bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Electrochemical Processing of Metal-Insulator-Semiconductor (MIS) Photoelectrodes
Authors: Esposito Daniel , Labrador Natalie Yumiko
Published: February 2020

Photoelectrochemical (PEC) water splitting is a promising route to solar-driven H2 production, but the efficiency and stability of semiconducting photoelectrodes must be improved. One potential approach to achieving high efficiency and good electrochemical stability is the metal-insulator-semiconductor (MIS) photoelectrode design. [1-4] The MIS arrangement generally consists of catalytic metal structures, or collectors, deposited on an oxide-covered semiconductor as illustrated in Fig. 1. A crucial element of this design is the insulating oxide layer, which protects the semiconductor from the potentially corrosive electrolyte while facilitating minority carrier tunneling between the semiconductor and collectors. The oxide layer must be ultra-thin (1-3 nm) and exhibit minimal defects at the SiO2/Si interface in order to facilitate efficient tunneling and maximize photovoltage.

            In this work, we have systematically investigated electrodeposition of Pt nanoparticle collectors on SiO2-covered p-Si(100) MIS photoelectrodes, with the goal of obtaining a high degree of control of nanoparticle coverage, catalytic surface area, and nanoparticle size. These three parameters strongly influence photoelectrode optical, catalytic, and photovoltage performance, respectively, and electrodeposition offers an exciting opportunity to optimize these properties. This work has studied the influence of key deposition parameters (potential, current density, surface treatment) on the physical properties of the Pt nanoparticles, as well as the resulting PEC performance for photo-driven hydrogen evolution reaction (HER).  Through systematic investigation of the structure-property relationships in this MIS photoelectrode system, this study deconvolutes the optical, electronic, and catalytic influences of Pt nanoparticle geometries on photoelectrode performance. Such loss analysis is highly useful for guiding the design of more efficient photoelectrodes. Finally, opportunities and challenges of utilizing electrochemical processing for the manufacture of efficient photoelectrodes are discussed.        

References

1. H.J. Lewerenz, et al., Electrochem. Acta, 56, 10726 (2011).

2. A.G. Munoz and H.J. Lewerenz, ChemPhysChem, 11, 1603 (2010).

3. Y. Chen, P. McIntyre, et al., Nature Materials, 10, 539 (2011).

4. D.V. Esposito, I. Levin, T.P. Moffat, A.A. Talin, Nature Materials, 12, 562 (2013).

Figure 1
Formation of Si Nanowires By Electroreduction of Porous Ni/SiO2 Blocks in Molten CaCl2
Authors: Fang Sheng , Yang Juanyu , Wang Han , Yu Bing , Lu Shigang
Published: February 2020

Electroreduction of porous SiO2 in molten CaCl2 is a promising approach to prepare silicon nanowires (SiNWs) in large quantities. However, it is difficult to control the morphologies and surface topologies of the produced SiNWs. In this work, pure nickel metal powders are added into SiO2, and SiNWs with straight morphology are prepared by electroreduction of solid Ni/SiO2 blocks in molten CaCl2 in a wide temperature range. The prepared SiNWs have a diameter distribution of 80 to 350nm, and nickel silicide is found at the tip of the nanowire. Cyclic voltammograms indicate that nickel does not change the mechanism of electrochemical reduction of SiO2.  The growth process of SiNWs is investigated by XRD, FESEM, HRTEM, EDS, and SAED. It is confirmed that nano-sized nickel-silicon droplets formed at the Ni/SiO2/CaCl2 three-phase interface lead the growth of SiNWs, and adding nickel metal into SiO2 can promote the growth of straight nanowires during the electroreduction of Ni/SiO2 in molten CaCl2.
Silane-Free Adhesive Electroless Deposition of a Nickel/Phosphorous Layer on Si Wafer
Authors: Wei Tzu Chien , Hsu Chin Wei , Wang Wei-Yan , Chen Chih-Ming , Lai Kuei-Chang
Published: February 2020

Electroless deposition (ELD) of nickel/phosphorous (Ni/P) layers has been a valuable method for creating diffusion barriers in the silicon (Si) industry, particularly in the formation of metal contact or interconnection structure in integrated circuits or microelectromechanical systems [1,2]. The ELD of Ni/P layers is a catalytic reaction that requires either a trace amount of seed Ni [3] or noble metals such as palladium [4] to lower the activation energy for nucleation and growth. Because the ELD process occurs on the catalyst-attached Si surface, the adhesion of Ni/P films is related to the interfacial properties of the catalyst and Si surface. In the first part of this presentation, we develop a post-annealing-free, adhesive Ni/P layer on an aminosilane-modified (ETAS-modified) Si surface through an ELD catalyzed by a novel, home-made polyvinylpyrrolidone-capped palladium nanocluster (PVP-Pd). X-ray photoelectron spectroscopy analysis reveals that ETAS was covalently bonded on the Si surface, whereas the amino groups on ETAS bridged with the palladium core in the PVP-Pd. Because of above two effects, the ELD Ni/P layer showed superior adhesion on the Si wafer without the need of conventional post-annealing treatment. Compared with the Ni/P films deposited on bare Si surfaces by using commercial Sn/Pd colloids, the adhesion of the Ni/P film catalyzed by either PVP-Pd on the ETAS-modified Si wafer improved more than 4-fold.

Later on, we report our new finding regarding to prepare adhesive ELD Ni/P film on Si wafer without the requirement of silane-modification and post annealing by innovating catalyst system. Switching from PVP-Pd to polyvinyl alcohol-capped palladium nanocluster (PVA-Pd), it is found the surface modification by aminosilane-compound can be omitted, while the resulting ELD Ni/P film still exhibits adequate adhesion.

Reference:

[1] S. Furukawa, M. Mehergany, Sensors Actuators 56 (1996) 261.

[2] K.Y. Lee, J.T. Huang, P.S. Chao, J.M. Lin, H.J. Hsu, Microelectron. Eng. 113 (2014) 147.

[3] S.J. Cherng, C.M. Chen, W.P. Dow, C.H. Lin, S.W. Chen, Electrochem. Solid-State Lett.

14 (2011) P13.

[4] C. R. Shipley Jr., U.S. Pat. 3,011,920 (1961).
Advancements in Copper Interconnect Technology: The Effect of Sulfuric Acid on the Adsorption & Desorption of an Advanced MLI Suppressor
Authors: Olson Wyatt , Schmidt Manning , Wetterer Anna , Willey Mark
Published: February 2020

In the last five years the size of the copper plated interconnect features for the logic and memory market has dropped below 30nm.  This decrease in size has forced plating chemistries to operate on copper seed that is often times either non continuous or has morphology that requires special tuning of the additives to create the bottom up phenomenon.  In the past, the traditional path of development led to the continued optimization of the organics additives (accelerators, suppressors, levelers) to help generate the void free fill in the plated interconnects while mostly fixing the inorganic concentrations.  A new approach to additive development is to optimize the organic additives in different electrolyte concentrations. 

Traditionally, the copper chemical vendors were focused on the traditional 40g/L Cu2+, 10g/L sulfuric acid, 50ppm electrolyte formulation.  However, optimization of electrolytes can allow for a decrease in defectivity across the wafer.  This change in electrolyte formulation has sparked a new set of chemistry development at MLI to tune the organic chemistry to the electrolyte concentrations and also expand the understanding of the effect of electrolyte on the organic additives.

 The current set of work aims at showing how acid affects the adsorption and desorption of a new advanced MLI suppressor.  This work starts with a basic understanding of how acid affects the plating bath with no suppressor present and then expands to show how this new suppressor is affected by the acid changes.  A surface adsorption and desorption model is then hypothesized based on the electrochemical signal. 

The figure below outlines a typical adsorption result where an applied current of 10mA/cm2 is run while solution over the electrode is transitioned from one containing the electrolyte only to one containing the electrolyte and the MLI suppressor. 

The two plots in the graph show the difference in the adsorption rate as a function of acid concentration.  One will note that the higher acid concentration shows a stronger steady state suppression and also a slower adsorption rate.  Experiments similar to these will be disclosed and the adsorption / desorption model discussed.

Figure 1
Coupling Phenomena Between Micromorphological Evolution and Ionic Mass Transfer Rate during Ag Electrodeposition in AgNO3 Aqueous Solution
Authors: Fukunaka Yasuhiro , Wakatsuki Takao , Homma Takayuki
Published: February 2020

The rechargeable battery concept with maltreat tolerance and safety is essentially indispensable not only in the space application but also in terrestrial renewable energy storage systems. Higher energy density, power capability and longer life requirements make the targets more challenging.  A better understanding of the electrolyte/electrode interface phenomena including electrode kinetics is crucial.  “Electrochemical Nucleation & Growth” aspect is a fundamental approach how to control the coupling phenomena between nano-structural interface evolution and ionic mass transfer rate enclosed a meso-scale space filled with electrolyte.    Such a research has not been frequently challenged in designing the longer life energy storage devices. 

Metal negative electrode surface shows various morphologies after repetition of electrodeposition and electrochemical dissolution reaction.  Dendrite precursor is finally grown after electrochemical nucleation and growth process where the coupling phenomena govern.  It is also indispensable for us to prolong the charging/discharging operation of secondary battery after longer term utilization under various environments.  For liquid electrolyte, a precise study of these morphologies may be complicated by convective motion caused by gravitational force of buoyancy.  Now the coupling phenomena are discussed in the case of silver because it has been employed as negative electrode in space application.  

3M AgNO3 aqueous solution was contained in a quasi-2D cell. Holographic interferometry was employed to monitor the ionic mass transfer rate. The concentration profiles were formed around dendrite tips of silver electrodeposited at extremely high current densities.     A uniform diffusion layer was formed along the cathode surface at the start of electrolysis.  Following a certain incubation period, several dendrite tips began to protrude into the diffusion layer.  The growth rates of these dendrites were related to concentration gradients around the tips, diffusivity, and transfer number of Ag+ ion.  Giant-Macro step flow accompanied with Ag dendritic growth was dynamically observed with Laser Confocal Scanning Microscope.  

Transient current variation measurements are now engaged under the double pulse potential which introduces Ag nucleus on the foreign substrate in order to develop a multi-scale physical model of dendritic growth.
Nanoparticle Electrocatalysts for the Oxidation of Biomass
Authors: Arroyo-Torres Christian , Staser John A , Movil-Cabrera Omar
Published: February 2020

Biomass fuels come from things that once lived: wood products, dried vegetation, crop residues, aquatic plants and even garbage. Lately, there is a constant supply of waste – from construction and demolition activities- in which this waste is generally burned during the chemical recovery process to generate heat. Unfortunately, catalytic processes are difficult to implement for the degradation of biomass because selective oxidation is difficult and these processes produce an unacceptable amount of solid residue like char. Electrochemical processes, on the other hand, have several advantages over catalytic processes, including the use of mildly basic solvents as electrolytes, and control over the rate of reaction and the products. Thus, the electrochemical oxidation of biomass would be an ideal process to utilize this renewable raw material. We have begun to investigate the mechanism of biomass oxidation via electrochemical processes, in which several proceeding chemical or electrochemical reactions are possible.  We will present GC/MS data that identify biomass oxidation products. This process could provide an economic way of reducing the organic waste from bio-refinery industries.
3D Printed Membraneless Water Electrolysis Cells
Authors: O'Neil Glen D , Esposito Daniel
Published: February 2020

Hydrogen (H2) has emerged as a promising candidate for both clean energy storage and as an alternative to fossil fuels. Currently, the majority of H2 is produced via methane reformation, which emits one molecule of CO2 for every three molecules of H2 and thus contributes to climate change.1 Alternative methods towards H2 production include direct photoelectrochemical water-splitting using semiconducting photoelectrodes,2 or using a membrane electrode assembly (MEA), which can be powered using renewable power sources. Direct production of H2 using semiconductor photoelectrodes is very promising, but there are issues remaining with electrode stability and efficiency. While remaining the industry standard, electrolysis using a MEA is costly and is most commonly performed in acidic solutions.

Here we present novel device architectures for water splitting which utilizes additive manufacturing (e.g. - 3D printing) to produce hydrogen and oxygen gas with minimal product crossover. Additive manufacturing has the benefits of: low-cost, ability to rapidly prototype, and use renewable materials (e.g. – poly(lactic acid)).3 In our design, a flowing electrolyte solution impinges upon two electrodes, which are placed in close proximity to minimize solution resistance (measured to be ~3 Ω in 0.25 M H2SO4). The low Ohmic losses enable current densities up to 300 mA cm-2, and can be used in acidic, basic and neutral electrolytes because no membrane is required. The product gas streams are separated by a thin divider placed downstream of the electrodes, so that product crossover is essentially zero.  The results compare well with previously reported studies,4 but eliminate the complicated processing times and device complexities required.

References

(1)          Navarro, R. M.; Peña, M. A.; Fierro, J. L. G. Hydrogen Production Reactions from Carbon Feedstocks: Fossil Fuels and Biomass. Chem. Rev.
2007, 107, 3952–3991.

(2)          Walter, M. G.; Warren, E. L.; McKone, J. R.; Boettcher, S. W.; Mi, Q.; Santori, E. A.; Lewis, N. S. Solar Water Splitting Cells. Chem. Rev.
2010, 110, 6446–6473.

(3)          Chisholm, G.; Kitson, P. J.; Kirkaldy, N. D.; Bloor, L. G.; Cronin, L. 3D Printed Flow Plates for the Electrolysis of Water: An Economic and Adaptable Approach to Device Manufacture. Energy Environ. Sci.
2014, 7, 3026–3032.

(4)          Hosseini Hashemi, S. M.; Modestino, M. a.; Psaltis, D. Membrane-Less Microelectrolyzer for Hydrogen Production across the pH Scale. Energy Environ. Sci.
2015, DOI: 10.1039/C5EE00083A.
(Invited) Membranes of Mixed Ionic and Electronic Conductors for Gas Separation: Effect of Surface and Interfaces
Authors: Liu Meilin , Liu Mingfei
Published: February 2020

Dense membranes of mixed ionic-electronic conductors represent a highly efficient and economically viable approach to hydrogen and oxygen separation. For example, a “cermet” membrane consisting of a ceramic proton conductor and a metal (e.g., nickel) could be a promising technical solution for recovery of high-purity hydrogen from synthetic gas mixtures during various industrial processes such as coal gasification and water gas-shift reaction.  In particular, yttrium/ytterbium doped barium zirconate-cerate (BZCYYb) exhibits the highest proton conductivity in the temperature range suitable for hydrogen separation.  Further, Ni-BZCYYb cermets have high tolerance to sulfur poisoning and coking under typical conditions for hydrocarbon reformation.  To date, however, there is little fundamental understanding of the surface processes relevant to hydrogen separation.  A fundamental understanding of the charge and mass transport processes associated with H2 dissociation and proton incorporation (or H2 evolution) on the surfaces of a cermet hydrogen permeable membrane is vital to achieving rational design of a new generation of hydrogen permeable membranes.  In this presentation, we will highlight our recent progress in understanding the effects of surface and interfaces on gas separation processes, aiming at elucidating the mechanisms that control proton incorporation or H2 dissociation at the surfaces of the membranes, the nature of the proton solubility sites, and the diffusion process through the membrane.
Recovery Cyanide from Cyanide-Containing Wastewater By Selective Electroconcentration
Authors: Yang Yang , Tian Yun , Fan Zheng , Wu Xingxing , Wu Zucheng
Published: February 2020

A large amount of hydrogen cyanide poisonous gases released from Polyacrylonitrile（PAN）-basis carbon fiber manufacturing process. Stimulated by its value and harmfulness to human and environment, electrochemical methods have proposed to deal with the double-edged materials. A novel electrodeionization technology, named as selective electroconcentration (SEC), was used to segregate targeted ions from mixed aqueous solution. SEC is an approach not only removes needless ions，but also obtains concentrated ions in brine water. In this paper, synthetic water contained cyanide and carbonate was investigated to examine the separation and enrichment effects of SEC. It was found that the pH raise in divalent ions concentrated chamber prevented carbonate conversion, which avoided bicarbonate competing with cyanide. Thus monovalent ions were able to migrate to next concentrated chamber. To acquire details about how to optimize the SEC apparatus, operation parameters like current, pH change, and proportion were discussed here.

   Practical results show that cyanide purity can reach 90%, with a high cyanide concentration (250mmol/L). The cyanide product can be used as plating solution. Beyond that, the concentration of treated cyanide wastewater conformed sewage discharge standard. It is proved that SEC is feasible to concentrate cyanide and the separation efficiency is satisfactory.
(Invited) An Industry Perspective on Atomic Layer Etching
Authors: Suri Satyarth , Carver Colin T. , Turkot Robert , Romero Patricio E , Tronic Tristan A , Plombon John
Published: February 2020

As we celebrate the 50th anniversary of Moore’s Law, the scaling of transistors on a microprocessor at a two year cadence continues.  While scaling of critical dimensions (CD) and pitch is widely recognized, the thickness of films that need to be patterned has also scaled down.  Additionally, the etch stop films have also become thinner. With pitch scaling, the role of sidewall damage during plasma etch process has become more significant. As the films become thinner and damage free process become more relevant, atomic layer etch as a manufacturing option has become more attractive.  This talk will evaluate different atomic layer etch options, discuss the respective pros and cons.  Potential enabling examples of atomic layer etch will be presented focusing primarily on atomic layer control, damage reduction and extreme selecitivities.
Understanding Photovoltage in Insulator-Protected Water-Splitting Half-Cells
Authors: Scheuermann Andrew G. , Chidsey Christopher E.D. , McIntyre Paul C.
Published: February 2020

Metal oxide protection layers for photoanodes may enable the development of large-scale solar fuel and solar chemical synthesis.  ALD-TiO2 remains the most widely used material because of its excellent stability under water oxidation conditions and potential for high electrical conductivity both as an ultrathin film and with thicknesses exceeding 100 nm [1-3].  However, the most conductive ALD-TiO2films exhibit poor photovoltages of ~ 400 mV and less [3]. Even assuming near-ideal fill factors, these voltages fall far short of the values needed for viable water splitting devices. Photovoltage optimization is especially difficult in MOS photoanodes due to the range of factors which influence the conductivity and stability of the protection layer as well as the presence of electrically active defect states at the semiconductor/oxide interface. Therefore, understanding how to optimize photovoltage and stability is of utmost concern for the advancement of the field.

Here we report a novel observation of photovoltage loss associated with charge transfer in these metal-oxide protected devices, and by eliminating it, achieve photovoltages as high as 630 mV, the maximum reported to date for single-junction water-splitting silicon cells. The loss mechanism is systematically probed in MOS Schottky junction cells compared to buried junction p+n cells, revealing the need to maintain a characteristic hole density at the semiconductor/insulator interface.  A capacitor model that predicts this loss is developed, and is related to the dielectric properties of the protective oxide, achieving excellent agreement with the data.  From these findings, we extract design principles for simultaneous optimization of charge transfer resistance and interface quality to maximize the photovoltage of metal-oxide protected MOS water splitting devices.

[1] Y.W. Chen, et al. Nature Mat. 2011, 10, 539-544.

[2] A. G. Scheuermann, et al. Energy Environ. Sci. 2013, 6, 2487–2496.

[3] S. Hu, et al. Science 2014, 344, 1005−1009.

Figure 1 | Charge transfer in three cell types for water splitting applied to silicon: The Type 0 Semiconductor-Liquid (SL), Type 1 Metal-Insulator-Semicondcutor (MIS), and Type 2 p+n junction.  The density of states on either side of the oxides and the excition splitting position with respect to these layers play a crucial role in mediating efficient charge transfer. These effects are so strong that Type 0 protected silicon cells exhibit essentially no photovoltage, Type 1 nSi cells show a linear photovoltage loss with oxide thickness, and Type 2 cells--where the hole concentration on the Si/SiO2 interface is always high--exhibit record photovoltages at all oxide thicknesses and pH values studied.

Figure 1
(Invited) Atomic Layer Deposition of Metals and Oxides on Graphene for Future Nanoelectronics
Authors: Bol Ageeth A. , Vervuurt Rene H. J. , Thissen Nick F. W. , Sharma Akhil , Kessels W.M.M.
Published: February 2020

Graphene is a two-dimensional material with very high intrinsic charge carrier mobilities. Graphene is therefore a promising candidate for post-silicon electronics. Two of the critical issues in unlocking the potential of graphene are the ability to deposit ultra-thin high-K dielectrics on grapene and fabricate low resistance contacts to graphene. Technologically, it is desirable to use atomic layer deposition (ALD) for this purpose. Since ALD is based on self-limiting surface reactions, ultrathin films can be deposited that make an intimate contact with the underlaying surface. The inert nature of graphene however has made ALD on graphene very challenging. Therefore, seed layers or functional groups need to be placed on the graphene to initiate ALD growth. The seed layers or functional groups can however have a detrimental effect on the properties of graphene. This presentation will give an overview of techniques that are being used in literature and in our own lab to stimulate ALD on graphene.
Improving Graphene Conductivity through Selective Atomic Layer Deposition
Authors: Liu Chanyuan , Han Xiaogang , Bao Wenzhong , Pearse Alexander J , Hu Liangbing , Rubloff Gary W
Published: February 2020

One of the most promising approaches for massive production of transparent conducting electrodes (TCE) is roll-to-roll printing of graphene flakes solution. However, graphene flakes inevitably contain structural defects like grain boundaries and dislocations, together with macroscopic defects such as wrinkles and cracks during transfer. In addition, the printed flakes can’t align with each other perfectly. All these defects and the gaps between detached flakes hinder electrical transport and limit the mechanical strength and reliability of the graphene. 

Here we report a technique to electrically heal and connect graphene flakes via selective atomic layer deposition (ALD) of conductive materials. We have demonstrated selective growth of ALD aluminum-doped zinc oxide, ruthenium and platinum on pristine graphene surface prepared from exfoliated highly ordered pyrolytic graphite (HOPG). ALD materials nucleate on graphene cracks and edges but exhibit a significant nucleation barrier on intact basal planes due to the chemical inertness from delocalized π-orbitals. We also present a high-throughput fabrication method to create graphene patterns via metal shadow mask and O2 plasma. This model system of patterned CVD graphene islands demonstrates electrical connection of separated graphnene flakes by selective ALD processes. In addition, shadow-mask-patterned CVD graphene field effect transistors (FETs) are used to monitor graphene carrier density and mobility variation after ALD growth. We found considerable carrier density and conductivity increase of a single graphene flake after V2O5 ALD, which can be explained by p-doping of graphene due to the high work function V2O5.
New Insights into Sequential Infiltration Synthesis
Authors: Elam Jeffrey W , Biswas Mahua , Darling Seth , Yanguas-Gil Angel , Emery Jonathan D. , Martinson Alex B. F. , Nealey Paul F. , Segal-Peretz Tamar , Peng Qing , Winterstein Jonathan , Liddle J. Alexander , Tseng Yu-Chih
Published: February 2020

Sequential infiltration synthesis (SIS) is a process derived from ALD in which a polymer is infused with inorganic material using sequential, self-limiting exposures to gaseous precursors.  During the initial SIS cycles, the organometallic precursor (e.g. trimethyl aluminum, TMA) reacts preferentially with specific functional groups within the polymer, while in later cycles growth occurs in an ALD-like fashion on the inorganic “seeds” that have been planted inside the polymer.  Consequently, it is possible to start with a blend of two polymers, such as a diblock coplymer, and selectively infuse just one of the two components.  As a result of this selective, step-wise infusion, SIS can create novel composites with intermediate or even unique properties compared to those of the pure polymeric and inorganic constituents.  Alternatively, the organic component can be removed through oxidation leaving a purely inorganic material, but with a mesostructure that mimics that of the starting polymer.  One particularly attractive application for SIS is lithography: SIS can harden polymer resists rendering them more robust towards subsequent etching, and this permits deeper and higher-resolution patterning of substrates such as silicon.  With this objective in mind, we have performed a series of investigations using in-situ Fourier transform infrared absorption spectroscopy (FTIR), in-situ synchrotron grazing incidence small angle X-ray scattering (GISAXS), and high resolution scanning  transmission electron microscope (STEM) tomography of a model system: Al2O3 SIS using TMA and H2O within the diblock copolymer, poly(styrene-block-methyl methacrylate) (PS-b-PMMA).  While the picture is far from complete, these studies reveal some important details: 1) TMA adsorption on PMMA occurs through a weakly-bound intermediate; 2) the SIS kinetics are diffusion-limited, but desorption is 10x slower than adsorption; 3) dynamic structural changes occur during the individual precursor exposures.  All of findings impact the resulting composite, and hence will dictate the success of the lithography.

Figure 1
(Invited) Selective Etch of Si and SiGe for Gate All-Around Device Architecture
Authors: Wostyn Kurt , Sebaai Farid , Rip Jens , Mertens Hans , Witters Liesbeth , Loo Roger , Hikavyy Andriy Yakovitch , Milenin Alexey , Horiguchi Naoto , Collaert Nadine , Thean Aaron , Mertens Paul W. , De Gendt Stefan , Holsteyns Frank
Published: February 2020

The next era in CMOS technology scaling seeks not only to introduce SiGe or Ge [1] but also aims at replacing the FINFET technology by a gate all around concept, requiring selective removal of Si1-xGex to Si1-yGey(with 0 ≤ x, y ≤ 1).  Gate All-Around (GAA) integration schemes are investigated for improved short channel control. In this paper we will show how alkaline solutions can be used for selective etch of Si and SiGe up to 50% and that the alkaline etch behavior of SiGe is not merely an extension of Si, even at low to moderate Ge concentrations (Ge ≤ 50%). 

The exponential decrease in alkaline etch rate of SiGe with increasing Ge concentration enables the selective removal of Si to Si0.75Ge0.25. [2] Alkaline etching of Si has been studied extensively and is very well understood. [3] The oxidation of Si by water is catalyzed by the hydroxyl anion and results in anisotropic etch properties. The Si (001) and (110) directions etch much faster compared to the Si (111) crystallographic planes. The alkaline dissolution mechanism of SiGe is much less studied and understood.

Figure 1 shows a Si-Si0.75Ge0.25 multilayer stack after alkaline selective etch in 5% TMAH at 60¢ªC. The stack was made by FIN patterning of an epitaxial Si0.75Ge0.25 / Si / Si0.75Ge0.25 / Si multilayer. The TEM picture shows the complete removal of the top Si layer. The selective etch of the Si layer sandwiched between two Si0.75Ge0.25 layers is limited by the slowly etching Si (111) planes, resulting in the formation of inverted pyramids. Figure (1) shows that the Si0.75Ge0.25 layer is also limited by the (111) crystallographic planes. The shape of convex corners results from the crystallographic planes with the highest etch rate. [4] The pyramidal shape of the Si0.75Ge0.25 layer indicates that the Si0.75Ge0.25(111) plane etches faster than (110). This is very different from Si where (111) planes etch much slower than the (110) planes.  

In this paper we will show how SiGe (Ge ≤ 50%) alkaline etching behaves differently compared to Si and its implications to Si or SiGe selective etch. In addition we will show how improper control of process conditions can change SiGe etching from anisotropic to isotropic.

[1] M.L. Lee et al. Appl. Phys. Rev. 97 (2005) 011101.

[2] Seidel et al. J. Electrochem. Soc. 137 (1990) 3626.

[3] M.A. Hines, Annu Rev Phys Chem 54 (2003) 29-56.

[4] P. Pal et al. J. Micromech. Microeng 17 (2007) R111-R133.

Figure 1
(Invited) Thermal Energy Conduction in a Surface Phonon Polariton Crystal
Authors: Cola Baratunde
Published: February 2020

Surface phonon polaritons are coupled states of polar atomic vibrations (optical phonons) and electromagnetic waves that are known to enhance near-field thermal radiation from polar materials.
Theory
suggests that surface phonon polaritons could also increase the thermal conductivity of nanoscale materials under certain conditions. This concept, however, is difficult to demonstrate experimentally,

especially at room temperature. Here we design, predict, and demonstrate a different approach to observe thermal energy conduction by surface phonon polaritons – that is, a surface phonon polariton crystal. Packed beds of silicon dioxide nanoparticles have ultralow thermal conductivity at room temperature
and large internal surface area, such that, when several water molecules are adsorbed on the nanoparticles to increase the effective relative permittivity of their surrounding medium (a mix of air and water), thermal energy conduction from surface phonon polaritons can dominate that generated by phonons. Using this material, we resolve experimentally a surface phonon polariton thermal conductivity that is as high as 1.7 times the phonon value near room temperature. Long-range coupling of surface phonon polaritons in the ordered nanoparticle bed, analogous to the extension of phonons in an atomic crystal, enable this enhancement. In contrast to expectations,
the surface phonon polaritons dictate the total thermal conductivity of the material due to an apparent quenching of phonon conduction. The effects of nanoparticle diameter and surrounding medium on thermal conductivity data are in excellent agreement with theory, providing strong evidence for significant thermal energy conduction by surface phonon polaritons. We anticipate that the theoretical, and practical, framework established here will enable heat conduction by surface phonon polaritons to be explored in detail experimentally, to build on recent interesting theoretical predictions,
and to potentially provide an alternative route
to engineer thermally conductive dielectric materials for thermal management.
Investigation of Silver Oxide Electrochemical Behavior to Improve Silver-Zinc Battery Rechargeability
Authors: Ortega Jeffrey Vincent , Dueber Ross Eugene , Renkin Troy William
Published: February 2020

Cyclic voltammetry and galvanostatic cycling experiments where performed on silver thin films in conjunction with a quartz crystal microbalance (QCM) to identify the intermediate species and mass transport properties at the surface of a silver cathode in the presence of gelled aqueous electrolyte. Scanning electron microscopy (SEM) was then employed to characterize the physical effects from changing the discharge rates and the state-of-charge.  The use of additives on the surface and in the electrolyte was also explored and characterized. The results were then utilized in silver-zinc rechargeable button cell batteries and tested for increased electrode utilization, charge rate capability, and cycle life improvement.
A Prototype Rechargeable Aluminum Battery
Authors: Guo Juchen , Geng Linxiao , Lv Guocheng , Xing Xuebing
Published: February 2020

Although Lithium-ion battery technologies have made significant positive impact on portable electronics and electric vehicle industries, the feasibility of wide deployment of lithium-based batteries for land-based renewable energy storage and grid applications may be questionable due to the limited lithium resource, the resource geographic distribution, and the cost of lithium mining and recycling. Therefore, alternative rechargeable battery technologies based on abundant elements need to be developed for sustainable energy storage. Among the potential candidates, aluminum (Al) may be the ultimate choice as the anode material: Al is not only the most abundant metal in earth’s crust, but also has attractive capacity due to its trivalency. Al has the second highest specific capacity of 2980 mA h g-1 (Li has 4634 mA h g-1) and the highest capacity density of 8046 mA h cm-3 (Li has 2456 mA h cm-3) among all metal anodes. To date, there were only scarce investigations on rechargeable Al batteries with little success.  For the first time, we demonstrate a new prototype rechargeable Al battery comprised of Chevrel phase molybdenum sulfide (Mo6S8) as the intercalation-type cathode, Al metal as the anode, and a mixture of AlCl3 and 1-butyl-3-methyimidazolium chloride (AlCl3-[BMIm]Cl) as the electrolyte. The Mo6S8 cathode shows unambiguous electrochemical activity for reversible Al intercalation and extraction and good cycle stability. The chronopotentiometric plateaus in Al-Mo6S8 charge-discharge curves indicate phase-transition type of electrochemical reactions. In addition to the electrochemical analysis, XRD studies provide the crystallographic information of the Al intercalated Mo6S8. We conclude that the theoretical chemical formula of fully Al intercalated Mo6S8 is Al2Mo6S8 with Al occupying two different sites in the Mo6S8 crystal lattice. The theoretical material-level specific energy of the Al-Mo6S8 battery is approximately 90 Wh kg-1 (assuming 0.5 V nominal voltage), which makes this new rechargeable battery technology an attractive alternative for large-scale sustainable energy storage.
Design & Development of Powerful Next Generation Layered Cathode Materials for Na-Ion Batteries
Authors: Buchholz Daniel , Keller Marlou , Vaalma Christoph , Passerini Stefano
Published: February 2020

Sodium-Ion Batteries (SIBs) have established themselves as possible low-cost alternative to the common lithium-ion battery (LIB). The cost advantage is underlined by a powerful electrochemical performance, superior to any other secondary battery except for LIBs. Consequently, this has led to a rapidly increasing scientific interest within the last five years. In accordance with the economical concept of diversification SIBs are discussed to be promising alternative for applications, in which cost-efficient energy storage (in terms of $/kWh) is the most important criterion. In order to boost SIBs into such applications (e.g. for the decentralized and fragmented power grid of the future) new, powerful but also rather cheap materials composed of abundant and environmentally friendly elements, need to be used in order to cover the lower electrochemical performance. In fact, research community and research efforts are, currently, focusing on the material screening and development. [1-3]

With respect to layered materials strong progress in terms of their understanding, characterization and their performance has been achieved. In this presentation we will focus on the design and development of layered cathode materials for powerful next generation SIBs.

In the past, we have synthesized and characterized layered P2- NaxNi0.22Co0.11Mn0.66O2material. [4-6] In this presentation we will show how the composition of this material can be modified and reveal the effect on the electrochemical performance.[7-9] Final intention of the presentation is to:

-illustrate the influence of the composition on the electrochemical performance,

-illustrate how layered cathode materials can be designed,

-demonstrate the feasibility of these principals via a new layered Na- based oxide.

The final material delivers a stable capacity of about 110 mAh g-1 (3.4 V average discharge potential) at a high current rate of 1C (180 mA g-1) between 4.3-2.5 V (vs. Na/Na+) in conventional organic carbonate based electrolyte. This performance is among the best reported for layered Na-based oxides so far and certainly is promising for the application in future Na-based electrochemical energy storage devices.

[1] S.-W. Kim et al. Adv. Energy Mater. 2 (2012), 710.

[2] J.M. Tarascon Nature Chemistry 2 (2010), 510.

[3] N. Yabuuchi et al. Chem. Rev. 114 (2014), 11636.

[4] D. Buchholz et al. Chem. Mater. 25 (2013), 142.

[5] D. Buchholz et al. J. Mater. Chem. A 2 (2014), 13415.

[6] L.G. Chagas et al. J. Mater. Chem. A 2 (2014) 20263.

[7] I. Hasa et al. Adv. Energy Mater. 4 (2014), 140083.

[8] I. Hasa et al. ACS Appl. Mater. Interfaces 7 (2015), 5206.

[9] D. Buchholz et al. J. Power Sources 282 (2015), 581.
Applying Reconfigurable Networks of Charge-Transporting Polycyclic Aromatic Hydrocarbons to Problems in Energy Storage
Authors: Helms Brett A. , Frischmann Peter D. , Gerber Laura C. H. , Doris Sean E. , Fan Frank , Chiang Yet-Ming , Jain Anubhav , Qu Xiaohui , Persson Kristin A
Published: February 2020

I will report our recent work in understanding and controlling adaptive charge-transport behaviors in reconfigurable molecular networks of polycyclic aromatic hydrocarbons in non-aqueous electrolytes.  This will include a detailed look into their network forming ability as a function of concentration, temperature, and imposed state of charge. Their application as embedded 3-D redox mediators will be discussed in the context of a hybrid Li-S redox flow battery. The design of our network-forming redox mediators was informed by a new high throughput computational platform developed by our team, where we can selectively amplify or dampen electronic charge transport at specific stages in a charge or discharge sequence.
Catholyte Development for Non-Aqueous Redox Flow Batteries
Authors: Zhang Lu , Huang Jinhua , Shkrob Ilya A , Brushett Fikile R. , Wei Xiaoliang , Burrell Anthony K. , Cheng Lei , Curtiss Larry , Duan Wentao
Published: February 2020

Non-aqueous redox flow battery is a promising large scale stationary energy storage technology. Unlike traditional battery systems, the active energy storage material is in mobile phase and stored in external tanks. The energy and power of RFBs thus can be decoupled and independently scaled, which offers remarkable design flexibility for applications with various energy-to-power ratios.

Material development for this technology is crucial for practical implementation. Molecular engineer of organic redox active molecules could lead to tunable physical and electrochemical properties, including solubility in organic solvents, molecular mobility, redox potential, and electrochemical reversibility, which are key factors to energy storage applications. The dimethoxybenzene based catholyte molecules have been systematically developed and evaluated towards various purposes. For instance, ANL-8, ANL-9 and ANL-10 molecules were developed by incorporation of PEO chains with different lengths on one or both sides of the dimethoxy-di-tert-butyl-benzene based redox structure in order to afford higher solubility. Another category of the molecules, including JH-100 and JH-200, were developed by striping down the non-essential structures, such as tert-butyl groups and ether chains, in order to boost the intrinsic capacities. While many of these molecules can afford electrochemically reversible behavior, some new promising features are discovered. ANL-8 and ANL-9 molecules are found to be liquid at room temperature, which was hoped to function as co-solvent for NRFBs, thus leading to much improved energy density. JH-100 and JH-200 molecules, on the other hand, offer much enhanced intrinsic capacity (nearly two times as big as DBBB), which also is believed to be a key to further improve the energy density and lower the cost of NRFBs.
Mo2c Nanoparticle-CNT Composite Electrode for Lithium-Oxygen Battery
Authors: Kwak Won-Jin , Curtiss Larry , Sun Yang-Kook , Lau Kah Chun , Amine Khalil
Published: February 2020

The five times higher energy density compared to conventional Li-ion batteries and its environment friendly reaction system make Li–O2 batteries a promising energy storage system. In spite of their great prospect, practical use of Li−O2 batteries still suffer many challenges such as low energy efficiency, poor rate capability and a poor cycle life. These problems are mainly attributable to excessive accumulation of discharge products (Li2O2), which induce poor reversibility and high polarization when they decompose during charging.1,2 Consequently, the number of operating cycles for Li−O2 batteries cannot yet match those of Li-ion batteries. Moreover, the energy efficiency (< 80%) of the present Li−O2 battery system is also too low. To improve the performance of Li−O2 battery systems, a key factor is finding ways to enhance the catalytic activity of the cathode for formation and decomposition of Li2O2, which is critical to decrease the polarization and increase the reversibility.3,4 Herein, we introduce well dispersed molybdenum carbide nanoparticles onto carbon nanotubes (Mo2C/CNT) as a cathode material for Li−O2 batteries. Mo2C could be a good catalyst for the oxygen evolution reaction (OER) in Li−O2 batteries and the carbon nanotubes could help the Mo2C nanoparticles be an ORR catalyst due to its electrical conductivity. In this report, a Mo2C/carbon nanotube composite as a cathode is demonstrated to reduce high over potentials during charge and improve the cycling performance of Li−O2batteries.

 

References

(1)         Lu, Y. C.; Shao-Horn, Y. Probing the Reaction Kinetics of the Charge Reactions of Nonaqueous Li–O2 Batteries J. Phys. Chem. Lett.
2013, 4, 93-99.

(2)         Xu, J. J.; Wang, Z. L.; Xu, D.; Zhang, L. L.; Zhang, X. B. Tailoring deposition and morphology of discharge products towards high-rate and long-life lithium-oxygen batteries Nat. Commun. 2013, 4, 2438-2449.

(3)         Lu, J.; Lei, Y.; Lau, K. C.; Luo, X.; Du, P.; Wen, J.; Assary, R. S.; Das, U.; Miller, D. J.; Elam, J. W. et al. A nanostructured cathode architecture for low charge overpotential in lithium-oxygen batteries Nat. Commun.
2014, 5, 2383-2391.

(4)           Li, F.; Tang, D. M.; Chen, Y.; Golderg, D.; Kitaura, H.; Zhang, T.; Yamada, A.; Zhou, H. Ru/ITO: A Carbon-Free Cathode for Nonaqueous Li–O2 Battery Nano Lett.
2013, 13, 4702-4707.
High Efficient Charge of Li-O2 Batteries with TEMPO Derivatives
Authors: Hase Yoko , Shiga Tohru , Mizuno Fuminori , Nishikoori Hidetaka , Iba Hideki , Takechi Kensuke
Published: February 2020

Li-O2 batteries, in which Li2O2 is formed and decomposed on the cathode during discharge and charge, respectively, have attracted considerable attention as one of the future energy storage devices demanding high energy density. Recently, we demonstrated the Li-O2 battery employing a ionic liquid, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide (DEME-TFSI), as the solvent of the electrolyte. In this battery, little amount of parasitic reaction products were obtained after discharge because of specific stability of DEME-TFSI against O2 radicals which is well known as one of the major causes decomposing electrolytes in Li-O2 batteries. In addition, relatively lower over potential in charging (< 3.5 V vs. Li/Li+) was observed, whereas the charge capacity was limited to approximately 80% of discharge. According to the quantification analysis, the major causes of the irreversible capacity is Li2O2 remained in the cathode even after charge and parasitic products accompanied by charge process.

We, therefore, focused on redox mediators in order to accelerate the charge reaction. Recently, several redox compounds dissolved in the electrolyte of Li-O2 batteries are reported as redox mediators which make formation or oxidation of Li2O2 more effectively. In this study, we applied 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (MeO-TEMPO) as a mediator because its oxidized compound, MeO-TEMPO+,  stoichiometorically oxidizes Li2O2. In charge process, dissolved MeO-TEMPO was oxidized to MeO-TEMPO+ on the cathode that encouraged the oxidation of Li2O2 and obviously improved the rechargeability (Fig. 1). However, during the detailed investigation, we found that the mediator itself was deactivated along with the deterioration of the carbon cathode during charging; therefore, it is essential to avoid electrochemical oxidation of Li2O2 on the carbon for more efficient battery system.

In order to solve these problems, we have developed new strategy to decouple discharge and charge by chemical regeneration mechanism with mediator. In our new Li-air battery system, the charging process is totally different from an ordinary Li-air battery, and is a replacement of its electrolyte by that containing MeO-TEMPO+ oxidized (charged) separately in advance. Li2O2 in the discharged cathode is stoichiometorically decomposed by the MeO-TEMPO+ (chemical regeneration of cathode), while MeO-TEMPO+ is recovered to the original MeO-TEMPO after the reaction. This indirect charging mechanism promotes the decomposition of Li2O2 without potential electrochemical parasitic reactions and provides a significant improvement of the cycle life. At the same time, the decoupled charge/discharge processes makes more flexibility for the usage of the Li-air battery.

Figure 1