bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Germanium at the Atomic Scale
Authors: Goldberger Joshua E.
Published: February 2020

Similar to how carbon networks can be sculpted into low-dimensional allotropes such as fullerenes, nanotubes, and graphene with fundamentally different properties, it is possible to create similar “allotropes” of Si or Ge with unique optoelectronic properties as well. Here, we will describe our recent success in the creation of hydrogen and organic-terminated germanium graphane analogues, or germananes, from the topochemical deintercalation of CaGe2. We will discuss how the optical, electronic, and thermal properties of these materials can be controlled by substituting either the surface ligand or via alloying with other Group IV elements. Additionally, we have also developed an epitopotaxial approach for integrating precise thicknesses of Germanane layers onto Ge wafers that combines the epitaxial deposition of CaGe2 precursor phases with the topotactic interconversion into the 2D material. These materials represent a new class of covalently terminated graphane analogues and have great potential for a wide range of electronic, optoelectronic and sensing applications, especially since theory predicts these materials to have direct and tunable band gaps around 1.5 eV and electron mobilities that are around five times higher than that of bulk Ge.
(Invited) High Ge Content SiGe Thin Films: Growth, Properties and Integration
Authors: Hikavyy Andriy Yakovitch , Rosseel Erik , Dhayalan Sathish Kumar , Witters Liesbeth , Mertens Hans , Bender Hugo , Favia Paola , Loo Roger
Published: February 2020

Although SiGe with low Ge content was used in BiCMOS devices for a relatively long time, its integration in pMOS transistors at 90 nm technological node opened for SiGe totally new horizons. During the course of years Ge content in SiGe gradually increased, as well as its influence. Nowadays, practically every pMOS transistor is using SiGe either as a strain booster in the case of high performance pMOS or as a SiGe channel allowing Vt correction of low power pMOS transistors. Integration of high mobility materials (SiGe, Ge) in the fin FET fashion seem to be rather logical step in order to move to the next 10 nm technological node and beyond.

In this contribution we will first discuss the growth of SiGe with high Ge content with different precursors like silane, disilane, germane and digermane (Fig. 1).

Next we will elaborate on relaxation of SiGe thin films (plastic and elastic (Fig. 2)) and SiGe processes selectivity.

Finally we will present the integration of high Ge content SiGe in different types of pMOS transistors: Si FinFETs, strained SiGe core FinFETs, strained SiGe cladding FETs and strained Ge FETs (Fig. 3).

Challenges and possible solutions for different pMOS approaches listed above will be put forward.

Acknowledgements

The imec core CMOS program members, European commission, local authorities and imec pilot line are acknowledged for their support.

Fig.1 Ge concentration of SiGe grown with different precursors at different temperatures.

Fig.2 An example of elastic relaxation of SiGe caused by too high process temperature.

Fig.3 Examples of SiGe integration in different device structures. 1) SiGe S/D of Si fin; 2) SiGe core pMOS; 3) SiGe cladding pMOS. 4) SiGe S/D on rGe pMOS.
(Invited) Integrating Classical Semiconductor Devices with Si/Sige Quantum Dots
Authors: Ward Daniel R , Foote Ryan H , Gamble John King , Savage Donald E , Lagally Max G , Coppersmith Susan N , Eriksson Mark A
Published: February 2020

As semiconductor based quantum devices scale up from single to multiple qubits there is an increasing need to integrate classical semiconductor based devices to manage and generate control signals. We discuss progress on integrating field-effect transistors with planar quantum dot devices to achieve a high level of device throughput by creating on-chip multiplexers for our devices. Using the on-chip multiplexers we can overcome the challenge of the limited number of electrical connections available in a typical dilution refrigerator while still working at the milli-Kelvin temperatures necessary for quantum operations. Additionally, we report on recent work on gate designs for scaling up to multiple, coupled Si/SiGe qubits. In particular we discuss the design, fabrication and initial characterization of quadruple quantum dot devices.

This work was supported in part by the U.S. Army Research Office (W911NF-08-1-0482, W911NF-12-1-0607), the United States Department of Defense, and by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressly or implied, of the US Government. Development and maintenance of the growth facilities used for fabricating samples is supported by DOE (DE-FG02-503ER46028).
Thermoelectric Properties of Small Bandgap Semiconductor Nanowires: The Effects of 1D Electron Subband Formation and Phonon Boundary Scattering
Authors: Gao Xuan
Published: February 2020

Nanomaterials such as nanowires or nanoribbons offer a promising platform for efficient thermoelectric energy conversion applications, owing to their greatly reduced thermal conductivity and potentially high power factor due to strong one-dimensional (1D) quantum confinement effects. While the thermal conductivity of nanomaterials is widely found to be suppressed, the 1D electronic quantum confinement effect tuned power factor remains elusive in experiment. Small diameter nanowires of InAs or InSb provides an opportunity to observe such 1D quantum confinement effect, thanks to their high electron mobility and small effective mass (i.e. long electron wavelength/large 1D subband spacing). We present a study of the thermoelectric properties of InAs nanowires where the gate was used to control the electrons' Fermi level. At temperatures below about 100K, oscillations in the thermopower and power factor due to the formation of 1D electron sub-bands are observed in semiconductor nanowires for the first time. We also discuss the limiting factors in the pursuit of 1D confinement enhanced thermoelectric performance in semiconductors and point out that disorder induced 1D energy level smearing sets the current bottleneck for achieving 1D quantum effect enhanced figure of merit or power factor at practical temperatures (e.g. 300K). We further discuss a recent study of Bi2Se3 nanoribbon's thermal conductivity by the three-omega method. The as measured thermal conductivity for a single Bi2Se3 nanoribbon is nearly two orders of magnitude smaller than the bulk value, which is attributed to enhanced phonon boundary scattering in nanostructured materials. This work is done together with M.R. Sakr, J.M. Kinder, M. J. MacDonal, D. Liang, G.D. Li, R. L.J. Qiu at CWRU and Y. Tian and H.J. Gao at Chinese Academy of Sciences. The authors acknowledge NSF CAREER Award (DMR-1151534), ACS PRF (48800-DNI10) and the NSF of China for support of this research.
Enhanced Thermoelectric Efficiency of Si-Ni Nanocomposite Films Grown on SOI and SOQ Substrates
Authors: Uchida Noriyuki , Ohishi Yuji , Miyazaki Yoshinobu , Kurosaki Ken , Yamanaka Shinsuke , Tada Tetsuya
Published: February 2020

To improve the poor thermoelectric performance of Si, reduction of the high thermal conductivity k
(~142 Wm–1K–1) is essential, and one of the effective methods to reduce the k
is making Si nanostructures such as Si nanocrystals (NCs) [1, 2] and nanowires[3], where the k
is dramatically reduced by enhancement of phonon scattering at the interfaces of the nanostructures. Recently, we developed semiconducting composite films of Si and Ni silicide NCs (Si-Ni nanocomposite film) deposited on SiO2 substrates [2]with the power factor of 1.9×10-3 W/mK2 , the thermal conductivity k of 4.4 W/mK, and the dimensionless figure of merit ZT of 0.13 for the B-doped (p-type ) nanocomposite film [2], which is much higher than that of bulk Si (ZT<0.01).

In this paper, we demonstrate the further improvement of the thermoelectric performance of B doped Si-Ni nanocomposite films by growing them on silicon-on-insulator (SOI) or silicon-on-quartz (SOQ) substrates. The B doped Si-Ni nanocomposite films were synthesized from amorphous Si-Ni-B films deposited on the SOI or SOQ substrates at room temperature (RT) with Ar sputtering of the B doped Ni-Si target (Ni:Si=1:20, 2mol% B). The amorphous films were annealed at 800°C in N2gas ambient, leading to crystallization and the phase separation of the films. After this annealing , rapid annealing of 10 sec at 1200°C was carried out to activate the B atoms.

In Fig.1, the ZT values are plotted against the k
valuesof Si-Ni nanocomposite films on SOI, SOQ, SiO2 substrates [ 2], and Si nanocomposite by Bux et al. [1] at RT. We observed low k
values (< 4 W/mK) of Si-Ni nanocomposite films on SOI and SOQ, which were similar k with Si-Ni nanocomposite film on SiO2, due to phonon scattering at interfaces on NCs. As seen, the ZTs (0.23-0.36) of the Si-Ni nanocomposite films on SOI and SOQ substrates were much higher than those of the Si-Ni nanocomposite films on SiO2 and the Si nanocomposite. We observed with cross-sectional transmission electron microscopy that Si NCs in Si-Ni composite films were epitaxially grown from thin Si crystal layers of SOI /SOQ substrates, leading to improvement of the crystal quality of Si NCs in the nanocomposite films and increase of the carrier conductivities, the Seebeck coefficients and the ZTs.

This work was partly supported by ALCA-JST.

[1] S. K. Bux, et al., Adv. Funct. Mater. 19, 2445 (2009). [2] N. Uchida et al., J. Appl. Phys. 114, 134311 (2013). [3] A. I. Hochbaum, et al., Nature 451,163 (2008).
Wrappable, Stretchable and Transparent Photodetectors using a Printed Nanowire Network Scheme
Authors: Lien Der-Hsien , Chen Shih-Bin , Chi Yu-Chieh , Wu Chung-Lun , Liao Ying-Chih , Lin Gong-Ru , Lee Si-Chen , He Jr-Hau
Published: February 2020

Flexible optoelectronics, a type of electronics that can be bended, wrapped and stretched, has attracted intensive interest and promise a variety of novel applications that are not achievable by current rigid substrates. Here we report the first fully-transparent, stretchable, and wrappable photodetector (PD) using an interlacing network nanowires scheme embedded in flexible polymer substrates by means of an all-printing approach. The devices made by ZnO nanowires, Ag nanowires and polyurethane (PU) show a transmittance over 80% in the visible region. Due to the protected junction between Ag and ZnO nanowires, the transparent PDs can work under extreme mechanical deformation, exhibiting excellent bending (bending radius < 5 mm) and stretching capability (strain > 80%). The robust nanoscale junctions enable the PD to be labeled on roughed surface or wrapped on curved surface, such as knees, noses, and optical fibers. The PD arrays wrapped on an optical fiber can serve as an optoelectronic instrument to characterize the leaky points of an optical fiber, capable of covering the blind zone of the conventional optical time domain reflectometer (OTDR) technique. The PD devices fabricated on curved surface can also treated as contact lens with bio-related applications. The PD would be a key electronic component directly to be implemented in the flexible electronic systems, such as wearable electronics, self-powered systems, functional clothes, and epidermal electronics.
Transparent Ga2O3 Photodetectors for Harsh Optoelectronics
Authors: Wei Tzu-Chiao , Tsai Dung-Sheng , Ravadgar Parvaneh , Ke Jr-Jian , Tsai Meng-Lin , Lien Der-Hsien , Huang Chiung-Yi , Horng Ray-Hua , He Jr-Hau
Published: February 2020

We fabricate fully transparent solar-blind DUV PD devices employing β-Ga2O3 as an active layer and indium zinc oxide (IZO) as the transparent electrodes, exhibiting the average transmittance up to 80% from visible to near IR wavelength region without image blurring. The β-Ga2O3 MSM PDs for the use in harsh environments show a very low dark current (~1 nA), no sign of breakdown even at a bias higher than 200 V, excellent thermal stability, and intrinsic solar blindness. The dark current of β-Ga2O3 MSM PDs under significantly different oxygen concentration in the ambiences is similar, indicating that the high inertness to surface effect due to superior crystallinity nature of β-Ga2O3. The working temperature is up to 700 K and the responsivity is 0.32 mA/W at 10 V bias under 185-nm illumination. β-Ga2O3 PDs can be fully recovered after 700-K operation, showing excellent thermal reliability and robustness. The intriguing optoelectronic and electrical properties of β-Ga2O3 promise a new generation of stable, solar-blind DUV PDs for the extremely harsh electronic applications, such as sensing, imaging, and intrachip optical interconnects in high-temperature environments.
Control of Thickness, Morphology and Band Gap of Poly-(3.4-ethylenedioxythiophene) Electrochemically Growth (e-PEDOT) to Use It as Anodic Buffer Layer in Organic Photovoltaic Cells
Authors: del Oso-Acevedo José Alfredo , Frontana-Uribe Bernardo A. , Maldonado-Rivera José Luis , Roa-Morales G. , Hernández Margarita Rivera
Published: February 2020

This contribution presents the electrochemical control of thickness, morphology and band gap of the polymer film poly[3,4-ethylenedioxythiophene] (PEDOT), which was obtained by electropolymerization of monomer 3,4-ethylenedioxythiophene (EDOT) in the transparent conductive indium-tin oxide (ITO). This study was carried out using mixtures of dry organic solvents such as acetonitrile, toluene and dichloromethane to determine the effect of the polarity solvent in the polymerization kinetics of the monomer EDOT. For this, cyclic voltammetry was used. It was observed that pure acetonitrile and the acetonitrile-dichloromethane mixture (2:1, v/v), the polymerization kinetics is very fast and the obtained films showed similar responses in both cases, however, the kinetics obtained for the mixture of toluene-acetonitrile (4:1, v/v) was slower, indicating that in a medium of higher polarity, the polymerization kinetics is much faster than in a medium of lower polarity. This fact coupled with low concentrations of monomer EDOT, let us to control the thickness and morphology of the electropolymerized PEDOT films (e-PEDOT). An optimization of the desired film properties was achieved through the implementation of the chronoamperometric technique (CA) for the electropolymerization. Here, the time of deposit and a low concentration of the EDOT monomer gave the desired thickness of the polymer film with a uniformly rough morphology. Furthermore, the study of the response UV -Vis of the films e-PEDOT was performed and found that optical band gap depends on the experimental conditions used to obtain the e-PEDOT films. Finally, these e-PEDOT films were used as buffer layers in organic photovoltaic cells (OPVs) with bulk heterojunction architecture and their performance was compared with those constructed with the classical spin cast deposited PEDOT-PSS buffer layer.

Acknowledgments: Funding for this research was obtained by CONACYT-CB project number 179356. The technical AFM support of Ing. Mario Monroy (Instituto de Física UNAM)
Study on Thermal Stability of Dendritic Silver-Coated Copper Powders Fabricated by Galvanic Displacement Reaction
Authors: Zhuo Kai , Park Yu-Seon , Seo Nary , Chung Chan-Hwa
Published: February 2020

Metals of Group IB due to their higher electrical and thermal conductivities have been thoroughly studied. Particularly, silver electronic slurry extensively used as electrode material in various resistance devices and electromagnetic interference(EMI) shielding materials. But Ag ions cause electro-migration phenomena in hot and humid conditions, which results in decreasing the conductivity and increasing the coating resistance in certain conditions. Copper relatively lower in cost and having good conductivity as silver, but the problem is copper oxidizes when exposed to air. To prevent oxidation of copper, silver coating on copper powder have been reported in many articles.

In structural perspective, the dendritic structure has many superior properties, such as large surface area and good conductivity. Therefore, it is commendable to explore the mechanism of dendritic copper metallic materials formation.

In this presentation, we are reporting a simple fabrication method for copper powder and silver coated copper powder with dendritic morphology at low temperature. To improve the dendritic structure, the galvanic displacement reaction and hydrogen evolution reactions have been applied together. The formation mechanism of Cu dendritic structures on the basis of effect of concentration, termination time, anion concentration, and additives have been prudently analyzed. In addition, we have also analyzed the thermal stability of silver-coated copper powders performance at different temperature.

Figure 1. SEM images of (a) dendritic copper powders and (b) cross section of silver-coated copper powders fabricated by galvanic displacement reaction.

References:

1. B. K. Min and C. M. Friend, Chem. ReV., 107, 2709 (2007).

2. X. Zhu, X. Gan, J. Wang, T. Chen and G. J. Li, Mol. Catal. A: Chem., 239, 201(2005).

3. X. Chen, C. H. Cui, Z. G, J. H. Liu and X. J. Huang, small, 7(7), 858 (2011).

4. X. G. Cao and H. Y. Zhang, Electron. Mater. Lett., 8(4), 467 (2012).

5. M. Wu, B. P. Lin, Y. Cao, J. G. Song, Y. Sun, H. Yang and X. Q. Zhang, J. Mater. Sci.: Mater. Electron., 24, 4913(2013).

6. Y. K. Zeng, T. T. Li, M. F, S. L. Jiang and G. Z. Zhang, J. Alloy Comp., 585, 277 (2014).

7. R. Qiu, H. G. Cha, H. B. Noh, Y. B. Shim, X. L. Zhang, R. Qiao, D. Zhang, Y. I. Kim, U. Pal and Y. S. Kang, J. Phys. Chem. C, 113, 15891 (2009).
Invited: Scaling Mosfets with Self-Aligned Super-Steep-Retrograde-Well
Authors: Zhu Huilong
Published: February 2020

With aggressively reducing of MOSFET area or IC manufacturing costs, the design space to satisfy both device performance and power consumption requirements becomes very limited. Although strain engineering and high-k/metal gate (HKMG) technique were successfully used to scale planar bulk device down to 28nm technology node, further reduction of gate length requires use of fully depleted channel (FDC) to control short channel effect (SCE). FinFET [1] and UTBB SOI [2] are two typical device structures using FDC. However, significant structural and process changes are involved for both FinFET and UTBB SOI implementations. Super steep retrograde well (SSRW) [3] can be used to reduce depleted depth in the channel of bulk MOSFETs with minor process changes. Two major drawbacks for the devices with SSRW are 1) large band-to-band tunneling (BTBT) or leakage between SSRW and source/drain/extension caused by high doping level and 2) difficult to keep abruptness of SSRW due to large thermal budget used in fabrication process, especially source/drain annealing. To fully take the advantage of state-of-the-art integration flow of all gate last HKMG [4], we propose a new method, called self-aligned SSRW, which forms a SSRW self-aligned to the gate of a bulk MOSFET in replacement gate process. The formation of self-aligned SSRWs can avoid source/drain annealing step and reduce the overlap between SSRW and source/drain/extension. A steep retrograde well can be achieved by a relatively low temperature spike annealing or laser annealing.

Self-aligned SSRW CMOS devices have been fabricated on 200mm Si wafers in our lab. In this paper, we will review and report the first self-aligned SSRW nMOSFETs and pMOSFETs with all-last HKMG process. To investigate the SCE control and BTBT effect by SSRW, an asymmetrical device structure, replaced metal spacer gate (RMSG) MOSFET with an asymmetrical SSRW doping is also introduced. The MOSFETs with self-aligned SSRWs show good SCE control and low off current at a gate length of 25 nm. Dramatically improved DIBL and Ion/Ioff characteristics have been achieved when SSRW doping is used to replace the conventional halo doping. It turns out that with self-aligned SSRW drain-to-body leakage is reduced by upto two decades due to reduction of BTBT leakage current between channel and SD/extension. We have demonstrated that the self-aligned SSRW process is simple and fully compatible with state-of-the-art all gate last CMOS technology, promising for device performance improvement and mass production towards scaling of MOSFETs. Simulations and further improvements for bulk and SOI MOSFETs with self-aligned SSRWs are also discussed.

[1] C. H. Jan et al., IEDM Tech. Dig., pp. 44-47 (2012)

[2] L. Grenouillet et al., IEDM Tech. Dig., pp. 64-67 (2012).

[3] Z. Ren et al., IEDM Tech. Dig., pp. 733 – 736 (2005).

[4] P. Packan et al., IEDM Tech. Dig., pp. 2841-2844 (2009)
Effects of Doping, Strain and Size on the Electrical Properties of MoS2 Nanoribbons
Authors: Yu Sheng , Li Qiliang , Eshun Kwesi
Published: February 2020

Two-dimensional (2D) transition metal dichalcogenides (TMDs), such as isolated monolayers or few-layers of MoS2 and WSe2, have recently gained intensive interest for their potential in future electronics [1]. The bulk of TMDs usually have a layer structure which is similar to graphene. Because the layers are bound together by weak van der Waals forces, an isolated monolayer of TMDs can be easily obtained by cleaving technique. Unlike graphene, these 2D materials have a significant band gap and exhibit attractive semiconductor properties. Therefore, the 2D TMDs have been widely considered for the ultimately thin channel materials in future Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs) to suppress short channel effects. Especially, TMD monolayers usually have a direct band gap, very attractive for the mixed electronic and photonic application in future logic and memory devices [2].

During the integration of these 2D materials into electronic devices, e.g., as the channel materials in MOSFETs, they will be defined by lithography into nanoribbons, doped into n- or p-type, and stressed by the strain induced from the metal contacts and dielectric interface. In this work, we have studied the effects of these factors on the band structure and electrical properties of MoS2monolayers by using a numerical simulation method based on density functional theory. We found that the doping, strain and size could induce significant variation in the electrical properties of these 2D materials. These will be very challenging issues for the 2D materials.

In this work, we first studied the size effect on the properties of MoS2 monolayer nanoribbons. We found that the band gap of MoS2 nanoribbons changed from 1.8 eV of an infinite MoS2 sheet to 1.2 eV of a 10×10 (in molecule) MoS2 nanoribbons or 0.5 eV of a 5×10 MoS2 nanoribbons. We also found that the doping level and dopant position have a significant effect on the electrical properties of MoS2 nanoribbons. The doping level and dopant position can induce large variation (30%) in sheet resistance. This variation in electrical properties may post a serious challenge on the application in logic and memory devices. In addition, we found that the strain will also significantly affect the electrical and carrier transport properties of MoS2 monolayer. Under different strain, the MoS2 will change from direct band-gap to indirect band-gap semiconductor. As the strain further increases to certain value, the MoS2will become metallic.

In summary, this work demonstrated that the size, doping and strain have a significant effect on the 2D materials and will induce large variation in electrical properties. Therefore, the future integration of such 2D materials for logic or memory circuit application, the size, doping and strain must be well engineered and controlled in order to minimize the device variation.

References:

1. B. Radisavljevic et al., Nat. Nano. 6, 147 (2011)

2. Z. Yin et al., ACS Nano. 6, 74 (2012)
1D Photonic and Electrochromic Nanomaterials Applications
Authors: Redel Engelbert
Published: February 2020

Porous hierarchical and photonic materials assemblies will be presented from a library of different metal oxide nanomaterials and hierarchical multilayer constructions. Potential applications of such materials will be presented, reaching from optical and tune able and porous 1D photonic crystals (PCs) to transparent and conductive oxides (TCOs) porous thin films, white light broad-band bragg reflectors as well as electrochromo-photonic switches. Furthermore, the optical and dielectric properties of single porous SURMOF thin films as well as multilayered photonic SURMOF-Hybrid and electrochromic SURMOF materials will be presented.

1 a) E. REDEL, C. HUAI, M. RENNER, G. V. FREYMANN, G. A. OZIN SMALL 2011, 7, 3465-3471. b) E. REDEL, P. MIRTCHEV, C. HUAI, S. PETROV, G. A. OZIN ACS NANO, 2011, 5, 2861-2869.

2 E. REDEL, C. HUAI, S. PETROV, D. OMER, P. O'BRIEN, M. G. HELANDER, J.MLYNARSKI, G. A. OZIN, SMALL 2012, 8, 3806-3809.

3 E. REDEL, J. MLYNARSKI, J. MOIR, A. JELLE, C. HUAI, S. PETROV, M. G. HELANDER, F. C. PEIRIS, G. V. FREYMANN, G. A. OZIN Adv. Materials 2012, 24, OP265-OP269.

4 E. REDEL, Z. WANG, S. WALHEIM, J. LIU, H. GLIEMANN, C. WOELL, Appl. Phys. Lett. 2013, 103, 091903; doi: 10.1063/1.4819836

5 J. LIE, E. REDEL, S. WALHEIM, Z. WANG, V. OBERST, J. LIU, S. HEISSLER, A. WELLE, T. SCHERER, M. BRUNS, H. GLIEMANN, C. WOELL Adv. Materials 2014, doi: adma.201402505
Electrokinetic Trapping and Patterning of Colloidal Particles in Asymmetric Ratchet Microchannels
Authors: Kale Akshay , Lu Xinyu , Patel Saurin , Xuan Xiangchun
Published: February 2020

Insulator-based dielectrophoresis offers advantages over electrode-based dielectrophoresis in many ways, and has been extensively used to manipulate particles and biological species in lab-on-a-chip devices. This work exploits insulator-based dielectrophoresis in two configurations of asymmetric ratchet microchannels to trap and concentrate microscale particles using DC-biased AC voltages. It demonstrates that the dynamics of the trapping pattern in ratchet microchannels changes in response to voltages higher than the threshold trapping voltages, and also changes with progression of the trapping experiment. Numerical modeling is used to support and validate the results, and the physical interpretations of the changing dielectrophoresis are explained using a defined dimensionless trapping number. It is revealed that the orientation of the asymmetric ratchet relative to the direction of the applied DC electric field plays a key role in determining the particle trapping patterns in the ratchets.
Micro-Fabrication of a Compact Air-Breathing Microfluidic Fuel Cell and Its Electrochemical Evaluation for Formic Acid and Glucose
Authors: Chávez Ulises , Dector Andres , Moreno Alonso , Ledesma-García Janet , Arriaga Luis Gerardo
Published: February 2020

Microfluidic fuel cells (μFFC) are emerging as a promising solution for small-scale power demands. Some fuels frequently used in microfluidic fuel cells are formic acid [9–13], methanol [14,15] and glucose [16–18]. This work reports the air-breathing μFFC evaluation using 1.5 M formic acid in 0.5 M H2SO4 or 5 mM Glucose in KOH as fuels and the integration of an air-exposed electrode as cathode enabling oxygen delivery directly from air.

The formic acid μFFC employed Pd/XC-72 and Pt/XC-72 as electrocatalyst for anode and cathode respectively. Moreover, Au/C and Pt/XC-72 were employed as anode and cathode respectively for the glucose μFFC.

Both μFFCs were assembled using a polymethylmethacrylate (PMMA) plate where the microfluidic channel was engraved as shown in figure 1. Polarization curves were obtained from an Epsilon/Bas potentiostate 1.40.67 (Bioanalytical Systems).

Fig. 1. Schematic diagram of the air-breathing μFFC. All elements were assembled and tightened homogeneously by screws. The μFFC microchannel is 900 µm wide, 2 cm long and 50 µm depth; the electrode active area is 0.09 cm2.

The maximum power densities achieved were 27 mW cm-2 for the formic acid μFFC and 1.63 mW cm-2 in the case of glucose μFFC. These results have shown that the oxygen reduction reaction have been enhanced by the air-breathing adaptation in comparison with similar acid formic or glucose-μFFCs which operate with an oxygen-saturated aqueous stream.
Design of a Microfluidic Chip System Based on Magnetoelastic Sensors for Blood Coagulation Measurement
Authors: Chen Xi , Yang Jun , Hu Ning , Luo Hong-yan , Gao Xue-mei , Song Ling-ju , Liao Yan-jian
Published: February 2020

Blood coagulation measurement can provide the valuable indicators for diagnosing the hemorrhagic and thrombus disease, observing the curative effect of dissolving thrombus as well as preventing clotting. The novel design of a microfluidic chip system based on the magneto-elastic sensors for blood coagulation measurement is presented in this paper. Firstly, several thick films of iron-based amorphous alloy with the different specifications were selected to compose a magnetoelastic sensor group. Then this sensor group was packaged and bonded in a PDMS microfluidic chip to form a plurality of detection channels that can be used to simultaneously detect the multiple coagulation factors. The whole chip was fixed into a coil through a specific mold. Once the reagent and sample flow path was connected, the magneticelastic detection system could be used to measure multiple parameters including prothrombin time (PT), thromboplastin time (APTT), prothrombin time (TT). The preliminary experimental results have verified the feasibility of the design. The magnetoelastic sensor exhibits the wireless, passive, easily miniaturized and integrated features. These are combined with the microfluidic chip detection technology in this design to realize the multi-channel simultaneous detection of multiple parameters. Therefore, it has great potentials for clinic applications.
Study on a Microchip-Integrated Hemorrheology Analysis System
Authors: Chen Li , Zheng Xiao-lin , Hu Ning , Jiang Fan , Lin Bing-wen , Yang Jun , Liao Yan-jian , Luo Hong-yan
Published: February 2020

Blood circulation disorders are usually caused by abnormal blood rheology properties, among which blood viscosity is the most important physiological parameter. The level of blood viscosity can reflect blood transportation situation and blood supply. Along with the increase of viscosity and circulation resistance, blood flow velocity slows down. Blood flow to organs and tissues, especially microcirculation perfusion is inevitably reduced. Thus, ischemia hypoxia will result in tissue metabolism and function, even further symptoms of disease.

Although there are many pathogenic factors, such as hypertension, coronary heart disease, diabetes, cancer, peripheral vascular disease and anxiety, they are all related to abnormal blood viscosity. Currently most blood viscosity measuring instruments are single-purpose, expensive and non-portable, which can't fully satisfy patients’ requirements. In this paper, a rapid, accurate and versatile rheological analysis based on microfluidic systems is designed and realized. The system consists of micro-injection module, microchip module, image acquisition module and data analysis module. First, diluted blood was injected into a chip via micro-injection module. Furthermore, image acquisition module collected pictures of flowing liquid. By the analysis of data analysis module, we could obtain the viscosity of blood.

It’s worth mentioning that a novel lensless imaging device was designed and applied to image acquisition module compared with conventional microscopy at high magnification observation method. This device offers a relatively good image quality and has some obvious advantages as simple, low cost, small volume. Our experiment was carried on by using microscope imaging system, lensless imaging device and a commercial rheometer. Relative parameters were obtained and analyzed carefully.
Influence of Electrolytes on the Electronic Transfer in Electrode Materials: Ex- and In-Situ Dielectric Spectroscopy Study between 103 and 1010 Hz
Authors: Badot Jean-Claude , Seid Kalid Ahmed , Perca Cristian , Dubrunfaut Olivier , Soudan Patrick , Guyomard Dominique , Lestriez Bernard
Published: February 2020

The fruitful contribution of Broadband Dielectric Spectroscopy (BDS) to study hierarchical materials applied to batteries electrodes has been previously shown [1-5]. The results demonstrate that the broadband dielectric spectroscopy technique is very sensitive to the different scales of the electrode architecture involved in the electronic transport, from interatomic distances to macroscopic sizes, as well as to the morphology at these scales, coarse or fine distribution of the constituents. When the frequency increases, different kinds of polarizations appear from interatomic distances to macroscopic sizes (Fig. 1) and give rise to dielectric relaxations in the following order: (a) space-charge polarization (low-frequency range) due to the interface sample/current collector; (b) polarization of clusters of particles (micronic scale) and (c) polarization of particles due to the existence of resistive junctions between them; d) electron transfers (nanometric or interatomic scale).

The BDS measurement was up to now ex situ measurement, on dry electrode. They provide a fundamental insight into the conduction properties at all scales of the materials before being integrated in a real battery. An innovative device (measurement cell) has been developed to make synchronized BDS measurements and electrochemical cycling. The frequency range is about 103 - 1010 Hz. In this work, data acquisitions were made on dry electrode (LiNi1/3Co1/3Mn1/3O2 / Carbon black / PVdF) and then on the same electrode wetted with an electrolyte. Short- and long-range motions of ions are evidenced in the low-frequency region. At higher frequencies, the study shows for the first time the influence of the ions of the electrolyte on the transfer of the electronic charges (holes) in LiNi1/3Co1/3Mn1/3O2at the micronic scale.

Acknowledgements

Financial funding from CNRS, Université de Nantes, UMICORE, and the ANR program n° ANR-09-STOCK-E-02-01 is acknowledged.

References

1. J.C. Badot, E. Ligneel, O. Dubrunfaut, D. Guyomard, and B. Lestriez, Adv. Funct. Mater. 2009, 19, 2749.

2. J.C. Badot, E. Ligneel, O. Dubrunfaut, J. Gaubicher, D. Guyomard, B. Lestriez, Phys. Chem. Chem. Phys. 2012, 14, 9500.

3. K. Seid, J.C. Badot, O. Dubrunfaut, S. Levasseur, D. Guyomard, B. Lestriez, J. Mater. Chem. 2012, 22, 2641.

4. K. Seid, J.C. Badot, O. Dubrunfaut, S. Levasseur, D. Guyomard, B. Lestriez, J. Mater. Chem. 2012, 22, 24057.

5. K. Seid, J.-C. Badot, O. Dubrunfaut, M.T. Caldes, N. Stephant, L. Gautier, D. Guyomard B. Lestriez. Phys. Chem. Chem. Phys. 2013, 15, 19790.

Figure 1. Schematic description of a hierarchical architecture at different scales of a powdered material: different sources of polarizations vs. frequency and size.
State-of-Charge Mapping with Spatially Resolved XPS in Patterned Thin Film Battery Electrodes
Authors: Pearse Alexander J , Gillette Eleanor , Rubloff Gary W
Published: February 2020

Nanostructures offer the opportunity to design-in higher power capability and cycling robustness, but their spatial distribution of active ion storage material can pose major challenges in transporting electrons to all regions of active material. For example, high aspect ratio nanowire or nanotube electrodes on a planar current collector may require electrons to diffuse 10’s – 100’s μm though highly resistive oxide material before meeting an incoming lithium ion. While adding a conformal or coaxial current collector can improve performance at high rates, the characterization of this improvement must typically be inferred though bulk electrochemical measurements.

In this work, we develop a model system with which to directly measure the spatial distribution of state-of-charge (SOC) for a poorly conductive cathode material as a function of distance from a current collector and discharge rate using spatially resolved x-ray photoelectron spectroscopy (XPS). Our system includes a geometrically restricted electrode/current collector interface but a relatively unrestricted electrode/electrolyte interface. We fabricate electrodes with patterned planar current collectors using standard microfabrication techniques and deposit pinhole-free ultrathin films of the cathode material V2O5 using atomic layer deposition. These cathodes are then discharged in a liquid electrolyte under different rates and conditions, and the resulting SOC distribution is mapped using XPS with a lateral resolution as good as 15µm. Unlike microspot Raman or XRD, XPS provides a direct quantitative measurement of the SOC through the concentration of lithium ions and/or reduced vanadium ions (Figure 1). The latter is particularly appealing in that it is independent of surface contamination, providing an avenue towards SOC characterization even in the presence of a thin SEI layer. We also explore the depth dependence of the SOC using angle resolved XPS and ion beam depth profiling. Our measurements demonstrate that the electrode SOC decreases over a distance of order millimeters from the current collector at moderate rates, and that the shape and magnitude of the SOC gradient depends on the discharge rate. Finally, we compare our observations with simulations of the structure using COMSOL Multiphysics, and attempt to resolve discrepancies between the two. We believe this approach can provide design guidance for heterogeneous nanostructures applied to electrical energy storage. We anticipate this technique to be broadly applicable to other electrode materials and active ions.
Bis(fluorosulfonyl)Amide Anion Transfer at Graphite Electrode
Authors: Abe Takeshi , Miyazaki Kohei , Fukutsuka Tomokazu
Published: February 2020

As is well-known, many atoms and molecules can enter into graphite to form graphite intercalation compounds GICs). The application of GICs ranges from lithium-ion batteries to hybrid capacitors. The hybrid capacitor, which utilizes anion intercalation/de-intercalation at graphite positive electrode, can possess higher energy densities than electric double layer capacitors whose capacity is dominated by the amount of cation and anion adsorbed (desorbed) on activated carbons.

To increase the capacities of hybrid capacitors, it is necessary to increase the amount of anions intercalated into graphite. In other words, low-stage graphite intercalation compounds (GICs) must be formed. For the electrochemical anion intercalation, low-stage GICs are synthesized at higher potential exceeding 4.5 V vs. Li+/Li and therefore, oxidative decomposition of electrolyte solutions are not negligible at such high-potential region. Here we report electrochemical intercalation/de-intercalation properties of various anions at graphite electrodes, and show the anion intercalation kinetics.
XPS Study of the Porous Carbonaceous Positive Electrode Interface in Li-O2 Batteries upon Cycling
Authors: Guéguen Aurélie , Berg Erik J. , Novák Petr
Published: February 2020

Deep understanding of the reactions taking place upon cycling between the reduced oxygen species and the electrolyte and the porous electrode components is required in order to improve the electrochemical performance of Li-O2 batteries. Electrochemically formed products deposit in nano-meter thin layers on the cathode. X-ray Photoelectron Spectroscopy (XPS) is the most suitable characterization technique to investigate the extreme surface of materials.

0.2 M LiTFSI in diglyme was chosen as electrolyte for our study. In order to evaluate the influence of the nature of the carbon cathode on the electrochemical properties of the cell, electrodes containing different carbons (graphite SFG6 (TIMCAL), amorphous carbons Super C65 (TIMCAL)) were prepared by mechanical rolling using PTFE as a binder. The specific charge at the end of the 1st discharge was lower for graphite SFG6 (76-96 mAh/g) than for Super C65 (~ 350 mAh/g). It is consistent with the lower specific surface area of the graphite SFG6 (16 m2/g) compared to Super C65 (60 m2/g).

XPS data were collected on the carbonaceous electrodes at the end of the first discharge. For all electrodes the component belonging to the carbon backbone dominates the C 1s spectra (Figure 1c), indicating a thin interface layer (≤5 nm). LiF was detected at the surface of both electrodes but in a higher amount for graphite SFG6 (Figure 1a). Components at 54.8 and 531.7 eV on the Li 1s and O 1s spectra for the electrode containing amorphous carbon Super C65 can be attributed to the presence of Li2O2 (Figure 1a and 1b), but were not observed for graphite SFG6. Hence the type of carbon has an influence on the chemical composition of the interface layer formed on its surface upon discharge. In both cases, electrolyte degradation could be evidenced by presence of components on the C 1s spectrum at 287, 289 and 290 eV resulting from degradation of the diglyme. Upon the following charge, most of the discharge products disappear.
Mesoscopic Li Distribution Analysis on an All Solid Battery
Authors: Saito Toshiya , Yamazaki Akiyoshi , Kamiya Tomihiro , Fujita Kazuhisa , Mima Kunioki , Kato Yoshiaki , Iba Hideki
Published: February 2020

All solid batteries (ASB) are one of the most promising candidates for post Li-ion battery, especially for large scale applications such as electric vehicle, plug-in hybrid vehicle and stationary use. The most characteristic feature of ASB is that organic solvent in a Li-ion battery is replaced by inorganic solid electrolyte. It is generally expected wider operation temperature and higher thermal stability than conventional liquid Li-ion battery derived from nature of solid electrolyte.

On the other hand, there are several obstacles for the practical application of ASB. One of the major drawbacks is the poor power density of the ABS. We sometimes face to large “interfacial resistance” of electrodes in the ASB. The origin of interfacial resistance is cracks and/or resistive layer between active material and solid electrolyte. To figure out a quantitative view of the poor power density, it is useful to observe Li ion distribution in an electrode especially under working condition, i. e. in-situ observation of Li distribution in an ASB.

Recently, it was reported that the ion beam analysis is applicable to observe Li atom distributions in an electrode of Li-ion battery [1]. The principle of this method is to analyze Li and/or other elements by detecting γ-ray, X-ray or charged particles. When a high energy proton beam is irradiated on an electrode, characteristic X-rays are emitted from transition metal elements through ionization interaction, and , γ-ray or α-particles from 7Li through nuclear reaction of 7Li(p, p’γ)7Li or 7Li(p, α)4He, respectively. At the Takasaki Institute of Japan Atomic Energy Agency, high energy proton micro-beam was irradiated on samples. The minimum diameter of the beam was focused down to about 1 μm. This means that 2D elemental images of a sample including Li can be obtained with μm resolution. We’ve tried to apply this new analysis technique to an ASB. The result will be shown in the conference and the possibility of in-situ observation will be discussed.

Acknowledgement:

This work was supported by funding received from the CONCERT-Japan Joint Call on Efficient Energy Storage and Distribution, and by the Japan Science and Technology Agency, the Spanish Ministry of Economy and Competitiveness, the German Federal Ministry of Education and Research and the German State of North Rhine-Westphalia.

Reference:

[1] K.Mima, et al.," Distribution characterization in Li-ion batteries positive electrodes containing LixNi0.8Co0.15Al0.05O2 secondary particles", Nucl. Instr. Meth. B, 290 (2012) 79-84
Invited: Interfacial Lithiation of Layered Heterostructures Measured by Real-Time X-ray Reflectivity
Authors: Fister Timothy , Fenter Paul , Shi Bing , Esbenshade Jennifer , Gewirth Andrew , Chen Xiao , Evmenenko Guennady , Hu Xianyi , Bezyk Michael
Published: February 2020

Intermetallics, such as silicon or tin, tend to have limited reversibility in batteries due to their substantial volume change during lithiation that amorphizes the electrode and leads to delamination. Numerous methods have been proposed to direct the volume change using nanofabrication, but many of these routes require partial lithiation and can suffer from reduced Coulombic efficiency related to the electrode’s resulting high surface area. In the spirit of layered crystal structures that support intercalation, we fabricated superlattices consisting of alternating layers of amorphous silicon and chromium silicide that maintain their 1D ‘crystal structure,’ despite 300% vertical expansion of the silicon layers. Diffraction peaks from the repeated bilayer structure confirm the reversibility of the overall reaction despite four-fold vertical expansion from each silicon layer. X-ray reflectivity also shows that the metallic layers remain intact during the entire process and that structural changes can be influenced by using potentiostatic or galvanostatic boundary conditions. Similar results were found in germanium/titanium multilayers, where intermixed GeTix regions were found to also participate in the lithiation. In each case, the long term cycling and Coulombic efficiency of the multilayers far outperform pure-phase thin films and show similar rate capabilities. We discuss the universality of this approach and prospects for using the layered structure to tailor phase separation in multicomponent conversion reactions.
Effect of Asymmetric Performance of Ionic Liquid Electrolyte Ions on Maximum Operation Potential of Symmetric Supercapacitors
Authors: Van Aken Katherine L , Beidaghi Majid , Gogotsi Yury
Published: February 2020

While known for their high-power performance compared to batteries, supercapacitors

lack the energy density capability for some energy storage applications. Since the

energy density of the device is proportional to the square of operating potential window,

increasing the potential window is an effective way to increase energy density of the

device. Ionic liquid electrolytes are beneficial for this reason since they can theoretically

operate at up to 6 V, though experimentally, the value is between 3-4 V depending on

the properties of electrode materials. By employing a novel electrochemical technique to

study symmetric supercapacitors of carbon electrodes and ionic liquid electrolytes, we

have found one of the possible reasons for smaller operation potential of ionic liquids

in practical applications. We observed that even for a symmetric device with electrodes

similar in size and weight, the different properties of cations and anions of the electrolyte

results in an asymmetric performance of the two similar electrodes. By performing a

systematical study on model electrode materials and ionic liquid electrolyte systems, we

show that a symmetric behavior of the electrode can be achieved by mixing ionic liquids

with different cation and anion properties. This ultimately results in a higher operation

potential window of the device and higher energy density. In our model electrochemical

device, onions like carbons (OLCs) were used to fabricate the device electrodes and two

ionic liquids EMI-TFSI and EMI-BF4 and their mixtures were used as electrolytes.