bluuebunny/crossref_metadata_2025 huggingface dataset:
Exploring the Impedance Signatures of Electrochemical/Mechanical Transport Coupling in Concentrated Liquid Electrolytes
Authors: Goyal Priyamvada , Monroe Charles W
Published: February 2020

The Warburg impedance response [1] in electrochemical impedance spectroscopy data is commonly recognized as a signature of molecular diffusion processes. One can go beyond a qualitative perspective based on equivalent circuits and employ impedance data to quantify material properties relevant to transport phenomena. The Warburg impedance in particular provides useful data for electrolyte characterization. More often than not, however, properties such as transference numbers and diffusivities have been extracted by applying the Poisson-Nernst-Planck (PNP) model [2] to impedance data; the PNP model neglects Darken factors, and therefore does not bear accurate results when applied to concentrated solutions.

This work builds on the detailed impedance formulation discussed by Pollard and Comte [3], who rely on Onsager-Stefan-Maxwell theory instead of PNP theory. As well as accounting for thermodynamic factors and using thermodynamically meaningful potentials [4], the Pollard-Comte model involves parameters that quantify solute-volume effects, namely, the excluded-volume effect and Faradaic convection [5]. Faradaic convection, which refers to bulk electrolyte flow induced by interfacial electrochemical reactions, is one instance of the electrochemical/mechanical coupling this presentation will explore. The Pollard-Comte analysis is extended to an asymmetric cell, in which different half-reactions occur at the working and counter electrodes.

Faradaic convection is an essentially kinematic phenomenon. A far more substantial augmentation of the Pollard-Comte model is needed to account for dynamical effects, such as those arising from local pressure variations. Liu and Monroe showed that in multiple spatial dimensions, Newman’s concentrated-solution theory requires a local momentum balance in addition to the volume-explicit equation of state [5]. Appending the momentum balance, and its associated state-variable definitions and constitutive laws, is a non-trivial exercise, because the pressure dependence of partial molar volumes makes the governing system of transport equations highly coupled – even in a one-dimensional case.

Mechanical responses whose characteristic times differ substantially from those associated with molecular diffusion or capacitive relaxation arise from both liquid inertia and viscosity. Impedance analysis is therefore a good strategy for deconvoluting dynamical effects and validating the augmented transport model. It also appears that mechanical effects may be associated with new impedance elements that have not been considered to date.

 

 

References

1. E. Warburg, Annalen der Physik und Chemie 67, 493 (1899)

2. D.R. Franceschetti, J.R. Macdonald, and R.P. Buck, J Electrochem Soc, 138, 1368 (1991)

3. R. Pollard and T. Comte, J Electrochem Soc, 136, 3734 (1989)

4. A.M. Bizeray, D.A. Howey, and C.W. Monroe, J Electrochem Soc, 163, E223 (2016)

5. J. Liu and C.W. Monroe, Electrochim Acta, 135, 447 (2014)
Direct and Efficient Simulation of Battery Models for Standalone PV-Battery Microgrids
Authors: Lee Seong Beom , Ramadesigan Venkatasailanathan , Gao Wenzhong , Subramanian Venkat R.
Published: February 2020

With renewable energy based electrical systems becoming more prevalent in homes across the globe, microgrids are becoming widespread and could pave the way for future energy distribution. Accurate and economical sizing of a standalone power system components has been an active area of research, but current control methods do not make them economically feasible. Typically, batteries are treated as a black box that does not account for their internal states in current microgrid simulation and control algorithms.1 This might lead to under-utilization and over-stacking of batteries. In contrast, detailed physics-based battery models, accounting for internal states, can save a significant amount of energy and cost, utilizing batteries with maximized life and usability.2 However, typical microgrid controls including feedback algorithms cause a significant time-delay as detailed physics-based battery models are coupled to the entire microgrid system.3 It is important to identify how efficient physics-based models of batteries can be included and addressed in current grid control strategies.

In this talk, we will show that perhaps the best way to integrate detailed battery models is to write the microgrid equations in mathematical form and then identify an efficient way to solve those models simultaneously with battery models, which gives better results. Implementation of the maximum power point tracking controller algorithm and physics-based battery model along with microgrid components as differential algebraic equations will be discussed. The results of the proposed approach will be compared with the conventional control strategies and improvements in performance and speed will be reported.

Acknowledgements

This work was supported by the Clean Energy Institute located in University of Washington, Seattle and Washington Research Foundation.

References

1. D. A. Beck, J. M. Carothers, V. R. Subramanian, and J. Pfaendtner, AIChE Journal,
62(5), 1402-1416 (2016).

2. M. T. Lawder, B. Suthar, P. W. Northrop, S. De, C. M. Hoff, O. Leitermann, M. L. Crow, S. Santhanagopalan, and V. R. Subramanian, Proceedings of the IEEE,
102(6), 1014-1030 (2014).

3. B. Subudhi and R. Pradhan, IEEE Transactions on Sustainable Energy,
4(1), 89-98 (2013).
Atomistic Simulations of Ionic Liquid and Polymer Electrolytes: From Bulk Phases to Interfacial Behavior
Authors: Lawson John W , Haskins Justin B
Published: February 2020

Ionic liquids and polymers are candidate electrolytes for high-energy density, rechargeable batteries. We present an extensive computational analysis with experimental comparisons of bulk and interfacial properties of three ionic liquid electrolytes ([pyr14][TFSI], [pyr13][FSI], and [EMIM][BF4]) as a function of Li-salt doping. We investigated the bulk electrolyte using quantum chemistry and ab initio molecular dynamics to elucidate the solvation structure of Li+. MD simulations using polarizable force fields were performed, from which we obtained an array of thermodynamic and transport properties. We computed the electrochemical window of the electrolytes across a range of Li+-doping levels, including the effect of the liquid environment. In addition, we considered these Li-doped electrolytes at ideal electrified interfaces to evaluate the differential capacitance and the equilibrium Li+ distribution in the double layer. Finally, we investigated polymers as candidate structural electrolytes. We report results for ionic conductivity, glass transition temperature and bulk modulus for representative polymer systems.
A Reaction-Diffusion Phase-Field Model and Its Application to Lithiated Selenium-Doped Germanium Electrodes
Authors: Wang Xiao , Zhu Likun , Mullins Charles Buddie , Meyerson Melissa , Chen Lei
Published: February 2020

Recent experiments observed micrometer (µm)-sized Selenium (Se)-doped Germanium (Ge) particles forms a network of active Ge inclusions amidst an amorphous Se-containing inactive phase during initial lithiation/delithiation cycles. Such an inactive coating phase is supposed to be responsible for the superior performance of cycling stability and capacity over un-doped Ge particles of similar size, however, the understanding of fundamental mechanism still remain elusive. A reaction-diffusion phase-field model, coupling the large elastoplastic deformation, is therefore originally developed investigate the role of the inactive phase in morphology and stress variation of Se-doped Ge electrode upon lithiation. The incorporation of both the Butler-Volmer electrochemical reaction kinetics and Li diffusion, for the first time, enables to directly determine the conditions at which the lithiation process exhibits the diffusion and/or reaction controlled behavior. We find that the hoop stress at the surface of Ge particles is significantly suppressed by the protection of the inactive coating phase, especially when characterized by the soft nature and the high Li diffusivity. The present study reveals the physical underpinnings of previously unexplained favorable electrochemical reaction, diffusion and fracture behavior of active/inactive-phase anodes, and thus offers valuable insights and guidance toward high-performance anodes for lithium-ion batteries.
Numerical Simulation Method for the Heat and Voltage Behavior of Thermal Battery in the Activation Process
Authors: Wang Chao , Liu Xiaojiang , Cao Yong , Yang Xiaowei , Zhao Yu , Cui Yanhua
Published: February 2020

A numerical simulation method, basing on finite element analysis, for the activation process of thermal battery is discussed in this manuscript, and which can be applied to predict the heat distribution, open-circuit voltage and on-load voltage of thermal battery in the activation process. The sequenced combustion and heat releasing of igniter, pyrotechnic cylinder and pellet, combined with the melting process of electrolyte, are considered in the simulation model, which can accurately exhibit the heat distribution characteristics of thermal battery in the activation process to some extent. Basing on the simulation results of heat distribution, the model can predict the open-circuit voltage of thermal battery in activation process by loading the open-circuit voltage curve of single cell thermal battery along with temperature. The on-load voltage was calculated basing on the butler-volmer equation in the model. In addition, the time of thermal battery with full-load capacity can be predicted by analyzing the melting characteristics of electrolytic. Compared with the experimental results, it can be found that the simulation method has a relatively high precision. Fig.1 is the temperature simulation results of thermal battery in the activation process.

Figure 1
Multiscale Imaging and Spectroscopy on a Lithium-Ion Pouch Cell : Experiments and Modelling
Authors: Nanda Jagjit , Zhou Hui , Allu Srikanth , An Ke , Li Jianlin , Ruther Rose Emily , Bilheux Hassina , Pannala Sreekanth , Subramanian Venkat R. , Turner John A
Published: February 2020

Majority of electrode materials used for advanced lithium based batteries have well defined chemical composition and particle morphology. The chemistry as well as the microstructure can undergo reversible or irreversible changes under continuous electrochemical charge-discharge cycles. These could have measurable impact on the battery capacity and life. Combining multi-length scale characterization with electrochemical modelling can provide vital information regarding battery electrode degradation and inomogeneity. The talk will cover our recent work related to applying a number of neutron, X-ray and laser based spectroscopy and imaging methods to a number of relvant battery chemistries such as NMC and multi-lithium transition metal based compostions. These techniques covers from meso to micron length scale truly providing the mulit-scale nature of transport in batteries. Specifcally, we demonstrate lithiation in graphitic anodes using insitu neutron imaging in a pouch cell format. The neutron absorption contrast shows a direct correlation between degree of lithiation and the discharge voltage plateau at various time steps. We further provide a semi-quantitative comparison between the observed spatial variations of neutron absorption contrast in graphite with the calculated lithium concentration profiles computed using a 3D electrochemical transport model. In conjunction with imaging,
in situ
neutron diffraction of a similar pouch cell under identical test protocol was carried to obtain information about the local phase changes upon lithiation. Combined in-situ radiography and diffraction opens up a powerful nondestructive method to understand the multi-scale nature of lithium transport and degradation in practical lithium-ion cells.
Simulation of Nanoscale Confinement for Process Intensification
Authors: Chavan Kanchan Suklal , Calabrese Barton Scott
Published: February 2020

Simulation of nanoscale confinement for process intensification

Efficient multi-step reaction cascades can directly benefit the manufacture of advanced materials, energy conversion/harvesting, and human-machine interfaces. Nature has developed very efficient pathways to carry out multi-step reactions with controlled transport and kinetics.1One such approach to reaction control is the confinement of active sites and the resulting reaction intermediates within a physical tunnel, by which the intermediate can be restricted from the bulk. Studying transport properties and kinetics of the confined systems provides a framework for the design of integrated catalytic systems and process intensification.

In the present study, computational modeling has been performed to study the effect of geometric, kinetic, and transport parameters on intermediate channeling via confinement, using a continuum model(Figure 1 a). The efficiency of transport is quantified by reactant yield and flux control coefficients (FCC).2 Interaction of the intermediate with the confined channel has been addressed by molecular dynamics studies of diffusion coefficient and retention time(Figure 1 b). Electrostatic effects of the tunnel edge on the intermediate significantly increase retention of intermediate within the tunnel. Such retention of intermediates within the confined assembly, with minimal access to bulk solution, is shown to be the key to efficient channeling.

Acknowledgement

We gratefully acknowledge support from Army Research Office MURI (#W911NF1410263) via The University of Utah.

References 1. I. Wheeldon et al., Nat. Chem., 8, 299–309 (2016). doi:10.1038/nchem.2459

2. D. A. Fell, Biochem. J., 330, 313–330 (1992). doi:10.1042/bj2860313

Figure 1
3D Printed Hybrid Electrodes for Lithium-Ion Batteries
Authors: Li Jie , Leu Ming , Panat Rahul , Park Jonghyun
Published: February 2020

A novel hybrid 3D structured electrode, with a high-aspect ratio, is fabricated via extrusion-based additive manufacturing to achieve high mass loading and combine the advantages offered by a conventional laminated structure and a 3D digital structure. This structure is designed to enhance interfacial reactions and species transport by utilizing the 3D structure. Two key challenges in 3D structured electrodes are addressed, including solution preparation and scale-up. The paste is optimized with a high viscosity to avoid the typical complexity encountered in preparing a solution for 3D printing, and the proposed hybrid 3D structures can be easily added to the conventional laminated structures. This is demonstrated by using a CR2032 coin cell, which also solves the typical assembly problems that occur with 3D structured electrodes. This innovative design and fabrication process demonstrates high areal energy and power density, which are critical requirements for energy storage systems in transportation and stationary applications.
Nano-Engineered Materials for Energy Conversion and Storage Applications: Synthesis, Characterization, and Mathematical Modeling
Authors: Karimi Shahram
Published: February 2020

Pulsed current electrodeposition (PCE) was employed to deposit a number of metals on different substrates for various applications. Influence of key PCE parameters, including duty cycle, peak deposition current density, pulse on-time-on and off-time and type of pulse waveform, on the morphology, size, distribution and catalytic activity of the electrodeposited layers were investigated. Platinum and palladium were electrodeposited on carbon substrates for fuel cell applications and nickel, copper, cobalt and platinum were electrodeposited on highly ordered titania nanotubes (TNTs) for solar hydrogen generation and wastewater treatment processes. The presence of nanocrystalline platinum and palladium, ranging from 2-10 nm in diameter, on carbon paper and cloth were confirmed by scanning electron microscopy and x-ray diffractometry. Their catalytic activity also was examined by fabricating membrane-electrode assemblies and testing them in single-cell proton exchange membrane and direct methanol fuel cells. Doped TNTs also were characterized by microscopy, x-ray diffractometry and UV-Vis spectroscopy. Structural investigation of the prepared TNTs via a simple anodization technique followed by metal doping, utilizing the aforementioned PCE method, confirmed the presence of anatase nanocrystalline TNTs after annealing in air and vacuum at elevated temperatures. The presence of nickel and copper nanoparticles 10-50 nm in diameter also was observed and, subsequently, confirmed. The efficiency of the photoanodes was found to increase as the amount of dopant increased to 3%. Further increase in metal dopants, however, resulted in a decrease in efficiency.

A comprehensive mathematical model based on progressive nucleation was developed to accurately predict the influence of the aforementioned electroplating parameters on the resulting layers and films with the aim of process optimization for a particular plating system. The model takes into account contributions from both nucleation and growth currents and assumes a dynamic; i.e., changing, diffusion coefficient during electrodeposition. According to this model, high peak deposition current densities, low duty cycles, pulses delivered in microsecond range and employing a ramp-down waveform yielded the highest nucleation rates, leading to the smallest average grain size of the deposited nanoparticles, and confirming the experimental findings.
New Opportunities in Pulse Plating Via Self-Terminated Electrodeposition Reactions
Authors: Moffat Thomas P. , Liu Yihua , Ahn Sang Hyun , Ritzert Nicole L. , Wang Rongyue , Gokcen Dincer , Hangarter Carlos , Bertocci Ugo
Published: February 2020

Recently, electrodeposition of Pt and Ir was shown to exhibit an unanticipated self-terminating characteristic that enables controlled deposition of monolayer thick films from simple binary electrolytes. Specifically, film growth at negative potentials is quenched by the formation of a saturated layer of adsorbed H, and alteration of the double layer structure, that in combination block adsorption of the metal halide precursor complex. Periodic pulsing of the potential to desorb H enables sequential deposition of additional Pt and Ir layers to fabricate films of desired thickness relevant to a range of advanced technologies. Overall the process is tantamount to a “wet” form of atomic layer deposition (ALD). More recently, self-terminated deposition of the iron group metals, Fe, Co and Ni, was also observed. In contrast to the Pt group metals, growth termination of the iron group metals is attributed to OH- adsorption that is coincident with the onset of water reduction. The application of the above deposition processes to a variety of substrates, e.g. Au, Ni, etc, is underway along with an assessment of the catalytic activity of the resulting electrodes towards water electrolysis and related fuel cell reactions. In this lecture details of the growth process and resulting electrocatalytic performance will be summarized.
(Invited) Determining Solid/Liquid Junction Energetics By Operando Ambient-Pressure X-Ray Photoelectron Spectroscopy
Authors: Richter Matthias Hermann , Lichterman Michael Frankston , Brunschwig Bruce S , Lewis Nathan S , Lewerenz Hans Joachim
Published: February 2020

The performance of a photoelectrochemical solar cell (PEC) depends strongly on the electrochemical nature of the semiconductor/electrolyte junction. Operando ambient pressure X-ray photoelectron spectroscopy (OAP-XPS) investigation of solid/liquid junctions provides quantitative understanding of the energetic relations in PECs [1-3]. We demonstrate that OAP-XPS can be used to determine these relationships for solid/liquid systems. The OAP-XPS data can be analyzed to determine the relationship between the energy bands in a semiconductor electrode and the redox levels in the solution as well as directly analyze the energetics of the double layer at a metal-aqueous solution interface. From the response of the core level binding energy shifts and the broadening to variations in applied potential, we obtain the energetics of the solid/electrolyte interface. All major conditions for semiconductor-electrolyte contacts including accumulation, depletion, and Fermi-level pinning were observed, and the flat-band potential was determined. The data are compared to theoretical evaluations of the potential in the solid and electrolyte near the interface.

1. H.J. Lewerenz et al., Electrochimica Acta, 211, 711–719 2016

2. M. F. Lichterman et al., Journal of the Electrochemical Society, 163(2), H139–H146, 2016

3. M. F. Lichterman et al., Energy & Environmental Science, 8(8), 2409–2416, 2015
Measurement of Charge Transfer Kinetics and Energetics at Microscopic Si/Liquid Contacts
Authors: Lancaster Mitchell , Maldonado Stephen
Published: February 2020

Understanding the fundamental processes that govern charge transfer at semiconductor/liquid interfaces is paramount for the efficient operation of photoelectrochemical systems. Quantitative voltammetric studies at macroscopic semiconductor electrodes have long been hindered by the lack of a complete analytical expression for the current-potential response and contribution from defect-induced surface states. This presentation will highlight the recent application of recessed semiconductor ultramicroelectrodes to voltammetric measurements of heterogeneous charge transfer rate constants, band edge positions, and diode quality factors at semiconductor/liquid interfaces. Three aspects will be discussed. First, a general description of the observed current-potential response will be provided along with considerations necessary for extraction of kinetic and energetic information. Second, measured charge transfer rates, band edge positions, and diode quality factors at poised and unpoised microscopic Si/electrolyte contacts with varying crystal orientation, doping, and electrolyte solutions will be presented. These results will be placed in the context of previous measurements at macroscopic Si/liquid contacts. Third, an overview of unique opportunities afforded through use of microscopic and nanoscopic semiconductor/liquid contacts will be given, with an emphasis on investigating charge transfer theories.
Cu2(ZnSn)(SSe)4 Electrodeposition from a Single Bath and Sulfur-Selenium Atomic Ratio Optimization
Authors: Saeed Mahfouz Ali
Published: February 2020

Cu2(ZnSn)(SSe)4 (CTZSS) has an important advantages over CuInGaSe2 (CIGS) as photovoltaic thin film due to its high band gap. Generating such thin film materials by electrochemical methods is particularly attractive because of its high throughput and low cost1-3. Numerous publications reports CTZS electroplating; however, the electroplating process still has a serious challenges such as a sulfur atomic ration and the annealing process due to low partial pressure4.

We present in this work a new electrolyte composition which allows the direct electroplating of CTZSS from a single bath. The electrolyte is significantly more dilute in comparison to common electrolytes designated in the literature1-4. The bath composition we introduce is: 0.0031 M CuSO4, 0.0023 M ZnSO4, 0.026 M SnCl2, 0.004 M Na2S2O3, 0.026 M H2SeO3 and 0.11 mM Na2S2O3. PHydrion is used to buffer the electrolyte to pH=2, and 0.76 M LiCl is used as supporting electrolyte.

Electrodeposition experiments was carried at a rotating disk electrode which provides quantitative characterization of the flow (ambient temperature). Comprehensive electrochemical behavior study at different electrode rotation rates are provided in Fig. 1. The effects of flow speed on the CTZSS alloy atomic composition and its adhesion to the back contact are discussed. The post treatment annealing was conducted under sulfur element atmosphere with no need for material addition at this step. The amount of sulfur and selenium was optimized. The final composition was investigated using Energy-dispersive X-ray spectroscopy technique (EDS) Fig. 2. XRD technique used to analyze CTZS crystallography and thickness.

Acknowledgements

Case Western Reserve University for using their instruments

References

[1] M. Cao, L. Li, B. L. Zhang, J. Huang, L. J. Wang, Y. Shen, Y. Sun, J. C. Jiang, G. J. Hu,

Sol. Energy Mater. Sol.Cells, 93, 583 (2009). [2] Y. Lin, S. Ikeda, W. Septina, Y. Kawasaki, T. Harada, M. Matsumura, Sol. Energy Mater. Sol. Cells, 120,

218 (2014).

[3] H. Guan, H. Shen, C. Gao, X. He, , J. Mater. Sci.:Mater. Electron., 24, 1490 (2013).

[4] S. Abermann, , Solar Energy, 94, 37 (2013).

Figure 1
(Invited) Challenges for Ion Implantation in Power Device Processing
Authors: Schustereder Werner
Published: February 2020

In power device technologies distinct challenges have to be addressed. These are partly in contrast to needs and developments in advanced DRAM and Logic products that dominantly strive for ultrafast switching speed provided by lowest nm node technologies. Power devices in general are facing the main demand to lower dissipation losses caused by increased current density at decreasing structure sizes and optimized performance of device switching behavior at the same time.

Today modern power device fabs are facing a variety of wafer sizes ranging from 100mm to 300mm, mainly depending on the availability of distinct base materials for power devices. For minimizing static and dynamic power losses of high voltage switches the main keys are local control of charge carrier lifetime and the use of thin and ultrathin wafers. Besides that, high dose implants with energies higher than the actually supported 60 keV to 80 keV on modern implanters are and will be necessary for source and p+ implantations in power devices.

In mainstream power technologies the main application driven key factors are lowest RDSon for compensation devices as well as minimal power dissipation for high voltage switches. Advanced in-situ metrology will be demanded for charge compensation devices of the next generation. The shrinkage of the pitch size and the related demand for a limitation of the lateral out-diffusion is driving the need for reliable energy stability as well as careful tuning of secondary process parameters. Implantations for material modification purposes are gaining relevance.

As of today the vast majority of power devices are still fabricated on silicon substrates. However, other semiconductors like SiC and GaN obtain superior material characteristics compared to silicon. That is why considerable development effort is put into the understanding of how to fabricate devices based on those materials. One ingredient is the knowledge how ion implantation can affect and tailor their semiconductor properties. An overview on effects of ion implantation into these materials will be given.

Overall, a summary of today’s challenges towards ion implantation for power device technology as well as an outlook to next generation demands will be presented.
The Role of Polysilicon Slurry and Its Application in 7nm CMP
Authors: Chao Tai Fong , Penigalapati Dinesh , Yang JI Chul , Huang Haigou , Koli Dinesh R
Published: February 2020

Poly silicon is the preferred gate material in terms of fabrication process in the fab, and gate height control is one of the factors determining transistor performance. If we can have a better uniformity control of poly CMP, it will be beneficial not only to CMP but also to the downstream etch process. Thus, we evaluated two poly slurries (Slurry A, B), analyzed each characteristic and performance on the device area and applied to 7nm CMP process furthermore.

We found that slurry A, ceria-based poly slurry, has excellent WiD uniformity, less than 2nm, and good end-point (motor torque) detection point which is good in terms of manufacturing perspective. However, shelf life is a big challenge that we loss the selectivity of nitride and oxide after 15 days and also found visible white precipitate in the slurry loop. We did the shelf life test for both the additive only and the slurry. Data shows that the removal rate, pH and particle size of the additive only did not change a lot; however, the slurry became more unstable after 11 days with the increasing of the nitride loss, ten times the baseline. Chemical reaction happened between the abrasive and the additive. We can avoid the slurry deterioration by using the in-line mixing instead of pre-mixing. Table 2 shows the center die uniformity of slurry A is 1.9nm, much less than our target, 5nm. We also measured the CMP house pad topography for the slurry marginality test. Slurry A also has the better capability to stop on nitride, however, slurry B, the silica based slurry, has no removal rate at donut and center area. It can be caused by the slurry distribution on the pad or the high additive concentration. We will have a completed analysis of the ratio of slurry B and additive analysis and also dig more deeply about how slurry react with additive and what factor would be the major driving force of poly process in the full paper.

Figure 1
(Invited) Development of Periodically Oriented Gallium Nitride for Frequency Conversion
Authors: Hite Jennifer K , Freitas Jaime A. , Mastro Michael A , Brown Christopher G. , Leach Jacob , Udwary Kevin , Kub Francis J , Bowman Steven R. , Eddy Charles R.
Published: February 2020

Gallium nitride is a semiconductor widely used in both optical and electronic devices. The polarity of GaN (+/- c-direction) influences many properties of the resultant material, including chemical reactivity and electric field in these ‘spontaneously polarized’ materials. By engineering inversion layers, we have demonstrated control of GaN polarity on both polar faces of GaN. By employing a selective growth method to deposit the IL, the lateral polarity of the GaN can be alternated, thus enabling structures referred to as periodically oriented (PO) GaN. We have shown such structures on both N-polar and Ga-polar native substrates by changing the IL material.

On N-polar substrates, we demonstrated that optimization of the MOCVD growth rates resulted in sharp, vertical interfaces and smooth surfaces. This work has moved the technology substantially closer to practical non-linear optic emitters by using HVPE to extend the PO GaN templates on N-polar substrates to total thicknesses of up to 500 μm, while faithfully maintaining the pattern of alternating polarity. Additionally, cross-sectional cathode-luminescence (CL) imaging of such an extension shows that the large initial dislocation densities occurring in the original inversion layers greatly decreased after about 25 μm of regrowth. The results of phase matching experiments with these structures will be presented, with discussion on fabrication issues.

These methods of GaN polarity inversion offer the promise of engineered materials with custom lateral and vertical polarity variations for applications in novel electronic and optoelectronic devices, a subset of which are expected to be suitable for non-linear optics.
Formation of CdS Thin Film on Different Substrates Using Electrochemical Atomic Layer Deposition (E-ALD)
Authors: Shen Sheng , Stickney John Lewellen
Published: February 2020

With solar energy being a promising alternative to fossil fuels, the need for high quality and high efficiency photovoltaic (PV) materials is obvious. As a major component in thin film solar cells, CdS thin film can be combined with absorber layers such as CdTe or CIGS (Cu, In, Ga, Se) to form p-n junction for light energy conversion.1 Electrochemical deposition is a low cost and controllable method for the fabrication of CdS thin films. Electrochemical atomic layer deposition (E-ALD) is the electrochemical form of atomic layer deposition that utilizes surface limited reaction to deposit one or less than one layer of element each time.2-3 High quality thin films can be using E-ALD but may take a relatively long time. Thus E-ALD is particularly suitable for making CdS films where a thickness as low as 50 nm is sufficient for the heterojunction formation.4 CdS thin films on Au have been made using E-ALD, and the film thickness increases linearly with increasing cycle number. The resulting CdS thin film is a single crystal with cubic <111> structure. SEM images show a conformal coating of CdS on Au substrate with a grain size of around 70 nm.

The same method is applied to form CdS thin film on Ag and Ag nanorods for enhanced photoelectrochemical response. Preliminary study of CdS deposition on indium-tin-oxide (ITO) has been conducted by reducing the oxide substrate to a minimum amount of metallic surface to increase the nucleation sites for film growth.
Terahertz Dielectric Response of Nonpolar a-plane GaN Films
Authors: Jang Soohwan , Jung Sunwoo , Park Jaehun , Kim Seungheun , Baik Kwang Hyeon
Published: February 2020

The generation and the detection of the THz radiation in the frequency range of 0.1 to 10 THz have attracted much research interest, which was mainly driven by the particular applications of THz time-domain spectroscopy (TDS) in physics, chemistry, nano and life sciences. THz TDS has shown many advantages due to its non-destructive analysis feature in characterizing complex dielectric properties and understanding the carrier-dynamics in various semiconductor materials. Extensive studies have been reported on the THz dielectric and optical properties such as electro-optical effects, optical rectification, and birefringence. In addition, the ultrafast relaxation and recombination dynamics of photogenerated carriers were investigated for new materials such as carbon nanotube, graphene, and perovskites using optical pump THz-probe spectroscopy.

Recently, the terahertz (THz) quantum cascade lasers and intersubband transition devices has attracted considerable attention based on AlGaN/GaN quantum well structure for far-infrared applications. It is necessary to investigate the optical and dielectric properties of GaN and sapphire crystals in the far IR as well as THz frequency regions. In the previous report, nonpolar and semipolar GaN crystals in the hexagonal crystal system are found to show multi-phonon mode behavior in the far-infrared frequency region. In addition, the polarized IR reflectance response of sapphire is reported to exhibit the dependence on the crystal orientation. In this paper, we investigated the optical properties and dielectric response of nonpolar a-plane GaN (a-GaN) films in the terahertz (THz) frequency using polarized femto-second THz TDS. The phase separation and amplitude ratio were measured by changing the crystal orientation with respect to the polarization of the incident THz pulse. In sharp contrast with polar c-plane GaN, nonpolar a-GaN films exhibited the angle dependence of the THz absorptions at room temperature, presumably due to the birefringence in nonpolar a-GaN films. The transmitted THz signal intensity, the time delay, and the Fourier-transformed amplitude were investigated by rotating the azimuth angle of the crystal orientation. Strong THz field absorptions around 1 THz frequency were observed at the azimuth angle of 0°, 90°, and 180° for a-GaN films. We believe that the birefringence in the THz frequency region originates from the difference of the transverse-optical and the longitudinal optical phonon splitting between the optical phonon branches.
(Invited) Application of Extended-Gate Field-Effect Transistor Sensors with Molecularly Imprinted Polymer Recognition Layers for Determination of Renal Dysfunction Biomarkers
Authors: Iskierko Zofia , Sharma Piyush Sindhu , Fronc Krzysztof , D'Souza Francis , Noworyta Krzysztof R.
Published: February 2020

In this presentation, we will discuss development of molecularly imprinted polymer (MIP) films selective towards some prospective biomarkers of renal dysfunction, namely, inosine and lipocaline-2. This artificial recognition units can easily be integrated with extended gate-field effect transistors (EG-FETs) allowing for development of selective and robust chemosensors for the target analytes [1, 2].

For the last decade, chemically-sensitive ﬁeld-effect transistors (ChemFETs) have been applied as transduction units in chemosensors. They offer numerous advantages, such as, ease of miniaturization, possibility of high-throughput sensing, high sensitivity, important detection limit, and possibility to adjust sensitivity according to specific needs. Various reports have described great variety of such devices for determination of different analytes of interest, ranging from ions, gases, small molecules, macromolecules and even whole viruses [3, 4]. Selectivity of the devised chemo- and biosensors is typically introduced by modifying gate region of the FET with suitable recognition units selective towards the analyte. In this regard, MIPs are attractive artificial recognition units offering good sensitivity and selectivity combined with robustness and resistance to harsh experimental conditions [5]. Here, we have made an attempt to combine the selectivity and robustness of MIPs with sensitivity and amplification features of EG-FET transducers to devise sensitive and selective chemosensors for selected bioanalytes.

Bibliography

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Y. Cheng, et al., Biosens. Bioelectron., 26, 4538, (2011).

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Acad. Sci. U.S.A., 101, 14017 (2004).

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Figure 1
Investigation of DNA Detection Mechanism with AlGaN/GaN High Electron Mobility Transistor (HEMT) Biosensor in High Ionic Strength Solution
Authors: Chen Yen Wen , Hsu Chen-Pin , Sarangadharan Indu , Wang Yu-Lin
Published: February 2020

In this research, the electrical double layer HEMT device is used to serve as the DNA biosensor. In this experiment, we try to use the DNA sequence of miRNA-126, which serve as a novel biomarkers of cardiovascular disease (CVD), to test the ability of the novel DNA sensors.

Debye length has been a haunted problem among all the field effect transistor (FET) biosensor for years. As the Debye length is extremely low in high ionic strength solutions, the traditional FET may not be direct detect the biomolecular. The novel HEMT sensors using AlGaN/GaN can performs high sensitivity and great specificity in DNA sequences testing. The sensitivity can be down to the 1fM and the specificity measurement can separate the signals between two DNA sequences with two mismatch differences. Furthermore, the mechanism of the sensor structure has also been studied. Since the structure of the device has the separation between source drain channel and gate electrode, the comparison with different electrode area and gap distance has been done as well. With repeating electrical measurement confirming, the reusability can also be seen after the 95℃ dehybridization process.

With the Gibbs free energy of the specific sequences, we can also predict the equilibrium reaction constant and the binding ratio of probe DNA with the target DNA. The comparison between the thermal dynamics with the experiment consequence has been demonstrated too.

Figure 1
(Invited) Plasmon-Enhanced Hybrid Materials for Global Health Solutions
Authors: Urban Jeffrey J
Published: February 2020

New methods for scalable water desalination has been identified as the most impactful and necessary scientific technology for human prosperity in a 2015 report by the Institute for Globally Transformative Technologies, surpassing malaria vaccines, synthetic fertilizers, and improved TB drugs. Due to the climate change, rapidly expanding global population, and worldwide water scarcity, the demand for purification of non-traditional sources such as brackish and seawater with low environmental impacts is extensively growing. There is an increasingly urgent need for low-cost methods for water desalination that can effectively couple to, or piggyback on, renewable energy sources. In this talk I will describe our efforts in developing new materials to enhance the efficacy and utility of forward osmosis using new plasmonically-enhanced hybrid materials.

Classical membrane-based water separation and purification processes such as forward osmosis (FO) is gaining renewed attention as a potentially low-energy alternative technique to energy intensive methods such as distillation, reverse osmosis (RO), multiple effect distillation (MED), etc. Unlike RO, the industry standard for desalination, where energy intensive hydraulic/external pressure drives water flow, here an internal pressure (osmotic) drives flow. It has the characteristics of no/low pressure operation compared to standard RO processes. Consequently, membrane fouling is potentially much less severe and thinner membranes can be used. These advantages make FO extensively applied to a variety of fields to date, which could potentially relieve the stress of freshwater scarcity. As the draw solution is one of the main contributing factors to the FO process, the lack of suitable draw agent has become the obstacle jeopardizing the real application of FO in desalination process. In general, an ideal draw agent needs to provide high osmotic pressure and expel water from itself with minimal energy input. Present FO technology relies on either non-reusable draw agents or draw agents that require complicated process for regeneration.

This talk will discuss development of new classes of inorganic/organic hybrid draw agents, which exhibit high osmolalities and easy regeneration process by utilizing industrial waste heat or naturally abundant (solar, geothermal) sources. Results on the design, performance, and integration of these new draw agents will be discussed.
(Invited) Nanostructured Silicon for Optical Modulation of Biological Systems
Authors: Tian Bozhi
Published: February 2020

Biological systems are organized hierarchically, with unique characteristics and functionalities spanning multiple length scales; some examples include collagen fibers, metabolic networks, and chromosome organization. It is important to select the right organizational length scale for device and biointerface design. In the case of sub-cellular organization, this length scale is on the order of tens to hundreds of nanometers. In this talk, I will present several chemical strategies for nanostructured silicon-based materials. These materials are deformable and have been tested with extra- and intracellular components (i.e., cytoskeleton and phospholipid bilayer) with an initial emphasis on optical control. These studies will deepen our understanding of the fundamental limits of physical and biological signal transduction between subcellular components and synthetic systems. At the end of my talk, I will discuss future opportunities in materials science toward seamless biointegration.
(Invited) Flexible Piezo-, Tribo-Electric Energy Harvesting Devices for Self-Powered Nanosensor Systems
Authors: Lee Minbaek
Published: February 2020

Flexible devices have been drawn a great attention as next-generation electronic devices. Especially for flexible and wearable system, the challenge to achieve such systems are the development of functional and flexible new materials and unique integration method of conventional devices into flexible ones including high performances. Nevertheless, such nanosystem also requires a power source to make the entire package small, sustainable and even long lasting. In this regards, harvesting energy from the environment is a choice for powering nanosystems. As for the goal, it is desired to explore flexible and wearable devices for scavenging energy around our surroundings, thus it can supply the power to nanosensor system without consuming much battery or to supporting battery life. Here, we will present some approaches for converting mechanical energy into electric energy using piezoelectric or triboelectric effects. This technology may make it possible to harvest energy from certain mechanical movements or human activity. Moreover, self-powered nano-sensor systems have been fabricated by combining the energy harvesting technology which ensures its compatibility and perspective. The presentation will be continuously dedicated to recent developments and improvements of energy harvesting technology towards self-powered nano-systems such as mobile electronics and wearable healthcare.
(Invited) Point-of-Care Diagnostics with Inkjet-Printed Microchips
Authors: Lesch Andreas , Jović Milica , Baudoz Marie , Zhu Yingdi , Tacchini Philippe , Gumy Frédéric , Girault Hubert H
Published: February 2020

Point-of-Care (POC) diagnostics grows currently in importance. Portable devices with electrochemical detection are very attractive for the rapid and low cost identification of diseases, especially when centralized laboratories with well-equipped, automatized analytical setups are either not available or results need to be obtained rapidly on site. There is a need for portable POC devices in developing and emerging countries, but also in developed countries. Electroanalysis, often in combination with immunoassay-based detection, provides sensing platforms with high sensitivity and reproducibility without suffering from optical interferences as optical detection methods can often do.

For electroanalytical sensors, the selection and costs of the electrode materials and sensor fabrication strategies play major roles. Such considerations need to be made for the complete development chain from designing a sensor, fabricating and optimizing prototypes until reaching the industrial production scale. We found that inkjet printing, which is a digital and mask-less material deposition technique where picoliter droplets of functional inks are jetted with high precision, is the ideal tool for process development of commercial electroanalytical platforms.

Herein, we demonstrate the large-scale fabrication of electrochemical microchips with up to eight parallel 50 µL wells containing each carbon nanotube working and counter electrodes, silver/silver chloride quasi-reference electrodes and a dielectric layer to define accurately the dimensions of the electrodes. The employed carbon nanotubes show a superior electrochemical behaviour and the multi-layer inkjet printing process provides highly reproducible electrode surfaces. We shall demonstrate the application as sensing platforms for antioxidants and hormones in several biological fluids using a portable, in-house made multichannel potentiostat.

References

[1] http://lepa.epfl.ch/SENSaSION

[2] A. Lesch, F. Cortés-Salazar, M. Prudent, J. Delobel, S. Rastgar, N. Lion, J.-D. Tissot, P. Tacchini, H. H. Girault, J. Electroanal. Chem., 2014, 61-68, 717.

[3] M. Jović, Y. Zhu, A. Lesch, A. Bondarenko, F. Cortés-Salazar, F. Gumy, Hubert H. Girault, J. Electroanal. Chem., submitted.

[4] A. Lesch, F. Cortés-Salazar, V. Amstutz. P. Tacchini, H. H. Girault, Anal.
Chem., 2015, 87, 1026.

[5] A. Lesch, S. Maye, M. Jović, F. Gumy, P. Tacchini, H. H. Girault, In Biotech, Biomaterials and Biomedical TechConnect Briefs, 2016, 3, Chapter 4: Sensors, Diagnostics & Imaging, 121.