bluuebunny/crossref_metadata_2025 huggingface dataset:
Maskless Macrosale Generation of Periodic 3D Semiconductor Nanostructures in Response to Defined Illumination Inputs
Authors: Carim Azhar I , Batara Nicolas A. , Premkumar Anjali , Atwater Harry A , Lewis Nathan S
Published: February 2020

Template-free photoelectrodeposition of semiconducting chalcogen alloys resulted in the spontaneous generation of highly periodic nanostructured films over macroscopic length scales. The exact nature of the optical excitation was encoded in the deposit morphology in terms of the feature sizes, periodicities, anisotropies, and orientations of the nanoscale pattern. The use of unpolarized light generated isotropic morphologies consisting of ordered arrays of nanopores whereas linearly polarized light resulted in a highly-anisotropic lamellar morphologies with the long axes of the patterns aligned along the E-field vector. Utilization of two same-wavelength, non-orthogonally polarized sources simultaneously generated patterns oriented along the average E-field vector and with degrees of anisotropy related to the difference in orientation between the two input E-field vectors and the phase correlation between the sources. The illumination spectral profile encoded the pattern periodicity and feature width. A single periodicity in a single in-plane direction was consistently observed even with the use of broadband and multimodal spectral profiles and this periodicity was found to be sensitive to all investigated tuning of such profiles. The incidence of the illumination set the direction the material grew from the substrate, mimicking natural phototropism: grazing illumination resulted in growth at significant angle to the surface normal. Modeling of the growth using a combination of full-wave electromagnetic simulations of light absorption and scattering coupled with Monte Carlo simulations of mass addition accurately reproduced the experimentally observed morphologies and indicated that the encoding process was a consequence of the fundamental light-matter interactions during growth.

This photoelectrochemical deposition process is unique from other methods of generating ordered mesostructures with electrochemical means as no photomask, no photoactive substrate, no lithographic processing, nor any chemical templating agents (ligands, surfactants) were utilized. Illumination was simply conformal over the entire substrate surface (no far-field spatial modulation was used nor required). Complete nanoscale patterning over cm2 areas required only several minutes. Moreover, films were deposited from aqueous solution using oxide precursors at room temperature with low-intensity illumination (~10 mW cm-2). Thus, this process displays significant potential to possibly enable the generation of complex morphologies for functional materials without several limitations imposed by traditional fabrication techniques.
DFT Study of Surface and Interface Issues in High-Voltage Cathodes for Li-Ion Batteries
Authors: Soto Fernando Antonio , Sharifi-Asl Soroosh , Shahbazian-Yassar Reza , Balbuena Perla B
Published: February 2020

The development of stable materials for cathodes in lithium-ion batteries (LiBs) is a major bottleneck for the commercialization of high-energy density rechargeable batteries. Lithium cobalt oxide (LiCoO2) is one of the most heavily used cathodes for LiBs. LiCoO2 exhibits fair electrical conductivity and Li+ mobility with an operational voltage of 4 eV. Moreover, the theoretical capacity of LiCoO2 is 274 mAh/g corresponding to a full Li+ extraction, producing CoO2. However, its practical capacity is only 130–150 mAh/g, indicating that only half of the Li atoms can be used during the “rocking-chair” de/intercalation process. Moreover, because of safety concerns (e.g. thermal stability and interaction with organic electrolytes with high volatility and flammability) its usage in high power and high energy density batteries is abandoned. Indeed, at high temperatures or high cut-off voltages, LiCoO2 decomposes and desorbs oxygen. The evolved oxygen reacts exothermically with the flammable electrolyte. This oxygen evolution jeopardizes the safety of the cell due to the magnitude of this highly exothermic reaction.

In our previous work, we found that the (104) and (012) surfaces are more prone to O2 release. Ab-initio molecular dynamics (AIMD) results show that the under-coordinated oxygen atoms from the delithiated structures can combine and eventually evolve as O2. Thus, the intrinsic surface properties of cathodes and the interfacial interactions between cathode and electrolyte need to be considered to enhance the cathode stability. The surface engineering and design of the electrode material have been proposed as a promising path to achieving safe and high-voltage cathodes for LiBs. In this work, firstly we report the stability, interfacial chemistry, oxidation-reduction behavior and surface thermodynamics of the major surfaces of LiCoO2 based on the calculations obtained with the density functional theory (DFT) approach. Further, we present the results achieved from DFT-based calculations and experimental techniques (e.g. electrochemical cycling, in-situ heating transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Raman characterizations) on the surface coating approach to enhance the structural stability of LiCoO2 by providing a physical barrier for oxygen evolution. Our experimental work shows that the coated sample could exhibit more than 75% capacity retention after 40 cycles while the pristine sample failed after 20 cycles with the same condition. Our computations suggest that the interaction between the physical barrier and the electrode’s surface leads to an interfacial chemical bonding that prevents O2 evolution. Overall, we expect that this combined approach will allow improving the overall performance of the battery by addressing the multifaceted problems that play a role in the safety problems of cathodes.
Flow Cells with Integrated Electrodes Prepared By Digital Light Processing Projector-Based 3D Printing for Electrochemical Sensing Applications
Authors: Bishop Gregory William , Alabdulwaheed Abdulhameed Hussain , Muili Ahmad Ajibola
Published: February 2020

3D printing is a fast and simple method for creating and refining objects from representations based on computer-aided design files. Recent improvements in accessibility, affordability, and capabilities of 3D printing technologies have resulted in several successful applications of such techniques in electrochemistry and sensing research. One particular example that has garnered a great deal of interest is 3D-printed flow cells. These devices can enable more efficient design and implementation of flow-through laboratory devices with channel dimensions of tens to hundreds of micrometers or more by eliminating barriers, such as geometrical restrictions, equipment needs, and technical expertise that are associated with other methods used for producing fluidic devices. Electrochemical and electrochemiluminescence sensing capabilities can be introduced into these flow-cells by incorporating design elements that enable the integration of electrodes and optical components. Here, we demonstrate the production and application of flow-through electrochemical sensors based on 3D-printed flow cells prepared using a digital light processing projector-based 3D printer.
Patchable Ion Channel Pressure Sensors Inspired By Somatic Organs
Authors: Chun Kyoung-Yong , Son Young Jun , Han Chang-Soo
Published: February 2020

Among vital elements in our body, ion channel are essential units which sustain life in all living cells as continuously transporting appropriate ions through plasma cell membranes. In addition, the somatic functions of ion channels are fundamentally indispensable for sensory organ homeostasis. For decades, biological ion channels have led to much inspiration because of their unique and exquisite operational functions in living cells. Specifically, their extreme and dynamic sensing abilities can be realized by the combination of receptors and pores coupled together to build ion channel systems.

In this presentation, we demonstrate that artificial ion channel pressure sensors inspired by nature for detecting pressure are highly sensitive and wearable. Our ion channel pressure sensors basically consisted of receptors and nanopore membranes, enabling dynamic current responses to external forces for multiple applications. The ion channel pressure sensors had a sensitivity of ∼5.6 kPa−1 and a response time of ∼12 ms at a frequency of 1 Hz. The power consumption was recorded as less than a few μW. Moreover, linear regression was performed in terms of temperature, which showed no significant variations, and there were no significant current variations with humidity. The patchable ion channel pressure sensors were then used to detect blood pressure in humans, and different signals were clearly observed for each person. Additionally, modified ion channel pressure sensors detected complex motions including pressing and folding in a high-pressure range.

In comparison to previous pressure sensors, our ion channel pressure sensors engaged sensory organs could provide feasible control of the bandwidth via selecting different electrolytes and unique signal shape according to the type of pressure receptor chosen, and the dynamic output signal may offer discrete information for an object. We expect that if the diverse functions of ion channels in nature could be further modified or mimicked for various applications, then artificial sensory systems such as the one described in this study would be tremendously greeted in a new era of sensors.
A Wearable Gas Sensor of GO and TiO2 Composite with High Selectivity
Authors: Lee Eunji , Chung Yoonsung , Lee Doohee , Yoon Jaesik , Lincoln Christopher , Prorok Bart Charles , Woo Sungpil , Yoon Youngsoo , Kim Dong-Joo
Published: February 2020

With aging population and prevalence of chronic diseases, daily healthcare system became an important interest for many people. There has been much research to combine medical knowledge and engineering technology for easy access of self-health management, and wearable respiratory monitoring system which is the result of sensing and wearable technological integration is considered as a cornerstone in daily healthcare system. Since early detection essentially equals to more chances of treatment that ultimately result in improvement of patient outcomes, the device for continuous respiratory monitoring could be life-saving system. Wearable gas sensor is anticipated as a promising daily healthcare device to play an important role of physiological monitoring by checking human’s breath. For wearable gas sensors, sensor should be weaved into clothing or accessories in which functional materials that distinguish amounts of gases also should be coated.

Many recent studies have discussed to improve the gas response of resistive metal oxide gas sensor (MOGS). However, selectivity is one important parameter for the implementation of MOGS. Little efforts to investigate selective gas sensing were made in graphene based sensor. In MOGS, incorporating two materials such as zinc oxide and tin dioxide is known as a heterostructure. As two Fermi levels equilibrate to the same energy, charge carrier was transferred from one another, resulting in increasing sensor performance. As a similar approach, graphene oxide nanocomposite would enhance selectivity.

In this study, graphene oxide (GO) was constructed into the fabrics by simple solution method after sputtering interdigitated electrode, and ammonia gas sensing was conducted at room temperature. After that, we newly explored to use heterostructure of GO and TiO2 composite in order to improve selectivity which is the ability to discriminates the response of target gas from other interferents. The use of photon source enabled ethanol and methanol gas sensing at room temperature as the electrons stored in TiO2 reduced GO, which the color of solution was clearly changed. The morphologies of GO+TiO2 nanocomposite film on fabrics were analyzed with SEM and XRD, and comprehensive mechanism on GO’s ammonia, ethanol and methanol gas sensing will be drowned in detail.

This research was partially supported by the KIET Evaluation and Planning (20158520000210) grant funded by the Korea Government Ministry of Trade, Industry and Energy, and Agency for Defense Development (ADD) as global cooperative research for high performance and light weight bio-urine based fuel cell (UD160050BD).
An LED-Based Portable Multi-Excitation Fluorometer
Authors: Shin Young-Ho , Choi Jin-Woo
Published: February 2020

Fluorophore microbeads are widely used in biomolecule detection/quantification, flow tracing reference for gases and liquids, pathogen detection, and other life science applications [1, 2]. Often multiple fluorophores need to be simultaneously detected using spectral multiplexing detection system which is typically operated at a single excitation wavelength with multiple fluorescent emission filters or vice versa [3]. However, it significantly limits the use of different fluorophores since they have different absorption and emission peak wavelengths. Here, we propose a portable multi-excitation fluorometer combined with 12 different bandpass emission filters that can a viable option for detecting multiple fluorophores. Six fluorophore microbeads were selected as target subject for this study: Nile blue, FITC, Cy3, Cy5, Quinine, and Rhodamine B.

The sensing system has six excitation light sources for stimulating different fluorophore microbeads in a solution. Each fluorophore bead has different peak absorption and excitation spectra enabling particle differentiation by measuring fluorescent responses under different excitation lights. A PDMS microfluidic chip technology was used to load an aliquot volume of the sample. A highly sensitive silicon photomultiplier tube (SiPM), MicroFC (SensL Inc., Cork, Ireland), was used to detect corresponding fluorescence signals from each fluorophore microbead. A filter wheel containing 12 different bandpass filters controlled by microprocessor was deployed above SiPM to selectively measure corresponding fluorescent signals, as illustrated in the figure.

In summary, we have developed an LED-based portable fluorescent sensing system that is capable of differentiating multiple fluorophore microbeads. Future work includes full characterization of the sensor system and fabrication of integrated electronic circuitry for a standalone and field-deployable fluorometer.

References

[1] Dai, C. et al. American Journal of Infection Control43, (2015), 78-81.

[2] Wu, S., Duan, N., Shi, Z., Fang, C. and Wang, Z. Analytical chemistry86, (2014), 3100-3107.

[3] Wan, Y., Sun, Y., Qi, P., Wang, P. and Zhang, D. Biosensors and Bioelectronics 55, (2014), 289-293.

Figure 1
A Novel Approach for the Preparation of Carbon Supported Intermetallic Cu3sn Nanoparticles and Their Electrocatalytic Performance for CO2 Reduction
Authors: Liu Yubin , Gunji Takao , Tanabe Toyokazu , Kaneko Shingo , Ohsaka Takeo , Miyauchi Masahiro , Matsumoto Futoshi
Published: February 2020

Carbon supported ordered intermetallic Cu3Sn nanoparticles (NPs), which had a Cu3Ti type structure (1), was successfully prepared through a wet-chemical method (2) using lithium triethylborohydride as reducing agent. The prepared ordered intermetallic Cu3Sn was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electronic microscope (TEM). Cu3Sn intermetallic structure not only showed a higher electrocatalytic activity towards CO2 electrochemical reduction, but also selectively converted CO2to CO, compared with pure Cu NPs.

Figure 1 allows us to confirm the crystal structure of intermetallic Cu3Sn, disordered Cu-Sn alloy and pure Cu NPs, respectively. The main diffraction peaks of Cu NPs and disordered Cu-Sn alloy can be observed which are assigned as FCC-type structure while the XRD pattern of intermetallic NPs shows a good fit with stoichiometric Cu3Sn structure based on Cu3Ti-type lattice (1). Figure 2 shows the Faradaic efficiency (FE) for gaseous products which was evaluated in CO2 reduction for intermetallic Cu3Sn under the potential varying from -0.8 V to -1.6 V vs.RHE. It is suggested that the FE of CO production reaches the highest value of 40 % at -1.4 V, while the FE of hydrogen production is suppressed under 17%.

[1] Y. Watanabe, et al., Acta Cryst., B39, 1983, 306-311.

[2] F. Wang. et al., J. Alloys Comp., 439, 2007, 249–253.

Figure 1
Work Function Extraction of Indium Tin Oxide Used As Transparent Gate Electrode for Mosfet
Authors: Nehate Shraddha , Sundaram Kalpathy B
Published: February 2020

Recent commercialization has peaked interest in transparent conducting oxides being implemented in display technology. Indium Tin Oxide (ITO) is a popular transparent conducting oxide which has been utilized as high work function electrode in liquid crystal displays, solar cells, gas sensors and heat reflecting films. Indium Tin Oxide films exhibit excellent transmission characteristics in the visible and infrared spectrum while maintaining high electrical conductivity. High work function electrodes are used to inject holes into organic materials. In majority applications the ITO work function has an impact on the device performance as it affects the energy barrier height at the hetero-junction interface. Hence, the work function of ITO is of critical importance.

In this article, we discuss work function extraction of ITO from a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) device for the first time. Two MOSFET devices are fabricated using a four level mask under identical conditions. Aluminum metal is used as a drain and source contact for both MOSFETs. One of the MOSFET has aluminum gate contact and transparent conducting ITO is used as gate contact for the second MOSFET. From the threshold voltage equation of both the fabricated MOSFETs, work function of ITO is extracted. Further optical transmission studies of ITO performed in the visible spectra are also reported in this study.
Electrodeposition of Compositionally Modulated Nife Alloys in Porous Anodic Alumina
Authors: Ramsey Keaton M. , Sides William D. , Huang Qiang
Published: February 2020

Since the discovery of hexagonally self-ordered pore arrays in anodized of aluminum oxide (AAO)1, great strides have been made not only in understanding the mechanistic underpinnings of pore formation2-4
but also refinements to improve in the uniformity of arrays produced and enhance control over pore sizes5-8. Much interest in these arrays stems from their potential applications in microfabrication processes. AAO membranes have been used as templates in the production of nanowires through electrodeposition of metals, alloys, and nanostructured alloys9-13.

This paper presents a systematic study investigating the development of NiFe compositionally modulated nanowires for applications in biomedical devices. AAO membranes with different pore sizes were obtained with different electrolytes to fabricate nanowires with different diameters. Compositional modulation in NiFe alloy nanowires were created using double pulse scheme in electrodeposition. In addition, pulse schemes with different ramping schemes are used to create different compositional transitions between the modulations, which is characterized and verified using transition electron microscope with energy dispersive x-ray spectrometer. The anomalous interaction between Ni and Fe will be discussed in conjunction with the ramping pulse schemes and the ionic diffusion in the pores to explain the compositional profile along the wires.

References:

1. H. Masuda and K. Fukuda, Science
268(1995).

2. O. Jessensky, F. Müller and U. Gösele, Journal of the Electrochemical Society
145(1998).

3. J. E. Houser and K. R. Hebert, Nature materials
8(2009).

4. Ö. Ö. Çapraz, P. Shrotriya, P. Skeldon, G. E. Thompson and K. R. Hebert, Electrochimica Acta
159(2015).

5. H. Masuda, K. Kanezawa and K. Nishio, Chemistry Letters(2002).

6. O. Jessensky, F. Müller and U. Gösele, Applied Physics Letters
72(1998).

7. S. Z. Chu, K. Wada, S. Inoue, M. Isogai and A. Yasumori, Advanced Materials
17(2005).

8. W. Lee, J. C. Kim and U. Gösele, Advanced Functional Materials
20(2010).

9. F. Yang, K. Liu, K. Hong, D. Reich, P. Searson and C. Chien, Science
284(1999).

10. J. Garcıa, A. Asenjo, J. Velazquez, D. Garcıa, M. Vázquez, P. Aranda and E. Ruiz-Hitzky, Journal of Applied Physics
85(1999).

11. W. Schwarzacher, O. Kasyutich, P. Evans, M. Darbyshire, G. Yi, V. Fedosyuk, F. Rousseaux, E. Cambril and D. Decanini, Journal of magnetism and magnetic materials
198(1999).

12. P. Evans, G. Yi and W. Schwarzacher, Applied Physics Letters
76(2000).

13. Q. Huang, D. Davis and E. Podlaha, Journal of Applied Electrochemistry
36 (2006).
Comparison of Electropolishing Behavior of Two Grades of Brass Alloys
Authors: Rotty Chloé , Mandroyan Audrey , Doche Marie-Laure , Hihn Jean-Yves
Published: February 2020

Brasses are widely used in watch manufacturing and jewelry as based materials, thanks to their cost, good mechanical properties and corrosion resistance. These industrial sectors face major changes in substrate composition in particular due to environmental regulations (changes in the grade of lead-free brass substrates) leading to investigate other brass grades.

Smooth and bright surfaces are usually obtained by mechanical polishing requiring a succession of manual operations. Electropolishing is an anodic dissolution process currently used in industries to replace mechanical polishing entirely or as a finishing treatment for complex shapes. The first patent for copper polishing in an aqueous orthophosphoric acid solution at high current density, was deposited by Jacquet in the 30s (1). The electropolishing quality depends on the material/electrolyte pair and the operating conditions (potential, time process, temperature…) (2,3).

The aim of this work is to observe the impact of alloying composition on polishing quality. Two grades of brass were used CuZn42 which has a diphasic composition, and CuZn37 which has a monophasic composition. They were electropolished in a phosphoric acid solution using a rotating disk electrode. At first, an electrochemical study was performed to investigate the electropolishing mechanism. A kinetic dependence on diffusion following the Levich law, is verified for the two grades of brass. This electrochemical study also allows to determine the best treatment conditions which correspond to the middle of electropolishing current density plateau.

The quality of polishing was evaluated by surface characterization which consists of a set of methods (Stylus Profiler, Secondary Electron Microscopy, Atomic Force Microscopy, X-Ray Diffraction). SEM and AFM images highlight a discrepancy between the two grades of brass (Figure 1). Indeed, CuZn37 sample (monophasic composition) shows a smooth surface and grain boundaries are almost not visible, while CuZn42 sample still presents a biphasic composition with a slight level difference between α and β phases. The roughness parameter Ra confirmed this behavior difference. Because CuZn37 sample presents a roughness equal to 42 nm, while CuZn42 is about 10 times rougher. All these characterization results indicate that there is a preferential attack of β phase (richer in Zn) for biphasic materials which induces some difficulties to apply standard conditions for the electropolishing process.

1. Jacquet PA. Electrolytic Method for obtaining Bright Copper Surfaces. Nature. 1935;135:1076.

2. Lin C-C, Hu C-C, Tai-Chou Lee. Electropolishing of 304 stainless steel interactive effects of glycerol content bath temperature and current density on surface roughness and morphology. Surf. Coat. Tech. 2009;448-54.

3. Gabe DR. Electropolishing of copper and copper-based alloys in ortho-phosphoric acid. Corros Sci. 1972;12:113-20.

Figure 1
PV Absorber Layered Materials Formation Using Potential Pulse Atomic Layer Deposition (PP-ALD),
Authors: Sisk Peter W , Czerniawski Justing , Stickney John Lewellen
Published: February 2020

Thin film photovoltaic solar cells are a promising avenue for solar technology. However, they currently are not as cost effective as fossil fuels. Several absorber layer materials have been formed using various methods in the past. CuIn(1-x)GaxSe2(CIGS) is a promising material due to its tunable direct bandgap, allowing thin films to be used in photovoltaic devices.

Previous studies of CIGS done by the author’s group investigated thin film deposition using electrochemical atomic layer deposition (E-ALD). Potential Pulse Atomic Layer Deposition (PP-ALD) is an electrochemical method of atomic layer deposition that relies on alternating cathodic and anodic potential pulses. Cathodic potential pulses long enough to form fractions of a monolayer are used. This is followed by an anodic potential which makes use of the underpotential deposition (UPD) phenomenon to strip away excess bulk, allowing stoichiometric deposits. Because short pulses are used, there is not enough time for excess elemental layers to be formed. PP-ALD is also a one solution co-electrodeposition technique. This differs from the previous E-ALD, which required multiple solution switching, allowing for PP-ALD to have shorter deposition cycles, saving solution and time. Initial results for the formation of In2Se3 and other components of the CIGS compound will be discussed.
Nanotechnology for Water-Less Cleaning of Solar Panels†
Authors: Das Sanjana , Silic Stephanie , Das Biswajit
Published: February 2020

Clean energy technologies are the present focus for fulfilling the rising demand for energy across the globe. Whereas vast majorities of researchers are working on increasing the efficiency, far less investment and research have been done in addressing the externalities that can be a setback for the technology deployment.

One of the very important externalities among them is dust and airborne sedimentation on the solar panels over time. In order to clean the dust off the solar panels, most Photo Voltaic (PV) installations perform periodic water cleaning. However, as locations with higher annual solar flux are usually arid, there is a strong demand for water-less cleaning of solar panels. While some water-less cleaning technologies currently exist, primarily based on NASA’s lunar and mars expeditions, most of these techniques are expensive and not cost effective for large-scale PV power generation.

We are currently using nanotechnology to develop a process for the water-free cleaning of solar panels, which we believe will be cost-effective for large scale PV generation. The technology involves the use of arrays of transparent nanoparticles deposited on the solar panels using a low cost technique. The nanostructure arrays provide focused electric field to modify the electrical properties of the dust particles; the charged dust particles are then removed by electrostatic sweeping.

† This work is supported by the National Science Foundation under Grant No. IIA-1301726
Synthesis and Characterization of a Novel Plasmonic Nanocomposite Photocatalyst: Ag/MoS2 Nanodots/TiO2 Mesoporous Beads
Authors: Alido John Peter Miras , Ting Jyh-Ming
Published: February 2020

In this present work, the photodegradation ability of TiO2 mesoporous beads having a higher surface area and better light scattering effect than commercial P25 was further improved. A novel plasmonic nanocomposite photocatalyst Ag/MoS2 nanodots/TiO2 mesoporous beads was developed in order to overcome the inactivity of TiO2 under visible light and the high recombination rate of photogenerated electron-hole pairs. TiO2 mesoporous beads were first synthesized through sol-gel process followed by hydrothermal method. Then, Ag/MoS2 nanodots were deposited onto the TiO2 mesoporous beads through facile liquid ultrasonic mixing and chemical reduction method. Nanocomposite photocatalysts having different ratios of Ag, MoS2 nanodots, and TiO2 mesoporous beads were synthesized and investigated. Their photocatalytic activities were then determined through the photodegradation of a methylene blue solution.
Copper Nanowire Array Electrodes with Electropolymerized Polyaniline Corrosion Barrier
Authors: Moncada Jorge , Carrero Carlos , Oh Tae-Sik
Published: February 2020

High surface area electrodes are essential for the performance of electrochemical devices for energy storage and water treatment. Carbon-based materials, mostly carbon aerogels and activated carbon, have been the usual choice for supercapacitors and capacitive deionization systems while organic-inorganic composite electrodes, featuring dispersed oxide particles on organic backbone in most cases, are currently getting attention for their distinct electrosorption properties. To expand the materials boundary even further to metallic nanowire arrays, it is necessary to develop a corrosion protection scheme that is compatible with the structural complexity of the electrode. To this end, we investigated electropolymerization route to form conformal polymeric corrosion protection barrier on a high surface area electrode based on copper nanowire array. We started from polyaniline since its electropolymerization process has been applied for smooth copper substrate [1]. Copper foils were heat treated in air to grow an intermediate array of copper oxide nanowires. After reducing copper oxide nanowires to copper nanowires preserving the high surface area [2], various polymer coatings were electrochemically grown on the surface of the copper nanowires [3]. We confirm the corrosion protection performance of the polymer coatings in an acidic environment by cyclic voltammetry and electrochemical impedance spectroscopy. The correlation between electropolymerization parameters and copper nanowire corrosion kinetics is discussed.

[1] Berrin Duran, Metehan C. Turhan, Gözen Bereket, A. Sezai Sarac, Electrochim. Acta, 55, 104 (2009).

[2] Evan C. Brown, Ph.D. thesis, Caltech, 2011.

[3] J. Heinze, Synthetic Met., 41-43, 2805 (1991).
Physics of Graphene/Organic Heterojunction Devices
Authors: Kim Chang-Hyun , Kymissis Ioannis
Published: February 2020

The material hybridization and multi-scale integration is considered to be an important direction of research in modern electronics. Simultaneous use of graphene and organic semiconductors in reduced-dimensional device architectures is a promising approach in this context, as they possess both structural compatibility and functional complementariness. In this presentation, we overview recent advances in understanding and exploitation of physical properties of the characteristic van der Waals interface formed between these materials. We first describe fundamental issues in charge transport and injection associated with the traps in fully depleted organic metal-contact diodes, which form the foundation of the advanced graphene/organic junction devices. We then explore the unique templating property of graphene as a bottom injection contact for the growth of vacuum-evaporated molecular semiconductors, which leads us to demonstrate the efficient single-layer organic rectifiers. The results from broad-band impedance spectroscopy on these devices are discussed in detail. Finally, we introduce the high-performance low-voltage graphene/organic heterojunction field-effect transistors, realized from the vertical integration of a junction diode and external gating. This new generation of devices shows a particularly promising switching performance with high current densities, and we focus on the mechanism behind the asymmetrical electrical transport and substantial work-function modulation at the graphene/organic interface through inverse modeling approaches, and suggest a strategy for further performance improvement.
Physical SPICE Model of Organic Thin Film Transistor
Authors: Bonnassieux Yvan , Jung Sungyeop , Horowitz Gilles
Published: February 2020

Electronic devices operate through charge carrier injection and transport, which are strongly dependent to the electronic structure of the semiconductor. For disordered organic semiconductors, Gaussian density-of-states (Gaussian DOS) and hopping transport are often proposed, described by analytical expressions for the charge carrier mobility as a function of the charge carrier density, electric field and temperature. However, due to the mathematical complexity of this approach, device level modelling is still lacking. In particular, for OFETs, correlation between charge carrier mobility and field-effect mobility is not sufficiently understood.

We proposed an analytical model, easy adaptable to spice model, for the linear regime transfer characteristics of OFETs with power-law dependent μ and RC. The ratio method provides a set of parameters that give good match between transfer characteristics from experiment and model.

This work has been funded by Horizon 2020 Marie Skłodowska-Curie Research and Innovation Staff Exchange (RISE) Program (2015–2019) entitled DOMINO.
Mapping Changes Induced By Few Monolayers of Al2O3 on a CuO Nanowire Surface
Authors: Banerjee Sriya , Gao Zhengning , Myung Yoon , Banerjee Parag
Published: February 2020

Thermal oxidation of copper leads to the spontaneous growth of single crystalline and pristine CuO nanowires which is an attractive materials platform for photoelectrochemical and photochemical applications. However, our limited understanding of CuO nanowire surfaces remains a bottleneck for its widespread adaptation as a material for energy conversion. One approach to probe the CuO nanowire surface is to investigate changes to its chemical and electrical signature upon deposition of a few monolayers (< 2 nm) of Al2O3; a chemically and electrically passivating film. Exactly how Al2O3 might achieve this passivity is the subject of this talk.

We progressively map, ex situ
, the effect of adding few monolayers of Al2O3 on the surface chemistry and electrical characteristics of a single CuO nanowire. The CuO nanowire is contacted electrically via electron beam lithography (Figure 1a), prior to the deposition experiments. Using atomic layer deposition (ALD), Al2O3 is deposited using trimethyl aluminum (TMA) and H2O as reactants. A deposition rate of 1Å/cycle is obtained. The chemical changes on the nanowire surface are studied by X-ray photoelectron spectroscopy (XPS) and electrical properties of the nanowire are recorded after every monolayer deposition.

XPS fine spectra of Cu 2p reveal a clear reduction of Cu2+ to Cu1+ after only a single pulse of TMA. The O 1s fine spectra reveals the formation of Al-O and Cu+1-O bonds and removal of adsorbed O species after 1 cycle of Al2O3
(Figure 1b). The Al 2p fine spectra shows a clear Al-O bond formation after ~ 3 cycles of ALD. Thus, a clear surface reduction of CuO nanowire and subsequent formation of Al2O3 is noted in XPS studies. This change in surface chemistry manifests itself in the electrical characteristics as a detectable photocurrent response under ambient (760 Torr) conditions; where, for a pristine CuO nanowire, no such response is previously observed (Figure 1c). Current-voltage characteristics are mapped as a function of temperature and discussed in light of the changes to surface properties observed via XPS.

Figure 1
Frequency and Area Dependence of High-K/Ge Mos Capacitors
Authors: Mitevski Ivan , Ding Yiming , Misra Durga
Published: February 2020

Abstract

– Ge substrate devices in Complementary Metal Oxide Semiconductors (CMOS) technology have been extensively studied due to its high electron and hole mobility [1]. However, most of the Ge devices have some limitation as making a high-quality Ge/High-k gate stack is rather difficult compared to Si/High-k system. The purpose of this work is to further study the capacitance measurements of a MOS capacitor at different frequencies for square devices with different side lengths (10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 100 μm). The series resistance corrected capacitance (Cc) for accumulation region increases on a faster pace when a lower frequency (1KHz) is used than at a higher frequency (1MHz) (Figure 1(a)) as a function of side length, a. Accumulation capacitance has a strong dependence on frequency in metal oxide semiconductor devices. Our devices follow the same trend as previous studies have reported [2]. On the other hand, our study shows substantial decrease of Cc per unit area in Ge/High-K in comparison to High-K/Si devices (Figure 1(b)). This decrease is attributed to the large non-uniform interface defect density [3], high leakage current [3] associated with Ge stacks and fringing field effect [4]. Capacitance at accumulation condition depends on interface capacitance (Cit) which changes with defects density. Defect density increases proportionally with area and High-K/Ge devices, being leakier, experience a higher decrease of Cc per unit area than High-K/Si devices. The impact of fringing field capacitance (CL) on parallel plate capacitance (CP) decreases when device area is increased (Figure 1(c)) and this contributes to further decrease in total capacitance Cc per unit area. This work explains the frequency dispersion of high-k MOS capacitance in accumulation region and the unit capacitance decrease when Ge substrate is used. The study also models the fringing field capacitance [5] and its effect on MOS devices.

Figure 1 (a) Corrected capacitance (C
c) measured at -1.5 V (accumulation) at 1 MHz and 1 KHz shows frequency dependence; (b) Unit Capacitance is plotted against area for Ge substrate and Si substrate sample for measurements at frequency of 1MHz. C
s is substrate capacitance and C
ox is oxide capacitance; (c) CL/CP as a function of area. CL and CP are calculated as per Yuan & Trick’s model [5].

[1] D. Kuzum, A. J. Pethe, T. K., K. C. S, IEEE T. Electron. Dev., vol. 56, p. 648, 2009.

[2] P. R. Lee, J. R. Ruzyllo, Electrochemical Society, vol. 9, p.353-362, 2007.

[3] Y. M. Ding, D. Misra, J. Vac. Sci. Technol. B, vol. 34, p. 021203 2016.

[4] S. Maurya, B. R. Singh, Solid States Physics, AIP Conf. Proc. 1512, 742-743, 2013.

[5] E. Barke, IEEE Transactions on Computer Aided Design, vol. 7, No. 2, 1988.

Figure 1
Hydrothermally Synthesized Copper Gallium Delafossite Nanoflakes for (Photo)Electrocatalytic Water Splitting
Authors: Mao Yuanbing , Mohan Swati
Published: February 2020

The surge of alternative clean energy with minimal environmental impact in a cost-effective way requires the exploration of new materials and/or structures as efficient electrodes for industry-level photoelectrochemical (PEC) water splitting into usable H2 fuel. Considerable efforts have been made on anodic/cathodic photoelectrolysis of water with metal oxides, which have been featured by their abundance, environmental friendliness, and chemical stability. As a type of fascinating functional materials, delafossites with an ABO2-type general composition, where ‘A’ is monovalent (1+ metals of Cu, Ag, etc.) and ‘B’ is trivalent (3+ metals of Al, Ga, In, Fe etc.) have been highly oriented for applications as optoelectronics. Recently some aspects have been uncovered in the delafossite material field, e.g. they can be used as electrocatalysts and photocatalysts which are invaluable to rational design and optimization for various catalytic applications. Therefore, it is emergent to improve their optical and electrochemical activity for their electrochemical and photoelectrochemical (PEC) catalytic applications. One widely used strategy is to increase the surface area of functional materials. Here delafossite CuGaO2 nanoflakes have been synthesized by a hydrothermal method in the presence of sodium dodecyl sulfate (SDS) as surfactant at 190oC for 60 h and compared with CuGaO2 microplates synthesized under the same conditions without SDS. The synthesized samples were thoroughly characterized by powder X-ray diffraction, SEM, EDX, XPS, FT-IR, UV-Vis and BET surface area measurements. Moreover, their electrocatalytic and photoelectrocatalytic performance for OER in 0.5 M KOH electrolyte versus Ag/AgCl along with their stability were studied for cost-effective and active electrode material. It was demonstrated that the delafossite CuGaO2 nanoflakes synthesized in the presence of SDS showed better (photo)electrocatalytic performance and stability for OER than those synthesized without surfactant SDS. Thus, this hydrothermal method in combination of surfactant was an efficient approach towards the synthesis of delafossite CuGaO2 with reduced size as cost-effective and high performance (photo)electrocatalysts.
Synthesis and Highly Effective Purification of Silver Nanowires to Enhance the Transmittance at Low Sheet Resistance with Simple Polyol and Scalable Selective Precipitation Method
Authors: Gebeyehu Molla Bahiru , Chala Tolosa Fita , Chang Shao-Yen , Wu Chang-Mou , Lee Jiunn-Yih
Published: February 2020

Networks of metal NWs have the highest performance of any solution-coatable to replace expensive indium tin oxide (ITO) as the transparent conducting electrode material in next generation devices. However, there is as yet no published process for producing NW films with an optoelectronic performance that exceeds that of ITO. Here, we examine a process for the synthesis and purification of uniform AgNWs that, when coated with a spin coating to create a transparent conducting film (TCF), show properties exceed that of ITO. The morphology AgNWs can be controlled by adjusting the concentration of silver nitrate (AgNO3) and [PVP] to [AgNO3] molar ratio. AgNWs with average diameters of 20 nm and aspect ratios >1000 were obtained by added 30.5 mM of AgNO3 and 6:1 molar ratio of [PVP] to [AgNO3] to a silver nanowire synthesis, but these NW were contaminated by some Ag nanoparticles. Selective precipitation was used to purify the NWs from nanoparticles, resulting in a transmittance improvement as large as 2%. The transmittance of the purified AgNW film was 97.5% at a sheet resistance of below 70 Ω sq−1. The synthesized and purified AgNWs were analyzed by field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), Energy Dispersive Spectrometer (EDS), Energy Dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Ultraviolet−visible−near-infrared (UV−Vis−NIR) and four-point-probe technique.

Figure 1
Preparation of Cu2znsn(S
x
Se1-x
)4 (CZTSSe) Single-Phase Sputtering Target By Sintering Binary Alloy Powders and Its Applications to Cztsse Thin-Film Solar Cell
Authors: Lee Meng-Huan , Lin Yu-Pin , Hsieh Tsung-Eong
Published: February 2020

Cu(In,Ga)Se2 (CIGS) is the main photo-absorption layer of thin-film solar cells; however, relative scarcity of In and Ga elements and the selenization using toxic H2Se gas inhibit its practical usage. Cu2ZnSnS4 (CZTS) becomes the promising alternative due to its similar physical properties to CIGS, abundance of Zn and Sn elements in earth and low toxic preparation method. Moreover, the bandgap of CZTS can be modulated by adding selenium (Se) to form the CZTSSe so as to improve the performance of photovoltaic (PV) devices.

This work adopts the CuSe, ZnS and SnS2 binary alloy powders as the starting ingredients to prepare thesingle-phase CZTSSe sputtering target. The powders were mixed at the molar ratio of Cu:Zn:Sn = 1.6:1:1, pressured into the pellets form with 6 mm in diameter, sintered in the N2 ambient at temperatures ranging from 200 to 600°C for 8 hrs. The microstructures and phase constitutions of pellets subjected to various sintering treatments were then characterized in order to identify the sintering condition that may yield the single-phase CZTSSe structure.

The phase evolution in pellets characterized by x-ray diffraction (XRD) revealed that the single-phase kesterite CZTSSe structure can be obtained by the sintering at 600°C and the energy dispersive spectroscopy (EDS) indicated its stoichiometric ratio is Cu26.18Zn13.73Sn12.02S35.22Se11.86 which is close to the ideal ratio of 2:1:1:4.

The 2-inch CZTSSe sputtering target was then prepared for CZTSSe layer deposition in accord with the optimized sintering condition. XRD and Raman spectroscopy analyses revealed the deposited CZTSSe layer subjected to the post annealing at 570°C for 1 hr in N2 ambient also possesses the single-phase kesterite structure. EDS analysis found its stoichiometric ratio is Cu24.50Zn14.02Sn13.92S38.20Se9.36 which are close to the ideal ratio of 2:1:1:4 with the Cu-poor/Zn-rich feature. Presently, the CZTSSe layers with desired grain morphologies and compositions are transferred to the preparation of thin-film solar cell and its PV performance is evaluated.
Tuning the Carbon Crystallinity for Highly Stable Li-O2 Batteries
Authors: Bae Youngjoon , Yun Young Soo , Lim Hee-Dae , Park Hyeokjun , Lee Hongkyung , Kim Yun-Jung , Kwon Hyuk Jae , Kim Hyunjin , Kim Hee-Tak , Im Dongmin , Kang Kisuk
Published: February 2020

The increasing demands for emerging high-energy-density applications, such as electric vehicles, have prompted considerable efforts to design a new type of innovative, sustainable battery. Li–O2 batteries can deliver much higher energy densities than current Li-ion batteries and have thus attracted much attention; however, their poor cyclic stability remains a major obstacle to their use in high-energy-density applications. The carbon-based cathode materials (CCMs) used for Li–O2 batteries are considered one of the origins of this cycle-life degradation, which has led to the development of several alternative types of cathode materials, such as Au or TiC.1,2,3 However, there is currently no practical substitute for CCMs, which exhibit desirable properties such as high specific surface area, high electrical conductivity, light weight, and chemical stability and involve the use of well-known technologies with low processing and raw material costs. This study provides a new perspective on Li–O2 batteries, for which the cyclic stability can be dramatically increased using well-ordered graphitic CCMs. Through a systematic investigation on the controlled carbon, we demonstrate that the graphitic crystallinity of carbon is an important factor in determining the stability of not only the cathode but also the electrolyte. To discern the degradation factors affecting the cathode from those affecting the electrolyte, we used carbon isotope (13C)-based air electrodes with various degrees of graphitic crystallinity. Furthermore, in situ differential electrochemical mass spectroscopy analysis clearly demonstrates that as the crystallinity of the carbon increases, the CO2 evolution from the cell is reduced, which leads to a three-fold enhancement in the cycle stability of the cell.

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