bluuebunny/crossref_metadata_2025 huggingface dataset:
In-Situ Corrosion Screening of Co-Sputtered (Fe-Cr-Ni) Alloy Thin Film Library in Simulated Human Physiological Condition
Authors: Lone Shaukat Ali , Mardare Cezarina Cela , Mardare Andrei Ionut , Hassel Achim Walter
Published: July 2021

High throughput combinatorial analysis is a cost effective and time saving approach for characterizing a wide range of alloys. This technique can be used to optimize the chemical composition for several applications i.e. corrosion resistance and pharmaceutical[1-2]. Austenitic stainless-steel (AISI 316L and ASTM F-55) exhibits excellent load bearing and tribocorrosion resistance in human body condition[3]. However, these alloys have shown ineffectiveness to resist the localized form of corrosion and harmful release of metallic ions i.e. Ni, Cr and Fe in the human body[4].

Hereby a ternary library with a compositional matrix of Fe (59-86 at.%), Ni (3-15 at.%) and Cr (9-30 at.%) is produced through co-sputtering. All compositions exhibited a columnar grain structure with pointy tips. The grain size ranged between 10-50 nm. Broad peaks corresponding to respective (110) and (211) planes of rt Fe (BCC) were detected in XRD patterns. These peaks were tentatively assigned to the solid solution of Fe with Cr and Ni. All electrochemical experiments were undertaken in Ringer’s solution at 37 oC by means of an in house-built flow type scanning droplet cell microscope. Additionally, the used electrolyte was analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES). It was observed that as the Fe concentration increases more than 82 at.%, the preferential dissolution of Fe occurred continuously during cyclic voltammetry experiments. Simultaneously, Cr exhibited a surface enrichment (non-congruent dissolution) at all concentrations, but a minimum of (14-16 at.%) is required to behold the significant passivity. Interestingly, no metal was detected above detection limit during cyclic voltammetry for the alloys with compositions containing Ni > 11 at.% and Cr > 20 at.%. This work shows the influence of each constituent (Fe, Ni and Cr) on the passivity of Fe-Cr-Ni ternary system. Hence, it can also be perceived as a guideline for the surge of better performing Fe-Cr-Ni ternary alloys as a biomedical implant.

References

[1] Natalia Pimenova and Thomas Starr, Electrochemical Corrosion Investigation of 49-Cell Combinatorial Library of Titanium-Based Alloys Fabricated by DMD, J. Electrochem. Soc, 155, 303-305, (2008); DOI: 10.1149/1.2899021.

[2] John Murphy, Tetsuo Uno, Janice Hamer, Fred Cohen, Varavani Dwarki, Ronald Zuckermann, A combinatorial approach to the discovery of efficient cationic peptoid reagents for gene delivery, PNAS, 95, 1517-1522, (1998); DOI:10.1073/PNAS.95.4.1517

[3] M. Sumita, Y. Ikada, T. Tateishi, Metallic Biomaterials Fundamentals and Applications, ICP, Tokyo, 629 (2000).

[4] M. Sumita, Present status and future trend of metallic materials used in orthopedics, Orthop. Surg, 48, 927 (1997).
Monitoring Coating System Changes Using Equivalent Circuit Fit Parameters
Authors: Policastro Steven , Anderson Rachel , Hangarter Carlos M , Arcari Attilio , Iezzi Erick
Published: July 2021

Organic coating systems are used to manage the corrosion of metal surfaces subjected to atmospheric degradation. These coating systems are frequently complex and multilayered and capable of providing several functions, including: substrate adhesion, corrosion inhibition and electrolytic barriers. In addition, the service environment can be equally complex with exposure to UV radiation, wet/dry cycling, and application of thermal and physical stresses on the substrate and coating system alike.

Refining our ability to predict service life and explain how these coatings evolve over the course of their lifetimes provides an opportunity to decrease maintenance costs and aid in future coating development. These objectives can be achieved by the development of predictive models that incorporate the fundamental effects of relevant service environment parameters. This would provide reliable damage predictions based upon the measured environmental data thereby decreasing our dependence on proxy corrosion sensors.

To that end, the first phase of this project has focused on testing and monitoring an aircraft coating system that is comprised of a surface pretreatment, an epoxy primer with inhibitors, and a polyurethane topcoat exposed to a variety of degradation conditions that simulate the extreme ranges of environmental stresses expected to be seen in-service. Coating condition was monitored using electrochemical impedance spectroscopy (EIS) and characterized with equivalent-circuit models so that changes to the coating system properties could be quantified and tracked over time.

Regression models for the changes in the coating system properties are being developed and will be validated by follow-on outdoor exposure testing in the next phase of the program.

Acknowledgments

The Department of Defense Strategic Environmental Research and Development Program (SERDP) sponsored this work under program WP19-1017. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the Office of Naval Research, the U.S. Navy, or the U.S. government.
Oil-Immersed Scanning Micropipette Contact Method Enabling Long-Term Corrosion Mapping
Authors: Li Yuanjiao , Mauzeroll Janine
Published: July 2021

Scanning micropipette contact method (SMCM) suffers from droplet evaporation and crystallization which limits the use of most saline electrolyte solutions under natural air humidity. To overcome the limitations and expand the application of SMCM, we improve this technique by scanning the droplet under mineral oil that covers on the substrate surface. The hydrophobic and inert oil significantly enhances the droplet stability, allowing for prolonged mapping and the use of highly evaporative saline solutions regardless of ambient humidity levels. This systematic mapping technique was used to conduct a detailed investigation of localized corrosion taking place at the surface of an AA7075-T73 aluminum alloy in a 3.5 wt% NaCl electrolyte solution, which is typically challenging in the conventional SMCM. Maps of corrosion potentials and corrosion currents extracted from potentiodynamic polarization curves showed good correlations with the chemical composition of surface features and known galvanic interactions at the microscale level. This demonstrates the viability of the oil-immersed SMCM and opens up the avenue to mechanistic corrosion investigations at the microscale level using aqueous solutions that are prone to evaporation under noncontrolled humidity levels.
Barrier and Packaging Level CMP Optimization
Authors: Basim G. Bahar , Sur Debashish , Langhout John
Published: July 2021

The yield of chip packaging operations is a function of the surface finish that is solderable and wire-bondable. It has been shown that the use of palladium (Pd) plated lead-frame for packaging has improved the processing cost and reliability by simplifying the process integration [1]. Pd can also be used as a sacrificial layer to protect the copper (Cu) substrate material from oxidation and interdiffusion before the SnPb solder application. In packaging applications, Pd is advantageous in forming a Ni(Pd)Si allowing a lower sheet resistance at higher temperatures as compared to the NiSi in addition to much better surface morphology [2].

The new integration schemes of Pd into the circuitry at the packaging level also require a CMP application where the Pd is deposited on the dielectric layer with bond-pad recess and polished to form a Pd based pad surrounded by Ni [3]. In combination with the applications of the 2.5 and 3-D microelectronics packaging technologies, the CMP electivity becomes critical where a competitive removal rate is desired between the Cu, Cu-barrier (TaN) and Ni films

It has been demonstrated on W-CMP in an earlier study that the 1:1:1 removal rate selectivity of the W/Ti/TiN layers can be achieved through adjusting CMP formulations in terms of the slurry chemistry and the particle concentrations. The systematic study has demonstrated a methodology for developing optimal CMP configurations for the newly introduced films to CMP applications based on electrochemical evaluations [5].

In this paper, we study the removal rate selectivity for Pd integrated packaging level CMP applications through electrochemical and surface energy evaluations in commercial bulk and barrier CMP slurries. It can be seen that the thin film dissolution rates relate to the surface passivation as well as the surface energy measured by the contact angle evaluations on the Cu, Pd, TaN and Ni wafer coupons. Pd being a novel metal shows strong passivation that results in minimal dissolution in the slurry environment which requires alternative formulations for CMP slurries to promote the removal rate performance.

References:

Kajija, I.V., Absy, J.A., Maisano, J.J., Kudrak, A.J., Shimada, S. “Thin Multilayer Palladium Coating for Semiconductor Packaging Applications. Part I: Solderability. NASF Surfcae Technology White Papers, 80 (6), 6-19 (2016).

Karabko, A., Dragasius, E. Nisi and Ni(Pd)Si as possible interconnect and electrode material for film bulk acoustic resonators and microelectromechanical systems. Journal of Vibroengineering, 15 (1), 2013.

Eisa, M., Zinn, B. “Aluminum Enhanced Palladium CMP Process” US Patent 8,288,283, October 16, 2012.

Song, C., Wang, Z., Chen, Q., Cai, J., Liu, L. “High aspect ratio copper through-silicon-vias for 3D integration”, Microelectronic Engineering, 85 (10), P1952-P1956,

Yagan, R., Basim, G.B., “A Fundamental Approach to Electrochemical Analyses on Chemically Modified Thin Films for Barrier CMP Optimization," ECS J. Solid State Sci. Technol. 8-5, P3118-P3127, 2019.
Effect of Radial Groove Pad on Copper Chemical Mechanical Polishing
Authors: Bae Chulwoo , Oh Shinil , Kim Taesung
Published: July 2021

Chemical mechanical polishing (CMP) is a process that reduces step height by making the flat surface when several types of layers are accumulated in a semiconductor device. The three main factors affecting CMP are pad, slurry and conditioner. Among these factors, the pad helps the flow of the slurry and polish the wafer with direct contact. Through changing characteristic of pad that is number of grooves, design of groove, depth and width of pitch, we can control wafer removal rates, with-in wafer non-uniformity and roughness.

In this study we added a radial groove (RG) at the circular groove (CG) pad to investigate what effect of the RG to Cu CMP. A study was conducted on how the number of RG affects the slurry flow, how changes in slurry flow affect the pressure distribution between the pad and the wafer, and how this affects CMP. The number of RG was divided into 0, 8, 16, 32, and the actual CMP process and simulation experiment were conducted together. In simulation part, we use computational fluid dynamics (CFD) to compare for slurry transport rates according to the number of RG. Fig. 1 shows the removal rates according to the number of RG, and when the number of RG increases to 32, it shows that removal rates of RG pad is almost 23% higher than CG pad. We consider that these results are related to changes in slurry flow during polishing. This is due to role of RG in quickly replacing the old slurry with the new slurry.

Figure 1
Multiple Technique Characterization of the Physical and Chemical Properties of Silica Abrasives Used in Chemical-Mechanical Planarization
Authors: Moinpour Mansour , Vacassy Robert , Kamiti Mungai , Campbell Kristine , Jones Evan , Remsen Edward
Published: July 2021

The performance of chemical-mechanical planarization (CMP) slurries in the commercial fabrication of integrated circuits depends critically on the physical and chemical properties of abrasive particles used in CMP slurries. A host of analytical methods are used for characterizing the properties of CMP abrasive particles including spectroscopic,1,2 sedimentation,3 viscometric4 and fractionation5 techniques. One particular method, fluorescence correlation spectroscopy (FCS),1 has demonstrated significant versatility in this application due to its ability to simultaneously analyze the particle size distribution and the surface chemistry of abrasive particles in aqueous mixture containing small molecule CMP additives. The need for further characterization of these properties, especially the surface chemistry, is the product of the increasing use of nano-abrasives with reduced hydrodynamic diameters (< 20 nm) in CMP slurries in order to minimize surface defect creation during CMP processes. Incorporation of nano-abrasives in CMP slurries will promote surface chemistry-driven CMP additive adsorption on abrasive particles due to the increase in the total particle surface area as the hydrodynamic diameters of nano-abrasives decrease. The use of FCS in conjunction with the application of complementary techniques, such as dynamic light scattering and fluorescence lifetime analysis, is described in the presentation for the comprehensive characterization of the physical and chemical properties of representative silica abrasives used in CMP slurries.

1. Jacobson, L.M.; Turner, D.K.; Wayman, A.; Rawat, A.; Carver, C.T..; Moinpour, M.; Remsen, E.E. “Characterization of Particle Size and Surface Adsorption for SiO2 Abrasives Used in Chemical Mechanical Planarization via Fluorescence Correlation Spectroscopy”, ECS J. Solid State Sci. Tech.
2015,
4, P5053-P5057.

2. Marsh, J.L.; Wayman, A.E.; Smiddy, N.M.; Campbell, D.J.; Parker, J.C.; Bosma, W.B.; Remsen, E.E. “Infrared Spectroscopic Analysis of the Adsorption of Pyridine Carboxylic Acids on Colloidal Ceria”, Langmuir
2017, 33
, 13224-13233.

3. Kamiti, M.; Boldridge, D.; Ndoping, L.M.; Remsen, E.E. “Simultaneous Absolute Determination of Particle Size and Effective Density of sub-Micron Colloids by Disc Centrifuge Photosedimentometry”, Anal. Chem.
2012,
84, 10526−10530.

4. Boldridge, D.; Kamiti, M.; Remsen, E.E. “Avoiding the Spherical Particle Assumption: Fractal Particle Density, Size and Structure Characterization through Combined Sedimentation and Viscometry Measurements”, Anal. Chem.
2020, 92, 15034-15041.

5. Williams, S.K.R.; Park, I.; Remsen, E.E.; Moinpour, M. “New Particle Metrology for CMP Slurries”, Mater. Res. Soc. Symp. Proc. 2007,
991, 249-251.
Development of Particle Detecting Technology for Measurement Slurry Particle Property in Chemical Mechanical Polishing Process
Authors: Kim Chang min , Park Kihong , Jeon Sanghcuk , Kim Taesung
Published: July 2021

Recently, particle size and analysis technology are used for various industry filed and become very important. Because small particle can affect to manufacture process and product yield. Especially. As design rule of semiconductor device is miniaturizing to 10 nm class. Because of this, very fine particle which size is below 100 nm can affect to the wafer as shown Fig. 1. In addition to this, after chemical mechanical polishing (CMP) process many defects can occur by fine particles in CMP slurry which are remain on the wafer. In this reason, we need a technology which is measure the particle property of slurry in CMP process.

In this study, particle detecting technology has been investigated which is can detect a particle in the CMP slurry for wafer polishing. In this experiment, single particle sizing system (SPOS) is used for particle detecting in CMP slurry. The SPOS system is a single particle detecting system which system is the principle of measuring scattering light generated by particles. It can get a high resolution from detecting a small size particle also analysis of particle property such as size, shape and so on.

Fig, 2 shows a schematic of the experiment set-up and result, which experiment was consisting of five devices that is He-Ne laser, laser power meter, tubing pump and lens system. The experimental principle is firstly preparing the solution which contain particles to flow the quartz tube. Second, prepare the focusing and collecting lens system. Third, aligning the laser to the quartz tube where the solution flows and turning it on will cause the laser light to hit the particles present in the solution, which will measure the scattered light with a laser power meter.

Figure 1
First Principles Study of Reactions in Hybrid Film Growth: The Role of the Organic Precursor
Authors: Muriqi Arbresha , Nolan Michael
Published: July 2021

Hybrid materials are a special class of materials with tunable features. This is related to their diphasic structures that leads to multifunctional materials with a wide range of applications. Molecular layer deposition (MLD) enables the fabrication of ultrathin and conformal hybrid films using sequential, selflimiting reactions, similar to ALD. Despite growing interest in these materials, there is little understanding of the atomistic mechanism of MLD film growth.

In this contribution, we explore the molecular mechanisms of the growth of different hybrid organic−inorganic thin films by using density functional theory (DFT). The prototype for MLD organic−inorganic hybrids are composed of thin films of aluminium alkoxides, known as ”alucones”. We investigate the MLD reaction products between the post-TMA Monomethyl-Al2O3 (Al-CH3-Al2O3) and Dimethyl-Al2O3 (Al(CH3)2-Al2O3) surface and the organic precursors ethylene glycol (EG) and glycerol (GL). The DFT calculations show that while the organic precursors can bind to the TMA fragments via formation of Al-O bonds and loss of CH4, it is most favorable for the organic precursors to lie flat and create so-called double reactions through two terminal hydroxyl groups with the surface fragments, where the terminal groups bind to Al. For EG this potentially removes all the active sites and growth will be less favorable. For GL the third hydroxyl group is available and growth can proceed. We also showed that the TMA in the next pulse reacts favourably with this OH from GL.

We also explored the growth mechanism of magnesium containing hybrid films known as “magnesicone” from the reaction of EG and GL at MgCp-terminated MgO(100) as a model system. Interaction energies presented some clear differences in reaction mechanism of films grown with EG and GL. While the ligand elimination process is favorable for both precursors, EG prefers to orient in a flat configuration and interacts at the MgO(100) surface and GL species prefers to lie in an upright position. As a consequence the change in thickness for GL-based process is larger than for EG-based process, resulting in a thicker GL-based magnesicone compared to the EG-based magnesicone.

Finally we use DFT to explore the growth mechanism of titanium-containing hybrid organic−inorganic films known as “titanicones”. We investigate the reaction mechanism of titanicones grown using titanium tetrachloride (TiCl4) as metal source and either ethylene glycol (EG) or glycerol (GL) as organic reactants. This investigation contributes to the understanding of growth process of EG and GL based hybrid films at the molecular level and is valuable in supporting experimental data on hybrid film growth.
(Invited) Precise Control of Nanoscale Cu Etching via Gas-Phase Oxidation and Chemical Complexation
Authors: Sheil Ryan , Martirez J. Mark P. , Sang Xia , Carter Emily , Chang Jane P.
Published: July 2021

We present a cyclic process for selective and anisotropic atomic layer etching of copper: an oxygen plasma modulates the depth and directionality of the oxidized layer while formic acid vapor selectively removes the copper oxide scale from the metallic copper. Via density functional theory, with finite temperature and pressure free energy corrections, we evaluate the feasibility of formation of gas-phase Cu(II) and Cu(I) complexes with formate, water, formic acid, and combinations thereof as ligands. These complexes result from the neutralization reaction between copper oxide (CuO and Cu2O) and formic acid, with and without water. We identified and evaluated the formation free energies of formato, formic acid, aquahydroxo, and aquaformato complexes of Cu(II) and Cu(I). Under relevant experimental pressures, we find the water-free dimeric tetra(μ-formato)dicopper(II) “paddlewheel” complex (Cu2(HCOO)4) to be the most favorable etching product, with its formation reaching equilibrium conditions from CuO. The most likely precursor for the dimer is the diformatodi(formic acid)copper(II) monomer, which favorably dimerizes under the same water-lean condition at which the dimer persists. Stabilization of gas-phase Cu (oxide) derivatives thus can be achieved through complexation, enabling gas-phase etching of Cu. This work provides complementary experimental and theoretical studies that illuminate the nature of highly controlled etching with formic acid of nanoscopic CuO(s) layers covering Cu nanoarchitectures, which is relevant for the fabrication of next-generation integrated circuits.
(Invited) Novel Chemistries for Layer-by-Layer Etching of 2D Semiconductor Coatings and Organic-Inorganic Hybrid Materials
Authors: Elam Jeffrey W. , Mane Anil U. , Young Matthias J. , Choudhury Devika , Letourneau Steven , Yanguas-Gil Angel
Published: July 2021

Here we report two new advances in atomic layer etching (ALEt) that extend our range of capabilities in nanoscale device fabrication. Semiconductor device manufacturing is limited by our ability to precisely deposit and remove thin film layers at the various levels of multistep device fabrication processes. Consequently, innovations in atomic layer deposition (ALD) and etching methods are essential. ALD-based methods have matured significantly and are now used extensively in semiconductor fabs. Recently, there has been an intense focus on developing ALEt methods. In particular, thermal ALEt has been shown to precisely remove ALD inorganic thin films selectively and on complex structures. These capabilities have opened new possibilities for nanoscale device design. Here, we report a new thermal etching process similar to ALEt for removing hybrid inorganic-organic layers that we call molecular layer etching (MLEt). This MLEt process uses vapor phase lithium organic salts in combination with trimethyl aluminum to perform layer-by-layer etching of molecular layer deposition (MLD) coatings.

Ultra-thin layers of two dimensional (2D) transition metal dichalcogenide (TMD) semiconductors can exhibit exceptional electrical, optical, magnetic, mechanical and chemical properties. This allows the exploration of internal quantum degrees of freedom of electrons and their potential application in optoelectronic, energy, and sensor devices. Among the various 2D-TMDs, MoS2 has shown exciting material properties and this has stimulated the exploration of a variety thin film synthesis methods such as physical vapor deposition (PVD), chemical vapor deposition (CVD), and solution based methods. In addition, the ALD community is investigating ALD methods for MoS2 growth. Here we report the thermal ALEt of ALD MoS2 thin films. We believe the successful combination of both ALD and ALEt of MoS2 and other TMDs can pave the way to control the synthesis of 2D-TMD layers over large areas. Combining ALD and ALEt will allow MoS2 interface engineering and enable MoS2 integration into the large-scale manufacturing of future complex device structures.
(Invited) Electrodeless Organic Electrosynthesis By Plasma-Liquid Interface
Authors: Thimsen Elijah
Published: July 2021

The plasma-liquid interface can promote selective redox reactions involving organic molecules without the need for solid electrodes. More specifically, our group’s work on model organic compounds has revealed that selective reduction occurs near the surface of water in contact with an RF plasma jet generated using helium or argon as working gas, for positions located near the centerline of the impinging free jet. The complementary oxidation half reaction occurs further away from the centerline, and the products of reduction and oxidation can be isolated by placing a semipermeable membrane between the reduction and oxidation zones, which are termed electrodeless cathode and anode respectively. The reduction potential in the liquid near the surface at the plasma jet centerline can be tuned by changing the plasma parameters. Correlations between reduction potential and plasma parameters, specifically electron density and temperature as characterized by Thomson scattering, will be presented and a simple model proposed to theoretically connect the two. Finally, envisioned applications for this unique type of electrodeless organic electrosynthesis will be discussed in the fields of water quality, renewable carbon utilization, and pharmaceuticals. The work described in this presentation is collaborative between research groups at Washington University in Saint Louis, Princeton Plasma Physics Laboratory, and the University of Michigan; and was supported by the Department of Energy under award DE-SC0020352, the Princeton Collaborative Low Temperature Plasma Research Facility (PCRF), and the National Science Foundation through grant CBET-2033714.
The Selectivity of CO2 Reduction By the Solvated Electron Tuned By the Acid Scale
Authors: Mota-Lima Andressa , A. O. do Nascimento Claudio
Published: July 2021

The electrified plasma/liquid interface (PLI) induces the CO2 reduction (CO2R) by mediation of the solvated electron. Recent theoretical analysis of the chemical reaction network (chemical mechanism) revealed a 100% faradaic efficiency for CO2R [1] provided that the liquid surface was a flowing electrolyte; however, the theoretical analysis did not consider the proton concentration as a chemical variable, or the pH of the electrolyte so to speak, disabling to predict the distribution of products over the entire acid scale. For this reason, in this work, the proton has been categorically considered as a reactant and an essential variable for the dynamical model describing the CO2R via electrified PLI.Two new routes toward formic acid production are proposed namely the disproportionation-like (via-2) and radical cross-combination (via-3) reactions, see figure 1. Both consume the radical H formed by the scavenging of the solvated electron by the proton. The computational results reasonably matched the concentration ratio formate to oxalate around 3.0 for pH 2.45, which features the physical experiments [2]. This ratio would represent 25% selectivity toward formate at pH 2.45 for a flowing-electrolyte experiment. With this reasonably assertive mechanism, it was possible to predict that, at the same conditions of flowing electrolyte, an extremely acid pH (~1) would increase the selectivity toward formate, between 46 and 90% repectivelly for via-2 and via-3.

Fig 1. Chemical reaction networks are shown in the LHS, and the predictions on the concentration ratio oxalate to formate are shown in the RHS for each path of formate synthesis (via–3 and via–2) and both combined.

References

[1] A. Mota-Lima, J.Phys. Chem. C, 124, 10907(2020).

[2] P. Rumbach, R. Xu, and D. B. Go, J. Electrochem.
Soc., 163, F1157 (2016).

Figure 1
(Invited) Leveraging Plasmas for Electrochemical Fuel Production: Synthesizing Novel Low-PGM Water Oxidation Catalysts and Enhancing the Rate of Electrochemical Ammonia Production
Authors: Spurgeon Joshua M. , Kumari Sudesh , Pishgar Sahar
Published: July 2021

Plasmas have a number of unique properties which researchers may be able to leverage to enhance desired electrocatalyst material properties and steer electrochemical reaction performance. Two examples of the recent application of plasmas for advancements in electrochemical fuel production are presented. In the first, the nonequilibrium reaction environment of an air plasma enabled the synthesis of homogeneous phases of metastable compositions of a mixed W1-xIrxO3-δ alloy. For a low-platinum-group-metal (PGM) composition of only 1% Ir, plasma-synthesized W0.99Ir0.01O3-δ was observed to be an acid-stable oxygen evolution reaction (OER) catalyst of competitive overpotential. Moreover, the plasma-synthesized alloy was observed to have an OER overpotential ~ 570 mV less than that of a thermally oxidized alloy of the same composition. In the second example of a plasma enhancement, a nitrogen plasma was coupled into the cathode of a proton exchange membrane electrolyzer to provide energetically activated N2 species to the electrocatalyst surface and demonstrate a proof-of-concept synergistic enhancement in the rate of ammonia production. At an applied bias of ~3.5 V across the electrolyzer, plasma-assisted operation was observed to produce 47% more ammonia than the combination of plasma-without-bias and bias-without-plasma conditions.
(Invited) Models and Opportunities in Plasma-Catalytic Transformations
Authors: Ma Hanyu , Schneider William F
Published: July 2021

Heterogeneous catalysis is essential to industrial chemical processes, from those that transform petroleum into fuels and chemicals to those, like the Haber Bosch process, that create fertilizers to feed the planet. Catalysis science has revealed that the most common heterogeneous catalysts, which include the later members of the d block transition metals, present a tableau of reactivity limited by intrinsic correlations between the various reaction steps that make up a surface catalytic reaction. Coupling of heterogeneous catalysts with non-thermal plasmas offers the potential to break these constraints. While empirical evidence suggests that such combinations can enhance apparent catalytic function relative to plasmas or catalysts alone, the absence of basic models to rationalize this behavior and guide material and plasma selection has limited progress. In this talk I will describe our recent work to bridge this gap, focusing on nitrogen reduction (ammonia synthesis) and nitrogen oxidation (NO synthesis) as two different approaches to realize chemical transformations that are difficult or impossible to achieve through catalytic routes alone.
(Invited) The Interplay between Thermal and Mechanical Properties in Colloidal Quantum Dot Assemblies
Authors: Wang Robert Y
Published: July 2021

The ongoing interest in colloidal quantum dot assemblies for real-world electronic and photonic devices necessitates that their thermal and mechanical properties be well understood. Large thermal conductivities are desirable because this minimizes the temperature rise during operation and thereby improves device performance and lifetime. In addition, large elastic moduli and hardness directly impact device durability.

In this talk, I present my group’s findings on two separate correlation regimes between thermal and mechanical properties in colloidal quantum dot assemblies. These two correlation regimes correspond to (i) assemblies with weak inter-particle forces and (ii) assemblies with strong inter-particle forces.

In the weak inter-particle force regime, thermal and mechanical properties intersect via the speed of sound. This stems from the speed of sound being linearly-related to thermal conductivity and quadratically-related to elastic modulus. In the strong inter-particle force regime, thermal and mechanical properties intersect via quantum dot diameter. We find that the quantum dot diameter primarily effects thermal conductivity via the mean free path of the thermal energy carriers. The interrelationship between diameter and mechanical properties in this regime is similar to an effective medium approximation, but with added subtleties. In particular, we find that the surface ligand properties and particle diameter can be intercoupled. This in turn has important impacts on the mechanical properties of the overall quantum dot assembly.

In order to demonstrate the above thermomechanical relationships, I present my group’s combined experimental and modeling studies on three classes of colloidal particle assemblies. First, we use thermal processing methods to study the effect of native oleic acid ligands versus cross-linked oleic acid ligands. Second, we use single-domain superlattices and disordered thin films to study the effect of particle ordering. Lastly, we use ligand exchange methods to study the effect of organic versus inorganic ligands.
(Invited) Building Colloidal Quantum Dot Solids for Efficient Infrared Optoelectronics
Authors: Baek Se-Woong
Published: July 2021

Colloidal quantum dots (CQDs) are semiconducting nanoparticles, having quantum confinement effects and thereby rendering a strong advantage to adjust optical properties via tuning their physical structure. Therefore, CQD materials have drawn an attention as a next-generation optoelectronic material. In particular, broadband photo-response of CQD across visible to infrared enables to realize infrared luminescence, sensing, and energy conversion: essential function for the 4th industry revolutions, including autonomous driving, virtual reality (VR), Internet of Things (IoT), and smart systems. In this talk, we showcase the recent advances of CQD as infrared optoelectronics sources and discuss current limitations. We specifically describe various engineering methodology that can maximize quantum efficiency, which is a key factor in photodetection and photovoltaic. Finally, we present the future perspective of CQD-related optoelectronic research fields.
Intraband Quantum Dot Barrier Devices - Optimization of Energy Level Alignment
Authors: Hafiz Shihab Bin , Al Mahfuz Mohammad M. , Ko Dong-Kyun
Published: July 2021

Colloidal quantum dots have been a spotlight of nanoscience and technology due to their exquisite physical properties that can be harnessed for next generation nanoelectronics and optoelectronics. Particularly, semiconductor quantum dots that are active in the thermal infrared provide a new path for fabricating infrared devices with significantly reduced cost and enable capabilities beyond that offered by conventional semiconductor technologies. In this presentation, we report on recent advances in materials design and device structure for silver selenide mid-infrared quantum dots, building on our recent demonstration of uncooled photoconductive devices. We highlight two key approaches to reduce the high dark current associated with self-doped, intraband quantum dots used in these devices with detailed analyses of the device characteristics.
Evolution of UV/VIS Photoluminescence of Aged Zn(acac)2 Solutions in Correlation with Carbon Precipitation
Authors: Vasin Andriy V , Kysil Dmitriy V. , Isaieva Oksana F. , Rudko Galina Yu. , Naseka K. M. , Strelchuk Viktor V. , Piryatinski Yuri P, , Sevostianov S. V. , Tertykh V. A. , Savchenko D. V. , Nazarov Alexei N.
Published: July 2021

Photoluminescent carbon nanodots (CDs), a new class of inorganic nanocarbon materials, have become a significant segments of luminescent nanomaterials in last decade. However mechanism of light emission and detailed identification of the light emitting centers is still debated. A huge number of synthesis methods were suggested, however few of them allow to monitor formation of the CDs on the early stage and development in progress. Recently we have found that zinc acetylacetonat (Zn(acac)2) in ethanol solutions tends to be hydrolysed under room temperature laboratory conditions resulting in gradual conversion of colorless and non luminescent solution to yellowish liquid accompanied by cedimentation of nonluminescent amorphous ZnO:OH. The yellow component of the solution has been identified as dispersion of carbon precipitates. The most important is that the process of hydrolysis in very slow with changing color and PL development within several months. Such a slow process allows following the details of PL development and evolution in time correlation with carbon precipitation.

Ethanol solutions of Zn(acac)2 with concentrations in range of 0.1-4.0 % were prepared and their photoluminescence was monitored for time period of several months. It has been found that early stage of carbon precipitation is resulted in development of relatively narrow PL band with maximum at about 400 nm and corresponding excitation band at 360 nm. The spectrum of the emission band is excitation independent as well as excitation band is not dependent on emission wavelength. In the course of further aging and carbon precipitation the PL band is broaden and shifted to visible range with maximum intensity in range of 420-500 nm depending on excitation wavelength. Detailed emission/excitation study revealed that the visible emission band is composed of at list two components centered at about 420-450 nm and 500 nm, with the corresponding excitation bands at 365 nm and 420 nm. Time-resolved photoluminescence spectroscopy showed that the decay of low energy emission band follows the classical mono-exponential low with the characteristic time of several nanoseconds, while the behavior of high energy component can be described by the stretched exponential low with the average decay time of several nanoseconds. PL data is summarized and discussed in the terms of subnanometer molecular-like carbon emitters and core/shell structural model of amorphous carbon nanoparticles.
(Invited) Colloidal Quantum Dots for Enhancing Performance of Avalanche Amorphous-Selenium Photodetectors
Authors: Kannan Haripriya , Stavro Jann , Mukherjee Atreyo , Zhao Wei , Goldan Amirhossein , Sahu Ayaskanta
Published: July 2021

Photodiodes using amorphous-selenium (a-Se) have gained significant attention in medical diagnostic imaging due to their avalanche phenomena. At high electric fields above 70 V/μm, holes in a-Se undergo impact ionization which increases the effective sensitivity of the photodetector. However, at the high electric fields required for avalanche gain, dark current due to charge injection from metallic electrodes can become a significant source of noise, limiting the dynamic range of the device. To maximize gain while maintaining low dark conductivity, and to achieve reliable and repeatable impact ionization without irreversible breakdown, we need a non-insulating n-type hole-blocking/electron-transporting layer with a high dielectric constant. Among previously reported hole blocking layers that include both polymers and crystalline inorganic materials, vacuum deposited bulk cerium dioxide (CeO2) has shown promising results and has been successfully utilized in n-i-p avalanche a-Se sensors. However, bulk CeO2 cannot be directly deposited on a-Se owing to the low crystallization temperature of a-Se. In this talk, I will present our results on colloidal CeO2 quantum dots as potential hole blocking layers for a-Se devices. These CeO2 quantum dots are electronically passivated by surfactants/ligands and spin coated directly on a-Se at room temperature without inducing crystallization. Owing to quantum confinement, the QDs have a larger bandgap than bulk CeO2 thus raising the effective hole energy barrier. Prototype devices based on these QDs as interface layers on a-Se achieved an ultra-low dark current of 30 pA/cm2 at 70 V/μm which is three orders of magnitude lower than any avalanche a-Se device previously reported and may be the lowest dark current ever recorded for an avalanche device operated at room temperature.
(Invited) Non-Blinking Long Lifetime Quantum Dots and Passive Cell Delivery Strategies
Authors: Snee Preston , Emerson Nyssa , Yin Shuhui , Beckwith Joseph , Pálmai Marcell , Jing Haoran , Hu Ying , George Anne , Yang Haw
Published: July 2021

Over the past ~20 years there has been considerable effort towards the optimization of the photophysical properties of emissive nanomaterials to engender efficacy for biological imaging and sensing. The development of core-shell CdSe/ZnS and CdSe/CdS quantum dots (QDs) was instrumental due to those materials’ resistance to photobleaching and high quantum yields. However, these particles experience fluorescence intermittency (“blinking”), which is detrimental for single particle tracking studies. Furthermore, ~10 nanosecond lifetimes are not compatible with time-gating visualization, a technique that reduces background noise. Last, cytosolic delivery of QDs is a well-known problem due to the propensity for QDs to become sequestered in the endosomes of live cells.

Presented are developments that address these issues. Long lifetimes, >100 ns, and non-blinking behavior have been realized in “giant” quantum dots with a highly alloyed core/shell interface. This results in type-II behavior that separates the electron and hole, which slows emissive recombination. Also presented is a novel cell-penetrating peptide that can be conjugated to surfactants that are commonly employed for QD water solubilization. These materials can be passively delivered to the cytosol of live T-cell lymphocytes. Single particle tracking studies reveal fast diffusion of single dots that are not consistent with endosomal capture, which is observed in control nanomaterials. These developments create new inroads for chemical and biological sensing studies inside of live cells for basic research and diagnostic purposes.

Figure 1
Electrodeposition of Zinc for Redox Flow Batteries
Authors: Magagnin Luca
Published: July 2021

The redox flow batteries (RFBs) have received great attention due to their attractive features for large-scale energy storage applications. A RFB is a type of flow-based energy storage device capable of providing reversible conversion between electrical and chemical energy through two redox half-cell reactions. Nowadays the most common RFBs exploit the vanadium chemistry, followed by the zinc-bromine chemistries. Though RFB technology has advantage for energy storage and has successful demonstration of systems up to MWh levels, they have not enjoyed broad market penetration. Some of the reasons are relatively high capital and life-cycle costs. New applications are envisaged for RFBs, including the electric mobility which is becoming increasingly important. Zinc based redox flow batteries (Zn-RFBs) based on new chemistries with respect to the chlorine and bromine ones can be the answer to new market success devices, not only in the large storage field but also in the medium and mobility sector.

In this presentation, the electrodeposition of zinc will be discussed in light of its exploitation in the new generation of zinc based RFBs. Alkaline and acidic baths will be presented in combination with proper chemistries for the other half cells. The role of additives and pulse plating will be discussed in terms of nucleation and growth of the metallic layer and its dissolution during charging/discharging cycles. A zinc-iron RFB with low cost and high energy density will be presented. In particular, inorganic electrolytes based on high soluble salts have been developed, achieving a charge density of 30-70 Wh/l. Moreover, in order to enhance the capacity of Zn-Fe flow battery, the use of slurry dispersed electrodes to decuple capacity from the power rating have been studied. As another example, zinc electrodeposition and its optimization will be introduced in combination with the iodine chemistry for high energy efficiency Zn-I RFBs, in the order of 70% at 20 mA cm-2, with high energy density ranging from 25 to 60 Wh/l.
Anodic TiO2 Nanotube Layers As Scaffolds for Deposition of Functional Materials
Authors: Macak Jan M. , Bawab Bilal , Sopha Hanna , Zazpe Raul
Published: July 2021

The self-organized 1D TiO2 nanotubular layers have attracted considerable scientific and technological interest over the past two decades, all motivated by a great performance in the range of applications including photo-catalysis, solar cells, hydrogen generation and biomedical uses [1,2]. The synthesis of these nanotubular layers has been carried out by a conventional electrochemical anodization of Ti sheet. Except the 1D character, these nanotubes possess unique features such as tunable dimensionality, structural flexibility, unidirectional electron transport through nanotube walls, chemical and mechanical stability and biocompatibility.

One of the major application targets of TiO2 nanotubes has been their utilization as scaffolds or templates for deposition of secondary materials towards new applications [3]. In particular, for the photoelectrochemical applications (e.g. photovoltaics) ordered nanostructures, such as self-organized TiO2 nanotubes, offer the advantage of directed charge transport and controlled phase separation between the donor and acceptor materials, unlike within randomly ordered mesoporous TiO2 supports.

Numerous techniques were utilized for this purpose, such as for example hydrothermal routes, electrodeposition or Atomic Layer Deposition (ALD) techniques. Electrodeposition is very powerful technique to deposit metals [4], oxides [5] or other rather complex materials (such as CuInSe2 [6]) within the nanotubes various by means of complete filling or decoration with. On the other hand, ALD can deposit the widest range of secondary materials within TiO2 nanotubes by means of homogenous coatings [7-10].

The presentation will be focused in detail on TiO2 nanotube layers of various aspect ratios filled, decorated or coated by various materials using electrodeposition. Experimental details and some very recent photo-electrochemical and structural characterizations of a new type of heterostructured photo-chemical cell will be presented and discussed.

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