bluuebunny/crossref_metadata_2025_split huggingface dataset:
New Material Technologies in AlGaN/GaN Based Electronic Devices
Authors: Leszczynski Mike 
Published: February 2020

We will show a number of new material technologies which can be applied for the AlGaN/GaN electronic devices. These technologies are as follows:
i) Application of GaN bulk crystals with dislocation density as low as 104 cm-2as substrates to construct HEMTs and power devices. Schottky diodes with an ultra low leakage and high breakdown voltage (above 700 V) will be demonstrated. Fig. 1
shows the I-V characteristics for such diode.
ii) Lateral patterning of SiC substrates to modify locally the offcut. This approach has an advantage of paving the way to monolithically integrated GaN-based and SiC-based devices, as they deserve a different substrate off-cut (0.3 and 4 degrees, respectively).
iii) Lateral patterning of SiC and GaN substrates to get atomically smooth areas, as well as much higher concentration of Al in AlGaN layers avoiding cracking and other defect generation.
For all materials, we will show results of XRD, TEM and AFM studies, as well as electrical characteristics.
Nanomaterial-Based Macroscale Printable Flexible Sensors
Authors: Takei Kuniharu , Harada Shingo , Honda Wataru , Arie Takayuki , Akita Seiji 
Published: February 2020

Printable electronics are of great interests for flexible and wearable devices as next generation electronics. In fact, printable electrodes and transistors have been widely studied by using organic and inorganic materials on plastic substrates1-3. To realize the practical, flexible device systems, many components such as transistors, sensors, and displays need to be integrated by using printing methods or compatible macroscale and low-cost fabrication methods.
In this study, we propose printable sensor sheets using nanomaterial-based inorganic and organic solutions4,5. Especially here printable strain and temperature sensors for different kinds of applications are demonstrated on flexible substrates such as silicone rubber, PET, etc. by using a screen printer and a laser patterning technique. As a proof-of-concept, macroscale, low-cost sensor sheet in order to monitor the strain and cracking information from infrastructures and vehicles were fabricated on a silicone rubber using the screen printing method. The results exhibited that high sensitivity (~59%/Pa) strain sensor detected <10 µm displacement on a wall. This suggests that high sensitive low-cost sensor sheet can be used for the infrastructure monitoring system as an example.
Furthermore, we will also talk about our recent results of a self-cleaning passivation layer for the flexible devices and more sensor applications such as an artificial electronic whiskers4 and smart bandage5.
Our proposed printable flexible sensors may be applied to a variety of applications such as human interfaces, infrastructures, and vehicles.
References:

Z. Fan et al., Advanced Materials, 21, 3730, 2009.

K. Takei et al., Nature Materials, 9, 821, 2010.

P. H. Lau et al., Nano Letters, 13, 3864, 2013.

S. Harada et al., ACS Nano, 2014 (DOI:10.1021/nn500845a).

W. Honda et al., Advanced Functional Materials, 2014 (DOI:10.1002/adfm.201303874)
Voltage Control of Magnetization and Its Chemical Properties
Authors: Suzuki Yoshishige , Bonell Frederic , Shiota Youichi , Miwa Shinji , Nozaki Takayuki , Shinjo Teruya 
Published: February 2020

Magnetization control using an electric field [1] will be useful because of its expected ultra-low power consumption and coherent behavior. Several experimental approaches to realize it have been done using ferromagnetic semiconductors [2], materials with magnetostriction together with piezo-driver [3], multiferroic materials [4], ferromagnetic metal films sintered in a liquid electrolyte [5], and ultra-thin ferromagnetic layer in solid-state junctions[6-8].
One of the critical issues in the electric field switching is a realization of bi-stable switching. Since the electric field does not break time reversal symmetry, it does not remove degeneracy of two magnetic states with opposite magnetization. Therefore, a selection of an arbitral magnetic state is not straightforward [9]. Here, we demonstrate a realization of the bi-stable switching using a coherent precessional magnetization toggle switching in nanoscale magnetic cells with a few atomic FeCo (001) epitaxial layers adjacent to MgO barrier [10].
The control of the magnetization by voltage requires well controlled interface structure. We have investigated chemical states of the ferromagnetic atoms at interface with MgO using XAS and XMCD, and found several problems that may happen at the interfaces in voltage devices, i.e. segregation [11] and voltage controlled reversible oxidization/reduction [12]. We discuss the significance of those effects and the intrinsic effect.
References:
[1] Curie, P., J. Phys. 3, 393 (1894).
[2] Ohno, H. et al., Nature 408, 944-946 (2000), Chiba, D., et al, Science 301, 943-945 (2003).
[3] Novosad, V. et al., Journal of Applied Physics 87, 6400-6402 (2000), Lee, J.-W., et al., Applied Physics Letters 82, 2458-2460 (2003).
[4] Eerenstein, W., et al., Nature 442, 759-765 (2006), Chu, Y.-H. et al., Nature Materal 7, 478-482 (2008).
[5] Weisheit, M. et al., Science 315, 349-351 (2007).
[6] Maruyama, T. et al., Nature Nanotechnology 4, 158-161 (2009).
[7] M. Endo, et al., Appl. Phys. Lett. 96, 212503 (2010).
[8] D. Chiba, et al., Nat. Mat. 10, 853 (2011) .
[9] Shiota, Y. et al. Applied Physics Express 2, 063001 (2009).
[10] Shiota, Y. et al., Nature Materials, 11, 39-43 (2012).
[11] Bonell, F. et al., Surface Science 616, 125-130 (2013).
[12] Bonell, F. et al., Appl. Phys. Lett. 102, 152401 (2013).
Non-Equilibrium Transport Theory Applied to Nano Electronics Problems
Authors: Asai Yoshihiro , Nakamura Hisao 
Published: February 2020

Atomistic non-equilibrium transport theory has been developed a lot in a bit different community than the nano-electronics, i.e., the atomic and molecular junctions community.[1] The NEGF (non-equilibrium Green function) method has been combined with first principle electronic structure methods, which has become a standard tool in nano-electronics, too, nowadays. After making a brief overview of the latest progresses obtained in non-equilibrium transport theory including the heat problem and the noise problem, we will discuss some results obtained in our nano-electronics research. The subject of our discussions includes channel and electrode materials dependence of transport properties of some resistive RAM junctions. [2]
Ref.)
[1] Yoshihiro Asai, “Nonequilibrium phonon effects on transport properties through atomic and molecular bridge junctions”, Phys. Rev. B 78, 045434 (2008).
[2] Takehide Miyazaki, Hisao Nakamura, Kengo Nishio, Hisashi Shima, Hiroyuki Akinaga, and Yoshihiro Asai, ”First-Principles Transport Modeling for Metal/Insulator/Metal Structures”, JPS Conf. Proc. , 012075 (2014).
ACKNOWLEDGMENTS
The authors would like to thank to Drs. Takehide MIYAZAKI, Kengo NISHIO, Hisashi SHIMA, and Hiroyuki AKINAGA for their collaborations and discussions.
Dependence of Dark Processes on Film Thickness in Dye Sensitized Solar Cells
Authors: Garcia Rodrigo , Villanueva Julio , Escalante Renán , Heredia Beatriz , Oskam Gerko 
Published: February 2020

The development of new sources of energy that can be economically viable and environmentally friendly is, nowadays, one of the most important goals in scientific research. Dye Sensitized Solar Cells (DSSC) are photoelectrochemical systems that represent an interesting option in the development of new technology in the solar cells field. The analysis of this photolectrochemical system is necessary in order to understand the phenomena that take place into the solar cells, which is the basis to propose improvements for achieving high efficiency solar cells.
There exist several different parameters that directly influence the performance of the solar cells. However, in devising strategies to improve the performance of DSSCs, the effects of dark processes are often overlooked. One of these parameters is the exchange current density in the dark, Jo. The value of Jo is related to the rate constant of the recombination reaction, the film thickness, the order of reactions of electrons and oxidized redox species, and the concentrations of background electrons in the TiO2 and oxidized redox species in the electrolyte. It has been proposed from a theoretically analysis that this exchange current density is more relevant as the thickness of the semiconductor film is increased [1], following the relationship showed in Figure 1.
In this work we study the influence of thickness in different parameters of the cell, such as the short circuit density photocurrent, Jsc, open circuit photovoltage, Voc, the ideality factor, m, and the exchange current density in the dark, Jo. Electrochemical impedance spectroscopy (EIS) measurements were made in order to study the kinetic parameters of the cell. The results show that the exchange current density in the dark, Jo, is proportional to the semiconductor film thickness (Figure 1), as proposed theoretically [1], limiting the performance of the solar cells as the thickness of the semiconductor film is increased, resulting in an optimum thickness around 10 µm. In addition, the diffusion length measurements and collection efficiency values are in good agreement with an optimum film thickness around 10 µm [2].
References.
[1]. K. Zhu, S. Rim, A. J. Frank. Impact of High Charge-Collection Efficiencies and Dark Energy-Loss Processes on Transport, Recombination and Photovoltaic Properties of Dye-Sensitized Solar Cells. J. Phys. Chem. Lett. 2, 1070-1076 (2011).
[2] Renan Escalante-Quijano, Rodrigo Garcia-Rodriguez, Beatriz E. Heredia-Cervera, Nikte Gomez-Ortiz, Julio Villanueva-Cab and Gerko Oskam. Influence of TiO2 Film Thickness on the Performance of Dye Dye-Sensitized Solar Cells: Relation Between Optimum Film Thickness and Electron Diffusion Length. Energy Environ. Focus, 2, 280-286 (2014).
Application of ZnO with Different Morphologies to DSSCs
Authors: Lizama-Tzec Francisco Ivan , Rodriguez-Gattorno Geonel , Pal U. , Oskam Gerko 
Published: February 2020

ZnO is an attractive material for the fabrication of dye-sensitized solar cells (DSSCs) related to its good electron transport properties. It can be synthesized with different morphologies relatively easily by methods such as electrodeposition, sol-gel, either using forced hydrolysis or a microwave-assisted method [1].
There is a growing interest in linking the crystallographic planes of the material to performance of the solar cell. In this work, ZnO with different morphologies was obtained by the microwave-assisted technique at pH values of 5.5. 8, 10 and 12, and the materials were applied in the fabrication of DSSCs using the screen printing technique after preparing a paste. The surface area of the powders was characterized by BET, and the deposited ZnO layers were characterized by XRD, TEM and SEM. The cells were characterized by I-V curves and the amount of adsorbed dye was determined by UV-Vis spectrophotometry. It was found that the best cells were obtained with the morphology that resulted in the synthesis at pH 10, where the (100) plane is predominant.
References:
1. N. Morales-Flores, R. Galeazzi, E. Rosendo, T. Díaz, S. Velumani and U. Pal.
Morphology control and optical properties of ZnO nanostructures grown by ultrasonic synthesis.

Advances in Nano Research, Vol. 1, No. 1 (2013) 59-70.

Figure 1: SEM images of the different morphologies of the ZnO nanomaterials
Evaluation of ALD-Grown Metal Oxide Tunnel Junction Layer for Organic Tandem Cells
Authors: Kim Minjae , Chambers Conner , Berger Paul R. 
Published: February 2020

Since their inception, organic solar cells have been a cynosure of photovoltaic (PV) community, owing to their simplicity, affordability and mass-production capabilities. Research on organic solar cells has been propelled by advances in nanotechnology, polymer synthesis, and semiconductor processing; efforts to achieve high power conversion efficiencies (PCE) through refined device geometry, tailored synthesis and/or combination of new low-bandgap materials, and heuristic process optimization have fructified as ~10 % efficiency in single-junction organic solar cells. Recent PCE enhancement in organic solar cells has mostly attributed to the development of small bandgap materials that extend absorption of the sun into the red and infrared wavelengths.
Utilizing tandem cells comprised of both large and small bandgap sub-cells enables light harvesting of different parts of the solar spectrum to be separately optimized, yielding higher PCE than single junction solar cells. But the challenges in achieving highly efficient organic tandem solar cells include optimal combination of materials for each sub-cell and interconnecting layers between sub-cells that are process compatible. Optimal combination of materials can be achieved by selection of two materials having complementary absorption windows. The interconnecting layer provides electrical and optical coupling between the two sub-cells and plays a key role in the performance of tandem cells. For the design of the interconnecting layer, electrical, optical, chemical and structural characteristics should be considered. Ideally, it should effectively facilitate charge transport between two sub-cells. Moreover, high transmittance and negligible absorption in the spectral region where two sub-cells absorb is desirable. Last but not least, the interconnecting layer should be designed to survive the subsequent solution coating and provide conformal surface coating for tandem cells with solution processed top cells.
Here we evaluate some of candidate metal oxides for tunnel junction layers for organic tandem solar cells. Metal oxides are grown by Atomic Layer Deposition (ALD) for thin defect-free conformal layer to circumvent miscibility issues and negligible absorption. Normal and inverted interfaces are examined. The influence of annealing under different conditions and methods will be presented. Tunneling properties are qualified by J-V characteristics and optical properties evaluated by UV-Vis are contrasted to suggest optimal design tradeoffs of tunnel junctions for solution processed organic tandem solar cells.
Ambient-Pressure XPS Study of GeO2/Ge(100) and SiO2/Si(100) at Controlled Relative Humidity
Authors: Arima Kenta , Kawai Yoshie , Minoura Yuya , Saito Yusuke , Mori Daichi , Oka Hiroshi , Kawai Kentaro , Hosoi Takuji , Liu Zhi , Watanabe Heiji , Morita Mizuho 
Published: February 2020

Germanium (Ge) is a promising channel material for electronic devices in the next generation because it has higher mobilities for both holes and electrons than those of Si. Germanium oxide (GeO2) is one of the key materials in Ge-based transistors. However, GeO2 is permeable and soluble in water. This implies that GeO2 films will react with water vapor in air. In this study, water growth on ultrathin GeO2 films on a Ge(100) substrate and their effect on the electronic properties of GeO2 films are investigated using in-situ X-ray photoelectron spectroscopy. In addition, the wetting property of GeO2/Ge is compared with that of more familiar SiO2/Si.
In-situ XPS[1] measurements were performed at beamline 9.3.2 of the Advanced Light Source (ALS), of the Lawrence Berkeley National Laboratory.[2]A differentially pumped electrostatic lens system separates the analysis chamber from a hemispherical photoelectron spectrometer. Water vapor was introduced up to a pressure of 1.0 Torr while the sample temperature was controlled from room temperature to around -5°C by a chiller. This enabled us to control relative humidity from 0 % to around 15 %.
A simple estimation from O1s and Ge3d (or Si2p) indicates that thicker water layers are formed on GeO2 than on SiO2 at RH higher than 10-4%. Namely, the water thickness reaches one monolayer on SiO2 at 10% whereas it is two or three monolayers in the case of GeO2. We also find that the energy separation between Ge4+ and Ge0+ signals in Ge3d spectra increases more drastically at RH higher than 10-4% than that between Si4+ and Si0+ signals in Si2p spectra. This means that GeO2 films are charged more positively than SiO2 above the critical RH. We present two possibilities for the positive charging of the ultrathin GeO2 films in the presence of water vapor. One simple explanation is positive charging of the oxide with adsorbed water molecules by X-ray irradiation. The other explanation is that water-related species emit electrons to the Ge bulk and positive charges are created in GeO2, which may be the cause of the reported negative shift of the flatband voltage in Ge-based MOS capacitors with air-exposed GeO2.[3]

[1] M. Salmeron and R. Schlögl, Surf. Sci. Rep. 63, 169-199 (2008).
[2] M.E. Grass, P.G. Karlsson, F. Aksoy, M. Lundqvist, B. Wannberg, B.S. Mun, Z. Hussain and Z. Liu, Rev. Sci. Instrum. 81, 053106 (2010).
[3] A. Mura, I. Hideshima, Z. Liu, T. Hosoi, H. Watanabe and K. Arima, J. Phys. Chem. C 117, 165-171 (2013).
Graphene and 2-Dimensional Materials for Nanoelectronics Applications
Authors: Lemme Max Christian 
Published: February 2020

Graphene science and technology has evolved substantially over the past 10 years. It is now entering a phase, where researchers and industry start to collaborate more closely on applications and to address issues of scalability and manufacturability. In addition to the semimetal graphene, recent years have seen the emergence of a number of related two-dimensional materials. These include insulators such as hexagonal boron nitride, semiconducting transition metal dichalcogenides (TMDs) like molybdenum disulfide (MoS2) or tungsten diselenide (WSe2) or silicene and germanene, similar in structure but less stable than graphene.
The talk will focus on graphene-based hot electron transistors (Graphene Base Transistors, GBTs) for analog radio frequency applications [1], [2]. The operating principle of GBTs is based on vertical current flow by quantum mechanical tunneling through an insulating barrier (Figure 1). The current (red arrow) can be controlled over several orders of magnitude by a base electrode made of graphene (Figure 2). The advantage of graphene over a metal base electrode is its ultimate thinness while maintaining good conductivity. If the barrier materials are optimized, GBTs have the potential to reach cut off frequencies (fT) on the order of 1 THz [3].
In the second part of the talk, options for optoelectronic devices based on 2D materials will be discussed. These include photodetectors / phototransistors made from graphene [4], where the photoresponse can be tuned by the voltage applied to a gate. In addition, photodiodes based on MoS2/silicon heterojunctions will be discussed.
[1] W. Mehr, J. C. Scheytt, J. Dabrowski, G. Lippert, Y.-H. Xie, M. C. Lemme, M. Ostling, and G. Lupina, “Vertical Transistor with a Graphene Base,” IEEE Electron Device Lett., vol. 33, pp. 691–693, 2012.
[2] S. Vaziri, G. Lupina, C. Henkel, A. D. Smith, M. Östling, J. Dabrowski, G. Lippert, W. Mehr, and M. C. Lemme, “A Graphene-based Hot Electron Transistor,” Nano Lett., vol. 13, p. 1435−1439, 2013.
[3] F. Driussi, P. Palestri, and L. Selmi, “Modeling, simulation and design of the vertical Graphene Base Transistor,” Microelectron. Eng., vol. 109, pp. 338–341, Sep. 2013.
[4] M. C. Lemme, F. H. L. Koppens, A. L. Falk, M. S. Rudner, H. Park, L. S. Levitov, and C. M. Marcus, “Gate-Activated Photoresponse in a Graphene pn Junction,” Nano Lett., vol. 11, pp. 4134–4137, 2011.
Fabrication and Characteristic of Wrinkled Stiff Thin Films on Elastomeric Substrates by Surface Treatments
Authors: Lim Sang Chul , Koo Jae Bon , Park Chan Woo , Oh Ji Young , Jung Soon-Won , Na Bock Soon , Lee Sang Seok , Chu Hye Yong 
Published: February 2020

The wrinkle process comprises stretching of a soft elastic polydimethylsiloxane PDMS substrate1,2 and subsequent oxygen plasma treatment, resulting in a hard SiO2-like (SiOx-) layer on the surface.3

The PDMS system of choice for the presented process is Sylgard 184(DOW corning) which is usually applied in a 10:1 ratio (w/w) of siloxane and curing agent and requires a thermal curing step. These were treated on one side with oxygen plasma for 5, 10, 15 min to create a nanoscale silica skin, thus presenting identical surface chemistry in all experiments. This paper presents a cost-effective and simple method to form wrinkled stiff SiOx thin films on polydimethylsiloxane (PDMS) substrates at room temperature by oxygen plasma on pre-strained PDMS. The orientation of the generated structures was always perpendicular to the pre-stretched direction and the pitch of the structure could be adjusted ranging from 1.1 μm to 3 μm by controlling the strength of the pre-stretched strain and the thickness of the surface metal film. Upon relaxation, highly controlled and regular wrinkling of the silica skin resulted. Bi-layer substrates under uniaxial compression exhibit micron-scale features that can impart mechanical flexibility in functional electronic devices including interconnects, transistors and solar cells.
Systemic studies have been conducted to understand the dependence of the wavy profile on the PDMS pre-strain, UV/O exposure time, and PDMS modulus. The mechanics analysis has been verified to be quantitatively or qualitatively accurate by experimental comparisons. The wrinkled SiOx/PDMS system is stretchable and provides a wavy mold for stretchable electrodes. The constant electrical resistance during mechanical stretching shows the stretchability of this system. In this study, the metal thin film/contoured substrate is stretchable and has been demonstrated as stretchable electrical conductors.
References
1. J. Genzer and K. Efimenko, Science, 2000, 290, 2130.
2. K. Efimenko and J. Genzer, Adv. Mater., 2001, 13, 1560.
3. M. Ouyang, C. Yuan, R. J. Muisener, A. Boulares and J. T. Koberstein, Chem. Mater., 2000, 12, 1591.
SURMOFs as Ultra-low k Dielectric Thin Films
Authors: Redel Engelbert 
Published: February 2020

Here we present a particularly interesting class of surface-anchored (metal-organic frameworks) materials SURMOFs for the fabrication low-k dielectric thin films.
Since these materials are highly porous and the size of their pores are highly adjustable, they can be further functionalized (e.g. with different metal/oxo connectors or clusters linked with various organic linkers) e.g. in order to specifically bind target analytes (optical sensing), to electrically load and unload small ions (optoelectronic applications) inside the metal-organic pores.
In addition, the RI (Refractive Index) as well as the optical properties of SURMOF-materials can be tailored, e.g. through their organic linkers – a fact which makes these materials ideally suited for photonic, optical and low-k dielectric applications.