bluuebunny/crossref_metadata_2025_split huggingface dataset:
Organic Electrochemical Transistors for Bio-Sensing Applications
Authors: Wang Naixiang , Yan Feng 
Published: February 2020

Organic electrochemical transistors (OECT) have been demonstrated and extensively studied as an effective platform for the design of chemical and biological electronic sensing applications, based on their advantages on low-voltage operation, good biocompatibility and interaction with aqueous medium, facile chemical modification of semiconductors and electrodes, and applicability on varied substrates including flexible plastics.[1] However, conventional OECTs are normally fabricated in the scale of millimeter or larger, resulting in a slow response time for device operation.
To overcome this problem, here we develop a novel approach to miniaturize OECT by using only lithographic and magnetron sputtering technique. The channel of OECTs could be reduced to several to twenty microns therefore the speed of device response could be raised up to order of 10-5 s in aqueous medium.
Due to the improvement in transient response time of the micro OECT device, alternating current (AC) is possible to be introduced for device operation. Combined with lock-in amplifier, the small AC channel signal could be precisely extracted from an extremely noisy environment, which provides the possibility to enhance the sensing capability of the OECT devices in complex situations. A new detection method is then established based on AC signal driven micro OECT. The detection limit of dopamine, an important neuro transmitter within the central nervous system, is down to 10-8 M, which is comparable to previous OECT sensor in steady current mode[2]. Furthermore, the pre waiting time to stabilize the device under the newly established AC mode is much shorter (tens of seconds) than conventional device needs (more than 600 s), indicating that the AC signal driven micro OECT could be a promising candidate for rapid sensing and diagnosis applications.
In conclusion, we introduce a simple and easy-to-fabricate process for miniaturization of OECT devices to the cellular dimensions. The advantage of fast transient response makes the AC-driven micro OECT capable of in-situ cell activity monitoring and associated chemical sensing applications.
References:
[1] C. Z. Liao, M. Zhang, M. Y. Yao, T. Hua, L. Li, F. Yan, Adv. Mater.
2015, 27, 7493.
[2] C. Z. Liao, M. Zhang, L. Y. Niu, Z. J. Zheng, F. Yan, J. Mater. Chem. B
2014, 2, 191.
(Invited) Nanowire Electrodes for Electrochemical Capacitors and Nanoparticles for Current Conduction
Authors: Nakanishi Hideyuki , Kikuta Ikuo , Kawabata Yuto , Matsumoto Ikuko , Naitoh Yasuaki , Segawa Hiroyo , Norisuye Tomohisa , Tran-Cong-Miyata Qui 
Published: February 2020

Electrochemical capacitors (ECs) show the improved energy density, somewhat comparable to batteries, with excellent power density. Depending on the charge storage mechanism, ECs can be separated into two types: 1) supercapacitors, 2) pseudocapacitors. Supercapacitors store charges via the formation of the electric double layers at the interfaces of the electrode and electrolyte. In theory, the specific capacitance of supercapacitors can be linearly scaled with the surface area of the electrode. Hence, high-surface-area carbon nanotubes and graphenes are often used for the electrode of supercapacitors to increase the capacitance. The double layer capacitance is, however, intrinsically limited to a low value, typically in a range of 20 μF/cm2 to 50 μF/cm2. To this limitation, redox active substances have been incorporated with the porous electrodes to spuriously increase the capacitance based on their faradaic reaction (i.e. pseudocapacitance). This type of ECs is also known as pseudocapacitors. Thanks to the faradaic reaction, pseudocapacitors show higher energy density than that of supercapacitors. But instead, the power density of pseudocapacitors deteriorates plausibly due to the charge transfer resistance involved in the redox active substances. In developing pseudocapacitors, in most case, the energy density is increased at the expense of the power density. To improve the energy density without sacrificing the power density, a large number of metal oxides and conducting polymers have been recently examined on their morphology and electrochemical properties for the use of the electrode.
In the present study, we show that monolithic nanowire array electrodes mediate fast ion and electron transport, allowing for charge/discharge at fast rates. In a typical procedure, we prepare a gold nanowire array electrode by the electrodeposition of Au through the cylindrical pores of the in-house anodic aluminum oxide. The subsequent electropolymerization of pyrrole results in the coaxial nanowires in which polypyrrole is conformally coated with the preformed Au nanowires. Thus prepared coaxial nanowire electrodes are examined with galavanostatic charge/discharge measurement and cyclic voltammetry, showing ideal capacitive behaviors even at high charge/discharge rates. The performance of the coaxial nanowires is further examined with electrochemical impedance spectroscopy. The energy capacity and rate capability of the coaxial Ppy/AuNW based pseudocapacitors will be discussed.
(Invited) High-Performance Wearable Supercapacitor Textiles
Authors: Zheng Zijian 
Published: February 2020

Wearable supercapacitor textiles are supercapacitors that made use of and/or shaped into textile fibers, yarns, and fabrics, which are inevitable energy storage devices for wearable electronic applications. To date, the major challenge in the development of wearable supercapacitors is how to improve the electrochemical properties of the device while acquiring high flexibility and durability under wearing conditions. Recently, our laboratory has developed several supercapacitor yarns and fabrics, which show record-high electrochemical performances of their kinds as well as excellent flexibility. These textile-based devices can be readily integrated into different textile forms by means of weaving, embroidery, and heat pressing for wearable applications.
Keywords: supercapacitor; wearable electronics; textiles; nanocarbon materials; polymer-assisted metal deposition
References：
[1] Q. Huang, L. Liu, D. Wang, J. Liu, Z. Huang, Z. J. Zheng*, J. Mater. Chem. A. 2016, DOI: 10.1039/c5ta09309k.
[2] L. Liu, Y. Yu, C. Yan, K. Li, Z. J. Zheng*, Nat. Commun. 2015, 6, 7260.
[3] Y. Yu, C. Yan, Z. J. Zheng*, Adv. Mater. 2014, 26, 5508-5516.
(Invited) Contributions of Phase, Sulfur Vacancies, and Edges to the Hydrogen Evolution Reaction Catalytic Activity of Porous Molybdenum Disulfide Nanosheets
Authors: Ying Yin , Han Jiecai , Song Bo 
Published: February 2020

Contributions of Phase, Sulfur Vacancies, and Edges to the Hydrogen Evolution Reaction Catalytic Activity of Porous Molybdenum Disulfide Nanosheets

Ying Yin,1 Jiecai Han,1 and Bo Song2,
*

1Centre for Composite Materials and Structures, Harbin Institute of Technology, Harbin 150080, China

2Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150080, China
Molybdenum disulfide (MoS2) is a promising non-precious catalyst for the hydrogen evolution reaction (HER) that has been extensively studied due to its excellent performance, but the lack of understanding on the factors that impact its catalytic activity hinders further design and enhancement of MoS2-based electrocatalysts. Here, by using novel porous MoS2 nanosheets synthesized through a liquid ammonia-assisted lithiation route, we systematically investigated the contributions of crystal structure (phase), edges, and sulfur vacancies (S-vacancies) to the catalytic activity towards HER from five representative MoS2 nanosheet samples, including 2H and 1T-phase, porous 2H and 1T-phase, and sulfur compensated porous 2H-phase. Superior HER catalytic activity was achieved in the porous 1T-phase MoS2 nanosheets that have even more edges and S-vacancies than conventional 1T-phase MoS2. A comparative study revealed that not only phase serves as the key role in determining the HER performance, as 1T-phase MoS2 always outperforms the corresponding 2H-phase MoS2 samples, but also both edges and S-vacancies also contribute significantly to the catalytic activity in porous MoS2 samples. Then, using combined defect characterization techniques of electron spin resonance (ESR) spectroscopy and positron annihilation lifetime spectroscopy (PALS) to quantify the S-vacancies, the contributions of each factor were individually elucidated. This study presents new insights and opens up new avenues for designing electrocatalysts based on MoS2 or other layered materials with enhanced HER performance.
*Corresponding Author: songbo@hit.edu.cn
Synthesis of Alternate Layered Structure of Ruthenate Nanosheet-Graphene Oxide for Electrochemical Applications
Authors: Mochizuki Dai , Ishimoto Keita , Ayato Yusuke , Sugimoto Wataru 
Published: February 2020

As a power storage device with performances of rapid charge/discharge, long-life and high power density, electrochemical capacitor is receiving attention. As high power density materials, there are two types of materials: (1) carbon materials such as activated carbon, reduced graphene oxide (rGO), and carbon nanotube and (2) metal oxide materials such as RuO2 and MnO2. Studies have also been conducted to improve specific capacitance by supporting metal oxide on carbon materials.1 We focus on the combination of RuO2 nanosheet which has a high pseudocapacitance, with GO which has a high ion conductivity to enhance electrochemical performance.
As combining method of carbon material and ruthenium oxide, we focused on click chemistry. Click chemistry is a method to combine different materials by reacting them with surface functional groups.2 Click chemistry between two-dimensional nanosheets has been used to form alternate layers.3 Since the alternate layered structures are obtained in the form of powder, broader electrochemical applications are expected. Moreover, since the alternate layers are irregularly stacked, improved substance diffusion is expected compared to the regular stacking of nanosheets by Langmuir-Blodgett or Layer-by-Layer methods. In the present study, thiol-ene reaction is considered most useful among click reactions. This is because thiol-ene reaction makes use of a combination of alkene group and thiol group, and since GO has C=C bonds, the reaction with GO is possible by only modification of RuO2 nanosheet with thiol group.
We tried modification of layered ruthenium oxide with thiol group. As coupling agent, we used 3-mercaptopropyltrimethoxysilane. SEM-EDX observation results after silane coupling showed no substantial change in particle shape by silane coupling. The presence of S and Si after silane coupling was confirmed from the EDX results, indicating silane coupling was in progress. Following that we tried to exfoliate layered C3SH-RuO2 and synthesize C3SH-RuO2 nanosheet colloids. Figure shows the AFM image of substrate made by immersing silicon substrate in toluene. The AFM image showed a sheet-like morphology of approximately 1 nm thickness and 400 nm width, indicating the formation of the C3SH-RuO2 nanosheet.
Alternate layered structures were synthesized by thiol-ene reaction of C3SH-RuO2 nanosheet with GO in the addition of radical initiator. SEM-EDX observation of the product shows stacking of nanosheets. The compounding of ruthenium oxide and GO was confirmed by IR, suggesting the formation of the alternate layered structure after thiol-ene reaction.

Figure 1
Controlling the Temporal Pulse Shape of the Passively Q-Switched Laser by Nonlinear Feedback Control
Authors: Thitsa Makhin , Rice Zechariah , Nve-Nsi Marcos , Xue Xiaojie 
Published: February 2020

Q-switched lasers are high intensity laser pulses with extremely short durations of a few nanoseconds. The application of such laser pulses is ubiquitous [1,2]. In many dermatological procedures, intense energy pulses of Q-switched lasers are used to evaporate pigmented cells with high precision while the ultra-short pulse duration prevents damaging the surrounding healthy tissues. These lasers are also used in many industrial applications that require precision cutting, ranging from laser ablation and micromachining to the high-speed drilling of holes. However, the necessary precision of desired pulse characteristics has become increasingly demanding. Ever shrinking dimensions of micromachining call for reliable pulses with predictable properties. Currently, the difficulty of producing identical pulses of prescribed intensity, shape, and duration limits the use of Q-switched lasers.
While the authors have previously worked on actively Q-switched lasers [3], this work focuses on passive Q-switching, where saturable absorber materials function as the internal switch in the laser cavity. In this paper theoretical tools from the field of nonlinear dynamical control systems [4] are applied to design a feedback controller circuit, which can produce a Q-switched pulse with customized characteristics by varying the pump rate, which can be influenced by the pump power. The pump power is considered as the input to the system and the photon number is the output of the system. The population inversion, the saturable absorber concentration and the photon number are considered as the states of the system. First it is demonstrated that by applying nonlinear state feedback, the Q-switched laser system can be transformed into a pair of two cascaded integrators. Therefore, the desired output can be customized by applying its second derivative as the input. Cr:YSO Q-switched Cr:LiSAF laser is used as an example to demonstrate our method. Both theoretical analysis of the method and the numerical simulation results are presented.

References:

1. E. Lim, S. Alam, D. Richardson, IEEE Photon. Tech. Lett.,
23(2011).
2. S. Kolpakov et. al, IEEE Journal of Quantum Electron. 20, (2014).
3. M. Thitsa and W. S. Gray, ECS Trans. 53(4) (2013).
4. A. Isidori, C. Moog, De Luca. IEEE Conf Dec Contr.
25 (1986).

Figure 1
(Invited) Reliability Study of RF Power Amplifiers with GaN-on-SiC HEMTs
Authors: Lang Jenny , Lim Jang-Kwon , Hellen Johan , Nilsson Torbjörn M.J. , Schodt Bo , Poder Ralf , Belov Ilja , Bakowski Mietek , Leisner Peter 
Published: February 2020

In total 50 RF amplifier demonstrators consisting each of a PCB board containing one GaN-on-SiC, HEMT, CHZ015A-QEG, from UMS in SMD quad-flat no-leads package (QFN) were assembled for the study. Two types of solders, one of which is lead-free, (Sn63Pb36Ag2 and SAC305) and two types of TIM materials (NanoTIM and TgonTM805) for PCB attachment to liquid cold plate were tested for thermo-mechanical reliability. Out of the total number of the demonstrators 24 were subjected to thermal stress by 2300 thermal cycles (TC) between -20°C and 80°C and remaining 26 were subjected to the electrical stress by power cycling (PC) with drain current of 100 mA at drain voltage of 45 V and cycle time of 2 min. HF characterization of all the boards was done before subjecting them to the thermal and electrical stresses. All the devices were also subjected to static electrical characterization by measuring threshold voltage and output and voltage blocking characteristics. The static electrical and HF characterization was performed again after 2300 cycles of TC stress and after 1100, 4700 and 14500 cycles of PC stress. In addition failure analysis was performed on the TC and PC stressed demonstrators by using optical microscopy and 2D X-ray microscopy.
The results of electrical and HF characterization show clearly changes and degradation in device performance as a function of the number of the PC cycles and accumulated current stress time. No significant differences between the boards equipped with different solder or TIM materials are observed which means that the observed changes in performance are due to the degradation of the HEMT devices. A reduction in value of saturation current (VDS=10 V, VGS=0.8 V) of about 5, 12 and 16 % is observed after 1100, 4700 and 14500 cycles of PC stress, respectively. There is a clear tendency of the threshold voltage shift (measured at 10 mA) towards more negative values showed by devices from different groups. The shift is by -0.1 to -0.15 V from typical value of about -2.25 V. The leakage current is less well behaved. There are devices with no significant change in leakage current but also devices which show an increase in leakage current by a factor larger than 2, as a result of the PC stress. Results of HF measurements show a decrease in S11 and S21 parameters from -10.91±0.23 to -10.0±0.21 and from 16.04±0.24 to 15.51±0.28 after PC stress (measurement conditions VDS=45 V, IDS=100 mA, power level 5 dBm, 1.3 GHz).
The support of Sweden´s innovation agency, Vinnova, and Sweden Energy Authority is acknowledged.

Figure 1
(Invited) Investigation on the Carbon Supply in the Top Seeded Solution Growth of SiC Bulk Crystal
Authors: Jeong Seong Min , Ha Minh-Tan , Yoon Ji-Young , Lee Ji Eun , KIM Byeong-Guen , Lee Myung Hyun , Kim Younghee 
Published: February 2020

Top Seeded Solution Growth (TSSG) method is assumed to be a promising bulk growth technique for high quality SiC substrate. Generally, the sources of Si and C in the TSSG method are Si chunk and Graphite crucible, respectively. The crystal growth through TSSG method is achieved by the precipitation of solid SiC from C dissolved a Si melt on a seed crystal located at the top of the liquid. The C solubility in pure Si liquid is extremely low, so that metallic solvents such as Cr, Ti and Fe were added to increase the C solubility in Si liquid. Consequently, the growth rate of SiC crystal through the TSSG method has been reached up to 2 mm/hour. However, as increasing C solubility, the loss of the graphite crucible became another critical issue. Because the C source in the TSSG method is the graphite crucible, the reservoir of Si liquid, the increase of C solubility means the decrease of the crucible durability. The graphite crucible durability influences not only on the thickness of the grown crystal, but also on the temperature distribution in the reactor.
In this study, we introduce our recent progress on the carbon supply in the TSSG method to produce a reliable long-term growth technique. The interface between graphite crucible and Si liquid was first studied from point of thermodynamics. Considering the reaction between graphite crucible and Si liquid, several crucible structures with different materials and designs were suggested for the improvement of TSSG method based on theoretical understanding.
Investigation of Penetration Depth and Defect Image Contrast Formation in Grazing Incidence X-ray Topography of 4H-SiC Wafers
Authors: Yang Yu , Guo Jianqiu , Goue Ouloide Yannick , Raghothamachar Balaji , Dudley Michael , Chung G , Sanchez E , Maning I 
Published: February 2020

Synchrotron X-ray Topography has been shown to be a vital tool for the nondestructive characterization of defects in 4H-SiC crystals [1-2]. Techniques utilizing reflection geometry are particularly useful for discerning defects at different depths below the crystal surface. For example, in studying defects in SiC pin diode structures, which typically comprise a buffer layer homoepitaxially grown on a substrate, with the drift layer grown on top of the buffer layer, it is important to be able to discriminate the depth at which particular defect configurations reside. This is particularly important for the characterization of defects resulting from relaxation processes such as interfacial dislocations and half loop arrays [3]. There are generally two approaches adopted depending of the level of perfection of the crystal. In deformed regions (such as around dislocation cores) the penetration depth is simply determined by photoelectric absorption. In perfect regions it is determined by extinction. Extinction contrast predicts particularly shallow penetration depths in these geometries, whereas kinematical theory predicts much deeper penetration depths. However, even under the kinematical diffraction conditions, the penetration depth calculated theoretically by just considering a dislocation as a single line is much smaller than the value measured experimentally. In our study we compared two models involving different diffracting volumes. In one model, the volume is defined by the misorientation larger than the FWHM of the rocking curve in the vicinity of the dislocation core. In another model, the contrast is naturally formed by simulating the photoelectric absorption profile of the diffraction beam according to the local lattice plane tilt by assuming the dislocation image formation is dominant by orientation contrast. We will present a comparison between measured penetration depths in grazing incidence geometry with these two approaches and develop an optimized model to explain our observations.
[1] Muller, G.S., et al., Volume production of high quality SiC substrates and epitaxial layers: Defect trends and device applications. Journal of Crystal Growth, 2012. 352(1): p. 39-42.
[2] Dudley, M., et al., Characterization of 100 mm diameter 4H-Silicon carbide crystals with extremely low basal plane dislocation density, Material Science Forum,2001. 65: p. 353-356.
[3] Wang, H., Dudley, M., et al., Studies of the Origins of Half-Loop Arrays and Interfacial Dislocations Observed in Homoepitaxial Layers of 4H-SiC. Journal of Electronic Materials, 2015. 44(5): p. 1268-1274
Design and Fabrication of Ag / AgCl Composite Reference Electrode Based on Microfluidic Chip
Authors: Chen Li , Zheng Xiaolin , Hu Ning , Liao Yanjian 
Published: February 2020

Polydimethylsiloxane (PDMS) has been widely used in chip fabrication. However, PDMS itself is a non-conducting polymer, and the adhesion between metal and PDMS is also really weak. Hence, integrating microelectrodes on PDMS microchips has become a technical bottleneck in many applications such as miniaturized electrochemical (EC) sensing systems. A new method was presented to integrate Ag/AgCl electrode on microfluidic chips by using a new conductive composite. It was made of the mixture of PDMS and silver powders, so good electrical conductivity was achieved. Two chloridizing methods were selected to fabricate Ag/AgCl reference electrode. In the electrolysis method, Ag-PDMS composite electrode (as anode) was electrolyzed for 24 hours in saturated KCl solution. In the second one, silver chloride powder was uniformly mixed with silver powders and PDMS pre-polymer, and then cured 1 hour at 90 oC. These composite materials could be efficiently shaped as different electrode structures. Its potential response was measured in different chloride solutions, and its stability was also measured in water (10 days) and 3 mol/L KCl solution (14 days), respectively. Electrochemical characteristics of the electrode were also analyzed in potentiometric and amperometric measurements. SEM pictures showed that the surface of the electrode was fluffy and of rough morphology, which might increase its contacting area with solution, so as to improve the measuring adequacy and accuracy. The electrodes had a fast and stable potential response toward Cl− concentration change.The much tiny potential fluctuation indicated that the composite electrode was stable, which could be served as a good reference for EC measurements. Its CV curves showed its performance was almost as good as a standard reference electrode. Based on its excellent properties, the composite material can be widely applied in microfluidic field. The new method has many advantages such as simple operation, low cost and no special environmental requirements.