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Theory of all-silicon two-photon receivers for monolithic on-chip interconnects

We theoretically analyze the use of an all-silicon PIN two-photon absorption detector integrated in a deep-submicron CMOS technology as a receiver for on-chip interconnects. Exploiting a new type of nanocavity with deep sub-wavelength light confinement, a low capacitance detector integrated with a CMOS amplifier front-end can provide a logic-level voltage output at 5 Gbps even when operating at low quantum efficiency and at BER levels suitable for on-chip signaling for a transmitter energy of just 1 fJ/bit

Photothermal Infrared Spectroscopy of Airborne Samples with Mechanical String Resonators

Micromechanical photothermal infrared spectroscopy is a promising technique, where absorption-related heating is detected by frequency detuning of microstring resonators. We present photothermal infrared spectroscopy with mechanical string resonators providing rapid identification of femtogram-scale airborne samples. Airborne sample material is directly collected on the microstring with an efficient nondiffusion limited sampling method based on inertial impaction. Resonance frequency shifts, proportional to the absorbed heat in the microstring, are recorded as monochromatic IR light is scanned over the mid-infrared range. As a proof-of-concept, we sample and analyze polyvinylpyrrolidone (PVP) and the IR spectrum measured by photothermal spectroscopy matches the reference IR spectrum measured by an FTIR spectrometer. We further identify the organic surface coating of airborne TiO₂ nanoparticles with a total mass of 4 pg. With an estimated detection limit of 44 fg, the presented sensor demonstrates a new paradigm in ultrasensitive vibrational spectroscopy for identification of airborne species

Using TiO₂ as a Conductive Protective Layer for Photocathodic H₂ Evolution

Surface passivation is a general issue for Si-based photoelectrodes because it progressively hinders electron conduction at the semiconductor/electrolyte interface. In this work, we show that a sputtered 100 nm TiO₂ layer on top of a thin Ti metal layer may be used to protect an n⁺p Si photocathode during photocatalytic H₂ evolution. Although TiO₂ is a semiconductor, we show that it behaves like a metallic conductor would under photocathodic H₂ evolution conditions. This behavior is due to the fortunate alignment of the TiO₂ conduction band with respect to the hydrogen evolution potential, which allows it to conduct electrons from the Si while simultaneously protecting the Si from surface passivation. By using a Pt catalyst the electrode achieves an H₂ evolution onset of 520 mV vs NHE and a Tafel slope of 30 mV when illuminated by the red part (λ > 635 nm) of the AM 1.5 spectrum. The saturation photocurrent (H₂ evolution) was also significantly enhanced by the antireflective properties of the TiO₂ layer. It was shown that with proper annealing conditions these electrodes could run 72 h without significant degradation. An Fe²⁺/Fe³⁺ redox couple was used to help elucidate details of the band diagram

Evaporation of Water Droplets on “Lock-and-Key” Structures with Nanoscale Features

Highly ordered poly­(dimethylsiloxane) microbowl arrays (MBAs) and microcap arrays (MCAs) with “lock-and-key” properties are successfully fabricated by self-assembly and electrochemical deposition. The wetting properties and evaporation dynamics of water droplets for both cases have been investigated. For the MBAs case, the wetting radius of the droplets remains unchanged until the portion of the droplet completely dries out at the end of the evaporation process. The pinning state extends for more than 99.5% of the total evaporation time, and the pinning–shrinking transition is essentially prevented whereas in the case of the MCAs the contact radius exhibits distinct stages during evaporation and the contact line retreats significantly in the middle of the evaporation process. We explain the phenomenon by a qualitative energy balance argument based on the different shrinkage types of the nanoscale-folded contact line

Supplementary document for Bidirectional electrostatic MEMS tunable VCSELs - 6817023.pdf

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In Situ TEM Creation and Electrical Characterization of Nanowire Devices

We demonstrate the observation and measurement of simple nanoscale devices over their complete lifecycle from creation to failure within a transmission electron microscope. Devices were formed by growing Si nanowires, using the vapor–liquid–solid method, to form bridges between Si cantilevers. We characterize the formation of the contact between the nanowire and the cantilever, showing that the nature of the connection depends on the flow of heat and electrical current during and after the moment of contact. We measure the electrical properties and high current failure characteristics of the resulting bridge devices in situ and relate these to the structure. We also describe processes to modify the contact and the nanowire surface after device formation. The technique we describe allows the direct analysis of the processes taking place during device formation and use, correlating specific nanoscale structural and electrical parameters on an individual device basis

In Situ TEM Creation and Electrical Characterization of Nanowire Devices

We demonstrate the observation and measurement of simple nanoscale devices over their complete lifecycle from creation to failure within a transmission electron microscope. Devices were formed by growing Si nanowires, using the vapor–liquid–solid method, to form bridges between Si cantilevers. We characterize the formation of the contact between the nanowire and the cantilever, showing that the nature of the connection depends on the flow of heat and electrical current during and after the moment of contact. We measure the electrical properties and high current failure characteristics of the resulting bridge devices in situ and relate these to the structure. We also describe processes to modify the contact and the nanowire surface after device formation. The technique we describe allows the direct analysis of the processes taking place during device formation and use, correlating specific nanoscale structural and electrical parameters on an individual device basis

In Situ TEM Creation and Electrical Characterization of Nanowire Devices

We demonstrate the observation and measurement of simple nanoscale devices over their complete lifecycle from creation to failure within a transmission electron microscope. Devices were formed by growing Si nanowires, using the vapor–liquid–solid method, to form bridges between Si cantilevers. We characterize the formation of the contact between the nanowire and the cantilever, showing that the nature of the connection depends on the flow of heat and electrical current during and after the moment of contact. We measure the electrical properties and high current failure characteristics of the resulting bridge devices in situ and relate these to the structure. We also describe processes to modify the contact and the nanowire surface after device formation. The technique we describe allows the direct analysis of the processes taking place during device formation and use, correlating specific nanoscale structural and electrical parameters on an individual device basis

Protection of p⁺‑n-Si Photoanodes by Sputter-Deposited Ir/IrO_<i>x</i> Thin Films

Sputter deposition of Ir/IrO_<i>x</i> on p⁺-n-Si without interfacial corrosion protection layers yielded photoanodes capable of efficient water oxidation (OER) in acidic media (1 M H₂SO₄). Stability of at least 18 h was shown by chronoamperomety at 1.23 V versus RHE (reversible hydrogen electrode) under 38.6 mW/cm² simulated sunlight irradiation (λ > 635 nm, AM 1.5G) and measurements with quartz crystal microbalances. Films exceeding a thickness of 4 nm were shown to be highly active though metastable due to an amorphous character. By contrast, 2 nm IrO_<i>x</i> films were stable, enabling OER at a current density of 1 mA/cm² at 1.05 V vs. RHE. Further improvement by heat treatment resulted in a cathodic shift of 40 mV and enabled a current density of 10 mA/cm² (requirements for a 10% efficient tandem device) at 1.12 V vs. RHS under irradiation. Thus, the simple IrO_<i>x</i>/Ir/p⁺-n-Si structures not only provide the necessary overpotential for OER at realistic device current, but also harvest ∼100 mV of free energy (voltage) which makes them among the best-performing Si-based photoanodes in low-pH media