bluuebunny/crossref_metadata_2025 huggingface dataset:
Room-Temperature Wafer Direct Bonding Using Ne-Beam Surface-Activation
Authors: Takagi Hideki , Kurashima Yuichi , Maeda Atsuhiko
Published: February 2020

In the surface activated bonding (SAB) at room temperature, the surfaces of specimens are sputter etched by high-energy ion/atom beam of inert gas to remove surface contaminants and create active surfaces, which are ready to form inter-atomic bonds even at room temperature. Ar has been used for the purpose. However, sputter etching by Ar high-energy ion/atom beam causes increase of surface roughness. In case of wafer direct bonding, the surface roughness has large influence on the quality of bonding interface such as bonding strength, local strain, and so on. Therefore a surface activation process which does not cause surface roughening has been desired.

In this work, we have examined the applicability of Ne fast-atom-beam (FAB) to SAB of Si wafers at room temperature. We confirmed that Ne-FAB does not cause surface roughening and Si wafers are successfully bonded by Ne-beam surface activation. In addition, we found that Ne-FAB sputter etching has surface smoothing effect which improves quality of the bonding interface.

The room temperature wafer bonding apparatus (MWB-12-ST: Mitsubishi Heavy Industries) with the FAB 104 (Atom Tech Ltd.) beam sources were used for bonding of Si wafers. The etching rate of Si surface by Ne-FAB was about half of that of Ar-FAB using the beam source operation parameters of 1.8 kV applied voltage and 100 mA input current. With etching depth more than 1.5 nm, the bonding strength comparable to Si bulk strength was attained by Ne-FAB surface activation. With etching depth of 30 nm, we measured surface roughening of Si wafers using Ne, Ar and Xe gas. The surface roughness of Si wafers largely increased by the Ar and Xe-FAB sputter etching. In case of Ne-FAB, the surface roughness did not increase by the sputter etching and kept the initial rms value of 0.18 nm of CMP-polished Si wafers.

Moreover, we found surface smoothing effect of the Ne-FAB. We prepared Si wafers which had been roughened by Xe-FAB etching. They could not be bonded directly by SAB. Surface roughness of the roughened Si wafer decreased from 0.40 to 0.17 nm rms by applying Ne-FAB of 30 nm etching depth. Along with the surface smoothing, the bonding strength was largely improved and finally became equivalent to Si bulk strength. It was confirmed that strain near the bonding interface was decreased by the smoothing effect as shown in Figure.
Invited: Room Temperature Bonding Using Thin Metal Films (Bonding Energy and Technical Potential)
Authors: Shimatsu Takehito , Uomoto Miyuki , Kon Hitoe
Published: February 2020

Bonding of two flat wafers using thin metal films is a promising process to achieve wafer bonding at room temperature [1-3] along with surface-activated bonding [4-6]. Any mirror-polished wafers can be bonded using thin metal films. High surface energies of metal films and a large atomic diffusion coefficient at the grain boundaries and film surfaces enable bonding at room temperature without unusually high loading pressure.

Of bonding processes using thin metal films, one is bonding in vacuum: metal films are fabricated on two flat wafers’ surfaces using sputter deposition with subsequent bonding of the two films on the wafers in vacuum. Bonding in vacuum can be done using almost any metal films, including tungsten (Fig.1). Wafers can be bonded even with film thickness of a few angstroms on each side [2] (Fig.2), which is useful to bond wafers having electric devices on their surfaces while causing no marked damage to electrical properties of devices. Moreover, electrons or spin-current, in addition to incident light, can be transmitted through thin bonded films without marked reduction in intensity. Actually, bonding in vacuum is starting to be used to mass produce new thin film devices.

Another bonding process is bonding in air. Bonding of the two films on the wafers can be performed in air after sputter film deposition in vacuum [3]. This process is limited to use with Au and Au alloy films, but it is extremely convenient. For instance, bonding of patterned Au films can be done with sputter film deposition using metal masks. It is actually used for mass-production of new etalon filters for optical fiber communication [7]. Moreover, bonding of wafers with mirror-polished metals for enhancing the heat dissipation efficiency was also achieved [8] (Fig.3).

Further discussion can be made of the bonding energy of wafers that are bonded using various material films as a function of film thicknesses related to the surface energy of the metal films used for bonding and the bonded interface microstructure. This process holds great potential for new device fabrication.

[1] T. Shimatsu, R. H. Mollema, D. Monsma, E. G. Keim and J. C. Lodder, J. Vac. Sci. Technol., A
16, 2125 (1998)., [2] T. Shimatsu and M. Uomoto, J. Vac. Sci. Technol., B
28, 706 (2010)., [3]T. Shimatsu and M. Uomoto, ECS Transactions, 33(4), 61-72 (2010)., [4] T. Suga, Y. Takahashi, H. Takagi, B. Gibbesch and G. Elssner, Acta Metall. Mater., 40, s133 (1992)., [5] T. Suga, K. Miyazawa and Y. Yamagata, MRS Internal Meeting on Advanced Materials, Materials Research Society, 8, 257 (1989)., [6] E. Higurashi, T. Imamura, T. Suga and R. Sawada, IEEE Photonics Technology Letters, 19, 1994 (2007)., [7] T. Shimatsu, M. Uomoto, K. Oba and Y. Furukata, Proc. of Third IEEE Intl. Workshop on Low Temperature Bonding for 3D Integration, 103 (2012)., [8] H. Kon, M. Uomoto and T. Shimatsu, Conference on Wafer Bonding for Microsystems and Wafer Level Integration, Stockholm, Sweden, Dec. (2013) P18.
(Plenary) Extending the FETs: Challenges and Opportunities for New Materials and Structures
Authors: Uchida Ken , Takahashi Tsunaki
Published: February 2020

Toward the end of CMOS technology roadmap, three-dimensional structure and new channel materials have been pursued and in recent years partly utilized in scaled FETs. Firstly, channel structures for FETs with channel length of less than 20nm will be discussed and challenges to realize the nanoscale three-dimensional structures will be addressed. In particular, trade-off between parasitic resistance and capacitance, low-frequency noise, and variability of three-dimensional structures will be shown. Then, the opportunites for new materials will be investigated. The importance of thermal management in nanoscale, new channel materials will be also discussed.
(Invited) Challenges and Opportunities in the Design of Tunnel FETs: Materials, Device Architectures, and Defects
Authors: Esseni David , Pala Marco G. , Revelant Alberto , Palestri Pierpaolo , Selmi Luca , Li Mingda (Oscar) , Snider Gregory , Jena Debdeep , Xing Huili Grace
Published: February 2020

Most of the digital systems around us today are power limited, and their performance is essentially the best that it can be obtained with the available power or energy budget. The scaling of the supply voltage is the most effective measure to improve the energy efficiency of CMOS circuits, however the degradation of dynamic performance with decreasing VDD
is today particularly challenging, and practically limits further VDD
reduction. A better tradeoff between dynamic performance and standby power may be achieved thanks to small slope switches (i.e. transistors having a sub-threshold swing, SS, better than 60mV/dec at room temperature), and the ITRS has singled out Tunnel FETs as the most promising small SS devices.

In this framework, I will then briefly introduce the working principles of Tunnel FETs and emphasize how the choice of the material systems plays a crucial role in the overall design of the devices. I will then discuss examples of challenges and opportunities in the design of Tunnel FETs, touching strain engineering, hetero-junctions, size induced quantization effects, interface defects related design issues and variability. I will also introduce, time permitting, some very recent developments in the field, which try to exploit transition metal dichalcogenides (TMD) MX2 (M = Mo, W and X = S, Se), which form a family of quasi-2D crystals having an energy band-gap ranging between 1eV to 2eV, to design vertical tunnel based transistors.
Low Temperature Geometrically Confined Growth of Pseudo Single Crystalline GeSn on Amorphous Layers for Advanced Optoelectronics
Authors: Li Haofeng , Brouillet Jeremy , Salas Alan , Chaffin Ian , Wang Xiaoxin , Liu Jifeng
Published: February 2020

The geometrically confined growth of highly crystalline semiconductor materials like Ge on amorphous layers (without epitaxial template) has been a challenge in materials science. The success of this technology, especially at low fabrication temperature can enable 3D Si photonics by building photonic devices on metal/interconnect layers, and enable inexpensive, high-throughput fabrication of devices such as tandem solar cell and thin-film transistor.

Here we report that, by incorporating Sn into Ge, we are able to obtain highly crystalline GeSn thin film on amorphous substrates at low crystallization temperatures ranging from 340 to 464 ºC through enhanced crystallization from the Ge-Sn euetectic system, and are able to transform the material toward a direct band-gap material through band structure modification. A highly textured Ge0.91Sn0.09 is obtained from the sample with 9.5 at. % as-deposited Sn composition, which shows grain sizes up to tens of microns, as revealed by electron backscatter diffraction (EBSD), X-ray diffraction (XRD) and Raman spectroscopy. EBSD confirms that most grain boundaries are either twin or low angle boundaries, which are benign to optoelectronic properties. Strikingly, the nucleation center distances range from 0.1 to 1 mm, orders of magnitude larger than common solid state crystallization, which indicates an exceedingly high grain growth rate vs. a low nucleation rate. As a result of this feature, we are able to fabricate geometrically confined pseudo single crystalline GeSn grain using patterning techniques. Another remarkable result is that 9 at.% Sn is incorporated substitutionally into Ge, far exceeding the equilibrium solubility limit of ~1%. The high Sn composition, with the addition of ~0.24% tensile strain in the film, shifts the direct band gap to 0.5 eV (2500nm), right on the verge of indirect-to-direct band gap transition. This transition will greatly enhance the material’s optoelectronic performance as a photonic device, and will also broaden the absorption spectrum for a tandem solar cell.
Electrochemical Control of Thermal Conduction in Thin Films
Authors: Cahill David G , Cho Jiung , Braun Paul V
Published: February 2020

Controlling the flow of heat through materials is important for many technologies. While materials with high and low thermal conductivities are available, materials with variable and reversible thermal conductivities are rare, and other than high pressure experiments, only small reversible modulations in thermal conductivities have been reported. We will describe our in-situ and ex-situ measurements of the electrochemical modulation of the thermal conductivity of sputtered films of LixCoO2 using time-domain thermoreflectance (TDTR). The thermal conductivity ratio between the lithiated and delithiated state can exceed 2.5. The oxidation-state dependent thermal conductivity of electrolytically active transition metal oxides provides opportunities for dynamic control of thermal conductivity and may be important for understanding the thermal management of electrochemical energy storage devices.
Advanced Nanostructured Thermoelectric Materials for Energy Conversion
Authors: Wu Yue
Published: February 2020

The rapid development of nanomaterials in the past decade has provided a possibility of directly converting waste heat back to electricity based on the thermoelectric Seebeck effect. In the past four years, we have developed a transformative approach to pioneered low cost and scalable solution-phase growth methods to mass produce thermoelectric nanowires and nanowire heterostructures to match the physical and economic magnitudes of energy use and economical entertainment in the manufacture/recycling. These nanostructured thermoelectric materials show a significantly enhanced performance compared to the bulk crystals based on the quantum confinement and energy filtering.
Atomic-Monolayer Thermoelectric Conversion in Two-Dimensional Chalcogenides
Authors: Jo M.-H.
Published: February 2020

Electronic structures of bismuth telluride, the highest thermoelectric figure of merit at room temperature, are substantially modified by electronic confinements and strong spin-orbit coupling in the few-monolayers thickness regime. Here, by local optical probes, we show direct evidence that efficient thermoelectric current generation is available at the few-monolayers thick bismuth telluride by hot electrons motions through two-dimensional subbands and topologically protected surface states. Our study offers a challenging opportunity to investigate the fundamental photoresponse of topological quantum states, and provides a new design rule for the highly efficient thermoelectric circuitry.
Transparent Conducting ITO Nanowires: Orientation Control, Phase Selection, and Light Emission
Authors: Wu Tao
Published: February 2020

As a new paradigm of synthesis, the vapour-liquid-solid (VLS) growth of nanowires has received considerable attention in the past decade due to the vast potential of nanowire-based devices. Indium tin oxide or ITO is the most important transparent conducting oxide, dominating the touch-screen and other emerging technology markets. In this talk, I will discuss the synthesis and characterization of single-crystalline ITO nanowires. We found that the growth of planar, vertical and randomly oriented tin-doped indium oxide (ITO) nanowires can be realized on yttria-stabilized zirconia (YSZ) substrates via the epitaxy-assisted VLS mechanism. In addition, with properly tuned growth conditions, a rare cubic phase of In-Sn-O (ISO) epitaxially forms at the catalyst/nanowire interface, forming a self-assembled axial nanowire heterostructure. Finally, we also found that ITO nanowires can emit UV light, exhibiting optical properties different from the bulk counterpart.
The Effect of Band-Bending on Hybrid Bulk Heterojunction Solar Cell Performance
Authors: Haring Andrew J , Morris Amanda J
Published: February 2020

Hydrid bulk heterojunction solar cells (HBHJs) consist of nanostructured metal oxide (TiO2 and ZnO) acceptors and polymer light absorbing donors. To date, these promising architectures have only achieved moderate efficiency due to surprisingly low short circuit photocurrents. To elucidate the underlying properties that result in this low current, a detailed understanding of interfacial properties is required. Herein, we quantify a vacuum level offset of 0.8 eV between the polymer and the TiO2 created by spontaneous charge transfer upon heterojunction formation. This offset imparts a barrier to charge separation at the TiO2-polymer interface and explains the poor performance of cells to date. New materials for improved photocurrent are proposed by tuning the energetics of the heterojunction.
Functionalized Germanene as Emerging Nanomaterials
Authors: Li Junwen , Datta Dibakar , Shenoy Vivek B.
Published: February 2020

Using first principle calculations, we propose functionalized germanene (GeX, X=H,F,Cl,Br,I,OH,CH3) as emerging nanomaterials. While germanene has no band gap, complete functionalization with H induces band gap of around 1.80 eV. 50% H functionalization shows a dangling band at the Fermi level. While GeI is a 2D Topological Insulators (TI); GeH,GeF,GeCl and GeBr can be transformed into TI by applying strain.The methyl-functionalized two-dimensional germanium monolayer sheets have been synthesized with a facile, one-step metathesis approach from CaGe2 crystals. We find that tensile strain can induce topological phase transition with band inversion at Gamma point. The band gap opened by spin-orbit coupling in this quantum spin Hall insulator can be as large as 0.1 eV ample for practical applications at room temperature.
Synthesis of Metal Nano-Powders in Nonstationary Electrolysis Conditions
Authors: Lipkin Mikhail Semenovich , Lipkin Valery Mikhailovich , Naumenko Alexander Alexandrovich , Misharev Alexander Sergeevich , Tulaeva Firuza Rakhimzhonovna , Rybalko Elena Alexandrovna , Lytkin Nikolay Alexabdrovich , Shishka Vasily Grigorievich , Bogdanchenko Anatoly Nikolaevich
Published: February 2020

An increasing productivity of electrolytic method of metal powder manufacturing is very important for a lot of application. A perspective way of this is combination of pulse electrolysis with cathode vibration. Using vibrating cathode, one can obtain metal powders from dilute solutions, including electrolytes, sintering by anodic dissolution of metals and alloys. Such a possibility provides many electrolytes, but ammonia based is much of interest.

Copper powders, obtaining from anodic synthesized electrolytes, has prevailing fraction with particle size according to Microtrac analyzer data of about 110 nm (fig. 1). The shape of copper particles is polyhedral (fig. 1) with dendrite nano-wiskers. This result was obtained due to combination of pulse electrolysis with cathode vibration. Nickel powders, obtained in these conditions from ammonia complex electrolyte, have prevailing fraction of about 20 nm and spherical shape.

A productivity of copper powders in ammonia chloride electrolyte is 0.064 g/sm2 per hour, that is much higher, than from sulphate one. We assume this is due to reduction of copper from [Cu(NH3)2]+complex, which equivalent mass is two times higher. It is interesting, that in ammonia electrolytes there is a way of copper powder formation near insoluble anode, such as graphite or platinum. This reaction is possible due to Cu(I) complex disproportion or generation of hydrazine by ammonia anodic oxidation.

Ammonia chloride electrolytes provide blocking effect for powder particle growth, which is strengthening by low frequency pulse electrolysis.

A method of electrolysis with vibrating cathode and anodic synthesized electrolyte was applied also for iron, and cadmium powders. All synthesized powders exhibit high activity in powder metallurgic processes, tribology systems and as electrode active materials of nickel-cadmium secondary cells.
Invited: Electronic Devices Based on Vertical Si Nanowires
Authors: Yu Hongyu
Published: February 2020

In this work, several electronic devices (e.g. Tunneling FETs and SONOS flash memory) are demonstrated based on vertical Si nanowires manufactured by CMOS process technologies, aiming at ultra-high density applications. The corresponding process technologies and device characteristics will be discussed in this work. Our results suggest that vertical SiNW can be considered as a possible building block for novel electronic devices, especially for sub-10nm technology node.
Pd/TiO2-Multiwall Nanotubes toward Electrocatalytic Oxidation of Formic Acid in Acid Media
Authors: Aldana-González Jorge , Montes de Oca Maria Guadalupe , Olvera Juan Carlos , Sánchez-Guajardo Rebeca , Garfias-García Elizabeth , Romero-Romo Mario Alberto , Palomar-Pardavé Manuel
Published: February 2020

The formic acid (HCOOH) oxidation was studied in acid medium at Pd nanoparticles (NPs) supported on TiO2 electrode. TiO2 nanotube electrode was prepared using the anodizing method. This method was modified by Pd NPs onto the tube surface, via Pd electrodeposition, Pd NPs supported on vulcan carbon XC-72R and Pd NPs impregned. Pd NPs were synthesized following the colloidal method and characterized by XRD, UV-Vis spectroscopy and SEM. The TiO2 MWNTs electrode is homogeneously covered by Pd NPs. The Pd/TiO2-MWNTs performance and electrocatalytic activity were characterized by cyclic voltammetry and chronoamperometry in 0.5 M H2SO4 and 2.0 M HCOOH. Results demonstrate that Pd NPs onto TiO2 nanotubes (NTbs) increased the catalytic activity of Pd NPs for HCOOH oxidation.
Deformation and Approaching of Droplet Pair in a Microchannel under AC Electric Fields
Authors: Chen Xiaodong , Xue Chundong , Hu Guoqing
Published: February 2020

Electric fields are widely used to induce the coalescence of water-in-oil emulsion droplets in droplet-based microfluidics. The dipole-dipole interaction amplifies the dielectrophorectic force experienced by two neighboring droplets to drive them toward each other. An ac electric field can act in a cumulative manner to merge the adjacent interfaces of the two droplets, even if the electric field is weak. Here we perform a combined numerical and theoretical analysis to explore the coupled flow and electric field of droplet pair in a rectangular microchannel under ac electric fields. Numerical simulations are carried out by solving of the conservation equations coupled with an improved volume-of-fluid/adaptive-mesh-refinement method and a charge-conservative leaky-dielectric model for two-phase electrohydrodynamic problems. To improve the fidelity and efficiency of the simulations, several adaptive mesh refinement criteria are used simultaneously, including gradient-based refinement along the interface, curvature-based refinement for interface with high curvature, and thickness-based refinement for thin region between confinement walls and interfaces. The evolutions of deformation parameter and droplet separation, as well as the distribution of the electric force are analyzed to reveal the responses of droplet pair to the ac field. A theoretical model with correlation parameter is established for the time needed for droplet coalescence in terms of initial droplet separation and ac field intensity. By taking account into the deformation and movement of the droplets, this model can predict more precisely the droplet manipulation for arbitrary electric field frequencies.
Analytical Study of Surface Film on the Li Metal
Authors: Kuwata Hiroko , Matsui Masaki , Imanishi Nobuyuki
Published: February 2020

Introduction

Li metal is one of the most promising materials as a negative electrode because of its theoretical capacity > 3800 mAh g-1. However the formation of the dendritic lithium during the deposition process has to be prevented for the rechargeable batter applications.

Though a lot of studies have been conducted to suppress the dendritic growth of lithium metal [1], it can be easily formed at a high current density or during a cycling process. Hence it still needs more studies to prevent the dendritic growth of the lithium metal completely.

Recently we reported that the interfacial resistance of a lithium metal electrode and an electrolyte solution mainly consists of the lithium ion transfer in SEI film [2]. This result suggests that the ionic conductive property of the SEI significantly affects to the formation process of the dendritic lithium. In the present study, we investigated relationship between surface morphology of electrodeposited lithium and the SEI films using various electrolyte additives used in commercial Li ion batteries.

Experimental

A 1 mol dm-3 LiPF6EC:DEC (1:1 vol%) was employed as a standard electrolyte solution. Three additives: 5 vol% Vinylene carbonate (VC), 5 vol% Fluoroethylene carbonate (FEC) and 1 wt% Lithium bis(oxalate)borate (LiBOB), were added to the standard solution as the SEI formation source.

The electrodeposition of the lithium was carried out using a two-electrode Swagelok cell. The deposited lithium electrodes were carefully rinsed with DEC and dried in argon filled glove box. The surface morphology of the deposited lithium was observed using SEM and the SEI film was analyzed by XPS.

Results and Discussion

Fig.1 shows SEM images of lithium electrodes deposited in the electrolyte solutions with / without VC. The lithium electrode from VC-free electrolyte showed a smooth surface morphology, while the electrodeposited lithium form the electrolyte solution with 5 vol% VC had dendritic-shaped deposits. It suggests that the difference of ion conductivity in the SEI films on the Li metal affects to the surface morphology of lithium as we expected.

Fig. 2 shows XPS spectra of O 1s for the Li metal immersed in 1 mol dm-3 LiPF6 EC:DEC (1:1 vol%) with / without VC. In the case of the VC-free electrolyte, a relatively broad peak corresponds to lithium alkyl carbonate overlapped with a peak of Li2CO3 was observed while polyether like compounds form the surface film in the case of VC containing electrolyte solution. Furthermore Li2CO3and lithium alkyl carbonate was observed after 30 sec of argon etching process. Therefore it clearly shows that the SEI composition directly affects to the surface morphology of lithium. Further detailed discussion concerning the the SEI composition and surface morphology would will be presented and discussed in the meeting.

Reference

[1] K. Kanamura, S. Shiraishi, Z. Takehara, J. Electrochem. Soc., 143, 2187 (1996)

[2] H. Kuwata, M. Matsui, N. Imanishi, Abstract of The 54thBattery Symposium in Japan, 1D18, 2013
Direct Observation of Bandgap Shift in the Dislocations Using High Resolution Cathodoluminescence in Transmission Electron Microscopy
Authors: Kim Sung-Dae , Kwon Soon Yong , Sheen Mi-Hyang , Kim Youngwoon
Published: February 2020

InGaN/GaN multi-quantum well (MQW) is the leading structure for the next generation of lighting systems. Even though silicon and silicon carbide are used as substrates to grow GaN thin films, majority of the GaN are being grown onto sapphire substrates, whose techniques were well exercised for the past decades and had wide variation to reduce the strain induced by the lattice mismatch. Dislocations are unavoidable because of the large lattice mismatch between GaN and substrate, regardless of the substrates being used. Dislocations formed in InGaN/GaN MQW have different lattice periodicity and should deliver different emission characteristics compared to the perfect periodic lattice. Dislocations can be seen using transmission electron microscopy (TEM) and in order to link the emission characteristics with the dislocations, cathodoluminescence capability in TEM. Cathodoluminescence in transmission electron microscopy (CL-TEM) delivers superior performance to the CL-SEM because of its higher spatial resolution with short diffusion length and the capability of one-to-one mapping of the interested microstructural area with point-luminescence and the internal microstructure. In this study, luminescence characteristics were investigated using CL-TEM to identify the shift of the emission wavelength with different types of dislocations. Dislocations revealed short wavelength shift in the region with QW and threading dislocations. No emission was observed with the edge dislocations, but the screw dislocations either close to the surface or close to the substrate delivered shift of wavelength toward the higher energy side. Plane-view TEM revealed the fluctuations of the wavelengths, which gave low and high band gap area and local minima might be the contribution of the high efficiency of InGaN/GaN light emitting system.
Behaviors of Carbon Atoms during Plasma Oxidation of 4H-SiC(0001) Surfaces near Room Temperature
Authors: Saito Naoki , Mori Daichi , Imafuku Akito , Kawai Kentaro , Sano Yasuhisa , Morita Mizuho , Arima Kenta
Published: February 2020

Epitaxial graphene on silicon carbide (SiC) is promising for future electronic devices. A well-known scheme for the epitaxial growth of graphene is to heat a Si-face SiC(0001) surface to 1100-1300°C in ultrahigh vacuum (UHV), which results in the sublimation of Si. However, this simple process produces a SiC surface with a pitted morphology, which degrades the transport properties of graphene on it.

The pitted morphology originates from the rapid and random sublimation of Si from the terraces that are not covered by a carbon-rich buffer layer. Thus, a strategy to avoid the pitted morphology is to form a homogeneous buffer layer on the entire SiC surface. For this purpose, a key technique is the deposition of carbon at the monolayer level on a SiC substrate in a controllable manner. Researchers have reported various methods to enrich carbon concentration on a SiC surface with a Si face. Some examples are the direct deposition of carbon onto SiC, the rapid annealing of SiC surfaces, and the enhanced removal of silicon atoms by atomic hydrogen, all of which are based on sophisticated UHV techniques.

In this study, we demonstrate that carbon atoms are segregated at the SiO2/SiC interface at the monolayer level when a SiC surface, atomically flattened by a solution-based process[1-3], is oxidized by an atmospheric-pressure plasma (He-based plasma with a small amount of O and OH species) at near room temperature. The behavior of carbon atoms has been an object of study in thermal oxidation of SiC. We discuss the mechanism of carbon aggregation at the SiO2/SiC interface occurring in the plasma oxidation at room temperature. After the plasma oxidation, the sample was etched in HF solution to strip off the oxide layer, which leaves a carbon source for graphene growth on the SiC substrate. And we show the carbon-rich surface yields a surface morphology with reduced pits on graphene when it is treated at elevated temperatures in vacuum. We speculate this is achieved by the additional carbon atoms assisting the formation of the buffer layer more uniformly over the surface prior to graphene growth.

[1] K. Arima, K. Endo, K. Yamauchi, K. Hirose, T. Ono, and Y. Sano, J. Phys.: Condens. Matter 23, 394202 (2011).

[2] A.N. Hattori, T. Okamoto, S. Sadakuni, J. Murata, K. Arima, Y. Sano, K. Hattori, H. Daimon, K. Endo and K. Yamauchi, Surf. Sci. 605, 597 (2011).

[3] K. Nishitani, H. Sakane, A.N. Hattori, T. Okamoto, K. Kawai, J. Uchikoshi, Y. Sano, K. Yamauchi, M. Morita and K. Arima, ECS Transactions, 41(6), 241 (2011).
Simulation of Radiation Damage in GaN HEMT Structures
Authors: Patrick Erin , Choudhury Mo , Law Mark E
Published: February 2020

GaN based HEMT structures are of interest for a variety of high performance applications. Of natural interest is their tolerance to radiation damage. Devices damaged with protons exhibit several interesting features. First, there is little change in the threshold voltage. This implies that there can be little change in the charge under the gate stack. Additional charges there would shift the threshold voltage. Second, there is a change in the drain voltage for increased gate leakage. The nominal theory for this is that the peak field increases the mechanical strain and induces new leakage paths. For a given drain to gate voltage, the peak field can be decreased by charging along the top of the buffer layer adjacent to the gate. To simultaneously account for both features, the uniform irradiation of protons must produce localized charges between the gate and drain, above the channel.

To further complicate the issue, significant degradation of mobility and transconductance are observed. Normally, this would be accounted for by increased impurity scattering near the channel. However, we do not observe an increase in charges in the gate stack. Additionally, back side irradiation where the damage is contained below the channel, exhibit much the same behavior as front side irradiation. Are the defects migrating? Is it electronic charging?

Simulation can help answer these types of questions. We will describe our simulation approach and discuss results that can help separate and identify the mechanisms responsible for these results.
Surface Roughness Influences on the ZnO Reram
Authors: Ke Jr-Jian , Namura Kyoko , Wei Tzu-Chiao , He Jr-Hau , Suzuki Motofumi
Published: February 2020

The oxygen chemisorption raising from surface roughness associated with the formation/rupture of conductive ﬁlaments dramatically affects the electrical properties of ZnO ReRAM, which is conﬁrmed by the oxygen adsorption induced threshold voltage shift of the FET measurements. The lower oxygen adatom concentration changes of rougher surface under various measuring ambient condition, leading to the improvement of the electrical property stability on both SET/RESET switching voltage and HRS/LRS resistance. The thickness-independent HRS resistance and the better switching probability shown in the ZnO with rougher surface, indicating that the oxygen chemisorption on the surface dominates resistive switching process. Our ﬁndings give a guidelines for developing practically useful applications of ZnO-based ReRAM.
Li+ Co-Doping Effect on the Photoluminescence Time Decay Behavior of Y2O3: Er3+ Films
Authors: Meza.Rocha Abraham , Huerta Evelyn , Zaleta-Alejandre Efrain , Falcony Ciro
Published: February 2020

The incorporation of rare earth ions in metal oxides has received considerable attention for great variety of applications such as, biomedical, optical amplifier, active waveguide, solar cell, etc. In particular, Er3+ ion shows interesting characteristic emissions in the 520-580, 640-700, 1520-1580 nm ranges, which are suitable for most of the applications mentioned above. The use of thin film phosphors offers some advantages over bulk powders such as a better thermal stability, better adhesion, and good uniformity coverage of substrate surfaces. However, the main drawback of phosphor films has been their low brightness in comparison with bulk powders. Recently, it has been reported that the incorporation of Li+, Na+ and K+ alkali ions enhances considerably the luminescent efficiency of rare earths. In this work, the effect of Li+ co-doping on photoluminescent time decay characteristics of Y2O3: Er3+ is reported for films deposited by ultrasonic spray pyrolysis at 500°C. The Er3+ content was fixed at 1.5 at% while the Li+ content in the spraying solution was varied from 1 to 4 at% in relation to Y3+. It is observed that the addition of Li+ content up to 2 at%, besides resulting in an increase of the luminescence emission intensity, modifies the luminescence time decay behavior as well. In general, the decay profiles under 207 and 414 nm excitation are not fitted to a simple exponential. They seem to be composed by an initial slow decay followed by a faster decay. This behavior is associated with a charge transfer process. A simple model in which charge transfer from localized centers to the Er3+ ions is used to describe the evolution with time of the luminescence emission. The introduction of Li+ ions in the Y2O3: Er3+ seems to have an impact on both the effectiveness of the charge transfer process and on the total number of Er3+ ions contributing to the luminescence emission.
Synthesis, Physicochemical and Electrochemical Characterization of TiO2 Nanotubes Arrays and Self-Standing Membranes as Susbtrate for Electro-Catalysts
Authors: Díaz-Real Jesús Adrián , Arriaga Luis Gerardo
Published: February 2020

TiO2 nanotubes (NT) were synthesized by electrochemical anodization using 0.1 M NH4F in ethylene-glycol and water by applying a two different potentials of 20 and 60 V during 0.5, 1, 2 and 4 h as anodization times. The material was thermally treated at 450°C under air atmosphere for 2h. TiO2-NT membranes were produced by soaking as-prepared samples in ethanol. The material was characterized physicochemically by XRD, SEM, Raman spectroscopy and electrochemically by cyclic voltammetry. Current density behavior was monitored during material synthesis which is in agreement with anodization phases previously reported. SEM analysis allowed to confirm the morphology and measuring nanotubes length. In the case of the material prepared at 20 V, several morphologies clogged the surface. The nature of the TiO2-NT in the underneath surface were confirmed by EDX. For the 60 V material, well-defined nanotubes were obtained which length varies depending on the anodization time from 6.35 to 46.0 μm. Nanotubes growth rate achieves a linear tendency after 1h and up to 4h of anodization. XRD pattern show that as-prepared samples are amorphous, while thermally-treated samples are crystalline (anatase phase). Raman spectroscopy information for the thermally treated samples was compared to that of the literature and is in well-agreement with previous reports. It also revealed that with both increasing, anodization time and potential, the crystallinity degree is affected. Finally, cyclic voltammetry was performed in a 0.5M H2SO4, N2-saturated using a SCE and a Pt foil as reference and counter electrode, respectively. This electrochemical assessment showed that a capacity behavior is observed for these samples which increases directly proportional with anodization time.
Urea Oxidation on Ni(OH)2
-X(SO4)0.5
x·yH2o / C-PVC Composite Electrodes
Authors: Romero-Morán Alejandra , González Fuentes Miguel Ángel , Elizalde-González Ma. de la Paz , Dávila-Jiménez M. M.
Published: February 2020

The structural and physical properties of α-Ni(OH)2 materials have been studied because the great importance of this compound in catalysis and for the development of high performance devices. Recently, research efforts have been focused on the synthesis of nanostructured nickel hydroxide with several morphologies [1]. It has been reported that electrodes modified with nickel species present a strong electrooxidation activity in front of organic compounds in alkaline medium [2].

The objective of this work was the preparation of nanostructured Ni(OH)2
-x(SO4)0.5
x·yH2Oby hydrothermal method and their characterization by XRD, IR, AFM and SEM. These nanopowders of nickel hydroxide were supported on C-PVC composite electrodes for their electrochemical characterization by cyclic and differential pulse voltammetry.

The Ni(OH)2
-x(SO4)0.5
x·yH2O/C-PVC electrode showed good eletrocatalytic activity in the oxidation of urea and high anodic current was observed during the reverse scan (Figure 1).

Figure 1.Electrocatalytic response of Ni(OH)2
-x(SO4)0.5
x·yH2O/C-PVC electrode in absence (a) and presence of urea (b) in alkaline medium.

References

[1] T. Gao, B. P. Jelle, J. Phys. Chem. C117 (2013) 17294−17302

[2] D. Wang, W. Yan, S. H. Vijapur, G. G. Botte, J. Power Sources217 (2012) 498-502

Acknowledgements

We acknowledge the financial support of VIEP- BUAP under project No.2014 and CONACyT by the scholarships to A. Romero-Morán.
White Light Emission of Polystyrene (PS) Thin Films Deposited by Spray Pyrolysis
Authors: Carmona S. , Alarcón G. , Zaleta E. , Agular-Frutis M. , Rivera Z. , Pineda A. , Murrieta H. , Falcony Ciro
Published: February 2020

The optical, structural and luminescent characteristics of polystyrene PS films doped with luminescent organic pigments (LOP) and deposited by spray pyrolysis technique are reported. The films are deposited on glass, quartz and GaN at low temperatures, using chemical solutions of recycled PS (from stayfoam) and LOPs as precursors, and N.N-dimethylformamide, as solvent.

The thickness of the films was around 2.5 μm films showed at deposition rates between 100 and 200 Å/s. Doped films have roughness between 100 and 2500 Å depending on the kind of pigment used and the surface morphology shows that the organic pigments incorporate into the polystyrene host forming globular particles of about 2 µm in diameter. The organic pigments used have luminescent emissions peaked at 445, 510 and 590 nm.

Non-doped films are very transparent and smooth; on the other hand, doped films are opaque and rough. The LOPs luminescent emission wavelengths were preserved when they were incorporated in the PS films. Using an appropriate mix of OPs it was possible to obtain films that have white light emission. These multi doped films were deposited on violet and blue light emitting LED chips, achieving a complete white light source device. It was determined that the exposure to the violet light from the LED degrades the luminescent characteristics, however, the blue light has is not energetic enough to cause a degradation of the luminescent layer over similar period of time.

Emissions intensity behavior of photoluminescence depends of doping concentration and deposition temperature. The luminescence intensity had a maximum when the films were deposited at 240 0C in every case, save for the use of different concentrations of LOPs (~0.025 to 4%) in solution.

The surface morphology and the root mean square surface roughness for PS thin films were determined by Atomic Force Microscopy, By UV-Vis technique, %T was measured. In addition, infrared spectra, Scanning Electron Microscopy images and EDS chemical composition results are also shown.

Acknowledgments:

The authors would like to thank SECITI (before ICyTDF) project PICSO12-119, and CONACyT México because of financial support.

[1] S. Carmona-Téllez et.al., White light emitting transparent double layer stack of Al2O3 :Eu3+, Tb3+, and Ce3+ films deposited by spray pyrolysis, ECS Journal of Solid State Science and Technology, 2 (6) (2013)

[2] A. E. Esperanza-García et. al. Luminescent and Morphological characteristics of Al2O3:Tb films deposited by spray pyrolysis using acetylacetonates as precursors. Journal of the electrochemical society, 150 (2) H53-h56 (2003)
Development of a Silver/Silver Ibuprofenate Potentiometric Sensor for Ibuprofen Quantification in Pharmaceutical Products
Authors: Rivera-Hernández Selene Irisais , Álvarez-Romero Giaan Arturo , Galán-Vidal Carlos Andrés , Páez-Hernández María Elena , Corona-Avendaño Silvia
Published: February 2020

Nonsteroideal antiinflamatory drugs (NSAIDs) are the most used drugs due to their analgesic, antipyretic and antiinflamatory properties, along with the fact that these are sold without the requirement of a medical prescription. Within this group of pharmaceutical compounds, ibuprofen (acid-α-methyl-4(isobutyl)-phenylacetic) is found. The use of Ibuprofen has increased because it is useful for treating headaches and arthritis. It is considered a safe drug since the human body can degrade it to its main metabolites and then excrete them through urine.

Nevertheless, to assure consumer’s health, it is necessary the development of analytical methodologies to allow an accurate and exact quantification of ibuprofen. Potentiometry has demonstrated to be an advantageous technique, where stands out the use of second type electrodes, which in accordance with the Nernst equation can detected anions activities.

Considering this last, in this work we present the development and analytical characterization of a second-type electrode based on the Silver/Silver Ibuprofenate (Ag/AgIbu) pair.

A pure silver wire was modified using a 0.05 M sodium ibuprofenate solution and 0.1 M of sodium nitrate as supporting electrolyte. Chronoamperometry was used to achieve the modification of the electrode (Ag/AgIbu), the technique parameters were optimized and the registered optimums where: 0.8 V (vs Ag/AgCl) potential for 30 s. Calibration curves were performed to obtain the best analytical parameters: it was registered a sensitivity of -41.69 ± 1.61 mV/log (ibuprofenate molar activity), a linear range of 1.22x10-4 - 8.98 x 10-3 M, and a detection limit of 8.11x10-5 M. Repeatability interpreted as the relative error percentage, was 2.46%. The pH effect on the system response was studied, it was found that the best working pH is 7.0. The electrode’s time response was 3.3 min with a drift of -0.01 mV s-1. With the Matched Potential Method it was possible to determine that chloride and carbonate are the most important interferents.

Ibuprofen was measured in commercial drugs with no significant differences found between the manufacture’s reported value and the one obtained with the proposed sensor.
The Study of Electrodeposition of Si in Tmhatfsi-SiCl4 analyzed by EQCM Method
Authors: Tsuyuki Yasuhiro , Pham Anh Huynh Tram , Komadina Jason , Fukunaka Yasuhiro , Homma Takayuki
Published: February 2020

An inexpensive fabrication method of Si is required for achieving Ultra-Large-Scale Si solar power generation. Electrodeposition method has attracted recently because it has numbers of advantages such as simplicity of process and precision control of reaction etc. compared with conventional methods such as CVD, sputtering and e-beam evaporation.

Si electrodeposition has been conducted using nonaqueous solvents (molten solt1), organic solvent2) and ionic liquid3)) because the reduction potential of SiO2 is very negative. However, the organic solvents have a drawback due to safety concerns, with high flammability. On the other hand, ionic liquids (sometimes referred as room temperature molten salts) exhibit low volatility and in many cases are nonflammable. The primary benefit of both systems is the large electrochemical window, allowing for study of elements such as Si and Li. We have reported the electrodeposition of Si from an ionic liquid.4)

However, high purity Si electrodeposition has not been demonstrated yet. Si electrodeposition layers include some impurities stemmed from ionic liquids.5) It is caused by the uncertainty on Si electrochemical reaction mechanism.

Electrochemical quartz microbalance (EQCM) impedance method could provide us to obtain in-situ information about the mass change during electrodeposition. Such information might further support our deduction on electrochemical reaction mechanism.

Here we present the results of our recent work on the analysis of Si electrodeposition using EQCM method. Si is electrodeposited at 40 °C in an ionic liquid, specifically tri-methylhexyl ammonium bis-(trifluorosulfonyl) imide (TMHATFSI). In particular, we focus on the mass change during cyclicvoltammogram and chronoamperometry. Figure1 demonstrates that Si deposition starts around -2.2 V because a significant mass increase is observed with the increase of the current density. It corresponds to our previous study.5) Therefore we could propose Si electrochemical reaction mechanism more clearly than before from this EQCM result.

This study was financially supported in part by CREST program by Japan Science and Technology Agency (JST).

1). Y. Nishimura, Y. Fukunaka, T. Nishida, T. Nohira, and R. Hagiwara. Electrochem. Solid State Lett. 11 (9) D75-79 (2008)

2). Y. Nishimura and Y. Fukunaka. Electrochim. Acta. 53, 111-116 (2007)

3). F. Endres, A.P. Abbott, and D.R. MacFarlane. Electrodeposition from Ionic Liquids. Wiley-VCH. 2008.

4). T. Homma, J. Komadina, Y. Nakano, T. Ouchi, T. Akiyoshi, Y. Ishibashi, Y. Nishimura, T. Nishida, Y. Fukunaka, Electrochem. Soc. Trans., submitted.

5). J. Komadina, T. Akiyoshi, Y. Ishibashi, Y. Fukunaka, T.Homma. Electrochim.Acta, 100, 236-241 (2013)