Applied Physics Letters Research Articles

Novel Fast-X-Ray Reflectivity Setup for Studying Electrochemical Interfaces

A fundamental understanding of atomic scale processes occurring at electrochemical interfaces is crucial for advancing the development of energy-related electrochemical systems such as ion batteries or fuel cells. For this purpose, operando experiments are imperative. X-ray reflectivity (XRR) is a non-destructive technique that enables operando analysis of buried structures with atomic resolution [1,2]. However, the time-resolution of typical XRR setups of minutes per XRR scan is limited by diffractometer motor motion and detector read-out times; this resolution is in many cases too slow to observe interfacial electrochemical phenomena [1,2].To overcome these limitations, we developed a novel fast-XRR setup, which employs a fast quasi-continuous rotation stage in combination with a stationary, high frame rate area detector. With this setup, the sample can be rotated with a frequency of up to 10 Hz, yielding sub-second time resolution for an individual XRR scan. In contrast to complementary fast-XRR setups [3,4], the presented setup can easily be combined with complex sample environments, as typically required for the investigation of electrochemical interfaces.We present first fast-XRR results obtained at PETRA III beamline P08 at DESY using 18 keV and a Dectris Eiger1M detector. We reached a time resolution below one second for an incident angular range between 0° – 6° (≙ 0 – 2 Å-1, i.e., covering the Fresnel XRR range). We measured several multilayer samples (e.g., 2 nm Ti / 20 nm Au coating on a Si substrate) and benchmarked the results to “standard” XRR measurements, where the measurements took several minutes. We find good agreement and conclude, that our novel setup provides significant XRR data within less than one second, demonstrating its usability for operando XRR measurements.Literature:[1] C. Cao, H.-G. Steinrück, Encyclopedia of Solid-Liquid Interfaces, 391–416, Elsevier, 2024.[2] C. Cao, H.-G. Steinrück et al., Nano Letters, 16, 12, 7394–7401, 2016.[3] M. Lippmann et al. Review of Scientific Instruments, 87, 113904, 2016.[4] H. Jorres et al., Applied Physics Letters, 114, 081904, 2019.

(Invited) Photoluminescence Properties of Single InAsP Quantum Dots Embedded in InP Nanowires

Non-classical light emitters that can generate single photons with a negligible multiphoton probability are one of the key components for quantum information technologies. Deterministically grown III-V semiconductor nanowires containing quantum dots are gaining interest as a viable platform for quantum key distribution applications. In this talk, we will report on our recent development of the fabrication of InAsP single quantum dots embedded within InP photonic waveguide nanowires. In particular, we outline the importance of the photonic waveguide design for optimum photon generation and coupling to external optics [1]. The measured count rate dependence on normalized wire diameter, D/λ (figure 1) of the nanowire sources is consistent with calculations of the spontaneous emission rate into the fundamental HE11 nanowire waveguide mode (ΓHE11). Manipulating dot growth conditions and engineering the band structure around the dot (dot-in-a-rod configuration) are applied [2] to enhance the photoluminescence emission rate at 1310 nm and 1550 nm. Single photon emission with very low multiple photon probability is demonstrated at O- and C-band [3,4]. Temperature dependent, second-order correlation measurements on the 1310 nm source show that these nanowire sources can generate single photons up to temperatures of 220 K [3].[1] S. Haffouz, et al., Nano Letters, 18, 3047 (2018).[2] S. Haffouz, et al., Applied Physics Letters, 117, 113101 (2020).[3] P. Laferriére, et al., Nano Letters, 23, 962 (2023).[4] A.N. Wakileh, et al., arXiv:2309.13381 (2023). Figure 1

Pathfinding Process Development for the Realization of Atomic Precision Advanced Manufacturing (APAM)-Based Vertical Tunneling Field Effect Transistors for Enhanced Energy Efficiency

Since the end of Dennard scaling, where metal oxide semiconductor field effect transistor (MOSFET) operating frequency and energy efficiency improved with shrinking device dimensions [1], increasing transistor density is predicted to increase the total power consumption of a system [2]. A key limitation for MOSFETs is that the minimum rate of turn-on, or subthreshold swing (SS), is ~60 mV/decade at room temperature because of the Boltzmann statistics that dictate charge density. Thus, maintaining constant electric field without increasing energy consumption (i.e. gate bias) requires decreasing the SS by investigating alternative materials or device designs, like tunnel FETs (TFETs) [3]. Recent advances in atomic-scale control promise to provide control over quantum mechanical degrees of freedom which have hindered TFET performance in practice. These considerations make atomic precision advanced manufacturing (APAM) an appealing platform to realize a proof-of-concept TFET with atomic scale features [4,5].APAM can produce a 2D sheet of dopants in silicon beyond the solid solubility limit that can be patterned in-plane and capped with epitaxial silicon for strong carrier confinement in the out-of-plane direction (Figure 1). Indeed, improvements to planar TFETs that effectively have 1D channels with low on:off current ratios have been proposed by changing to a vertical geometry that leverages the carrier confinement afforded by 2D materials to create a 2D channel [6], though these materials are not typical in a silicon foundry. In contrast, APAM provides this carrier confinement while exclusively using materials and chemicals that are used in silicon foundries and with compatible processes [7]. In the APAM TFET (Figure 1.8.), a gate bias induces a layer of holes at the oxide/silicon interface that extends from the source, enabling tunneling between the 2D phosphorus-doped layer that comprise the drain and the 2D induced hole layer.As tunnelling occurs vertically through the epitaxial silicon cap, it becomes critical to determine the optimal growth temperature, to keep the dopants in a 2D sheet at low temperatures versus producing low-defect silicon at higher temperatures. Similarly, for optimal electric field control, it becomes critical to determine the optimal processing temperature to maintain the 2D dopant sheet and produce a low-defect gate oxide. The electronic thickness of the dopant layer can be measured using weak localization and the segregation of dopants out of the 2D sheet can be measured using secondary ion mass spectrometry. Our intial attemps at evaluating the electrical quality of the epitaxial silicon cap used PMOS transistors made with an ALD gate dielectric on APAM material without the buried phosphorus layer. Intuitively, we expect material grown at a higher temperature to produce a lower density of defects and therefore more performant PMOS, but find instead that the initial results demonstrate no systematic trend. These results potentially indicate there is an unknown variable obscuring the intentionally changed variable of growth temperature. Here, we propose several possible causes for this observation – both the variability from APAM processing or low-temperature microfabrication could mask an underlying trend.In summary, an APAM TFET provides a path toward increasing energy efficiency of transistors by decreasing SS compared to MOSFETs. The process tradeoffs that produce tightly confined 2D doped layers compared to low defect materials are starting to be explored using PMOS devices. Here, we report on the impact of process variability in drawing conclusions from these devices toward the realization of an APAM TFET.SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.[1] R. H. Dennard et al., “Design of ion-implanted MOSFET's with very small physical dimensions”, IEEE J. Solid-State Circuits 9, 256 (1974).[2] https://irds.ieee.org/[3] J. Koga et al., “Negative differential conductance in three‐terminal silicon tunneling device”, Applied Physics Letters, 69, 1435 (1996).[4] T.-M. Lu et al., “Path towards a vertical TFET enabled by atomic precision advanced manufacturing”, 2021 Silicon Nanoelectronics Workshop (2021).[5] X. Gao et al., “Modeling and Assessment of Atomic Precision Advanced Manufacturing (APAM) Enabled Vertical Tunneling Field Effect Transistor”, 2021 SISPAD, 102 (2021).[6] H. Lu et al., “Tunnel Field-Effect Transistors: State-of-the-Art”, IEEE J. Electron Device Society, 2, 44 (2014).[7] S. Misra et al., “Method of chemical doping that uses CMOS-compatible processes”, U.S. Patent 11,798,808. Figure 1

(Nanocarbons Division SES Young Investigator Award) Surface Chemistry of Nanocarbon Field-Effect Transistors: From Fundamental Physics to Biosensing

Conductive carbon nanomaterials are particularly well-suited to form field-effect biosensors (bioFETs) because they are stable in aqueous media and can be chemically coupled to biomolecules. Their reduced dimensionality, either 2D (graphene) or 1D (carbon nanotubes), is key to their sensitivity: because they are entirely surfaces, these materials present remarkable electrical transport properties that are easily altered by microscopic surface interactions. Biochemical processes occurring in close proximity to their surface can therefore be transduced as changes in their electrical conductance. Selectivity for specific biochemical events, however, must be engineered via functionalization of the nanomaterial, i.e. by modifying its surface with bioactive or biorecognition elements (e.g., antibodies, aptamers, enzymes, polymer layer). Our group recently analyzed a corpus of studies presenting graphene field-effect transistors (GFETs) as bioanalytical sensors for the quantitative detection of biomarkers in the form of nucleic acids, proteins, ions or small molecules [1]. We found a striking variance in the reported sensing performance between these studies, that could not be explained by controlling for differences in graphene material, analyte type and for evolution over the years. Our hypothesis is that the lack of microscopic control on the biointerface is likely the most important source of variation in such bioFETs, highlighting the critical need to improve our knowledge and control of the functionalization of nanocarbon materials.In this talk, I will discuss our work investigating the interplay between surface chemistry and electrical properties in nanocarbon field-effect transistors. In the first part, I will focus on covalent additions using aryldiazonium salts. I will review what we have learned on the fundamental physics of this chemistry from experiments and simulations on carbon nanotube devices [2-5], in particular on its disruptive character because of the formation of sp 3 defects in the carbon lattice. More recently, we investigated this same chemistry on GFET devices and observed a heterogeneous response in their electrical conductance. Aiming to solve this, we developed a novel approach to precisely trigger and stop the reaction in situ using the applied gate voltage [6], enabling unprecedented control on the functionalization rate and yield on GFETs. In the second part, I will describe our ongoing efforts to characterize and control the biofunctionalization of GFETs through non-covalent pyrene derivatives, using a combination of electrical measurements, microscopy and spectroscopy techniques, and theoretical simulations. Finally, I will discuss our ongoing translational projects in oncology, on adapting nanocarbon-based bioFETs in cancer diagnostics applications.[1] Béraud et al, Analyst 146 (2), 403-428 (2021)[2] Bouilly et al, Applied Physics Letters 101 (5), 053116 (2012)[3] Bouilly et al, ACS nano 9 (3), 2626-2634 (2015)[4] Bouilly et al, Nano Letters 16 (7), 4679-4685 (2016)[5] Côté et al, Physical Chemistry Chemical Physics 24 (7), 4174-4186 (2021)[6] Bazan et al, Nano Letters 22 (7), 2635-2642 (2022)

(Invited) Strategic Cutoff Potential Selection Enables Safe and Long Cycle Life Li4Ti5O12/LiNi0.9Mn0.05Co0.05O2 Batteries for Behind-the-Meter Storage Applications

Behind-the-meter storage (BTMS) encompasses storage and distribution systems that bypass the electric grid. For example, energy stored in BTMS stationary batteries can be used for various purposes including electric vehicle charging or lowering the cooling load demands for large buildings. Many previous studies have focused on Li4Ti5O12/LiMn2O4 (LTO/LMO) batteries for BTMS applications1–3 rather than the more conventional electric vehicles comprised of graphite anodes paired with LiFePO4 or layered oxide materials. LTO/LMO batteries are appropriate for BTMS because they provide a favorable balance of cost, safety, and cycle life, which are the most important criteria for BTMS batteries. LTO’s minimal strain, high operating voltage, and relatively earth abundant materials promote cyclability, safety, and reasonable cost.4 LMO is very attractive to pair with LTO for BTMS applications due to abundancy of Mn, safety, and relatively high operating voltage to enable a higher voltage when paired with LTO.5 While LTO/LMO fulfills many requirements for BTMS applications, the high voltage of LTO and the low capacity of LMO limit energy density and specific energy. Improving energy density has the potential to decrease cost in addition to enabling a smaller battery footprint for space-constrained BTMS applications.With the goal of increasing the cathode capacity at high voltage to improve the BTMS battery energy density relative to LTO/LMO, we investigated LTO paired with LiNi0.90Mn0.05Co0.05O2 (NMC90-5-5). We selected NMC90-5-5 for its low Co content to minimize the impact of the cost volatility and supply chain challenges with Co in accordance with BTMS program goals. We investigated long term cycle life and rate capability of LTO/NMC90-5-5 coin cells with two different N/P ratios and two different charge termination potentials. Without the risk of Li plating at high LTO potentials, the cathode can be safely oversized in LTO systems (N/P < 1) such that the excess cathode capacity provides additional Li inventory to overcome losses during cycling and enables longer cycle life. We compared cells fabricated with N/P < 1 with N/P > 1 and we found that cells with N/P < 1 provided higher cell capacity during 1000 cycle tests. We also varied the full cell termination charge potential (2.6 V versus 2.7 V) for each N/P condition. While the 2.7 V termination potential enabled higher capacity, the 2.6 V termination enabled more stable cycling during 1000 cycle tests. Furthermore, because high Ni content layered oxide systems typically exhibit safety challenges,6,7 we also fabricated 18650 LTO/NMC90-5-5 full cells for accelerating rate calorimetry (ARC) testing. ARC testing revealed a significantly lower heating rate as well as a higher temperature where the max heating rate occurred for cells cycled to 2.6 V versus 2.7 V. These data suggest that the termination potential in NMC90-5-5 is critical for optimizing these cathodes for the long cycle life and safety required for BTMS applications.This work was authored in part by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. This work was performed, in part, at Sandia National Laboratories, a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC (NTESS), a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration (DOE/NNSA) under contract DE-NA0003525. Funding was provided by the U.S. Department of Energy's Vehicle Technologies Office under the Behind-the-Meter Storage (BTMS) Consortium directed by Samuel Gillard and managed by Anthony Burrell. The electrodes used in this manuscript are from Argonne's Cell Analysis, Modeling and Prototyping (CAMP) Facility, which is fully supported by the DOE Vehicle Technologies Office (VTO). The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.(1) Y. Ha et al., Journal of The Electrochemical Society 2023, 170 (5), 050520.(2) Y. Ha et al., Journal of The Electrochemical Society 2021, 168 (11), 110536.(3) Y. Ha et al., Energy Storage Materials 2021, 38, 581–589.(4) G. Xu et al., Coordination Chemistry Reviews 2017, 343, 139–184.(5) Z. Radzi et al. Journal of Electroanalytical Chemistry 2022, 116623.(6) L. Gan et al., Applied Physics Letters 2022, 121 (20).(7) J. Lamb et al., Journal of The Electrochemical Society 2021, 168 (6), 060516.

Direct Wafer Bonding of 128° Y-Cut LiNbO3: A Pathway to High Frequency (50 GHz) Filter Applications

In this work, room temperature direct wafer bonding of complementarily oriented 128° Y-cut LiNbO3 substrates is achieved with an interfacial layer less than 1 nm thick. This compares well to commercially available structures with thickness of 3 nm and this interfacial width is particularly important for eventual multilayer bonding sequences with each layer on the order of only tens of nm. The (0114) indices describe the surface plane of 128° Y-cut LiNbO3 wafers; and the wafers were bonded such that their in-plane [055.12] directions were antiparallel. Due to its trigonal crystal structure, this zone axis has 1-fold symmetry and therefore is crystallographically distinguishable from either side of the bonded interface. The wafers were cleaned with standard cleaning protocols and subsequently brought in contact face-to-face and bonded. The bonding was performed in ambient atmosphere and the applied pressure was on the order of ~kPa. The bonded pair was then annealed at 200 °C for 10 h in order to strengthen the bond, which is fully compatible with exfoliation of He-implanted LiNbO3 layers. Limited literature has been reported for direct bonding of LiNbO3 to LiNbO3 and even fewer investigate the atomic structure of the bonded interface.1-3 Tomita et al., observe structurally disordered bonded interfaces after annealing at high temperatures (up to 1000 °C). High resolution transmission electron microscopy of the interface presented here reveal an abrupt interface (≤ ~1 nm) and a φ X-ray scan has confirmed a relative twist of ~180° between substrates. This is a follow-up work for what has previously been achieved by our group demonstrating direct wafer bonding and layer transfer of LiNbO3 to substrates such as sapphire and oxidized silicon.4 Combining these latest results will enable the fabrication of a multilayer structure of complementarily oriented LiNbO3 thin films on a sapphire substrate, which has applications for high frequency (50 GHz) filters. Similar structures using a different LiNbO3 orientation (X-cut) have been demonstrated to maintain high quality factor (Q) at 15.8 GHz.5 The authors would like to acknowledge the support from DARPA through the Compact Front-end Filters at the ElEment-level (COFFEE) program.[1] Tulli, D., Janner, D. and Pruneri, V., “Room temperature direct bonding of LiNbO3 crystal layers and its application to high-voltage optical sensing.” Journal of Micromechanics and Microengineering, 21(8), p.085025 (2011).[2] Tomita, Y., Sugimoto, M., & Eda, K., “Direct bonding of LiNbO3 single crystals for optical waveguides.” Applied physics letters, 66(12), 1484-1485 (1995).[3] Berini, P., Mattiussi, G., Lahoud, N. and Charbonneau, R., “Wafer-bonded surface plasmon waveguides.” Applied physics letters, 90(6), p.061108 (2007).[4] Liao, M. E., Matto, L., Huynh, K., and Goorsky, M. S., “Direct Wafer Bonding of 128° Y-Cut LiNbO3 to Sapphire”. WaferBond ’22, Presentation (2022).[5] Lu, R., and Gong, S., 2021 Joint Conf. EFTF/IFCS, 1 (2021). Figure 1

Localized Electrochemical Deposition Using Copper Pyrophosphate-Based Electrolyte

Additive manufacturing (AM) has gained popularity across various industries due to its cost-effectiveness, low material consumption, and minimal environmental impact. Localized electrochemical deposition (LECD), as one of the AM methods, has the capability to produce microcomponents or structures at an microscale in a specific position as designed, without the need for any mask or support material[1]. By reducing copper ions in the local area according to the position of the micro-wire, 3D structures could be produced. This electrochemical deposition process has a significant advantage in that it is a low-temperature process and has lower costs compared to other processes[2].Using the LECD process, the micrometer of copper columns was conventionally deposited in copper sulfate-based electrolyte[3]. However, this electrolyte has the possibility to cause damage to the metal substrate used as the cathode due to its low pH, resulting in metal dissolution. The utilization of copper pyrophosphate-based electrolyte, which is a solution with a pH close to neutral, can solve this problem. Also, copper pyrophosphate-based electrolyte offers an advantage over conventional alkaline-based electrolytes in that it removes cyanide pollution of the environment and hazards to human health.[4]In this study, the microanode was employed using a platinum wire(100 μm in diameter), while a copper substrate was employed as the cathode in the electrochemical deposition process. The micrometer copper columns were deposited using copper pyrophosphate-based electrolyte by varying the main electrochemical deposition factors, such as applied potential and pulse duty cycle. In addition The surface morphology of the deposited micrometer-scale copper columns was observed through scanning electron microscopy.REFERENCES[1] Suryavanshi, Abhijit P., and Min-Feng Yu. "Probe-based electrochemical fabrication of freestanding Cu nanowire array." Applied Physics Letters 88.8 (2006): 083103.[2] Madden, John D., and Ian W. Hunter. "Three-dimensional microfabrication by localized electrochemical deposition." Journal of microelectromechanical systems 5.1 (1996): 24-32.[3] Lin, J. C., et al. "Localized electrochemical deposition of micrometer copper columns by pulse plating." Electrochimica Acta 55.6 (2010): 1888-1894.[4] Chen, C-C. "A New Process for Cyanide-Free Copper Plating."Electroplating and Pollution Control 23.4 (2003): 10-11.

Investigation of Growth Sectors in Gallium Nitride Substrate Wafers from Ammonothermal and Patterned Hvpe Growth Methods

Gallium Nitride (GaN) is a wide band gap semiconductor material that has the potential to replace silicon (Si) in power electronics. However, the quality and availability of bulk GaN substrates is currently limiting its use in high-performance power electronics. Several methods have been developed to grow bulk GaN crystals, including physical vapor transport (PVT) [1, 2], Na-flux [3], ammonothermal [4, 5], and hydride vapor phase epitaxy (HVPE) [6]. Additionally, patterned HVPE growth methods have been developed to produce GaN substrates with reduced dislocation densities [7]. Ammonothermal and patterned HVPE growth methods have shown promise in producing high-quality GaN crystals for use in power devices [8-10]. Ammonothermal-grown GaN has an overall low dislocation density of 1000 cm-2, while patterned growth can concentrate dislocations into small areas, leaving the rest of the crystal relatively dislocation-free (< 102 cm-2). Besides dislocations, the overall homogeneity of these wafers is also important for devices. Recent synchrotron X-ray topography studies revealed domain features in both ammonothermal and patterned HVPE GaN wafers. Using synchrotron X-Ray Plane-Wave Topography (SXPWT, previously known as synchrotron X-Ray Rocking Curve Topography), these domain features that have enclosed diamond or quadrilateral shapes are found to have relative compressive strain values (~ 10-5) (Figure 1b). These features are visible on SEM micrographs using a Robinson detector (RBSD) (Figure 1c). The origin of these strains is likely the different impurity incorporation rates in different growth sectors.In the patterned HVPE growth method, growth sectors have been reported to exist due to growth along different directions [11]. It is likely that a similar situation exists for ammonothermal substrates, although no studies have been reported on this. Understanding the nature of these domain areas is important for device fabrication as the inhomogeneities will likely be replicated into active regions. SIMS measurements are currently being conducted to characterize the differences in impurity concentrations in these domains. These results will be used to confirm the origin of the strain.Figure 1. (a) Synchrotron monochromatic beam X-ray topograph of a selected area on a patterned HVPE grown GaN substrate; (b) Cropped strain map of the same area obtained by SXPWT; (c) SEM image of the same area with RBSD contrast. All three images show contrast from the domains defined by the growth sectors.[1] H. Wu, J. Spinelli, P. Konkapaka, M. Spencer, MRS Online Proceedings Library Archive 892 (2005).[2] D. Siche, D. Gogova, S. Lehmann, T. Fizia, R. Fornari, M. Andrasch, A. Pipa, J. Ehlbeck, Journal of crystal growth 318 (2011) 406-410.[3] M. Aoki, H. Yamane, M. Shimada, S. Sarayama, F.J. DiSalvo, Journal of crystal growth 242 (2002) 70-76.[4] R. Dwiliński, R. Doradziński, J. Garczyński, L. Sierzputowski, A. Puchalski, Y. Kanbara, K. Yagi, H. Minakuchi, H. Hayashi, Journal of Crystal Growth 310 (2008) 3911-3916.[5] T. Hashimoto, F. Wu, J.S. Speck, S. Nakamura, Journal of Crystal Growth 310 (2008) 3907-3910.[6] H.P. Maruska, J. Tietjen, Applied Physics Letters 15 (1969) 327-329.[7] T. Nakamura, K. Motoki, GaN substrate technologies for optical devices, IEEE, vol 101, 2013, p. 2221.[8] B. Raghothamachar, Y. Liu, H. Peng, T. Ailihumaer, M. Dudley, F.S. Shahedipour-Sandvik, K.A. Jones, A. Armstrong, A.A. Allerman, J. Han, H. Fu, K. Fu, Y. Zhao, Journal of Crystal Growth 544 (2020) 125709.[9] Y. Liu, B. Raghothamachar, H. Peng, T. Ailihumaer, M. Dudley, R. Collazo, J. Tweedie, Z. Sitar, F.S. Shahedipour-Sandvik, K.A. Jones, Journal of Crystal Growth 551 (2020) 125903.[10] Y. Liu, H. Peng, T. Ailihumaer, B. Raghothamachar, M. Dudley, Journal of Electronic Materials 50 (2021) 2981-2989.[11] K. Motoki, T. Okahisa, S. Nakahata, N. Matsumoto, H. Kimura, H. Kasai, K. Takemoto, K. Uematsu, M. Ueno, Y. Kumagai, Journal of Crystal Growth 237 (2002) 912-921. Figure 1

Electrodeposition of Microfabricated Rhenium-Filaments

Metallic filaments comprised of refractory materials are a necessary part of mass spectrometers used to measure isotopes. The current state-of-the-art material, rhenium, is formed into filaments using a mechanical crimper, limiting the accuracy, speed, and quantity of filaments that can be fabricated. The current work describes the development of wafer-scale, microfabricated Re filaments using silicon molds followed by electrodeposition of Re. The goal is to develop filaments with tight dimensional tolerances, high purity, and mechanical rigidity for the desired application and offer the ability to create 100’s-1000’s of filaments on a single silicon wafer.Electrodeposition of Re is notoriously difficult as the reduction potential of rhenium is close to the hydrogen evolution reaction in aqueous solutions.1 While rhenium has been successfully deposited from alkaline, acid, and concentrated lithium chemistries,2 the films are often thin, porous, and contain many impurities such as hydrogen and oxygen. Rhenium oxide is susceptible to reaction with moisture in the air, resulting in poor quality films with short functional lifetimes. To electroform precise, pure rhenium structures, hardier chemistries must be developed.The current work seeks to address this challenge using a water-in-salt chemistry (WISE) comprised of up to 4M lithium salts, complexing agents, reducing agents, and oxygen scavengers. Numerous physical agitation techniques were utilized to improve the quality of the film. Solutions were analyzed using various electrochemical techniques, UV-VIS, and Raman spectroscopy. The optimized chemistry was used to electrodeposit bulk batches of microfabricated 2mm x 300 um x 300 um filaments. The filaments were analyzed using microscopy, XRF, XRD, SEM, and EDS with a goal of use in high temperature mass spectrometry experiments. References (1) Naor, A.; Eliaz, N.; Burstein, L.; Gileadi, E. Direct Experimental Support for the Catalytic Effect of Iron-Group Metals on Electrodeposition of Rhenium. Electrochemical and Solid-State Letters 2010, 13 (12), D91. DOI: 10.1149/1.3489532.(2) Pappas, D. P.; David, D. E.; Lake, R. E.; Bal, M.; Goldfarb, R. B.; Hite, D. A.; Kim, E.; Ku, H.-S.; Long, J.; McRae, C. Enhanced superconducting transition temperature in electroplated rhenium. Applied Physics Letters 2018, 112 (18), 182601. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. SAND2022-*****

Photovoltaics literature survey (no. 182)

Photovoltaics literature survey (no. 182)

Photovoltaics literature survey (No. 181)

Photovoltaics literature survey (No. 181)

Growth and Properties of Graphene and Graphene Nanoribbons on Ge

The synthesis of graphene directly on Ge and on Ge deposited on Si provides a scalable route toward integrating graphene onto conventional semiconductors. This presentation will first survey the growth modes of graphene on Ge(001), Ge(011), Ge(111), Ge(112), Ge(001)-6°, and Ge(001)-9° via chemical vapor deposition (CVD), reporting on the effect of Ge surface orientation on graphene island formation and shape, strain in large-area graphene films, and the nanofaceting of the Ge below graphene.[1] We will then focus on the anisotropic growth of semiconducting graphene nanoribbons on Ge(001) and Ge(001)-9° and of nominally single crystal graphene on Ge(110).On Ge(001), we have discovered how to drive graphene crystal growth with a large shape anisotropy through control of kinetics.[2-6] This discovery enables the direct synthesis of narrow, armchair, semiconducting nanoribbons. The ribbons are self-orienting, self-defining, and have smooth edges. The ribbons exhibit excellent transport properties (e.g., high on-state conductance and on/off ratio at room temperature) and provide a promising pathway towards the direct integration of high-performance nanocarbon electronics onto conventional semiconductor wafer platforms.On Ge(001), nominally single crystal graphene has been reported in limited cases; however, conflicting studies have evidenced polycrystallinity. Here, the factors affecting the mosaicity of graphene on Ge(110) will be elucidated using low energy electron diffraction and microscopy data.[7][1] R. M. Jacobberger, D. E. Savage, X. Zheng, P. Sookchoo, R. R. Delgado, M. G. Lagally, M. S. Arnold, SUBMITTED (2022).[2] R. M. Jacobberger, M. S. Arnold, et al., Direct Oriented Growth of Armchair Graphene Nanoribbons on Germanium, NATURE COMMUNICATIONS, 6, 8006 (2015).[3] B. Kiraly, M. S. Arnold, M. C. Hersam, N. P. Guisinger et al., Sub-5 nm, Globally Aligned Graphene Nanoribbons on Ge (001), APPLIED PHYSICS LETTERS, 108, 213101 (2016).[4] A. J. Way, R. M. Jacobberger, M. S. Arnold, Seed-Initiated Anisotropic Growth of Unidirectional Armchair Graphene Nanoribbon Arrays on Germanium, NANO LETTERS, 18, 898 (2018).[5] V. Saraswat, Y. Yamamoto, H.J. Kim, R.M. Jacobberger, K.R. Jinkins, A.J. Way, N.P. Guisinger, M.S. Arnold Synthesis of armchair graphene nanoribbons on germanium-on-silicon, THE JOURNAL OF PHYSICAL CHEMISTRY C 123 (30), 18445-18454 (2019).[6] A. J. Way, R. M. Jacobberger, N. P. Guisinger, V. Saraswat, X. Zheng, A. Suresh, J. H. Dwyer, P. Gopalan, Michael S. Arnold, SUBMITTED (2022).[7] R. M. Jacobberger, Z. Miao, T. Yu, V. Saraswat, M. G. Lagally, M. S. Altman, M. S. Arnold, SUBMITTED (2022).

Electrodeposition of Rhenium Sandwich Structures and the Superconducting Transition Behavior

Superconductors with enhanced superconducting critical temperatures (Tc) above the boiling point of liquid helium (4.2 K) are of interest for interconnections in superconducting quantum computing systems to avoid ohmic heating[1]. Crystalline Re in bulk is a type-I superconductor with a Tc of about 1.7K[2]. An elevated Tc up to about 6K in electrodeposited amorphous Re has been reported[3]. In addition, various elevation in Tc has also been reported for Re film under shear strain[4] or doped with foreign elements such as Tungsten (W), Osmium (Os), and Carbon (C)[5, 6].This work aims to test a hypothesis that the Tc of electrodeposited Re films can be tuned using compressive and tensile strains on the Re films generated with thermal expansions difference. Figure 1 shows a diagram of the strains on Re film sandwiched between metals with different coefficients of thermal expansions (CTEs) when the temperature is lowered. For example, Cu has a higher CTE than Re and Cr has a slightly lower CTE than Re. Such sandwich structures are prepared at room temperature using electrochemical deposition. The DC resistance measurements at cryogenic temperatures confirmed that the superconducting transition for the Re films sandwiched between Cu occurs at a lower temperature than the Re film alone. On the other hand, when Cr is used, the sandwiched Re structure shows a slightly enhanced superconducting critical temperature. The effect of thermal annealing i.e., the recrystallization of electrodeposited Re films at an elevated temperature, and electrochemical behavior of Re, Cr, and Cu electrodeposition will be discussed in the talk. References Radenbaugh, R., Refrigeration for superconductors. Proceedings of the IEEE, 2004. 92(10): p. 1719-1734.Hulm, J.K., Superconductivity of Pure Metallic Rhenium. Physical Review, 1954. 94(5): p. 1390-1391.Pappas, D.P., et al., Enhanced superconducting transition temperature in electroplated rhenium. Applied Physics Letters, 2018. 112(18): p. 182601.Mito, M., et al., Large enhancement of superconducting transition temperature in single-element superconducting rhenium by shear strain. Scientific Reports, 2016. 6(1): p. 36337.Chu, C.W., W.L. McMillan, and H.L. Luo, Superconductivity of Re-Os, Re-Ru, Ru-Os, and Re-W hcp Alloy Systems and Slightly Doped Re. Physical Review B, 1971. 3(11): p. 3757-3762.Zhu, Q., et al., Anisotropic lattice expansion and enhancement of superconductivity induced by interstitial carbon doping in Rhenium. Journal of Alloys and Compounds, 2021. 878: p. 160290. Figure 1

Equivalent Circuit Model of the RF Characteristics of Multi-Stage Infrared Photodetectors

Multi-stage infrared photodetectors such as quantum cascade detectors (QCDs) and interband cascade infrared photodetectors (ICIP) have been demonstrated with high detectivity and high-frequency operation. In the previous work published by Rui. Q. Yang [Applied Physics Letters 2021, 119 (14), 141107], an equivalent circuit model is used to derive the relation among quantum efficiency, collection efficiency, and particle conversion efficiency. The ultimate detectivities in multi-stage infrared photodetectors were discussed based on that model. However, the RF performance of multi-stage infrared photodetectors was rarely studied theoretically so far. In this work, a generalized equivalent circuit model is proposed with the AC term included. The detailed calculations and relevant discussion are provided to show how the normalized frequency response function of each stage impacts the overall 3 dB performance of the device. In the limit of weak absorption, such as QCDs or ICIP with very weak and identical absorption in each stage, the multi-stage infrared photodetectors show significant improvement in RF performance. Moreover, how the current mismatching issue between stages impacts 3 dB bandwidth performance quantitatively is derived and discussed for identical absorption stages architecture. The result and insights gained from this work can be beneficial for the understanding and optimization of high-speed multi-stage detectors.

(Invited, Digital Presentation) Macroscopically Aligned Carbon Nanotubes for Photonics, Electronics, and Thermoelectrics

The remarkable flexibility, stable chemical structure, and extraordinary thermal, electrical, and optical properties of carbon nanotubes (CNTs) are promising for a variety of applications in flexible and/or high-temperature electronics, optoelectronics, and thermoelectrics, including wearables, refractory photonics, and waste heat harvesting [1]. However, the long-standing goal in the preparation of CNT ensembles is how to maintain the extraordinary properties of individual CNTs on a macroscopic scale. The polydispersity and randomness remain two main challenges.Here, we will discuss different methods for creating macroscopically aligned CNTs, including spontaneous formation of wafer-scale aligned CNT films via controlled vacuum filtration [2-4] and production of ultrahigh-conductivity CNT fibers and films through solution spinning and coating [5,6]. We will then describe the optical [2,7-11], dc and ac electrical [2,12-17], thermal [18], and thermoelectric [19-21] properties of these materials. These results are promising for device applications in various fields such as flexible CNT broadband detectors [22-26], spectrally selective thermal emitters [11], and thermoelectric devices [20,21]. W. Gao et al., “Macroscopically Aligned Carbon Nanotubes for Flexible and High-Temperature Electronics, Optoelectronics, and Thermoelectrics,” Journal of Physics D: Applied Physics 53, 063001 (2020).X. He et al., “Wafer-Scale Monodomain Films of Spontaneously Aligned Single-Walled Carbon Nanotubes,” Nature Nanotechnology 11, 633 (2016).W. Gao and J. Kono, “Science and Applications of Wafer-Scale Crystalline Carbon Nanotube Films Prepared through Controlled Vacuum Filtration,” Royal Society Open Science 6, 181605 (2019).N. Komatsu et al., “Groove-Assisted Global Spontaneous Alignment of Carbon Nanotubes in Vacuum Filtration,” Nano Letters 20, 2332 (2020).N. Behabtu et al., “Strong, Light, Multifunctional Fibers of Carbon Nanotubes with Ultrahigh Conductivity,” Science 339, 182 (2013).L. W. Taylor et al., “Improved Properties, Increased Production, and the Path to Broad Adoption of Carbon Nanotube Fibers,” Carbon 171, 689 (2021).K. Yanagi et al., “Intersubband Plasmons in the Quantum Limit in Gated and Aligned Carbon Nanotubes,” Nature Communications 9, 1121 (2018).W. Gao et al., “Continuous Transition between Weak and Ultrastrong Coupling through Exceptional Points in Carbon Nanotube Microcavity Exciton–Polaritons,” Nature Photonics 12, 362 (2018).M. E. Green et al., “Bright and Ultrafast Photoelectron Emission from Aligned Single-Wall Carbon Nanotubes through Multiphoton Exciton Resonance,” Nano Letters 19, 158 (2019).F. Katsutani et al., “Direct Observation of Cross-Polarized Excitons in Aligned Single-Chirality Single-Wall Carbon Nanotubes,” Physical Review B 99, 035426 (2019).W. Gao et al., “Macroscopically Aligned Carbon Nanotubes as a Refractory Platform for Hyperbolic Thermal Emitters,” ACS Photonics 6, 1602 (2019).X. Wang et al., “High-Ampacity Power Cables of Tightly-Packed and Aligned Carbon Nanotubes,” Advanced Functional Materials 24, 3241 (2014).A. Zubair et al., “Carbon Nanotube Fiber Terahertz Polarizer,” Applied Physics Letters 108, 141107 (2016).D. Tristant et al., “Enlightening the Ultrahigh Electrical Conductivities of Doped Double-Wall Carbon Nanotube Fibers by Raman Spectroscopy and First-Principles Calculations,” Nanoscale 18, 19668 (2016).N. Komatsu et al., “Modulation-Doped Multiple Quantum Wells of Aligned Single-Wall Carbon Nanotubes,” Advanced Functional Materials 27, 1606022 (2017).F. R. G. Bagsican et al., “Terahertz Excitonics in Carbon Nanotubes: Exciton Autoionization and Multiplication,” Nano Letters 20, 3098 (2020).A. Baydin et al., “Giant Terahertz Polarization Rotation in Ultrathin Films of Aligned Carbon Nanotubes,” Optica 8, 760 (2021).S. Yamaguchi et al., “One-Directional Thermal Transport in Densely Aligned Single-Wall Carbon Nanotube Films,” Applied Physics Letters 115, 223104 (2019).K. Fukuhara et al., “Isotropic Seebeck Coefficient of Aligned Single-Wall Carbon Nanotube Films,” Applied Physics Letters 113, 243105 (2018).Y. Ichinose et al., “Solving the Thermoelectric Trade-Off Problem with Metallic Carbon Nanotubes,” Nano Letters 19, 7370 (2019).N. Komatsu et al., “Macroscopic Weavable Fibers of Carbon Nanotubes with Giant Thermoelectric Power Factor,” Nature Communications 12, 4931 (2021).S. Nanot et al., “Broadband, Polarization-Sensitive Photodetector Based on Optically-Thick Films of Macroscopically Long, Dense, and Aligned Carbon Nanotubes,” Scientific Reports 3, 1335 (2013).X. He et al., “Photothermoelectric p-n Junction Photodetector with Intrinsic Broadband Polarimetry Based on Macroscopic Carbon Nanotube Films,” ACS Nano 7, 7271 (2013).X. He et al., “Carbon Nanotube Terahertz Detector,” Nano Letters 14, 3953 (2014).X. He, F. Léonard, and J. Kono, “Uncooled Carbon Nanotube Photodetectors,” Advanced Optical Materials 3, 989 (2015).A. Zubair et al., “Carbon Nanotube Woven Textile Photodetector,” Physical Review Materials 2, 015201 (2018).

(Invited) Oxide Electronics and Recent Progress in Bipolar Applications

The discovery of oxide electronics is of increasing importance today as one of the most promising new technologies and manufacturing processes for a variety of electronic and optoelectronic applications such as next-generation displays, batteries, solar cells, memory devices, and photodetectors[1]. The high potential use seen in oxide electronics is due primarily to their high carrier mobilities and their ability to be fabricated at low temperatures[2]. However, since the majority of oxide semiconductors are n-type oxides, current applications are limited to unipolar devices, eventually developing oxide-based bipolar devices such as p-n diodes and complementary metal-oxide semiconductors.We have contributed to a wide range of oxide semiconductors and their electronics and optoelectronic device applications. Particularly, we have demonstrated n-type oxide-based thin film transistors (TFT), integrating In2O3-based n-type oxide semiconductors from binary cation materials to ternary cation species including InZnO, InGaZnO (IGZO), and InAlZnO. We have suggested channel/metallization contact strategies to achieve stable and high TFT performance[3, 4], identified vacancy-based native defect doping mechanisms[5], suggested interfacial buffer layers to promote charge injection capability[6], and established the role of third cation species on the carrier generation and carrier transport[7]. More recently, we have reported facile manufacturing of p-type SnOx through reactive magnetron sputtering from a Sn metal target[8]. The fabricated p-SnOx was found to be devoid of metallic phase of Sn from x-ray photoelectron spectroscopy and demonstrated stable performance in a fully oxide-based p-n heterojunction together with n-InGaZnO. The oxide-based p-n junctions exhibited a high rectification ratio greater than 103 at ±3 V, a low saturation current of ~2x10-10, and a small turn-on voltage of -0.5 V.In this presentation, we review recent achievements and still remaining issues in transition metal oxide semiconductors and their device applications, in particular, bipolar applications including p-n heterostructures and complementary metal-oxide-semiconductor devices as well as single polarity devices such as TFTs and memristors. In addition, the fundamental mechanisms of carrier transport behaviors and doping mechanisms that govern the performance of these oxide-based devices will also be discussed.ACKNOWLEDGMENTThis work was supported by the U.S. National Science Foundation (NSF) Award No. ECCS-1931088. S.L. and H.W.S. acknowledge the support from the Improvement of Measurement Standards and Technology for Mechanical Metrology (Grant No. 20011028) by KRISS. K.N. was supported by Basic Science Research Program (NRF-2021R11A1A01051246) through the NRF Korea funded by the Ministry of Education.REFERENCES[1] K. Nomura et al., Nature, vol. 432, no. 7016, pp. 488-492, Nov 25 2004.[2] D. C. Paine et al., Thin Solid Films, vol. 516, no. 17, pp. 5894-5898, Jul 1 2008.[3] S. Lee et al., Journal of Applied Physics, vol. 109, no. 6, p. 063702, Mar 15 2011, Art. no. 063702.[4] S. Lee et al., Applied Physics Letters, vol. 104, no. 25, p. 252103, 2014.[5] S. Lee et al., Applied Physics Letters, vol. 102, no. 5, p. 052101, Feb 4 2013, Art. no. 052101.[6] M. Liu et al., ACS Applied Electronic Materials, vol. 3, no. 6, pp. 2703-2711, 2021/06/22 2021.[7] A. Reed et al., Journal of Materials Chemistry C, 10.1039/D0TC02655G vol. 8, no. 39, pp. 13798-13810, 2020.[8] D. H. Lee et al., ACS Applied Materials & Interfaces, vol. 13, no. 46, pp. 55676-55686, 2021/11/24 2021.

(Digital Presentation) Measurements of the Average Droplet Charge Using a Low Density Stream of Microdroplets in Atmospheric Pressure Plasma Jet

A droplet passing through a low temperature plasma acquires a net negative charge, Q, and the droplet floating potential increases negatively until positive and negative charge fluxes are balanced. Subsequently electrons arrive at the droplet with a very low net electron energy. Low energy electrons (LEE) may play an important role in for example water chemistry, DNA damage (e.g. in radiotherapy) and electron-initiated nanomaterials synthesis [1]. However obtaining true LEE (< 5 eV) sources compatible with liquid water has not been possible to date. In a previous study, we have shown extremely fast and enhanced metal salt reactions within droplets and it is thought LEE reactions from charge on the droplets was the major contributor, in comparison to radiolysis and electron-beam studies [2]. Charging models of collisional high pressure plasmas have received little experimental validation, especially for particles in the size range (microns) where droplets can survive the plasma-induced evaporation. Measuring the small charge on fast moving droplets, however, in a high plasma RF noise environment presents very significant challenges. We present an experimental study of microdroplets charged in a helium atmospheric pressure plasma jet (APPJ) and, along with numerical modelling, determine the dependence of droplet charge, Q, on droplet diameter (D) and plasma conditions e.g. electron density, ne, and temperature, Te. Our measurements were carried out on aerosol droplet streams under various plasma conditions (power and flow) using a 4 mm plate collector. Without droplets, the collector assumed a mean positive potential. This is likely due to the effect of the upstream plasma potential which is estimated at ~12 V, assuming a Te of 2 eV. The background signal variation due to noise and other sources was ~250 mV. With the addition of droplets, the collector mean potential decreased due to the impact of the negative charge flux. At the maximum power, floating potential (VF) is a factor of ~100 greater at 3 mm collector distance compared to 15 mm. On the addition of droplets, the characteristics remain similar at 3 mm but at 15 mm, the potential remains positive until a much higher power. An image charge model [3] was used to obtain charge per droplet estimates from stream of droplets based on droplet rate and size distribution. High resolution imaging was used to obtain droplet statistics at the edge of the capillary. Here, the maximum droplet rate was ~ 5 x 104 s-1 [[4]]. The voltage – charge calibration factor, obtained from simulation, varies from 4.6 – 7.6 nV per electron, depending on velocity. The average value of charge per droplet can be obtained from the net potential and is shown in Figure 1 for low and high powers. The possible influence of the plasma gas flow (Q2) and liquid delivery rate (QL) on collector potential was explored and maximum charging capability was found to occur around a total gas flow of 3.5 slm and for lower QL values. [1] Léon Sanche, ‘Cancer Treatment: Low-Energy Electron Therapy’, Nature Materials, 14.9 (2015), 861–63 https://doi.org/10.1038/nmat4333 [2] Paul Maguire et al., ‘Continuous In-Flight Synthesis for On-Demand Delivery of Ligand-Free Colloidal Gold Nanoparticles’, Nano Letters, 17.3 (2017), 1336–43 https://doi.org/10.1021/acs.nanolett.6b03440 [3] E. Borzabadi and A. G. Bailey, ‘The Measurement of Charge on Microscopic Particles’, Journal of Physics E: Scientific Instruments, 12.12 (1979), 1137–38 https://doi.org/10.1088/0022-3735/12/12/005 [4] Paul Maguire et al., ‘Controlled Microdroplet Transport in an Atmospheric Pressure Microplasma’, Applied Physics Letters, 106.22 (2015) https://doi.org/10.1063/1.4922034 Figure 1

Control of Hydrogen Concentration in Ingazno Thin Film Using Cryopumping System

Recently, amorphous metal-oxide semiconductors (AOSs) such as indium gallium zinc oxide (IGZO) have attracted great attention with their lower power consumption and higher mobility than amorphous silicon in the display field. However, the threshold voltage (Vth) shift of IGZO thin film transistor (TFT) caused by their poor reliability leads to the drop panel luminance. Therefore, improvement of IGZO TFT reliability is necessary, which is largely influenced by oxygen vacancy and hydrogen. In particular, hydrogen has shown different roles inside the IGZO active layer by hydrogen concentration. At lower concentration, the hydrogen passivation of oxygen deficiency region induces the improvement of initial electrical characteristics and reliability [2]. Meanwhile, Vth shift and degradation reliability are generated at higher concentration owing to the hydrogen related defect states [3]. Therefore, controlling excess hydrogen is necessary for reliability enhancement.In this work, IGZO thin film was fabricated by cryopumping system instead of a turbo molecular pump (TMP) for radio frequency sputtering to reduce hydrogen concentration. Cryopump is an adsorption type that enables excellent evacuation ability of hydrogen and moisture taking up most of the partial pressure in high vacuum. As a result, deposition of IGZO thin film with lower hydrogen impurity is available. The hydrogen concentration in the IGZO thin film using both cryopump and TMP was quantitatively analyzed by elastic recoil detection (ERD) analysis. Then, electrical characteristics of the self-aligned top-gate structure TFTs fabricated by both pumps were measured with bias stress conditions.To sum up, we showed the improved reliability of IGZO TFT by controlling excess hydrogen using cryopumping system. Fig.1. (a) Schematic of RF magnetron sputtering process with cryopump. (b) TOF-SIMS depth profiles of hydrogen concentration in IGZO film using TMP and cryopump Acknowledgment This work was supported by the Korea Evaluation Institute of Industrial Technology(KEIT) grant funded by the Korea government (MOTIE) (No. 2021-11-1283) References Chung, Ui-Jin, et al. "15‐1: Invited Paper: Manufacturing Technology of LTPO TFT." SID Symposium Digest of Technical Papers. Vol. 51. No. 1. 2020.Hanyu, Yuichiro, et al. "Hydrogen passivation of electron trap in amorphous In-Ga-Zn-O thin-film transistors." Applied Physics Letters 103.20 (2013): 202114.Mativenga, Mallory, et al. "Origin of light instability in amorphous IGZO thin-film transistors and its suppression." Scientific reports 11.1 (2021): 1-12 Figure 1

(Digital Presentation) Biosensors – Researching at the Crossroads of Engineering and the Sciences

It has been a pleasure and honor to know Dr. Landheer for more than three decades and to have collaborated with him. In this invited presentation, I will focus on one aspect of our collaboration – the topic of Biosensors – which was our last research collaboration. In the list of references [1-15], I provide all publications we collaborated on since 1986.Biosensors are increasingly used in environmental applications, especially for water quality monitoring. This is because the availability of safe drinking water is fundamental to our good health. However, as water resources get increasingly stressed, ensuring a safe water supply and effective water treatment becomes increasingly important. In addition, waterborne illnesses are a significant public health problem. At the same time, current monitoring of microbiological contamination of water currently is time-consuming, laboratory based, and frequently compromises the timeliness of health advisory warnings even when contamination is found. Therefore, rapid detection of unsafe water can contribute greatly to mitigating the morbidity and mortality associated with waterborne diseases due to microbiological contaminants. Fortunately, the research community has shown increasing interest in the development of microtechnology-based sensors for the detection and identification of the bio-contaminants. These sensing systems use the same fabrication technology that has enabled the drastic lowering of cost, exponential increase in complexity of electronic chips and widespread availability of computing resources. In this presentation, we will discuss a low-cost, electrical, label-free microfabricated biosensor that we have been developing for pathogen detection related to water quality and also for ubiquitous-healthcare applications. The use of nano-dimensions devices to create futuristic nano-biosensors for both environmental and health applications will be introduced. And we will also describe our ongoing work to create highly integrated and parallel detection systems by integrating the sensor, the processing electronics and the pre-processing stages on the same cheap substrate. Finally, the success of such a low-cost, highly integrated sensing system demands a convergence of expertise from various engineering disciplines, the physical and life sciences as well as public health. References D Landheer et al, “Bioaffinity Sensors Based on MOS Field—Effect Transistors,” in Semiconductor Device-Based Sensors for Gas, Chemical, and Biomedical Applications, Eds. Ren, Pearton, Taylor & Francis Books, Boca Raton, 215-265, 2010.MW Shinwari, et al, Microfabricated Reference Electrodes and their Biosensing Applications, Sensors, Vol. 10(3), pp. 1679-1715, 2010.MW Shinwari, MJ Deen, D Landheer, “Study of the Electrolyte-Insulator-Semiconductor Field-Effect Transistor with Applications in Biosensor Design,” Microelectronics Reliability, Vol. 47(12), pp. 2025-2057, 2007.D Landheer, et al, Calculation of the Response of Field-Effect Transistors to Charged Biological Molecules, IEEE Sensors Journal, Vol. 7, 1233-1242, 2007.WH Jiang, et al, Post-processing of Commercial CMOS Chips for the Fabrication of DNA Bio-FET Sensor Arrays, Proceedings of MRS Symposium - Fall Meeting, 6 pages, 2006.Bioelectronics, Biointerfaces, and Biomedical Applications 2, Eds., D Landheer, R. Bashir, M. Deen, C. Kranz, C. Liu, M. Madou, A. Offenhaeusser, R. Schasfoort, ECS Transactions, Vol. 3, Issue 26, 2006.MJ Deen, et al, Noise Considerations in Field-Effect Biosensors, Journal Applied Physics, Vol. 100, #074703, 8 pages, 2006.MJ Deen, et al, High Sensitivity Detection of Biological Species via the Field-Effect, Proceedings of the IEEE ICCDCS, Playa del Carmen, Mexico, pp. 381-385, 2006.D Landheer, et al, Model for the Field-Effect from Layers of Biological Macromolecules on the Gates of Metal-Oxide-Semiconductor Transistors, Journal Applied Physics, Vol. 98, # 044701, 2005.Silicon Nitride and Silicon Dioxide Thin Insulating Films, Eds., R.E. Sah, MJ Deen, D Landheer, K.B. Sundaram, W.D. Brown, D. Misra, ECS Proceedings PV-03, 636 pages 2003.Silicon Nitride and Silicon Dioxide Thin Insulating Films, Eds., K.B. Sundaram, MJ Deen, D Landheer, W.D. Brown, D. Misra, M.D. Allendorf, R.E. Sah, ECS Proceedings Volume PV 2001-7, 2001.MJ Deen, et al, Low Frequency Noise in Cadmium Selenide Thin-Film Transistors, Applied Physics Letters, Vol. 77(14), pp. 2234-2236, 2000.MJ Deen, et al, Low Frequency Noise in CdSe Thin-Film Transistors, ESSDERC 2000, Cork, Ireland, pp. 592-595, 2000.MJ Deen, et al, NbN Thin Films Reactively Sputtered with a High Field DC Magnetron, Journal of Vacuum Science and Technology A, Vol. 6(4), pp. 2299-2303, 1988.MJ Deen, et al, The Effect of the Deposition Rate on the Properties of DC Magnetron Sputtered NbN Thin Films, Bull Am Phys Soc., Vol. 32(3), p. 646, 1987.

(Invited) Grain Boundary and Surface Atomic Structures and Diffusion in Li-Ion Battery Related Crystals

The properties of lithium ion battery cathodes strongly depend on the diffusion of lithium ions during charge/discharge process. Then, direct visualization of lithium site is required to understand the mechanism of the diffusion of lithium ions. In this study, aberration (Cs) corrected STEM were applied to directly observe the {010} surface, which corresponded to perpendicular to the 1-D diffusion orientation, of the olivine LixFePO4. The morphology of the interface between Li-rich and Li-poor phases of LixFePO4 after chemical delithiation were observed with atomic resolution at fit intervals during half a year. It was found that orientation of boundary layers at the FePO4/Li2/3FePO4 interface gradually changed from lower index planes to higher index planes. This indicates that intermediate phase plays an important role in healing crystal cracking by allowing the interface to remain coherent so that Li ions can diffuse back into regions depleted during delithiation. The mechanism of the lithiation/delithiation from and to the surface will be discussed based on the observation results.Lithium lanthanum titanate (LLTO) is expected to apply for an electrolyte in the all-solid-state Li-ion battery because of its high Li-ion conductivity in the bulk. However, it has been reported that Li-ion conductivity is strongly suppressed at the grain boundaries (GBs) in polycrystalline materials. It is therefore needed to understand the atomistic mechanism of the reduction of Li-ion conductivity at individual GBs in order to design suitable LLTO polycrystals. In this study, two different GBs, Σ5 and Σ13, were prepared by fabricating the bicrystals, and their structures were observed by Cs corrected STEM and atomic force microscopy (AFM). Then, the charge states, Li-ion conductivities, atomic and electronic structures at the respective Σ5 and Σ13 GBs of LLTO were systematically and quantitatively investigated. It was found that the Σ5 GB has no significant influence on Li-ion conductivity, but the Σ13 GB shows the significant reduction of the Li-ion conductivity. We further found that Σ13 GB is positively charged by the formation of large amount of oxygen vacancies at the GB. Li-ion depletion layers is considered to be formed at the Σ13 GB, which causes the significant reduction of Li-ion conductivity, to compensate such positive charge at the GB.References Kobayashi, C.A.J.Fisher, T.Kato,Y.Ukyo,T.Hirayama and Y.Ikuhara, Nano Lett. 16, 5409 (2016).Kobayashi, A. Kuwabara, C. A.J. Fisher, Y. Ukyo and Y. Ikuhara,Nat. Commun., 9, 2863 (2018)Sasano, R. Ishikawa, I. Sugiyama, T. Higashi, T. Kimura, Y. H. Ikuhara, N. Shibata and Y. Ikuhara, Applied Physics Express, 10, 061102 (2017)Sasano, R. Ishikawa, K. Kawahara, T. Kimura, Y. H. Ikuhara, N. Shibata and Y. Ikuhara, Applied Physics Letters, 116, 043901 (2020)