Showing papers by "Ali Javey published in 2017"

Autonomous sweat extraction and analysis applied to cystic fibrosis and glucose monitoring using a fully integrated wearable platform

Abstract: Perspiration-based wearable biosensors facilitate continuous monitoring of individuals’ health states with real-time and molecular-level insight. The inherent inaccessibility of sweat in sedentary individuals in large volume (≥10 µL) for on-demand and in situ analysis has limited our ability to capitalize on this noninvasive and rich source of information. A wearable and miniaturized iontophoresis interface is an excellent solution to overcome this barrier. The iontophoresis process involves delivery of stimulating agonists to the sweat glands with the aid of an electrical current. The challenge remains in devising an iontophoresis interface that can extract sufficient amount of sweat for robust sensing, without electrode corrosion and burning/causing discomfort in subjects. Here, we overcame this challenge through realizing an electrochemically enhanced iontophoresis interface, integrated in a wearable sweat analysis platform. This interface can be programmed to induce sweat with various secretion profiles for real-time analysis, a capability which can be exploited to advance our knowledge of the sweat gland physiology and the secretion process. To demonstrate the clinical value of our platform, human subject studies were performed in the context of the cystic fibrosis diagnosis and preliminary investigation of the blood/sweat glucose correlation. With our platform, we detected the elevated sweat electrolyte content of cystic fibrosis patients compared with that of healthy control subjects. Furthermore, our results indicate that oral glucose consumption in the fasting state is followed by increased glucose levels in both sweat and blood. Our solution opens the possibility for a broad range of noninvasive diagnostic and general population health monitoring applications.

Wearable Microfluidic Diaphragm Pressure Sensor for Health and Tactile Touch Monitoring

Abstract: Flexible pressure sensors have many potential applications in wearable electronics, robotics, health monitoring, and more. In particular, liquid-metal-based sensors are especially promising as they can undergo strains of over 200% without failure. However, current liquid-metal-based strain sensors are incapable of resolving small pressure changes in the few kPa range, making them unsuitable for applications such as heart-rate monitoring, which require a much lower pressure detection resolution. In this paper, a microfluidic tactile diaphragm pressure sensor based on embedded Galinstan microchannels (70 µm width × 70 µm height) capable of resolving sub-50 Pa changes in pressure with sub-100 Pa detection limits and a response time of 90 ms is demonstrated. An embedded equivalent Wheatstone bridge circuit makes the most of tangential and radial strain fields, leading to high sensitivities of a 0.0835 kPa-1 change in output voltage. The Wheatstone bridge also provides temperature self-compensation, allowing for operation in the range of 20-50 °C. As examples of potential applications, a polydimethylsiloxane (PDMS) wristband with an embedded microfluidic diaphragm pressure sensor capable of real-time pulse monitoring and a PDMS glove with multiple embedded sensors to provide comprehensive tactile feedback of a human hand when touching or holding objects are demonstrated.

Strain-Engineered Growth of Two-Dimensional Materials

Abstract: The application of strain to semiconductors allows for controlled modification of their band structure. This principle is employed for the manufacturing of devices ranging from high-performance transistors to solid-state lasers. Traditionally, strain is typically achieved via growth on lattice-mismatched substrates. For two-dimensional (2D) semiconductors, this is not feasible as they typically do not interact epitaxially with the substrate. Here, we demonstrate controlled strain engineering of 2D semiconductors during synthesis by utilizing the thermal coefficient of expansion mismatch between the substrate and semiconductor. Using WSe2 as a model system, we demonstrate stable built-in strains ranging from 1% tensile to 0.2% compressive on substrates with different thermal coefficient of expansion. Consequently, we observe a dramatic modulation of the band structure, manifested by a strain-driven indirect-to-direct bandgap transition and brightening of the dark exciton in bilayer and monolayer WSe2, respectively. The growth method developed here should enable flexibility in design of more sophisticated devices based on 2D materials. Strain engineering is an essential tool for modifying local electronic properties in silicon-based electronics. Here, Ahn et al. demonstrate control of biaxial strain in two-dimensional materials based on the growth substrate, enabling more complex low-dimensional electronics.

Mid-Wave Infrared Photoconductors Based on Black Phosphorus-Arsenic Alloys

Abstract: Black phosphorus (b-P) and more recently black phosphorus-arsenic alloys (b-PAs) are candidate 2D materials for the detection of mid-wave and potentially long-wave infrared radiation. However, studies to date have utilized laser-based measurements to extract device performance and the responsivity of these detectors. As such, their performance under thermal radiation and spectral response has not been fully characterized. Here, we perform a systematic investigation of gated-photoconductors based on b-PAs alloys as a function of thickness over the composition range of 0-91% As. Infrared transmission and reflection measurements are performed to determine the bandgap of the various compositions. The spectrally resolved photoresponse for various compositions in this material system is investigated to confirm absorption measurements, and we find that the cutoff wavelength can be tuned from 3.9 to 4.6 μm over the studied compositional range. In addition, we investigated the temperature-dependent photoresponse and performed calibrated responsivity measurements using blackbody flood illumination. Notably, we find that the specific detectivity (D*) can be optimized by adjusting the thickness of the b-P/b-PAs layer to maximize absorption and minimize dark current. We obtain a peak D* of 6 × 1010 cm Hz1/2 W-1 and 2.4 × 1010 cm Hz1/2 W-1 for pure b-P and b-PAs (91% As), respectively, at room temperature, which is an order of magnitude higher than commercially available mid-wave infrared detectors operating at room temperature.

Conductive and Stable Magnesium Oxide Electron‐Selective Contacts for Efficient Silicon Solar Cells

Abstract: A high Schottky barrier (>0.65 eV) for electrons is typically found on lightly doped n-type crystalline (c-Si) wafers for a variety of contact metals. This behavior is commonly attributed to the Fermi-level pinning effect and has hindered the development of n-type c-Si solar cells, while its p-type counterparts have been commercialized for several decades, typically utilizing aluminium alloys in full-area, and more recently, partial-area rear contact configurations. Here the authors demonstrate a highly conductive and thermally stable electrode composed of a magnesium oxide/aluminium (MgOx/Al) contact, achieving moderately low resistivity Ohmic contacts on lightly doped n-type c-Si. The electrode, functionalized with nanoscale MgOx films, significantly enhances the performance of n-type c-Si solar cells to a power conversion efficiency of 20%, advancing n-type c-Si solar cells with full-area dopant-free rear contacts to a point of competitiveness with the standard p-type architecture. The low thermal budget of the cathode formation, its dopant-free nature, and the simplicity of the device structure enabled by the MgOx/Al contact open up new possibilities in designing and fabricating low-cost optoelectronic devices, including solar cells, thin film transistors, or light emitting diodes.

Room temperature multiplexed gas sensing using chemical-sensitive 3.5-nm-thin silicon transistors

Abstract: There is great interest in developing a low-power gas sensing technology that can sensitively and selectively quantify the chemical composition of a target atmosphere. Nanomaterials have emerged as extremely promising candidates for this technology due to their inherent low-dimensional nature and high surface-to-volume ratio. Among these, nanoscale silicon is of great interest because pristine silicon is largely inert on its own in the context of gas sensing, unless functionalized with an appropriate gas-sensitive material. We report a chemical-sensitive field-effect transistor (CS-FET) platform based on 3.5-nm-thin silicon channel transistors. Using industry-compatible processing techniques, the conventional electrically active gate stack is replaced by an ultrathin chemical-sensitive layer that is electrically nonconducting and coupled to the 3.5-nm-thin silicon channel. We demonstrate a low-power, sensitive, and selective multiplexed gas sensing technology using this platform by detecting H2S, H2, and NO2 at room temperature for environment, health, and safety in the oil and gas industry, offering significant advantages over existing technology. Moreover, the system described here can be readily integrated with mobile electronics for distributed sensor networks in environmental pollution mapping and personal air-quality monitors.

Efficient solar-driven electrochemical CO2 reduction to hydrocarbons and oxygenates

Abstract: Solar to chemical energy conversion could provide an alternative to mankind's unsustainable use of fossil fuels. One promising approach is the electrochemical reduction of CO2 into chemical products, in particular hydrocarbons and oxygenates which are formed by multi-electron transfer reactions. Here, a nanostructured Cu–Ag bimetallic cathode is utilized to selectively and efficiently facilitate these reactions. When operated in an electrolysis cell, the cathode provides a constant energetic efficiency for hydrocarbon and oxygenate production. As a result, when coupled to Si photovoltaic cells, solar conversion efficiencies of 3–4% to the target products are achieved for 0.35 to 1 Sun illumination. Use of a four-terminal III–V/Si tandem solar cell configuration yields a conversion efficiency to hydrocarbons and oxygenates exceeding 5% at 1 Sun illumination. This study provides a clear framework for the future advancement of efficient solar-driven CO2 reduction devices.

Smart Actuators and Adhesives for Reconfigurable Matter.

Abstract: ConspectusBiological systems found in nature provide excellent stimuli-responsive functions. The camouflage adaptation of cephalopods (octopus, cuttlefish), rapid stiffness change of sea cucumbers, opening of pine cones in response to humidity, and rapid closure of Venus flytraps upon insect touch are some examples of nature’s smart systems. Although current technologies are still premature to mimic these sophisticated structures and functions in smart biological systems, recent work on stimuli-responsive programmable matter has shown great progress. Stimuli-responsive materials based on hydrogels, responsive nanocomposites, hybrid structures, shape memory polymers, and liquid crystal elastomers have demonstrated excellent responsivities to various stimuli such as temperature, light, pH, and electric field. However, the technologies in these stimuli-responsive materials are still not sophisticated enough to demonstrate the ultimate attributes of an ideal programmable matter: fast and reversible reconfigur...

3D Printed “Earable” Smart Devices for Real-Time Detection of Core Body Temperature

Abstract: Real-time detection of basic physiological parameters such as blood pressure and heart rate is an important target in wearable smart devices for healthcare. Among these, the core body temperature is one of the most important basic medical indicators of fever, insomnia, fatigue, metabolic functionality, and depression. However, traditional wearable temperature sensors are based upon the measurement of skin temperature, which can vary dramatically from the true core body temperature. Here, we demonstrate a three-dimensional (3D) printed wearable “earable” smart device that is designed to be worn on the ear to track core body temperature from the tympanic membrane (i.e., ear drum) based on an infrared sensor. The device is fully integrated with data processing circuits and a wireless module for standalone functionality. Using this smart earable device, we demonstrate that the core body temperature can be accurately monitored regardless of the environment and activity of the user. In addition, a microphone an...

Highly Stable Near-Unity Photoluminescence Yield in Monolayer MoS2 by Fluoropolymer Encapsulation and Superacid Treatment

Abstract: Recently, there has been considerable research interest in two-dimensional (2D) transition-metal dichalcogenides (TMDCs) for future optoelectronic applications. It has been shown that surface passivation with the organic nonoxidizing superacid bis(trifluoromethane)sulfonamide (TFSI) produces MoS2 and WS2 monolayers whose recombination is at the radiative limit, with a photoluminescence (PL) quantum yield (QY) of ∼100%. While the surface passivation persists under ambient conditions, exposure to conditions such as water, solvents, and low pressure found in typical semiconductor processing degrades the PL QY. Here, an encapsulation/passivation approach is demonstrated that yields near-unity PL QY in MoS2 and WS2 monolayers which are highly stable against postprocessing. The approach consists of two simple steps: encapsulation of the monolayers with an amorphous fluoropolymer and a subsequent TFSI treatment. The TFSI molecules are able to diffuse through the encapsulation layer and passivate the defect state...

Defect passivation of transition metal dichalcogenides via a charge transfer van der Waals interface

Abstract: Integration of transition metal dichalcogenides (TMDs) into next-generation semiconductor platforms has been limited due to a lack of effective passivation techniques for defects in TMDs. The formation of an organic-inorganic van der Waals interface between a monolayer (ML) of titanyl phthalocyanine (TiOPc) and a ML of MoS2 is investigated as a defect passivation method. A strong negative charge transfer from MoS2 to TiOPc molecules is observed in scanning tunneling microscopy. As a result of the formation of a van der Waals interface, the ION/IOFF in back-gated MoS2 transistors increases by more than two orders of magnitude, whereas the degradation in the photoluminescence signal is suppressed. Density functional theory modeling reveals a van der Waals interaction that allows sufficient charge transfer to remove defect states in MoS2. The present organic-TMD interface is a model system to control the surface/interface states in TMDs by using charge transfer to a van der Waals bonded complex.

A Low Resistance Calcium/Reduced Titania Passivated Contact for High Efficiency Crystalline Silicon Solar Cells

Abstract: Recent advances in the efficiency of crystalline silicon (c-Si) solar cells have come through the implementation of passivated contacts that simultaneously reduce recombination and resistive losses within the contact structure. In this contribution, low resistivity passivated contacts are demonstrated based on reduced titania (TiOx) contacted with the low work function metal, calcium (Ca). By using Ca as the overlying metal in the contact structure we are able to achieve a reduction in the contact resistivity of TiOx passivated contacts of up to two orders of magnitude compared to previously reported data on Al/TiOx contacts, allowing for the application of the Ca/TiOx contact to n-type c-Si solar cells with partial rear contacts. Implementing this contact structure on the cell level results in a power conversion efficiency of 21.8% where the Ca/TiOx contact comprises only ≈6% of the rear surface of the solar cell, an increase of 1.5% absolute compared to a similar device fabricated without the TiOx interlayer.

Band Tailing and Deep Defect States in CH3NH3Pb(I1–xBrx)3 Perovskites As Revealed by Sub-Bandgap Photocurrent

Abstract: Organometal halide perovskite semiconductors have emerged as promising candidates for optoelectronic applications because of the outstanding charge carrier transport properties, achieved with low-temperature synthesis. Here, we present highly sensitive sub-bandgap external quantum efficiency (EQE) measurements of Au/spiro-OMeTAD/CH3NH3Pb(I1–xBrx)3/TiO2/FTO/glass photovoltaic devices. The room-temperature spectra show exponential band tails with a sharp onset characterized by low Urbach energies (Eu) over the full halide composition space. The Urbach energies are 15–23 meV, lower than those for most semiconductors with similar bandgaps (especially with Eg > 1.9 eV). Intentional aging of CH3NH3Pb(I1–xBrx)3 for up to 2300 h, reveals no change in Eu, despite the appearance of the PbI2 phase due to decomposition, and confirms a high degree of crystal ordering. Moreover, sub-bandgap EQE measurements reveal an extended band of sub-bandgap electronic states that can be fit with one or two point defects for pure C...

Wafer-Scale Growth of WSe2 Monolayers Toward Phase-Engineered Hybrid WOx/WSe2 Films with Sub-ppb NOx Gas Sensing by a Low-Temperature Plasma-Assisted Selenization Process

Abstract: An inductively coupled plasma (ICP) process was used to synthesize transition metal dichalcogenides (TMDs) through a plasma-assisted selenization process of metal oxide (MOx) at a temperature as low as 250 °C. In comparison with other CVD processes, the use of ICP facilitates the decomposition of the precursors at low temperatures. Therefore, the temperature required for the formation of TMDs can be drastically reduced. WSe2 was chosen as a model material system due to its technological importance as a p-type inorganic semiconductor with an excellent hole mobility. Large-area synthesis of WSe2 on polyimide (30 × 40 cm2) flexible substrates and 8 in. silicon wafers with good uniformity was demonstrated at the formation temperature of 250 °C confirmed by Raman and X-ray photoelectron (XPS) spectroscopy. Furthermore, by controlling different H2/N2 ratios, hybrid WOx/WSe2 films can be formed at the formation temperature of 250 °C confirmed by TEM and XPS. Remarkably, hybrid films composed of partially reduced...

Calcium contacts to n-type crystalline silicon solar cells

Abstract: Direct metallization of lightly doped n-type crystalline silicon (c-Si) is known to routinely produce non-Ohmic (rectifying) contact behaviour. This has inhibited the development of n-type c-Si solar cells with partial rear contacts, an increasingly popular cell design for high performance p-type c-Si solar cells. In this contribution we demonstrate that low resistance Ohmic contact to n-type c-Si wafers can be achieved by incorporating a thin layer of the low work function metal calcium (ϕ ~2.9 eV) between the silicon surface and an overlying aluminium capping layer. Using this approach, contact resistivities of ρc ~ 2 mΩcm2 can be realised on undiffused n-type silicon, thus enabling partial rear contacts cell designs on n-type silicon without the need for a phosphorus diffusion. Integrating the Ca/Al stack into a partial rear contact solar cell architecture fabricated on a lightly doped (ND = 4.5 × 1014 cm−3) n-type wafer resulted in a device efficiency of η = 17.6% where the Ca/Al contact comprised only ~1.26% of the rear surface. We demonstrate an improvement in this cell structure to an efficiency of η = 20.3% by simply increasing the wafer doping by an order of magnitude to ND = 5.4 × 1015 cm−3. Copyright © 2016 John Wiley & Sons, Ltd.

Superacid-Treated Silicon Surfaces: Extending the Limit of Carrier Lifetime for Photovoltaic Applications

Abstract: Minimizing carrier recombination at interfaces is of extreme importance in the development of high-efficiency photovoltaic devices and for bulk material characterization. Here, we investigate a temporary room temperature superacid-based passivation scheme, which provides surface recombination velocities below 1 cm/s, thus placing our passivation scheme amongst state-of-the-art dielectric films. Application of the technique to high-quality float-zone silicon allows the currently accepted intrinsic carrier lifetime limit to be reached and calls its current parameterization into doubt for 1 Ω·cm n-type wafers. The passivation also enables lifetimes up to 65 ms to be measured in high-resistivity Czochralski silicon, which, to our knowledge, is the highest ever measured in Czochralski-grown material. The passivation strategies developed in this work will help diagnose bulk lifetime degradation under solar cell processing conditions and also help quantify the electronic quality of new passivation schemes.

Determining Atomic-Scale Structure and Composition of Organo-Lead Halide Perovskites by Combining High-Resolution X-ray Absorption Spectroscopy and First-Principles Calculations

Abstract: We combine high-energy resolution fluorescence detection (HERFD) X-ray absorption spectroscopy (XAS) measurements with first-principles density functional theory (DFT) calculations to provide a molecular-scale understanding of local structure, and its role in defining optoelectronic properties, in CH3NH3Pb(I1–xBrx)3 perovskites. The spectra probe a ligand field splitting in the unoccupied d states of the material, which lie well above the conduction band minimum and display high sensitivity to halide identity, Pb-halide bond length, and Pb-halide octahedral tilting, especially for apical halide sites. The spectra are also sensitive to the organic cation. We find that the halides in these mixed compositions are randomly distributed, rather than having preferred octahedral sites, and that thermal tilting motions dominate over any preferred structural distortions as a function of halide composition. These findings demonstrate the utility of the combined HERFD XAS and DFT approach for determining structural d...

Nanoscale Junction Formation by Gas-Phase Monolayer Doping

Abstract: A major challenge in transistor technology scaling is the formation of controlled ultrashallow junctions with nanometer-scale thickness and high spatial uniformity Monolayer doping (MLD) is an efficient method to form such nanoscale junctions, where the self-limiting nature of semiconductor surfaces is utilized to form adsorbed monolayers of dopant-containing molecules followed by rapid thermal annealing (RTA) to diffuse the dopants to a desired depth Unlike ion implantation, the process does not induce crystal damage, thus making it highly attractive for nanoscale transistor processing To date, reported MLD processes have relied on solution processing for monolayer formation Gas-phase processing, however, benefits from higher intra- and interwafer uniformity and conformal coverage of 3D structures and is more desirable for manufacturing In this regard, we report a new approach for MLD in silicon and germanium using gas-phase monolayer formation We call this technology gas-phase monolayer doping (GP

Measuring the edge recombination velocity of monolayer semiconductors

Abstract: Understanding edge effects and quantifying their impact on the carrier properties of two-dimensional (2D) semiconductors is an essential step toward utilizing these materials for high performance electronic and optoelectronic devices.1–5 WS 2 monolayers patterned into disks of varying diameters are used to experimentally determine the influence of edges on their optical properties. Carrier lifetime measurements show a decrease in the effective lifetime, τ effective , as a function of decreasing diameter, suggesting that the edges are active sites for carrier recombination. Accordingly, we introduce a metric called edge recombination velocity (ERV) to characterize the impact of 2D material edges on non-radiative recombination. The unpassivated WS 2 monolayer disks yield an ERV ∼ 4 × 104 cm/s. This work quantifies the non-radiative recombination edge effects in monolayer semiconductors, while simultaneously establishing a practical characterization technique towards experimental explorations of edge passivation methods for 2D materials.

Analysis of the interface characteristics of CVD-grown monolayer MoS2 by noise measurements.

Abstract: We investigated the current-voltage and noise characteristics of two-dimensional (2D) monolayer molybdenum disulfide (MoS2) synthesized by chemical vapor deposition (CVD). A large number of trap states were produced during the CVD process of synthesizing MoS2, resulting in a disordered monolayer MoS2 system. The interface trap density between CVD-grown MoS2 and silicon dioxide was extracted from the McWhorter surface noise model. Notably, generation-recombination noise which is attributed to charge trap states was observed at the low carrier density regime. The relation between the temperature and resistance following the power law of a 2D inverted-random void model supports the idea that disordered CVD-grown monolayer MoS2 can be analyzed using a percolation theory. This study can offer a viewpoint to interpret synthesized low-dimensional materials as highly disordered systems.

High-gain monolithic 3D CMOS inverter using layered semiconductors

Abstract: We experimentally demonstrate a monolithic 3D integrated complementary metal oxide semiconductor (CMOS) inverter using layered transition metal dichalcogenide semiconductor N-channel (NMOS) and P-channel (PMOS) MOSFETs, which are sequentially integrated on two levels. The two devices share a common gate. Molybdenum disulphide and tungsten diselenide are used as channel materials for NMOS and PMOS, respectively, with an ON-to-OFF current ratio (ION/IOFF) greater than 106 and electron and hole mobilities of 37 and 236 cm2/Vs, respectively. The voltage gain of the monolithic 3D inverter is about 45 V/V at a supply voltage of 1.5 V and a gate length of 1 μm. This is the highest reported gain at the smallest gate length and the lowest supply voltage for any 3D integrated CMOS inverter using any layered semiconductor.

Wearable Devices: Wearable Microfluidic Diaphragm Pressure Sensor for Health and Tactile Touch Monitoring (Adv. Mater. 39/2017)

Abstract: Author(s): Gao, Yuji; Ota, Hiroki; Schaler, Ethan W; Chen, Kevin; Zhao, Allan; Gao, Wei; Fahad, Hossain M; Leng, Yonggang; Zheng, Anzong; Xiong, Furui; Zhang, Chuchu; Tai, Li-Chia; Zhao, Peida; Fearing, Ronald S; Javey, Ali

Microchannel contacting of crystalline silicon solar cells

Abstract: There is tremendous interest in reducing losses caused by the metal contacts in silicon photovoltaics, particularly the optical and resistive losses of the front metal grid. One commonly sought-after goal is the creation of high aspect-ratio metal fingers which provide an optically narrow and low resistance pathway to the external circuit. Currently, the most widely used metal contact deposition techniques are limited to widths and aspect-ratios of ~40 μm and ~0.5, respectively. In this study, we introduce the use of a micropatterned polydimethylsiloxane encapsulation layer to form narrow (~20 μm) microchannels, with aspect-ratios up to 8, on the surface of solar cells. We demonstrate that low temperature metal pastes, electroless plating and atomic layer deposition can all be used within the microchannels. Further, we fabricate proof-of-concept structures including simple planar silicon heterojunction and homojunction solar cells. While preliminary in both design and efficiency, these results demonstrate the potential of this approach and its compatibility with current solar cell architectures.

Nanoscience and Nanotechnology Cross Borders

Abstract: Author(s): Khademhosseini, Ali; Chan, Warren WC; Chhowalla, Manish; Glotzer, Sharon C; Gogotsi, Yury; Hafner, Jason H; Hammond, Paula T; Hersam, Mark C; Javey, Ali; Kagan, Cherie R; Kotov, Nicholas A; Lee, Shuit-Tong; Li, Yan; Mohwald, Helmuth; Mulvaney, Paul A; Nel, Andre E; Parak, Wolfgang J; Penner, Reginald M; Rogach, Andrey L; Schaak, Raymond E; Stevens, Molly M; Wee, Andrew TS; Brinker, Jeffrey; Chen, Xiaoyuan; Chi, Lifeng; Crommie, Michael; Dekker, Cees; Farokhzad, Omid; Gerber, Christoph; Ginger, David S; Irvine, Darrell J; Kiessling, Laura L; Kostarelos, Kostas; Landes, Christy; Lee, Takhee; Leggett, Graham J; Liang, Xing-Jie; Liz-Marzan, Luis; Millstone, Jill; Odom, Teri W; Ozcan, Aydogan; Prato, Maurizio; Rao, CNR; Sailor, Michael J; Weiss, Emily; Weiss, Paul S

Autonomous Sweat Extraction and Analysis Using a Fully-Integrated Wearable Platform

Abstract: A device for on-demand sweat extraction and analysis is realized as a printed circuit comprising a microcontroller, an iontophoresis circuit, a sensing circuit, and an electrode array having iontophoresis electrodes for sweat induction and sensing electrodes connected for sweat sensing. The sensing electrodes are positioned between the iontophoresis electrodes. The iontophoresis electrodes are preferably crescent-shaped and comprise a layer of agonist agent hydrogel loaded with sweat stimulating compounds. The iontophoresis circuit has a programmable current source for iontophoresis current delivery, and the sensing circuit includes two signal conditioning paths, where each of the paths includes an analog front-end to amplify a sensed signal and a low-pass filter to minimize high frequency noise and electromagnetic interference. The iontophoresis circuit and the sensing circuit are electrically decoupled for independent functionality.

Metal Nanoparticle Hole Contacts for Silicon Solar Cells

Abstract: Recent years have seen the development of a broad range of novel contacting strategies for crystalline silicon (c-Si) solar cells. This study is focused on the use of a sparse layer of platinum nanoparticles to enhance the hole contact characteristics of a c-Si/transparent conductive oxide hole contact. It is shown that the addition of the Pt nanoparticle layer results in a 2 order of magnitude reduction in contact resistivity on both lightly and heavily doped p-type surfaces with values of ~3 and $\sim 0.2 m\Omega cm^{2}$ , respectively. A high transparency can be maintained for such contacts from strict control of the nanoparticle deposition process with a predicted Jsc loss of just 0.15 mA/cm2as a result of the Pt nanoparticle layer. Finally, the thermal and damp heat stability of the Pt nanoparticle contact is investigated, revealing promising initial results.

A Big Year Ahead for Nano in 2018

Abstract: In addition to publishing top work in nanoscience and nanotechnology from around the world, our goals for ACS Nano include: accelerating advances in the field by identifying and elaborating opportunities; leveraging nanoscience and nanotechnology strategies, techniques, and methods to impact other fields; being a public face for our fields; and linking together global science, engineering, and medicine. We have a number of strategies for achieving these goals and more. Among them is having our editors using our positions as active researchers to connect with you (and each other) around the world. This year, between our editors, we gave hundreds of talks in more than 35 countries, at universities, research institutions, and conferences, as well as to the public. We see the effects of our personal interactions during these visits in new submissions and our expanding readership. In the next year and beyond, we will have a sustained effort to engage even more at a number of special events.

Low Pressure Vapor-assisted Solution Process for Tunable Band Gap Pinhole-free Methylammonium Lead Halide Perovskite Films.

Abstract: Organo-lead halide perovskites have recently attracted great interest for potential applications in thin-film photovoltaics and optoelectronics. Herein, we present a protocol for the fabrication of this material via the low-pressure vapor assisted solution process (LP-VASP) method, which yields ~19% power conversion efficiency in planar heterojunction perovskite solar cells. First, we report the synthesis of methylammonium iodide (CH3NH3I) and methylammonium bromide (CH3NH3Br) from methylamine and the corresponding halide acid (HI or HBr). Then, we describe the fabrication of pinhole-free, continuous methylammonium-lead halide perovskite (CH3NH3PbX3 with X = I, Br, Cl and their mixture) films with the LP-VASP. This process is based on two steps: i) spin-coating of a homogenous layer of lead halide precursor onto a substrate, and ii) conversion of this layer to CH3NH3PbI3-xBrx by exposing the substrate to vapors of a mixture of CH3NH3I and CH3NH3Br at reduced pressure and 120 °C. Through slow diffusion of the methylammonium halide vapor into the lead halide precursor, we achieve slow and controlled growth of a continuous, pinhole-free perovskite film. The LP-VASP allows synthetic access to the full halide composition space in CH3NH3PbI3-xBrx with 0 ≤ x ≤ 3. Depending on the composition of the vapor phase, the bandgap can be tuned between 1.6 eV ≤ Eg ≤ 2.3 eV. In addition, by varying the composition of the halide precursor and of the vapor phase, we can also obtain CH3NH3PbI3-xClx. Films obtained from the LP-VASP are reproducible, phase pure as confirmed by X-ray diffraction measurements, and show high photoluminescence quantum yield. The process does not require the use of a glovebox.

Our First and Next Decades at ACS Nano

Abstract: Ten years ago this month, we published our first issue of ACS Nano. We had a grand vision, which we have kept to this day, that we would accelerate advances in the field by laying out the possibilities and implications for nanoscience and nanotechnology, in addition to identifying and reporting the required steps along the way.We felt that it was critical to provide comprehensive, high-profile descriptions of novel work on which others could build. We saw that previously missing venue as an important step for our field, and 10 years on, we can now see how far we have come as a result.