bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and Characterization of CuO Nanotubes (NTs) Formed By Anodization Sonoelectrochemical
Authors: Grez Paula Carolina , Ballesteros Luis Alberto , Celedón Carlos Eduardo , Schrebler Ricardo Silvio
Published: February 2020

The CuO is an important semiconductor material because this presents a narrow bandgap value (~1.2 – 1.7 eV), p-type conductivity, low toxicity and abundance in nature. From comparison of the photoelectrochemical behavior between CuO and others semiconductor, it is concluded that this oxide is sensible to visible radiation whereas others, more widely used such as; TiO2, ZnO, which absorb in UV region.

Despite the above, the copper oxide has a low diffusion rate of charge carriers. Therefore, new synthesis routes leading to a nanostructured oxide is required, so that the photogenerated electrons are accumulated in the vicinity of the surface. This is to facilitate the transfer process of charge per on the recombination.

This report shows the results concerning the preparation sonoelectrochemical of CuO nanotubes (NTs). Synthesis of CuO NTs is carried out on a copper (Cu) foil in organic media (x% water in ethylene glycol + 0.5 wt % CuC2O4) using the electrochemical anodization method at a constant room temperature. The anodization is carried out for 10 min at an applied potential of 25 V. Cu foil acts as anode and electrode of carbon (C) acts as cathode. The anodized samples are properly washed with distilled water, to remove the occluded ions, and dried in a furnace.

The CuO NTs were characterized by sweep electronic microscopy (SEM), energy dispersive X-ray analysis (EDXA) and Raman spectroscopy.

The micrographs show an array of nanotubes on the substrate. The composition of the nanotubes immediately formed consisted mainly of copper, when the synthesis was conducted in a solution with a higher % of water. However, when the samples were heat treated in oxygen atmosphere, an array of CuO NTs was obtained.

Furthermore, these samples were characterized by Photoelectrochemical Studies.

Acknowledgment

The financial support of Fondecyt-Chile (Project N° 1140963) and DI-PUCV (Projects N° 037.305/2013) is gratefully acknowledged by the authors.
Invited: Room Temperature Hydrogen Generation from Hydrolysis of Ammonia-Borane over an Efficient Niagpd/C Catalyst
Authors: Huang Kuo-Wei
Published: February 2020

Hydrogen is considered an ideal secondary fuel and energy carrier with a high energy density by weight and it can be used in proton exchange membrane (PEM) fuel cells to produce electrical power for vehicles and electronic devices. Current materials such as complex hydrides, and chemical hydrides have been used for hydrogen storage, but most of these materials have low volumetric and/or gravimetric capacity which cannot meet the ideal requirement proposed for the on-board hydrogen storage system by the US department of energy (volumetric capacity > 82 g/L and gravimetric capacity > 9 wt.%). Ammonia borane (NH3BH3, denoted as AB) which stores 19.5 wt.% of hydrogen is a promising material for this purpose. Hydrogen release from AB is typically achieved through two pathways: thermolysis and hydrolysis. Thermal dehydrogenation of AB can be catalyzed, but the product (BN complex) is hardly soluble in any solvent which make the reaction irreversible. Hydrolysis of AB is a different approach and hydrogen can be released at ambient temperatures in the presence of suitable catalysts. Herein, we report the synthesis of a trimetallic nanoalloy supported on carbon (NiAgPd/C) by reduction of the corresponding metal salts under mild reaction conditions. This trimetallic nanomaterial shows excellent catalytic activity and stability toward hydrogen generation though AB hydrolysis at room temperature, comparable to those of Pt-based catalysts.
Simulation of the Cell Electrofusion Chip
Authors: Han Xianwei , Yang Jun , Hu Ning , Liao Yan-jian
Published: February 2020

The process of cell electrofusion including cell alignment, cell electroporation cell electrofusion. Cell manipulation mainly related to the electric field gradient and electroporation is concerned with the intensity of the electric field. The first thing to consider in the design of Cell electrofusion chip is the control of the cell capacity , which depends on the intensity and distribution of the electric field, and this is associated with the applied voltage and the shape and distribution of the microelectrode. In the experiment, we can change the applied voltage, but the shape and distribution of the microelectrodes is hard to change. In order to improve the efficiency of the experiment, the optimum distribution and the size of the microelectrode in the chip should be determined before the experiment. Using COMSOL Multiphysics software to model and simulate the cell electrofusion chip to provide theoretical guidance for optimum chip design and experimental study late.

In this study, five different cell electrofusion chip are simulated. Using the finite element analysis method, combined with COMSOL simulation software, the electric field around the chip microelectrode is simulated and analyzed. Through the establishment of simulation model, to explore the influence on the internal electric field of the cell electrofusion chip be different parameters, including the distribution and spacing of microelectrode, , microelectrode length, width, and the size of the microstructure. Thus, best design parameters of chip microelectrode are achieved.
Centrifugation and Negative-Dielectrophoresis Assisted Cell Separation Method
Authors: Han Xianwei , Yang Jun , Hu Ning , Liao Yan-jian
Published: February 2020

Cell size is an important parameter for cell analysis and manipulation. Cell sample with similar size distribution can improve the performance in cell screening, cell electroporation and electrofusion. One approach for cell purification is to utilize constriction structures such as dams to trap cells in microfluidics. This paper presents a centrifugation and negative-dielectrophoresis assisted size-based cell separation method. The goal is to separate cell sample and get purified cells by size-based screening. We designed and fabricated a microfluidic chip with five octagon-shape screening-dams within a flow-through channel network. The radius of the octagon was from 10mm to 26mm, and the array space was 4 mm. The octagon-shape screening-dam contained hundreds of micro-filter and micro-dam structures. Each micro-filter was composed by two micro-dam structures. The width of filter between two adjacent micro-dams is 40, 30, 20, 15, 10 mm, respectively. After loaded cell sample into the central reservoir, the microfluidic chip was revolved in high speed. Cells with big size were immobilized and captured into micro-filter under centrifugal force. To avoid too much cells are concentrated into micro-filters and blocked these structures, negative-dielectrophoresis was applied per 2 minutes, to push cell leave to filter and move into independent chamber between two adjacent octagon-shape screening-dam arrays. In the end, purified cells with similar size were separated and collected into each independent chambers.
Size-Based Separation of Particles and Biological Cells Using Surface Acoustic Waves
Authors: Ai Ye
Published: February 2020

Acoustics has emerged as one of the most promising non-invasive techniques for particle manipulation in microfluidics. In this study, a surface acoustic wave (SAW)-based microfluidic device has been developed to manipulate micron-sized synthetic particles and biological cells. The microfluidic device is comprised of two components, a SAW transducer and a microfluidic channel made of polydimethylsiloxane (PDMS). The SAW transducer was fabricated by patterning two pairs of interdigital electrodes on a lithium niobate (LiNbO3) piezoelectric substrate. When exciting the SAW transducer by AC signals, a standing SAW is generated across the cross-section of the channel. Solid particles immersed in the standing SAW are accordingly pushed to the pressure-node arising from the acoustic radiation force acting on the particles, referring to the acoustic particle focusing phenomenon. The amplitude of acoustic radiation force highly depends on the properties of the particle, resulting in different acoustic responses for different types of cells. Separation of two types of fluorescent particles (Particle I: 1.2µm in diameter, green spectrum emission; Particle II: 5.8µm in diameter, red spectrum emission) has been demonstrated using the developed SAW-based microfluidic device. We also demonstrated the separation of E. coli bacteria from peripheral blood mononuclear cell (PBMC) samples. The purity of separated E. coli bacteria and separated PBMC are over 95% and 91%, respectively, obtained by a flow cytometric analysis. Conclusively, the developed microfluidic device can efficiently separate E. coli bacteria from biological samples, which has potential applications in biomedical analyses and clinical diagnosis.
Design and Fabrication of Ag / AgCl Reference Electrode Based on PDMS Conductive Composite Material
Authors: Chen Li , Zheng Xiao-lin , Hu Ning , Jiang Fan , Zheng Fei , Luo Hong-yan , Yang Jun , Liao Yan-jian
Published: February 2020

A vital part of any electrochemical sensing system is the reference electrode, which is a probe that is capable of measuring the potential on the solution side of an electrochemical interface. Ag/Agcl reference electrode is one kind of the most widely used among them. Common reference electrode is individually packaged and its volume is relatively large, which isn’t appropriate for microfludic systems. In microfluidic chips, electrochemical measurement is always challenging to realize, such as real-time monitoring of pH in micro-reactors.

In this paper, we introduce a kind of Ag / AgCl reference electrode in microchips based on PDMS-based conductive composites. This conductive composite of good electrical conductivity was synthesized by PDMS and silver powders via uniformly mixing. Two chloride methods, electrolysis and chemical immersion, were selected to the sample compared with pure silver wire as a reference. Packaging thin film was fabricated by mixing agar with saturated Kcl gel. A three-electrode system was used to measure the potential of Ag/Agcl reference electrode.

SEM pictures showed the surface profile of the reference electrode clearly. Here we demonstrate that electrolytic process and chemical immersion method both have great influence on the electrode surface. Fluffy and rough morphology increased the contact area between reference electrode and solution so as to improve the adequacy and accuracy of measurement.
Invited: Investigation of the Solid Electrolyte Interface (SEI) on Silicon Nano-Particle Anodes
Authors: Lucht Brett L. , Nie Mengyun , Nguyen Cao Cuong
Published: February 2020

The surface reactions of electrolytes with a silicon anode in lithium ion cells have been investigated. The investigation utilizes two novel techniques that are enabled by the use of binder-free silicon (BF-Si) nanoparticle anodes. The first method, transmission electron microscopy with energyndispersive X-ray spectroscopy, allows straightforward analysis of the BF-Si solid electrolyte interphase (SEI). The second method utilizes multi-nuclear magnetic resonance spectroscopy of D2O extracts from the cycled anodes. The TEM and NMR data are complemented by XPS and FTIR data, which are routinely used for SEI studies. Coin cells (BF-Si/Li) were cycled in electrolytes containing LiPF6 salt and ethylene carbonate or fluoroethylene carbonate solvent. Capacity retention was significantly better for cells cycled with LiPF6/FEC electrolyte than for cells cycled with LiPF6/EC electrolyte. Our unique combination of techniques establishes that for LiPF6/EC electrolyte the BF-Si SEI continuously grows during the first 20 cycles and the SEI becomes integrated with the BF-Si nanoparticles. The SEI predominantly contains lithium ethylene dicarbonate, LiF, and LixSiOy. BF-Si electrodes cycled with LiPF6/FEC electrolyte have a different behavior; the BF-Si nanoparticles remain relatively distinct from the SEI. The SEI predominantly contains LiF, LixSiOy, and an insoluble polymeric species. The depth dependence of structure of the SEI was further investigated by Hard X-ray photoelectron spectroscopy (HAXPES). Finally, the effect of different binders including PVDF, CMC, and PAA on the surface of silicon nanoparticles and on the structure of the SEI will be discussed.

We gratefully acknowledge funding from Department of Energy office of Basic Energy Sciences EPSCoR Implementation award (DE-SC0007074).
In-Operando X-ray Tomography Studies of Dendrite Formation in Zinc-Air Batteries
Authors: Yufit Vladimir , Tariq Farid , Wu Billy , Biton Moshiel , Merla Yu , Eastwood David , Lee Peter , Brandon Nigel P.
Published: February 2020

Rechargeable aqueous zinc-air systems are remarkably attractive power sources because of high specific energy, safety, environmental compatibility and low cost. However these systems are still under development and suffer from sufficiently short cycle life that prohibits their use for large electrical storage applications requiring several thousand cycles. One of the key factors responsible is dendritic growth when the system is recharged. Dendrites can grow sufficiently wide to penetrate the separator between the anode and the cathode and cause an internal short-circuit. Despite the substantial work accomplished in studying of zinc dendrite formation there are only few reports available on real time imaging of dendrite growth.

Recent developments in X-ray micro/nano tomography have demonstrated the great advantage of the technique for non-destructive ex- and in-situ characterisation of materials and devices for electrochemical energy storage and generation. We used synchrotron x-ray tomography to investigate the mechanism and kinetics of dendrite formation during zinc-air system operation. The dendrite growth was analysed in-operando in radiography mode while three-dimensional image of dendrites covering the electrode surface was reconstructed from multiple tomographic projections ( Figure 1).
Invited: In Situ Analytical Electron Microscopy for Probing Electrochemistry at Interfaces
Authors: Meng Shirley
Published: February 2020

Significant progress has been made in the past few years on the development of in situ electron microscopy for probing nano-scale electrochemistry. In situ electrochemical operation in the ultra-high vacuum column of a TEM has been pursued by three major strategies. In one strategy, an AFM type tip is used as a current collector and lithium oxide is used as the electrolyte to lithiate materials at low potential, however high voltage charging is not possible due to the low breakdown voltage of lithium oxide. A second strategy involves organic and/or liquid electrolyte, though this approach more closely resembles the actual operation conditions of LIB, it presents significant challenges for in situ cell design for TEM due to the volatility of the organic/liquid electrolyte. To this end, we have developed a novel in situ instrumental system combining analytical electron microscopy with advanced spectroscopy to probe the dynamic phenomena in an all solid-state nano-battery. An “all solid state battery” can be fabricated from an all-solid-state thin film battery using focused ion beam (FIB). The electrolyte is either polymer based or ceramic based without any liquid component. The interfaces between the active electrode material/electrolyte can be clearly observed at nano-scale under TEM imaging, in contrast to the composite electrodes/electrolyte interfaces in conventional lithium ion batteries, where quantitative interface characterization is extremely difficult if not impossible. In situ electron microscopy can be a versatile technique and provide us answers to questions that could not be provided using other techniques. However in order to fully exploit the capabilities, a very carefully thought-out plan is essential to minimize the beam damage and other artifacts. Io ensure transparency for spectroscopic analysis, the nano-battery must be made very thin, typically less than 100 nm if EELS are to be done quantitatively. Artifacts due to plural scattering can be reduced by increasing the inelastic mean-free-path (by higher kV) or restricting analyses to thin regions of the sample. We will present the main challenges that we have overcome to enable in situ nano-electrochemistry in the (S)TEM.
Invited: Surface Modification of Positive Electrode and its Effect to Bulk
Authors: Sakaebe Hikari , Taguchi Noboru , Akita Tomoki , Tatsumi Kuniaki , Ogumi Zempachi
Published: February 2020

Improvement technique of the life of Li-ion batteries has been intensively studied. Modification of the surface of positive electrode material including coating is effective to this purpose. In that process, it is very important to compare the bulk and surface structure of the positive electrode with/without surface modification to understand this effect.

For basic information concerning the effect of surface modification, authors have applied Transmission Electron Microscopy (TEM) to visualize the structural distribution inside the positive electrode particles after degradation [1]. As a model material, we synthesized sub-micron size particle of positive electrode such as LiCoO2 by Pechini sol-gel method [2, 3] that could provide the suitable sample for TEM observation without damages from sample preparation like ion-milling or FIB. Analytical TEM measurements by scanning transmission microscopy (STEM) with electron energy-loss spectroscopy (EELS) equipped with monochromator were applied. Li-K EELS peak around 62 eV was clearly found and this peak intensity changed with Li charge-discharge state. The EELS mapping from the spectrum imaging method using this Li-K region spectra showed a distribution of Li in the particle or among particles during the charge discharge cycle. We discuss precisely the change of chemical states at the surface and Li ion distribution inside particles of positive electrode material with/without surface modification using Si, Zr, Al, Mg oxide during charge-discharge cycle.

References

[1] N. Taguchi, T. Akita, H. Sakaebe, K. Tatsumi, Z. Ogumi, J. Electrochem. Soc., 160, A2293 (2013).

[2] Y. Sun, I. Oh, S. Hong, J. Mat. Sci., 31, 3617 (1996).
A Critique of Wide Bandgap (WBG) Power Semiconductor Datasheets
Authors: Shenai Krishna
Published: February 2020

Power switching devices made using wide bandgap (WBG) semiconductors such as Silicon Carbide (SiC) and Gallium Nitride (GaN) have the potential to make transformative impact on electrical energy generation, transmission, distribution and conditioning [1]. Although SiC power diodes and power MOSFETs are commercially available for voltage ratings up to 1,700 volts, a careful review of the datasheets suggests severe shortcomings and the need for improved consistency, parameter definition and standardization in order for application engineers to adapt this new technology with trust and confidence. This paper will provide a critique of WBG datasheets with recommendations for specific improvements.

[1] K. Shenai et al, “Current status and emerging trends in wide bandgap (WBG) semiconductor power devices,” ECS J. Solid State Sci. and Tech.
2(8), N3055-N3063, Jul 2013
Workforce Development for Electric Power Engineers
Authors: Guo Liping
Published: February 2020

Due to the rapid growth of renewable energy technology such as solar and wind power, the nation will have a shortage of skilled power engineers; however, an ample supply of these engineers is critical in making the nation’s energy system greener and smarter. This presentation will address how to increase knowledge of renewable energy and power engineering amongst college and pre-college (middle and high school) students. The presented project is funded by the National Science Foundation (NSF) Transforming Undergraduate Education in STEM program from 2012 to 2015.

This project uses a progressive approach as participants from different levels – high and middle school students, college students, teachers and faculty engage in collaborative learning about renewable energy. We are developing enabling teaching materials and courses to engage participants. This will enable students and faculty to research renewable energy technology and how these can solve environmental and societal issues. A broad-based advisory group representing industry has been used to identify areas of need in energy and the workforce related knowledge and skills needed in the enhancement of the curriculum. The curricular enhancements focus on authentic problems in renewable energy in ways in which students will be engaged in problem-based learning. In particular, we are developing and using sun tracking solar power systems as an enabling tool to create innovative teaching materials including demonstrations, hands-on experiments, and course modules. The progressive, scaffolding approach used in building content knowledge throughout the curriculum prepares graduates with strong content and research skills needed to advance the field of renewable energy. We are seeking to attract more students, especially women and under-represented groups, into power engineering, through outreach activities, open houses, lab tours and seminars.
Stacking Fault Formation during Homo-Epitaxy of 4H-SiC
Authors: Dudley Michael , Wang Huanhuan , Wu Fangzhen , Yang Yu , Guo Jianqiu , Zhang Jie , Thomas Berndt , Sanchez Edward K , Mueller Stephan , Hansen Darren , Loboda Mark
Published: February 2020

Nomarski optical microscopic observations are presented faint needle-like surface morphological features in 4H-SiC homoepitaxial layers. Close observation has revealed that these linear features often occur in pairs, composing triangles or trapezoids. Grazing incidence synchrotron white beam x-ray topographs recorded from the areas containing the linear features show V and Y shaped features which transmission topographs reveal to be ¼[0001] Frank-type stacking faults. Geometric analysis of the size and shape of these faults indicates that they are fully contained within the epilayer and appear to be nucleated at the substrate/epilayer interface. Detailed analysis shows that the positions of the V shape stacking faults match with the positions of c-axis threading dislocations with Burgers vectors of c or c+a in the substrate and thus appear to result from the deflection of these dislocations during epilayer growth. Similarly, the Y shaped defects match well with the substrate surface intersections of c-axis threading dislocations with Burgers vectors of c or c+a in the substrate which were deflected onto the basal plane during substrate growth. The observed morphology of these defect configurations allows us to propose a model for their formation mechanism. For the V shaped defects, this is based on the overgrowth of the surface spiral steps associated with the surface intersections of the threading dislocations. For the Y shaped defects this is based on overgrowth of the special configurations of steps at the surface intersections of the threading dislocations that were deflected onto the basal plane during substrate growth. Understanding the mechanism of formation of these stacking faults can enable the formulation of strategies for their elimination in order to mitigate their potentially detrimental influence on high power device performance.
Full Epitaxial Trench Type Buried Grid SiC JBS Diodes
Authors: Reshanov Sergey A. , Schöner Adolf , Kaplan Wlodek , Zhang Andy , Lim Jang-Kwon , Bakowski Mietek
Published: February 2020

The modern SiC Schottky barrier diodes utilize JBS concept that gives surge current capability. However, in planar structures the protection of the Schottky areas from high electric field is not sufficient thus resulting in high leakage currents.

It has been demonstrated that buried grid technology (implanted or epitaxial) gives extremely low leakage currents even at high temperature operation due to superior shielding [1-2]. But the manufacturing complexity limits this technology to niche markets.

Less complicated trench concept of implanted JBS diodes was utilized in [3]. It also enables to improve both the forward voltage drop and the leakage current.

In this paper we present the new concept of fully epitaxial trench JBS diodes. Simulations [3] revealed better trade off of forward and blocking behavior of epitaxial buried grid technology. Epitaxially grown p-n junctions result in increased bipolar injection at high current densities and thus lead to improved surge current capabilities.

The concept of fully epitaxial trench JBS diodes enables cost-efficient manufacturing. Implantation and high temperature annealing steps are replaced with one epi re-growth step that can be performed in multi wafer epi reactors. The re-growth step utilizes Ascatron’s 3D-SiC core technology based on embedded epitaxial growth techniques like presented in [4]. Ring type edge termination is formed simultaneously with the active area grid. The cross section of the epitaxial trench type buried grid JBS device is shown in Fig.1. To optimize the JBS performance the grid spacing is set below 2µm and the n channel has higher doping than the n- drift region.

Fig. 2 shows cross section of the device after p+ epi re-growth in the trenches.

Cross section of the active area of fabricated JBS device is shown in Fig. 3.

Fabricated devices are rated for 20A / 1200V and have leakage currents below 0.1µA at 1000V blocking voltage.

References

1. M. Bakowski, J-K. Lim, W. Kaplan, and A. Schöner, ECS Trans., 41 (8), p. 155 (2011).

2. M. Bakowski, J-K. Lim, W. Kaplan, ECS Trans., 50 (3), p. 415 (2013).

3. M. Aketa, Y. Yokotsuji, M. Miura, and T. Nakamura, Materials Science Forum, 717-720, p. 933 (2012).

4. A. Schöner, N. Sugiyama, Y. Takeuchi, and R.K. Malhan, Materials Science Forum, 600-603, p. 175 (2009).
Carbon Nanotube Flexible Electronics
Authors: Wang Chuan
Published: February 2020

Being mechanically flexible with superior electrical properties, thin-films of single-wall carbon nanotubes are proven to be one of the most promising material platforms for high performance flexible electronics. In this talk, I will discuss our solution-based platform for wafer-scale assembly of high-purity semiconducting carbon nanotube networks, which leads to low-cost fabrication of large quantity of thin-film transistors (TFTs) with excellent yield, uniformity, and respectable performance on flexible substrates. Based on the semiconducting carbon nanotube TFTs, a wide range of macro-scale system-level electronics have been demonstrated including flexible integrated circuits, flexible active-matrix organic light-emitting diode displays, and a user-interactive electronic skin that can simultaneously map and respond to various forms of stimuli. With emphasis on large-area systems where nm-scale accuracy in the assembly of nanotubes is not required, our demonstrations present a unique niche for nanotube electronics by taking full advantage of their superior electrical and physical properties. Our work shows carbon nanotubes’ immense promise as a low-cost and scalable TFT technology for nonconventional electronic systems with excellent performance.
Scalable Growth of Single-Crystal Graphene on Hydrogen-Terminated Germanium
Authors: Whang Dongmok
Published: February 2020

The uniform growth of single-crystal graphene over wafer-scale area remains a challenge in the commercial-level manufacturability of various electronic, photonic, mechanical, and other devices based on graphene. Here, I present scalable growth of wrinkle-free single-crystal monolayer graphene on a hydrogen-terminated germanium substrate. The anisotropic twofold symmetry of the Ge(110) surface allowed unidirectional alignment of multiple seeds, which were merged to uniform single-crystal graphene with pre-defined orientation. Furthermore, the weak interaction between graphene and underlying H-terminated Ge surface enabled the facile etch-free dry transfer of graphene and the recycling of the Ge substrate for continual graphene growth.
Optimal BaTiO3 BaTiO3 Cluster Formation for High Performance Piezoelectric Nanogenerators
Authors: Shin Sung-Ho , Lee Min Hyung , Nah Junghyo
Published: February 2020

Several piezoelectric materials, including ZnO, BaTiO3, and PZT, have been widely investigated to develop high performance piezoelectric nanogenerators (NGs).1-3 In particular, the NGs based on BaTiO3 (BTO) nanoparticles (NPs) are of interest due to their excelling piezoelectric properties and environmentally safe nature. However, the performance of the NGs largely depends on how well BTO NPs can be distributed in the active piezoelectric generation layer. To this end, we report BTO composite thin film formation method using rapid solvent evaporation process, where BTO cluster is formed by cementing NPs with P(VDF-HFP).4 By optimizing the process, the optimal BTO composite thin film, having high density of spherical BTO clusters on the composite film, is obtained and adopted for the NG fabrication. Our NGs show output voltage and current over 110 V and 22 mA, corresponding power density of 0.48Wcm-3, which is one of the highest value reported up to date.

References

1. Z. L. Wang, J. H. Song, Science, 2006, 312, 242–246.

2. J. H. Jung, M. Lee, J.-I. Hong, Y. Ding, C.-Y. Chen, L.-J. Chou, Z. L. Wang, ACS Nano, 2011, 5, 10041–10046.

3. Luo, Y. et al., Appl. Phys. Lett. 2003, 83, 440–442.

4. S.-H. Shin, Y.-H. Kim, M. H. Lee, J.-Y. Jung, J. Nah, ACS Nano, 2014, 8, 2766−2773.
Challenging Issues for Terabit-Level Perpendicular STT-MRAM
Authors: Park Jea-Gun
Published: February 2020

Recently, many researchers have intensively studied p-STT MRAM as an alternative terra-bit-integration nonvolatile memory since current Si-based dynamic-random-access-memory has a physical scaling limit of less than 20 nm. p-STT MRAM has demonstrated a fast write time of ~10 ns, non-volatile memory operation, and extremely low power consumption. However, for satisfying a commercial specification as a terra-bit-integration nonvolatile memory, perpendicular magnetic tunneling junction (p-MTJ) of p-STT MRAM essentially needs to satisfy critical device performances for p-MTJ spin-valves such as a high TMR ratio of 150 %, a high Jex of > 0.7 erg/cm2, a good Ku of 1x107 erg/cm3, a good ¢ of ~ 74,and a low critical writing current (JC0) of 13.4 MA/cm2, which should satisfy the thermal stability such as an ex-situ annealing above 400 °C. In general, a CoFeB based p-MTJ spin-valve in p-STT-MRAM has been fabricated with the stacked structure of bottom electrode/ amorphous Ta seed layer/amorphous CoFeB free layer/MgO tunneling barrier/amorphous CoFeB pinned layer/capping layer/buffer layer/ synthetic anti-ferromagnetic layer (SyAF) /top electrode. In particular, nano-scale thick amorphous CoFeB layer has been applied for free and pinned layer. However, the mechanism by which the perpendicular magnetic anisotropy (PMA) characteristic for amorphous CoFeB based p-MTJ using amorphous Ta seed layer could be achieved has not been clarified. In our study, we will review its mechanism and the thermal stability limit for amorphous CoFeB based p-MTJ using amorphous Ta seed layer. In addition, we will present the thermal stability enhancement for amorphous CoFeB based p-MTJ using bcc crystalline seed layer and its mechanism. For amorphous CoFeB based p-MTJ using amorphous Ta seed layer, the B atoms were segregated at the interface between the MgO tunneling barrier and the CoFeB free and pined layer after the ex-situ annealing of 275 °C, producing interface-PMA (i-PMA), as shown in Fig. 1(a). However, the PMA characteristics for amorphous CoFeB based p-MTJ using amorphous Ta seed layer was rapidly degraded as the ex-situ annealing temperature increased above 400 °C, which the mechanism was not proved yet. Surprisingly, the crystalline structure of both CoFeB free layer and pinned layer sustained at the amorphous structure although the p-MTJ was ex-tu annealed at 275 °C, as shown in Fig. 2.

In order to enhance the thermal stability of amorphous CoFeB based p-MTJ, a bcc crystalline seed layer is essentially necessary rather than amorphous Ta seed layer. During ex-situ annealing at 400 °C, the bcc crystalline seed layer could texture the amorphous CoFeB free and pinned layer into the bcc crystalline CoFe free layer, MgO tunneling, and CoFeB pinned layer, as shown in Fig. 3. As a result, amorphous CoFeB based p-MTJ could achieve the TMR of ~135 %, as shown in Fig. 4. In this presentation, I will challenging material issues for p-STT MRAM in the view of the perfect crystalline linearity for free layer, MgO tunneling barrier, and pinned layer, and SyAF layer.
Photon-Assisted Electrochemical Construction of <0001>-n-ZnO/<111>-p-Cu2O Photovoltaic Devices with Intermediate TiO2 Layer
Authors: Mohd Zamzuri Mohammad Zain , Sasano Junji , Binti Mohamad Fariza , Izaki Masanobu
Published: February 2020

The Cu2O/ZnO photovoltaic (PV) device is a realistic candidate for next generation thin film solar cell. The conversion efficiency for the electrodeposited super-straight type PV device was lower than that for the thermally prepared substrate-type PV cell. We developed a photon-assisted electrochemical process to construct the substrate-type PV device without the reduction of the Cu2O.1 Here, we show the photon-assisted electrochemical process to construct the substrate type Cu2O/ZnO PV device with a photovoltaic performance.

The Cu2O layer was prepared by heteroepitaxial electrodeposition on <111>Au/Si wafer substrate in an alkaline solution containing copper acetate and lactic acid. The ZnO layer was stacked on the Cu2O layer by elecrodeposition in a zinc nitrate solution with light irradiation. The PV device was fabricated by stacking the top Al electrode by evaporation.

The light irradiation was needed to grow the <0001>-ZnO layer having the columnar grain morphology and 3.3 eV bandgap energy on the Cu2O layer without the reduction to metallic Cu. The thickness increased with the deposition time up to 30 min and then decreased. And the pores could be observed for the ZnO layer at the deposition time over 30　min. The <0001>-ZnO/<111>-Cu2O PV device showed a photovoltaic performance under AM1.5 illumination, and the performance changed depending on the deposition time, which strongly affected the structure of the resultant ZnO layer. The best photovoltaic performance with short-circuit current density of 2.93 mAcm2 could be obtained for the substrate-type <0001>-ZnO/<111>-Cu2O PV device prepared at 30 min for the ZnO deposition.

Ref. 1. B. M. Fariza, M. Izaki, et al., Thin Solid Films, 520(2012), 2261.
Memory and Logic Electronics Based on Nanoscale Resistive Switches (Memristors)
Authors: Lu Wei
Published: February 2020

I will discuss our recent progress towards memory and logic applications based on two-terminal, nanoscale resistive switches (memristors). Two types of devices – one with abrupt resistance change (digital) and one with incremental resistance change (analog) have been developed by choosing the proper combinations of electrode and switching materials, film stack and programming conditions. The digital devices show excellent memory performance metrics in terms of scalability, speed, ON/OFF ratio, endurance and retention. Detailed TEM studies have been carried out to verify the switching mechanism. Functional high-density crossbar arrays have been integrated directly on top of CMOS circuits using a back-end-of-line (BEOL) process, enabling hybrid non-volatile memory and reconfigurable circuit applications. The analog devices exhibit incremental conductance changes that are analogous to the behaviors of biological synapses. Besides the ability to emulate synaptic behaviors phenomenologically, the internal ionic dynamics of these devices allow them to implement a number of important synaptic functions realistically. These analog memristive devices are well suited for hardware-based, bio-inspired neuromorphic logic systems. Device and SPICE models based on properly chosen internal state variables have also been developed for the understanding and applications of these devices at the system level. Prototype neuromorphic circuits based on memristor arrays have been shown to be able to perform tasks such as pattern recognition in an unsupervised fashion.
Crafting Semiconductor Organic-inorganic Nanocomposites Via Placing Conjugated Polymers in Intimate Contact with Nanocrystals for Hybrid Solar Cells
Authors: Lin Zhiqun , Jung Jaehan , Yoon Youngjun , Pang Xinchang
Published: February 2020

Recent advances in the synthesis and assembly of nanocrystals (NCs) provide unique opportunities to exploit NCs for the development of next generation organic/inorganic hybrid solar cells as one of the most promising alternatives to Si solar cells to deliver efficient energy conversion with inexpensive fabrication. Herein, we report two simple yet robust routes to conjugated polymer-quantum rod (CP-QR) nanocomposites, dispensing with the need for ligand exchange chemistry. In the first strategy CdSe QRs were passivated with bromobenzylphosphonic acid (BBPA) which not only induced elongated growth but also functionalized the CdSe QR surface, forming BBPA-CdSe QRs. Subsequently, P3HT-CdSe QRs were yielded by Heck coupling of vinyl-terminated P3HT with BBPA-CdSe QRs. The reduced insulating length of BBPA facilitated improved electron interaction between CP and QR, greatly promoting the potential of P3HT-CdSe QR nanocomposites for use in solar cells with enhanced performance. In the second strategy the alkyne–azide cycloaddition, which belongs to an emerging field of click chemistry, was utilized in the preparation of P3HT-CdSe QR nanocomposites. The aryl bromide of BBPA was converted into azide functional group, forming N3-BPA-CdSe QRs. Subsequent catalyst-free Huisgen 1,3-dipolar cycloaddition between ethynyl-terminated P3HT and N3-BPA-CdSe QRs successfully yielded intimate P3HT-CdSe QR nanocomposites without introducing any deleterious metallic impurity. The charge transfer occurred at the P3HT/CdSe QR interface and was confirmed by systematic UV-Vis absorption, photoluminescence (PL), and time-resolved PL studies. The nanocomposites made by the catalyst-free click reaction exhibited a faster charge transfer from P3HT to CdSe than those produced by Heck coupling.
High-Performance Sb-Based III-V Nanowires Synthesized on Amorphous Substrates: From the Formation Mechanism to p-Channel Transistor Applications
Authors: Ho Johnny C
Published: February 2020

Abstract:

In recent years, due to the narrow direct bandgap and outstanding carrier mobility, Sb-base nanowires (NWs), such as GaSb, have been extensively explored for high-performance electronics and optoelectronics. Importantly, these p-channel nanowires can be potentially integrated with n-type InSb, InAs or InGaAs NW devices via different NW transfer techniques to facilitate the III-V CMOS technology. However, there are still very few works till now focusing on the electronic transport properties of GaSb NWs. Here, we successfully demonstrate the synthesis of crystalline, stoichiometric and dense GaSb NWs on amorphous substrates, instead of the commonly used III-V crystalline substrates, InAs or GaAs NW stems as others reported. The obtained NWs are found to grow via the VLS mechanism with a narrow distribution of diameter uniformly along the entire NW length with minimal tapering and surface coating. Notably, when configured into FETs, the NWs exhibit impressive electrical characteristics with the peak hole mobility of ~200 cm2V-1s-1. All these have illustrated the promising potency of such NWs directly grown on amorphous substrates for various technological applications, as compared with the conventional MOCVD grown GaSb NWs.

Reference:

Yang Z., Wang F.Y., Han N., Lin H., Cheung H.Y., Fang M., Yip S.P., Hung T.F., Wong C.Y., Ho J.C. "Crystalline GaSb nanowires synthesized on amorphous substrates: from the formation mechanism to p-channel transistor applications", ACS Applied Materials & Interfaces, 5, 10946-10952, 2013.

Yang Z., Han N., Wang F.Y., Cheung H.Y., Shi X., Yip S.P., Hung T.F., Lee M.H., Wong C.Y., Ho J.C. "Carbon doping of InSb nanowires for high-performance p-channel field-effect-transistors", Nanoscale, 5, 9671-9676, 2013.
Investigation on Metal-Induced Crystallization of Amorphous Silicon Using Xenon Flash-Lamp
Authors: Mudgal Tarun , Reepmeyer Christopher , Cormier Denis , Manley Robert G. , Hirschman Karl D
Published: February 2020

Flash-lamp annealing (FLA) is an alternative technique for crystallization of amorphous silicon which can be scaled to large substrates. A process using FLA may have significantly reduced process complexity and time; however published results that demonstrate potential for use in flat panel displays have been limited [1]. This work investigates FLA in combination with metal-induced crystallization (MIC). The FLA system used in this work is a NovaCentrix PulseForge 3300, which anneals the material using a series of short but intense bursts of broad spectrum light from xenon flash lamps. High peak power over microseconds time scale can provide control over the depth of heating to avoid damage when processing on substrates such as glass or plastic. Input factors to the FLA system included lamp intensity, pulse width, number of pulses and repetition rate. Since samples are not in thermal equilibrium during FLA, power/time/flash-count combinations that deliver the same energy produce very different results. Additional factors included use of an anti-reflective SiO2 layer, and substrate heating (steady-state). Performing FLA on samples with trace amounts of nickel has demonstrated effective crystallization with single-pulse exposures delivering energy of ~ 5 J/cm2. Experiments which investigate the influence of both MIC and FLA process parameters on the material properties and electrical characteristics of TFTs will be presented.

[1] S. Saxena, D. C. Kim, J. H. Park, and J. Jang, "Polycrystalline silicon thin-film transistor using Xe flash-lamp annealing," IEEE Electron Device Letters, vol. 31, pp. 1242-1244, 2010
Effect of Negative Oxygen Ions on a-IGZO Thin Films by Superimposed RF/DC Magnetron Sputtering
Authors: Kim Doohyun , Jang JinNyoung , Yoon Soobok , Hong MunPyo
Published: February 2020

During the magnetron plasma sputtering process, the bombardment effects of the negative oxygen ions (NOIs) on the thin film properties of amorphous indium-gallium-zinc oxide (a-IGZO) has been investigated. While the kinetic energies of NOIs effectively adjusting by using a superimposed rf/dc magnetron sputtering system, the characteristics of NOIs extracted by in situ analyses with ion energy analyzer are good agreement with the calculated values by the Kevin Meyer equation as shown in Figs 1(a) and 1(b). Furthermore, we find that the observed energies of NOIs corresponding to the applied dc bias are enough high to influence a lattice distortion and/or displacement in a-IGZO thin films. Figure 2(a) and 2(b) show the results of the Hall measurement and work function of a-IGZO films at RT with different dc biases. The σ and ne
of a-IGZO films monotonically increases with increasing the dc bias in logarithmic scale. This is due to the increment in the ne
as a function of dc bias. Interestingly, the hall mobility (μhall
) drops rapidly with opposite direction against that of ne
, and σ until under the dc bias of 300V, and becomes flat over 300V. In general, μhall
largely depends on ne
in AOSs & TCOs owing to their structural randomness; μhall
of AOS thin film increases with ne
, while that of TCO decreases with ne
. However, the observed ne
(> 1019 cm-3) of IGZO films with relatively higher dc bias is too high as well as that of TCOs. It is obvious that the variation of σ, ne
, and μhall
above the dc bias of 300 V is quite different with that of the measured values at relatively lower dc bias (< 300 V). Furthermore, Fig. 2(b) shows the workfunction of a-IGZO films extracted by a kelvin probe method monotonically decreases from 4.986 to 4.940 eV with increasing the dc bias from 100 to 400 V, but it has also a knee point around the dc bias of 300 V. The overall analysis revealed that the bombardment of NOIs with high energy has a great influence on a-IGZO film properties. Our work demonstrates the bombardment of NOIs is one of a crucial issue to achieve the high quality a-IGZO films.
Effects of the Bombardment of Negative Oxygen Ions on Gate Bias Stability of InGaZnO Thin Film Transistors
Authors: Kim Doohyun , Yoon Soobok , Hong MunPyo
Published: February 2020

Amorphous InGaZnO (α-IGZO) thin-film transistors (TFTs) are very promising due to their potential use in thin film electronics and display drivers. However, the stability of AOS-TFTs under the various stresses has been issued for the practical AOSs applications. Up to now, many researchers have studied to understand the sub-gap density of states (DOS) as the root cause of instability. Nomura et al. reported that these deep defects are located in the surface layer of the α-IGZO channel. Also, Kim et al. reported that the interfacial traps can be affected by different RF-power during RF magnetron sputtering process. It is well known that these defect states can influence on the performances and stabilities of α-IGZO TFTs. Nevertheless, it has not been reported how these defects are created during conventional RF magnetron sputtering. In general, during conventional RF magnetron sputtering process, negative oxygen ions (NOI) can be generated by electron attachment in oxygen atom near target surface and accelerated up to few hundreds eV by a self-bias of RF magnetron sputter; the high energy bombardment of NOIs generates bulk defects in oxide thin films and can create the defects of α-IGZO thin films. The a-IGZO TFTs have been fabricated with different dc biases (200 V, 300V, and 400V). Figure 1 shows that the transfer characteristics of the a-IGZO TFTs with a positive bias stress (PBS in (a)), a negative bias stress (NBS in (b)), and a negative bias illumination stress (NBIS in (c)). It is observed that the changes of the transfer characteristics with PBS, and NBS are not depended on different dc biases. However, a huge shift of a threshold voltage on a-IGZO TFTs is observed under NIBS condition.

In this study, we have investigated that the NOIs accelerated by dc self-bias were one of the dominant causes of instability in α-IGZO TFTs when the channel layer was deposited by conventional RF magnetron sputtering system. Finally, we will introduce our novel technology named as Magnetic Field Shielded Sputtering (MFSS) process to prevent the NOIs bombardment effects and present how much to be improved the instability of α-IGZO TFTs by this new deposition method.
Nonvolatile Memory Device Using Mobile Protons via Insertion Hydrogen Neutral Beam Treatment Process between SiO2 Deposition Processes at Room Temperature
Authors: Jang Jin Nyoung , Lee Dong hyeok , Jeon Sanghun , Park Jeunghak , Hong MunPyo
Published: February 2020

We demonstrated the nonvolatile memory functionality of nano-crystalline silicon (nc-Si) field effect transistors (FETs) using mobile protons that are generated by very short time (within 2 minutes) hydrogen neutral beam (H-NB) treatment at room temperature (25 °C). Some researches try to hydrogen insertion process via long time (40 minutes) high-pressure hydrogen annealing (HPHA) at high temperature (400 °C) that also need several steps such as poly silicon deposition, HPHA process, and poly silicon etching process. However our hydrogen insertion process does not need any other additional process but only H-NB process during normal thin film transistor fabrication. Also the whole memory fabrication process kept under 50 °C (except SiO2deposition process; 300 °C). These nc-Si devices exhibited reproducible hysteresis, reversible switching, and nonvolatile memory behaviors in comparison with those of the conventional FET devices. We think that the memory characteristics are attributed to the movement of protons between the Si(gate)/SiO2(gate insulator) interface and the SiO2/nc-Si thin film (active layer) interface by the applied gate electric field. Our study will further provide a useful route of creating memory functionality and incorporating proton-based storage elements onto a modified CMOS platform for FET memory devices using nanomaterials, and probability of next generation flexible memorable electronics.