bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Proteins and Cells on Corrosion of Mg
Authors: Virtanen Sannakaisa
Published: February 2020

Mg based materials have been in the focus of increasing interest for temporary biomedical implants, where the device is only required for a certain time of healing. In spite of the large amount of work carried out in  the field, many critical issues still remain, such as limited understanding of the interactions between the corroding Mg (alloy) surface and the biological environment. Results concerning the effects of biomolecules, proteins (and/or) cells on Mg corrosion are scarce and somewhat controversial. For instance, both acceleration or inhibition of Mg corrosion has been reported by proteins in the electrolyte. As the different observations are related to different experimental approaches, it is not straightforward to elucidate the reasons for the seeming discrepancies or the underlying mechanisms.

The presentation will discuss some recent findings on interactions between Mg, proteins (mainly bovine serum albumin), and cells. Protein effects on corrosion were studied by electrochemical techniques on commercially-pure Mg and the Mg alloy AZ91. Surface analysis by XPS and ToF-SIMS indicate that proteins indeed adsorb on Mg surfaces and can inhibit corrosion but the effects are time- and material-dependent. In addition, the presence of proteins in solution change the composition of corrosion layers on the surface. Impedance spectroscopy investigations combined with in vitro cell culturing on Mg demonstrate a significant decrease of dissolution rate after certain time of cell growth.
Study of Single Al Corrosion Pit Growth By Electrochemical Techniques
Authors: Zhang Weilong , Kryzman Mike A , Jaworowski Mark R , Zafiris George S
Published: February 2020

Electrochemical techniques are commonly used for the study of localized corrosion growth [1]. However, pit growth at open circuit is hard to study by electrochemical techniques because of its difficulty of measuring current at open circuit while pit growth under potentiostatic or galvanostatic condition may be totally different from the open circuit.

For stable Al pit growth, it is widely accepted   that local pit chemistry and environment are critical; or a critical value of the stability product (x.i), where x the pit depth, and i the current density, must be maintained for pit survival [2-6].

Several techniques have been proposed for studying  pit growth rates, including (1) Use of artificial pit (“lead-in-pencil”) electrode[7]; (2) Single pit formed by implantation[8]; laser irradiation[9]; (3) Think film electrode [10] ; (4) The foil penetration technique [11].

In this work, we propose to employ a single Al wire (~100um dia.) mounted in epoxy with different initial pit depth d, which is produced by anodic dissolution, for singe Al corrosion pit growth by coupling with a large Al foil ring as its remote cathode through a zero resistance ammeter (ZRA), as schematically shown in Fig.1. The purpose of this study is, in combined with in-situ scanning vibrating electrode technique (SVET, Fig. 2), to determine quantitatively whether the single Al corrosion pit growth follows a depth-dependent growth model as often predicted.

Acknowledgements

This work was performed under United Technologies Corporate R&D funding.

Fig. 1 Schematic geometry of single al corrosion pit formed by an Al wire mounted in epoxy, by coupling with a large Al foil ring as its remote cathode through a zero resistance ammeter (ZRA).

Fig. 2 In-situ SVE images of single Al corrosion pit growth, showing  transition from (a) open circuit condition (before coupled) to (b) galvanically coupled condition.   

References

 

G. S. Frankel, Corros. Sci., 30, 1203 (1990).

J. R. Galvele, J. Electrochem. Soc., 123,464 (1976).

J. R. Galvele, Corros. Set, 21, 551 (1981).

Streblow H.H., Ives M.B., Corr.Sci. 16, 317 (1976).

T.R. Beck, Electrochimica Acta, 29, 485 (1984).

S.T. Pride, J.R. Scully J.R., Hudson J.L., J. Electrochem. Soc. 141, 3028(1994).

H. S. Isaacs and R. C. Newman, Corrosion Chemistry within Pits, Crevices and Cracks, A. Turnbull, Editor, HMSO Books, London (1987).

K. P. Wong and R. C. Alkire, J. Electrochem. Soc., 137, 3010 (1990).

 D. W. Buzza and R. C. Alkire, J. Electrochem. Soc., 142, 1104 (1995).

G. S. Frankel, Mat. Sci. For., 247, 1 (1997).

F. Hunkeler and H. Bohni, Corrosion (Houston),
37, 645 (1981).

Figure 1
On Stress-Corrosion Cracking Initiation: Pitting Susceptibility and Cathodic Activity Near Nonmetallic Steel Inclusions
Authors: Brophy Kyle , Eliyan Faysal , Kish Joseph
Published: February 2020

This study evaluates the pitting susceptibility and cathodic activity for endogenous, nonmetallic inclusions in the high-strength API-X52 and 60 in near-neutral, chloride and bicarbonate solutions. The inclusions are characterized in relation to the steel making method, particularly to the compositional variation across the thickness of a pipeline steel slab. Using conventional potentiodynamic scans, the pitting potentials (along with the transpassivation's) are first systematically linked to the constituents of a matrix of test solutions. The local kinetics of corrosion are studied by Scanning Vibrating Electrode Technique (SVET). The local physical phenomena, including the different modes of localized attacks are studied by suitable microscopic and spectroscopic techniques. For comparison, the electrochemical findings are corroborated by testing synthesized Al2O3 and MnS inclusions, mechanically alloyed to pure iron.
Modeling Aircraft Galvanic Stress Controlled By Kinetic Limitations
Authors: Lee Jason S
Published: February 2020

Repair and replacement of structural components due to galvanic corrosion degradation are high cost drivers in aircraft maintenance. Sea-based aviation platforms experience one of the most corrosive operational environments in the Navy.  Platform designs are not typically optimized for corrosion performance due to poor materials selection, lack of isolation of dissimilar materials, and geometric features which enhance susceptibility to corrosion. A technological gap exists in the capability of lifetime predictions for galvanically coupled airframe components. While traditional galvanic corrosion models evaluate galvanic stress based on the thermodynamic differences in potential, environmentally-dependent kinetic surface reactions are often not taken into account.  The models that do consider kinetic influences use theoretical estimates with little relevance to the exposure environment. A computational model has been designed to develop a basic understanding of the kinetic mechanisms controlling galvanic stress for different aerospace alloy combinations exposed in marine environments. The novelty of the model is that electrochemical boundary conditions are a function of electrolyte chemistry. Regression analysis of the critical boundary condition factors will be used to examine the effects of kinetic limitation on galvanic stress damage.
(Invited) Silicon Electrochemical Micromachining Technology: The Good, the Bad and the Future
Authors: Barillaro Giuseppe
Published: February 2020

Silicon electrochemical micromachining technology (ECM) has come a long way since the pioneering paper of Lehmann and Foll, dated 1990, which firstly reported about the possibility of controlling the electrochemical dissolution of silicon in HF-aqueous electrolytes by back-side illumination etching for the formation of nicely ordered array of macropores. Currently, ECM is routinely used in different laboratories around the world to fabricate silicon microstructures (e.g. microtips, spirals) and microsystems (e.g. microgrippers, microneedles) of much higher complexity than macropores, with application ranging from (bio)sensing to nanomedicine, from photonics to microelectronics.

ECM technology capitalizes on the experimental and theoretical results reported in the literature over the last two decades on the electrochemical dissolution of silicon in HF-aqueous electrolytes. Among others (e.g. aspect-ratio>100, verticality≈90°, surface roughness<10 nm), it is worth mentioning the peculiarity of dynamically controlling the electrochemical etching anisotropy from 1 to 0 in real-time, which has greatly advanced such a technology with respect to state-of-the-art etching technology. Nonetheless, a number of important limitations either remain unsolved or need to be improved towards future industrial applications of ECM technology (e.g. minimum and maximum etching features, etching rate).

In this paper, basic and advanced features as well as main limitations of silicon microfabrication by ECM technology are thoroughly reviewed and discussed, both from theoretical and experimental points of view, also with reference to future industrial applications. As case studies, fabrication by ECM technology (and characterization) of all-silicon, integrated microstructures and microsystems for different (bio)-sensing/medical applications will be detailed and discussed, with particular emphasis on (though not limited to): i) photonic crystal optofluidic microsystems for (bio)sensing applications, ii) microneedle-based chips for transdermal  glycemic control; iii) electrically-actuable silicon microgrippers for biology/medicine applications; iv) 3D microincubators for selection of cancer cells on the basis of their metastatic potential.
Low Doped n-type Localized Porous Silicon Made by Hole Injection from Back-side p+/n Junction for Power Switches Application
Authors: Fèvre Angélique , Menard Samuel , Defforge Thomas , Gautier Gael
Published: February 2020

Power switches are often present in electrical domestic environment directly connected to the mains supply. This kind of component operates in two principal modes, i.e. ON-mode and OFF-mode. The OFF-mode depends on the device periphery insulation capacity. Glass passivated grooves in the silicon are currently used giving good performances for reasonable cost. Changing this technology would permit higher wafer diameter and packaging simplification. Porous silicon (PS) is a potential candidate thanks to its electrical insulating behavior [1]. However, the usual substrate type and doping for such devices are n-type silicon and 1.1014 cm-3 respectively. At this doping level, porous silicon formation needs hole supply from an external source to avoid breakdown mechanism [1]. This can be achieved by either electron-hole pairs generation by illumination [2] or hole injection from a back-side p+/n junction [3][4]. This study focused on the second technique, which is easier to integrate in an industrial microelectronic process. Indeed, the presence in the active area (ON-mode) of a p+ region on the rear side could be used as a hole source. This junction is realized by boron implantation followed by an annealing. During the electrochemical etching, the p+/n junction needs to be forward biased to inject holes toward the anodic surface (Fig 1). Then, carrier lifetime must be sufficient to let holes cross n-type bulk silicon, featured by its thickness d (Fig 1).

First, a simplified case of non-localized p+/n junction is investigated (Fig 1). The influence of anodization parameters such as the current density and the electrolyte composition (additives) is presented for high HF concentration. A comparison with illumination technique is also discussed. Whatever the process case, the resulting PS morphology consists of a double layer (Fig 2): with a nucleation layer composed of mesopores and a macroporous layer filled with mesopores. To the best of our knowledge, this morphology has not been analyzed for low doped n-type silicon in the literature though it was mentioned in [5].

Electrical transverse characterization in DC (-10 to 10 V) of an Aluminum/PS/Si/Aluminum stack shows a gain in resistivity of 106Ω.cm compared to bulk silicon which is promising for the application.

As PS will be only present in the device periphery, a study of its localization is investigated. The resulting masking issues are analyzed.

1. M. Bouaïcha,  M. Khardani and B. Bessaïs, Material Science and Engineering,
C26, 486 (2006).

2. V. Lehmann, J. Electrochem. Soc., 140, 2836 (1993).

3. X. Badel , J. Linnros and P. Kleimann,, Electrochem. and solid-state letters, 6, C79 (2003).

4. L. Coudron, G. Gautier, B. Morillon, S. Kouassi, T. Defforge and L. Ventura, Electrochem. and solid-state letters, 14, H24 (2011).

5. X.Q. Bao, D.H. Ge, S. Zhang, L. Zhao, J.W. Jiao and Y.L. Wang, Chinese Science Bulletin, 54 (7), 1143 (2009).

Figure 1
Morphological and Optical Properties of Stain Etched Silicon in Vanadium Oxide (V2O5) / Hydrofluoric Acid (HF) Solution
Authors: Ayat Maha , Gabouze Noureddine , Sam Sabrina , Boarino Luca , Boukherroub Rabah
Published: February 2020

In the current semiconductor industry, silicon (Si) nanostructures represent the basic material for the conception of several devices in the field of nanoelectronics,  optoelectronics, energy conversion, energy storage, and also (bio) chemical sensors.Various methods have been developed to fabricate Si nanostructures such as reactive ion etching (RIE), electrochemical etching, metal-assisted etching or stain etching. This last one is an electroless method to form porous silicon (PSi) in a mixture based on hydrofluoric acid (HF) and an oxidant.

In this work we report the fabrication of ordered macroporous silicion structures by chemical etching of silicon in vanadium oxide (V2O5) and hydrofluoric acid (HF) solution. The effects of the different etching parameters, including the etching time and the presence of metal catalyst film deposition (Pd, Ag), on the morphologies and the optical properties of the etched Si surfaces were studied.  Scanning Electron Microscopy (SEM) was carried out to explore the morphologies of the as etched surfaces with and without the presence of catalyst. The obtained structures were characterized by Fourier Transform Infrared Spectroscopy (FTIR). A spectrophotometer UV-Vis-NIR was used to study the reflectance of the obtained structures.

It has been found that the morphology depends on  the etching time and on the presence and the type of the catalyst. The results show that the attack of the silicon surface coated with Palladium or Silver deposit begins by creating circular pores. Moreover the pore diameter can be easily varied by changing the etching parameters such as the concentration and the etching time. In addition, long etching time leads to the formation of porous pyramidal structures at the bottom of the pore silicon. Finally,the presence of metal catalyst (Pd or Ag) does not only accelerate the etch rate but also creates pyramidal structures within the macropores.

A reflectance around 1,78% for the Ag/Si structures and about 4% for Pd/Si structures was obtained after 60 min etching. The surface hydrophobicity was also studied for the obtained structures and we observe a contact angle of 145°.

Figure 1
(Invited) Ultrafine Porous Polyimide Membrane for Rechargeable Lithium Batteries
Authors: Kanamura Kiyoshi , Miyahara Kazuhei , Aoyama Yohei , Ouchi Kenya , Haibara Masaki , Munakata Hirokazu
Published: February 2020

Porous membranes have been used in various fields as key materials for separation. Their functionalities strongly depend on their structures such as pore size, pore distribution and porosity. Thus, the structure design of porous membranes has been focused over the years. Particularly, the research and development of ultrafine porous membranes has been intensively engaged. In the research field of battery, porous membranes are used as separators, whose role is to prevent electrical short circuits between anode and cathode but easy permeation of ions. Thus, the safety and power of batteries is strongly dependent on the porous separator, and many advanced porous membranes have been developed for batteries. In this study, we have developed an ultrafine porous polyimide membrane illustrated in Fig. 1, and investigated its performance as a battery separator. This structure is so-called three-dimensionally ordered macroporous (3DOM) structure and has an ideal porosity of 74%. The pores are in a hexagonal close-packed arrangement, so that uniform current distribution is expected during battery charge and discharge.

 3DOM polyimide membrane for a battery separator was prepared by using a colloidal crystal template composed of mono-disperse spherical particles [1]. Fig. 1 shows the characteristics of 3DOM polyimide separator with the pore size of ~300 nm. The uniformly ordered structure with a high porosity of ~ 70% resulted in a very low Gurley value (32 sec), which is about 1/20 of conventional polyolefin separators [2]. The smaller Gurley value leads to the smoother Li+-ion transport in the separator. Actually, the 3DOM polyimide separator provided uniform current distribution for rechargeable lithium batteries, and was particularly effective to lithium metal anode which has a serious problem to be used in rechargeable batteries due to dendrite-formed deposition during battery charge process (Fig. 3). This is very advantageous for realizing high capacity rechargeable batteries using lithium metal anode.

References

[1] H. Munakata, D. Yamamoto and K. Kanamura, J. Power Sources, 178(2008) 596-602.

[2] S. S. Zhang, J. Power Sources, 164 (2007) 351-364.

Figure 1
Porous Layers Composed of Oxide Crystallites Formed by the Combination of Laser Ablation and Anodization of Metal
Authors: Ganas Abbie S. , Znamensky Dmitry A. , Méndez Alba Nahúm , Hernández-Pozos José Luis , Kolasinski Kurt W
Published: February 2020

Self-limiting and self-organizing high voltage anodization is well known for making oxide nanostructures such as porous alumina and TiO2 nanotubes. The formation mechanisms of both of these materials involve an intricate balance between oxide growth and dissolution in which pore initiation and propagation is convoluted with the need for strain relief because of the expansion inherent to oxide formation. Laser ablation with a nanosecond pulsed Nd:YAG laser operating at 532 nm produces texture in the form of arrays of pillars, macropores and ripples. Nanoparticles produced in the ablation plume can also be deposited on the target or a remote substrate. These substrates are anodized in solutions typically used for porous film and nanotube production (including viscous fluoride containing electrolytes). Results for a number of metals including Al, Sn, Ti and Zn will be discussed. Laser pre-texturing results in the formation of structures unattainable by conventional anodization. Deposited nanoparticles, of e.g. Al, are found to act as seeds for the growth of oxide crystallites that fuse into porous films composed of these crystallites, as shown in the image below.

Figure 1
Pd-Pt Catalyst Layer Formation Based on Porous Si
Authors: Hayase Masanori
Published: February 2020

Our group proposed a Si based miniature fuel cell that has both fuel channel and catalyst layer on a Si substrate[1]. Maximum power density reached 500 mW/cm2 at 313 K with H2-O2 supply, which is comparable to conventional state-of-the-art fuel cells. In the fabrication process, initially porous Si is formed by anodization in a HF solution, then the Si is replaced by Pt in a wet plating process, and a porous Pt catalyst layer is formed on a Si chip. The catalyst layer consists of Pt, and amount Pt is estimated to be 3.6 mg/cm2, while typical conventional fuel cells use only 0.1 mg/cm2. We have to reduce the amount of Pt for practical use of the miniature fuel cell. 

We found that porous Pd layer can be also made with almost identical process to the porous Pt formation, and have discussed Pd-Pt catalyst for reduction of the Pt usage in our miniature fuel cells. In this study, slight Pt was deposited on the porous Pd, and prototype fuel cells showed increase of power output by only 0.01mg/cm2Pt deposition. Furthermore, the Pd-Pt catalyst showed promissing result to CO poisoning.

[1] M. Hayase, T. Fujii, J. G. A. Brito-Neto, J
. Electrochem
. Soc
., 158(4), B355-359 (2011)
High Efficiency Millimeter-Scale Crystalline Perovskite Solar Cells
Authors: Mohite Aditya , Nie Wanyi , Tsai Hsinhan , Asadpour Reza , Blancon Jean-Christophe , Neukirch Amanda , Gupta Gautam , Crochet Jared , Chhowalla Manish , Alam Muhammad , Wang Hsing-Lin , Tretiak Sergei
Published: February 2020

Current state-of-the-art photovoltaics utilize high purity single-crystal semiconductors grown by sophisticated, high temperature crystal-growth processes. Alternative emerging solar cell technologies based on solution-processed materials promise to deliver power at lower cost, but so far have had limited success due to the presence of defects in the bulk and at the grain boundaries. Improving the crystal size and quality of solution-processed films could lead to unprecedented improvements in photovoltaic performance. However, large-scale crystal growth is challenging in solution-based deposition where molecular kinetics are limited by the low processing temperature. Here, for the first time we demonstrate organometallic perovskites thin-films composed of extra-ordinarily large crystalline grains (1-2 mm), fabricated using a new processing technique. The increase in the grain-size directly correlates to a dramatic increase in the efficiency, as a direct consequence of increased charge carrier mobility and reduction in defect densities. Our measured efficiency values approach ~18%, which is among the highest reported. These devices are extremely robust, exhibiting no degradation with voltage sweep direction or the rate at which the voltage was scanned. We anticipate that this technique for growing high quality large-area crystals at low temperature with low defect concentration will be universally applicable to a wide variety of other material systems thus providing a solution to a long-standing scientific challenge of overcoming polydispersity, defects and grain boundary recombination in solution-processed thin-films. From the perspective of the global photovoltaics community, these results are expected to lead the field towards the synthesis of wafer-scale crystalline perovskites necessary for the fabrication of high-efficiency single-junction and hybrid (semiconductor and perovskite) tandem planar cells. In addition, I will also discuss design principles that govern the photostability in these systems.
Bandgap Engineering in TiO2 By Sulfurization
Authors: Shin Woo Jung , Granados Araceli Hernández , Hu Hailin , Tao Meng
Published: February 2020

Previous studies have proposed bandgap narrowing by anion (e.g. N, C, or S) or cation doping into the lattice of TiO2. Sulfur is of particular interest, as TiS2 has a close-to-zero bandgap. By mixing TiO2 and TiS2 into oxysulfide, a new semiconductor with a suitable bandgap for photovoltaics or solar water splitting may emerge. In this work, we investigate sulfurization of TiO2 thin films through H2S gas-phase diffusion. The TiO2 films were prepared by the sol-gel method. Transmittance and X-ray diffraction analyses indicate that the TiO2 films have an anatase phase with a direct bandgap of 3.2 eV. The films are sulfurized in H2S under different pressure, temperature and time. It is found that sulfurization results in a second, narrower bandgap phase in TiO2. At 600˚C, the anatase TiO2 almost completely disappears. The results suggest that sulfurization by H2S is effective in narrowing the bandgap of TiO2.
Low Stress and High Ductility Copper Electroplating Additive Development
Authors: Wei Lingyun , Kao Yu Hua , Hazebrouck Rebecca , Corona Robert , Lieb Bryan , Wang Ying , Lowe Michael A. , Lefebvre Mark , Pyo Sung-Ho , Tachikawa Wataru , Calvert Jeffrey
Published: February 2020

Copper electroplating is one of the most important metallization technologies to produce metal contacts in the fabrication of crystalline silicon solar cells. It has been adopted in three areas, including: Interdigited Back Contact cell (IBC); Heterojunction with Intrinsic Thin layer (HIT); and Fully Plated Front Contact solar cells. Due to cost concerns, significant changes have been made in the silicon manufacturing process leading to thinner Si wafers.  This change brings many challenges for copper metallization. One of the biggest challenges is to maintain a low internal stress of the copper deposit.  This is key to avoid solar wafer warpage and maintain good adhesion. Copper deposits with high ductility are also desired to prevent or reduce the potential for the copper deposit to crack under stress over time.  Ideal copper deposits exhibit low internal stress and high ductility. However, development of this plating chemistry is a challenge for the material supplier, as improvement in one attribute typically comes at the expense of another.  Accordingly, there is need to develop organic additives for copper electroplating baths that alleviate internal stress in copper deposits as well as providing good ductility. In this paper, the performance of new acid copper electroplating bath capable of achieving both low internal stress and good ductility will be highlighted. Additive impact on copper deposit material properties and correlation between these properties and performance will be discussed
Electrical Studies on Parylene-C Columnar Microfibrous Thin Films
Authors: Khawaji Ibrahim H , Chindam Chandraprakash , Orfali Wasim , Awadelkarim Osama Osman , Lakhtakia Akhlesh
Published: February 2020

Future advances in solid-state device technology are dependent on innovations in multifunctional materials and novel deposition processes and, hence, a wide spectrum of new material compositions and morphologies are being explored. For this study, microfibrous thin films (µFTFs) of Parylene C  [1,2] were deposited on top of p-type Si substrates using physicochemical vapor deposition in a PDS2010 Labcoater to form metal-insulator–semiconductor (MIS) and metal–insulator–metal (MIM) capacitor structures utilizing the Parylene-C µFTF as the gate dielectric. Each µFTF was deposited with a collimated vapor flux of Parylene-C monomers inclined at 60° to the substrate plane and had a thickness of about 100 µm. The Parylene-C µFTFs were characterized for electrical properties and dielectric integrity using leakage current, equivalent series resistance and reactance, capacitance measurements at temperatures ranging from –40 °C to 125 °C and frequencies ranging from 1 kHz to 1 MHz, as well as field-emission scanning electron microscopy. The observed variations in leakage current can be explained in terms of transport mechanisms involving thermionic emission and electron hopping. Capacitance and dielectric loss data were analyzed. We found that higher leakage current does not allow for a reliable estimation of the dielectric constant.

[1] Pursel, S., Horn, M. W., Demirel, M. C., & Lakhtakia, A. (2005). Growth of sculptured polymer submicronwire assemblies by vapor deposition, Polymer, 46(23), 9544–9548.

[2] Chindam, C., Wonderling, N. M., Lakhtakia, A., Awadelkarim, O. O., & Orfali, W. (2015). Microfiber inclination, crystallinity, and water wettability of microfibrous thin-film substrates of Parylene C in relation to the direction of the monomer vapor during fabrication, Applied Surface Science, 345(1), 145–155.
Electroless Deposition of Ferromagnetic CoxFe1-x alloys Using Metal Ion Reducing Agent
Authors: Joi Aniruddha , Chen Ernest , Dordi Yezdi
Published: February 2020

21st century computing applications such as big-data analytics, cloud-based computing, etc., require enormous memory capacity.  Shuttling large amounts of information between numerous levels of interconnects and memory hierarchies that are necessary for these kind of applications incurs substantial latency and energy costs which is not suitable for today’s low-power, high performance devices.  A different approach that is being considered involves inserting low-power non-volatile memory cells closer to logic/processor for faster and more efficient processing1 in so-called ‘monolithic integration’.  Due to its low power and high endurance, spin-based (spin-torque transfer, spin Hall effect) 2, 3 memories have recently gained attention.  In spin-torque transfer memories, information is stored in the spin orientation of a soft ferromagnetic layer, typically a CoFe or CoFeB alloy. A spin-polarized current is used to change the spin orientation in the ferromagnetic layer either ‘up’ or ‘down’, providing the binary states.  This memory stack is usually formed by a subtractive process. Individual stacks are deposited by physical vapor deposition followed by reactive ion etching to obtain the memory cells.  Alternatively, an additive process where the ferromagnetic layers are selectively deposited can be proposed.  The additive scheme does not have some of the negative consequences associated with subtractive processes such as non-uniform profile, re-deposition of etch by-products and difficulties in scaling. Here, we demonstrate a selective deposition process for CoxFe1-x (x=0-1) ferromagnetic alloy enabled by electroless deposition.  Trivalent TiCl3 is used as a reducing agent which facilitates growth of crystalline and contaminant-free (such as B or P) film even at room temperature.  Electrochemical characterization of the oxidation and reduction half-reactions are presented and are used to rationally design the electrolyte.  X-ray photoelectron spectroscopy (XPS) characterization indicates the presence of metallic Co and Fe in the bulk of the deposit. Finally, the magnetic properties of the CoFe film are investigated using vibrating sample magnetometer (VSM).  Electroless deposited CoFe thin films demonstrate magneto-crystalline anisotropy with distinct easy and hard axes and high saturation moment.  Effect of heat treatment and surface capping on magnetic properties are also discussed.  Finally, some challenges involving integration of such an additive process is highlighted along with possible solutions.

Figure 1: XPS characterization of the CoFe film deposited on a PVD Cu substrate.  Carbon and oxygen are mainly present at the surface and not shown for clarity.  Chemical state analysis indicates presence of metallic Co and Fe in the bulk film.

References:

H.-S. P. Wong and S. Salahuddin, Nat. Nanotech. 10 (2015)

S. Ikeda, K. Miura, H. Yamamoto et al, Nat. Mater. 9 (2010)

L. Liu, C-F. Pai, Y. Li et al, Science 336 (2012)

Figure 1
Non-Thermal Equilibrium Formation of Ge1-xSnx (0≤x≤0.2) Crystals on Insulator by Pulsed Laser Annealing
Authors: Moto Kenta , Matsumura Ryo , Chikita Hironori , Sadoh Taizoh , Ikenoue Hiroshi , Miyao Masanobu
Published: February 2020

Introduction

Formation of crystalline GeSn film on insulator with high Sn concentration exceeding thermal equilibrium solid-solubility is strongly expected to realize high-speed thin film transistors. To explore non-thermal equilibrium processing [1], we examined crystallization of amorphous-GeSn (a-GeSn) with various modulated Sn concentration by pulsed laser annealing (PLA). In the present study, we focus on the influence of the Sn concentration on crystallization of a-GeSn by PLA.

Experimental Procedure

Schematic sample structure and PLA conditions are shown in Fig.1. A-Ge1-xSnx (0≦x≦0.2) films (thickness: 100 nm) were deposited on quartz substrates by a molecular beam technique. These samples were irradiated with a pulsed laser (energy : 10 - 230 mJ/cm2, pulse period : 1 sec, pulse number : 100 shot). The laser annealed regions were analyzed by Nomarski microscopy and Raman scattering spectroscopy.

Results and Discussion

　Nomarski micrograph and Raman spectra of Ge0.8Sn0.2 samples before and after PLA with various energy are summarized in Fig. 2. In the samples after PLA, the contrast-changed regions were observed, compared with the as-deposited sample. Here, the contrast becomes stronger with increasing energy from 50 mJ/cm2 to 170 mJ/cm2, and finally the GeSn layer was damaged for energy of 230 mJ/cm2. Raman spectra reveales that Ge0.8Sn0.2 is crystallized on insulating substrates by 50 - 170 mJ/cm2 PLA.

The process-window to achieve crystalline GeSn is summarized in Fig. 3(a), where the energy for starting crystallization and the energy just before damaging are indicated as Ecryst. and Edamage , respectively. Substitutional Sn concentration estimated from shift of Ge-Ge peak obtained by Raman measurements is shown in Fig. 3(b). The process window necessary for crystallization is significantly expanded by introducing Sn, i.e. 16 mJ/cm2 for Ge, ~ 130 mJ/cm2 for GeSn.

High Sn concentration exceeding thermal equilibrium solid-solubility is obtained by PLA, for all GeSn samples. Interestingly, for samples with initial Sn concentration of 5 % and 10 %, almost all Sn atoms are incorporated into substitutional site, while for 20 % sample, only half of Sn atoms are incorporated into substitutional site. The detailed physics will be discussed in the presentation.

References

[1] M. Kurosawa, et al., Appl. Phys. Lett. 104, 061901 (2014).

Figure 1
A Study on Chamber Contamination Control of Rapid Thermal Nitridation Process By Applying Quartz Liner
Authors: Yun Jin Hyuk , Park Se Geun , Kang Byung Je , Lee Young Ho , An Jung Su , Cho In Su
Published: February 2020

To improve the characteristics of barrier wall in DRAM plug contact via, the rapid thermal nitridation(RTN)  process has been widely used via rapid thermal  process chamber. With combination of high temperature heat, process gas such as NH3 and wafer being processed, the Ammonium Chloride(NH4Cl) is generated as a byproduct of this process and chamber is contaminated by NH4Cl depositing on the reflector. This contaminant diffracts the thermal energy which comes into pyrometers and degrades process quality. To prevent this chamber contamination from the byproduct such as NH4Cl, the transparent quartz liner on reflector plate is adopted.

In this study, the influence of quartz liner on reflector plate, the improvement of chamber contamination and pyrometer sensitivity were investigated.

In RTN process, TiSix or CoSix is formed in Si contract area as an ohmic contact and improves the adhesion with tungsten by transducing Ti to TiN.[1]

Eq.1 shows how Ammonium Chloride (NH4Cl(s)) is generated during RTN process as a byproduct.

NH4Cl sublimes at 337.6°C and the reflector plate increases no more than 225.3°C at 1000°C, 90sec process condition. Therefore NH4Cl is deposited on the chamber wall as well as reflector plate. Fig.1 shows the diagram of NH4Cl deposition on reflector plate as a contaminant. This contaminant diffracts the thermal energy which comes into pyrometers and degrades the silicide uniformity.

In Fig.2, device “A” at target temperature has more uniform shape than device “B” which has been processed in lower temperature than target of “A”.

Fig.3 shows transparent quartz in RTP chamber to prevent reflector plate from the contaminant.

Fig.4 shows presence of quartz liner has very stable halogen lamps power dissipation than without quartz.

Fig.5 shows temperature error against target value with quartz liner is much lower than without quartz.

In this paper, the influence of quartz liner on reflector plate, the improvement of chamber contamination and pyrometer sensitivity were investigated. From experimental result, presence of quartz liner protects reflector plate from contamination and keeps power dissipation of halogen lamps in stable. As a result, it means that more accurate heat control is possible in RTN process which could affect the quality of plug contacts of semiconductor device.

Reference

[1] ] Zhao Wenbin, Chen Haifeng, XiaoZhiqiang, Li leilei, Yu Zongguang, Journal of Semiconductors (2009) 056001

Figure 1
Atomic Structure Evolution during First Charge of Layered-Layered Composite Lithium Ion Battery Cathode Materials
Authors: Iddir Hakim , Croy Jason R. , Gallagher Kevin G. , Johnson Christopher , Benedek Roy , Balasubramanian Mahalingam
Published: February 2020

Layered-layered composites with composition xLi2MnO3•(1-x)LiMO2 enable high capacity and energy density Li-ion batteries, but suffer from degradation with cycling. Evidence of atomic instabilities during the first charge are addressed in this work with X-ray absorption spectroscopy, first principles simulation at the GGA+U level, and existing literature. The pristine material of composition xLi2MnO3•(1-x)LiMn0.5Ni0.5O2  is assumed in the simulations to have the form of LiMn2 stripes, alternating with NiMn stripes, in the metal layers. The charged state is simulated by removing Li from the Li layer, relaxing the resultant system by steepest descents, then allowing the structure to evolve by molecular dynamics at 1000 K, and finally relaxing the evolved system by steepest descents. The simulations show that about ¼ of the oxygen ions in the Li2MnO3 domains are displaced from their original lattice sites, and form oxygen-oxygen bonds, which significantly lowers the energy, relative to that of the starting structure in which the oxygen sublattice is intact. The oxygen displacement facilitates the displacement of about (1/3) of the (Li2MnO3 domain) Mn ions to migrate to the delithiated Li layers.
Mesoscale Modeling of Phase Transformations in Layered Intercalation Materials
Authors: Radin Maxwell , Van der Ven Anton
Published: February 2020

The phase transformations that occur during the intercalation of layered materials can play an important role in the performance of many types of batteries. In particular, structural changes during these transformations are associated with degradation due to mechanical stress and deformation. However, the mechanisms by which such phase transformations occur are not well understood. To explore how these phenomena can affect battery performance, we present a mesoscale chemo-mechanical framework for describing phase transformations in layered intercalation materials, and illustrate how such an approach can be parameterized using first-principles simulations. Particular focus is given to common Li-ion electrode materials.
(Invited) A Mesoscale Approach Toward Elucidating Microstructure-Transport-Performance Interaction in Li-S Battery Electrodes
Authors: Mukherjee Partha P. , Liu Zhixiao , Chen Chien-Fan , Mistry Aashutosh
Published: February 2020

Lithium-sulfur (Li-S) battery is a promising energy storage technology, which offers improved performance in terms of higher energy density and material sustainability owing to the abundance of sulfur (S) as the active material. However, one of the key challenges centers on insoluble discharge product formation in the cathode and concomitant internal shuttle effect [1-5]. The polysulfide (such as Li2S) formation poses a deleterious consequence on the electrode microstructural change, thereby impacting the transport and electrochemical properties and ultimately resulting in capacity fade.

In this regard, the cathode architecture plays an important role in determining the Li-S battery performance. A desirable electrode microstructure should effectively deter the dissolution of polysulfide, and facilitate lithium ion transport. This warrants a fundamental understanding of the physicochemical interplay resulting from the underlying microstructure-transport-performance interaction.

In this work, a mesoscale computational model, shown schematically in Fig.1, will be presented in order to fundamentally investigate the morphology evolution due to Li2S precipitation and the resulting influence on the electrode microstructural and performance attributes.

Acknowledgement:

Financial support from the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, grant DE-EE0006832 (Program manager: Dr. Tien Duong) is gratefully acknowledged.

References:

1.             P. G. Bruce, S. A. Freunberger, L. J. Hardwick, and J.-M. Tarascon, Nat Mater,
11(1), 19-29 (2012).

2.             Y. Yang, G. Y. Zheng, and Y. Cui, Chem Soc Rev,
42(7), 3018-3032 (2013).

3.             X. Ji, K. T. Lee, and L. F. Nazar, Nat Mater,
8(6), 500-506 (2009).

4.             X. Ji, S. Evers, R. Black, and L. F. Nazar, Nat Commun,
2, 325 (2011).

5.             Z. Liu, D. Hubble, P. B. Balbuena, and P. P. Mukherjee, Phys Chem Chem Phys, 17, 9032 (2015).

Figure 1
Study of the Impedance Growth and Capacity Fade of High Power Lithium-Iron Phosphate, Valve Regulated Lead Acid, and Nickel Metal Hydride Batteries When Cycled in High Rated Pulsed Profiles
Authors: Williams Christopher , Martin Matthew Jene , Wetz David Alan , Gnegy-Davidson Clint Gerhard
Published: February 2020

Electrochemical energy storage has become more power and energy dense in recent years, considerably opening up the application space for which they can be used. Among these applications are high power loads which operate in a pulsed manner. The most common chemistries considered for use in these applications include valve regulated lead acid (VRLA), nickel metal hydride (NiMH), and lithium-ion (LI). The University of Texas at Arlington’s (UTAs) Pulsed Power and Energy Laboratory (PPEL) has assembled roughly 60 V modules of each chemistry and experimentally characterized their capacity fade and impedance growth when they are used to drive a 40 kW constant power load in a 5 seconds on / 5 seconds off pulsed profile. The VRLAs are discharged at four times their ten hour rating, the NiMH are discharged at eight times their one hour rating, and the LI are discharged at thirteen times their one hour rating. All of the batteries are recharged at elevated rates, in most cases the maximum allowed by the manufacturer. Using standard voltage, current, and thermal diagnostics as well as periodic electrochemical impedance spectroscopy (EIS) measurements, the capacity fade and impedance growth of each chemistry has been studied to understand how the high rate pulsed profile ages the cells. Empirical and lumped element models of the impedance rise have been developed to better understand what is aging internally and how it impacts the usable life of the batteries compared with manufacturers rated life predictions. The experimental and modeling efforts will be summarized and conclusions will be drawn to provide the audience with a better understanding of how each of these technologies ages when used in high rate, pulsed applications.
Thermal-Electrochemical Lithium-Ion Battery Simulations on Microstructure and Porous Electrode Scale
Authors: Latz Arnulf , Zausch Jochen
Published: February 2020

Heat production within a battery cell is governed by local fluxes of ions and electrical currents in the microstructure of the battery electrodes. These fluxes on the other hand are strongly coupled with thermal transport, leading to a fully coupled reaction transport model for batteries [1]. It describes ion, charge and heat transport on the length scale of the microscopic active particles that build up an electrode. The implementation of the model in our simulation software BEST [2] allows simulations of transport and reactions in three-dimensionally fully resolved electrode structures. Ion concentration, potential and temperature are obtained in each spatial point of the simulation domain. Thus the dependence of battery performance, heat production and heat distribution in the electrode microstructure can be studied.

Due to its geometric complexity this approach is not viable for a simulation on cell scale. To this end effective or homogenized models are commonly employed [3]. By applying the volume-averaging technique to our thermal-electrochemical microscopic theory the corresponding thermal-electrochemical porous electrode theory can be derived [4]. Since volume-averaging neglects the details of the electrode structure it is obvious that ion fluxes and electrical currents cannot be recovered in detail. However, many heat sources of our model depend on the magnitude and distribution of these fluxes (e.g. Joule heating) and are strongly localized on the interfaces between electrolyte and active particles. It is therefore a priory not clear whether upscaled models of this type are at all useful for predictive cell scale simulations if heat production and temperature distribution is of interest.

In our contribution we will present the fully coupled thermal battery models for both micro and cell scale. We focus on a simulation study where we compare micro- with equivalent cell scale simulations based on the derived porous electrode theory. Whereas the numerically averaged results agree very well with the results of porous electrode theory, strong fluctuations around this average (e.g. of the overpotential) are observed in microstructures. Especially for the prediction of degradation phenomena, these fluctuations are crucial and cannot be recovered in porous electrode theory. Our results raise the question to which extent porous electrode theory can be used to predict degradation phenomena in batteries.

[1]   A. Latz and J. Zausch, Journal of Power Sources 196 (2011) 3296.

[2]   www.itwm.fraunhofer.de/best

[3]   J. Newman and W. Tiedemann, AIChE 21, (1975) 25.

[4] A. Latz, J. Zausch, Multiscale modeling of lithium ion batteries : thermal aspects, Beilstein J. Nanotechnol. 6 (2015) 987–1007. doi:10.3762/bjnano.6.102.
A Computational Model for Sodium Sulfur Battery Analysis
Authors: Sezer Hayri , Aygun Mehmet , Mason Jerry Hunter , Baran Engin , Celik Ismail Bektas
Published: February 2020

Energy storage from the renewable energy sources is one of the challenging issue of clean energy technologies. Recently, sodium sulfur (Na-S) battery has gained considerable attention as a viable candidate of energy storage application. However, Na-S battery technology comes with the disadvantages of relatively high temperature operating conditions, brittle insulator and safety concern with regarded to temperature management. In this study, a two-dimensional heat transfer model is integrated with a zero-dimensional, transient electrochemical model for Na-S batteries to predict the temperature distribution inside the Na-S battery under cell operating conditions. Properties required for solving the heat transfer governing equation and electrochemical model, such as electronic and ionic conductivity, species concentrations and heat conductivity are calculated and updated as a function of time. Additionally, the instant outputs of these combined computational tool for single sodium sulfur battery, temperature, open circuit voltage, polarization and ohmic losses are used as input values for a designed Simulink model to analyze a stack of Na-S batteries. These computational tools aim to enable the thermal management and to complete design procedure of storage systems made of Na-S batteries. The present model is tested against experimental results found in literature. Good agreement is achieved between current model and the available experiment in the literature.  Validated model is used to perform a parametric study.