistors further allows multiple contacts to the channel region that mimic the behavior of biological neurons such as heterosynaptic responses [3]. Overall, this work introduces new foundational circuit elements for neuromorphic computing in addition to providing alternative pathways for studying and utilizing the unique charge transport characteristics of low-dimensional materials [4].

[1] V. K. Sangwan, et al., Nano Letters, 18, 1421 (2018).

[2] V. K. Sangwan, et al., Nature Nanotechnology, 10, 403 (2015).

[3] V. K. Sangwan, et al., Nature, 554, 500 (2018).

[4] D. Jariwala, et al., Nature Materials, 16, 170 (2017).
Improved Performance of Carbon Nanotube Based Strain Sensor
Authors: Kim jae Keon , Lee Junyeop , Jung Daewoong
Published: February 2020

Strain sensor has been used in variety of industrial applications for structural healthy monitoring and biological signal analysis. The fabrication of a highly sensitive strain sensors are underwent many complex and delicate processes, as many fabrication parameters and conditions must be keep equilibrium to achieve good sensor performance, such as high linearity and sensitivity, stable responsivity, fast response time, mechanical durability, and signal processing steps [1].

Carbon based-nano materials such as fullerene, carbon nanotube (CNTs), and graphene have been considered as sensing materials for optical sensor, chemical sensor, physical sensor and environmental sensor, which possess their own strengths and weakness.

Especially, CNTs have been widely employed as sensing species for strain/pressure, gas, temperature, and humidity sensor in recent years. CNT-based sensors were generally fabricated by transferring the individual or bundles of CNTs to the substrates using spin-coating, spraying, dip coating, and inkjet printing methods [1-2].

On the other hand, spin-capable CNTs were reported previously, which simply make transparent conductive CNT webs, ribbon or yarns. The spin-capable CNT forest can give an easy and effective way to fabricate highly-aligned CNT yarn with high flexibility and a electrical conductivity for sensor applications [1-3].

In this paper, we present performance of the CNT yarn based strain sensor. Especially, CNT yarn was associated with stretchable polymers to apply tensile and compressive force. The experimental results reveal that CNT yarn with elastic rubber can be stretch up to 300 %.

References

Jung et al, J. Vac. Sci. Technol.
32 (2014), 04E107.

Han et al. Microelectron. Eng., 168 (2017), 50-54.

Jung et al., J. Sensors. Sci. & Tech,.
22 (2013), 315-320
(Invited) sp3 Defects of Single Walled Carbon Nanotubes: Photonic and Electronic Integration
Authors: Htoon Han
Published: February 2020

Single walled carbon nanotubes with covalently functionalized sp3 defects have been rapidly emerging as a new class of transformational optical materials. Particularly, recent demonstration of room temperature, 1.55 µm single photon generation establish these covalent defects of SWCNTs as promising fundamental building blocks for defect driven quantum information technologies such as quantum key distribution. Defects also provide a significant boost in photoluminescence quantum yield (from <1% to ~28%) and emission stability, making envisioned applications of SWCNTs in optoelectronics, sensing, and imaging technologies more feasible. The key to full exploitation of these technological potentials lie in the ability to integrate these SWCNTs with defects into plasmonic/photonic cavities for enhancement of light matter interactions and into nano-electronic devices for electrical stimulation. Here in this talk I will report recent progresses we made together with our collaborators toward achieving this critical photonic and electronic integration. We have successfully integrated the SWCNTs with sp3 defects into 2D slab photonic crystals1 and metallo-dielectric antenna arrays.2 In case of coupling with 2D photonic crystal, we were able to demonstrate room temperature single photon generation with 3meV linewidth defined by the cavity quality factor and 50 fold enhancement in emission.1 We achieved narrowest low temperature emission linewidth of 35 µeV by coupling the defects with metallo-dielectric antennas.2 We were also successful in fabricating single SWCNT field effect transistors using dielectrophoresis and attained electroluminescence from the sp3 defects.

Ishii, A.; He, X.; Hartmann, N. F.; Machiya, H.; Htoon, H.; Doorn, S. K.; Kato, Y. K. Enhanced Single-Photon Emission from Carbon-Nanotube Dopant States Coupled to Silicon Microcavities.
Nano Lett. 18
, 3873-3878 (2018).

Shayan, K.; He, X.; Luo, Y.; Rabut, C.; Li, X.; Hartmann, N.F.; Blackburn, J.L.; Doorn, S.K.; Htoon, H.; Strauf, S.; “Suppression of Pump-Induced Exciton Dephasing in Sidewall-Functionalized Single-Walled Carbon Nanotubes”,
Nanoscale
10
, 12631 (2018).
Hydrothermally Prepared MnSe2 Nanosheets As a Novel Electrode Material for Supercapacitor
Authors: Ma Shuan , Wang Shaolan
Published: February 2020

Ever-increasing energy crises require the exploration of sustainable energy conversion and storage systems that are reliable, low-cost and environmentally friendly. The search for Earth-abundant and efficient electrode materials is significant for advanced supercapacitors. Transition metal chalcogenides has regarded as one of the most emerging new materials for electrochemical energy storage device. Manganese diselenide is a low-cost and eco-friendly semiconducting material with applications in lithium ion battery and oxygen reduction catalysis. However, there have been fewer reports on the electrochemical performance research of manganese diselenide. In this study, cubic manganese diselenide (MnSe2) were synthesized by using a one-pot hydrothermal method. Physicochemical characterizations revealed the formation mechanism of MnSe2 nanosheets. Electrochemical analysis suggested the pseudocapacitive nature of MnSe2 electrode, which delivered a specific capacitance of 423 F g-1 at a current density of 1 A g-1, and obtained 203 F g-1 at 30 A g-1. The superior electrochemical performance of MnSe2 nanosheets highlights the potential use as electrode material in supercapacitor.
Metal-Ionic Phase Reactions in Molten Salt Ionic Liquids: Experimental, Thermodynamic and Kinetic Analysis of the Alteration of Preformed-Oxides on Fe-Cr Alloys
Authors: HAN Junsoo , Wartenberg Marlene Grace , Scully John R.
Published: February 2020

Abstract

The object of this research is to develop a better experimental, thermodynamic and kinetic understanding of effects of various “harsh” environments on the passive preformed-oxide developed on model structural materials. Ultimately the passive oxide layer governs corrosion processes in molten salts. To this end, systematic studies were conducted on a range of model alloys from Fe to Fe-Cr and Cr as well as Ni and Ni-Cr alloys after passivation in aqueous solutions or by thermal “pre-oxidation in air”. The tested materials were Fe-8Cr, Fe-18Cr binary alloys and nominally pure Fe, Cr as reference metals. These model alloys were subsequently exposed to halide containing aqueous solutions, room temperature and high temperature ionic liquids with various salt species and impurities added in isolation. These may alter or dissolve the preformed-oxide film and ultimately govern the corrosion behavior. The final goal of this project will be to improve the scientific understanding using selected multi-component and model materials in classes of ionic liquids (molten salts) with and without radiation. Experiments have been focused on the non-irradiated materials to date. However, the irradiated materials will also be investigated in various molten salts and room temperature ionic liquids.

The specimens were tested in a borate buffer solution to form a passive oxide layer (2~5 nm thickness) without forming compounds with elements of structural materials. This oxide layer was firstly analyzed in an aqueous chloride containing solution in order to understand its electrochemical properties under more common aqueous condition. Thermally grown pre-oxides at various temperatures, T = 200, 400, 600 and 800°C, and oxides designed by controlled sputter deposition were also investigated. Diagnostics was used to elucidate the type of films on metals, the growth rate and the controlling factors as a function of driving force such as formation potential or temperature. Electrochemical impedance spectroscopy (EIS) was used to first characterize the preformed-oxide. Capacitance and Mott-Schottky plots were utilized in order to quantify film thickness, growth rates versus time, semiconductor dopant type and defect density. Altered oxides and intact oxides were also characterized by XPS and FIB TEM analysis. Changes in these attributes as a function of time of exposure of preformed-oxides to ionic liquids and molten salts will be discussed.

Acknowledgments

This work was supported as part of Fundamental Understanding of Transport Under Reactor Extremes (FUTURE), an Energy Frontier Research Center (EFRC) funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences.

Figure 1
(Invited) Improving Nanosynthesis By Means of Pulsed Anodic Arc Discharge
Authors: Corbella Carles , Portal Sabine , Zolotukhin Denis , Martinez Luis , Lin Li , Kundrapu Madhusudhan , Keidar Michael
Published: February 2020

Anodic arc discharge operated with a periodic voltage signal shows better performance in nanomaterial synthesis compared to steady DC arc discharge. The main advantages of pulsed arcs consist of improved process control, high arc stability, tailoring of material properties, and growth of high-quality materials thanks to reduced production of macroparticles. This study shows the relevance of pulse frequency (1-5 Hz), duty cycle (10-50%), peak arc voltage (~50 V) and peak arc current (~200 A) on determining arc discharge properties. All arc processes are performed in a helium atmosphere at around 300 Torr. Pulsed arc discharges show ablation rates and average power consumption values of the order of 1 mg/s and 1 kW, respectively, which are competitive with typical values of standard DC anodic arcs. Pulsed arc syntheses of low-dimensional carbon (graphene, nanotubes) and molybdenum disulfide nanomaterials are treated as examples for this new deposition method. Plasma parameters have been estimated by optical emission spectroscopy and fast Langmuir probe diagnostics. Characterization techniques such as Raman spectroscopy, scanning electron microscopy and x-ray diffraction have provided information on structural and morphological properties of the cathode deposit. The basic physical processes during arc discharge are described in terms of a global model that considers the total pressure evolution of the system. Such model provides a scenario for the observed erosion dynamics and optical emission patterns associated to the different arc discharge phases. The electrical properties of pulsed arc discharges have been characterized and related to basic plasma structure. In conclusion, pulsed anodic arc plasmas are promising for the synthesis of nanomaterials with special physical and surface properties suitable for electrical, mechanical and optical applications.
Process Intensification Approaches to Organic Electrosynthesis: Towards Sustainable Nylon Production
Authors: Modestino Miguel Antonio , Blanco Daniela Eugenia
Published: February 2020

The effect of fossil-fuel-derived carbon dioxide (CO2) emissions on the environment has fueled the interest in electrifying the chemical industry through electrochemistry. The implementation of electrochemical processes for the production of large volume chemicals can allow for the direct integration of renewable energy sources into chemical manufacturing. Additionally, these processes provide an opportunity for significant energy efficiency improvements and the introduction of previously unexplored chemical transformations. Although inorganic electrosynthetic processes have been successfully implemented in industry at scale (e.g. chloro-alkali and Aluminum production), the use of electrochemical methods for the production of organic chemicals has been limited, even if their potential impact is significantly larger.

In spite of their advantages, organic electrosynthetic processes face common challenges such as limited reactant concentrations in the electrolyte, a complex set of competing organic side reactions, and the narrow electrochemical stability window of aqueous electrolytes.1 The low solubility of organic reactants, together with the use of high current densities that maximize reaction throughput, often result in mass transport limitations that can lower reaction selectivity. As a model case study, this work focuses on the electrohydrodimerization of acrylonitrile (AN) to adiponitrile (ADN), a precursor to Nylon 6,6.2 Although this is considered the largest and most successful organic electrosynthesis implemented in industry, it faces many challenges owing to its limited energy conversion and selectivity. Through a combination of experimental insights and artificial-intelligence-enabled models, we elucidate process intensification guidelines for mass transport enhancement in organic electrosynthesis via electrolyte optimization, complex voltage dosing, and membrane-based electrochemical flow reactors. Moreover, this work explores the development of the sequential electro-hydrogenation of ADN to hexamethylenediamine (HMDA), paving the way for a continuous electrochemical process for the production of Nylon monomers. Our results provide insights on the main challenges faced in organic electrosynthesis, and demonstrate how innovative process intensification approaches can address these challenges and enhance the competitiveness of electrochemical routes for the production of valuable organic chemicals.

Blanco, D. E.; Modestino, M. A., Organic Electrosynthesis for Sustainable Chemical Manufacturing. Trends in Chemistry
2019,
1 (1), 8-10.

Blanco, D. E.; Dookhith, A. Z.; Modestino, M. A., Enhancing selectivity and efficiency in the electrochemical synthesis of adiponitrile. Reaction Chemistry & Engineering
2019,
4 (1), 8-16.
A Novel Metal-Free Robust Recyclable Electrosorbent for Removal Pb(II) from Low Concentrated Solutions in Complex Aqueous Matrices
Authors: Chernyshova Irina , Somasundaran Ponisseril , Bi Wenyan , Shah Darshil , Andreia Da Silva Sara , Ai Chengying , Ponnurangam Sathish
Published: February 2020

We have developed a novel metal-free highly robust recyclable electrosorbent for removal Pb(II) from water. It is based on a cost-efficient and biocompatible conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) which is synthesized through a facile green chemistry route. This electrosorbent demonstrates superior adsorption-desorption properties and recyclability as compared to conventional lead adsorbents and the same sorbent but without electrostimulation. Specifically, its Pb(II) uptake (>800 mg/g without saturation in the presence of excessive NaCl, Ca and Fe) is three-fold higher, while adsorption and desorption kinetics at 400 ppb Pb(II) are faster than without electrostimulation. Importantly, the electrosorbent has 100% reversibility and excellent stability for at least 30 adsorption-desorption cycles and after one-month storage in water. Using XPS and Raman spectroscopy, we link the outstanding properties of the electrosorbent to its unique cation-exchange properties which are enhanced by applied potential. Our results demonstrate a novel strategy for facile manufacturing of cost-effective robust recyclable electrosorbents from conjugated conducting polymers, as well as advantages of electrochemical stimulation for achieving highly repeatable electrosorption and reclamation of valuable metals from their dilute solutions in complex aqueous matrices.
The Chemical Stability of Nasicon As a Solid Electrolyte for Seawater Batteries
Authors: Wi Tae-Ung , Lee Chanhee , Rahman Fahmi , Go Wooseok , Kim Min-Ho , Kim Su Hwan , Hwang Daeyeon , Kwak Sang Kyu , Kim Youngsik , Lee Hyun-Wook
Published: February 2020

Seawater batteries have attracted significant attention for use as grid-scale energy storage systems (ESSs) due to the effective utilization of abundant resources of seawater as a catholyte. Sodium ions in seawater selectively transfer through a solid electrolyte to the anode for saving the chemical energy. For the selective transfer of sodium ions, NASICON (Na3Zr2Si2PO12) electrolytes are one of the suitable candidates for the solid electrolyte to prevent a short circuit between the catholyte and anode. However, NASICON powder is known to be dissolved in water because of the structural instability, leading to catastrophic failure of the system, while NASICON solid electrolytes are stable in seawater during the battery operation.

In this regard, we have carefully compared the stability of NASICON powder and pellets in both DI water and seawater associated with different degradation mechanism. Figure shows the structural stability of NASICON pellets after the immersion tests in DI water and seawater indicative of the chemical stability of NASICON in seawater. In addition, the electrochemical performance shows higher stability of the seawater-immersed electrolyte than the DI water-immersed electrolyte. The corresponding analyses are carried out to confirm the effect of the investigation.

Furthermore, we have employed polymer coating methods to enhance stability and performance as a seawater battery system. The coating layer enables to prevent direct contact with seawater, resulting in longer stability during operation without compromising ionic conductivity. These results reveal that NASICON solid electrolytes can be operated in seawater with high stability and performance.

Figure. The chemical stability comparison of NASICON in seawater and DI water

References

Mauvy, F., Siebert, E., & Fabry, P. (1999). Reactivity of NASICON with water and interpretation of the detection limit of a NASICON based Na+ion selective electrode.
Talanta
, 48(2), 293–303.

Fuentes, R. O., Figueiredo, F., Marques, F. M. B., & Franco, J. I. (2001). Reaction of NASICON with water,
Solid State Ionics
, 263, 309–314.

Kim, Y., Kim, H., Park, S., Seo, I., & Kim, Y. (2016). Na ion- Conducting Ceramic as Solid Electrolyte for Rechargeable Seawater Batteries.
Electrochimica Acta
, 191, 1–7.

Jung, J. Il, Kim, D., Kim, H., Jo, Y. N., Park, J. S., & Kim, Y. (2017). Progressive Assessment on the Decomposition Reaction of Na Superionic Conducting Ceramics.
ACS Applied Materials & Interfaces
, 9(1), 304–310.

Figure 1
Accelerated Screening for Carbon Dioxide Reduction Electrocatalysts and Implications for Reactor Design
Authors: Gregoire John M. , Lai Yungchieh , Jones Ryan , Wang Yu , Zhou Lan
Published: February 2020

CO2 reduction to valuable products is a centerpiece of future energy and sustainability technologies, yet progress in developing efficient and selective catalysts has been limited by the challenges in measuring the performance of electrocatalysts, including sensitivity to the electrochemical environment and the breadth of possible reaction products. The ideal characterization of a given catalyst is quantitative measurement of the activity and product distribution, as a function of time and for a large range of overpotentials since product distributions vary with aging of the operational catalyst as well as the operating potential. This combination of desired measurement attributes is incompatible with traditional experiments, perhaps most notably due to the duration of quantitative product distribution measurements, which impedes measurements over a range of overpotentials and severely limits the measurement frequency to observe variations in product distribution. We present principled design of high throughput screening systems and discuss the implications that these designs have for large-scale reactors. We will also discuss initial results of the high throughput screening that reveal surprising compositional trends in product distributions and provide key examples of where understanding of the uniqueness of Cu in producing high-order products needs to be further developed.
Wet Cleaning by Using Amphoteric Electrolyzed Water for Mask Cleaning
Authors: Ryoo Kunkul , Jung Younwon , Choi Insik , Kim Hyungwon , Lee Jaeyong , Choi Byungsun
Published: February 2020

Process achievement for manufacturing extreme ultraviolet(EUV) semiconductor device requires profound technical varieties such as extreme extension of the existing concepts or new evolutional ones. In this study, a new technology was proposed to fulfill technical details required for EUV semiconductor device cleaning and manufacturing. The special electrolysis technology of ultrapure water(UPW) was introduced to generate water possessing quite unexpectedly mixed character such as pH of 6.5 to 6.7 and oxidation reduction potential(ORP) of -540 to –560 mV at room temperature. Since ORP of –550 mV lasted for several days, it was postulated that water clustering reaction due to hydrogen bond could hinder or retard recombination of H+ and OH- ions by synchronously isolating them electronically and physically. This amphoteric water was applied to cleaning process of EUV device manufacturing to carry out the experiment requiring eventually no chemical use for wet cleaning because of 10 nm feature size. Some results were so excellent that it was convinced that this water clean was evolutional to meet EUV requirements. This water did eliminate adsorbed leftovers of previous chemical treatments and minimized surface modifications because of non-chemical character so that it did not provide any chance of haze formation. Since particle removal efficiency(PRE) was very high, it was proposed that there might be other cleaning mechanism than double layer repulsion(DLR) of colloids. Conclusively, it is time to review the conventional wet cleaning technology and to adopt new concept of the amphoteric water to realize the cleaning technology of EUV device era.
The Effect of Al2O3 ALD Precursors on the Electrochemical Performance of Cathode Materials for Lithium-Based Battery Applications
Authors: Kang Donghyeon , Mane Anil U. , Elam Jeffrey W. , Warburton Robert , Greeley Jeffrey
Published: February 2020

Al2O3 coatings prepared by atomic layer deposition (ALD) using trimethyl aluminum (TMA) and H2O on various cathode materials have been shown to enhance the battery cycle stability of lithium ion batteries. Interestingly, not all cathode materials are enhanced by Al2O3 ALD coating. For example, while Al2O3 coating on lithium cobalt oxide (LCO) using 1-2 TMA/H2O ALD cycles dramatically improves cycle performance [1], much less positive effect on lithium manganese oxide (LMO) was observed [2]. We revealed the TMA surface reactions on LMO are unusual in that they do not involve hydroxyls, ethane is released, and the manganese undergoes redox chemistry from our previous study [2]. Furthermore, density functional theory (DFT) calculations reveal that this unique mechanism is driven by the large free energy changes upon methyl loss from TMA [2].

This information leads us to speculate that the surface reactions and subsequent electrochemistry might also depend on different Al precursors. To evaluate our hypothesis, we are exploring a range of aluminum precursors including trimethyl aluminum (TMA), tris(dimethylamido) aluminum (Al-TDMA), aluminum trichloride (AlCl3), dimethyl aluminum isopropoxide (DMAI), and aluminum triisopropoxide (ATIP) on LCO and LMO cathode materials. Our preliminary results showed that very different ALD chemistries on between LCO and LMO cathode materials. It suggests a correlation between cation reduction on the cathode surface and the relative Lewis acidity of the Al precursor ligands. We will elaborate on these findings using results from XPS measurements, DFT calculations, electrochemical characterizations, and battery cycling studies.

[1] Y. S. Jung et. al., J. Electrochem. Soc.
157 (1) A75-A81, (2010).

[2] L. Chen et. al., Chem
4 2418-2435 (2018).
Controlling the Optical and Electronic Properties of Polyaniline (PAni) Using Vapor Phase Infiltration of Titanium Tetrachloride
Authors: Gregory Shawn A. , Li Yi , Yee Shannon K. , Losego Mark D.
Published: February 2020

This talk with discuss our use of vapor phase infiltration (VPI) to alter the optoelectronic properties of poly(aniline) (PAni). VPI is similar to atomic layer deposition (ALD), but instead of cycling viscous flows of co-reactants, VPI doses a single reactant vapor in a static atmosphere followed by a pump-purge cycle. ALD typically provides conformal surface coatings while VPI enables extensive sub-surface diffusion and reactions within organic substrates. In particular to our study, PAni was VPI treated with a single cycle of TiCl4­­-H2O, and the resulting hybrid films showed unique optoelectronic properties that have not been previously reported. As VPI hold time increased, PAni films turned from blue to nearly transparent to green. This color transition is because of the formation of polaronic charge carriers concomitant with the formation of TiOx; the polaronic carriers absorb the red-NIR-MIR spectra (700- 5000 nm) while TiO­x absorb the blue-UV region (450 - 350 nm). This combination of optical absorbances in PAni has not been observed before. Furthermore, these polaronic carriers enabled electrical conductivities as high at 0.2 S/cm- ca. 3 orders of magnitude higher than prior PAni VPI doping studies. By varying the TiCl4 exposure time and measuring ex-situ­ optical signatures, an effective diffusion coefficient of ca. 1·10-15 cm2/s was measured; this value is self-consistent with the measured film thicknesses and optical peak intensity evolution. Additionally, we demonstrated that the relative ratio of UV and IR absorbing species can be controlled by varying reaction temperature. Lastly, XPS measurements elucidated a reaction mechanism for the formation of TiO­x and PAni polarons. By better understanding this reaction mechanism and kinetics, ALD and VPI can be optimized for future organic semiconductor doping processes.
Electrochemical Atomic Layer Etching (e-ALE) of Copper - Thermodynamic and Diffusion-Reaction Considerations of the Surface-Limited Sulfidization of Copper
Authors: Gong Yukun , Akolkar Rohan
Published: February 2020

Deposition and etching of ultra-thin materials are critical to many technological applications including nano-electronics and electrocatalysis. Atomic layer etching (e-ALE) in particular is attractive because it can enable precise sub-nm control over the etching rate. Conventionally, atomic layer etching of materials is achieved using plasma-assisted techniques; however, when applied to metal etching, such techniques have several drawbacks including generation of volatile byproducts, low throughput and high cost. An alternative electrochemical atomic layer etching (e-ALE) approach, utilizing benign liquid-phase precursors and electrode potential control, is being developed in our group. The e-ALE process enables atomic layer-by-layer etching of metals such as Cu with unprecedented control over etching rate and surface smoothness. In our e-ALE approach, surface-limited sulfidization facilitates formation of a monolayer of cuprous sulfide (Cu2S) on Cu. The Cu2S monolayer is then selectively etched using a halide-containing etching solution. The two-step sequence (sulfidization + etching) can be repeated to achieve atomic layer-by-layer etching as confirmed using stripping coulometry measurements and atomic force microscopy. This talk will discuss the unique characteristics of the e-ALE chemistry and its applicability to a broader class of materials.

Figure 1
(Invited) Application of ALD-Grown Metal Oxide Layers for Energy Applications: Photovoltaic and Photoelectrochemical Water Splitting
Authors: Shin Byungha
Published: February 2020

ALD is a versatile growth technique for depositing a thin conformal layer of various functional materials. In this presentation, I will discuss two applications of ALD in energy materials research—photovoltaics (PV) and photoelectrochemical (PEC) water splitting. In the PV part, I will present how ALD-growth thin dielectric layers can be used to passivate both the top and bottom interfaces of Cu2ZnSnSe4 solar absorber, which has been drawing attention in the PV community as an earth-abundant, non-toxic and cheap solar material. The passivation strategy with the thin ALD-grown layers led to significant improvement in open-circuit voltage by suppressing charge recombination.[1] Another example of the ALD application in thin film PV is the replacement of CdS—the most common buffer layer in CIGS solar cells but with a toxic Cd—with ALD-ZnTiO.[2] I will present the application of ALD-ZnTiO whose materials properties were tuned In the PEC part, various metal oxide layers prepared by ALD were applied to Cu(In,Ga)Se2 (CIGS) photocathode as protection layers to prevent photo-corrosion of the CIGS in a liquid electrolyte.[3],[4] Different degradation mechanisms were identified for PEC devices with different ALD protective overlayers, details of which will be discussed.

[1] Kim et al., Progress in Photovoltaics, 25 (2017), 4.

[2] Hwang et al., ACS Applied Materials & Interfaces, 10 (2018), 20920.

[3] Koo et al., ACS Applied Materials & Interfaces, 9 (2017), 5279.

[4] Koo et al., Advanced Functional Materials, 28 (2018), 16.
(Invited) Emerging Low-Dimensional Material Electronics and Photonics
Authors: Wang Han
Published: February 2020

In this talk, I will discuss our recent work in studying the electronic, optical and ferromagnetic properties of emerging two-dimensional materials, and in developing them for novel electronic and photonic device applications. The first part of the talk will focus on discussing our recent research on the phonon-spin and phonon-electron coupling in ferromagnetic monolayer materials and its device applications. In the second part of the talk, I will discuss our work on developing black phosphorus for silicon integrated infrared sensing and imaging applications. Our work on characterizing the fundamental properties of black phosphorus and its application in high performance mid-infrared detector devices will be discussed. I will conclude with remarks on promising future research directions of low-dimensional material electronic and optical devices, and how they may impact future electronics and photonics technologies.
Device Structure and Passivation Options for the Integration of Scaled IGZO TFTs
Authors: Kabir Muhammad Salahuddin , Chowdhury Rahnuma Rifat , Manley Robert G. , Hirschman Karl D
Published: February 2020

The focus of this work is on the performance dependence of scaled IGZO TFTs with variations in gate electrode configuration and passivation options. A conservative process for the fabrication of long channel length devices (i.e. L ≥ 2 µm) exhibits long-channel behavior and excellent stability in both bottom-gate (BG) and double-gate (DG) configurations [1,2]. As the devices are scaled to shorter channel lengths, limitations of the device electrostatics begin to give way to short channel behavior. Dielectrics used for the gate and back-channel regions are typically adjusted to overcome short-channel effects as lateral dimensions are reduced. However certain interaction effects require additional process modifications for the desired device response and to accommodate the details of process integration. Scaled devices with channel lengths L < 2 µm are under investigation, with process conditions evaluated by quantitative measures on the materials properties, electrostatic behavior, and stability when subjected to bias and thermal stress. Process recipes for PECVD passivation layers, oxygen ambient annealing, and ALD capping materials are under reevaluation for their impact on short-channel devices. TCAD simulation is used as a resource to refine material and device models [3], and provide insight on the details which establish the limits of device operation. Design rule scaling and self-aligned gate device structures are also being studied for reduced parasitic capacitance and stage delay, and a reduction in overhead real estate.

[1] T. Mudgal, N. Edwards, P. Ganesh, A. Bharadwaj, Eli Powell, M.S. Pierce, R. G. Manley, and K. D. Hirschman, “Investigation on the Gate Electrode Configuration of IGZO TFTs for Improved Channel Control and Suppression of Bias-Stress Induced Instability”, ECS Trans. 75 (10), 189-197 (2016)

[2] M.S. Kabir, P. Ganesh, R.R. Chowdhury, H. Sethupathi, J. Okvath, J. Konowitch, R.G. Manley and K.D. Hirschman, “Channel-length dependent performance degradation of thermally stressed IGZO TFTs”, ECS Trans. 86 (11), 125-133 (2018) DOI: 10.1149/08611.0125ecst

[3] K.D. Hirschman, T. Mudgal, E. Powell and R.G. Manley, “A 2D empirical model for on-state operation of scaled IGZO TFTs exemplifying the physical response of TCAD simulation”, ECS Trans. 86 (11), 153-166 (2018) DOI: 10.1149/08611.0153ecst

Figure 1
(Keynote) Devices for Si Based Quantum Computing
Authors: Vinet Maud
Published: February 2020

Universal quantum computers offer potentially disruptive solutions to solve currently intractable problems. They provide a tool to artificially reproduce quantum systems with another quantum system that can be programmed at will by making use of phenomena that only occur in the quantum world such as superposition and entanglement. However, modern quantum processors are still relatively simple and their performance is still far from what current classical supercomputers can achieve. Technologies such as ion traps or superconducting qubits are leading the first wave of development with machines of a few tens of quantum bits or qubits1, the basic unit of quantum information processing. These two technologies are attracting the first rounds of public funding at the European level with the Flagship Programme on Quantum Technologies and a significant amount of private funding with superconducting qubit initiatives run by well-established American companies such as IBM, Google or start-ups like IonQ or Rigetti Computing.

However, the current qubit numbers are insufficient to realise quantum computation of significant practical use. To run a simulation of a simple material the predictions set the number of necessary qubits to 102-103 units and for an arbitrarily complex one to 106-108 units. Scaling up to a large number of qubits is hence the greatest challenge to fulfill the promises of quantum computing. Current hardware approaches to ion trap and superconducting qubits offer limited prospects for scalability with qubit densities of 1 and 100 qubits/cm2, respectively.

Compared to other quantum computing implementations, qubits silicon-based spin qubits offer the best prospects in terms of scalability. The typical footprint of silicon-based spin qubits manufactured with complementary-metal-oxide semiconductor technology is of the order of a few hundred nm².

In addition to their small footprint, Si spin qubits actually show promising performance and a rapid rate of improvement. Recent experimental demonstrations in several academic environments have demonstrated single-qubit gates with fidelities well-above error-correction protocols (>99%17) in cases exceeding those of superconducting qubits, whereas two-qubit gates (F2Q = 98%19) are already above the typical values observed in superconducting systems and are rapidly improving.

In this paper, we will first remind the principle of how to design a qubit based on silicon. Then we will review the current state-of-the-art and will present the architectures to design a large scale quantum computer based on Si spin qubits, their pros and cons regarding variability assumptions and technological achievements will be discussed. We will also show how the recent demonstration of long distance quantum information transfer can be implemented in silicon.
(Invited) Controlled Synthesis and Thermoelectric Properties of Tin Telluride-Based Topological Crystalline Insulator Nanowires
Authors: Zhang Shixiong
Published: February 2020

Tin telluride (SnTe) and its related alloys have recently attracted significant interest in the thermoelectric community because of their great potential as environmental-friendly alternatives to the conventional lead telluride-based thermoelectric materials. Meanwhile, they have been demonstrated by condensed matter physicists to be a class of novel quantum materials named topological crystalline insulators (TCI's), which host topological states on their high symmetry crystal surfaces. The SnTe-based TCI's possess intriguing surface properties, including Dirac cones in their electronic band structure and Van-Hove singularities in the density of states. One-dimensional TCI nanowires with large surface-area-to-volume ratios and well-defined facets provide an excellent platform to enhance topological surface contributions to the thermoelectric properties.

In this talk, I will present the controlled growth and thermoelectric studies of SnTe-based TCI nanowires. In particular, I will discuss how we control the facet, diameter, doping, and alloying in the vapor-liquid-solid growth of SnTe nanowires. Measurements of the Seebeck coefficient, and electrical and thermal conductivities were performed on the same single nanowires to accurately determine their thermoelectric figure of merit. I will discuss the enhancement of the Seebeck coefficient and suppression of thermal conductivity in connection with the topological states, doping, alloying, and nano-structuring.
A Novel Approach to Join Large Coefficient of Thermal Expansion (CTE) Mismatched Thermoelectric (TE) Materials for High Temperature Applications
Authors: Aranda Michell , Chi Ike Suchih , Ravi Vilupanur , Villalpando Obed , Singleton Brooke , Drymiotis Fivos , Li Billy Chun-Yip , Fleurial Jean-Pierre
Published: February 2020

Radioisotope thermoelectric generators (RTGs) have been used to enable deep space exploration where solar power is scarce. Various NASA missions such as Voyager 1 and Voyager 2 have used RTGs and have traveled over 11 billion miles from Earth. Heritage RTGs have reliably provided power throughout the lifetime of the various missions but thus far have been relatively inefficient and convert less than 10% of heat to electricity. A method to achieve higher thermal to electrical conversion efficiencies is via the segmentation of advanced thermoelectric (TE) materials. High thermoelectric efficiencies can be achieved by constructing a TE device that includes combining different TE materials optimized at different temperatures and joining them together. Though advantageous to achieve high performance, segmentation can be challenging due to differences in material properties such as the coefficient of thermal expansion (CTE). Thermal stresses induced by large CTE mismatch of TE materials during the joining process can cause cracking at the bonded interface, these stresses need to be minimized in order to reduce the probability of cracking at the joint interface. Additionally, the bonds formed between materials need to be both chemically and mechanically stable and require high thermal conductivity along with low electrical contact resistance. In this study two thermoelectric materials with dissimilar CTE at room temperature were joined by using a graded-CTE bonding approach. The thermal stress states of the two thermoelectric materials were modified to avoid cracking at the bonding interface. Optical and scanning electron microscopy (SEM) was used to characterize the cross-section of the bonded thermoelectric materials. Preliminary results of a stress model shows a reduction of stress at the bonded interface and is in agreement with experimental results.
(Invited) Energy Transport at the Nanoscale
Authors: Lee Woochul
Published: February 2020

Energy transport at the nanoscale differs fundamentally from that at the bulk scale. Characterization and understanding of the unique energy transport phenomena that arise at the nanoscale is key to developing novel technological applications such as energy conversion devices and atomic-scale device components. In this talk, I will present my work on understanding unique thermal transport in various nanomaterials. I will also discuss heat dissipation in atomic-scale junctions that are composed of single atomic chains or single molecules. Further, experimental techniques to perform challenging experiments will be briefly described.
(Invited) Balancing the Source and Sink of Oxygen Vacancies for the Resistive Switching Memory
Authors: Park Tae Hyung , Hwang Cheol Seong
Published: February 2020

The high non-uniformity and low endurance of the resistive switching random access memory (RRAM) are the two major remaining hurdles at the device level for mass production. Incremental step pulse programming (ISPP) can be a viable solution to the former problem, but the latter problem requires a material-level innovation. In valence change RRAM, electrodes have usually been regarded as inert (e.g., Pt or TiN) or oxygen vacancy (VO) sources (e.g., Ta), but different electrode materials can serve as a sink of VO. In this work, an RRAM using a 1.5nm-thick Ta2O5 switching layer is presented, where one of the electrodes was VO-supplying Ta and the other was either inert TiN or VO-sinking RuO2. While the TiN could not remove the excessive VO in the memory cell, the RuO2 absorbed the unnecessary VO. By carefully tuning (balancing) the capabilities of VO-supplying Ta and VO-sinking RuO2 electrodes, an almost invariant ISPP voltage and a greatly enhanced endurance performance can be achieved.
Optically Switchable Memristors: A Route to Hierarchical Control in Artificial Intelligent Systems
Authors: Kemp Neil Timothy
Published: February 2020

Modulation of resistive switching memory by light opens the route to new optoelectronic devices that can be switched optically and read electronically. Applications include integrated circuits with memory elements switchable by light and optically reconfigurable and tunable synaptic circuits for neuromorphic computing applications and brain-inspired artificial intelligent systems. A novel polarization and wavelength-specific optoelectronic memory device is presented1 that can be controlled purely optically, electronically or by both. Optical or electronic modulation switches the device between low and high conducting states whilst modulation by both facilitates fine-tuning of the resistive memory properties and switching characteristics of the device.

In biological synapses, the connection strength (plasticity) between two neurons is controlled by the ionic flow through the synaptic cleft and it is widely believed that the adaptation of synaptic weights enables biological systems to learn and function. Similarly, the conductance of a memristor depends on the history of the total charge that has travelled through it. A key feature of neuronal learning is habituation, whereby repeated stimuli strengthens the synaptic plasticity whilst a lack of stimuli results in weakening. Learning in biological systems also involves spike-timing-dependent plasticity (STDP). In STDP, learning the synaptic efficacy governing potentiation and depression is determined by the temporal order of pre-synaptic and post-synaptic spikes.

Using our optical memristor device, we demonstrate optical control of synaptic potentiation and depression, optical switching between short and long-term memory and optical modulation of the synaptic efficacy via spike timing dependent plasticity. The work opens the route to dynamic patterning of memristor networks both spatially and temporally by light, thus allowing the development of new optically reconfigurable neural networks and adaptive electronic circuits.2
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References

Jaafar, A. H. et al. Reversible optical switching memristors with tunable STDP synaptic plasticity: a route to hierarchical control in artificial intelligent systems. Nanoscale
9, 17091 (2017).

Kossifos, K. M., Antoniades, M. A., Georgiou, J., Jaafar, A. H. & Kemp, N. T. An Optically-Programmable Absorbing Metasurface. IEEE Int. Symp. Circuits Syst. (2018). doi:10.1109/ISCAS.2018.8351874

Georgiou, J., Kossifos, K. M., Antoniades, M. A., Jaafar, A. H. & Kemp, N. T. Chua Mem-Components for Adaptive RF Metamaterials. IEEE Int. Symp. Circuits Syst. (2018). doi:10.1109/ISCAS.2018.8351852

Figure 1
Superconformal and Bottom-up Filling of High Aspect Ratio Features
Authors: Josell Daniel , Braun Trevor Michael , Ambrozik Stephen , Moffat Thomas P.
Published: February 2020

Superconformal, and more particularly bottom-up, copper electrodeposition in fully metallized, high aspect ratio features enables the fabrication of interconnects, including in chip stacking technologies. I will discuss mechanistic understanding of such bottom-up filling processes for cobalt, nickel, gold and copper deposition in through silicon vias from electrolytes containing (only) deposition rate suppressing additives as well as analogous bottom-up gold filling of similar size trenches from electrolyte containing deposition accelerating bismuth additive. Electrochemical measurements on planar substrates combined with mechanistic understanding enable accurate a-priori prediction of filling evolution and, for the nickel, cobalt and gold suppressor-based systems, microstructural variation associated with additive incorporation.