bluuebunny/crossref_metadata_2025_split huggingface dataset:
Charge Transfer Kinetics in the Dark at Oxide Semiconductor/ electrolyte Interfaces
Authors: Firouzan Farinaz , Vali Abbas , Rajeshwar Krishnan 
Published: December 2020

Among all the requisite properties of an inorganic semiconductor, the dynamics of interfacial charge transfer is an important common denominator for numerous technologically important applications such as PEC water splitting, photocatalytic pollutant degradation, or photovoltaic solar energy conversion.Most attention in this regard has been paid to the dynamics of minority carrier transfer; only sporadic studies have focused on majority carrier transfer across the solid/electrolyte interface. However, recent studies have underlined the growing realization that the charge transfer kinetics of both minority and majority carriers are often coupled. Performance optimization of the interfaces must address both these charge transfer pathways such that deleterious carrier recombination can be minimized. Therefore, this study addresses the fundamental and experimental understanding of interfacial charge transfer dynamics at semiconductor/electrolyte interfaces
in the dark
. A variety of interfaces were studied to gain a unified and self-consistent picture.
Firstly, binary n-type TiO2 and WO3 semiconductors were chosen because of their excellent chemical/photoelectrochemical (PEC) stability, high PEC activity, and overall robustness over a wide pH range. Secondly, binary and ternary p-type semiconductors such as copper bismuth oxide (CuBi2O4),silver vanadate (AgVO3),and copper (II) oxide (CuO) were selected to compare their charge transfer kinetics in the dark. Such comparative studies are conspicuously absent in the literature, and in particular, dark current-forward bias potential measurements are lacking for these compounds. Tafel analyses were used to evaluate the standard rate constant, k
0 and the exchange current density, jo

in all these cases.

Based on these kinetics data, a general conclusion could be made that p-type oxide semiconductors exhibited faster kinetics than their n-type counterparts. For comparison, Pt and fluorine doped tin oxide (FTO) electrodes were included as benchmarks in these experiments. The data also indicated that heterogeneous charge transfer at metal/electrolyte interfaces had faster kinetics compared to the semiconductor/electrolyte interfaces. This contrasting and self-consistent behavior stems from surface state density variations in the two sets of cases. The practical implications of these data are finally discussed.
(Invited) Reliability of Ultra Nano-sheet InWO Thin Film Transistor for Back-end of Line Applications
Authors: Liu Po-Tsun , Li Zhen-Hao , Kuo Po-Yi , Lin Yi-Syuan , Tien Chung-Hao 
Published: December 2020

The amorphous indium-tungsten oxide (a-IWO) ultra nano-sheet (UNS) thin-film transistor (TFT) has been developed successfully and exhibited high device performance. It is also suitable for the back end of line (BEOL) technologies due to its superior electrical characteristic and low operation voltage[1, 2]. In this work, we study the reliability of TFT with nano-sheet IWO as channel layer for BEOL applications. The backchannel passivation with an organic layer was proposed to effectively isolate the humidity in the atmosphere. Experimental results have shown that the a-IWO nano-sheet TFT can exhibit the great potential and excellent reliability for BEOL IC applications.

Experiment

The bottom gate structure was used. A Mo films was deposited by DC sputter as gate electrode. Then, a layer of HfO2 film was deposited through the atomic layer deposition (ALD). Next, the 4nm-thick nano-sheet a-IWO thin film was deposition as the channel layer by RF sputter. The Mo source/drain contacts were deposited by DC sputter. Finally, the organic passivation layer covered on the device with spin coating method. The conditions of thermal annealing process were studied for the optimization of the interface quality between IWO nano-sheet backchannel and organic passivation layer.

Result and discussion

The amorphous oxide semiconductor (AOS) channel layer is easily affected by the atmosphere from the environments, like oxygen and moisture causing the electrical degradation [3, 4]. Therefore, the passivation effectively avoids the degradation of device features under positive bias thermal stress (PBTS) measurement, as shown in Fig. 1. The passivation layer can effectively improve the TFT device reliability and reduce the positive shift of threshold voltage.

Reference

[1] P. Y. Kuo, C. M. Chang, and P. T. Liu, pp. 21-22.
[2] P. Y. Kuo, C. M. Chang, I. H. Liu, and P. T. Liu, Scientific reports, vol. 9, no. 1, pp. 1-7, 2019.
[3] J. Yao, N. Xu, S. Deng, J. Chen, J. She, H. P. D. Shieh, P. T. Liu, and Y. P. Huang, IEEE Transactions on Electron Devices, vol. 58, no. 4, pp. 1121-1126, 2011.
[4] P. T. Liu, Y. T. Chou, and L. F. Teng, Applied Physics Letters, vol. 95, no. 23, pp. 233504, 2009.

Figure 1
A Ferroelectric Thin-Film Transistor Based on Sputtered HfZrO and IGZO
Authors: Ryu Suhwan , Seong Tae-Yeon 
Published: December 2020

In recent years, because of increased demand in IoTs devices, wearable displays, circuits, sensors, and other high technology devices, the thin film transistors (TFTs) gated by ferroelectric film as memory devices are of considerable interest. Ferroelectric (FE) materials including Pb(Zr0.4Ti0.6)O3 (PZT), (1-x)[Pb(Mg1/3Nb2/3)O3]-x[PbTiO3] (PMN-PT), and polymer poly (vinylidenefluoride-trifluoroethylene) (P[VDF-TrFE]) have been used to realize ferroelectric transistors with nonvolatile memory. Particularly, HfO2-based materials have attracted a great deal of attention since the breakthrough in the ferroelectricity of Si-doped HfO2, which can overcome some of limitations of current ferroelectrics such as scalability, lead-free materials and suitable for high-temperature process. Moreover, HfO2-based materials exhibit better performance in terms of a switching characteristic than low-k gate insulator (SiO2) as well as high-k materials.
In this study, the performance of sputter-deposited ferroelectric hafnium zirconium oxide (HfZrO)/high-k HfO2 gate dielectric for a-IGZO TFTs on glass substrates was investigated. The sputterd HfZrO film was crystallized with orthorhombic phases after rapid-thermal-annealing at temperature of 400 °C for 30 min in air and exhibited ferroelectricity. The performance of the FE-TFT based on HfZrO/HfO₂ (15 nm/185 nm) was compared to typical TFTs fabricated with PECVD-SiO₂ (200 nm) and sputtered HfO₂ only (200 nm) gate insulators. The transfer characteristics of the FE-TFTs were demonstrated with low operating voltage of 0.1 V, one order higher on-off ratio and drain current than the typical TFTs with the SiO₂ and HfO₂ gates, high field effect mobility 5.04 cm2V-1s-1 and small subthreshold slope (SS) about 117 mV/dec. The low operating voltage and small SS results of the HfZrO/HfO₂-based device indicates that the use of the HfZrO/HfO₂ could serve as a potential gate for the fabrication of high-performance FE-TFTs.
Unusual Thermoelectric Anisotropy in Rhombohedral Germanium Telluride
Authors: Askarpour Vahid , Maassen Jesse 
Published: December 2020

Developing high performance thermoelectrics to convert waste heat into useful electrical power is an important challenge that has the potential to impact our energy future. This requires exploring and discovering new materials with enhanced electronic and thermal (phonon) transport properties. Advances in computational modeling now allow the thermoelectric characteristics of materials to be calculated fully predictively, and thus represents a powerful tool to be partnered with experimental efforts.
In this talk, I will present our recent findings on rhombohedral GeTe, a layered quasi-2D material predicted to have unusual anisotropic transport properties [1]. Our approach combines density functional theory with the Boltzmann transport equation, to extract the detailed electron and phonon dispersions along with the electron-phonon scattering rates, in order to predict the thermoelectric transport coefficients. Our results show that the electrons preferentially conduct along the cross-plane direction, while the holes favor the in-plane direction. Interestingly, this feature enhances the thermoelectric figure-of-merit ZT for n-type GeTe, since the conductivity (and power factor) is maximized perpendicular to the atomic layers while the lattice (phonon) thermal conductivity is minimized - leading to a three-fold increase in ZT. The cross-plane power factor and mobility in n-GeTe reach roughly 32 μW/cm-K2 and 500 cm2/V-s, respectively. An analysis of the band structure reveals that the large cross-plane transport originates from high-velocity conduction states, formed by the Ge p-orbitals that span across the interstitial region. These findings illustrate how the dominant electron and phonon transport directions are effectively decoupled in n-GeTe; a feature that can potentially be found in other materials to achieve enhancements in thermoelectric performance.
[1] V. Askarpour and J. Maassen, “Unusual thermoelectric transport anisotropy in quasi-two-dimensional rhombohedral GeTe”, Phys. Rev. B 100, 075201 (2019).

Figure 1
All-Inorganic Perovskite Solar Cells Using Treated Carbon Materials for Effective Charge Extraction
Authors: Zhou Cheng , Chen Xiang , Zhang Meili , Pang Beili , Dong Hongzhou , Sun Qiong , Feng Jianguang , Yu Liyan , Dong Lifeng 
Published: December 2020

Perovskite solar cells (PSCs) have become the leader in the field of the third-generation solar cells due to their outstanding photovoltaic performance and low cost. However, the instability stemming from low tolerance to humidity and heat as well as residual solvents and ultraviolet illumination would be challenging for long-term stability. Recently, all inorganic perovskites, especially carbon-based hole-transporting material (HTM) CsPbBr3 perovskite, have attracted increasing attentions because of their enhanced moisture and thermal stability compared to hybrid counterparts.
For the CsPbBr3 device, a challenging route to increase power conversion efficiency (PCE) is to take interfacial charge transfer into consideration and reduce interfacial energy-level differences to reduce space charge accumulation and enhance charge extraction. It is known that graphene-based derivatives are promising candidates for interfacial materials due to their excellent electronic properties. For example, graphene quantum dots (GQDs) between perovskite and TiO2 could significantly enhance the performance of PSCs due to dramatically enhanced electron extraction by the inserted GQDs; polyaniline/graphite composites were incorporated into carbon electrode to tailor work function and to improve hole-selectivity of back electrode for enhanced energy level alignment and interfacial hole extraction, leading to a remarkably reduced energy loss and charge recombination.
Herein, we developed a strategy to use carbon dots (CDs) with tunable bandgaps and high absorption coefficients for electron extraction performance. The CDs were prepared by exfoliation method from oxidized graphite, and CDs in dimethylformamide solution were spin-coated onto FTO/c-TiO2/m-TiO2 substrate, then a multistep solution-processed method was used to prepare Cs-Pb-Br films with controllable CsPbBr3 phase. Specifically, CsBr/methanol solution (~15 mg mL-1) was spin-coated onto PbBr2 film and then annealed at 250 °C for 5 min, and the processes were repeated for 5 times. The obtained cesium lead bromide films were washed by 2-propanol. Finally, a carbon back-electrode with an average area of 0.09 cm2 was deposited onto the device. We fabricated all-inorganic PSCs with the FTO/c-TiO2/m-TiO2/CDs/CsPbBr3/carbon structure. Arising from the suppressed interfacial charge recombination, the optimal device yielded a PCE up to 10.67% under one sun illumination. These findings suggest that graphene-based derivatives can be used as interfacial modification materials toward high-performance carbon-based HTM-free PSCs.
Ceria Nanodots Anchored on ZIF67-Derived Framework By Atomic Layer Deposition for Efficient Bifunctional Oxygen Electrocatalysis
Authors: Liu Ziqi , Andrade Angela Macedo , Grewal Simranjit 
Published: December 2020

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which are the two most important reactions for electrocatalytic activities, has been widely studied for sustainable and renewable electrochemical applications, including fuel cells[1]
,
[2], metal-air batteries[3] and water electrolysis[4]. For the development of new catalysts alternative to noble metal-based materials, metal organic frameworks (MOFs) are being actively used as the precursor structure. ZIF-67, a kind of MOF structure made of cobalt nitrate and 2-methylimidazole ligands, has proved to be a good candidate for ORR catalysis due to their rich of Co-N-C active sites. However, ZIF-67 tends to aggregate during the pyrolysis process by breaking C-H or C-O bonds.
In this study, atomic layer deposition (ALD) was applied to coat an atomically thin cerium oxide (CeO2, ceria) coatings the MOF structure, which is expected to incur synergistic catalytic activity and suppress the thermal agglomeration. ALD is a self-limiting surface chemistry process, and is able to create highly conformally layer-by-layer thin film on any complex 3D structure with controllable thickness at an atomic level.[5] Ceria has shown good synergistic effect with other metals for OER performance due to its ability for electron exchange and ion reduction.[6] We demonstrates a facile synthesis of Co/Ce co-doped porous carbon nanomaterials by pyrolyzing the ceria-coated ZIF structure. The resultant samples showed uniform crystal structure which are in well accordance with ZIF-67 precursors. The as-prepared samples also showed enhanced electrocatalytic activities for both ORR and OER comparable to that of noble metal benchmarks (Pt/C and IrO2) and in terms of onset potential, half-wave potential, and current density. A sample prepared by performing 15 cycles of ceria ALD followed a pyrolysis at 700 °C shows the highest onset potential (0.95 V versus RHE) for ORR and superior stability in comparison to commercialized Pt/C. Meanwhile, a sample with 5 cycles of ceria ALD exhibits an excellent OER performance (1.48 V at 10 mA cm-2) and maintained a good OER durability performance (from 1.48 V to 1.50 V after 2,000 potentiodynamic cycles).

References

[1] W. Xia, R. Zou, L. An, D. Xia, S. Guo, 2015, 8, 379.
[2] X. Wang, H. Zhang, H. Lin, S. Gupta, C. Wang, Z. Tao, H. Fu, T. Wang, J. Zheng, G. Wu, X. Li, Nano Energy
2016, 25, 110.
[3] M. Khalid, A. M. B. Honorato, H. Varela, L. Dai, Nano Energy
2018, 45, 127.
[4] B. Y. Xia, Y. Yan, N. Li, H. Bin Wu, X. W. (David) Lou, X. Wang, Nat. Energy
2016, 1, 15006.
[5] C. Guerra-Nuñez, Y. Zhang, M. Li, V. Chawla, R. Erni, J. Michler, H. G. Park, I. Utke, 2015, 7.
[6] S. Xu, C. Lv, T. He, Z. Huang, C. Zhang, J. Mater. Chem. A
2019, 7, 7526.
Overcoming Limitations in Evaluation of Memristor Technologies for Neural Networks
Authors: Whitehead William , Veksler Dmitry , Bersuker Gennadi 
Published: December 2020

Intrinsic switching characteristics of two resistive memory technologies, hafnia (RRAM)- and carbon nanotube (CNT)- based, are evaluated with respect to their implementation in deep neural networks (DNN) and possible mitigation approaches to performance degradation. Both RRAM (poly-crystalline metal oxide) and NRAM (fabric of interlocking matrix of CNTs) operations employ modulations of the conductive paths through a semi-isolating layer sandwiched between electrodes. RRAM and NRAM characteristics demonstrate similar features when evaluated employing commonly used switching times > 100 ns: variability of the weights update values linked to stochasticity of the switching processes, asymmetric weight change, and memory update saturation.
Though materials are different, the observed undesirable trends have a common cause that is excessive energy released within the duration of switching operations: it induces gradual changes in the material structure surrounding conductive paths. Such changes, in turn, affect temperature distribution and related structural rearrangements during the subsequent switching. In particular, memory update saturation reflects on exhaustion of the number of structural blocks (atoms, CNTs) available for expanding the conductive path under specific used operation conditions. As follows, by reducing energy released in each operation we may suppress excessive structural changes, hence related performance degradation features. Indeed, under sub-ns switching conditions relevant to high-frequency circuitry operations, both RRAM and NRAM demonstrate significant performance improvement making them promising for DNN implementations.
(Invited) Computing with Memristive Devices and Arrays
Authors: Yang J. Joshua 
Published: December 2020

Memristive devices have become a promising candidate for unconventional computing due to their attractive properties(1). The computing can be implemented on a Resistive Neural Network (ResNN) with memristor synapses and neurons or a Capacitive Neural Network (CapNN) with memcapacitor synapses and neurons(2).
For ResNNs as computing accelerators, we have built a dot-product engine based on a 128 x 64 1T1R crossbar array using traditional non-volatile memristors with 64 stable analog resistance levels(3). With such computation accelerators, we have demonstrated efficient inference and learning with traditional Machine Learning algorithms(4-7), which is expected to significantly improve the speed and energy efficiency of neural networks.
For ResNNs beyond accelerator applications, we developed diffusive memristors(8)with diffusion dynamics that is critical for neuromorphic functions. Based on the diffusive memristors, we have further developed artificial synapses(8)and neurons(9)to more faithfully emulate their bio-counterparts. We then integrated these artificial synapses and neurons into a small neural network, with which pattern classification and unsupervised learning have been demonstrated(9).
For CapNNs, we have developed pseudo-memcapacitive devices based on the diffusive memristors. Capacitive synapses and neurons enabled by these memcapacitive devices have been developed and used to form a fully integrated CapNN(10), which can implement spiking signal classification and Hebbian-like learning.

Z. Wanget al., Resistive switching materials for information processing. Nature Reviews Materials
5, 173–195 (2020).

Q. Xia, J. J. Yang, Memristive crossbar arrays for brain-inspired computing. Nature materials
18, 309-323 (2019).

C. Liet al., Analogue signal and image processing with large memristor crossbars. Nature Electronics
1, 52-59 (2018).

Z. Wanget al., Reinforcement learning with analogue memristor arrays. Nature Electronics
2, 115-124 (2019).

Z. Wanget al., In situ training of feed-forward and recurrent convolutional memristor networks. Nature Machine Intelligence
1, 434-442 (2019).

C. Liet al., Long short-term memory networks in memristor crossbar arrays. Nature Machine Intelligence
1, 49-57 (2019).

P. Linet al., Three-dimensional memristor circuits as complex neural networks. Nature Electronics
3, 225–232 (2020).

Z. Wanget al., Memristors with diffusive dynamics as synaptic emulators for neuromorphic computing. Nature Materials
16, 101-108 (2017).

Z. Wanget al., Fully memristive neural networks for pattern classification with unsupervised learning. Nature Electronics
1, 137-145 (2018).

Z. Wanget al., Capacitive neural network with neuro-transistors. Nature Communications
9, 3208 (2018).
Effects of ITO Electrode on Electrochromic Properties of WO3 Thin Films in Visible and Near-Infrared Region
Authors: Ayauchi Yasuhiro , Abe Yoshio , Kawamura Midori , Kim Kyung Ho , Kiba Takayuki 
Published: December 2020

Indium tin oxide (ITO) thin films have been incorporated into electrochromic (EC) devices as a transparent conductive film. It is highly desirable that EC devices applied to a smart window can control both visible and infrared light, because infrared light accounts for about half of the energy of sunlight. In this study, we fabricated WO3 thin film on ITO thin films with different sheet resistances and studied their EC properties in visible and near-infrared region.
ITO thin films deposited on glass were used as substrates. Tungsten oxide (WO3) thin films were deposited using RF magnetron sputtering system. Crystal structure was characterized by X-ray diffraction. Optical properties of the prepared samples were measured using UV-VIS-NIR spectrophotometer. The electrical resistance of the ITO thin films was measured by a four probe method. EC properties of the WO3 thin film were measured by cyclic voltammetry (CV) and chronoamperometry (CA) in a 0.01 M H2SO4 aqueous electrolyte.
The transmittance of the high sheet-resistance ITO thin film (177 Ω/sq) decreased at a short wavelength region below 455 nm. However, it showed high transmittance above 70% in the visible and near-infrared region (455-2050 nm). In contrast, the low sheet-resistance ITO thin films showed high transmittance above 70% in a wavelength region of 335-1350 nm and its transmittance decreased above 1350 nm. The differences of the transmittance in short and long wavelength regions are considered to be caused by the Burstein-Moss effect and Drude model, respectively. Fig. 1 shows the transmittance spectra of the WO3 thin film with a thickness of 200 nm deposited on the ITO/glass substrates measured in air. Lines (1) and (2) show the transmittance spectra of colored and bleached states of WO3 thin film deposited on high sheet-resistance ITO thin film, and lines (3) and (4) show those of colored and bleached states of WO3 thin film deposited on low sheet-resistance ITO thin film. The WO3 thin film deposited on the high sheet-resistance ITO thin film showed a larger transmittance change and higher transmittance in bleached state in the near-infrared region than those of the WO3 thin film deposited on the low sheet-resistance ITO thin film.
From these results, it was found that the selection of appropriate ITO electrodes is very important to obtain good EC property of WO3 thin films in visible and near-infrared region.

Figure 1