Quantum Informed Machine-Learning Potentials for Molecular Dynamics Simulations of CO2's Chemisorption and Diffusion in Mg-MOF-74.

Among various porous solids for gas separation and purification, metal-organic frameworks (MOFs) are promising materials that potentially combine high CO2 uptake and CO2/N2 selectivity. So far, within the hundreds of thousands of MOF structures known today, it remains a challenge to computationally identify the best suited species. First principle-based simulations of CO2 adsorption in MOFs would provide the necessary accuracy; however, they are impractical due to the high computational cost. Classical force field-based simulations would be computationally feasible; however, they do not provide sufficient accuracy. Thus, the entropy contribution that requires both accurate force fields and sufficiently long computing time for sampling is difficult to obtain in simulations. Here, we report quantum-informed machine-learning force fields (QMLFFs) for atomistic simulations of CO2 in MOFs. We demonstrate that the method has a much higher computational efficiency (∼1000×) than the first-principle one while maintaining the quantum-level accuracy. As a proof of concept, we show that the QMLFF-based molecular dynamics simulations of CO2 in Mg-MOF-74 can predict the binding free energy landscape and the diffusion coefficient close to experimental values. The combination of machine learning and atomistic simulation helps achieve more accurate and efficient in silico evaluations of the chemisorption and diffusion of gas molecules in MOFs.

Silicon Nanowire Field Effect Transistor Sensors with Minimal Sensor-to-Sensor Variations and Enhanced Sensing Characteristics.

Silicon nanowire field effect transistor (FET) sensors have demonstrated their ability for rapid and label-free detection of proteins, nucleotide sequences, and viruses at ultralow concentrations with the potential to be a transformative diagnostic technology. Their nanoscale size gives them their ultralow detection ability but also makes their fabrication challenging with large sensor-to-sensor variations, thus limiting their commercial applications. In this work, a combined approach of nanofabrication, device simulation, materials, and electrical characterization is applied toward identifying and improving fabrication steps that induce sensor-to-sensor variations. An enhanced complementary metal-oxide-semiconductor-compatible process for fabricating silicon nanowire FET sensors on 8 in. silicon-on-insulator wafers is demonstrated. The fabricated nanowire (30 nm width) FETs with solution gates have a Nernst limit subthreshold swing (SS) of 60 ± 1 mV/decade with ∼1.7% variations, whereas literature values for SS are ≥80 mV/decade with larger (>10 times) variations. Also, their threshold voltage variations are significantly (∼3 times) reduced, compared to literature values. Furthermore, these improved FETs have significantly reduced drain current hysteresis (∼0.6 mV) and enhanced on-current to off-current ratios (∼106). These improvements resulted in nanowire FET sensors with the lowest (∼3%) reported sensor-to-sensor variations, compared to literature studies. Also, these improved nanowire sensors have the highest reported sensitivity and enhanced signal-to-noise ratio with the lowest reported defect density of 2.1 × 1018 eV-1 cm-3, in comparison to literature data. In summary, this work brings the nanowire sensor technology a step closer to commercial products for early diagnosis and monitoring of diseases.

Wireless Sensor Platform for Cultural Heritage Monitoring and Modeling System.

Results from three years of continuous monitoring of environmental conditions using a wireless sensor platform installed at The Cloisters, the medieval branch of the New York Metropolitan Museum of Art, are presented. The platform comprises more than 200 sensors that were distributed in five galleries to assess temperature and air flow and to quantify microclimate changes using physics-based and statistical models. The wireless sensor network data shows a very stable environment within the galleries, while the dense monitoring enables localized monitoring of subtle changes in air quality trends and impact of visitors on the microclimate conditions. The high spatial and temporal resolution data serves as a baseline study to understand the impact of visitors and building operations on the long-term preservation of art objects.

Sub-wavelength bolometers: uncooled platinum wires as infrared sensors.

We present characterization results of microscopic platinum wires as bolometers. The wire lengths range from 16 µm down to 300 nm. Thus they are in many cases significantly smaller in size than the wavelength of the radiation from the 1200 K blackbody source they were exposed to. We observe a steep rise in both responsivity ℜ and detectivity D* with decreasing wire size, reaching ℜ = 3.1×10(4) V/W and D* = 2.7×10(9) cm Hz(1/2)/W at room temperature for a 300×300 nm(2) device. Two significant advantages of such small wires as bolometers are their low power requirement and fast response time. Our numerical estimations suggest response times in the order of nanoseconds for the smallest samples. They could help improve resolution and response of thermal imaging devices, for example. We believe the performance may be further improved by optimizing the design and operating parameters.

Changing the emission of polarized thermal radiation from metallic nanoheaters.

The polarization of the thermal radiation emitted from individual nanoheaters is investigated for nanoheaters with widths ranging from 500 nm to 2000 nm. The polarization is oriented along the long axis of the nanoheater for widths below 600 nm and rotates by 90 degrees and becomes perpendicular for widths above 900 nm. For certain width nanoheaters the orientation of the polarization of the thermal emission can be rotated from parallel to perpendicular by changing the temperature of the nanoheater. The change in the direction of the emitted thermal radiation is explained by thermally excited transverse plasmon modes.

Enhanced thermal emission from individual antenna-like nanoheaters.

Here we report polarization-sensitive, thermal radiation measurements of individual, antenna-like, thin film Platinum nanoheaters. These heaters confine the lateral extent of the heated area to dimensions smaller (or comparable) to the thermal emission wavelengths. For very narrow heater structures the polarization of the thermal radiation shows a very high extinction ratio as well as a dipolar-like angular radiation pattern. A simple analysis of the radiation intensities suggests a significant enhancement of the thermal radiation for these very narrow heater structures.

Ultra-high-density phase-change storage and memory.

Phase-change storage is widely used in optical information technologies (DVD, CD-ROM and so on), and recently it has also been considered for non-volatile memory applications. This work reports advances in thermal data recording of phase-change materials. Specifically, we show erasable thermal phase-change recording at a storage density of 3.3 Tb inch(-2), which is three orders of magnitude denser than that currently achievable with commercial optical storage technologies. We demonstrate the concept of a thin-film nanoheater to realize ultra-small heat spots with dimensions of less than 50 nm. Finally, we show in a proof-of-concept demonstration that an individual thin-film heater can write, erase and read the phase of these storage materials at competitive speeds. This work provides important stepping stones for a very-high-density storage or memory technology based on phase-change materials.

Active control of slow light on a chip with photonic crystal waveguides.

It is known that light can be slowed down in dispersive materials near resonances. Dramatic reduction of the light group velocity-and even bringing light pulses to a complete halt-has been demonstrated recently in various atomic and solid state systems, where the material absorption is cancelled via quantum optical coherent effects. Exploitation of slow light phenomena has potential for applications ranging from all-optical storage to all-optical switching. Existing schemes, however, are restricted to the narrow frequency range of the material resonance, which limits the operation frequency, maximum data rate and storage capacity. Moreover, the implementation of external lasers, low pressures and/or low temperatures prevents miniaturization and hinders practical applications. Here we experimentally demonstrate an over 300-fold reduction of the group velocity on a silicon chip via an ultra-compact photonic integrated circuit using low-loss silicon photonic crystal waveguides that can support an optical mode with a submicrometre cross-section. In addition, we show fast (approximately 100 ns) and efficient (2 mW electric power) active control of the group velocity by localized heating of the photonic crystal waveguide with an integrated micro-heater.

Polymer mediated self-assembly of magnetic nanoparticles.

We present a simple polymer-mediated process of assembling magnetic FePt nanoparticles on a solid substrate. Alternatively absorbing the PEI molecule and FePt nanoparticles on a HO-terminated solid surface leads to a smooth FePt nanoparticle assembly with controlled assembly thickness and dimension. Magnetic measurements show that the thermally annealed FePt nanoparticle assembly as thin as three nanoparticle layers is ferromagnetic. The magnetization direction of this thin FePt nanoparticle assembly is readily controlled with the laser-assisted magnetic writing. The reported process can be applied to various substrates, nanoparticles, and functional macromolecules and will be useful for future magnetic nanodevice fabrication.