bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrochemical Oxidation and Bond Cleavage of Lignin-Derived Model Compounds with Nanoparticle Catalysts
Authors: Ngo Ken , Baddour Frederick , Ruddy Daniel , Schaidle Joshua
Published: February 2020

Electrochemistry offer an environmentally friendly approach to convert biomass or biomass derived material into valuable organic chemicals, petrochemical substitutes, and energy-intensive chemicals. Monomers could be generated by cleaving ether (C-O-C) linkages in lignin via thermal decomposition process such as reductive catalytic fraction (RCF). However, this process leaves behind a significant portion of soluble lignin oligomers with recalcitrant C-C linkages. Monomer yields from the RCF pathway are approaching theoretical limits based on ether bond cleavage. Therefore, with broader goal of improving lignin utilization within a biorefinery, we probed the electrocatalytic oxidation of model dimer compounds with C-C linkages representative of RCF oligomers.

Electrochemical studies offer several advantages including operation at low temperatures and pressures, applied potentials can be used to control reaction rates and selectivities, and renewable electricity can be used, thus lowering overall greenhouse gas emissions. According to previous studies, several metals such as nickel, cobalt, copper, and platinum can be used to build electrocatalysts for biomass conversion. Therefore, we have synthesized a series of low-cost nickel and molybdenum nanoparticle catalysts for the electrocatalytic oxidation of model compounds. Besides the high surface and high stability advantages of supported nanoparticles in general, these candidates exhibit interesting catalytic activities resembling that of noble metal catalysts such as platinum in oxygen reduction reaction (ORR) which could also be beneficial in bond cleavage reactions in biomass or biomass derived material.

The focus of this talk will be on the electrochemical studies of the selected nanoparticle catalysts toward C-C bond cleavage in RCF dimer model compounds. The results from the studies also lead to some insights we may be able to use to guide the future development of electro-oxidation of RCF oil/ biomass stream. Besides metallic, phosphide and carbide nanoparticles on carbon support, metal foils were also tested and were used as a comparison. Notably, a MoC catalyst on carbon support showed C-C and C-O bond cleavage activities in aqueous alcoholic solution with sodium hydroxide as the electrolyte.
Understanding Metal Structure Sensitivity during the Electrocatalytic Hydrogenation and Oxidation of Biomass-Derived Molecules at Normal Temperature and Pressure
Authors: Lopez Ruiz Juan A , Sanyal Udishnu , Koh Katherine , Qiu Yang , Andrews Evan , Nguyen Manh-Thuong , Karkamkar Abhijeet , Derewinski Miroslaw , Rousseau Roger , Gutiérrez Tinoco Oliver Y , Holladay Jamelyn
Published: February 2020

In recent years there has been growing interest in using electrochemical methods for the upgrading of biomass-derived molecules for the formation of biofuels. Conventional upgrading processes require moderate temperatures between 433 and 678 K, pressures of 14,000 kPa, and external sources of dihydrogen for the stabilization and formation of biofuels. However, the same reaction can be performed using electrochemical reactors and much lower temperatures and pressures (293 K and 101 kPa) and with no supplied dihydrogen.

In this work, we evaluate the use of Pd, Pt, Rh, and Cu-based heterogeneous electrocatalysts for the electrocatalytic hydrogenation (ECH) and oxidation (ECO) of organic molecules present in biocrude. In particular, we studied the effect of electrolyte composition, half-cell (WvR) potential, and metal particle size on the Faradaic efficiency (FE) and catalytic activity (TOFECH and TOFECO) for different bio-oil derived-molecules such as aldehydes, ketones, phenolics, and carboxylic acids. Our results show that whereas the reduction of aldehydes and ketones into alcohols can be achieved electrocatalytically at normal temperature and pressure, carboxylic acids cannot be reduced. However, carboxylic acids can be oxidized to alcohols, olefins, and ketones via Kolbe and non-Kolbe mechanism. Further, we observed there the TOF and FE depend on metal, fractional exposure, substrate concentration and WvR potentials. For example, as shown in Figure 1, the FE and TOFECH are the highest when using Pd electrodes with low Pd weight loading (and small metal particle size). The FE and TOFECH decreases as the Pd weight loading (and particle size) increases. Eley-Rideal-type kinetics were used to understand the structure sensitivity of the Pd electrocatalysts and revealed that it is related to changes in rate constants and substrate surface coverage. That is, small Pd nanoparticles have higher ECH rate constant and higher benzaldehyde surface coverage compared to large Pd particles. Structure sensitivity was also observed on Pt and Rh-based electrocatalysts, but with opposite trend. That is, large Pt and Rh nanoparticles were more active than small nanoparticles. Cu-based catalysts were structure insensitive.

Figure 1. TOFECH (A) and Faradaic Efficiency (B) as a function of WvR potentials under normal conditions for the benzaldehyde ECH to benzyl alcohol. Catalysts with different Pd loadings were used where represents 0.05wt% Pd/CF, represents 0.10wt% Pd/CF, represents 0.50wt% Pd/CF, represents 1.0wt% Pd/CF, and represents 4.0wt% Pd/CF.

Figure 1
(Invited) Design of Effective Pulse Deposition Process for Functional Cr Coatings from Cr3+ Electrolyte
Authors: Ahmadi Kamyar , Hall Timothy D. , Taylor E. J. , Robles Francisco , Brankovic Stanko
Published: February 2020

The presented work investigates the pulse current deposition as an approach for electrodeposition of functional Cr films. Our data suggest that observed growth stress during DC Cr deposition are negative, i.e. compressive with steady state values in the range below -100 MPa. The negative stress is associated with blistering in Cr films and accumulation of different defects on the Cr film surface during deposition which indicated significant amount of dissolved hydrogen either as interstitial impurity or as a part of chemically bonded H as Cr-hydride. Stress, impedance and optical results undoubtedly suggest that weakened structure of the Cr films by oxidation process has a true origin in Cr-hydride formation and subsequent oxidation of its degradation by-products (H and Cr). Therefore, the electrodeposition process that produces less Cr-hydride in the deposit should be more desirable when the crack free Cr films are the goal. Our pulse current function design is therefore driven by the goal to achieve Cr-films with minimum amount of Cr-hydride phase. The off time of the pulse current cycle is designed to allow break up and decomposition of hydride phase which has been formed in preceding current on part of the pulse cycle. Our in situ stress data show that using such approach, it is possible to completely change the sing of the insitu stress in Cr films during deposition from compressive to tensile. More importantly, we will show the first indications that pulse electrodeposited Cr films have similar micro-cracked structure as Cr films electrodeposited from Cr6+ solutions.

This work is supported by Gift Grant from NASF-AESF Research Foundation.
Electrochemical Conversion of CO2 into Valued Added Products on High-Surface-Area Tin Catalysts
Authors: Zhang Sheng , Liu Hai , Xia Rong , Kuang Siyu , Ma Xinbin
Published: February 2020

The electrocatalytic reduction of carbon dioxide (CO2) to value-added fuels and useful chemicals has been considered as one of the most effective routes to mitigate the greenhouse effect as well as energy crisis. CO2 electro-reduction reaction undergoes complex pathways involving multiple electrons coupled with protons and thus various products can be obtained. Among the wide variety of products, the conversion of CO2 to C2+ species is more favorable owing to their high energy density as well as complicated synthesis route in traditional industrial process.1

Sn-based catalysts have been proved to be the most suitable candidate for the electro-reduction CO2 to formate due to their low cost and non-toxic properties.2 For example, in our previous work, we have synthesized ultrasmall SnO2 nanoparticles supported on carbon black via ethylene glycol method.3 Based on this work, a series of Sn-based binary catalysts have been prepared with different compositions. At present, we are carrying out experiments to convert CO2 to C2+ products using Sn-based catalysts through appropriate structural and electronic modification of tin oxide to achieve C-C coupling.

References:

Genovese, C.; Schuster, M. E.; Gibson, E. K.; Gianolio, D.; Posligua, V.; Grau-Crespo, R.; Cibin, G.; Wells, P. P.; Garai, D.; Solokha, V.; Krick Calderon, S.; Velasco-Velez, J. J.; Ampelli, C.; Perathoner, S.; Held, G.; Centi, G.; Arrigo, R., Operando spectroscopy study of the carbon dioxide electro-reduction by iron species on nitrogen-doped carbon. Nat. Commun.
2018,
9 (1), 935.

Li, Q.; Rao, X.; Sheng, J.; Xu, J.; Yi, J.; Liu, Y.; Zhang, J., Energy storage through CO2 electroreduction: A brief review of advanced Sn-based electrocatalysts and electrodes. Journal of CO2 Utilization
2018,
27, 48-59.

Zhang, S.; Kang, P.; Meyer, T. J., Nanostructured tin catalysts for selective electrochemical reduction of carbon dioxide to formate. J. Am. Chem. Soc.
2014,
136 (5), 1734-7.
Effect of Ionic Liquid Additives on the Product Selectivity and Activity in CO2 Electroreduction over Cu Catalysts
Authors: Sharifi Golru Samaneh , Biddinger Elizabeth J
Published: February 2020

Electrochemical reduction of CO2 has been proposed as a promising way to attenuate the CO2 level in the atmosphere and consequently, mitigate the global warming. Furthermore, several valuable chemicals and fuels can be produced by CO2 electroreduction. Although copper catalysts are of interest due to their ability to produce hydrocarbons and alcohols, they produce a wide verity of products and need high overpotentialsin traditional aqueous electrolytes1. One of the methods to address these obstacles is to use ionic liquids (ILs) in the electrolyte. ILs are cation-anion couples which have unique properties such as high CO2 solubility. In CO2 electroreduction, ILs can play different roles such as co-catalyst, electrolyte, or CO2 absorbent. It has been reported that product selectivity and the reaction rate in CO2 electrocution is significantly impacted when using ionic liquids2, 3.

Here, the effect of using ionic liquids in CO2 electroreduction on product selectivity and activity of Cu catalysts has been studied. For this purpose, Cu foils were first electropolished in 1M phosphoric acid for 300 sec. CO2 electroreduction was then performed on Cu catalysts for 30 mins at different potentials. According to the results, ionic liquids affected the product selectivity even in a diluted IL/water mixture. The results showed that adding 10 mM 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][NTF2]) to the 0.1 M KHCO3 electrolyte leads to a 63% increase in the total current density at -1.1 V (vs RHE). A 50% increase in formate faradaic efficiency at -0.91 V was also detected when adding the IL to the electrolyte. Moreover, the faradaic efficiency of methane increased by 80% at -1.1 V (vs RHE) in the ionic liquid/water mixture. The results demonstrate how ILs influence the CO2 reduction on Cu catalysts.

Hori, Y., Electrochemical CO2 reduction on metal electrodes. In Modern Aspects of Electrochemistry, Vayenas, C. G.; White, R. E.; Gamboa-Aldeco, M. E., Eds. Springer: New York, 2008; Vol. 42, pp 89-189.

Mu, T.; Chen, Y., Conversion of CO2 to value-added products mediated by ionic liquids. Green Chemistry
2019.

Zhou, F.; Liu, S.; Yang, B.; Wang, P.; Alshammari, A. S.; Deng, Y., Highly selective and stable electro-catalytic system with ionic liquids for the reduction of carbon dioxide to carbon monoxide. Electrochemistry Communications
2015,
55(0), 43-46.
Towards Durable, Selective Catalysts and Electrodes for CO2 Electroreduction to Value-Added Chemicals and Fuels
Authors: Nwabara Uzoma O , Cofell Emiliana R. , Henckel Danielle A. , Lu Shawn , Gewirth Andrew A. , Kenis Paul J.A.
Published: February 2020

Rising atmospheric carbon dioxide (CO2) levels and the associated rise in global temperatures are major global concerns. Annual atmospheric CO2 emissions have risen from about 2 Gt to 10 Gt in the last 5 decades.1 Electricity production and transportation are large atmospheric CO2 contributors (~70% of total emissions), and therefore scientists have developed renewable energies and fuel cells vehicles as a mitigation strategies.2,3 Another widely-studied mitigation approach is the electrochemical reduction of CO2 (CO2RR) to value-added chemicals and fuels. Depending on the electrocatalyst and operating conditions used for CO2RR, a variety of products including carbon monoxide, formic acid, ethylene, ethanol, and acetate can be made, which can serve as chemical feedstock for a variety of chemical processes.4

Most research on the CO2RR has focused on developing catalysts around four metrics: high product Faradaic efficiency (selectivity), high current density (activity), low overpotentials (high energy efficiency), and robust durability/stability. Product selectivity greatly affects economic feasibility (separation costs). Many groups have successfully concentrated on catalyst selectivity and activity. State-of-the-art catalysts for CO2 electroreduction can produce CO and HCOOH at high selectivity (>80%), but the selective production of high energy density hydrocarbons and oxygenates is still lacking.5 Moreover, increasing electrode and system durability aids in decreasing costs. Specifically, benchmarks set by technoeconomic analyses suggests system CO2RR lifetimes of >3000h.7,8 However, a majority of durability studies show lifetimes of <20h.

In the first part of this talk, we will focus on developing selective electrocatalysts and defining their stability in an alkaline flow electrolyzer at ambient conditions. The second part of this talk addresses durability, specifically cathodes and the mechanisms by which they fail. With this, we explore strategies for developing more robust CO2RR cathodes and propose accelerated testing protocols to determine durability in a timely fashion.

Acknowledgement

We gratefully acknowledge financial support from Royal Dutch Shell, I2CNER and the SURGE Fellowship for UN.

References

Hansen, P. Kharecha, et al., PLoS One, 2013.

Oerlemans, Science, 2005, 308(5722), 675-677.

https://www.eia.gov Accessed 05/29/2017.

R.M. Jhong, S. Ma, P.J.A. Kenis, Curr. Opin. Chem. Eng., 2013, 2, 191-199.

J. Martin, G.O. Larrazabál, J. Pérez-Ramírez. Green Chem., 2015, 17(12), 5114-5130.

Verma, B. Kim, H.R.M. Jhong, S. Ma, P.J.A. Kenis, ChemSusChem, 2016, 9(15), 1972-1979

Jouny, W. Luc, F. Jiao, Ind. Eng. Chem. Res,
2018, 57(6), 2165-2177
Liquid Fuels Synthesis from Carbon Dioxide on Membrane-Electrode-Assembly (MEA) Under Ambient Conditions
Authors: Adegoke Kayode Adesina , Radhakrishnan Shankara G. , Roduner Emil
Published: February 2020

The undeniable emission of anthropogenic greenhouse gases into the atmosphere remain a foremost cause of global climate changes threatening global peace [1-3]. A number of thermal catalysts are available that can convert carbon dioxide (CO2) to methanol with reasonable yield and selectivity at significantly elevated temperature and pressure, using gaseous molecular hydrogen. Hydrogen has to be produced first in a separate, preceding step via water electrolysis. However, renewable energy is available primarily in the form of electrical power. Currently, the available catalysts for electrochemical reduction of CO2 stop at CO or formic acid as the reduction products. At present, the copper is the only catalyst that can convert CO2 to products beyond CO or formic acid to higher order alcohols.

In this study, we have developed a metal oxide catalyst that is capable of converting formic acid to C1, C2 and C3 alcohols at an overall efficiency of >60%. The electrochemical characteristics were thus examined via linear sweep voltammetry and chronoamperometric (CA) methods. The formic acid reduction reaction result revealed a current density of 62 mA/cm2 at 2.4 V with ohmic resistance of 5.8 Ωcm2. The Tafel slope was also used to evaluate the rate-determining step for the electrochemical reaction of formic acid reduction reaction which is 580 mV/dec. Tafel values of 40 cycles were consistent with each other and with the bulk metal, therefore it can be concluded that there were perhaps no significant changes in the mechanism of reduction. However, the chronoamperometry result at 2.4 V showed the current density of 33 mA/cm2; during which methanol, ethanol and isopropanol were detected as products of formic acid reduction reactions (Fig. 1). First experiment with CO2 electroreduction was also conducted, the findings and the reliance of the study shall be presented. This study therefore successfully developed and converted a thermal metal oxide catalyst to an electrocatalyst that could do the conversion of formic acid and CO2 near room temperature and with water as a source of hydrogen.

[1] C. F. Shih, T. Zhang, J. Li, C. Bai, Joule
2018, 2, 1925.

[2] O. Martin, A. J. Martín, C. Mondelli, S. Mitchell, T. F. Segawa, R. Hauert, C. Drouilly, D. Curulla-Ferré, J. Pérez-Ramírez, Angew. Chemie Int. Ed.
2016, 55, 6261.

[3] L. Wang, Y. Yi, H. Guo, X. Tu, ACS Catal.
2018, 8, 90.

Figure 1
Electrochemical Reduction of Carbon Dioxide to Formate on Tin and Polyaniline-Modified Tin Electrocatalysts
Authors: Portela James M. , Lucas Francisco Willian Souza , Lima Fabio H. B.
Published: February 2020

Tin is one of the most efficient electrocatalysts for the carbon dioxide reduction to formate1, but the real feature that is responsible for such activity is not yet well-understood2. Herein, the carbon dioxide electrochemical reduction to formate ions was studied on Sn and on polyaniline-modified Sn electrocatalysts. The results showed that tin foil electrodes, even having different initial degree of oxidation, as revealed by XPS, exhibited similar faradaic efficiencies, ca. 92%, suggesting that the oxidation state is not the principal factor that control the electrocatalytic activity. Interestingly, when Sn foils and Sn nanoparticles were superficially modified by polyaniline, the rate of formate production was considerably increased, and the faradaic efficiency to formate was maintained close to 92%. In this study, the main features that actually govern the faradaic efficiency of Sn electrodes, and the role of the alkaline nitrogen atoms of polyaniline on detaining CO2 molecules in the vicinities of the electrode producing an increased reaction rate are discussed.

References

[1] J. Wu, F. G. Risalvato, F-S. Ke, P. J. Pellechia, X-D. Zhou, J. Electrochem. Soc., 159 (7) (2012) F353-F359.

[2] C. Cui, J. Han, X. Zhu, X. Liu, H. Wang, D. Mei, Q. Ge, J. Catal. 343 (2016) 257 - 265.

Acknowledgements

The authors gratefully acknowledge financial support from FAPESP (2016/13323-0 and 2013/16930-7), CNPq (306469/20162), and Capes.
(Invited) Reaction of Aqueous Tetramethylammonium Sulfide on SiGe(100) 25% as a Function of pH
Authors: Zhang Zhonghao , Muscat Anthony J.
Published: February 2020

Large improvements in the performance of CMOS (complementary metal oxide semiconductor) devices are possible with nonplanar architectures, such as finFET (fin field effect transistors) and NW-FET (nanowire field effect transistors), combined with semiconductors that have higher charge mobilities than Si. Silicon germanium (SiGe) alloys are especially useful channel materials because the carrier mobility and bandgap can be tuned by changing the percentage of Ge. Integrating SiGe into CMOS technology requires an understanding of the similarities and differences between the way Si and Ge react. Tetramethylammonium sulfide (TMAS) is an aprotic source of sulfide ions (S2-). Clean SiGe(100) 25% reacted with aqueous TMAS ([(CH3)4N]2S) forming covalent Ge-S bonds based on x-ray photoelectron spectroscopy (XPS). Lowering the pH of the solution by adding aqueous HF and HCl increased the S coverage. The highest S/elemental Ge molar ratio of 0.158 was calculated based on XPS data after treatment in TMAS at a pH of 2.0-2.5. The Ge-S bond is broken and S start to desorb from the surface at 450 K based on temperature programmed desorption spectroscopy. During TMAS solution treatment, the SiGe 25% surface was oxidized, as shown by the increased O/Si molar ratio calculated from XPS data compared to a control surface. Reducing the pH of the aqueous TMAS solution reduces the amount of oxide that forms. The surface oxidation is likely due to the formation of oxidizing species in solution such as thiosulfate (S2O3
2-). The comproportionation between thiosulfate and sulfide at lower pH can explain the reason for less surface oxidation when the surface is treated with the low pH TMAS solution.
(Invited) Capillary Pattern Collapse: Prediction and Prevention from Past to Future
Authors: Bassett Derek W
Published: February 2020

In the past twenty years, the collapse of semiconductor features due to capillary forces has evolved from a curious phenomenon to a major hurdle requiring increasing amounts of research, experiments, and innovation in order to avoid and overcome. The first paper to analyze capillary pattern collapse was by Tanaka et al in 1993, where they successfully quantified the effects of pattern geometry, material stiffness, wetting liquid surface tension, and contact angle on whether a wetted feature is likely to collapse or not. Although they were looking specifically at photoresist pattern collapse, the analysis has proven remarkably robust and has applied equally well to stiffer structures with a much higher aspect ratio, and is still used today essentially unchanged in form.

This paper will first summarize analytical efforts to understand and predict capillary pattern collapse: starting from Tanaka's paper, then continuing from there looking at additional effects such as repeating geometry, collapse of pillars instead of only lines, more complex feature shapes, modeling of stiction and restoration, 3D effects, and time dependent effects. Though useful as a qualitative predictor as to how susceptible to collapse features are in comparison to each other, there appears to be a disconnect between these analytical models and a true quantitative prediction of when capillary pattern collapse will occur. The paper will discuss what missing effects may cause this.

For the next section the paper will review what techniques have been used and are currently being used to try to reduce and prevent capillary pattern collapse and showing how they relate directly to the analysis of the system: first in reducing the surface tension by changing the liquid from water to IPA, improving the drying technique, then increasing the contact angle with surface chemical treatment, and then to methods currently being researched: a solid phase eliminated by pyrolysis/sublimation and supercritical dry. It will also discuss what metrology has traditionally been used and brie y present new methods being looked at to better understand capillary pattern

collapse.

For the last section, the paper will discuss the future and the ultimate limits of both analysis and prevention of pattern collapse. The decreasing of feature size in state of the art devices will take us to a point where continuum modeling will no longer be able to provide meaningful results and so molecular dynamic simulations might be the only way to effectively model these nano-systems.
Effect of SiO2 Etching Inhibitor to H3PO4 for the Selective Si3N4 Wet Etching of 3D NAND
Authors: Kim Taehyeon , Son Changjin , Park Taegun , Lim Sangwoo
Published: February 2020

As the number of stacked layers of the 3D NAND structure increases, the memory density of 3D NAND flash memory device increases [1]. In the fabrication of 3D NAND device, it is essential to selectively etch Si3N4 by an etchant flowing along a narrow slit followed by metal deposition. However, as the number of Si3N4/SiO2 multi-stack increases, selective etching of Si3N4 becomes difficult. In order to increase the Si3N4-to-SiO2 etch selectivity, SiO2 etching inhibitor should be added to H3PO4. Unfortunately, most of SiO2 etching inhibitors added to H3PO4 generate oxide regrowth around SiO2 layer on the Si3N4/SiO2 multi-stack structure. In this study, the mechanism of oxide regrowth occurred on the 3D NAND structure was investigated.

Patterned Si3N4/SiO2 multi-stack structures were prepared. Etching experiments were performed using coupon wafers in 85% H3PO4 or etching inhibitor-added H3PO4 at 160 °C. The Si3N4 and SiO2 etching rates and Si3N4-to-SiO2 etch selectivity were measured using spectroscopic ellipsometry and oxide regrowth on the Si3N4/SiO2 multi-stack structure was analyzed using FE-SEM and HR-TEM.

When the Si3N4/SiO2 multi-stack structure was etched in the SiO2 etching inhibitor-added H3PO4, oxide regrowth was observed on the SiO2 layered trenches on the Si3N4/SiO2 multi-stack structure, as shown in Fig. 1. The oxide regrowth occurred intensively at the corner of SiO2 layered trench and oxide regrowth occurred heavily at the bottom of Si3N4/SiO2 multi-stack structure as compared to the top. The overall amount of oxide regrowth on the SiO2 layered trench increased as the concentration of SiO2 etching inhibitor added to H3PO4 increased. In addition, it is shown that generation rate of etching product is an important factor to occur oxide regrowth. Based on the results, it is suggested that etching inhibitor addition and high generation rate of etching product and mass transfer limitation are responsible for the oxide regrowth. Through their optimization, selective Si3N4 etching on the Si3N4/SiO2 multi-stack structure without oxide thinning and regrowth could be obtained, as shown in Fig. 2.

References

[1] S. Aritome, NAND flash memory technologies, p. 273, John Wiley & Sons, Hoboken, NJ (2015).

[2] J. Jang, et al, in Symp. VLSI Tech. Dig., 192 (2009).

Figure 1
Development of “Soft” Cleaning Chemistries for Enhanced STI Post-CMP Cleaning
Authors: Graverson Carolyn F. , Wortman-Otto Katherine M. , Linhart Abigail N. , Zubi Tala B. , Keleher Jason J.
Published: February 2020

Due to the emergence of sub-10 nm technologies, limiting device defects has become of utmost importance in maintaining high performing integrated circuits. Shallow trench isolation (STI) chemical mechanical planarization (CMP) uses a synergistic balance of ceria (CeO2) nanoparticles and functional chemistry to modulate critical surface adsorption interactions necessary to remove excess topography. Literature has identified that the surface redox state of the CeO2 nanoparticle (Ce3+/4+) is a critical factor in controlling CMP performance. More specifically, controlling the oxygen vacancies has been shown to directly impact removal rate (Ce3+ state), as well as post-CMP cleaning efficiency (Ce4+ state). Current post-CMP cleaning processes utilize oxidation/reduction reactions, etching, encapsulation, and ultrasonic methods as a means of undercutting the particle from the substrate surface. These methods have proven to be highly effective at particle removal but have shown to potentially induce further defectivity due to the aggressive cleaning conditions. This work aims to develop a post-CMP cleaning chemistry that enhances particle removal via soft encapsulation of undesirable nanoparticle/slurry chemistry non-covalent complexes on the wafer surface. By employing a polyelectrolyte/surfactant (PES) matrix, a surface adsorbing/charge-flipping encapsulation process is proposed as a vehicle to remove slurry contamination at low friction. Investigation into the synergy between slurry chemistry and PES cleaning chemistry, with respect to defect aggregate formation, was correlated to the cleaning efficiency as well as friction. Techniques were developed to study real-time properties such as the defect aggregate formation mechanism via in-line dynamic light scattering (DLS), coefficient of friction (COF), particle removal, and scratch defectivity to draw a correlation between cleaning chemistry structure and post-CMP performance.
Proactive Contamination Control for Sub 10nm Particle in Advanced Semiconductor Manufacturing
Authors: Libman Slava , Van Schooneveld Gary , McIntosh Bob
Published: February 2020

Advanced Semiconductor Manufacturing has reached the limits of metrology measuring contamination and defects on both the wafers and in the high purity materials (i.e., killer size particles in liquid chemicals and ultrapure water). Furthermore, ability of the most advanced filters to control particles in sub-10nm range is also limited. High purity materials used in liquid delivery systems have never been qualified for sub-10nm size particles. Finally, particle shedding of sub-10nm particles from high-purity components located post-filter cannot be directly measured and only be estimated using power-law extrapolation.

Yield Enhancement IFT (international focus team) of IRDS (International Roadmap for Devices and Systems) is working together with the Liquid Chemical Committee of SEMI Standards to establish the methodology to enable proactive technology management in the space of contamination control.

This presentation will provide the most recent experimental data generated by UPW IRDS team and SEMI Standards Liquid Chemical task forces, demonstrating the issues related to the contamination occurrence. The presentation will also include information about the SEMI standards and corresponding systematic approach that supports supply chain effort for developing and commercialization of new solutions to proactively address the contamination issues.
(Invited) Selective Area Growth of Deactivating Polymers
Authors: Wojtecki Rudy James
Published: February 2020

As the semiconductor community continues scaling, area selective atomic layer deposition (ASD) offers the potential to relax down-stream processing steps by enabling self-aligned processes (e.g. self-aligned via). ASD can be achieved under a variety of conditions and, with the use of organic inhibiting materials, exhibit some of the highest levels of selectivity. However, the organic materials exploited are generally relegated to small molecules and may require multiple cycles of etch-back processes followed by renewal of the surface protection coating. The chemical composition of polymeric materials offers significant potential to broaden the number and film compositions that can be selectively deposited as they draw from such a vast number of chemical functionalities that can be exploited to tailor surface properties [1,2]. There are two approaches to exploiting polymers for ASD, (i) grafting to a substrate with polymer brushes or (ii) growing polymers from a surface. Grafting polymer brushes, with materials shown to inhibit ALD film growth and functionalized with metal binding ligands, exhibited poor selectivity to surfaces and resulted in high defectivity on patterned surfaces where polymer particles were observed on both a metal and dielectric. Growing polymers from a substrate is an attractive strategy, though difficult to realize experimentally. Using a facile synthetic route, a surface binding monomer was engineered that maintained high activity for surface polymerizations and which selectively adheres to a nanoscale metal features, in a field of dielectric material. The resulting surface afforded the ability to produce polymers in an area selective manner and chemically engineer the surface, as desired. The resulting surface polymers were both thermal and chemically stable under ALD conditions and highly selective at guiding the ALD of several films including TiO2 and ZnO for extended periods of time that allow the growth of film thicknesses greater than 48nm, relevant in a number of device applications. This method was also found to be scalable where initial experiments were carried out on laboratory scale experiments and could be scaled to a full 300mm wafer. Furthermore, the mechanism of inhibition was shown where ALD films inhibition is the result of precursor solubility in the polymer film. This unique strategy of growing polymers in an area selective manner and the inhibiting mechanism, present a set of design rules for engineering surfaces to direct the formation of inorganic films.

References:

[1] J. Vac. Sci. Technol. A,
2019, 37(2), 020923-1.

[2] ACS Appl. Mater. Interfaces, 2018, 10(44), 38630.

Figure 1
(Invited) Selective Atomic Layer Deposition Strategies for Catalytic Applications
Authors: Chen Rong , Cao Kun , Liu Xiao , Cai Jiaming , Shan Bin , Wen Yanwei
Published: February 2020

Atomic layer deposition (ALD) is a mainstay of the semiconductor industry since it allows depositing nanometer thin layers of a desired material onto a substrate in a very controlled and uniform manner. Recently, ALD has been adapted to design and synthesize composite catalysts that allow them to enhance multiple chemical reactions. In fabrication of composite catalysts, the selective approaches of ALD are of great importance to exert spatial control of deposition to fabricate three dimensional nanostructures.

In this talk, strategies for selective ALD and enabled nanostructures for catalytic applications will be discussed. The atomically ccomposite nanostructures allows motivations of selective-ALD enable directionally and precisely tailoring of the structural parameters, interfaces, and active sites, that is of great significance for advanced catalysis. Both metal and oxide selectively decorated nanoparticle catalysts will be discussed. With these methods, core shell structures, oxide overcoating structures, facet selective structures are fabricated. The DFT calculations for precursors’ chemisorption and binding energies are carried out to verify the results. These strategies of selective ALD have demonstrated unique advantages to design and fabricate highly active and thermal stable catalysts in atomic scale, and also provided insights to understand the structure–activity relationship.
(Invited) Atomic Layer Deposition for Stabilizing Surface-Bound Molecules for Photoelectrochemistry and Catalysis
Authors: Losego Mark D.
Published: February 2020

Molecularly sensitized devices that rely on surface bound molecules to impart functionality are keenly susceptible to device degradation via hydrolysis of anchor group chemistries and subsequent molecule detachment. Recent commercialization success in dye-sensitized solar cells is largely possible due to brute-force encapsulation engineering. However, using molecular sensitizers in aqueous environments as water oxidation catalysts or biological sensors poses an even greater challenge. This talk will highlight advances in the use of low temperature atomic layer deposition (ALD) applied after surface functionalization to drastically improve molecular attachment in aqueous environs. We have shown that ultrathin (< 1 nm) ALD coatings of inorganic oxides "surrounding" the molecular sensitizers improve attachment by orders of magnitude. These “coated” molecules still function as light absorbers, electron transfer agents, and catalytic species. The current state-of-the-science will be discussed including what has been learned about the changes in chemical structure upon ALD processing via in-situ FTIR spectroscopy and ex situ sum frequency generation spectroscopy. Finally, we will show the utility of this approach in creating new hybrid catalysts that combine the selectivity of homogeneous molecular catalysts with the recoverability of heterogeneous inorganic catalysts.
Impact of Atomic Layer Deposition on the Photoluminescence of Colloidal Quantum Dots
Authors: Kuhs Jakob , Werbrouck Andreas , Zawacka Natalia , Drijvers Emile , Smet Philippe F , Hens Zeger , Detavernier Christophe
Published: February 2020

Colloidal QDs are hybrid objects that feature an inorganic, crystalline core surrounded by an organic ligand shell. The ligands are required for stabilising QD dispersions and, by passivating under-coordinated surface atoms, reducing the density of localized surface states that would quench their photoluminescence (PL). The integration of QDs in optoelectronic devices typically requires embedding of the QDs in a host material. Atomic layer deposition (ALD) is often considered as a deposition technique for such purpose. However, the ALD process chemistry can affect the surface of the QDs and their ligand shell, thus potentially leading to a reduction of the PL efficiency after embedding of the QDs. Hence, a fundamental understanding of the interplay between the ALD process chemistry and the QD photoluminescence stands out as a key challenge for turning ALD into a viable encapsulation method for QDs. In this work, a reactor for plasma enhanced ALD was equipped with the possibility to conduct in situ photoluminescence measurements during ALD encapsulation of QDs. This setup was used to investigate the influence of plasma treatment, precursor and reactant exposure on the PL of CdSe/CdS/ZnS core/shell/shell QDs during ALD of Al2O3, TiO2, HfO2, and ZnS. The in situ PL approach proved a versatile technique to screen suitable precursors, reactants and ALD processes for QD embedding and to investigate the interaction between QDs and reactive gaseous species in general.
(Keynote) Nitrogen-Ion Implantation Doping of Ga2O3 and Its Application to Transistors
Authors: Higashiwaki Masataka , Wong Man Hoi , Goto Ken , Murakami Hisashi , Kumagai Yoshinao
Published: February 2020

As a key ultra-wide bandgap semiconductor, gallium oxide (Ga2O3) has been attracting much interest for power device applications due to its excellent material properties based on an extremely large bandgap of 4.5 eV and the availability of high-quality, large-diameter wafers produced from bulk single crystals synthesized by melt growth methods. Despite having received only little attention, the ease of both n- and p-type ion implantation doping is another very attractive and important feature for Ga2O3 device technologies.

Recently, we succeeded in developing nitrogen (N)-ion implantation doping technology to form p-type Ga2O3 [1]. Note that it is almost impossible to obtain p-type Ga2O3 with effective hole conductivity as for conventional semiconductors. This is not only due to a lack of shallow acceptors with moderate activation energies but also because the valence band structure of Ga2O3, which is composed of O 2p orbitals, is characterized by a very large hole effective mass and conduces to self-trapping of holes with associated characteristic lattice distortions. Therefore, p-Ga2O3 is only useful for engineering large energy barriers in the form of p-n junctions. We have experimentally confirmed that a N-ion implanted p-Ga2O3 region formed in n-Ga2O3 can be utilized as a current blocking layer.

In this talk, we first discuss the material properties of p-Ga2O3 formed by N-ion implantation doping. Then, the device process and characteristics of vertical normally-on Ga2O3 MOSFETs fabricated by using multiple Si- and N-ion implantations are presented [2].

This work was partially supported by Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), “Next-generation power electronics” (funding agency: New Energy and Industrial Technology Development Organization).

[1] M. H. Wong, C.-H. Lin, A. Kuramata, S. Yamakoshi, H. Murakami, Y. Kumagai, and M. Higashiwaki, Appl. Phys. Lett. 113, 102103 (2018).

[2] M. H. Wong, K. Goto, H. Murakami, Y. Kumagai, and M. Higashiwaki, IEEE Electron Device Lett. 40, 431 (2019).
(Invited) GaN-Based Multiple 2DEG Channel BRIDGE (Buried Dual Gate) HEMT Technology for High Power and Linearity
Authors: Shinohara Keisuke , King Casey , Regan Eric , Gomez M P , Bergman Joshua , Carter Andrew , Arias Andrea , Urteaga Miguel , Brar Berinder , Page Ryan , Chaudhuri Reet , Islam Moudud , Xing Huili Grace , Jena Debdeep
Published: February 2020

A unique combination of high mobility, high velocity and high sheet density of the 2DEG formed in GaN-based heterostructures has enabled GaN-based HEMTs to be used in a wide range of applications from RF power amplifiers to efficient power converters. Today’s complex communication systems require transceivers to process RF signals efficiently with large bandwidth and high fidelity. While GaN-based HEMT technology has advanced to reach higher power densities, it has not fundamentally changed the power requirements for the linearity performance.

To address fundamental limitations of HEMT’s power/linearity/efficiency/frequency tradeoff, we proposed a transistor structure called BRIDGE FET (buried dual gate FET) where gate electrodes are buried into AlGaN/GaN heterostructures and contact laterally with multiple 2DEG channels [1]. A deliberate elimination of a conventional top-contact gate leads to a unique device operation principle and performance advantages for improved linearity and efficiency at large signal operations; (1) The drain-source current is controlled solely by modulating the width of the 2DEG channels by the lateral gate electric field while maintaining the 2DEG density. (2) The MESFET-like device operation enables gradual pinch-off, greatly reducing g
m derivatives near pinch-off. (3) Lack of density modulation with V
gs leads to a constant electron velocity at high electric field, eliminating a typical g
m roll-off at high V
gs. This results in a constant gain along a resistive load line. (4) The buried gates forms Schottky contacts to the GaN channels below the 2DEG layers. This enhances electron confinement and improves electrostatic isolation between the source and drain, significantly reducing g
d at high V
ds. (5) Elimination of the top-contact gate prevents electrons from being trapped on the surface, suppressing current collapse at high voltage operations. (6) An absence of inverse piezoelectric effect due to the reduced vertical electric field at the drain-side of the gate improves device reliability under high voltage stress.

In this presentation, current status of our development of multi-2DEG channel BRIDGE FETs will be discussed. This work was sponsored by DARPA-MTO DREaM program under DARPA/CMO Contract No. FA8650-18-C-7807. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressly or implied, of the Defense Advanced Research Projects Agency or the U.S. Government.

[1] K. Shinohara et al., IEEE EDL, vol. 39, no. 3, p. 417, March 2018.
Electrochemical Behaviour of Expanded Graphite for Thermogalvanic Cells and Thermally-Charged Supercapacitors Applications in Ionic Liquids
Authors: Torres Bautista Blanca Estela , Bhattacharya Kakoli , Bonetti Marco , Roger Michel , Nakamae Sawako
Published: February 2020

In the present times of ever-increasing energy demands, escalating fuel prices and environmental concerns such as global warming, thermal energy harvesting emerges as a promising source of clean and sustainable energy. Thermogalvanic effect observed in liquid electrolyte-based thermoelectrochemical cells (TECs) offers direct heat to electricity conversion with zero gas emission. TECs in comparison to conventional solid-state thermoelectric materials are reliable, cost effective and require little maintenance, as they have no moving parts.

Furthermore, these TECs can also serve as potential storage devices for waste-heat energy, which can be later recovered and converted into electrical energy. The objective of the present work is to study the combinations of different expanded graphite electrodes with different ionic liquid based electrolytes using traditional electrochemical methods such as open circuit potential, cyclic voltammetry and electrochemical impedance spectroscopy, coupled with the thermoelectric characterizations. The results allow a better understanding of the thermoelectrochemical energy conversion and stored charge efficiency in thermogalvanic cells and thermally-charged supercapacitors.

This work is supported by European Union’s Horizon 2020 research and innovation programme under the grant agreement No 731976 (MAGENTA).
(Invited) Nanoengineered Thermoelectric Energy Devices for IoT Sensing Applications
Authors: Ono Takahito , Nguyen Trung Huu , Samat Khairul Fadzli , Li Jinhua , Toan Nguyen Van
Published: February 2020

Flexible thermoelectric micro power generators have been developed for wearable devices such as body area network. Also in order to store the generated power, a solid state micro-supercapacitor using a thin film composed of graphene nanowall are developed.

The flexible thermoelectric micro power generator is fabricated by electrochemical deposition of Bi2Te3 and Sb2Te3, which is embedded by PDMS as shown in Fig. 1 (1). A power generation of 4 μW/cm2 are demonstrated from human body temperature. In order to improve the power generation performance, nanocomposites processes of Bi2Te3 are developed. In this method, nanomaterials such as metal nanoparticles and carbon nanomaterials are included in the film by a co-electrodeposition method (Fig. 2).

For the fabrication of the solid state micro super capacitor, plasma-enhanced chemical vapor deposition is used to deposit graphene nanowall on a spiral-shaped silicon electrode pattern, as shown in Fig. 3. On the graphene nanowall Ru oxide or Ni oxide is deposited for electrochemical charge storage layer. Areal energy density of ~15 μWh/cm2 and areal power density of ~2.49 mW/cm2 are achieved (2).

References

(1) T. N. Huu, T. Nguyen, and T. Ono, "Fabrication of π-type flexible thermoelectric generators using an electrochemical deposition method for thermal energy harvesting applications at room temperature" Journal of Micromechanics and Microengineering 27, (2017) 125006.

(2) J. Li, M. Zhu, Z. An, Z. Wang, M. Toda, T. Ono, Constructing in-chip micro-supercapacitors of 3D graphene nanowall/ruthenium oxides electrode through silicon-based microfabrication technique, Journal of Power Sources 401, (2018) 204-212.

Figure 1
(Invited) Hybrid Monolithic Nanomanufacturing of 3D Liquid-Solid Heterojunction Devices for Self-Powered Smart Skin
Authors: Wu Wenzhuo
Published: February 2020

The seamless and adaptive interactions between functional devices and their environment are critical for advancing emerging technologies, e.g. wearable devices, consumer electronics, and healthcare. The state-of-the-art electronics are based on planar and rigid structures, limiting their integration with three-dimensional soft biological systems. Mechanically deformable devices incorporating confined liquids present an ideal platform for enabling the conformal coverage of electronics on curved and soft surfaces in related applications. However, to date, liquid-based devices have been limited to merely incorporate liquid components as the passive electrodes given the difficulty in the fabrication of liquid-based heterojunctions. The heterogeneous interfaces between functional materials are the central constituents in the state-of-the-art electronics and optoelectronics. Moreover, there is a lack of the fundamental understanding and technological capability of monolithically integrating liquid structures (e.g. electrodes) with functional materials, in particular, the inorganic semiconductors that offer desired electronic and optoelectronic properties in the anticipated applications.

Here, we demonstrate for the first time a versatile platform for the monolithic integration of liquid-solid heterojunction devices through the hybrid manufacturing of self-assembled two-dimensional inorganic semiconductor nanostructures on additively-manufactured liquid electrodes. This new class of wearable devices are conformable to human skins and can sustainably perform non-invasive physiological functions, e.g. detection of pulses and vocal vibration, by harvesting the operation power from the human body. This research is expected to have a positive impact and immediate relevance to many societally pervasive areas, e.g. biomedical monitoring, consumer electronics, and human-machine interface.