bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterisation of Novel Organic Sodium Salts
Authors: Bitner Anna , Niedzicki Leszek , Plewa-Marczewska Anna , Marcinek Marek , Dranka Maciej , Zukowska Grazyna Zofia , Wieczorek Wladyslaw
Published: February 2020

Growing application of Li-ion and Li-polymer batteries for hybrid electric cars, electric vehicles, mobile devices etc. requires a large amount of lithium in the form of Li2CO3 every year. High price and relatively small world reserves of 13 million tons, forced to look for new materials possible to use in battery technology.

That is a clear reason for research effort to find out new types well performed batteries of high energy density, low cost, increased safety and tolerated by the environment. The logical way is to look for lithium analogues with similar chemistry properties and higher resources on the planet (sixth most abundant element and the most abundant alkali metal on Earth).

Sodium has molar mass and only slightly lower than lithium red-ox potential (2.73V). Low cost (about 7 times lower than lithium) and enormously easier and almost unlimited worldwide reserves makes him a really promising candidate. Metallic sodium does not form dendrites being a key issue if lithium metallic anodes (with gigantic theoretical capacity of 1190 mAh·g-1) were tested in present batteries. Several secondary advantages only promotes sodium concept for ex. cheaper than aluminum current collectors might be applied

Novel sodium salts, with five-membered ring imidazolium anion, were synthesized. Salts were found extremely stable up to more than 300oC (TGA). Moreover interesting properties of synthesized salts and their solutions in the PC solvent were proven by structural characteristic, electrochemical testing and Raman spectroscopy. NaTDI and NaPDI based electrolytes in PC show good conductivity with the values about 4mScm-1 at 20oC for salt concentration 0.5M and 1M for both salts. Ionic conductivities collected for both salts are almost the same considering slope over temperatures and pure values. Interestingly the high values of the conductivities are reached for 0.5M salt concentrations which is extreme advantage if we consider material savings. Superior properties were also confirmed by Raman spectroscopy used for the ionic association monitoring. Raman spectroscopy showed excellent salts dissociation in carbonate as PC and absence of ion-pairs for concentration up to 0.5M. A long distance framework type ordering of both TDI- and PDI- anions were also observed via extensive X-ray studies (data not presented here). According to previous computional simulations such a superfine structures are suspect to play the crucial role of sodium coordination and by that facilitating substantially cation transport properties. Combining this with thermal stability over 300oC plus the elevated electrochemical stability over 4.5V for NaTDIand 4.2V NaPDI vs Na/Na+ makes these salts interesting as acandidate for electrolyte’s sodium salt carrier.
SU8 Derived Glassy Carbon for Lithium Ion Batteries
Authors: Sharma Swati , Khalajhedayati Amirhossein , Rupert Timothy J , Madou Marc J
Published: February 2020

We have fabricated single carbon nanowires (CNWs) suspended between carbon MEMS (CMEMS) structures with good Ohmic contacts employing photolithography, electrospinning and pyrolysis of SU8. By applying a current between the underlying CMEMS electrodes the CNW alone are Joule-heated, which initiate a chemical vapor deposition (CVD) process. We have successfully deposited a granular tungsten oxide (WO3) film by decomposing tungsten hexacarbonyl [W(CO)6] selectively onto these heated CNWs using this technique. WO3 is a well known metal oxide semiconductor material extensively researched for its highly selective nitrogen oxide NOx sensing ability. It is a wide band-gap (~2.7 eV) n-type semiconductor material, which exhibits high sensitivity, quick response and an enhanced selectivity to detect NOx gases at low concentrations. The CNWs coated with WO3 nanoparticles could become an invaluable addition to the nanosensor options as they might allow for NOx gas sensor fabrication with at an affordable cost. The W(CO)6 to WO3 conversion reaction takes place at 400-700oC,[30] which is likely the actual temperature of the CNW. In other words the CVD deposition temperature is a good indicator of the actual temperature and the temperature profile along the length of the CNW. In addition, this fabrication technique can be utilized for a wide variety of applications by depositing any desired material from a volatile precursor at elevated temperatures selectively on to CNWs.
Recent Advances on Multifunctional Nanocarbons Used in Dye-Sensitized Solar Cells
Authors: Guldi D. M.
Published: February 2020

Throughout recent years the implementation of nanocarbons into dye-sensitized solar cells (DSSC) has resulted in important breakthroughs. Most relevant are in this context: i) the enhancement of charge transport and charge collection in nanocarbon-doped electrodes, ii) the introduction of nanocarbon interlayers that simultaneously reduce the charge recombination and increase the charge collection efficiency, iii) the use of nanocarbon-based, iodine-free, solid-state electrolytes featuring excellent diffusion coefficients and catalytic efficiencies, iv) the use of novel nanocarbon-based hybrid dyes, and v) the use of nanocarbons towards platinum-free counter electrodes. The first four aforementioned aspects are thoroughly described in this review.
Phosphorus-Doped Carbon as Efficient Electrocatalysts for Oxygen Reduction Reaction
Authors: Yang Zhenrong , Wu Jiao , Gong Xin , Strasser Peter , Yang Ruizhi
Published: February 2020

Electrocatalytic oxygen reduction reaction (ORR) has attracted much attention due to its importance in fuel cells and metal–air batteries [1-3]. The ORR in fuel cells and metal-air batteries require catalysts to accelerate the reaction rate owing to its sluggish kinetics and complicated reaction mechanism. Pt-based ca talysts are known to be the most active catalysts. However, Pt is scarce and expensive. The development of low-cost and efficient catalysts for the ORR is highly desirable [4,5]. Heteroatoms-doped carbon meterials have been explored as alternative electrocatalysts for the ORR due to their more abundance, lower price and high activity [6,7].

In this work, phosphorus (P)-doped carbon is facilely synthesized by both ex-situ and in-situ doping method. The catalytic activity of P-doped carbon for the ORR in 0.1 M KOH solution has been studied by using a rotating ring-disk electrode (RRDE) technique. The RRDE results show that P-doped carbon exhibits excellent catalytic activity for the ORR (Fig.1 and Fig.2)and long-term stability in basic media (Fig.3 ). The high elecctrocatalytic activity and durability of P-doped carbon are primarily attributed to the P-doping in the carbon lattice. Moreover, the factors that influence the ORR activity of P-doped microporous carbon are studied in detail. This kind of low cost, highly active and sustainable P-doped carbon xerogels could be used as a potential electrocatalyst for the cathodic ORR in fuel cells and metal-air batteries.

Acknowledgements

This work is supported by National Natural Science Foundation of China (Nos. 51272167 and 21206101 ), Natural Science Foundation of the Higher Education Institutions of Jiangsu Province, China (12KJB430010) and Sino-German Network on Electromobility.

References

[1] P. G. Bruce, L. J. Hardwick, K. M. Abraham, Mater. Res. Soc.Bull. 36,506 (2011).

[2] M. Armand, J. M. Tarascon, Nature 451,652 (2008) .

[3] V. Neburchilov, H. J. Wang, J. J. Martin & W. Qu, J. Power Sources 195,1271 (2010).

[4] P.H. Matter, U.S. Ozkan, Catal. Lett. 109, 115(2006).

[5] T.Fujigaya , M.Okamoto, N.Nakashima , Carbon 47, 3227(2009).

[6] J.-S.Lee, G.S. Park, S. T. Kim, M.L. Liu and J.Cho, Angew. Chem. Int. Ed. 51, 1 (2012).

[7] N.S.Stephanie, A. Wieckowski, J.Electroanal. Chem. 652, 44 (2011).

Figure 1. Linear sweeping voltammograms (LSVs) on rotating ring-disk electrode (RRDE) for carbon and P-doped carbon with different amount of P. The disk potential was scanned at 10 mV s-1 and the ring potential was fixed at 0.5 V.

Figure 2. Tafel plots of carbon, P-doped carbon and commercial Pt/C (20 wt.% Pt on carbon) derived by the masstransport correction of corresponding LSV data recorded in O2-saturated 0.1 M KOH.

Figure 3. LSVs of P-doped carbon and of commercial Pt/C (20 wt.% Pt on carbon) for the 1st cycle and 2000 th cycle in O2-saturated 0.1 M KOH at a rotating speed of 1600 rpm.
Invited Presentation: SWCNT-Based Fluorescent Immunoprobes for Short-Wave Infrared Cancer Detection
Authors: Beckingham Kathleen , Vu Michael , Lin Ching-Wei , Williams Ada , Bast Robert C. , Weisman R. Bruce
Published: February 2020

One of the most unusual properties of semiconducting single-walled carbon nanotubes (SWCNT) is the emission of distinct fluorescence peaks at short-wave infrared (SWIR) wavelengths that depend on specific nanotube structure, or (n,m) indices. This emission is promising for biological marker applications because the peaks are spectrally sharp and distinguishable, they fall in a spectral region of very low autofluorescence backgrounds, and the nanotubes are highly resistant to photobleaching. In order to exploit these properties, we are conjugating structure-sorted SWCNTs to antibodies to make novel fluorescent immunoprobes. Our initial approach has involved covalent linkage of generic IgG antibodies to the polyethylene glycol sidearm of a phospholipid surfactant used to noncovalently coat surfaces of individual SWCNTs. We have optimized our protocols by SWIR fluorescence imaging of flow cytometry beads linked to Protein G to capture the SWCNT-antibody conjugates. Studies to generate similar probes against important cancer biomarkers, such as the CA125 (MUC16), a 1.5mD heavily glycosylated mucin that is displayed on the surface of ovarian cancer cells, are in progress. We will describe results of experiments linking the OC125 antibody, which detects an epitope on the CA125 molecule, to (n,m)-sorted SWCNT samples followed by detection of CA125 on cultured ovarian cancer cells.
In Situ Atomic Force Microscopy Studies of Silicon Lithiation and Delithiation in Liquid Electrolytes
Authors: Becker Collin R. , Strawhecker Kenneth E. , McAllister Quinn P. , Lundgren Cynthia A.
Published: February 2020

Understanding the chemical and mechanical response of silicon (Si) to lithiation and delithiation in liquid, organic electrolytes is critical to successfully introducing Si into rechargeable lithium ion batteries. Among Si materials, nanoscale Si, especially amorphous Si (a-Si), has demonstrated some of the best performance to date. Nevertheless, an understanding of solid electrolyte interphase (SEI) growth and volume change hysteresis during cycling is limited. To this end, in situ experiments are conducted using an atomic force microscope (AFM) to acquire both qualitative and quantitative data. Using several electrolytes and electrolyte additives, the growth of SEI on thin film Si is analyzed. Additionally, precision Si nanostructures are fabricated using electron beam lithography, and the SEI growth, volume changes, and mechanical properties of these structures are recorded. The mechanical properties including elastic modulus and hardness are determined by indenting the nanopillar with a well-characterized AFM tip such that images of the pillar are acquired along with the numerical data of the indent. The results demonstrate the Si suffers permanent degradation of mechanical properties on the first cycle despite appearing to physically remain intact. The ability to determine the structural integrity of the Si before, during, and after lithiation in conventional, liquid electrolytes with and without additives is unique to AFM techniques which physically probe the sample. Additionally, in situ AFM studies of nanoporous Si and nanoscale Si structures covered by atomic layer deposition (ALD) thin films are discussed. The in situ AFM results presented in this work will help to guide experimental and computational modeling research by providing both qualitative information on how SEI on Si grows as well as numerical values for mechanical properties of Si as it is lithiated and delithiated.
In Operando Neutron Reflectometry Measurements Demonstrate Structural Stability in Thin Film Silicon Anodes for Lithium Ion Batteries
Authors: DeCaluwe Steven C , Dhar Bal-Mukund , Dura Joseph , Wang Howard
Published: February 2020

Despite its incredibly high theoretical capacity (~4200 mA-h/g), implementation of Si electrodes as high-capacity Li-battery anodes is hindered by poor mechanical durability. Si lithiation is accompanied by very high mechanical strain values, with nearly 370% volume expansion at maximum capacity, which typically leads to fracture and pulverization of the material and eventual battery failure. While numerous strategies have been employed to improve the durability of Si anodes, including nano-structured anode architectures, composite anode materials, and protective coatings, efforts have yet to identify a Si anode design that is mechanically robust and maintains a stable anode capacity. At least part of the difficulty is due to a lack of fundamental insight into the correlation between structure, mechanical properties, and function for Si anodes, owing to a paucity of in situ techniques to definitively observe them.

In this presentation, we report the structural and composition changes in an amorphous thin-film silicon anode with a protective Al sub-oxide (AlOx) capping layer, using in operando neutron reflectivity (NR) and electronic impedance spectroscopy (EIS) measurements. NR measurements were carried out in situ on an operating Li half-cell at various charge states over six shallow charge-discharge cycles. These measurements quantify the correlation between mesoscopic strain and the degree of lithiation in a 10-nm thick amorphous silicon thin-film anode, which expands and contracts with repeated cycling (Figure 1).

Results demonstrate the mechanical durability of both the Si thin-film anode and the protective AlOx layer, which maintain their low surface roughness and film integrity over the course of the measurements. While the macroscopic strain of the Si shows significant non-linearity with Li content after several shallow charge-discharge cycles, in agreement with previous reports1, careful inclusion of a-Si microstructural effects (via direct measurement of the a-Si porosity) reveal that the volumetric strain for the solid portion of a-Si thin films varies linearly with lithium content (Figure 2). Results demonstrate that the porosity is eliminated during the expansion that accompanies lithiation, and is then recovered during subsequent de-lithiation. Furthermore, it is shown here that the delithiated a-Si porosity does not vary significantly over the course of the measurements – ranging from 10.0 [5.4 – 28.0]% in the as-deposited state to 13.1 [10.02 – 15.73]% after 6 shallow charge and discharge cycles – demonstrating the structural reproducibility of the thin-film anode.

References:

1. Chevrier, V. L. and Dahn, J. R., J. Electrochem. Soc.
2009,
156 (6), A454-A458.
Electrochemical Strain Microscopy of Nanostructured Lithium Iron Phosphate
Authors: Chen Qian Nataly , Balke Nina , Jesse Stephen , Kalinin Sergei V. , Li Jiangyu
Published: February 2020

Lithium iron phosphate (LFP) has been explored as a promising alternative to the most commonly used lithium cobalt oxide as a cathode material for lithium ion batteries. Due to its olivine structure, lithium ions within LFP travel along one-dimensional channels, and the lithiation mechanism in LFP occurs through two-phase reactions that are still a major area of study. In this paper, we use electrochemical strain microscopy (ESM) in band excitation mode to probe lithium ion motion within thin films of LFP. ESM is a nanoscale probing technique in which an AC bias is applied to the surface of the electrolyte material, locally inducing lithium ion motion and causing strain changes, which can then be detected by the tip of an scanning probe microscope probe. Using band excitation techniques, strain amplitudes as well as energy losses can be evaluated for very rough samples of LFP. Furthermore, lithium ion motion was also studied in terms of its second harmonic response to AC bias, which can be compared to its first harmonic response within the same topographic area. These experiments can lead to increased fundamental understanding of lithium iron phosphate and other cathode materials of similar structures.
Numerical Simulation of Electrolyte-Supported Planar Button Solid Oxide Fuel Cells with Layered Electrolytes
Authors: Aman Amjad , Gentile Russell , Chen Yan , Lugovy Mykola , Xu Yunjun , Huang Xinyu , Orlovskaya Nina
Published: February 2020

Multi-layered (Y2O3)0.08(ZrO2)0.92 / (Sc2O3)0.1(CeO2)0.01(ZrO2)0.89 (YSZ/SCSZ) electrolytes were designed for intermediate temperature Solid Oxide Fuel Cells (SOFCs), so that the inner SCSZ layers provided superior ionic conductivity and the outer YSZ layers provided chemical and phase stability. A total of nine electrolyte designs were developed and tested. Due to the mismatch in the thermal expansion coefficients between the two electrolyte materials, residual stresses develop between the layers. It was noticed that the ionic conductivity of the electrolytes is enhanced due to the presence of residual stresses. To study the electrochemical performance of the SOFC with different electrolyte materials and configurations, an electrolyte-supported planar button SOFC is modeled using COMSOL Multiphysics® 4.3. The main governing equations include the charge conservation equation, Maxwell-Stefan diffusion model, Butler-Volmer equation, and Brinkman equation. The cathode and anode materials used are (La0.6Sr0.4)0.95-0.99Co0.2Fe0.8O3 and Ni-YSZ respectively. Validation of the model was done against experimental results of another planar SOFC by Joongmyeon et al. (Journal of Power Sources, 2007). The simulations show that SOFCs with 3-layered pure SCSZ electrolyte produced the highest power density while the single cell with 6-layered pure YSZ electrolyte produced the least power density. These results make sense, since the increase in the electrolyte thickness increases the ohmic losses. The model developed can be used in further studying the behavior of the cells.

In order to study the mechanical properties of the electrolytes, biaxial flexure tests were performed via a ring-on-ring method at room temperature and 800 °C. Due to the high deflection of the electrolytes, a non-linear dependence between stress and load was observed. Therefore, the geometric non-linearity feature was utilized in the modeling to calculate the maximum tensile stress in the specimen at a given load. Results showed that layered electrolytes have higher biaxial flexure strength. This is theorized to be due to the presence of compressive stresses at the outer YSZ layers. Weibull statistics was used on stress calculations to verify the results.
Invited Presentation: Effect of Elastic Strain and Dislocations on Oxide Ion Diffusion and Oxygen Exchange Kinetics on Oxides
Authors: Yildiz Bilge
Published: February 2020

How can the oxygen non-stoichiometry, oxygen diffusion and oxygen reduction kinetics be altered in functional oxides by lattice strain? This question has recently attracted wide interest for enabling a new route for attaining fast oxygen exchange and transport kinetics, and obtaining fundamental answers to this question is important for a range of technologies including high performance solid oxide fuel cells, oxide based sensors, separation membranes and memristors. By applying mechanical stress, the inherent energy landscape of the reactions involved on the material can be altered. For example, in theory one can turn an endothermic reaction into an exothermic one, and reduce the energy barriers by applying lattice strain. This is the so-called mechano-chemical coupling, and when applied on electrochemical systems we can introduce the term mechano-electro-chemistry.

In this talk, we will discuss recent work that probes quantitatively the mechanisms by which elastic strain impacts surface reactivity and diffusion kinetics in fluorite and perovskite oxides. Computationally, using ab initio and atomistic simulations, we discovered that lattice strain can accelerate the ionic transport in 8%Y2O3-ZrO2 by reducing the ion migration energy barriers. Combining surface chemical characterization on model thin films with ab initio modeling, we demonstrated for the first time that tensile lattice strain favors oxygen exchange kinetics on both the oxygen-deficient (La,Sr)CoO3-d and (La,Sr)MnO3-d and the oxygen-excess Nd2NiO4+d by impacting the energies of oxygen adsorption and dissociation, oxygen vacancy formation, oxygen diffusion, cation segregation and the electron transfer process. The favorable impact of tensile lattice strain on these elementary reactions was validated at the collective level by quantifying the oxygen surface exchange and diffusion kinetics with isotope exchange measurements on (La,Sr)CoO3-d. Lastly, we will discuss the impact of dislocations in ionic crystals, as doped CeO2 and ZrO2 on the distribution of charged defects and mobility of oxygen vacancies. These results together put forth both elastic strain and the dislocations to be important factors that impressively changes the kinetics of charge transport and reactivity in functional oxides.
Highly Diastereoselective Cyclopropanation of Olefins Catalysed By a C2-Symmetrical Chiral Iron Porphyrin Complex
Authors: Gallo Emma , Intrieri Daniela , Le Gac Stéphane , Caselli Alessandro , Rose Eric , Boitrel Bernard
Published: February 2020

Compounds containing cyclopropane units play a crucial role in both synthetic and pharmaceutical chemistry due to high reactivity and biological properties of the three-membered ring.[1] Consequently, the interest of the research community in developing new methodologies to synthesise cyclopropanes is strongly increasing. Amongst the synthetic procedures available, the one-pot reaction of diazo compounds with olefins is a sustainable and atom-efficient strategy due to the formation of N2as the only stoichiometric by product.

Catalytic enantio- and diasteroselective olefin cyclopropanations [2] have been extensively explored and metal porphyrin complexes represent a very active and stereoselective class of catalysts. Some years ago we reported on the catalytic efficiency of chiral cobalt(II)-binaphthyl porphyrins in asymmetric cyclopropanations, [3] and recorded positive data encouraging us to synthesise the structurally related chiral porphyrin 1 and its iron(III) complex 2 (see figure). The catalytic activity of 2 in the asymmetric cyclopropanation of olefins by diazo compounds was investigated. Cyclopropanes were obtained with excellent yields (up to 99%), enantio- and diasteroselectivities (eetrans
up to 80%, cis/trans ratios up to 99%). In addition to that, outstanding values of TON and TOF (20,000 and 120,000/h respectively) were achieved. [4]

References

[1] A. K. Kumar, Intern. J. Pharm. and Pharm. Sci.
2013,
5, 467-472.

[2] D. Intrieri, A. Caselli and E. Gallo, Eur. J. Inorg. Chem.
2011, 5071-5081.

[3] (a) S. Fantauzzi, E. Gallo, E. Rose, N. Raoul, A. Caselli, S. Issa, F. Ragaini and S. Cenini, Organometallics, 2008, 27, 6143-6151. (b) A. Penoni, R. Wanke, S. Tollari, E. Gallo, D. Musella, F. Ragaini, F. Demartin and S. Cenini, Eur. J. Inorg. Chem.
2003, 1452-1460.

[4] D. Intrieri, S. Le Gac, A. Caselli, E. Rose, B. Boitrel and E. Gallo submitted
Reactive Oxygen Species Involved Cancer Cellular Specific 5-Aminolevulinic Acid Uptake
Authors: Matsui Hirofumi , Ito Hiromu
Published: February 2020

Photodynamic therapy (PDT) and photodynamic diagnosis (PDD) using 5-aminolevulinic acid (ALA) are clinically useful for cancer treatments. Cancer cells have been reported that ALA is incorporated via peptide transporter 1 (PEPT1), which is one of the membrane transport proteins, and has been reported to be significantly expressed in various gastrointestinal cancer cells such as Caco-2. However, the mechanism of this protein expression has not been elucidated. Concentration of Reactive oxygen species (ROS) is higher in cancer cells in comparison with that of normal cells. We have previously reported that ROS derived from mitochondria (mitROS) is likely related to invasions and proliferations of cancer cells. Since ALA is the most important precursor of heme which is necessary protein for cellular proliferations, mitROS may be also related to PEPT1 expressions. In this study, We used a rat gastric mucosal cell line RGM1 and its cancer-like mutated cell line RGK1, and we clarified the ALA uptake mechanism and its relations between mitROS and PEPT1 expression in RGK1. We also used our self-established stable clone of cell which over-expresses manganese superoxide dismutase, a mitROS scavenger. We studied differences of the PDT effects in these cells after ALA administrations to clear the influence of mitROS.
Single Molecule Force Spectroscopy (Invited)
Authors: Meyer Ernst , Pawlak Remy , Glatzel Thilo , Kawai Shigeki , Baratoff Alexis
Published: February 2020

Recently, intramolecular resolution is studied on a variety of molecules. A further challenge is the manipulation of molecules on surfaces, including the controlled rotation, which means that the direction of rotation of the molecule can be chosen by the experimentalist [1]. The control of the probing tip is of central importance for a quantitative understanding of nc-AFM imaging and force spectroscopy. Progress has been made by a variety of preparation procedures: sputtering, indentation or pick-up of molecules, such as CO. The attachement of a single molecule to the end of the tip is shown for the case of a functionalized porphyrin, which can used as a stable probing tip for imaging in the attractive as well as the repulsive regime.

[1] R. Pawlak, S. Fremy, S. Kawai, T. Glatzel, H. Fang, L.-A. Fendt, F. Diederich, and E. Meyer , Directed rotations of single porphyrin molecules controlled by localized force spectroscopy, ACS Nano, 6, (2012), 6318–6324
(Invited) Frequency Dispersion and Band Alignments in ZrO2/n-GaAs MOS Capacitor
Authors: Konda R B , White C , Thomas D , Yang Q , Sahu D , Pradhan Aswini K
Published: February 2020

Compound III-V semiconductors such as GaAs have the potential to replace Si as the channel material in metal-oxide-semiconductor-field-effect-transistors (MOSFET) due to their high electron mobility. However, it is extremely important to remove native oxide from the surface of GaAs. GaAs surfaces were self-cleaned through fast pulsing of the Trimethylaluminum (TMA) precursor by reducing and restraining the regrowth of native oxides using the atomic layer deposition (ALD). The thermal conversion of As-O in to Ga-O reduction was evaluated by the x-ray photoelectron spectroscopy. Metal oxide semiconductor (MOS) capacitor was using ZrO2 as high-k gate dielectric on n-GaAs substrates, and their superior performance in electrical properties has been demonstrated. ZrO2/GaAs capacitor exhibits superior capacitance-voltage characteristics reduced leakage current due to reduced interfacial trap density. These studies have remarkable significance for the development of high-throughput innovative electronics, using ZrO2 as high-k dielectric.

The interfacial characteristics and band alignments of high-k ZrO2 on n-GaAs have been investigated by experimentally and density functional theory. We have demonstrated that the frequency dispersion due to interface traps in capacitance-voltage characteristics of ZrO2/GaAs interface was significantly reduced through self-cleaning by trimethylalumina. The experimental valence band offset of 2.10 eV from X-ray photoelectron spectroscopy is found to be lower than that of the calculated value of 3.02 eV. The calculated conduction band offset is 1.21 eV compared to the experimental value of 1.38 eV confirms significant reduction of interface traps due to the Fermi-level pinning minimizing band misalignment.
(Invited) Flexible GHz Frequency and Low-Power Nanoelectronics Based on 2D Nanomaterials
Authors: Akinwande Deji , Chang Hsiao-Yu , Lee Jongho
Published: February 2020

2014 is the 10th year anniversary of the groundbreaking work on graphene by several pioneering workers. Since then, the field has expanded exponentially and now includes two-dimensional (2D) atomic sheets beyond graphene such as hexagonal boron nitride (hBN), transition metal dichalcogenides (TMDs), and group IV elemental monolayers (e.g. silicene, germanene). While there are many opportunities for these 2D crystals to enable transformational impact, it is widely understood that their greatest prospects are for flexible nanoelectronics where their combined synergistic properties are unmatched by conventional organic or inorganic materials. The 2D atomic sheets have emerged as near ideal nanomaterials to overcome the long running challenge of achieving Si CMOS like performance on soft substrates at scales that can be suitable for large integration. For instance, the high mobility and velocity accessible in monolayer graphene affords GHz analog transistor devices while the large bandgap of graphene’s semiconducting analogues (MoS2 and similar dichalcogenides) naturally lead to near ideal digital transistors with high on/off current ratio and low subthreshold slope while sustaining mobilities much larger than organic semiconductors or amourphous bulk semiconductors. Together, these physically similar atomic layers with vastly different electronic properties can serve as the electronic platform for low-power digital, high-speed mixed-signal, and high-frequency analog transistor building blocks for flexible nanoelectronic systems.

In this work, we present the latest findings on the high frequency properties of graphene with record frequencies in the microwave regime. These high frequencies are suitable for realizing GHz wireless analog circuits on soft substrates. The current frequencies are limited by the poor thermal conductivity and reliability of the plastic substrates. In addition, we report on the coupled device mechanics and device physics of 2D semiconducting sheets. The device mechanics on plastic substrate as a function of tensile strain reveal that dielectric cracking is responsible for off-current degradation while buckling is largely responsible for on-current degradation. The buckling scales with the thickness of the dichalcogenide semiconductor and can be mitigated by reducing the driving force for delamination. Optimized dielectric patterning for strain relaxation was found to improve device reliability at low bending radius. Our results collectively indicate that graphene is the most suitable material for flexible radio-frequency transistors while TMDs are ideal for low-power flexible transistors.
Effect of Using Ethanol as the Oxygen Source on the Growth and Dielectric Behavior of Atomic Layer Deposited Hafnium Oxide
Authors: Selvaraj Sathees Kannan , Colon Albert , Rossero Jorge Iván , Shi Junxia , Takoudis Christos G
Published: February 2020

Hafnium oxide (HfO2) is widely identified as a suitable high-k material to replace conventionally used low-k silicon oxide for gate dielectric layers in complementary metal-oxide semiconductor (CMOS) devices. High dielectric constant (~ 25) and compatibility with silicon substrate makes HfO2 an ideal candidate for future scaling of transistors.1

HfO2 has been deposited using various methods. Of all, atomic layer deposition (ALD) seems to be the suitable method to deposit ultra-thin conformal layers on deep trenches and future 3D transistor structures. ALD is a vapor phase deposition technique, in which sequential exposure and purging of a surface to reactive elements in vapor phase is used to grow thin films in layer-by-layer fashion with excellent control on film thickness and composition down to Å level.2

There were numerous studies on ALD of HfO2 using different precursor and oxygen source combinations.3 The property of the resultant HfO2films depends on the precursor combination, deposition conditions, post deposition treatment conditions etc.

ALD of HfO2 is traditionally performed using oxygen, ozone or water as the oxygen source. These oxidizers oxidize the underlying silicon substrates during the initial ALD cycles and form thick interfacial silicon oxide layer. This layer reduces the dielectric constant of the structure. To reduce the risk of forming such thick interfacial layer we used ethanol as the ALD oxygen source. Ethanol showed good reactivity towards the hafnium precursor, tetrakis(diethylamino)hafnium, and displayed clean ALD growth behavior with a wide ALD process temperature window of 200-280 °C (Fig. 1). In this paper, ALD growth behavior, ALD process temperature window and dielectric characterization of the ALD HfO2films will be discussed in detail along with film compositional analysis.

References

1. J. Robertson, The European Physical Journal - Applied Physics, 28, 265 (2004).

2. S. M. George, Chem. Rev., 110, 111 (2009).

3. L. P. Riikka, J. Appl. Phys., 97, 121301 (2005).
Effect of Various W Film and Barrier Material on the Corrosion during W CMP
Authors: Kang Min Cheol
Published: February 2020

The Tungsten (W) has been widely used as contact or wire material in the integrated circuit (IC) fabrication because of its low resistance and superior gap-fill property. The damascene process based on chemical mechanical polishing (CMP), which is used to remove the protruding W, make it possible to use W as interconnection material. During the W CMP, the W loss, well known as dishing and erosion, leads to resistance increase. Recently, undesirable metal loss, such as corrosion, was observed at the interface between the W and barrier metal. In this paper, the effect of various W film and barrier material on W CMP performance was investigated through surface analysis and electrochemical analysis.
Performance of Sintered Iron Electrodes for Rechargeable Alkaline Batteries for Large Scale Energy Storage
Authors: Yang Chenguang , Manohar Aswin K , Malkhandi Souradip , Prakash G. K. Surya , Narayanan S. R.
Published: February 2020

With increased concerns about fossil fuel depletion and carbon dioxide emissions, renewable power generation from solar and wind sources is a promising solution for meeting our increasing need of energy. However, with renewable power there is a principal issue of power availability to match the demands. Therefore, inexpensive, long life and high-rate- capable energy storage systems are needed.

Iron based alkaline batteries are a promising candidate for large scale energy storage due to its low cost and abundance of raw material, long cycle life and high theoretical energy density of iron electrodes. [1] Despite these advantages, historically, iron electrodes have had low charging efficiency due to the hydrogen evolution reaction, and low utilization rate and poor rate capability due to the non-conducting nature of the discharge product. [2] In this study, a sintered iron electrode with high charging efficiency, high utilization rate and long cycle life is presented.

The iron electrode in this study was prepared by loading carbonyl iron on to a degreased nickel mesh and sintering under inert atmosphere. The iron electrode was then tested in a three-electrode configuration with two sintered nickel-oxide counter electrodes and a mercuric oxide reference electrode was used for electrode potential measurements. Sodium sulfide was added into the electrolyte to prevent passivation.

After the initial formation cycles, the utilization rate of the sintered iron electrode stabilized at 0.23 Ah/g. About 80% of this value was realized at C rate (Figure 1). This type of performance is very promising for large-scale energy storage applications since the high rate capability is necessary for rapid load-leveling. Following initial characterization of capacity, the electrodes were subjected to charge/discharge cycles with C/2 rate over 500 cycles without any significant change in capacity. The average faradaic efficiency during this high rate cycling is above 96% (Figure 2).

The properties of long cycle life and high faradaic efficiency are expected to lower the cost of implementing and operating iron-based energy storage systems. The future work of this study is focused on understanding the role of electrode design parameters (porosity, thickness and pore utilization) and sulfide additives on the performance of the iron electrode.

Acknowledgement

The research reported here was supported by the U.S. Department of Energy ARPA-E (GRIDS program, DEAR0000136), the Loker Hydrocarbon Research Institute, and the University of Southern California.

References

1. S.R. Narayanan, G. K. Surya Prakash, A. Manohar, B. Yang, S. Malkhandi, A. Kindler, Solid State Ionics,
216, 105 (2012).

2. A. K. Manohar, S. Malkhandi, B. Yang, C. Yang, G. K. Surya Prakash, S. R. Narayanan, J. Electrochem.
Soc., 159 (8), A1209 (2012).
Developmental Update on Vanadium Redox Flow Battery Stacks at Pacific Northwest National Laboratory
Authors: Sprenkle Vincent , Thomsen Ed , Wang Wei , Nie Zimin , Reed David , Li Bin , Wei Xiaoliang , Koeppel Brian J , Chen Baowei
Published: February 2020

Electrochemical energy storage (EES) systems offer the potential for a more secure and cleaner electrical grid, from improving resiliency and reliability to improving the implementation of renewable into the current infrastructure. Pacific Northwest National Laboratory (PNNL) is currently conducting extensive research and development efforts into multiple energy storage systems under the Department of Energy – Office of Electricity (DOE-OE.) Energy Storage Program including vanadium redox flow batteries. This talk will focus on the latest developments in redox stack development including stack design and performance validation utilizing PNNL’s mixed acid redox electrolyte.
Study of Transient Behavior of Vanadium Redox Flow Battery at Varying Flow Rates and States of Charge
Authors: Poudyal Aditya , Denisov Evgeny , Bund Andreas
Published: February 2020

The Vanadium Redox Flow Battery (VRB) is one promising candidate for grid type storage because of its long life time, modularity, active thermal management, and good cycle life. There are various parameters that affect the performance of VRB for example: temperature, flow rate, state of charge etc. Flow rate is an important parameter, since the electrolyte flow rate influences the reaction rate of the vanadium ions. It is also important because it has a substantial influence on the system efficiencies.

Ma et al. [1] investigated the effect of flow rate on the system capacity and the efficiency. Fetlawai [2] investigated the effect of flow rate on the charge-discharge characteristics and on the gas evolution. It was established that flow rate is one of the important parameters which should be controlled to obtain high efficiency of VRB. The effect of the flow rate on the transient behavior of the battery has not got much attention which motivated this study.

We will present experimental results on the transient behavior of a VRB at various flow rates up to ca. 1 L/min. The battery was at 80% state of charge during experiment. It was observed that flow rate has a strong effect on the transient behavior of the battery (a typical examples is shown in Fig. 1). The load of the battery was varied in a regime typical for applications of VRBs. The results showed clear trends of the transient behaviour of the battery with changes of flow rate. The implications of these findings for the development of control systems in grid energy storage system design with VRBs will be discussed.

[1] X. Ma, H. Zhang, C. Sun, Y. Zou, and T. Zhang, “An optimal strategy of electrolyte flow rate for vanadium redox flow battery,” J. Power Sources, vol. 203, pp. 153–158, Apr. 2012.

[2] H. A.-Z. A.-Y. Al-Fetlawi, “Modelling and simulation of all-vanadium redox flow batteries.” 14-Apr-2011.

[3]J. Chahwan, C. Abbey, and G. Joos, “VRB Modelling for the Study of Output Terminal Voltages, Internal Losses and Performance,” 2007 IEEE Canada Electr. Power Conf., pp. 387–392, Oct. 2007.
Inorganic-Organic Heterojunctions in Nanocrystals Based Photonic Devices for Energy Conversion
Authors: Palomares Emilio , Palomares Emilio
Published: February 2020

During my leacture I will show recent examples of how to modify the interface between semiconductor nanocrystals and organic materials and the ffects over the interfacial charge transfer reactions occurring upon photoexcitation. The lecture will also illustrate the use of “click-chemistry” to modify the surface of the semiconductor nanocrystal as a versatil approach to attach covalently molecules to the semiconductor surface. The results of CdSe-C60 quantum dots polymer bulk-heterojunction solar cells will be shown. The CdSe-C60/P3HT solar cells shows 3 times higher light-to-energy conversion efficiency than CdSe/P3HT using pyridine as capping agent.
(Invited) Simulation of GaN Device Reliability
Authors: Law Mark E , Patrick Erin , Horton David
Published: February 2020

Device simulation is a well established tool, and is used to predict performance of devices. It can include both carrier and lattice temperature simulations to enhance the simulation accuracy. Process simulation accounts for materials property and structural change, and includes point defects, extended defects, mechanical strain, and reaction kinetics. When the two are fused, you can begin to simulate the structural changes over operation time to a device. This talk will present a simulation platform to address this and share results on both off- and on- state degradation of AlGaN / GaN HEMT transistors. In the off-state, the gate contact degrades due to induced mechanical stress from high electric fields. In the on-state, degradation is driven by hot-carrier injection and accumulation of charge at the AlGaN surface.
(Invited) Deep Ultraviolet Light Emitting Diodes: Physics, Performance, and Applications
Authors: Shur Michael , Gaska Remis , Dobrinsky Alex , Shatalov M.
Published: February 2020

Materials quality is the one of the key factors determining the Deep UV LED performance. It could be dramatically improved by using novel MEMOCVD® technique [1] using overlapping precursor pulses, optimized precursor waveforms and lower growth temperatures compared to the conventional MOCVD growth. Another key factor is the Deep UV LED design. Using very narrow quantum wells (QWs), we achieved an improved overlap between electron and hole wave functions and increased the Internal Quantum Efficiency. We also used “the energy tub” [2] to increase the electron capture into the QWs and eliminate or reduce the “blocking layer.” These approaches and a novel transparent and reflecting top contact have led to a high internal quantum efficiency, high power output and high external quantum efficiency of our Deep UV LEDs. Research is now under way to use these devices for improving quality and extending storage time of fruits and vegetables.[3] Other applications include water and air purification, sterilization, biological threat identification, applications in medicine, biology, industrial processes, defense, and homeland security. Deep UV LEDs have a potential of replacing conventional ultraviolet Hg vapor, Xenon and Deuterium lamps that are bulky, contain mercury, produce ozone, require high voltages, slow to turn on, and have a limited set of available wavelengths. DUV LEDs will also enable new applications that were not even possible with conventional deep UV technology.

[1] R. Gaska, J. Zhang, and M. Shur “Nitride-based light emitting heterostructure”, US Patent 7,326,963, Feb. (2008)

[2] Q. Fareed, R. Gaska and M. S. Shur, Methods of Growing Nitride-Based Film Using Varying Pulses, US patent 7192849, March 20 (2007)

[3] M. Shur and S. Britz, Fluorescent-based ultraviolet illumination, United States Patent Application Publication, US 2011/0147617, June 23 (2011), US patent 8,384,047, Feb. 26 (2013)
(Invited) Microstrucutural Characterizaton of Stressed AlGaN/GaN HEMT Devices
Authors: Holzworth Monta Ray , Whiting Patrick , Pearton Stephen J. , Lu L. , Kang Tsung-Sheng , Ren Fan , Patrick Erin , Law Mark E , Jones Kevin Scott
Published: February 2020

AlGaN/GaN high electron mobility transistors are used in high temperature, high power, and high frequency applications due to their superior combination of high breakdown voltage and high frequency performance. Unfortunately, their reliability in the field has warranted further investigation because of the stochastic nature of the variety of defects that arise during their operation. Many analytical techniques are not well suited to this analysis because they sample regions of the device which are either too small or too large for accurate observation. This talk will give a review of recent studies that employ structural, chemical, and electrical device characterization paired with simulation in order to develop structure-property relationships between defects and device performance. This includes the use of a new approach to chemical deprocessing combined with surface-sensitive analysis techniques such as scanning electron microscopy and scanning probe microscopy in the analysis of large-area defect formation. Wet etching of the passivation nitride and metal contacts was used to strip the transistor surface features and remove organic contaminants. This exposed the top surface of the AlGaN epilayer for analysis. This processing revealed and surface analysis revealed three different defects. One of these defects is a nanoscale crack which emanates from metal inclusions formed during alloying of the ohmic contacts of the device prior to use in the field, and could impact the yield of production-level manufacturing of these devices. This defect also appears to grow, in some cases, during electrostatic stressing. Another defect, a native oxide at the surface of the semiconductor under the gate, appears to react in the presence of an electric field, which could play a role in the degradation of the gate contact during high-field, off-mode electrostatic stressing. This defect could also facilitate the formation of the pitting of the AlGaN epilayer beneath the gate contact. The composition of the as-grown gate interfacial layers were characterized using atom probe tomography and are composed of two distinct oxide layers, NiOx and AlOx. Furthermore, using off-state reverse bias electrical stress, Ni-gate metal reactions with AlGaN epilayers emulate the shape and size of the electric field contours between 5 – 6 MV/cm; suggesting a critical field for defect formation. This talk will summarize these finding and place them in the overall context of failure mechanisms in AlGaN/GaN HEMT structures.
Enhanced Electrical and Nuclear Radiation Detection Performance in BiI3 Wide Bandgap Semiconductor Detectors
Authors: Han HyukSu , Hong Minki , Gokhale Sasmit S. , Sinnott Susan B. , Baciak James E. , Nino Juan C.
Published: February 2020

BiI3 is a wide band-gap compound semiconductor with a high effective atomic number that is anticipated to exhibit higher detection efficiency than other compound semiconductors such as HgI2, PbI2, and CdZnTe. This makes BiI3 of particular interest for moderate and high energy gamma-ray detection applications. However, the low resistivity of BiI3 results in high leakage currents and degrades the electrical properties and detecting performance of the detectors. Here we show that the main reason for the low resistivity in BiI3 is due to the high volatility of iodine and the high concentration of intrinsic Schottky defects. Furthermore, we will discuss novel defect engineering strategies that successfully mitigate the obstacles associated with iodine vacancies in the material. Density functional theory (DFT) calculations, as well as experimentally measured electrical properties, and radiation response will be presented for undoped and Sb-doped BiI3 (SBI) single crystals grown via the vertical Bridgman growth technique. Most importantly, we will demonstrate the first ever recorded gamma-ray spectrum using BiI3-based detectors.