bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical Characterization of Dry and Wet Processed Interface Layer in Ge/High-K Devices
Authors: Ding YI Ming , Misra Durga , Bhuyian Mdnasiruddin , Tapily Kandabara , Clark Robert D. , Consiglio Steven , Wajda Cory S. , Leusink Gert J.
Published: February 2020

Even through Ge/high-k interface has been extensively studied the high leakage current associated with these gate stacks continues to introduce frequency dispersion and hysteresis in capacitance-voltage (CV) and conductance-voltage (GV) characteristics. These dispersions severely limit the understanding the interface and accurate estimation of interface state density, Dit
and equivalent oxide thickness (EOT). Since several parameters like EOT, flatband voltage, bulk doping, surface potential as a function of gate voltage are important and bulk defect and interface defect concentration affect the CV and GV characteristics several corrections to the characteristics are required to obtain accurate values.

We have measured the CV and GV characteristics of Ge/ALD 1nm-Al2O3/ALD 3.5nm-ZrO2/ALD TiN MOS capacitors with three different interface treatments by HP4284 LCR meter using different frequencies. The interface treatments are (i) simple chemical oxidation (Chemox); (ii) chemical oxide removal (COR) followed by 1 nm oxide by slot-plane-antenna (SPA) plasma (COR&SPAOx); and (iii) COR followed by vapor O3 treatment (COR&O3).  The plots were corrected by three different methods. Firstly, we removed the effect of sheet resistance, RS
. The second approach uses data (capacitance and conductance) measured at two different frequencies to solve two unknown variables (capacitance and conductance) (1). The solved CV plot is closer to the corrected CV plot at 1 MHz rather than that at 100 KHz. This allows us to use 1MHz corrected data to obtain the EOT information. Additionally, this approach helps to verify that 1MHz data is robust assuming that defects do not respond to the other frequencies used here. The third approach is to modify the measurement circuits (2) to enhance CV and GV characteristics. Fig. 1 shows the CV characteristics after the corrections by three different approaches for three different samples. COR&SPAOx samples show excellent CV characteristics. The details of all the correction methods and the advantages of these methods to correct CV and GV will be discussed. We will demonstrate that the correction methods are suitable for accurately measure the interface characteristics. The Dit
calculated by two method (conductance and capacitance spectroscopy) (Fig. 2) are compared and discrepancy of the results between different samples and different methods will be explained.

 

References

Y. Ding and D. Misra, J. Vac. Sci. Technol. B, 33, 021203, 2015.

K.J. Yang and C. Hu, IEEE Trans on Electron Dev, 46(7), 1500, 1999.

K.S.K Kwa, S. Chattopadhyay, N.D. Jankovic, S.H. Olsen, L.S. Driscoll, and A.G. O'Neill, Semicond. Sci. Technol., 18(2), 82, 2003.

Figure 1
(Invited) Electronic Properties of Self-Assembled Trimesic Acid Monolayer on Graphene Layers
Authors: Shayeganfar Farzaneh
Published: February 2020

The adsorption of trimesic acid (TMA) on graphene surface has been studied with density functional theory (DFT). By considering the adsorption of a single TMA molecule on different sites on graphene, we have been able to perform a detailed analysis of the equilibrium geometry, charge transfer, electronic properties in terms of density of states and band structure, and finally scanning tunnelling microscopy (STM) simulations on those simple systems. The results for isolated adsorption were then compared to the behaviour of TMA unit within two different self-assembled monolayers. Our results indicate that structural deformations of TMA may significantly contribute to the magnitude of p-doping and band gap opening in graphene. The formation of an hydrogen bonding network within the assembly improves the stability of the adlayer but its adhesion on graphene is significantly lowered. The magnitude of p-doping in graphene per TMA unit remains nearly constant from the isolated to the assembled systems, but the magnitude of the band gap opening appears strongly correlated with the breaking of symmetry of $\pi$-states of graphene by the TMA patterning on the surface. Our results suggest that polymorphism in self-assembled adlayers could be used to tune and control the electronic properties of graphene.\\

\emph{Keywords}: Tunable band gap; Electrical field; Ab-initio calculation; Electronic properties;
Utilization of a Non-Ionic Surfactant in the Fabrication of Water-Borne Polymeric Semiconductor Nanoparticles for High-Performance, Green Organic Electronics
Authors: Cho Jangwhan , Yoon Seongwon , Ha Jaeun , Chung Dae Sung
Published: February 2020

We report a novel method for synthesizing water-borne nanoparticles of semiconducting polymers for use in environmentally benign processes involving organic electronics, without compromising the high charge carrier mobility of the polymeric semiconductors. Non-ionic surfactants were utilized as a key material to fabricate aqueous nanoparticles of semiconducting polymers via a miniemulsion process for the first time. To maximize the charge transport between polymer nanoparticles, the surface adsorption density and polarity of the non-ionic surfactant were carefully controlled. By introducing such non-ionic surfactants onto a donor-acceptor type polymeric semiconductor with an inherently high charge carrier mobility, we could realize a high-mobility (>0.5 cm2/Vs) water-borne polymer field effect transistor. Structural analyses based on X-ray diffraction showed that films consisting of polymer nanoparticles still maintained some degree of edge-on crystalline orientation, which was enough to render high charge carrier mobility.
Using Copolymers As Suppressors in a Copper Plating Bath for through-Hole Filling
Authors: Wen Shih-I , Dow Wei-Ping
Published: February 2020

Recently, a copper electroplating technique, namely butterfly technique (BFT) [1], was developed to achieve a void-free filling of a through hole (TH) of a printed circuit board (PCB). However, the BFT for TH filling caused an issue of thick copper layer on the PCB surface, which increases the process cost due to a requirement of post copper etching process. Literature has mentioned that copolymers have strong suppression on copper electroplating than poly(ethylene glycol) (PEG). The strong suppressor can minimize surface copper thickness to achieve excellent filling performance. In this work, we employ a copper filling formula to perform the TH filling. Several copolymers were employed as suppressors to replace PEG. The result shows that the surface copper thickness is decreased by using the copolymer. It can not only enhance the copper filling performance but also increase plating efficiency.

Reference

W. P. Dow, H. H. Chen, M. Y. Yen, W. H. Chen, K. H. Hsu, P. Y. Chuang, H. Ishizuka, N. Sakagawa, R. Kimizuka, “Through-Hole Filling by Copper Electroplating”, Journal of The Electrochemical Society, 2008, 155, D750-D757.

Figure 1
(Invited) Reversible Co-Intercalation of Sodium and Solvent in Graphite
Authors: Kim Haegyeom , Hong Jihyun , Yoon Gabin , Kim Hyunchul , Park Kyu-Young , Park Min-Sik , Yoon Won-Sub , Kang Kisuk
Published: February 2020

Graphite is a universal host materials that can accommodate various guest species in its galleries. Its capability of reversible lithium de/intercalation facilitates graphite as a standard anode for lithium ion batteries, while the thermodynamic instability of sodium intercalation made it not suitable for sodium ion batteries. We recently discovered that reversible solvated-Na ion intercalation enables graphite to become a promising anode for sodium ion batteries. As a continuous effort to exploit the graphite as an anode in sodium ion batteries, here we investigate the solvated-Na intercalation mechanism through in operando X-ray diffraction analysis, electrochemical titration, real-time observation of graphite expansion and density functional theory-based calculations. This work demonstrates the formation of first-stage graphite intercalation compound where the solvated-Na ions are doubly stacked in parallel with graphene layers. We further provide insights on tuning energy storage potentials of solvated ion intercalation electrodes by introducing various solvents.
(Invited) Development of Bimetallic Electrocatalysts and Electrodes for Carbon Dioxide Electrolysis Via Direct Deposition Strategies
Authors: Carroll Kyler , Hsiao Yung Wei , Brown Steven , Su Liang , Brushett Fikile R.
Published: February 2020

The development of energy efficient carbon dioxide (CO2) electroreduction processes would simultaneously curb anthropogenic CO2 emissions and provide suistainable pathways for fuel generation.  If such electroreactors employed CO2 feedstocks from major emission sources (e.g., thermal power plants) and excess electricity from intermittent locally-available renewable resources (e.g., solar, wind), then chemicals of economic value could be generated in a carbon neutral fashion [1].  While significant efforts have been focused on heterogeneous CO2 electroreduction to various products including carbon monoxide (CO), formic acid, and methanol; to date, no process has been able to demonstrate both high energetic efficiencies and high current densities [2].  A key challenge in the development of active, selective, and stable electrocatalysts is translating performance nanomaterials to appropriate electrodes which augment catalyst activity by maximizing surface area, facilitate species transfer, and minimize undesirable side reactions [3,4].

Direct deposition (e.g., electrodeposition, galvanic replacement) of nanostructured electrocatalysts onto microporous metal foam electrodes may offer a pathway to high performance electrodes.  Metal foams hold two key advantages: (i) their porous nature facilitates extended tunable electrochemical interfaces without sacrificing transport of reactants and ions; and (ii) they can act as a conductive substrates for the direct deposition of active materials eliminating the need for conductive additives and binders [5].  Further, as many active metals can form foams, surface alloys and multi-metallics could be created through deposition and annealing.  This talk will focus the development of Au/Cu and Ag/Cu core/shell catalysts via galvanic replacement reactions.  First, we will discuss the synthesis, characterization, and performance evaluation of Cu nanoparticles / nanowires with a few Au or Ag monolayers.  We will then describe the translation of these active materials to microporous Cu foam electrodes, subjected to various electrochemical pretreatments, which, in turn, will be evaluated in small-scale flow cells.

Acknowledgements

We gratefully acknowledge the financial support from the MIT Center for Materials Science and Engineering.

References

[1] D.T. Whipple, P.J.A. Kenis, J. Phys. Chem. Lett., 2010, 1, 3451-3458

[2] A.M. Appel et al., Chem. Rev., 2013, 113, 6621-6658

[3] H.R.M. Jhong, F.R. Brushett, P.J.A. Kenis, Adv. Energy Mater., 2013, 3, 589-599

[4] J. Wu, F.G. Risalvato, P.P. Sharma, P.J. Pellechia, F.-S. Ke, X.-D. Zhou, J. Electrochem. Soc., 2013, 160, F953-F957

[5] Y. Li, Z.-Y. Fu, B.-L. Su, Adv. Funct. Mater., 2012, 22, 4634-4667
On the Applications of Newly Architectured CdTe Nanostructures from Ionic Liquid Medium
Authors: Chauhan Khushbu R , Patel Dipal B , Mukhopadhyay Indrajit
Published: February 2020

The 2D nanostructures are gaining lot of interest in the field of electronics and solar photovoltaics. We have recently developed new shape and architecture of CdTe nanostructures on low cost F:SnO2 (FTO) substrate by electrodeposition from ionic liquid medium. It was observed that the ionic liquid medium facilitate the fabrication of nanostructured thin film directly on the substrate. By using two different substrates, FTO and CdS coated FTO it was possible to fabricate Schottky and p-n junction solar cells out of developed CdTe nanostructured films. It was interesting to observe that the Schottky junction solar cells of such nanostructured films result in higher Voc of 805 mV which is a quite high value for such solar cells. However, low connectivity between nanostructures resulted in lower Jsc values. On the other hand we found that the growth of semiconductor films from ionic liquid medium is highly substrate dependent. It was found that stoichiometric CdTe films can only be deposited on 50 nm thick film of CdS. Increasing the thickness of CdS layer always lead to non stoichiometric CdTe films which no longer can be utilized in solar cells. The first ever successful deposition of stoichiometric CdTe film on CdS buffer layer resulted in a solar cell with Voc of 150 mV, Jsc of 500 μA/cm2, FF of 27% and efficiency of 0.02%. This initial study will be helpful in understanding the growth of binary alloy on different substrates from ionic liquid medium.

Figure 1
Reaction Mechanism Analysis of a Li-O2 Battery: Structure of Electrode/Electrolyte Interface Probed Via Soft-x-Ray Absorption Spectroscopy, Hard x-Ray Photoelectron Spectroscopy, and in-Situ Hard x-Ray Diffraction
Authors: Yogi Chihiro , Kamiguchi Kazuhiro , Takao Naoki , Watanabe Takeshi , Kubobuchi Kei , Matsumoto Masashi , Ohwaki Tsukuru , Imai Hideto
Published: February 2020

Rechargeable Li-air batteries have been attracting much attention because of their extraordinary high energy capacity, viz, theoretically it reaches more than ten-times than those of existing Li-ion secondary battery. Recent materials development, such as use of glyme-series electrolytes, effective electrodes (metal based catalysts and/or high surface area carbon materials with nitrogen doping), or use of Redox-mediators, is about to find realistic solutions to overcome long-term crucial issues of Li-air battery, such as large over-potential at charge process, electrolyte degradation due oxygen radicals, and low cycleabilty presumably caused by unstable electrode properties at both anodes and cathodes.

Thus, additional deeper information on the reaction mechanism, involving unwanted side reactions, could be expected to accelerate such improvement. In this context, we performed reaction mechanism analysis by utilizing various experimental techniques, such as in-situ time-resolved x-ray diffraction, soft x-ray absorption spectroscopy at Li, C, O, and S K-edges, and hard x-ray photoelectron spectroscopy (HAXPES), combined with other conventional laboratory analysis methods.

Charge/discharge tests of Li-O2 battery were performed by using standard coin-type or electrochemical cells under various conditions including impact of moisture to the reaction. Soft x-ray absorption spectroscopy measurements were carried out at SR center of Ritsumeican University (BL-11) and Aichi synchrotron radiation center (BL6N1). Hard x-ray photoelectron spectroscopy and in-situ hard x-ray diffraction measurements were performed at SPring-8 on beamlines BL46XU and BL19B2.

We observed formation and dissolution processes of Li2O2 via in-situ time-resolved hard x-ray diffraction, which exhibited non-linear behaviors reflecting difference of nature of deposited Li2O2 particles. Also we analyzed the structure and chemical compositions of interface between Li2O2 and/or carbon electrodes and electrolyte solutions via soft x-ray and hard x-ray spectroscopy. The result indicates the structure of interface is significantly affected by the operation condition, and consists of various species decomposed from electrolyte and/or Li-salts. More detailed discussion will be presented at the Meeting.
Progress Towards a Rechargeable Multivalent Battery
Authors: Lipson Albert L. , Proffit Danielle L. , Pan Baofei , Lapidus Saul , Liao Chen , Burrell Anthony K. , Vaughey John T. , Ingram Brian J.
Published: February 2020

Cheaper batteries with higher capacity would increase the market penetration of electric vehicles and grid storage systems.  One way to achieve these gains in battery performance is to utilize a metal anode such as lithium, magnesium or calcium.  Lithium metal anodes have been extensively studied for decades, but still have not been commercialized.  On the other hand, comparatively little research has been performed on magnesium or calcium systems.  Magnesium metal has been shown to be less susceptible to the formation of dendrites than lithium.  No one is yet able to plate and strip calcium, however, it does possess a lower voltage than magnesium and a non-passivating oxide.  In order to rapidly explore the potential of these battery systems, we have developed techniques to study cathode materials without the need for a working metal anode.  In doing this we have determined that corrosion issues are more severe in these electrolytes than their lithium counterparts.  Furthermore, we have determined a class of materials that can intercalate Mg and Ca in nonaqueous electrolytes.  These materials are characterized by a combination of techniques including energy dispersive X-ray spectroscopy (EDX), X-ray absorption near-edge spectroscopy (XANES) and X-ray diffraction (XRD) to prove intercalation of the multivalent ion.  Additionally, we have made the first attempts to pair these materials with low voltage anode materials.  These anode materials include using Mg metal and metallic anodes that react with the multivalent ion.
Sulfur Nanoparticles Coated with Polyelectrolyte Nanomembranes for Sulfur Cathode
Authors: Osada Naoki , Bucur Claudiu B , Muldoon John
Published: February 2020

Elemental sulfur is the very attractive cathode for the post Li ion battery since the sulfur has high theoretical capacity of 1672 mAh/g1). Despite these attractive properties, practical application of Li-S battery is still unrealized by some big challenges on a sulfur cathode such as high resistance, low loading of active material and dissolution of the intermediate polysulfide into the electrolyte during charge and discharge. These issues cause low columbic efficiency, fast capacity fade and self-discharge of the Li-S battery. In order to suppress the dissolution of the intermediate polysulfides and minimize the addition of conductive carbon2); our group has created a controlled nanoarchitecture template in which sulfur nanoparticles encapsulated with the conductive polyelectrolyte nanomembranes coated with nanocarbon similar to “chocolate hazelnut truffle”3) (figure 1). The findings of this work will be discussed.

Figure 1. A three-dimensional view of our concept depicting the carbon infused sulfur core, the hollow carbon nanoparticles and multilayer selective polymer membrane decorated with functionalized carbon.

References

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

[2] Bucur, C. B., Muldoon, J., Lita, A., Schlenoff, J. B., Ghostine, A. R., Dietz, S. and Allred, G., Energy and Environ. Sci., 6, 3286-3290 (2013).

[3] Muldoon, J., Bucur, C. B., Boaretto, N., Gregory, T. and N. di Vito, Polymers: Opening Doors to Future Batteries, Polymer Reviews, (2015, Accepted).

Figure 1
Ultra-Thin Film Solid-Oxide Fuel Cell Technology Development: Status, Challenges, and Opportunities
Authors: Tsuchiya Masaru
Published: February 2020

Solid oxide fuel cell (SOFC) is one of the cleanest ways to convert chemical energy stored in fossil fuel into electricity. SOFC offers over 50 % electrical efficiency with low pollutant emission and low noise, and it can be utilized in various applications including portable electronics, remote power, and combined heat and power unit for homes. However, the technology has been under development for many decades, but not yet seen large scale commercialization due to issues in cost and durability.

SiEnergy Systems is developing low temperature ultra-thin solid oxide fuel cell that potentially offer major cost reduction and reliability improvement. The use of ultra-thin films reduces the amount of materials required in creating fuel cells, including rare-earth materials, therefore significantly reducing the material cost of the fuel cell. Additionally, the reduced thickness leads to the enhanced ionic conductance across the electrolyte, and enables SOFC operation at 350-550 °C, which is substantially lower than operating temperature of conventional SOFCs that is at 750 °C or above. SOFC operating at this temperature range avoids the disadvantages of conventional SOFCs, such as slow start-up time, costly materials and bulky thermal insulation, while potentially taking advantages of high energy conversion efficiency.

In this talk, recent advancement in thin film solid oxide fuel cell research and development will be reviewed with particular emphasis on electrode materials development and large-area cell demonstration.
Synthesis and Properties of a Multiblock Copolymer with Long Side Chains for Anion Exchange Membrane Fuel Cells
Authors: Kohl Paul A , Ahlfield John M. , Liu Lisha , Chu Deryn
Published: February 2020

Anion Exchange Membrane (AEM) fuel cells are a possible route to overcoming fundamental issues with acid-based fuel cells. The issues include the high cost of platinum catalysts, complex water transport, and sluggish electrochemical reactions, etc. However, the performance of AEM fuel cells is not as good as that of Proton Exchange Membrane (PEM) fuel cells because of the limitations of current anion exchange membranes, such as low ionic conductivity, poor stability at high pH, and high water uptake.

A series of novel multiblock copoly(arylene ether)s with long side chains were synthesized for AEM fuel cells. The multiblock copolymers were synthesized by polycondensation of separately-prepared hydroxyl-terminated oligomers with fluoro-terminated oligomers. The resulting multiblock structure, in which one block is hydrophilic and one block is hydrophobic, was designed to ensure a nanophase-separated morphology. Multiblock copolymers with different block lengths and ion exchange capacities (IEC) were synthesized to maximize ion conductivity and explore the relationship between chemical structures and properties in anion exchange membranes. Furthermore, copolymers with long side chains exhibited higher stability in high pH environment than their counterparts without long side chains. The degradation mechanism was also studied for the long side chain block copolymers.

Financial support from US Office of the Deputy Assistant Secretary of the Army for Defense Exports and Cooperation (DASA-DE&C) is gratefully acknowledged.
Electrochemical Oxidation of Borohydride for Direct Fuel Cells
Authors: Grimmer Christoph , Grandi Maximilian , Zacharias Robert , Friedrich Theo , Hacker Viktor
Published: February 2020

The direct borohydride fuel cell (DBFC) is gaining more and more interest in recent years because of high energy density and the easy handling of liquid fuels. The oxidation of the borohydride anions at the anode delivers up to eight electrons per molecule at a theoretical potential of -1.24 V vs. SHE [1,2]:

BH4
- + 8OH-  →  BO2
- + 6H2O + 8e-

In combination with an oxygen cathode and an alkaline membrane or electrolyte an electrochemical cell with a nominal voltage of 1.64 V is formed.

The electrochemical oxidation is investigated on various noble metal catalysts such as Pt/C, Au/C and Pd/C and bimetallic alloys thereof with first row transition metals. The electrochemical properties of the catalysts are characterized by cyclic voltammetry in alkaline electrolyte containing NaBH4 in standard three electrode configuration with a rotating disc electrode (RDE) [3].

Figure
1
: Cyclic voltammograms of Pt/C with 5mM NaBH4 on a RDE,  anodic sweeps at 200, 400, 600, 900, 1200, 1600 and 2000 rpm.

The borohydride oxidation on Pt/C starts at around -50 mV vs. RHE getting diffusion limited at 200 mV vs. RHE with a complete eight electron transfer. Due to diffusion limitation data processing according to Levich and Koutecky-Levich is possible.

Figure
2
: Levich plot of Pt/C catalyst at 0.50 V vs. RHE (data from Fig. 1)

 

Figure
3
: Koutecky-Levich plot of Pt/C catalyst at 0.50 V vs. RHE (data from Fig. 1)

Levich and Koutecky-Levich (Fig. 2 and 3) analysis show an eight electron transfer reaction at a potential of 0.5 V vs. RHE in the diffusion controlled region and as well at 0.01 V vs. RHE in the kinetic controlled region.

Although platinum shows excellent catalytic activity towards borohydride electrooxidation, the main side reaction, namely the hydrolysis reaction is also catalyzed. Besides the loss of fuel, the formation of gaseous hydrogen can harm the electrode due to mechanical stress. This issue can be addressed by replacing platinum with less active catalysts. Gold based electrocatalysts for example do not catalyze the hydrolysis side reaction.

On the roadway towards a practicable application it is necessary to improve the selectivity at the anode catalyst system.

Acknowledgements

Support by NAWI Graz and financial support by the Austrian Federal Ministry of Transport, Innovation and Technology (BMVIT) and The Austrian Research Promotion Agency (FFG) through the program a3plus and the IEA research cooperation is gratefully acknowledged.

References

[1]         E. Gyenge, Electrochim. Acta 49 (2004) 965.

[2]         D. Finkelstein, N. Mota, J. Phys. Chem. C 113 (2009) 19700.

[3]         M. Chatenet, M.B. Molina-Concha, N. El-Kissi, G. Parrour, J.-P. Diard, Electrochim. Acta 54 (2009) 4426.

Figure 1
Red Emitting Ca2SiO4:Eu2+ Phosphors for White Light Emitting Diodes
Authors: Sato Yasushi , Kuwahara Hiroki , Kato Hideki , Kobayashi Makoto , Kakihana Masato
Published: February 2020

Development of highly efficient red phosphors available in the excitation by UV-and/or blue-LEDs is one of the most important issues to improve the performance of white-LEDs because the color rendering index of most commercial white-LEDs which consisted of blue-LEDs and YAG:Ce3+ is relatively low owing to a lack of red-light region. Silicon-based nitride phosphors such as CaAlSiN3:Eu2+ and Sr2Si5N8:Eu2+ possess excellent red-light emission when excited by blue-light region. However, preparation of such silicon-based nitride phosphors in pure form should be needed to sinter precursor powders under high pressure and temperature conditions. Alkaline earth orthosilicate phosphors activated with Eu2+ have been reported as high efficient phosphors. Such silicon-based oxide phosphors in pure form can be easily obtained by simple preparation techniques without any critical conditions mentioned above. Therefore, productivity and production cost for silicon-based oxide phosphors are advantageous for the commercial production of red phosphors. We have already reported red-emitting CaSrSiO4:Eu2+ phosphors excited by blue-light region.1) The wavelength at the maximum emission of CaSrSiO4:Eu2+ with Eu2+ of 10 mol.% was 615nm. In addition, we have recently discovered new red-emitting Ca2SiO4:Eu2+ phosphors with higher Eu2+ concentrations at 20-40 mol.% excited by blue-light region.2) Although Ca2SiO4:Eu2+ phosphors with Eu2+ of 0.1–5.0 mol.% exhibited a strong green emission excited under UV light region,3) Ca2SiO4:Eu2+ with Eu2+ of 20–40 mol.% exhibited red emission peaking at 640–655 nm when excited at 450 nm and the emission intensity was 1.05 times higher than that of commercial YAG:Ce3+ (P46). The new red-emitting Ca2SiO4:Eu2+phosphors should be one of the promising candidates for the next-generated red phosphors in the white LED applications.

Reference:

1) S. Tezuka, Y. Sato, T. Komukai, Y. Takatsuka, H. Kato and M. Kakihana, Appl. Phys. Express
6 (2013) 072101, 2) Y. Sato, H. Kato, M. Kobayashi, T. Masaki, D. H. Yoon and M. Kakihana, Angew. Chem. Int. Ed.
53 (2014) 7756, 3)
Y. Y. Luo, D. S. Jo, K. Senthil, S. Tezuka, M. Kakihana, K. Toda, T. Masaki, D. H. Yoon, J. Solid State Chem.
189(2012) 68.

Figure:

Fig. 1 Emission and excitation spectra of Ca1.2Eu0.8SiO4.

Figure 1
Cathodoluminescence Studies of Phosphor Particles
Authors: Harris Paul Gregory , Engelsen Daniel den , Silver Jack
Published: February 2020

Cathodoluminescence (CL) studies carried out in a field emission scanning electron microscope are reported.  CL images of phosphor powders frequently manifested a bright ring around the periphery of the particles.  Additionally, particles resting on top of others were noted to be substantially brighter than under-lying ones.  Similar effects are often seen in secondary electron images and are usually ascribed to the electron beam spending more time in the surface region near the edges and therefore generating more secondary electrons close to the surface that are able to escape into vacuum.  This explanation, however, does not explain why we see such effects in CL microscopy.  To exclude the possibility of charging artefacts conductive ZnO:Zn phosphor powders (~1-2µm) were studied and these also exhibited the effect.  Studies have been made of model systems with both luminescent and non-luminescent materials adjacent to one another and on the basis of these results the origins of these phenomena are believed to be due to the combined effects of electrons backscattered out of the crystals onto adjacent particles, together with light absorption by the substrate.

Figure 1.  Cathodoluminescent micrograph of ZnO:Zn phosphor particles.

Figure 1
Thermal Properties of Mn4+-Doped Complex Fluoride Phosphors
Authors: Setlur Anant A , Murphy James , Garcia-Santamaria Florencio , Sista Srinivas
Published: February 2020

Red phosphors based upon Mn4+-doped complex fluorides are currently being implemented in a variety of LED display and lighting applications.  These phosphors can enable high CRI (for lighting) or high color gamut (for LCD backlit displays) without significant efficiency losses.  However, the properties of these phosphors can significantly differ based upon the specific phosphor host.  One example is in the temperature quenching of luminescence where T0.5, the temperature where emission intensity reaches 50% of the room temperature value.  Different Mn4+-doped complex fluoride phosphors can have T0.5 values that vary by more than 100oC.  In many applications, these differences in thermal quenching can prevent the use of these materials In this presentation, we discuss the various properties of numerous Mn4+-doped complex fluoride phosphors as a function of temperature.  Correlations between composition, vibrational properties, and luminescence properties will be discussed and analyzed.  Finally, the presence (or absence) of thermal quenching as a function of Mn4+ concentration will also be presented.
Nickel (III) Salt Dispersed Poly-aniline film: Preliminary SECM Examination
Authors: Haque Inam ul
Published: February 2020

Various matrices including poly-aniline have been used recently to incorporate nickel salts within the polymer. These films have been shown to be of utility for exploiting the oxidizing characteristic associated with nickel (III) under the right conditions, for example when the film is subjected to anodic bias. 

Preliminary SECM examination of the above films was undertaken. The results suggested the presence of active sites on the surface originating from higher-valent nickel cation. 

Reference

Inam-ul-Haque, Aakifa Raza and Shamaila Sadaf, Dispersed nickel oxide films for electro-oxidation of 1, 4-butanediol, Journal of the Chemical Society of Pakistan, 33 (1) 21-28 (2011).

Acknowledgments

Inam-ul-Haque thanks German Academic Exchange Service, DAAD, for a study and research stay; September to November 2010 at Department of Pure and Applied Chemistry University of Oldenburg Germany, and gratefully acknowledges kind and gracious hospitality of Professor Dr Gunther Wittstock.
Changes in Photoanodes during Solar Water Oxidation, the Wet Part of Artificial Photosynthesis
Authors: Braun Artur
Published: February 2020

Combination of animate matter with inanimate matter poses a difficult task for materials engineers, but opens up new horizons for scientists. I present the case where the iron oxide photoanode for photoelectrochemical solar water splitting is functionalized with C-phycocyanin, a protein known from blue green algae which has a light harvesting complex - one important structural motif in natural photosynthesis. The low cost and abundant mineral has a number of positive properties that make it suitable as a photoanode in photoelectrochemical cells (PEC). However, some deficiencies in its electronic structure prevent it from outperforming its costly and less abundant competitors in terms of quantum efficiency and photocurrent. Further functionalization of hematite with phycocyanin, i.e. coating and covalent cross linking, causes a doubling of the photocurrent. Detailed structural and spectroscopic analysis shows that it is the chromophore porphyrin in the phycocyanin which survives harsh pH conditions and provides also a light funnelling effect, which in the end makes an enhanced photocurrent. Our operando combination of PEC water splitting with soft x-ray spectroscopy provided new insight in the interaction of DC bias and photo-excitation with iron oxide. Anodization of hematite at bias potentials from 300 to 700 mV during illumination forms at least two new pre-edge structures in the O1s NEXAFS spectra, which can be assigned to eg spin up symmetry transitions in the O2p CTB and in the Fe3d-type UHB. We find a parallel evolution of the relative spectral weight of these transitions with the photocurrent vs. DC bias, strongly supporting that two types of electron holes are contributing to the historically suggested two types of photocurrent in hematite. The experiment was carried out entirely in situ during x-ray spectroscopy and strongly supports previous speculations that the electronic structure of the surface, and not only the short hole diffusion length in the bulk, may impede the performance of hematite photo-anodes. Meanwhile, we have made progress with probing also bio-organic motifs and hybrids with spectroscopy methods.

[1] D.K. Bora, A. Braun, E.C. Constable, “In rust we trust”. Hematite - the prospective inorganic backbone for artificial photosynthesis, Energy Environ. Sci.6, 407 (2013).

[2] A. Braun, K. Sivula, D. K. Bora, J. Zhu, L. Zhang, M. Grätzel, J. Guo, E. C. Constable, Direct observation of two electron holes in hematite during photo-electrochemical water splitting, J. Phys. Chem. C 116 (23) 16870 (2012).
Wide Bandgap Copper Indium Gallium Disulfide Thin Film Materials for Photoelectrochemical Hydrogen Production
Authors: Gaillard Nicolas
Published: February 2020

Photoelectrochemistry (PEC) is one of the most efficient methods to produce alternative fuels, although the efficiency, cost, and durability of lab-scale systems are currently not at the level required to make this technology economically feasible. The chalcopyrite material class provides exceptional candidates to meet the requirements identified for cheap, sustainable solar fuels production. As we recently reported, co-evaporated 1.7 eV CuGaSe2 offers very high-saturated photocurrent densities (>15 mA.cm-­2), long durability (>400 hours) and high Faradaic efficiency (>85%). However, CuGaSe2 photocathodes suffer from non-ideal surface energetics, requiring additional PV cells to drive the water splitting process. The hybrid photo-electrode (HPE) device, in which one PEC electrode is placed on top of one solar cell, is by far the most efficiency approach for unbiased solar water splitting. Unfortunately, CuGaSe2’s narrow bandgap prohibits this integration scheme.

In the present communication, we report on our efforts to synthesize 1.8-2.2 eV band-gap chalcopyrite materials for PEC water splitting. Specifically, we investigated the effect of sulfur on the optical and photoelectrochemical characteristics of the copper chalcopyrite material class. Using co-evaporated 1 μm-thick CuGaSe2 as baseline system, we demonstrate that the substitution of selenium with sulfur is accomplished through a simple annealing step. As a result, a dramatic change in optical properties was observed, with a bandgap increase from 1.6 eV (CuGaSe2) to 2.4 eV (CuGaS2). Then, by simply adjusting the indium content in the film during the initial growth process, the bandgap of sulfurized copper chalcopyrite was decreased from 2.4 eV to 2.0 eV. X-ray diffraction data indicated successful bulk sulfurization by the shift of the prominent (112), (220), and (312) reflections to higher angles. PEC analyses revealed an anodic shift of the flatband potential with increasing bandgap when compared to CuGaSe2. This suggests that the bandgap modification in sulfurized films primarily stems from a downward shift of the valence band, an ideal situation for p-type PEC systems. Saturated photocurrent densities of 5 mA/cm2 were achieved with 2.0 eV red CuIn0.3Ga0.7S2 photocathodes in 0.5M H2SO4 under AM1.5G simulated illumination. From this proof of concept experiment, we have further developed new synthesis approaches and innovative characterization protocols to achieve PV-grade wide bandgap sulfide-based chalcopyrites capable of generating photocurrent densities in the 10-15 mA/cm2 range.
A Facial Liquid Plasma-Induced Polymerization of a Highly Ion-Conductive Polymeric Membrane
Authors: Choi Ho-Suk , Tran Quoc-Chinh
Published: February 2020

We first report the synthesis of a highly ion-conductive polymeric membrane through using a liquid plasma system under an atmospheric pressure. The 1-butyl-3-methylimidazolium tetrafluoroborate ([BMI]BF4) and Triton X-100 were used as reacting monomers. These radical monomers, which form cross-linked polymeric films after reaction, are generated at a gas-liquid interface through the irradiation reaction of plasma species with a homogenous solution of [BMI]BF4 and Triton X-100.  The as-synthesized polymer films were eventually observed at the gas-liquid interface under an atmospheric pressure. The thickness of the polymer film was controlled with different molar ratios of [BMI]BF4 and Triton X-100, and plasma reduction time. The maximum thickness of polymer film was 3.043 µm after plasma irradiation for 10 min at a molar ratio of 65:1 for [BMI]BF4:Triton X-100. Furthermore, the application of the synthesized polymer film as an alternative lithium ion conductive polymer leads to high ionic conductivity as well as small impedance as seen in Figure 1 and 2.

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Covalently Cross-Linked Cholesterol Oxidase for an Indirect Detection Cholesterol Biosensor
Authors: Ashby Jarryd Noah , Ramasamy Ramaraja P.
Published: February 2020

Nearly a third of the population in the United States suffer from high cholesterol. This condition approximately doubles one's risk of cardiovascular disease, which is the leading cause of death in the country. As such, increasingly cost-effective, robust, easy-to-use, and accurate methods of detection of cholesterol are necessary to curtail such health risks. A particularly accurate method for this includes enzymatic electrochemical detection; however, most electrochemical detection methods use enzyme-modified electrodes developed based on the physisorption of enzymes onto the electrodes. This approach does not result in high activity and severely limits the enzyme stability on the electrode. This can be mitigated by immobilizing the enzyme onto carbon nanotubes using molecular tethers. Our biosensor was fabricated using Cholesterol oxidase, from Streptomyces, immobilized on multi-walled carbon nanotubes (MWCNT) with 1-pyrenebutanoic acid, succinimidyl ester (PBSE) as a molecular tethering agent. The biosensor shows a linear detection region ranging from at least 0.03-0.5 mM and high selectivity against common interferents, such as glucose at less than five percent.

Fig. 1:(top): Differential Pulse Voltammetry study of Cholesterol oxidase immobilized on MWCNT with PBSE in an oxygen-saturated 0.1 M phosphate buffer (pH 7.4) at varying cholesterol concentrations ranging from 0 to 0.5 mM. (bottom): Standard plot of cholesterol concentration versus amperometric signal (change in peak current).

Acknowledgments:

The authors extend gratitude to Dr. Nicole S. Sampson of Stony Brook University for the cholesterol oxidase enzyme used herein.

* Corresponding Author: rama@uga.edu

References:

1. R. P. Ramasamy, H. R. Luckarift, D. M. Ivnitski, P. B. Atanassov, and G. R. Johnson, High electrocatalytic activity of tethered multicopper oxidase–carbon nanotube conjugates. Chem. Commun.,  
2010, 46, 6045-6047.

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Influence of Probe Size and Probe Position for Local Electrochemical Impedance Spectroscopy
Authors: Vivier Vincent , Camila Molena de Assis , Abreu Caio P. , Costa Isolda , de Melo Hercilio G. , Keddam Michel
Published: February 2020

Local electrochemical impedance spectroscopy (LEIS) has received a significant attention these last two decades mainly for corrosion applications [1, 2]. The assessment of local current density in solution requires the measurement of at least 3 local potentials in the electrolytic solution using 3 independent micro-reference electrodes positioned close to the electrochemical interface. Then, the different contributions of the local current density (namely the normal and the radial components) are obtained using the Ohm’s law. The spatial resolution is mainly governed by the probe size, the distance between the two independent potential probes (i.e. silver micro-wires), and the distance between the probes and the interface. Interestingly, resolutions in the micrometre range have already been reported [3], but the apparition of two main drawbacks accompanies the diminution of the probe dimension.

First, a non-negligible capacitance is observed in the high-frequency domains corresponding to a coupling capacitance between two of the micro-wires, as shown in Fig. 1. 

Second, the position of the reference electrode for measuring the potential and calculating the local impedance plays a significant role [4]. Indeed, depending on the location of the probe for measuring the potential, the measurement may be insensitive to local heterogeneity. As a result, such a measurement is no longer a local impedance measurement since it is obtained as a ratio of global potential to local current density.

In this paper, we present experimental results on platinum electrode and on the steel / copper system in order to characterize the influence of the probe size and the probe positioning. A specific attention will be paid to data analysis, and some guidelines for performing LEIS measurements (probe characterisation and probe positioning) will be presented.

[1] R.S. Lillard, P.J. Moran, H.S. Isaacs, A novel method for generating quantitative local electrochemical impedance spectroscopy, J. Electrochem. Soc. 139 (1992) 1007-12.

[2] V.M.-W. Huang, S.-L. Wu, M.E. Orazem, N. Pebere, B. Tribollet, V. Vivier, Local electrochemical impedance spectroscopy: A review and some recent developments, Electrochim. Acta 56 (2011) 8048-57.

[3] I. Annergren, D. Thierry, F. Zou, Localized electrochemical impedance spectroscopy for studying pitting corrosion on stainless steels, J. Electrochem. Soc. 144 (1997) 1208-15.

[4] E. Bayet, F. Huet, M. Keddam, K. Ogle, H. Takenouti, Local electrochemical impedance measurement: scanning vibrating electrode technique in ac mode, Electrochim. Acta 44 (1999) 4117-27.

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Fig. 1: dual probe used for measuring local electrochemical impedance spectroscopy and equivalent circuit used for taking into account the stray capacitance ascribed to this setup.

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Finite Elements Approach to Predicting Impedance Response of Geometrically Convoluted Samples
Authors: Vanýsek Petr , Vyroubal Petr , Haňka Jiří , Novák Vitězslav , Maxa Jiří
Published: February 2020

The geometry of a sample is of utmost importance in interpretation of impedance measurements and correlating them to the properties of the studied material. The first, always considered, issue is inclusion of the geometrical dimensions, so that capacitance and resistance of a sample can be interpreted and reported for proper comparison based on values per unit dimensions.  In ideal measurements the samples prepared are a prioriprepared in simple geometries, allowing proper electric contact connections so that the calculations are simplified and measurements in a single laboratory, even without data interpretation, lend themselves to quick visual side-by-side comparison.

              However, such arrangement is not always possible and therefore we investigated, by method of computer simulation, dependence of impedance results on geometry of a sample and location of electrode connection.  As an example is a ceramic disc with grain and boundary resistance and capacitance, that could be encountered in studies of advanced high temperature materials, e.g.,for sensors of high-temperature fuel cells. The disks prepared by various methods of synthesis are contacted on their flat sides to the impedance analyzer circuitry. Our study correlates the (simulated) measured data to data that would be expected if perfectly symmetrical all-covering contacts were used.    

              While in part the correlation reveals that a simple multiplication factor can be used in some cases to correct for the geometry of the electrode placement, under conditions of more extreme electrode placements the response is such, that equivalent modeling of the obtained impedance data is not adequately described only by RC circuits. Instead, a constant phase element has to be introduced.

              The simulation for this work was done using the ANSYS software package. The figure shows the geometric layout used for simulation. In this case a sample disk of a 30-mm diameter, thickness 7 mm is connected to the measurement circuit by two symmetrical, centrally placed metal circular electrodes of diameter 14 mm. In the process of simulations the size of the electrodes and their placement vs. the centerr of the sample was varied.  For the data fitting to the suitable equivalent circuits was used the ZView package from Scribner Associates.

This work was supported by the project “CEITEC - Central European Institute of Technology” (CZ.1.05/1.1.00/02.0068) from European Regional Development Fund.

Figure 1