bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development of Materials Integration for Laser Gain Media: Single Crystals and Ceramic (Polycrystalline) Materials and Applications
Authors: McKay Jeffrey , Bai Tingyu , Goorsky M. S. 
Published: February 2020

A study of the fundamental issues of materials integration for wafer bonding offers new pathways for achieving photonic materials with unique properties.
First, the bonding of single crystal oxide crystals (YAG and yttria, for example) with different compositions and even different orientations is shown to critically depend upon several important parameters. A detectable level of subsurface damage usually accompanies the polishing of these crystals. We studied chemical mechanical polishing (CMP) of these oxide crystals to provide surfaces which exhibit sub-nm roughness, and the absence of subsurface damage. These surfaces are then activated and we use XPS and other surface sensitive techniques to assess the state of the surface after different processes. Next, we demonstrate that we can significantly reduce the bonding time and temperature to attach two single crystal pieces based on these improved polishing techniques. These techniques also apply to polycrystalline (ceramic) materials as well.
Second, we demonstrate wafer bonding for polycrystalline laser gain media. Two issues are important here. First, the grain composition – and hence chemistry – may be different than the bulk composition / chemistry. Under ideal conditions, the grain boundaries may simply be regions of misorientation and be nearly atomically abrupt. The second issue is that the different grain orientations present on a surface may (i) exhibit different hardnesses and / or (ii) different chem-mech polishing rates. Therefore, the issues of chemistry are more important than is the case with single crystal materials. We determined that the best combination of solution chemistry and polishing parameters involves the use of the SUBA 500 (yellow) pad and the same applied force as for the single crystal YAG. For many combinations of force, chemistry, and pad material, a clear delineation of the grain boundaries was revealed. However, we were able to achieve a set of polishing conditions for which the boundaries are not preferentially etched. These surfaces also proved to be damage-free and were able to show a high fraction of bonded interface (>90%) on 50 mm diameter gain media disks.
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.
(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.
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.
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
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.
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.