bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Development of Blue Vertical Cavity Surface Emitting Lasers (VCSELs) with Nanoporous GaN
Authors: Han Jung , Elafandy Rami , Kang Jin-ho 
Published: July 2021

Blue and green vertical cavity surface emitting lasers (VCSELs) are expected to be used in future generation display and lighting applications. Applications in virtual reality (VR), augmented reality (AR), retinal scanning display (RSD), and portable projection devices are only a few of the anticipated applications. However, in spite of vigorous pursuit for more than two decades, GaN VCSELs have yet reached commercialization.
The main challenge in the technology of III-nitride VCSELs is the fabrication of distributed Bragg reflectors (DBRs) that can provide near-unity reflection and thus support the formation of high-quality vertical cavity. Several groups reported VCSEL operations using epitaxial DBRs (using AlGaN/GaN or AlInN/GaN) and dielectric DBRs (involving lift-offs or epitaxial lateral overgrowth). In this talk, we will discuss an alternative approach to this challenging problem by using electrochemistry to create nanoporous GaN as a low-index medium, toward a manufacturable DBR mirror technology to support blue and green VCSELs. This nano-engineering based on electrochemistry can help to circumvent impasses and creates new dimensions in the exploration of optoelectronic devices using GaN.
We acknowledge research support from US Department of Energy, National Science Foundation, DARPA, and IP Group.
Investigation of Electrical and Optical Properties of Low Resistivity Indium Oxide Thin Films
Authors: Sundaresh Sreeram , Nehate Shraddha Dhanraj , Sundaram Kalpathy B. 
Published: July 2021

Indium Oxide (In2O3) is a wide bandgap (~3.6eV) n-type transparent conducting oxide (TCO) semiconductor with high conductivity and good transparency in the visible region [1]. In2O3 finds several applications such as photovoltaic devices, transparent windows in liquid crystal displays and heterojunction solar cells [2]. The electrical and optical properties of In2O3 films vary depending on the partial pressure of the reactive gas used for the specific deposition technique, target to substrate distance, temperature at which the substrate is exposed during heat treatment following deposition, and the ambience in which it is treated [3]. In2O3 films has been deposited using vacuum evaporation, sputtering [4], chemical vapor deposition [5], spray pyrolysis [6], ion assisted deposition [7], spin coating [8] and atomic layer epitaxial growth [9].
In this work, In2O3 films are deposited on glass substrates by reactive sputtering of In2O3 target in presence of oxygen gas. The deposition was carried out under different flow rates of oxygen. The influence of oxygen gas flow on electrical and optical characteristics of the films are studied. Influence of oxygen gas flow on electrical resistivity of In2O3 thin films is investigated. Transmission characteristics of the deposited films are studied using UV-visible spectrophotometer. Absorption coefficient is calculated from the transmission values and optical bandgap is extracted from Tauc-plot.

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Abbas bagheri khatibani, Seyed Mohammad Rozati, Z. Bargbidi (2012). Preparation, Study and Nanoscale Growth of Indium Oxide Thin Films. Acta Physica Polonica Series a. 122. 220. 10.12693/APhysPolA.122.220.

Radhouane Bel Hadj Tahar, Takayuki Ban, Yutaka Ohya, and Yasutaka Takahashi, Tin doped indium oxide thin films: Electrical properties, Journal of Applied Physics 83:5, 2631-2645.

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Cheng, G., Stern, E., Guthrie, S. et al. Indium oxide nanostructures. Appl. Phys. A 85, 233–240 (2006).

Memarian, N., Rozati, S.M., Elamurugu, E. and Fortunato, E. (2010), Characterization of SnO2:F thin films deposited by an economic spray pyrolysis technique. Phys. Status Solidi (c), 7: 2277-2281.

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(Invited) Defects in Cast-Mono Crystalline Silicon
Authors: Yang Deren 
Published: July 2021

Crystalline silicon, including Czochralski silicon (Cz-Si) and multicrystalline silicon (mc-Si),is main material for photovoltaic (PV) industry. How to produce more productive and less expensive crystalline silicon materials is still a big challenge. As we know, the seed-assisted growth method can be used to fabricate cast-mono (CM-Si) silicon by directional solidification, which should combine the both advantages of Cz-Si and mc-Si. However, there remain some problems to be resolved in growing CM-Si silicon ingots, particularly the control of dislocations which are the major and most detrimental defects in CM-Si. They can act as precipitation sites for impurities and thus reduce the carrier lifetime in ingots. Unlike mc-Si ingots, once dislocations are generated in the bottom of CM-Si ingots, they will glide and propagate along the growth direction without hindrance due to the lack of grain boundaries.
In this presentation, we review our recent work of how to control defects, specially dislocations, in CM-Si. We induce a grain boundary by adjusting the orientation of seeds which can suppress the generation of dislocations originated from the junction of seeds. We have investigated the effect of Σ5, Σ13a grain boundary relationship at seed junctions of <100>-oriented CM-Si on dislocations and solar cell performance. We also use <110>-oriented seeds to grow new orientation CM-Si ingots to control the generation and propagation of dislocations. The results show that by designing the orientation of seeds, the dislocation density can be decreased and the solar cell efficiency can be improved obviously.
(Invited) Interface Treatment Related Defects During Ge Gate Stack Formation
Authors: Misra Durga 
Published: July 2021

Germanium as a high mobility channel material is currently of considerable interest since Ge has both higher electron and hole mobility as compared to silicon (1). The deposition of high-k dielectrics on Ge has been a significant challenge because of high interface defects density, Dit
(2). By considering the interface reaction kinetics, thermal budget various atomic layer deposition (ALD) schemes and interface treatments can be identified to get a stable dielectric with a robust interface. However, understanding of the interface kinetics and defect distribution into gate stack and/or Ge is still limited.
In this work, we report the impact of different interface treatments on the p type Ge prior to any high-k layer deposition on defect generation. Ge surface was oxidized by a controlled chemical oxidation, slot-plane-antenna plasma oxidation and oxidation through vapor O3 treatment before ALD deposition of 1nm Al2O3/3.5nm ZrO2 for gate stack formation. These devices were characterized to evaluate the interface and possible bulk defects by deep level transient spectroscopy (DLTS), capacitance spectroscopy, conductance method in addition to standard I-V and C-V measurements. DLTS has the advantage to have the spectrum comparison among the interface treatments. Signature of these spectra can reveal the difference, which is more accurate than the defects estimated by Conductance method. DLTS also provides the signature of slow traps (~1ms) (Fig. 1) originating from the bulk or interface depending on the type of GeOx formation.
Furthermore, we evaluate the defect distribution when the gate stack was subjected to a slot-plane antenna plasma oxidation prior to metal deposition. A TiN/Hf1-xZrxO2/Al2O3/Ge gate stack with six different Zr content was investigated (Fig. 2). Al2O3 was used to impede the Ge diffusion into the gate stack. Interface state density (Dit) and C-V hysteresis show that the mid-gap Dit tend to increase with decrease in EOT, possibly due to the undesirable native oxide formation on Ge.
The author would like to thank Drs. Y.M. Ding (Western Digital Corporation, Shanghai, China), M.N. Bhuyian (Globalfoundries, Malta, NY, USA), K.L. Ganapathi (Indian Institute of Technology Madras, India), N. Bhat, (Indian Institute of Science, Bangalore, India) and K. Tapily, R. D. Clark, S. Consiglio, C. S. Wajda, G. Nakamura, and G. J. Leusink of TEL Technology Center, America, Albany, NY, for their help in this work.

References

Arimura et al, IEDM Technical Digest, (2020)

N. Bhuyian et al, ECS Journal of Solid-St. Sci. and Tech., vol. 7(2), N1-N6, (2018)

G. Kolla et al, J. Vac. Sci. Technol. B, 36(2), 021201 (2018)

Ding et al, IEEE Trans. on Dev. and Materials Reliability, 17(2), 349-354, (2017)

Ding, et al, J. of Vac. Sci. and Technol. B, 34(2), 021203, 2016.

Figure 1
(Invited) Flexible, Stretchable and Healable Electronics
Authors: Cicoira Fabio 
Published: July 2021

Organic electronics, based on semiconducting and conducting polymers, have been extensively investigated in the past decades and have found commercial applications in lighting panels, smartphone and TV screens using OLEDs (organic light emitting diodes) technology. Many other applications are foreseen to reach the commercial maturity in future in areas such as transistors, sensors and photovoltaics.
Organic electronic devices, apart from consumer applications, are paving the path for key applications at the interface between electronics and biology, such as in polymer electrodes for recording and stimulating neural activity in neurological diseases. In such applications, organic polymers are very attractive candidates due to their distinct property of mixed conduction: the ability to transport both electron/holes and ionic species. Additionally, conducting polymers offer the possibility to tune their surface properties (e.g., wettability or chemical reactivity) by changing their oxidation state, thus promoting or hindering the adhesion of biomolecules. This feature can be particularly useful for enhancing the biocompatibility of implantable electrodes.
My talk will deal with processing and characterization of conducting polymer films and devices for flexible, stretchable and healable electronics.
Self-healing electronic materials are highly relevant for application in biology and sustainable electronics. We observed mechanical and electrical healability of PEDOT:PSS thin films. Upon reaching a certain thickness (about 1 µm), PEDOT:PSS thin films damaged with a sharp blade can be healed by simply wetting the damaged area with water. The process is rapid, with a response time on the order of 150 ms. Significantly, by blending with other polymers, the films are transformed into autonomic self-healing materials without the need of external stimulation. This reveals a new property of PEDOT:PSS and enables its immediate use in flexible and biocompatible electronics, such as electronic skin and bio-implanted electronics, placing conducting polymers on the front line for healing applications in bioelectronics.
References
[1] S. Zhang, F. Cicoira, Water-Enabled Healing of Conducting Polymer Films, Adv. Mater. 29, 1703098, 2017.
[2] Y. Li, X. Li, S. Zhang, L. Liu, N. Hamad, S. R. Bobbara, D. Pasini, F. Cicoira, Autonomic self-healing of PEDOT:PSS achieved via polyethylene glycol addition, Adv. Funct. Mater. 30, 2002853, 2020.
[3] Y. Li, S. Zhang, N. Hamad, K. Kim, L. Liu, M. Lerond, F. Cicoira, Tailoring the Self-Healing Properties of Conducting Polymer Films, Macromol. Biosci. i2000146, 2020.
Phase Formation during Reduction-Oxidation of Ni-Substituted Sr(Ti,Fe)O3-δ Solid Oxide Fuel Electrodes
Authors: Schmauss Travis Anthony , Mogni Liliana , Barnett Scott A 
Published: July 2021

High performance solid oxide fuel cell anodes have recently been achieved via the exsolution of bimetallic (Ni,Fe) particles from a parent Sr(Ti,Fe,Ni)O3-δ (STFN) matrix. However, a number of unknowns remain regarding the detailed nature of the exsolution process, the role of initial A-site deficiency, and the effect of the change in perovskite stoichiometry during exsolution. In this study, the dynamics of exsolution are explored via thermogravimetric analysis (TGA), X-ray diffraction (XRD), and transmission electron microscopy (TEM), both during exsolution and redox cycling. The diffraction results show that the (Ni,Fe) phase starts Ni-rich during the initial exsolution, gradually shifting to more Fe-rich with time; this result indicates that Ni diffusion towards the surface is occurring faster than for Fe. The TGA results suggest that holding STFN under too-reducing conditions can lead to continued Fe exsolution instead of reaching a stable equilibrium. TEM images display regions where SrO formed after Fe-Ni exsolution, likely as a consequence of increased A-site excess in the perovskite. In-situ re-oxidation and subsequent re-incorporation of exsolved species into the parent oxide have been suggested as a means to “reset” exsolution electrodes after degradation by, e.g., particle coarsening. The present TGA results taken during redox cycling suggest that a shorter oxidation step results in faster exsolution, a hint that, in this case, the exsolved surface species do not have sufficient time to fully re-incorporate into the oxide. The effects of new phase formation, changes in exsolved particle composition, and redox cycling on electrochemical characteristics will also be reported.
Figure 1. Ex-situ X-ray diffraction scans from Sr(Ti,Fe,Ni)O3-δ after reduction in 30% H2 – 3% H2O – 67% Ar, showing peaks from the perovskite matrix along with a peak associated with exsolved (Ni,Fe) metal alloy; the latter shifts with increasing reduction time indicating that the alloy becomes increasingly Fe-rich.

Figure 1
Defect Chemistry of Mixed Conducting Pcfc Cathode Materials with Protons, Oxygen Vacancies and Holes
Authors: Merkle Rotraut , Raimondi Giulia , Hoedl Maximilian F. , Kotomin Eugene A. , Maier Joachim 
Published: July 2021

In recent years significant progress was achieved for protonic ceramic fuel cells (PCFC) concerning fundamental understanding, materials processing, and device performance. PCFC cathode materials require sufficient proton conductivity to extend the reaction zone beyond the three phase boundary. The hydration thermodynamics of BaFeO3-
d-related perovskites was studied using thermogravimetry.[1] Despite a high oxygen vacancy concentration, the degree of hydration is lower for cathode materials compared to Ba(Zr,Y)O3-x electrolytes. A partial substitution of iron by redox-inactive, oversized Zn2+ or Y3+ drastically increases the proton uptake. Measurements of oxygen nonstoichiometry and proton uptake indicate pronounced deviations from ideally dilute defect chemistry (assigned to hole-hole and hole-proton defect interactions [1]). Based on DFT calculations [2] and EXAFS/XRS measurements [3], these interactions are related to the partial transfer of electron holes from iron to adjacent oxygen ions, which in turn disfavors protonation. The obtained detailed defect-chemical understanding serves as the basis for further PCFC cathode optimization, in particular since proton uptake, catalytic activity, electronic conductivity, and stability show conflicting dependencies on cation composition.
[1] R. Zohourian, R. Merkle, G. Raimondi, J. Maier, Adv. Funct. Mater. 28 (2018) 1801241.
[2] M.F. Hoedl, D. Gryaznov, R. Merkle, E. A. Kotomin, J. Maier, J. Phys. Chem. C 124 (2020) 11780.
[3] G. Raimondi, F. Giannici, A. Longo, R. Merkle, A. Chiara, M. F. Hoedl, A. Martorana, J. Maier, Chem. Mater. 32 (2020) 8502.
We thank GIF (I-1342-302.5/2016) for financial support.
Figure 1: (a) Increase of proton uptake by Y or Zn doping [1]. (b) Dependence of hydration enthalpy on formal Fe oxidation state [2]. (c) Increased local deformations by Y doping [3]. (d) Conflicting trends; e.g. Ba is beneficial for proton uptake and catalytic activity but detrimental for electronic conductivity and chemical stability.

Figure 1
Assessing Perovskite Electrode Materials Stability for Electrochemical Oxidative Coupling of Methane
Authors: Denoyer Luke H , Ramaiyan Kannan , Benavidez Angelica , Garzon Fernando H 
Published: July 2021

Identification of large shale gas reserves has reduced the price of methane significantly. Interest in converting methane to value-added commodity chemicals has increased as a result of these findings [1]. Direct conversion of methane to ethylene using heterogeneous methods such as oxidative and non-oxidative coupling of methane (OCM and NOCM) utilize metal oxide catalysts with varying success. However, a catalyst with commercial viability remains elusive. Recently, iron-doped Sr2Fe1.5+0.075Mo0.5O6-δ electrodes (SFMO-075) have been shown to convert methane to ethylene more efficiently in an electrochemical OCM set up (EC-OCM) [2]. However, one of the main concerns with perovskite electrodes is the stability and durability of these materials. We have developed two different perovskites comprising Ba, Mg, Ca, Nb and Fe and evaluated them for EC-OCM. However, the chemical and electrochemical stability of these materials is largely unexplored. Specifically, during EC-OCM, these materials are exposed to CH4, CO2 and H2O. Each metal oxide’s chemical stability needs to be evaluated under these gases at concentrations relevant to EC-OCM. Further, pure methane supplied at the anode presents a highly-reducing atmosphere, necessitating a study on the redox stability of these materials under very low oxygen partial pressures. We shall report our results on the chemical stability of three different perovskite materials (including SFMO) in EC-OCM relevant conditions. We evaluate these perovskite powders before and after gas exposure using TGA, XPS, XRD and FT-IR measurements. While SFMO was found to be unstable in these conditions with a crystal structure collapse, the other two perovskites show promising stability. Their thermodynamic stability in these conditions along with the feasibility of various reaction mechanisms (analyzed through HSC Chemistry) will be discussed. Our study demonstrates important characteristics of catalysts for EC-OCM and may lend to the design of innovative perovskites capable of converting methane to ethylene electrochemically.
References:
1) P. Schwach, X. Pan, and X. Bao, “Direct Conversion of Methane to Value-Added Chemicals over Heterogeneous Catalysts: Challenges and Prospects,” Chem. Rev., 117, 8497, 2017.
2) C. Zhu, S. Hou, X. Hu, J. Lu, F. Chen, and K. Xie, “Electrochemical conversion of methane to ethylene in a solid oxide electrolyzer,” Nat. Commun., 10, 1173, 2019.
Quantifying the Density and Mobility of Mobile Ions in Solid Electrolytes By Transient Current Measurements
Authors: Futscher Moritz H. , Sastre Jordi , Romanyuk Yaroslav E. 
Published: July 2021

Solid electrolytes are a key component in enabling new technological advances for rechargeable batteries by mitigating many of the challenges associated with the use of liquid organic electrolytes. One of the key properties of solid electrolytes is their ability to transport ions between the anode and the cathode. This ion migration is usually characterized by measuring the ionic conductivity by means of impedance spectroscopic measurements. However, the ionic conductivity is proportional to both the density and the mobility of mobile ions. Only the mobility represents the actual velocity of the mobile ions.
Using lithium phosphorus oxynitride (LiPON), we show how measuring the temperature-dependent current transients can be used to independently quantify both the mobility and the density of mobile ions in solid electrolytes. By changing the mobile ion density in Li7La3Zr2O12 (LLZO) solid electrolyte by co-sputtering LLZO and Li2O, we show how samples that seem to have the same ionic conductivity can still differ in ionic mobility. Finally, we employ this method to quantify the effects of Al and Ga doping on the ion migration in LLZO solid electrolytes. The proposed approach in quantification of mobile ions can be extended to other solid electrolytes for a better understanding of ion migration and the influence on battery performance.
Electrochemical Properties of High-Temperature Polymer Electrolyte Thin Films
Authors: Venugopalan Gokul , Briceno-Mena Luis A , Bhattacharya Deepra , Romagnoli Jose A , Arges Christopher G. 
Published: July 2021

Electrode binders based on ionomer chemistries have a profound impact on the performance of polymer electrolyte membrane (PEM) fuel cells. High temperature PEM fuel cells (HT-PEMFCs) typically use phosphoric acid (H3PO4) imbibed polymers or polymers without ionic moieties as the binder (e.g., PTFE). The former materials hinder gas reactant transport and compromise electrode kinetics, while the latter materials suffer from severe ohmic penalties in the electrode layers. The ionomer binder limitations for HT-PEMFCs stymie power density and lead to poor utilization of the costly platinum catalyst.
This talk presents our work probing the electrochemical properties of high-temperature ionomer thin films. The polymer electrolytes investigated are phosphoric acid imbibed polycations as well as phosphonated polymers. Thin films are examined because they mimic the structure found in electrode layers and they can be interrogated with interdigitated electrode (IDE) arrays featuring nanoscale electrocatalysts. The IDE platform is useful for drawing definitive conclusions about the electrochemical behavior of ionomer binder materials without being muddled by the complexity of bulk electrodes. Our work has shown that phosphonated ionomers display better hydrogen diffusivity and hydrogen oxidation reaction kinetics than acid imbibed polycations. The phosphonated ionomers can match the anhydrous proton conductivity of acid imbibed polymers provided they contain electron withdrawing moieties in the polymer. The final part of the talk presents Machine Learning (ML) tools (e.g., support vector regression, density-based clustering, and self-organized maps) that use data from IDEs and single-cell polarization. The ML bridges materials properties to device performance and is poised to accelerate the timeline for realizi