bluuebunny/crossref_metadata_2025 huggingface dataset:
Exploring Different Concepts for 2D Cu Growth on Ru(0001) Assisted By Pb UPD Monolayer
Authors: Wu Dongjun , Brankovic Stanko R
Published: February 2020

The properties of heteroepitaxial thin films are much dependent on the method used for their deposition. The electrodeposition represents the ambient temperature process offering the opportunity to grow many heteroepitaxial metal overlayers while preserving the integrity of their interface. In recent years, a significant progress has been made in understanding the kinetic aspects controlling the growth modes [[i],[ii],[iii]]. The improved understanding has led to various discoveries in which the growth kinetics was manipulated to enhance the evolution of atomically flat epitaxial overlayers [[iv],[v],[vi]]. Exploiting some of these results has led to development of several new methods and protocols for electrodeposition of heteroepitaxial thin films assisted by UPD monolayer serving as a mediator, surfactant or sacrificial template.  [[vii],[viii],[ix],[x]]. 

In this talk we will briefly review the progress in the electrochemical thin film growth assisted by UPD ML. Our focus is examining the epitaxial growth of Cu on Ru(0001) assisted by Pb UPD ML. Cu and Ru represent the overlayer/substrate system which has significant epitaxial strain (-5.5%). This fact together with room temperature growth conditions favor a 3D growth. However, as we will show in our talk (Figure 1), with convenient use of Pb UPD ML serving as surfactant, or mediator, a 2D growth of Cu on Ru is induced. Characterization of 2D Cu overlayers indicates that their quality is comparable to MBE grown films which qualifies our approach as relevant for many high-tech applications. Our results also re-confirm the fact that Pb UPD ML-assisted electrochemical growth could be used to produce smooth 2D films of various metal overlayers even in situations where both thermodynamics and kinetics conditions do not favor positive outcome.

The authors acknowledge the support from NSF Chemistry division under the contract # 0955922.

[i] Physics of Crystal Growth, A. Pipinelli and J. Villain, University Press, Cambridge, UK (1998).

[ii] J. Tersoff, A.W. Denier van der Gon, and R.M. Tromp, Phys. Rev. Lett. 72, 266 (1994).

[iii] G. Rosenfield, B. Polesma and G. Comsa in Chemical Physics of Solid Surfaces  ed. D. A. King and D. P. Woodruff, vol. 8, Elsevier, New York (1997), p. 70.

[iv] G. Rosenfeld, R. Servaty, C. Teichert, B. Poeselma and G. Comsa, Phys. Rev. Lett., 71, 895 (1993).

[v] H. A. van der Vegt, H.M. van Pinxteren, M. Lohmeier, E. Vlieg and J.M.C. Thornton, Phys. Rev. Lett. 68, 3335 (1992).

[vi] H. A. van der Vegt, H.M. van Pinxteren, M. Lohmeier, E. Vlieg and J.M.C. Thornton, Phys. Rev. Lett.
68, 3335 (1992).

[vii] K. Sieradzki, S.R. Brankovic and N. Dimitrov, Science,
284, 138 (1999).

[viii] S. R. Brankovic, Electrochemical Mediated Growth, PhD Thesis,  Arizona State University, Tempe (1999)

[ix] S.R. Brankovic, N. Dimitrov and K. Sieradzki, Electrochem.Solid-State Lett., 2, 443 (1999).

[x] S.R. Brankovic, J.X. Wang and R. R. Adzic, Surf. Sci., 474, L173 (2001).

Figure 1
Electrodeposition of Cobalt Selenide Thin Films Using Combined Voltammetry and Electrochemical Quartz Crystal Microgravimetry
Authors: Paeng ki-Jung , Jee hyung Woo
Published: February 2020

Electrodeposition and composition of CoSe thin films have been studied using electrochemical quartz crystal microgravimetry and stripping voltammetry. CoSe thin films were synthesized using 0.1 M KNO3 solution containing SeO2 and Co(NO3)2 at room temperature. During the electrodeposition, selenium was electrodeposited first, followed by the induced under potential deposition of cobalt to result in CoSe films. Photocurrent transients proved that as synthesized Se and CoSe are p-type semiconductors and their band gaps have been determined with reflectance spectrometry. Deposition mechanism and effect of electrolyte composition on the film composition were studied in detail using electrolyte containing different ratio. Composition of CoSe thins films has been determined by combining EQCM and stripping voltammetry. First, free selenium in the electrodeposited film was reduced to soluble Se2- at –0.8 V in 0.1 M Na2SO4 solution and frequency change was used to determine the content of free selenium. The film was again subjected to –1.5 V in the same blank electrolyte to reduce CoSe to Co+Se2- and accompanied frequency change was used to determine selenium in CoSe based on the 1:1 stoichiometry. Finally, the content of free cobalt in the electrodeposited film was determined from the frequency change during the oxidation of Co to Co2+ and difference between total cobalt and cobalt in CoSe thin film. Compositional analysis indicated that film composition is sensitive to electrodeposition potential as well as composition of electrolyte.
Cobalt-Palladium Alloys for Hydrogen Generation Via Water Electrolysis
Authors: Kutyla Dawid , Kolczyk Karolina , Kowalik Remigiusz , Mech Krzysztof , Zabinski Piotr
Published: February 2020

The d-Block metals such as cobalt and nickel are widely applied in chemical industry as catalysts in reactions producing, among others, liquid or gaseous fuels. The best parameters are featured by precipitation catalysts modified with precious metals. Due to a very high price of platinum metals, it is important to search for solutions that could lower their quantity while maintaining similar catalytic properties.

An innovative approach is the use of a magnetic field to modify the crystalline structure of coatings, which, especially for ferromagnetic elements, can improve their catalytic properties.

Magnetic field applied parallel to the surface of the electrode generates convection of the electrolyte; it results in a laminar flow on the surface of the electrode which reduces the diffusion layer and increases the concentrations gradients. This results in change of the size of the grains and thus can also influence the texture and formation of various phases of the deposits. These various effects can be caused at the same time by the above mentioned convection but also by the magnetic properties, when the field is superimposed the growth in the direction of easier magnetization appears.

Optimal composition, structure and morphology of cobalt matrix alloys with respect of hydrogen evolution performance will be sought through selection of proper composition of electrolyte, changes of electrolysis parameters and by application of external electromagnetic field with intensity up to 12 Tesla.
CuIn(Ga)Se2 Solar Cell Fabricated By All Wet-Processes
Authors: Park Kangju , Park Sungkyu , Lee Dajeong , Jin Hyunsoo , Gwak Jihye , Kim Yang Do , Lee Dongyun
Published: February 2020

CuIn(Ga)Se2, I-III-IV chalcopyrite compound semiconductors, are attractive for thin film solar cells. Recently, energy conversion efficiency of CuIn(Ga)Se2 solar cells has been achieved over 20% based on vacuum process. To reduce fabrication cost, many efforts have been focused on non-vacuum process, and in this study we tried to fabricate the cells by almost all wet-processes; CuIn(Ga)Se2
absorption layers and In2S3 buffer layers were electrochemically deposited, and ZnO window layers were formed by solution based chemical methods. The deposited CuIn(Ga)Se2 absorption layers were heat-treated to improve crystallinity; however, due to surface cracks formed during heat-treatment, it was hard to adopt electrochemical method to form the absorption layers. Authors solved the problem to compensate the cracks by two-step electrodeposition process. Cd-based thin films had been used as buffer layers for a while, but nowadays many studies reported Cd-free buffer layers for CuIn(Ga)Se2 solar cells due to environmental destruction by toxicity of Cd. Therefore, we used In2S3 buffer layers forming by electrochemical method instead of Cd-bsed thin films. ZnO window layers were then deposited by solution based process in compact wire forms. We will discuss in this presentation about microstructures, chemical compositions, and light absorption abilities of each layer. And solar cell efficiency will also be presented.
Effects of Additives on Performance of Zinc Air Battery
Authors: Wu Ching-Chen , Huang Shih-Hsuan , Hsueh Kan-Lin , Chang Wen-Sheng , Yang Chang-Chung
Published: February 2020

Abstract

Appropriate energy storage plays a very important role in a wide range of applications, including frequency regulation of renewable energy sources, peak-shaving of electrical grid, emergency power, and portable power. Metal-air batteries have long been a subject of research since they can be used in many applications, such as small batteries for watches, acoustical devices, and as large batteries for electric vehicles. There is a wide variety of applications for zinc metal as high capacity anodic material in the secondary alkaline batteries due to its high specific energy, good reversibility, environmental friendliness, low equilibrium potential, low cost, and no-toxicity.

During battery charging, formation of zinc dendritic deposits in alkaline electrolytes severely decreases the cycle life of zinc rechargeable batteries. Uneven current density distribution, local concentration gradient variation, preferential crystalline growth of zinc causes the formation of dendrites. In order to suppress the dendritic growth, many inorganic additives such as CdO, PbO, Pb3O4, In2O3, and Bi2O3 have been tested. To decrease the hydrogen production potential, organic materials also have been studied, such as, poly vinyl alcohol (PVA), triethanolamine (TEA), ethylene-diamine-tetra-acetic acid (EDTA), poly-oxye-thylene sorbitan mono-laurate (Tween 20) and tartaric acid.

In this study, the electrochemical behavior of zinc deposition in electrolyte with various additives is investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The corrosion behavior of zinc in alkaline solution with different additives is also studied. The morphologies and crystalline structures of various Zn deposits are examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. We found that zinc dendrite was eliminated by addition of EDTA and Tween 20. Same components can also improve the stability of zinc in alkaline solution. This work was supported by Bureau of Energy, Ministry of Economic Affairs.

Key word: zinc dendrite, corrosion, solution additives
A Study on Workability and Durability of Different Plating Thickness of Silver on Monel As a Cathode Material for Oxygen Reduction
Authors: Dotel Utsav Raj
Published: February 2020

The higher overvoltage for the oxygen reduction reaction (ORR) limits the performance of electrochemical system such as alkaline fuel cell, deoxygenation cell, etc. where the higher oxygen reduction rate is desirable. Silver, having similar mechanism for oxygen reduction as platinum, is one of the cheaper alternative as oxygen reduction. Silver plated on suitable substrate can significantly decrease the cost of oxygen reduction material. The study focuses on the cathodic property of four different silver plating thickness (0.2, 0.5, 1.0, 2.0 µm) on monel, high nickel-copper alloy, for oxygen reduction, and their durability in oxygen reduction process. A special two chamber electrochemical cell separated by cation exchange membrane (CEM), is constructed for conducting the electrochemical experiments. The experiments were performed at room temperatures and 0.5 M NaCl solution and seawater was used as electrolyte. The potentiodynamic and potentiostatic test were performed for the analysis of oxygen reduction property of different thickness of silver on monel. The anodic polarization and scanning electron microscope (SEM) were used for studying the durability of the specimen, with focus on erosion and erosion induced corrosion of the silver plated monel. The electrochemical experiments were performed with the dimensionally stable anode (DSA) and the saturated calomel electrode (SCE) as counter electrodes. The current density for oxygen reduction for four different thickness silver layer was similar, and the oxygen reduction to water by 4- electron pathways was evident in on all samples. The plated layer of 0.2 µm was observed to be the most affected sample and there was observation of small pits throughout the surface. There was no significant effect on 0.5, 1.0 and 2.0 µm silver plated layer. Energy-dispersive x-ray spectroscopy (EDS) showed the formation calcium hydroxide on the surface of the cathode material after 48 hours potentiostatic test on seawater. The result indicate that the durability is of more concern than electrochemical property for oxygen reduction on different thickness silver plated layer on monel.
The Characteristics of the Bismuth Telluride Based Materials Via Gas Phase Reaction Method
Authors: Koo Hye Young , Ha Gook Hyun
Published: February 2020

Bismuth telluride based alloys powders are well known as thermoelectric materials near room temperature in 200~450K. Thermoelectric effect is direct conversion between thermal and electrical energy. Thermoelectric generator has several advantages such as eco-friendly (reusing the waste heat), reliable source of energy, simple maintenance, no-noise, long life time etc. But the low convert energy efficiency and high unit cost of production is still problem to solve. Energy conversion efficiency is involved with figure of merit ZT (ZT=σS2T/κ) where σ is the electrical conductivity, S is the Seebeck coefficient, T is the absolute temperature, κ is the total thermal conductivity. To enhance the energy conversion efficiency of thermoelectric materials, stoichiometrically dispersed powders within fine sized one particle has an advantage because of its composition uniformity. Spray pyrolysis is well known process as gas phase reaction method. The effects of the morphological, electrical and thermal properties of thermoelectric materials prepared by spray pyrolysis were investigated in this study. The phase of powders and bulk were analyzed by X-ray diffraction (XRD). The microstructures of powders and bulk were characterized by field emission scanning electron microscopy (FESEM). The thermoelectric properties of bismuth telluride based materials were analyzed using ZEM-3 (Ulvac-Rico) and thermal conductivity were calculated by the thermal diffusivity measured by the laser flash method (LFA457, Netzsch).
Using of Finite Elements Modeling Computer Simulation in Impedance Prediction and Data Evaluation
Authors: Vanýsek Petr , Vyroubal Petr , Novák Vitězslav
Published: February 2020

With the electrochemical impedance measurement capability becoming more and more standard in the present day electrochemical instrumentation, the technique is also being introduced in experimentation and more routinely at that. While the danger of misinterpretation based on analogs derived from equivalent circuits remains as it always has been, the occurrence of such interpretation is increasing because the impedance nonlinear least square fitting procedures are often included in the instrumental software package and allow mechanical modeling without requirement of deeper understanding the fundamentals. While this is natural consequence of the mass availability, some undesirable outcome may be for example alleviated by closer attention to the chosen sample geometry.

The sample geometry and the location of the electrodes (often four, in the 4-point measurement) is crucial in collecting proper impedance data, interpretation of the impedance measurements, and correlating the results to the properties of the studied material. As an example, the included picture shows a simulation of resistance as it would be measured on a rod (left) of a varying length. The rod has a radius of 14 mm and the contact electrode (“zero resistance”) covers the entire cross sectional bottom of the rod. However, the upper electrode, placed on the axis of the rod, has a radius of only 7 mm, thus only area under the electrode is covered. The graph on the right shows the calculated measured resistance, divided by the rod length, as a function of the length of the rod. If the upper electrode covered the entire cross section, then the value of such resistance should be constant (expected, but also verified by a simulation). However, with the upper electrode smaller, the scaled resistance is higher for thinner disks (shorter rods) and then it decreases, reaching a limiting constant value for long rods. This value corresponds to the value calculated, for any distance, for rods with electrodes completely covering both ends. The simulation for this work was done using the ANSYS software package.

In our experimental work the impedance measurements that we perform on doped conducting ceramics, the electrode placement is extremely crucial as the samples are thin disks and the advantage of the long rods cannot be utilized. We will demonstrate some experimental measures that we utilized to maintain uncertainly arising from the geometry issue minimal.

Acknowledgement

This research has been financially supported in part by the Ministry of Education, Youth and Sports of the Czech Republic under the project CEITEC 2020 (LQ1601), under NPU I program (project No. LO1210) and the COST project LD15068.

Figure 1
(Invited) Electrochemical Impedance Spectroscopy for Polymer Electrolyte Membrane Fuel Cells: Understanding the Relationship Between Liquid Water and Performance
Authors: Bazylak Aimy
Published: February 2020

The hydrogen polymer electrolyte membrane (PEM) fuel cell provides enormous potential for a future with clean energy. However, due to cost and inefficiency barriers, PEM fuel cells have not yet reached widespread commercial adoption. Mass transport limitations arising from liquid water flooding in the PEM fuel cell leads to inefficiencies. If these issues become resolved, smaller and more reliable devices could be produced at a lower cost. Mass transport limitations can be minimized through the development of optimized materials, which have tailored pore structures, connectivities, conductivities, and surface wettabilities. Currently, the porous materials in PEM fuel cells have not been customized for mass transport, due to the lack of information about their structure and the dominating mass transport mechanisms. In this talk, our use of electrochemical impedance spectroscopy (EIS) techniques for investigating the role of liquid water transport in the PEM fuel cell will be discussed. I will also discuss how we combine our EIS measurements with complementary models and measurements to inform the design of next generation porous materials for advanced performance.
Practical Evaluation Method of Oxygen Precipitation in the Czochralski Silicon
Authors: Lee Anselmo Jaehyeong , Hong Sejun , Kim Ja-Young , Kang Hee-Bog , Lee Sung-Wook
Published: February 2020

Oxygen precipitates in Czochralski silicon (CZ-Si) are still considered as the major process-induced defects found in semiconductor device fabrication process because the role of oxygen precipitates in device process such as gettering of metal impurity, prevention of undesired wafer deformation, and degradation of carrier lifetime is quite significant to manufacture high-performance devices. Until now, various theoretical models to predict the oxygen precipitation in CZ-Si with respect to the interstitial oxygen (Oi), vacancy (CV), and the process temperature T have been suggested. However, the complexity and calculation time of a model strongly depend on the accuracy of the model. Thus, it is difficult to apply them on the evaluation of oxygen precipitation regularly in conventional wafer production. Hence, a practical and simple method to evaluate oxygen precipitation should be proposed.

In this work, we derived the parameters that indicate the thermal stability and formation rate of the precipitate nuclei by analyzing as-grown oxygen precipitates formed in a p-type CZ-Si. First, we calculated a cumulative distribution function (CDF) of as-grown precipitate density with respect to the thermal history of CZ-Si crystal from the theoretical nucleation rate J(Oi, CV, T) [1]. After that, we fitted the CDF mathematically into the temperature-dependent precipitate density measured after slow ramped anneals with 1 K/min [2] at various stability temperatures followed by a growth anneal at 1000°C for 16 hours. Moreover, the first derivative Je
(T) of the CDF was also calculated which was associated with an effective nucleation rate. The extreme point (T
C, Je
(TC)) on the Je
(T) was determined as a new parameter that represents the precipitate behavior at a measured point. Finally, we correlated the parameters to the experimental results measured in various crystals after the test heat cycle started at 800°C for 4 hours and followed by 1000°C for 16 hours. As shown in Fig. 1, we found that both T
C and Je
(TC) were strongly correlated to the precipitate density, which means that the parameters were possibly applied to evaluate the behavior of oxygen precipitation in a crystal after various thermal processes.

Fig. 1 Correlation of the T
C (a) and Je
(T
­C) (b) to the precipitate density measured after 2-step annealing starts at 800°C for 4 hours and followed by 1000°C for 16 hours.

[1] G. Kissinger, D. Gräf, U. Lambert, and H. Richter, J. Electrochem. Soc.
144, 1447 (1997).

[2] G. Kissinger and J. Dabrowski, J. Electrochem. Soc.
155, H448 (2008).

Figure 1
(Invited) Silicon Nanowires: Donors, Surfaces and Interface Defects
Authors: Fanciulli Marco , Paleari Stefano , Belli Matteo , Lamperti Alessio
Published: February 2020

Group IV semiconductor nanowires have been investigated experimentally and theoretically for several years. Their intriguing and yet not fully understood properties and the potential for applications in nanoelectronics, spintronics, energy harvesting, production and storage, sensors, and neuroelectronics motivate this research effort. Due to the high surface area SiNWs and GeNWs represent also a perfect material science lab to investigate with high accuracy specific issues related to defects and interfaces. The investigation of defects at the interface between silicon and silicon oxide becomes very important when the SiNW diameter reduces below 10-20 nm and the surface-to-volume ratio increases [1, 2]. In the present work we focus on the investigation of the doping of silicon nanowires addressing the role of hydrogen, as well as other passivating species, and Pb defects at the Si/SiO2 interface [3-5] in the donor deactivation mechanisms and the role of the confinement and dielectric mismatch in determining the donor electronic wave function. To address these intriguing issues we have used different complementary experimental techniques such as electron paramagnetic resonance (EPR), both continuous wave and pulsed, FT-IR, and MD-PICTS. Silicon nanowires have been produced by metal-assisted chemical etching (MACE) [6, 7] using either Ag nanoparticles or a thin Au layer as catalyst and further processing has been used to reduce the size of the nanowires. The reported results are relevant for the wide range of applications exploiting the peculiar silicon nanowires electronic properties and surface reactivity. GeNWs and core-shell heterostructures (Si/Ge) produced by vapor-liquid-solid growth have been also investigated and results on the dominant defects in these nanostructures will be discussed.

References:

[1] V. Schmidt, S. Senz, and U. Gösele, Appl. Phys. A. 86, 187 (2007)

[2] M. T. Björk, H. Schmid, J. Knoch, H. Riel and W. Riess, Nature Nanotech. 4, 103 (2009)

[3] M. Fanciulli, A. Vellei, C. Canevali et al., Nanosci. Nanotechnol. Lett. 3, 568 (2011)

[4] M. Fanciulli, A. Molle, S. Baldovino, A. Vellei , Microelectronic Engineering 88, 1482 (2011)

[5] M. Fanciulli, M. Belli, S. Paleari, A. Lamperti, M. Sironi, and A. Pizio, ECS J. Solid State Sci. Technol. 5(4), 3138 (2016)

[6] Z. Huang, N. Geyer, P. Werner et al., Adv. Mater. 23, 285 (2011)

[7] C. Canevali, M. Alia, M. Fanciulli, M. Longo, R. Ruffo, C.M. Mari, Surface & Coatings Technology 280, 37 (2015)
Conductive AFM Topography of Intrinsic Conductivity Variations in Silica Based Dielectrics for Memory Applications
Authors: Buckwell Mark , Zarudnyi Konstantin , Montesi Luca , Ng Wing Hung , Hudziak Stephen , Mehonic Adnan , Kenyon Anthony Joseph
Published: February 2020

As flash memory approaches its scaling limit, resistive RAM (ReRAM) devices are showing promise in providing the next generation of electronic memories. This comes about as a result of their simple structure, small size and low operating voltages, enabling denser device packing and lower power consumption. Many materials have shown desirable properties as thin film active layers in ReRAM architectures, yet silicon based memories allow for facile integration into existing CMOS infrastructures, making them a particularly suitable class of devices for development. We have looked specifically at devices containing amorphous silicon suboxide or hydrogen silsesquioxane (HSQ) active layers sandwiched between a number of different electrode materials, including titanium nitride and platinum. Here, we present recent characterisation results in which we have probed the three-dimensional structure of conducting filaments in our silicon memories. These filaments govern the switching mechanism that gives dielectric materials their memory function and are thought to be composed of oxygen vacancies, generated as the device is subjected to an electric field. Such features are difficult to image with conventional topographical and cross-sectioning techniques, owing to their low contrast against the background of pristine material. Our results demonstrate the importance of conductive atomic force microscopy for three-dimensional analyses and show that the filament formation is closely linked to the pristine structure of the dielectric. Growth pathways conform to the intrinsic inhomogeneities of the films, a feature that is thought to produce defect clustering and thus promote the generation of oxygen vacancies under electrical stress. We have also been able to demonstrate, for the first time in an intrinsic switching material, that multiple growths compete to bridge the active layer while only a single pathway is finally successful.
(Invited) Electrochemical Gating-Induced Hydrogenation in VO2 Nanowires at Room Temperature
Authors: Kanki Teruo , Sasaki Tusbasa , Tanaka Hidekazu
Published: February 2020

The transport characteristics of transition metal oxides are sensitive to redox reactions because the valence numbers of the transition metal ions are easily changed by the reactions, which affect the carrier density and/or stabilization of the crystal structure. Conventionally, controlling the amount of hydrogen/oxygen ions in an oxide has been conducted by annealing the samples under redox gas atmospheres, in an aqueous solution and with a hydrogen spillover method. Every method requires high temperatures of at least 150 °C. Recently, on the other hand, an electric field has been shown to be a means of both hydrogenation and oxidization in oxides at room temperature. Thus electrochemical gating including water electrolysis has a full potential to allow hydrogen storage and tuning of doping level of electron carriers at room temperature.

In this research [1], reversible and drastic modulation of the transport properties in vanadium dioxide (VO2) nanowires by electric field-induced hydrogenation at room temperature was demonstrated using the nanogaps, separated by humid air in field-effect transistors with planer-type gates (PG-FET). These PG-FETs allowed us to investigate behavior of revealed hydrogen intercalation and diffusion aspects with time and spatial evolutions. These results show that air nanogaps can operate as an electrochemical reaction field, even in a gaseous atmosphere, and offer new directions to explore emerging functions for electronic and energy devices in oxides and will lead to the realization of new gas-sensing, storage applications and also ion pumps in a wide range of solid-state materials.

[1] T. Kanki et al, Sci. Rep. 5, 17080 (2015).
(Invited) Gate Stack Technology for Advanced AlGaN/GaN Mos-Hemt Power Devices
Authors: Watanabe Heiji , Asahara Ryohei , Ito Joyo , Watanabe Kenta , Nozaki Mikito , Yamada Takahiro , Nakazawa Satoshi , Anda Yoshiharu , Ishida Masahiro , Ueda Tetsuzo , Yoshigoe Akitaka , Hosoi Takuji , Shimura Takayoshi
Published: February 2020

AlGaN/GaN high electron mobility transistor (HEMT) has gained much attention as next-generation high frequency and high power devices. Since AlGaN/GaN HEMT with Schottky gate is restricted in device application due to large gate leakage current and normally-on operation, metal-oxide-semiconductor (MOS) gate stack with deposited gate insulator has been widely investigated to overcome these limitations. Among various insulating materials, aluminum based oxide such as Al2O3 is one of the potential candidate because of its wide bandgap and high thermal stability. However, large amount of interface traps at MOS interfaces severely degrade both carrier mobility and threshold voltage (Vth) stability. Furthermore, significant electron injection into Al2O3 layer causing positive Vth shift was often observed for Al2O3/AlGaN/GaN MOS-HEMT. We have recently reported that N incorporation into Al2O3 (aluminum oxynitride) significantly reduces not only the negative fixed charges but also the electron traps in Si and SiC MOS devices. In this study, superior physical and electrical properties of AlON gate dielectrics on AlGaN/GaN substrates were demonstrated. We fabricated high-quality AlON/AlGaN/GaN MOS capacitors with improved stability against charge injection and a reduced interface state density. Moreover, the impact of nitrogen incorporation into the gate insulator will be discussed on the basis of results from physical characterizations.
Particle Removal in Wet Wafer Cleaning Processes
Authors: Zhu Ji , Xia Man , Mui David , Kawaguchi Mark
Published: February 2020

Defects in semiconductor manufacturing that originate from add-on particles can contribute to device yield loss. One possible avenue in removing these particles is a wet wafer cleaning process. Single wafer wet cleaning systems are the current industry standard for defect removal due to their superior ability to control particle re-deposition, especially near wafer edge, as compared to batch cleaning systems. However, our experiments have shown that large micron-sized particles re-deposit during a typical single wafer cleaning process in a model system. These particles were moved and re-deposited primarily during the initial wetting stage. A mechanistic model has been developed to estimate the forces acting on the particles at the three-phase contact line during the wetting stage. The model results show that the forces acting on a particle in the wetting stage are orders of magnitude higher than those in the steady state condition (Fig. 1). Thus, particles are more likely to be moved during the initial wetting step. However, if these moved particles were not transported out of the flow boundary, they could re-deposit and stress produced in steady state flow condition is insufficient to remove them.

To further remove smaller particles from wafer surface, a novel particle removal technology based on a polymer solution is reported in this paper. Physical cleaning methods, such as cryogenic aerosol spray, two-phase fluid aerosol spray and megasonic cleaning, have been used in both front-end- and back-end-of-line cleaning processes for a long time. However, all these methods have the risk of damaging fine features on the wafer in today’s advanced process nodes. Thus, there is a need for a damage-free high efficiency particle removal technology. Polymer solutions have long been used in paper making and water treatment industries to aggregate particles either to deposit them on papers or for their removal from water. The same particle aggregation property of polymer solution has been successfully applied to particle removal. High particle removal and no pattern damage have been demonstrated. The particle removal effect is also highly synergistic with SC1 chemistry. By combining these two approaches, particles 25 nm and above can be removed with >90% efficiency.

Fig. 1 Schematic of forces acting on defects during wetting stage. FM is motion induced interfacial force, Fdis the hydrodynamic drag force.

Figure 1
Preventing TSV Protrusion Via Controlling Impurity Content in Copper Electrodeposits
Authors: Lee Ui-Hyoung , Park Chae-Min , Lee Hyo-Jong , Lee Kihyeob , Kim Kangsoo
Published: February 2020

3D IC integration is the latest technological breakthrough for maximizing its performance while reducing wiring lengths, interconnection latency, and power consumption. Through-silicon via (TSV) is an essential feature of the 3D IC integration. Filling high aspect ratio TSVs by the conductive materials can be a challenging task. Copper electrodepostion is often adopted due to its optimal electrical preoperties, simplicity, and cost-effectiveness. However, the coefficient of thermal expansion (CTE) of copper is much higher (16.7 ppm/℃) than that of silicon (2.3 ppm/℃). Therefore, the CTE mismatch between copper and silicon substrate can induce thermal stresses, which may lead to TSV protrusion and interfacial delamination. In previous studies, this is mostly managed via suitable heat treatment. This study however proposes a novel method for controlling TSV protrusion. Copper with JGB (Janus Green B, C30H31ClN6) concentration increases (and at the level of 0.2mM of JGB), while the sheet resistance decrease by 7% for the initial resistance. Here, the crystal growth is not observed that is due to impurity pinning or solute dragging effect at grain boundaries. This leads to the conclusion that controlling impurity contents may relieve stress of TSV overhang area. To prevent TSV protrusion, we also perform the same concentration split tests on TSV pattern wafers.

Figure 1. EBSD IPF maps of Cu electrodeposit after annealing at 80 ℃ for 90 min with various JGB concentrations of (a) 0, (b) 0.01, (c) 0.03, (d) 0.1, (e) 0.2 and (f) 1 mM in the Cu plating bath.

Figure 1
Comparison of Various Low Dielectric Constant Materials
Authors: Hung Wei-jie , Cheng Yi-Lung
Published: February 2020

In order to reduce resistance-capacitance (RC) delay of back-end-of-line (BEOL), a low-dielectric constant (low-k) material with the dielectric constant (k) below 4.0 has been introduced to be used as an insulator of Cu integration from 130 nm technological node. In this study, the electrical and reliability characteristics of various commercial low-k dielectric films with k value ranging from 3.6~2.5 deposited using plasma-enhanced chemical vapor deposition (PECVD) were investigated. In addition to FSG and dense OSG low-k dielectric films, porous OSG (P-OSG) films with two different sacrificial organic porogen precursors (alpha terpinene (ATRP) and cyclooctane (C8H16) were also compared. Although P-OSG films have a low k value, their resistance to the process integration is relatively low, resulting in a higher increase of k value and a degraded reliability performance as compared to OSG film. Hence, it is doubtable to use porous OSG films with a higher porosity in the following advanced technology nodes. Furthermore, the sacrificial porogen precursor used for porous OSG film deposition influences the film’s property. The P-OSG film for ATRP precursor has a better mechanical, electrical, and reliability characteristics as compared to that for C8H16 precursor in this study.
ALD Coatings on Lithium Metal for High Energy Lithium Batteries
Authors: Chen Lin , Elam Jeffrey W
Published: February 2020

Global energy needs demand high-performance energy storage technology for powering portable electronic devices and electric vehicles. However, current lithium ion batteries, the primary energy storage system, cannot meet the increasing demands. The lithium metal battery has attracted much attention due to the extremely high energy density (3,861 mAh/g). However, the dendrite formation during cycling impedes its practical usage. Herein, we will employ atomic layer deposition to design metal oxide coating (Al2O3) and study the mechanism reactions upon the doses of precursors on lithium metal. Latest results including electrochemical testing for different thickness of Al2O3 and in-situ as well as ex-situ investigations will be presented.
(Invited) Template Assisted Synthesis of Porous Metal Oxide and Metal Nanostructures by ALD
Authors: Deng Shaoren , Kurttepeli Mert , Bals Sara , Cott Daire J. , Detavernier Christophe
Published: February 2020

Atomic layer deposition (ALD) has been intensively used to coat porous templates and duplicate the morphology after template removal. Here, we present a systematic investigation on the synthesis of nanoporous Pt and metal oxides via ALD on a sacrificial carbonaceous template: multiwalled carbon nanotubes (MWCNTs).1-3 Pt, Al2O3, TiO2, ZnO and VOx were deposited on MWCNTs, and the samples were subsequently annealed in air to remove the MWCNTs. Scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) showed surprising morphological transitions at the nanoscale, while still maintaining the overall forest-type structure at the micro scale. Hollow Al2O3 nanotubes, chains of TiO2 nanoparticles and 3D networks of interconnected V2O5 and ZnO nanoparticles and Pt nanowires were observed after the removal of the MWCNTs templates (see Fig.1). The following photocatalytic test also revealed that the interconnected TiO2 nanoparticle chains showed high catalytic activity towards the degradation of acetaldehyde under UV light. The investigation in the morphological transition in the case of TiO2 nanoparticle chains showed that the crystallization temperature plays an important role in the formation of the final morphology. In the case of 3D network of Pt nanowires, it showed that a continuous coating of metal on the MWCNTs is not indispensable for achieving a self-supported porous structure after template removal.

1S. Deng et al., Nanoscale, 2014, 6, 6939. 2S. Deng et al., J. Mater. Chem. A., 2015, 3, 2642. 3S. Deng et al., RSC Advances, 2014, 4, 11648.

Figure 1
(Invited) Nanostructured Photocatalysts Prepared By Atomic Layer Deposition
Authors: Szilagyi Imre Miklos
Published: February 2020

Semiconductor oxides are widely used photocatalysts to decompose organic contaminations with solar energy. The activity of these photocatalysts can be further improved by doping them with heteroatoms, by making composites of them with other semiconductor oxide materials, noble metal nanoparticles, organic dyes and other organic absorbers, or by increasing their specific surface using highly structured substrates. Since by ALD uniform thin films with thickness control of sub-nanometer precision can be deposited on nanopatterned surfaces, it is a unique tool for preparing, doping and programming nanoscaled photocatalytic material.

In the lecture several examples will be shown about how various nanostructured photocatalysts can be obtained by ALD, based on our own experience. By combining electrospinning and ALD, WO3/TiO2, ZnO/TiO2 and TiO2/ZnO core/shell Vis or UV active nanofiber photocatalysts were prepared. By using sol-gel and ALD, SiO2/TiO2 core/shell photocatalytic nanoparticles were obtained. Photocatalysts based on biological substrates can be also manufactured by ALD, e.g. TiO2 coated lotus leaves with both superhydrophobic and photocatalytic activities. C60/TiO2 (Fig. 1), graphene oxide (GO)/TiO2, CNT/TiO2, carbon aerogel/TiO2 and PMMA/TiO2 composites are examples for ALD prepared carbon and polymer nanostructure based photocatalysts.

On the previously mentioned substrates, TiO2 thin films were deposited by ALD using TiCl4 or Ti(OPr)4 and H2O as precursors at various temperatures (80, 160, 250, 300 °C), and therefore nanocomposites containing both crystalline and amorphous TiO2 layers were prepared. While TiO2 is considered to have photocatalytic activity only in the crystalline state; unexpectedly, we observed that when TiO2 was deposited in amorphous form on biological or organic substrates, i.e. lotus leaf, C60-OH, GO or PMMA, the amorphous TiO2 layer clearly exhibited photocatalytic property.

Figure 1
A Precise and Scalable Post-Modification of Mesoporous Metal-Organic Framework NU-1000 Via Atomic Layer Deposition
Authors: Kim In Soo , Farha Omar K. , Hupp Joseph T. , Gagliardi Laura , Chapman Karena W , Cramer Chris , Martinson Alex B. F.
Published: February 2020

The connectivity of NU-1000 gives rise to Zr nodes with hydroxyl-containing functional groups pointing into the large 1D mesoporous hexagonal channels of the framework. These free and exposed –OH groups are ideal grafting sites, and they can be easily tailored to serve a specific function. We demonstrate that by performing atomic layer deposition in MOFs (AIM), several oxides can be formed with atomic precision at the exposed –OH sites of NU-1000. Importantly, this process occurs without changing the overall structure of the framework. This talk will discuss recent progress in scaling AIM to 0.2 gram quantities of the ultrahigh surface area (2300 m2/g) framework as well as progress in pinpointing the location and mechanism of surface chemical reactions of catalytically relevant metals. Computational, synchrotron, and in-situ analytical methods including DFT, differential electron diffraction, and in situ FTIR are brought to bear on several new metal systems, many of which show remarkably self-limiting behavior.

The Figure shows a representation of the DFT-derived model of a Zr6 node, highlighting the newly installed metal location. 

Figure 1
Effect of Thickness on Flexible, Electrical and Optical Properties of Ti- ZnO Films on Flexible Glass By Atomic Layer Deposition
Authors: Lee Woo-Jae , Kwon Jung-Dae , Kwon Se-Hun
Published: February 2020

TCO (Transparent Conducting Oxide) on flat glass is used in thin-film photovoltaic cell, flat-panel display. Nowadays, Corning® Willow Glass®, known as flexible substrate, has attracted much attention due to its many advantages such as reliable roll-to-roll glass processing, high-quality flexible electronic devices, high temperature process. Also, it can be an alternative to flexible polymer substrates which have their poor stability and degradation of electrical and optical qualities. For application on willow glass, the flexibility, electrical, optical properties can be greatly influenced by the TCO thin film thickness due to the inherent characterization of thin film in nanoscale. It can be expected that while thick TCO layer causes poor transparency, its sheet resistance become low. Also, rarely reports were focusing on the influence of flexible properties by varying TCO thickness on flexible glass. Therefore, it is very important to optimize TCO thickness on flexible Willow glass.

In this study, Ti-ZnO thin films, with different thickness varied from 0 nm to 50 nm, were deposited on the flexible willow glass by atomic layer deposition (ALD). The flexible, electrical and optical properties were investigated, respectively. Also, these properties of Ti-doped ZnO thin films were compared with un-doped ZnO thin film. Based on the results, when Ti-ZnO thin films thickness increased, resistivity decreased and then saturated; transmittance decreased. The Figure of Merit (FoM) and flexibility was the highest when Ti-ZnO thickness was 40nm. The flexible, electrical and optical properties of Ti-ZnO thin films were better than ZnO thin film at the same thickness.
Plasma-Enhanced Atomic Layer Deposition of Silicon Nitride Thin Film at 100oc Using Novel Silicon Precursors
Authors: Jang Se-Jin , Park Joong-Jin , Kim Sung-Gi , Lee Sang-Do , Yang Byeong-il , Park Jung-Ju , Park Gun-Ju , Seok Jang-Hyeon , Lee Sang-Ick , Kim Myoung-Woon , Park Jae-Min , Hwang June , Lee Won-Jun
Published: February 2020

Recently, the demand for moisture barrier has been increasing as the encapsulation layers of organic electronic devices, such as organic light-emitting diode (OLED) display, organic solar cells, and organic thin-film transistors. Dielectric thin films prepared by plasma-enhanced chemical vapor deposition (PECVD), hot-wire CVD, and atomic layer deposition (ALD) at low temperatures lower than 150°C have been investigated as the moisture barrier. Among them, the multilayered thin structure composed of aluminum oxide or silicon nitride prepared by ALD showed the best results [1,2]. In the present work, we prepared silicon nitride thin films by plasma-enhanced ALD (PEALD) at 100°C using novel silicon precursors, 1,3-di-iso-propylamino-4,4-dimethylcyclodisilazane (CSN-2) and bis-(di-methylamino-dimethylsilyl)- trimethylsilyl amine (DTDN-2H2), and investigated the properties of the deposited films, such as growth rate per cycle, composition, density, wet etch rate, and water vapor permeability. The effects of deposition temperature and plasma condition on the barrier properties were also discussed.

[1] F. Nehm, ACS Appl. Mater. Interfaces, 7 (2015) 22121.

[2] A.-M. Andringa, et al., ACS Appl. Mater. Interfaces, 7 (2015) 22525.

Fig.1. The FTIR spectrum of silicon nitride thin films prepared by PEALD at 100°C using CSN-2 as the silicon precursor.

Figure 1
Determination of Atomic-Layer-Deposited Multilayer Antireflection Coating Parameters Using a Novel X-Ray Reflectivity Approach
Authors: Li Chao , Shahriarian Firouz , Goorsky Mark S.
Published: February 2020

The thicknesses and densities of coatings prepared by atomic layer deposition (ALD) and by other deposition techniques are important to understand their optical, electrical and mechanical properties. Specular X-ray reflectivity (XRR) is a powerful tool that is capable of nondestructively extracting layer thicknesses with angstrom resolution, and what is distinct, determining the layer densities through modeling structures with simulation programs. Unfortunately, problem with modeling usually arises when other layers form at the surface or interfaces, and it is also common to other nondestructive techniques such as ellipsometry. A recent development1 has shown that with differentiating the specular XRR intensity with respect to vertical reciprocal space coordinate, a Fourier transform (FT) approach can provide straightforward information about the layer thicknesses in multilayer systems, which will make it easier to build the XRR simulation model. Therefore, a novel combination of FT and specular XRR simulation would be quite efficient in layer thickness extraction compared with other conventional techniques (e.g. transmission electron microscope (TEM) and ellipsometry). In this study, the novel XRR approach, together with other techniques including optical microscope (OR), spectroscopic ellipsometry (SE), TEM, energy dispersive X-ray spectroscopy and glancing incidence X-ray diffraction, was utilized to characterize the effect of annealing on optical properties of Al2O3/TiO2/Al2O3 multilayer antireflection stack. The films were deposited on (0 0 1) Si wafers using ALD which is a good candidate for multilayer antireflection coatings, due to the self-limiting nature of chemical reactions resulting in the precise control of film thickness and large-area uniformity. The thickness values of the as-deposited layers determined by XRR agree quite well with those obtained from OR, SE and TEM, with the difference below uncertainty levels. This, together with the good correlation between layer densities extracted from XRR and refractive indices measured by OR and SE, demonstrates the validity of the XRR approach. On the other hand, it is revealed that air annealing at 400 °Ϲ for 10 min induces the densification of the TiO2 layer as well as the initiation of crystallization. Meanwhile, both Al2O3 layers keep amorphous after annealing, with the thickness of top Al2O3 layer decreased that is likely due to interdiffusion of Al and Ti atoms between the top two layers, while the thickness of bottom Al2O3 layer increased accompanied with a decrease in density, which is probably attributed to the diffusion of Si atoms from the substrate into layers.

Reference

1B. Poust, R. Sandhu, and M. Goorsky, Phys. Status Solidi A. 206, 1780 (2009).