bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Is Ion Migration Needed for Resistance Memory and Memristor?
Authors: Chen I-Wei 
Published: February 2020

This presentation will focus on the electronic behavior of resistance switching memory, and contrast it with the expectation of ionic and Joule heating mechanisms that have received much attention in this field. Several prototypical memories, ranging from the filamentary type to the nanometallic type, will be examined. Filamentary memory is believed to undergo resistance switching along a nanoscale filament between the electrodes, and there is extreme concentration of ion and heat flow along the filament. It usually requires dielectric breakdown (called “forming”) prior to operation, or else the device remains resistive and cannot be switched. Nanometallic memory is believed to undergo resistance switching only when the film is thinner than a certain thickness, and it switches uniformly by way of voltage-trapping/detrapping of electrons, which alter the localization length of electron wave function. Although their switching and conduction mechanisms have been thought to be entirely different, one relying on ions, the other electrons, there are surprising similarities between the two, summarized below.
*Their high resistance states are insulating, and their low resistance states are metallic, having opposite signs of temperature sensitivity of resistance, as evidenced by resistivity data down to 18 mK.
*Their high resistance states are unstable under a mechanical pressure, which triggers them to switch to the low resistance states in less than a picosecond without any voltage assistance.
*Their low resistance states are stable under a mechanical pressure.
*Their on/off switching is triggered when their switching elements experience a critical voltage, which because of load sharing can be substantially less than the device voltage.
Since as-fabricated nanometallic memory is already in the low resistance state, it is also stable under a mechanical pressure. However, a virgin, highly resistive filamentary memory can be alternatively “formed” to the low resistance state by a pressure alone, without going through dielectric breakdown. This, along with pressure-triggered switching from the high resistance state to the low resistance state, provides unequivocal evidence that forming and switching can proceed without any ion migration, even in a filamentary memory.
In addition to the above, voltage-controlled switching is difficult to rationalize by the existing switching models for filamentary memory. These models all invoke a critical amount of electric current and joule heating to break and reconnect filaments, which are not likely to be voltage-controlled processes.
Lastly, filamentary memory has been used to emulate synapses. But all synaptic ion channels (Na or Ca) are voltage-gated. Therefore, the finding that both nanometallic and filamentary memories are voltage-controlled is fundamentally relevant to using memristors for neuromorphic computing.
Mercury Selective GaN HEMT Sensor for Dynamic Water Quality Monitoring
Authors: Sukesan Revathi , Chen Yi-Ting , Wang Yu-Lin 
Published: February 2020

Mercury is an extremely toxic metal that can cause irreversible damage to human, animal and plant life. Even a very low level exposure to mercury over a long period of time is detrimental. Monitoring mercury levels in drinking water, water bodies and other drinks are thus necessary.
A method which can detect mercury level instantly from the sample would be ideal, but traditional methods are really complex and time consuming, they also require bulky and costly apparatus and in some cases requires really high temperature up to 10000K.
Recently ion-selective electrodes have been quite popular due to their portability and selectivity also they are economical than the traditional methods. In our research, we utilize an AlGaN/GaN high electron mobility transistor by functionalizing the gate area with a polyvinyl chloride (PVC) based ion selective membrane. The functionalized HEMT device is applied with pulsed gate bias at reference gate electrode positioned at fixed distance from the membrane functionalized channel region. The gate bias drops across the test solution, influencing the membrane on the channel where specific ionophore captures the target heavy metal ion. Thus the liquid gated HEMT’s drain current response is a function of the concentration of the target heavy metal ion. The unique sensing structure design enables direct detection of target ions in a background matrix of high ionic concentration solution. Ionophores are added to the membrane which increases the affinity to the particular ion and promises high specificity and low affinity for other ions.
The sensing technique enables direct detection of target ions in the medium using GaN HEMT and innovative biosensor packaging methodology, a portable biosensor system has been designed and fabricated which can provide quantitative detection in 10 minutes with a 10 µl sample.
The sensor showed a rapid and stable response when introduced to solutions of varying Hg2+ concentrations. An interesting thing about the technique is that that the pH of the sample is between 6-7, which helps in real time testing and have a fast response time. ISFET sensors are portable and robust, they also show better selectivity and sensitivity when compared to traditional electrochemical ion selective electrodes and for AlGaN/GaN devices with other forms of functionalization. These devices have much greater possibilities for development and integration as they don't require a reference electrode which reduces the manufacturing costs of ISFET. The development of this sensor will help in providing real time monitoring of water quality in rivers or water bodies, tap water and even beverages which will be a great boon to humankind.

Figure 1
(Invited) Low-Resistance Ohmic Contacts to Al0.45Ga0.55n/ Al0.3Ga0.7n HEMTS
Authors: Klein Brianna , Baca Albert G. , Armstrong Andrew M. , Allerman Andrew A. , Douglas Erica A. , Sanchez Carlos , Kotula Paul , Miller Mary , Reza Shahed 
Published: February 2020

RF amplifiers and power electronics transistors in III-N semiconductors are increasingly important in emerging applications, as are photo-transistors for the purpose of UV light detection. Increasing the Al fraction in AlGaN-based HEMT devices enables transistors with higher breakdown voltages and a potentially favorable breakdown - specific on-resistance tradeoff. However, the advantages of higher aluminum content comes with a major challenge: Ohmic contacts with acceptable contact resistance become increasingly problematic with increasing Al content in the channel and barrier layer. We report sub 10-4 W-cm2 specific contact resistivity (rc) for a 30% channel, improving on the best prior result of approximately 2x10-4 W-cm2for AlGaN channels of at least 30% Al.
We investigated five different Ohmic contact metallizations consisting of X/Al/Y/Au where X = Ti, Nb/Ti, Zr, or V, and Y = Ni, Mo, or V (Table 1) as function of alloying conditions. The MOCVD-grown structure (Figure 1) is on sapphire substrates and consists of a 1.6 µm AlN buffer layer, a 4.15 µm thick Al0.3Ga0.7N channel layer and a 50 nm thick Al0.45Ga0.55N barrier with Rsheet of 3500 Ω/□ and ns= 5x1012/cm2. Representative current-voltage plots measured on circular TLM structures are shown in Figure 2. Ohmic contacts with average specific contact resistance (pc) of 7x10-5 Ω-cm2 (3.3x10-5 Ω-cm2) extracted from device (TLM) data were achieved with a conventional Ti/Al/Ni/Au metal stack and a multi-temperature stepped-anneal process. Structural characterization was carried out on the Ti/Al/Ni/Au contacts, to compare Ohmic and Schottky conditions. TEM was used to characterize the interaction between the contact metals and the AlGaN, revealing an interface consisting primarily of Ti-Au with limited indication of spiking behavior. Using the optimized Ohmic contact process, HEMTs with 10 µm source-to-drain spacing and 2 µm gate lengths were fabricated; current densities of 78 mA/mm were achieved, and parasitic loading of RON was reduced.

This work was supported by the Laboratory Directed Research and Development (LDRD) program at Sandia. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Figure 1
An Investigation of Smart Aqueous Binder for Novel Solid Electrolyte Interphase Formation on Silicon in Lithium Ion Battery
Authors: Lin Pin-Ling , Wang Fu-Ming 
Published: February 2020

Polysiloxane is an environmental friendly chemical that is used in adhesives, medicine, and insulations, respectively. Currently, the solid electrolyte interphase (SEI) formation on cathode and anode in lithium ion battery is important due to the ionic diffusivity enhancement and lowers the irreversibility of electrochemical reaction. Silicon is regarded as one of the most promising anodes for lithium ion battery owing to its large theoretical energy density (about 4200 mAh g−1). However, its practical application is limited by structure degradation.
In this study, a new compound has been developed, which is combined with the functions of SEI formation and particle adhesion in electrode. This new technology is used to eliminate the huge irreversible reaction on first cycle and effectively extend the cycle life. The new compound was composed by the bismaleimide (BMI) and the polymethylhydrosiloxane (PMHS) through hydrosilylation reaction (shown in Figure 1). The functionalized aqueous product provides three performances including excellent adhesion property with silicon particles on backbone structure, high ionic conductive SEI with high reduction potential on imide structure, and ionic hopping site on acrylate ethyl oxide side chain.
It is the first time that combines binder, SEI, and ionic transfer functions in one material in order to solve the uneven distribution of electrochemical reaction on silicon particles. In addition, we anticipate that the volume expansion and irreversible reaction on silicon can be effectively eliminated by this new technology. We also expect that this functionalized smart aqueous binder delivers outstanding electrochemical behavior and are looking forward to eradicate the disadvantages of silicon.

Figure 1
(Invited) 2-Dimensional Layered Materials for Si Technology
Authors: Shin Hyeon-Jin 
Published: February 2020

Two dimensional (2D) layered materials are crystalline materials with layered structures, including Graphene, h-BN, and Transition Metal Di-chalcogenides (TMD’s). Each of their layers is consisting of one or a few atomic layers and they form van der Waals interactions with neighboring layers. Recently, they have been studied intensively due to their extraordinary properties, such as, flexibility and transparency. In addition, they have exceptional electronic, optoelectronic, chemical and mechanical properties. For example, Graphene has high electron mobility, chemical inertness, and thermal conductivity, while TMD has high photo responsivity. Based on their properties, many potential applications were proposed and demonstrated.
We have been investigated 2D layered materials for Si technology, but not for the active materials. We have focused 2D layered materials as interface materials due to the chemical inertness and their atomically thin nature. Especially, Graphene has been suggested as a promising material for future interconnects because of its unique electrical and chemical properties. For instance, they are good candidates for diffusion barrier.[1]
Also, they are good candidates for interface materials between metal and Si to reduce the Schottky barrier heights and contact resistance in source and drain, which is one of the most critical issues for scaling down.[2]
In this talk, we will cover and discuss the possibility of Graphene and other 2D layered materials for interconnects and contact resistance reducer in Si technology. In addition, we will also cover other potential applications based on 2D materials’ unique properties, such as, chemical inertness and atomic thick nature.
[1] L.Li et al., “Verticle and lateral copper transport through graphene layer”, ACS Nano, 9 (8), pp. 8361-8367 (2015)
[2] K.-E. Byun et al., “Graphene for true ohmic contact at metal-semiconductor junctions”, Nano Letters, 13 (9), pp. 4001-4005 (2013)
(Invited) Orientation Dependent GaAs Nanowire Schottky Solar Cells with 16% Efficiency
Authors: Han Ning , Ho Johnny C 
Published: February 2020

Nowadays, high efficiency and low cost solar cell is still technological challenging. In this study, crystalline GaAs NWs with the uniform, pure <110>, <111> orientations and other different mixture ratios can be successfully prepared by tuning the catalyst thickness, nucleation and growth temperatures in the two-step chemical vapor deposition. The single GaAs NWs are fabricated into Au-Al asymmetric Schottky contact solar cells 1 by a simple ultraviolet photolithography process. The low-cost NW solar cell shows a record high efficiency of ~16% under air mass 1.5 global (AM 1.5G) illumination, which produces another record in addition to the vertically aligned p-i-n GaAs NW solar cells previously reported (40%), where the superior photovoltaic performance is attributed to the light concentrating effect of NWs with diameter in the order of light wavelength 2. Employing lift-off resists, three-layer NW parallel arrays can be easily attained for X-ray diffraction in order to evaluate their growth orientation along with the fabrication of NW parallel arrays based Schottky photovoltaic devices for the subsequent performance assessment3. Notably, the open circuit voltage of purely <111>-oriented NW arrayed cells is far higher than that of <110>-oriented NW arrayed counterparts, which can be interpreted by the different surface Fermi level pinning existed on various NW crystal surface planes due to the different As dangling bond densities.
Fig1. (a) Output IV curve of a single GaAs NW solar cell and (b) the orientation dependent PV property of printed GaAs NW array solar cells
Ref.
1. Han, N.; Yang, Z.; Wang, F.; Dong, G.; Yip, S.; Liang, X.; Hung, T. F.; Chen, Y.; Ho, J. C., High performance GaAs nanowire solar cells for flexible and transparent photovoltaics. ACS Appl. Mater. Interfaces
2015,
7, 20454-20459.
2. Krogstrup, P.; Jorgensen, H. I.; Heiss, M.; Demichel, O.; Holm, J. V.; Aagesen, M.; Nygard, J.; Morral, A. F. I., Single-nanowire solar cells beyond the Shockley-Queisser limit. Nat. Photonics
2013,
7 (4), 306-310.
3. Han, N.; Yang, Z. X.; Wang, F. Y.; Yip, S.; Li, D. P.; Hung, T. F.; Chen, Y. F.; Ho, J. C., Crystal Orientation Controlled Photovoltaic Properties of Multilayer GaAs Nanowire Arrays. ACS Nano
2016,
10 (6), 6283-6290.

Figure 1
(Invited) Controllable Growth of High-Performance Gasb Thin Nanowires By a Surfactant Assisted CVD Process
Authors: Yang Zaixing 
Published: February 2020

Although various device structures based on GaSb nanowires have been realized, further performance enhancement suffers from uncontrolled radial growth during the nanowire synthesis, resulting in non-uniform and tapered nanowires with diameters larger than few tens of nanometers. However, high-quality and uniform GaSb NWs with diameters down to 20 nm have been prepared by using a sulfur surfactant technique in our previous works, which efficiently stabilizes the high-energy sidewalls for homogenous NW formation during the chemical vapor deposition (CVD) process.1 At the same time, the growth direction and corresponding carrier mobilities are still found to be heavily depended on the NW diameters, in which the <111>-orientated GaSb NWs exhibit the highest hole mobility because of the optimized surface passivation and roughness in preference to the minimized surface traps, indicating the potential applications of these phase pure NWs for high-performance electronics.2

Using CMOS-compatible Pd catalysts and a complementary experimental and theoretical approach, we demonstrate successfully the formation of high-performance, <111>-oriented GaSb nanowires (NWs) via vapor-solid-solid (VSS) growth mode in surfactant-assisted chemical vapor deposition. When back-gated field-effect transistors (FETs) are fabricated using these NWs, the Pd-catalyzed GaSb NW exhibits a superior peak hole mobility of ~330 cm2V-1s-1, and this value is close to the mobility limit for a NW channel diameter of ~30 nm with a free carrier concentration of ~1018 cm-3, indicating excellent homogeneity of the NW phase purity, the growth orientation, the surface morphology and the electrical characteristics. Contact printing process is also used to fabricate large-scale assembly of Pd-catalyzed GaSb NW parallel arrays, and a calculated peak hole mobility of ∼65cm2V-1s-1 is achieved, confirming the potential construction and application of these high-performance electronic devices. 3

Acknowledgment

We acknowledge “Qilu young scholar” program of Shandong University.

References

1. Yang, Z.-x.; Han, N.; Fang, M.; Lin, H.; Cheung, H.-Y.; Yip, S.; Wang, E.-J.; Hung, T.; Wong, C.-Y.; Ho, J. C., Surfactant-assisted chemical vapour deposition of high-performance small-diameter GaSb nanowires. Nature Communications
2014,
5, 5249.
2. Yang, Z.-x.; Yip, S.; Li, D.; Han, N.; Dong, G.; Liang, X.; Shu, L.; Hung, T. F.; Mo, X.; Ho, J. C., Approaching the Hole Mobility Limit of GaSb Nanowires. Acs Nano
2015,
9 (9), 9268-9275.
3. Yang, Z.-x.; Liu, L.; Yip, S.; Li, D.; Shen, L.; Zhou, Z.; Han, N.; Hung, T. F.; Pun, E. Y.-B.; Wu, X.; Song, A.; Ho, J. C., Complementary Metal Oxide Semiconductor-Compatible, High-Mobility,< 111>-Oriented GaSb Nanowires Enabled by Vapor-Solid-Solid Chemical Vapor Deposition. ACS nano
2017, DOI:
10.1021/acsnano.7b01217.
(Invited) Investigation of Single WS2 Nanotubes Leads to New Observations and Potential Applications
Authors: Tenne Reshef 
Published: February 2020

Multiwall nanotubes and fullerene-like nanoparticles of WS2 are produced in large amounts, offering numerous opportunities for their investigation and future applications. While many studies focus on the preparation and studying the characteristics of bulk matrices incorporating these nanotubes, the investigation of individual nanotubes permits addressing intriguing issues, encompassing their unique optical, electrical and mechanical properties.
In this report, the author will dwell on several new studies. FET of WS2 nanotubes with liquid ionic gating demonstrated that the nanotubes become superconducting at low temperatures (5.8 K).1 The magnetoresisitance exhibited strong Little-Parks oscillations under magnetic field parallel to the tube axis, which originates from the interference of the supercurrent along the circumference of the nanotube. The coupling of the supercurrent with the magnetic field in the chiral tubes produces nonreciprocal second harmonic signal.
In another study, the electromechanical characteristics of a torsion device based on single nanotube was studied.2 A high frequency resonator with high quality factor was established. The high quality factor of the WS2-based device was attributed to the interlocking of the layers, which minimize the dissipative losses due to reciprocating motion of the nanotubes walls during torsion.
The wetting of single WS2 nanotube retracted from a liquid surface was studied experimentally and by detailed computational anlaysis.3 Nanotubes with different diameter and having open or closed tips were studied. It was found that the water does not wet the outer wall of the nanotubes. However, nanotubes with open end of diameter below say 40 nm exhibited strong interaction with the water surface. Careful analyses indicated that strong capillary action leads to the filling of the hollow nanotube core which leads to large dissipated energy during withdrawal of the nanotube.
At the end of the talk, the author will briefly deliberate on the commercial applications of fullerene-like WS2 nanoparticles in advanced lubrication and the industrial prospects of nanotubes thereof.

References

1. F. Qin, W. Shi, T. Ideue, M. Yoshida, A. Zak, R. Tenne, T. Kikitsu, D. Inoue, D. Hashizume, and Y. Iwasa, Nature Comm., DOI: 10.1038/ncomms14465 (2017).

2. Y. Divon, R. Levi, J. Garel, D. Golberg, R. Tenne, A. Ya’akobovitz and E. Joselevich, Nano Lett.
17, 28-35 (2017).
3. O. Goldbart, S.R. Cohen, I. Kaplan-Ashiri, P. Glazyrina, H.D. Wagner, A. Enyashin and R. Tenne, Proc. US Natl. Acad. Sci. (PNAS)
113, 13624-13629 (2016).
(Invited) Performance Improvement of Silver-Nanowire-Based Flexible Transparent Electrodes By Capillary-Force-Induced Cold Welding
Authors: Liu Yuan , Ren Zhifeng , Guo Chuan-Fei 
Published: February 2020

Currently, silver-nanowire-based (AgNW-based) flexible transparent electrodes exhibit the most promising performance. The electrical performance of a AgNW network depends strongly on the wire-wire junction contact. Several techniques of nanowelding or soldering have been reported to reduce the wire-wire junction resistance, but these methods may either have adverse effects on the nanowires or the substrate, or require either specific facilities or additional materials as the “solder”.
We would like to report on a new method based on capillary-force-induced cold welding. We show at nanoscale, capillary force can be used as a powerful driving force to effectively induce the self-limited cold-welding of wire-wire junctions for AgNWs. The capillary-force-induced welding can be performed by a moisture application process which is simple, fast and does not require additional materials or expensive facilities. We are able to achieve a significant improvement in electrical conductivity and flexibility, but negligible changes in transparency.
We have also demonstrated that this method is effective to heal damaged AgNW films of wearable electronics. Our capillary-force-based method may also be useful in the welding of other metal NWs and the fabrication of nanostructures or smart assemblies for versatile flexible optoelectronic applications.