bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic Layer Deposition of Iridium Oxide Thin Films on Tungsten and Si Substrates
Authors: Zhang Kai , Lin Pengtao , Chen Xin , Baumgart Helmut , Bradas James
Published: February 2020

Both Iridium and Iridium oxide thin films have been extensively investigated for their various applications. For Ir, it is a potential optical material in Fresnel zone, X-ray microchannel plates, inductive grid filters. On the other hand, iridium Oxide films can be used as a reference electrode and PH measurment in the field of biology environment and the food, nuclear, gas and oil industry due to their low resistivity, high transmittance, biocompatibility and good oxygen diffusion barrier properties [1,2].

The Atomic layer deposition (ALD) is considered as a half reaction of a chemical vapor depositon (CVD), where diferent ALD chemical precuresors are alternatively introduced into an ALD reaction chamber. The self-limiting surface reactions in each ALD cycle consequently result in precise layer thickness control, stoichiometry, composition, uniformity of large area on the substrate. ALD also can be used to deposit conformal film onto very complex substrate or template surfaces. In addition the ALD thin films can be deposited at low growth temperature. Therse are the advantageous properties of ALD which make it more competitive and promising.

In this work, the irdium oxide films were grown on Si and tungsten substrates by ALD using (Ethylcyclopentadienyl) (1, 5-cyclooctadien) iridium (C14H19Ir) and H2O/O2 as precursors for iridium and oxygen, respectively. The C14H19Ir was heated to 50 oC, while the H2O and O2 precursors remained at room temperature. The ALD for growth temperature was varied over a range of various temperatures in order to determine the ALD process window. The iridium oxide thin films were subsequently annealed at 700 oC for 1 hour in a furnace under O2 atmosphere. In this study we report successful synthesis of IrO2 films on tungsten metal substrates and native oxide covered Si wafers. Detailed physical characterization of ALD Iridium oxide thin films has been performed using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), UV-VIS-NIR spectrometer.

References:

J. Hämäläinen, E. Puukilainen, M. Kemell, L. Costelle, M. Ritala and M. Leskelä, Chem. Mater. 21 (20), 4868 (2009).

T. Aaltonena, M. Ritalaa, V. Sammelselgb and M. Leskeläa, Journal of The Electrochemical Society, 151(8) G489 (2004).

Figure 1
Electrochemical Behavior and Analysis of Organic Additives in Cobalt Damascene Baths
Authors: Pavlov Michael , Lin Danni , Shalyt Eugene , Yan Xiaodong
Published: February 2020

The copper dual damascene process has been used in semiconductor manufacturing since it was introduced by IBM in mid-1990. Since then, copper interconnects shrunk dramatically following the principles of Moore’s law. Currently, there are questions regarding the extendibility of the copper dual damascene flow as the IC industry moves beyond the 10 nm node. Copper interconnects are becoming more compact at each node, causing an increase in the resistance-capacitance delay. Furthermore, voids that occur in heavily scaled vias severely impact yield. Leading semiconductor manufacturers are exploring novel metallization methods to solve these issues. One way to solve the problem is to identify metallization alternatives that provide resistance benefits over conventional technology without compromising reliability and yield. Cobalt is considered as a potential replacement candidate for copper.Cobalt plating baths typically contain cobalt salt, boric acid, and organic additives . We have recently developed new analytical techniques for complete analysis of cobalt damascene plating baths.

Electrochemical methods are used to study behavior and analyze multiple organic additives present in cobalt plating baths , while other bath components can be effectively analyzed with traditional titration and/or spectroscopic methods. 

Fig. 1 shows the effects of commercial Suppressor and Accelerator additives used for cobalt plating. The voltammograms indicate decreased plating rate when Suppressor additive is injected into the VMS electrolyte. VMS stands for Virgin make-up solution, which contains only inorganic components. The injection of Accelerator into the electrolyte with Suppressor causes increased plating rate. Fig. 2 shows response curves of Suppressor and Accelerator. All responses are reproducible and allow accurate determination of organic additives in plating baths. This article will also reveal the effects of other bath components on the plating properties of cobalt. We will also present statistical results of electrochemical analysis of both organic additives.

Figure 1
Oxidation Extent of Graphene Oxide on Copper Electroplating for Fabricating Printed Circuit Boards
Authors: Hsieh Chun , Zeng Wei-Yang , Dow Wei-Ping
Published: February 2020

Single layer and multi-layer graphite, known as graphene, is currently a star in material science, due to their excellent mechanical stiffness, outstanding barrier resistance, remarkable electron mobility, and their outstanding thermal and electrical conductivity. The most common way to exfoliate graphite is to use a strong oxidizing agent to produce graphene oxide (GO). Since GO has a large amount of oxide functional groups, it is not only well dispersed in water but also can be coated on a substrate by chemical grafting method using a wet process. Traditional process for metallizing a printed circuit board (PCB) used copper electroless deposition as conducting layer, herein, we used graphene to substitute the copper electroless deposition as the conducting layer of through holes of PCBs. In this work, GO was prepared by modified Hummer’s method, and then to be grafted on the sidewall of through holes of PCBs. However, only reduced GO (rGO), that is graphene, has excellent conductivity, so it can be used as seed layer for copper electroplating. In this work, we discussed the effects of oxidation extents of graphene oxide on copper electroplating on a PCB. The parameters which influence the quality of GO such as oxidation temperature, reaction time and quantity of oxidizing agent were investigated by using electron spectroscopy for chemical analysis (ESCA) and Raman spectroscopy techniques, respectively.

Keywords

Graphene, Oxidation reaction, copper electroplating, printed circuit board

References

[1] S. Peng, X. Fan, S. Li, and J. Zhang, J. Chil. Chem. Soc., 58, 2213 (2013)
UV Laser Annealing Effect on Mechanical Properties of Boron Doped Amorphous Carbon Films As Hardmasks
Authors: Youn Chulmin , Yang Jaeyoung , Lee Sungwoo , Hur Ginyung , Choi Taekjib
Published: February 2020

The hard forms of amorphous carbon (a-C, diamond like carbon) include hydrogenated amorphous carbon (a-C:H) and tetrahedral amorphous carbon have raised interest as coating materials. Recently, boron doped amorphous carbon films have been studied as hardmask materials. The hardmasks are utilized to fabricate advanced semiconductor devices, including dynamic random access memory (DRAM) and vertical NAND flash memory. As decreasing of feature sizes on DRAM and NAND, the hardmask materials need to exhibit a high etch selectivity with low internal stress and good mechanical strength.  In this work, we have prepared boron doped amorphous carbon film deposited with the fixed B2H6 flow rate as a function of the process temperature using plasma enhanced chemical vapor deposition (PECVD). Boron has been widely known efficient dopant for passivating the oxidation of various carbon materials. We investigated the physical and optical properties of film with the refractive index, hardness and chemical bonding configuration. Especially, the effect of ultraviolet (UV) laser annealing on the hardness was studied using nano-indentation. UV annealing caused a change of chemical bonding configuration, i.e., sp2/sp3 bonding ratio and C-H bonds, through analysis of the Fourier transform-infrared (FT-IR) and RAMAN spectrum. UV annealed boron doped amorphous carbon thin films exhibited an enhanced hardness, which leads to high etch selectivity. Our results could provide a route to high etch selective hardmask materials development.
A Silicon Hollow Graphene Nanoshell Li-Ion Anode Composite Material
Authors: Banek Nathan A , Hays Kevin Alan , McKenzie Kevin R. , Wagner Michael J
Published: February 2020

The Li-ion battery provides the majority of powertrain energy for today’s electric vehicles (EVs). The usable range of EVs is largely limited by the Li-ion storage capacity in a Li-ion cell. In addition to low range, most EVs require 4 - 12 hours of charge time. Silicon, a Li-alloy alternative anode, has much greater gravimetric and volumetric capacities compared to graphite (3579 mAh/g vs. 372 mAh/g and 8335 mAh/cm3 vs. 818 mAh/cm3 for Li15Si4 vs. LiC6). In addition to the increase in capacity, Si is nontoxic, highly abundant, and inexpensive. Despite these advantages, the volumetric expansion of LixSi and poor electrical conductivity of Si makes developing a pure silicon anode with reasonable cycle life a seemingly insurmountable challenge. Composite electrodes of Si and C could represent the next-generation of Li-ion anodes for EVs. Hollow graphene nanoshells (HGNS) are a conductive graphitic carbon ~50 nm in diameter that can charge in minutes and have cycle lives of over 1000 cycles with minimal fade making them a promising support material for silicon nanostructures of higher capacity. Utilizing a facile low-temperature solution synthesis method, silicon was synthesized onto the HGNS to produce Si/HGNS composites in high yield and purity. The electrochemical performance of the composite material had a reversible capacity of ~3500 mAh/g Si (1400 mAh/g composite) after a C/20 formation cycle with 80% first cycle Coulombic efficiency. At an increased rate of C/2, a reversible capacity of ~2800 mAh/g Si (1100 mAh/g composite) is achieved with stable cycling performance. Utilizing this solution synthesis method, efficient mixing of Si with HGNS can produce Li-ion anode composites greater than 3 times the capacity of graphite with stable performance at charging rates required for upcoming EV powertrains.
Direct Observation of Lattice Aluminum Environments in Li-Ion Cathodes NCA and Al-Doped NMC Via 27al MAS NMR Spectroscopy
Authors: Dogan Fulya , Vaughey John T. , Iddir Hakim , Key Baris
Published: February 2020

Direct observations of local lattice aluminum environments have been a major challenge for aluminum bearing Li-ion battery materials such as LiNi1-y-zCoyAlzO2 (NCA) and aluminum doped LiNixMnyCozO2 (NMC). 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy is the only structural probe currently available that can qualitatively and quantitatively characterize lattice and non-lattice (i.e. surface, coatings, segregation, secondary phase etc.) aluminum coordination and provide information that helps discern its effect in the lattice. In the present study, we use NMR to gain new insights into transition metal (TM)-O-Al coordination and evolution of lattice aluminum sites upon cycling. With the aid of first principles DFT calculations, we show direct evidence of lattice Al sites, non-preferential Ni/Co-O-Al ordering in NCA, and the lack of bulk lattice aluminum in aluminum doped NMC. Aluminum coordination of paramagnetic (lattice) and diamagnetic (non-lattice) nature is investigated for Al-doped NMC and NCA. For the later, the evolution of the lattice site upon cycling is also studied. A clear re-ordering of lattice aluminum environments due to nickel migration is observed in NCA upon extended cycling.
Investigating the Influence of Transition Metal Composition on High-Voltage Cathodes Performance By Using Magnetic Susceptibility
Authors: David Lamuel , Sefat Athena S , Cakmak Ercan , Sheng Yangping , Li Jianlin , Wood David L , Daniel Claus , Mohanty Debasish
Published: February 2020

High-voltage cathodes are indispensable to enable the high-energy-density batteries. This work demonstrates the effect of Ni/Mn composition on structure of pristine and cycled layered Li-Ni-Mn/Al-Co oxide (NMC and NCA) during high-voltage operation (4.75V vs. Li). Particle morphology and elemental composition of all material was investigated by using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX) analysis. Among the various materials NMC622 had the best uniformity in particle size at ~10um while the other materials ranged from ~5-10um. X-ray diffraction (XRD) spectra of the as-obtained powders showed little variation in the structure of layered oxide with different transition metal ion compositions. Temperature dependent magnetic susceptibility results show that NMC622 (with 60% Ni) is layered with less magnetic ordering which was very similar to that of NCA811 (80% Ni) while NMC442 (40% Ni) showed strong magnetic ordering, which suggests exchange of strong magnetic interaction among transition metal ions in NMC442 material. The structural differences that were observed from magnetic susceptibility results were correlated with the electrochemical performance. The detailed pristine structure and structural evolution in layered oxides varying the Ni concentration in the light of magnetic susceptibility will be presented.
High Capacity and High POWER Ncm/Graphite Lithium ION Battery Using Microgrid® Expanded Metal Current Collectors
Authors: Hart John
Published: February 2020

To achieve better sustainable power application of LiNi1/3Co1/3Mn1/3O2/graphite lithium ion battery, new cell structures using Microgrid® expanded metal current collectors were studied. By adopting the Microgrid® foil for cathode electrodes, the performance of LiNi1/3Co1/3Mn1/3O2 electrodes was significantly improved at high rate discharge at both room and low temperature. Scanning electron microscopy was carried out to reveal coating features of Microgrid® cathode electrodes. The loading density of active materials can be increased by the pore structure, and the 10C capacity retention of Microgrid® electrode is 25.8% higher than that of a conventional electrode after 100 cycles, and nearly doubled for the initial discharge at 10°C. There is the potential for enhancement of cell performance using Microgrid® foils in place of conventional foils with LiNi1/3Co1/3Mn1/3O2 cathode and graphite anode. The Microgrid® full cell shows 209.0% increase of capacity with respect to conventional cells of Al and Cu foils for 10C after 100 cycles and keeps the retention rate 12% higher than the latter.  Microgrid® foils can potentially be applied to other electrode materials which are suffering from capacity fade at high C-rates and at higher loading densities.
Ternary Cathode Materials Prepared By Induction Sintering Incorporated with Carbon Coating Technique for High Performance Li-Ion Batteries
Authors: Hsieh Chien-TE
Published: February 2020

Lithium-ion battery has become the front-runner among rechargeable-battery technologies, having found applications in industries as diverse as portable electronics and electric vehicles (EVs) [1,2]. Recently, a number of attempts have been made to partially substitute Ni with other elements such as Co and Al doping. Among the resulting cathodes, LiNi0.8Co0.15Al0.05O2 (LNCA) is considered as one of the promising alternatives to replace LiCoO2 owing to its higher specific capacity and better environmental friendliness [3,4]. Generally, solid-state calcination was carried out under oxygen-containing atmosphere at 700–900°C for 15 hr. To shorten the growth period, this work proposes an efficient method of preparing LNCA cathode material by using induction sintering incorporated with carbon coating technique. The electrochemical performance of C-coated LNCA cathodes was well characterized by cyclic voltammetry (CV) and charge-discharge cycling. This study aims at examining the possibility of induction sintering route for preparing C-coated LNCA cathode materials for high-performance Li-ion batteries in practical or industrial applications.

 

We have successfully investigated the electrochemical performance of LNCA cathodes, using CV and charge-discharge cycling at 0.1−5C. An efficient induction route was adopted to synthesize LNCA powders at 700°C within a shorter calcination period (3 h), as compared with traditional heating methods. The as-prepared layered C-coated LNCA crystals possessed a low degree of cation mixing with highly hexagonal ordering. For 0.1C charge-discharge cycling, the discharge capacity of LNCA cathode could attain as high as 201 mAh g-1, and there was an increased capacity of 10.3% as compared with the fresh one. On the basis of the experimental results, the C-coated LNCA cathode remained higher capacity retention of 88.1% after 50 cycles at 1C. Accordingly, the induction route offered a promising pathway to commercially synthesize high-crystalline LNCA cathode materials for high-performance Li-ion batteries, favoring the application of EVs in the near future.
Influence of LiFePO4 Electrode Structure on Electrochemical Property
Authors: Yasumiishi Hirofumi , Yamaya Ryuta , Kitagawa Takao , Nakabeppu Tetsuya
Published: February 2020

１．Introduction

Well known as safety, non-toxicity and remarkable thermal stability, LiFePO
4
(LFP) is one of a promising candidate for the cathode material of large size lithium ion batteries. However, LFP is also known as the material with poor electrochemical property at low temperature. In order to improve the low temperature properties of LFP, several attempts were made to control the particle size and the morphology of LFP particle to increase the diffusion in solid and the surface reaction area.
1

）

On the other hand, along with the increase of LFP’s specific surface area, the problems arised for the manufacturing of the electrode. The problems are the increase of the amount of binder needed and the LFP agglomeration which leads to the increase of the surface roughness of the electrode. In this research, we have studied the influence of the LFP’s primary and secondary particle size and the morphology of the secondary particle to improve the electrochemical properties.

２．Experimental

LFP was synthesized by a hydrothermal process. Spherical secondary particle with the size ranging from 10 to 30 μm in diameter was observed from the spray-drying of the LFP slurry. The electrode slurry mixing ratio was LFP:AB:PVdF=90:5:5 wt.%. After the slurry was coated on Al foil current conductor, it was vacuum dried under @120℃ for 12h、and pressed by a load of 200kgf. The cross-section image of the obtained electrode was observed by SEM. The particle size of the secondary particle was observed with particle size distribution measurements. The electrochemical properties were measured with pouch cell (anode：Li4Ti5O12 electrode, separator：porous polypropylene, electrolyte：1M LiPF6/EC:DEC=1:1 +VC2wt%)

３．Result

The relationship between LFP’s secondary particle size and Output – Direct Current Resistance (DCR) was shown in Fig. 1. The smaller the secondary particle size, the DCR decreased. The porous structure of the LFP’s electrode was thought to have a correlation to the electrochemical characteristics.

Fig.2 shows the cross-sectional SEM images of the electrode which showed the different structure for the electrode manufactured with different particle sized LFP. The bigger the secondary particle size, the bigger the vacant spaces present inside the electrode and the small secondary particle was enclosed in the large secondary particle. The non-uniform structure was observed for the electrode made with large secondary particle compared with the uniform structure made with the small secondary particle. The main factor of DCR increase for the large secondary particle size was thought to relate to the non-uniformity of secondary particle structure and electrode structure.

The relationship between the electrode structure, the secondary particle shape and the electrochemical properties will be studied further.

Ref. 1)　A. Yamada, S. C. Chung and K.Hinokuma , J. Electrochem. Soc., 144, p. A224 (2001)

Figure 1
Understand the Voltage Fade Mechanism of Li-Rich Layered Oxide Cathodes during Extended Cycling
Authors: Ma Quanxin , Dai Changsong
Published: February 2020

Recently, Li-rich layered oxides have attracted much attention for Lithium-ion Batteries (LIBs) because of their high theoretical capacities, low cost, and friendliness. Like other cathodes for a widespread use, Li-rich layered oxides also suffer from natural obstacles, such as low coulombic efficiency at initial charge/discharge process, insufficient rate performance and inferior ability to remain output voltage during the cycles. In this work, Li1.2Mn0.6Ni0.2O2 cathode material was synthesized via a co-precipitation method. Both ex
-
situ X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) measurements are used to reveal its fundamental voltage fade mechanism. The collected results confirm that the change in valence state of Mn ions and structural evolution lead to its voltage fade. Along with increasing the cycles, a shift of the Mn K-edge gradually shifts to a lower energy region, suggesting that an increasing amount of trivalent manganese ions. In contrast, no change is observed on Ni2+ ions. Ligand oxygen ions are directly involved in the charge compensation mechanism.

Figure 1
A Novel Technique to Evaluate the Adhesion Property Between Ceramic Coated Layer and Separator Using Saicas
Authors: Gong Seokhyeon , Lee Yunju , Yeon Daeyong , Lee YongMin , Ryou Myung-Hyun
Published: February 2020

Polyolefin-based microporous membrane has been widely used as a separator for lithium-ion batteries (LIBs), where they impede an internal short between positive and negative electrodes. Consequently, as the large-scale LIBs targeting electric vehicles (EVs) and energy storage systems (ESSs) is attracting the consumers’ interests, the development of safety enforced separators is getting important.

To achieve this goal, the surface coating based on inorganic ceramic particles Al2O3, SiO2, MgO, CaCO3, and etc. have been widely used to improve the mechanical and the thermal properties of the separators. However, the detachment of ceramic composites from the separator surface, which happens during separator preparation and cell assembly process, can cause serious problems in safety and cell performance of LIBs.

Unfortunately, however, there is no quantitative manner to examine the adhesion strength between ceramic composite layer and the separator surface yet. Here in, we introduced a Surface and Interfacial Cutting and Analysis System (SAICAS) to fulfil this purpose. Contrary to the traditional peel-off technique, SAICAS can measure the adhesion strength at a specific depth of coating of operator. Thus, SAICAS can compare adhesion properties in a systematic manner.

We measured the adhesion strength between the ceramic coating layer and the separator, and moreover, the adhesion strength inside the coating layer. Furthermore, we could compare the adhesion strength measured via traditional peel-off test technique. Finally, we investigated the adhesion strength of ceramic coating layer as a function of types and composite ratio of polymeric binder.

 

Acknowledgement

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (2014R1A1A1005861).
Poly(fluorene phenylene) Graft Copolymer As a Novel Binder with Polyvinylpyrrolidone for High-Capacity Silicon Anode in Lithium-Ion Batteries
Authors: Avci Ipek , Taskin Omer Suat , Yuca Neslihan , Cetintasoglu Mehmet Emre , Doğdu Murat Ferhat
Published: February 2020

Rechargeable lithium ion batteries (LIB) have been vastly used in portable devices like cellular phones, laptops, tablets and also in electric vehicles because of their relatively high energy density, good power performance and cycle life. Carbonaceous negative electrode materials, especially graphitic carbons are conventionally used as anode materials at LIBs due to their good cycle-ability and low stable discharge voltage plateau. However, graphite has a low Li atomic density at full Li capacity in carbon intercalation compound (LiC6) which leads to lower theoretical capacity (372 mAh/g). Therefore, different types of anode active materials have been investigated as an alternative to graphite in order to achieve higher capacities. Among them, silicon (Si) is one of the most promising candidate as an anode active material because of its high theoretical capacity (more than 3500 mAh/g at room temperature) and low average discharge potential (∼0.5 V vs Li/Li+).Unfortunately, huge volume expansion (310% at full lithiation of Si) due to the lithium ion diffusion during the lithiation/delithiation process causes drastic capacity fade because of the high internal stresses, loss of electrical contact and the formation of non-electronic and ionic conductive passivation film between the anode surface and electrolyte. Low electrical conductivity of silicon is also another problem that remarkably hinders the rate performance.

In the present work, above mentioned shortcomings are overwhelmed by incorporating tri(ethylene glycol) (TEG) groups over phenylene base units as side chains on the framework of the PFP based conductive polymer. Polyvinylpyrrolidone (PVP) was also used as adhesive to enhance the property of binding, thus decreasing stress-induced cracks. The synthesis was achieved through Suzuki polycondensation reaction in the presence of Pd(PPh3)4 catalyst by using independently prepared TEG functionalized dibromo benzene in conjunction with dioctylfluorene-diboronic acid bis(1,3-propanediol) ester. The obtained conductive and flexible polymer was used as a binder for Si-anode with high performance. It was demonstrated that the designed and fabricated binder polymer with multi-functionality displays a high electronic conductivity, mechanical strength, high polarity, adhesion, and more importantly, the electrolyte uptake arising from its excellent ductility.

Figure 1
(Invited) GeSn Short-Wave Infrared Photodetectors
Authors: Cheng Buwen , Liu Zhi , Zheng Jun , Su Shaojian , Zhang Dongliang , Wu Wenzhou , Xue Chunlai , Wang Qiming
Published: February 2020

Ge photodetector is very success in the Si-based photonics. But due to the limitation of the bandgap, Ge photodetector can’t be operated at light wavelength longer than 1600nm. The incorporation of Sn into Ge adjusts the band structures, and effectively shrinks the bandgap relative to pure Ge. This makes GeSn photodetector a promising device for short-wave infrared light detection (about 2000nm wavelength). In this paper, growth of GeSn alloys on Si and Ge substrates by MBE and sputtering will be introduced. GeSn PIN photodetectors were fabricated by CMOS compatible process. The performance of the GeSn PDs, such as dark current, response spectra and quantum efficiency will be presented and discussed.
(Invited) Variability and Performance on FDSOI Technology with Strained SSOI Substrate and SiGe Channel
Authors: Mazurier Jérôme
Published: February 2020

Fully Depleted SOI (FDSOI) technology has been introduced at the 28nm node as a low-cost alternative strategy to FinFET. Developments on-going on 22nm and 14nm demonstrates the interest of this technology for CMOS scaling. In this talk, mismatch on FDSOI technology will be presented in order to list the main contributors of local variability. Back-bias impact on electrical parameters and variability will be discussed. Then, the effect of strain boosters on device variability and performance will be presented, including strained SOI substrates (sSOI), SiGe channel and compressive/tensile CESL layer.
(Invited) Realizing 2D Materials Via MOCVD
Authors: Briggs Natalie , Subramanian Shruti , Lin Yu-Chuan , Eichfeld Sarah , Jariwala Bhakti , Bhimanapati Ganesh , Zhang Kehao , Robinson Joshua A
Published: February 2020

The last decade has seen nearly exponential growth in the science and technology of two-dimensional materials.  Beyond graphene, there is a huge variety of layered materials that range in properties from insulating to superconducting. Furthermore, heterogeneous stacking of 2D materials also allows for additional “dimensionality” for band structure engineering. In this talk, I will discuss recent breakthroughs in two-dimensional atomic layer synthesis and properties, including novel 2D heterostructures and novel 2D nitrides. Our recent works include development of an understanding of substrate impact on 2D layer growth and properties, doping of 2D materials with magentic elements, selective area synthesis of 2D materials, and the first demonstration of 2D gallium nitride (2D-GaN). Our work and the work of our collaborators has lead to a better understanding of how substrate not only impacts 2D crystal quality, but also doping efficiency in 2D materials, and stabalization of nitrides at their quantum limit.

Z.Y. Al Balushi, K.Wang, R.Krishna Ghosh, R.A. Vilá, S.M. Eichfeld, P.A. DeSario, D.F. Paul, J.D. Caldwell, S.Datta, J.M. Redwing, J.A. Robinson; Graphene stabilization of two-dimensional gallium nitride; arXiv preprint:1511.01871

Eichfeld, S. M.; Hossain, L.; Lin, Y.-C.; Piasecki, A. F.; Kupp, B.; Birdwell, A. G. G.; Burke, R. A.; Lu, N.; Peng, X.; Li, J.; et al. Highly Scalable, Atomically Thin WSe2 Grown via Metal-Organic Chemical Vapor Deposition. ACS Nano 2015.

Y.C. Lin, C.-Y. Chang, R. Ghosh,J.Li, H.Zhu, R.Addou, B.Diaconescu, T.Ohta, X.Peng, N.Lu, M.J. Kim, J.T. Robinson, R.M.Wallace, T.Mayer, S.Datta, L.J. Li, J.A. Robinson; Atomically Thin Heterostructures based on Single-Layer Tungsten Diselenide and Graphene; Nano Letters

M. S. Bresnehan, G. Bhimanapati, K. Wang, D.Snyder, J.A.Robinson; Impact of Copper Overpressure on the Synthesis of Hexagonal Boron Nitride Atomic Layers; ACS Appl. Mater. Interfaces, 6, 16755–16762 (2014)

S.M. Eichfeld, C.M. Eichfeld, Y.C. Lin, L. Hossain, J.A. Robinson; Rapid, non-destructive evaluation of ultrathin WSe2 using spectroscopic ellipsometry; APL Materials 2 (9), 092508

Y.C.  Lin, N. Lu, N. Perea-Lopez, J. Li, C.H. Lee, Z.Lin, P.N. Browning, M.S. Bresnehan, L. Calderin, M.J. Kim, T.S. Mayer, M. Terrones, J.A. Robinson; Direct Synthesis of van der Waals Solids on Epitaxial Graphene; ACS Nano 8 (4), 3715-3723 (2014)
(Invited) The Structure-Dependent Properties of InAs Nanowires and Their Devices
Authors: Fu Mengqi , Shi Tuanwei , Li Xing , Chen Qing
Published: February 2020

InAs nanowire is an important III-V group semiconducting nanomaterial with direct and narrow bandgap and small effective electron mass. It has great potential in high-performance electronic nanodevices and infrared detectors. In this talk, I will introduce our recent progresses on the structure-dependent properties of InAs nanowires and their devices.

Various properties of individual InAs nanowires are studied and correlated with their structures through a comprehensive in situ platform we have developed in a scanning electron microscope. Remarkable piezoelectric and piezoresistive effects are observed for the first time in single-crystalline <0001> WZ InAs nanowires, but negligible effect is found in WZ nanowires with other orientations and nanowires with ZB structures. An ultrafast and reversible electrochemical lithiation of InAs nanowires are observed for the first time.

Field effect transistors (FETs) based on MBE-grown InAs nanowires are studied. Importantly, based on nano-manipulation and microlithography, we develop a new method to characterize the same individual InAs nanowires in the FETs by transmission electron microscopy to obtain the atomic-level structures. Our study shows that not only the diameter, but also the crystal structure and the orientation of the InAs nanowires remarkably affect the electronic properties of the FETs, such as the threshold voltage, On/OFF current ratio, on-state current, subthreshold swing and electron mobility, etc. Ohmic contact are obtained for the nanowires with different diameters down to 7 nm.
RAMAN Characterization of Ge1-XSnX Allows By Using a SPACE Correlation MODEL
Authors: Pérez Ladrón de Guevara Héctor , Vidal Borbolla Miguel Angel , Rodriguez Vazquez Angel Gabriel , Navarro Contreras Hugo Ricardo
Published: February 2020

Ge1-xSnx alloys present important optoelectronic properties due to the possibility for obtain a direct and tunable energy gap group IV semiconductor. Ge1-xSnx alloys were grown on different substrates by using a R. F. Magnetron Sputtering. Raman spectroscopy and HRXRD were used in order to determinate the structural properties of these alloys. We determined a linear shift of the Raman peak that depends directly on the Sn concentration of the alloy. We also find that the Raman peak has an asymmetrical shape attributed to a small crystal size. In this work we present the characterization of the Raman peaks by fitting a Space Correlation Model. We obtain a strong correlation among FWHM, asymmetrical shape and Sn concentration of the alloys.

Keywords: HRXRD, Raman.
(Invited) Finely Controlled Heterointerfaces between Ge(111) and Metallic Alloys or Insulators for Next Generation Ge-Based Devices
Authors: Hamaya Kohei , Yamada Shinya , Kasahara Kenji , Kanashima Takeshi
Published: February 2020

For next generation Ge-based devices, we have developed epitaxial growth techniques of high-performance ferromagnetic alloys or high-k insulators on Ge(111). By using low-temperature MBE or PLD, high-quality heterointerfaces for source/drain or gate-stack structures can be achieved, respectively. We detect spin transport in n-Ge(111) and p-Ge(111) through the high-quality ferromagnetic alloys/Ge(111). In addition, the Fermi level pinning is markedly suppressed even for the metal/Ge contacts and the Schottky barrier height of the metal/p-Ge contacts can be controlled by the metal work function. Finally, we show a new approach for gate-stack structures with crystalline high-k La2O3 layers. We obtained atomically smooth heterointerfaces between La2O3 and Ge(111). These results will open a road to integrate finely controlled structures into next generation Ge devices.
Steps Towards Reactive Hydrogen Pumping
Authors: Fane Brian , Goenaga Gabriel A. , Zawodzinski Thomas A.
Published: February 2020

Polymer electrolyte membrane (PEM) fuel cells are an attractive energy conversion device because of the potential for extremely high efficiency and low emissions. Pure hydrogen is an ideal fuel for PEM fuel cells but it is energy intensive to produce. Currently, the main method of producing hydrogen is steam reforming of natural gas. This is a break from the renewable energy future promised by hydrogen fuel cells. A greener approach to producing hydrogen is electrochemical reforming, the most obvious feedstock is water. Water electrolysis occurs at a relatively high potential (1.23 V), which makes it expensive both in terms of materials required and electricity. To fulfill the promise of fuel cells, more efficient methods of producing hydrogen must be found.

One way to reduce the energy required is to depolarize the PEM electrolyzer anode by using an alternate feed. This feed must have a lower oxidation potential than water and be generated renewably. Two alternative feeds we have looked at are methanol and phosphomolybdic acid.

Oxidation of methanol-water solutions to hydrogen takes place at a theoretical voltage of 0.03 V. Methanol fuel cells are a well-studied problem and the issues are known. The main issue is crossover of methanol to the cathode, lowering the total cell potential. We looked to see if this would be as problematic in a hydrogen pumping environment since there would be no oxygen at the cathode for the methanol to react with.

The other feed we examined was phosphomolybdic acid (PMA). PMA is a keggin ion which is readily reduced by biomass substrates in the presence of sunlight or heat.1Our idea was to apply the concept of a depolarized anode electrolyzer to a mediated electrochemical system. This system has the PMA in solution as a combination catalyst and charge carrier. The PMA is reduced by biomass and circulated to an anode where it is oxidized to release the hydrogen removed from the biomass. This gives many of the advantages of a flow battery, where power and capacity scale separately. Our focus has been on studying the anode performance characteristics of PMA.

 References.

1. Liu W, Mu W, Liu M, Zhang X, Cai H, Deng Y. Solar-induced direct biomass-to-electricity hybrid fuel cell using polyoxometalates as photocatalyst and charge carrier. Nat Commun. 2014;5:3208. doi:10.1038/ncomms4208.
Spectrometric Quantification of the Rate of Carbon Corrosion on Oxygen Evolving Electrodes in Alkaline Media
Authors: Uddin Jasim , Tan Hongjin , Giordani Vincent , Chase Gregory V , Addison Dan
Published: February 2020

Carbon-based electrodes are known to undergo corrosion in acidic and alkaline media during the oxygen evolution reaction (OER), yet studies on the efficacy of OER catalysts frequently employ carbon as catalyst support. Carbon remains a material of interest in the development of bifunctional air electrodes, particularly due to its utility in supporting efficient oxygen reduction reaction (ORR) catalysis. Methods to quantify carbon corrosion rates are needed in order to assess the practical utility of carbonaceous materials in bifunctional air electrodes and other OER electrodes. In-situ electrochemical mass spectrometry enables direct and precise assessment of carbon corrosion in acidic media by quantifying gaseous CO2 that is generated as a product of the corrosion reaction. For alkaline media, this in-situ approach is unsuitable since CO2 generated during corrosion reacts with and is sequestered within the alkaline electrolyte as carbonate.

In this presentation, we describe a method to precisely quantify carbon corrosion in alkaline media. The method is direct and sufficiently sensitive to provide rapid (1-2 days) characterization of carbon corrosion, whereas methods based on electrochemical characterization or mass measurement may yield ambiguous results and take months. We report on the use of this method to quantitatively compare the rate of corrosion using different types of carbon, including reduced graphene oxide, doped carbon and carbons with various coatings and catalysts. A critical assessment of the use of carbon in bifunctional air electrodes will be provided.
Pfaem: A Novel Anionic Exchange Membrane for Fuel Cell Applications and Its Characterization
Authors: Divekar Ashutosh G , Park Andrew Michael , Owczarczyk Zbyslaw R. , Pivovar Bryan S , Herring Andrew M
Published: February 2020

Anionic exchange membrane fuel cell is a promising new technology which potentially meets the challenges faced by other low-temperature fuel cells like Proton-exchange membranes. Anionic exchange membrane can be operated with non-noble catalyst. To design a robust material which is hydroxide conductive, chemically stable and mechanically strong is the biggest challenge to make this technology commercial. This research focuses on the characterization of a novel anionic exchange membrane with PTFE backbone. The experimental ion-exchange capacity of this polymer is 0.9 mmol/gm. The conductivity of this membrane was measured in its chloride form. We observed the highest value of 0.039 S/cm conductivity at 80 0C and 95%RH. The polymer also shows water uptake of 11 % and λ value of 6.8 at 60 0C and 95% RH. The small-angle x-ray scattering analysis of this membrane shows the polymer’s ionomer peak and we understand that the swelling of the polymer is higher at higher temperature. From this analysis, this material can be expected to exhibit higher hydroxide conductivities and good mechanical stability and hence this polymer is a promising candidate for anionic exchange membranes.

Keywords: Anionic exchange membrane, PTFE backbone

Figure 1
Effect of Bulky Cations on the Stability and Properties of Anion Exchange Membranes
Authors: Liu Ye , Yuan Haomiao , Wang Junhua , Zhang Bingzi , Coughlin Bryan E , Yan Yushan , Liberatore Matthew W , Herring Andrew M
Published: February 2020

Alkaline anion exchange membrane fuel cells are widely investigated recently as promising alternative to well-established proton exchange membrane fuel cells. Anion exchange membranes, using as solid electrolytes, are required to be thermally, chemically and mechanically stable in base at the operation temperature and humidity, as well as have an efficient OH- transport along the membrane across two electrodes.

This study aims at studying AEMs functionalized with three different bulky cations. They are 1,4,5-trimethyl-2-(2,4,6-trimethoxyphenyl) imidazolium functionalized polyphenylene oxide (Figure 1(a)) [1], tris(2,4,6-trimethoxyphenyl) phosphonium functionalized PPO (Figure 1(b)) [2], and phenylene cobaltocenium functionalized norbornene (Figure 1(c)).

Degradation study on 1,4,5-trimethyl-2-(2,4,6-trimethoxyphenyl) imidazolium functionalize PPO and unsubstituted imidazolium PPO by soaking both two membranes into 1 M sodium hydroxide at 80°C indicates attachment of 2,4,6-trimethoxyphenyl group efficiently improve OH- stability due to the enhanced volumetric steric and basicity of the central cation. Super hydrophobic and bulky phosphonium cation attached by three 2,4,6-trimethoxyphenyl groups has the chemical stability surpassing benzyl trimethyl ammonium by 30% after degrading in 1 M KOH at 80°C for 20 days. The cobaltocenium cation, which has 18 valance electrons further improve the chemical stability by 60% higher than trimethyl ammonium after treating in 1 M NaOH/CH3OH at 80°C for 20 days (Figure 2).

Besides enhanced chemical properties from these bulky cations, their influence on the other polymer properties include thermal stability, water uptake, conductivity as well as transport property are also discussed.

Figure 1. Structure of 1,4,5-trimethyl-2-(2,4,6-trimethoxyphenyl) imidazolium functionalized PPO (a), tris(2,4,6-trimethoxyphenyl) phosphonium functionalized PPO (b) and phenylene cobaltocenium functionalized norbornene (c).

Figure 2. Degradation studies performed at 80°C on 1,4,5-trimethyl-2-(2,4,6-trimethoxyphenyl) imidazolium (solid diamond, 1 M KOH), tris(2,4,6-trimethoxyphenyl) phosphonium (solid square, 1 M KOH), phenylene cobaltocenium (solid triangle, 1 M NaOH/CH3OH) and benzyl trimethyl ammonium (open square, 1 M KOH; open triangle, 1 M NaOH/CH3OH).

Reference

[1] Y. Liu, J. Wang, Y. Yang, T.M. Brenner, S. Seifert, Y. Yan, M.W. Liberatore, A.M. Herring, J. Phys. Chem. C 118 (2014) 15136-15145.

[2] Y. Liu, B. Zhang, C.L. Kinsinger, Y. Yang, S. Seifert, Y. Yan, C.M. Maupin, M.W. Liberatore, A.M. Herring, J. Membr. Sci. 506 (2016) 50-59.

Figure 1
Preparation and Characterization of Cgo-Based Catalyst for Methanol Steam Reforming By Glycine-Nitrate Process
Authors: Lee Junghun , Choi Eunyeong , Ji Hyunjin
Published: February 2020

Methanol is a liquid fuel which can be produced from renewable energy sources and has high energy density. It has a low boiling point, a high H:C ratio of 4:1 without any C-C bond, therefore can be reformated at a relatively low temperature. In this work, we investigated the application of CGO(Gd:CeO2)-based catalyst for hydrogen production via methanol steam reforming. CGO-based powder material for a catalyst of methanol steam reforming was synthesized by glycine-nitrate process(GNP). GNP is one of the solution combustion synthesis methods, Metal nitrate and glycine were mixed with deionized water and solution heated by hot plate. After evaporation of water, solution converted to a viscous gel. The gel ignited with gases and powders. The synthesized powders were calcined for 4 hours at 800°C to remove moisture and impurity. Their properties such as micro structure, surface morphology, surface area and composition were investigated with XRD(X-ray diffraction), SEM(Scanning electron microscopy), BET (N2 adsorption-desorption), EDS(Energy dispersive spectroscopy) and ICP-MS(Inductively coupled plasma mass spectrometry). The performance of catalysts was examined with reactor at 200 - 400°C range. The reactants and reaction products were analyzed by GC(Gas chromatography). The catalytic performance for hydrogen production was analyzed in terms of methanol conversion and selectivity of products.
Design of Highly Active Fe-N/C Catalysts with Abundant Fe-Nx Sites for Oxygen Reduction Reaction
Authors: Joo Sang Hoon
Published: February 2020

The development of highly active, durable, and low-cost oxygen reduction reaction (ORR) catalysts is central to making polymer electrolyte fuel cells (PEFCs) commercially viable. In this direction, tremendous recent efforts have been devoted to replacing expensive, scarce Pt-based electrocatalysts with non-precious metal catalysts (NPMCs) for the ORR. Among a wide range of NPMCs, the Fe-N/C catalysts have emerged as the most promising ORR catalysts due to their high ORR activities. A growing body of literature based on spectroscopic studies suggests that the active sites of these catalysts involve Fe-Nx coordination. We have endeavored to develop general synthetic strategies towards high-performance Fe-N/C catalysts that can host a high density of catalytically active Fe-Nx sites. We have prepared transition metal-doped ordered mesoporous porphyrinic carbons (M-OMPCs) by nanocasting mesoporous silica templates. The M-OMPC catalysts contain predominantly molecularly dispersed Fe-Nx sites and have high surface areas and tunable pore structures. Among the M-OMPC catalysts, the FeCo-OMPC catalyst exhibited an excellent ORR activity in an acidic medium, higher than other non-precious metal catalysts. It showed higher kinetic current at 0.9 V and superior long-term durability and MeOH-tolerance than Pt/C catalyst. Second strategy is based on a generalized “silica-protective-layer-assisted” method that can preferentially produce catalytically active Fe-Nx sites towards highly efficient Fe-N/C electrocatalysts. This method is applicable to any type of carbon supports including carbon nanotubes, reduced graphene oxide, and carbon black. One of resulting catalysts, consisting of CNT wrapped with thin porphyrinic carbon layer (CNT/PC), contained relatively high density of Fe-Nx sites, and showed very high ORR activity and remarkable stability in alkaline media. Importantly, the CNT/PC-based cathode demonstrated excellent performances in both alkaline anion exchange membrane fuel cell as well as acidic proton exchange membrane fuel cell.