Mid-infrared (IR) photothermal spectroscopy of adsorbed molecules is an ideal technique for molecular recognition in miniature sensors with very small thermal mass. Here, we report on combining the photothermal spectroscopy with electrical resonance of a semiconductor nanowire for enhanced sensitivity, selectivity, and simplified readout. Wide band gap semiconductor bismuth ferrite nanowire, by virtue of its very low thermal mass and abundance of surface states in the band gap, facilitates thermally induced charge carrier trapping in the surface states, which affects its electrical resonance response. Electrical resonance response of the nanowire varies significantly depending on the photothermal spectrum of the adsorbed molecules. We demonstrate highly selective detection of mid-IR photothermal spectral signatures of femtogram level molecules physisorbed on a nanowire by monitoring internal dissipation response at its electrical resonance.

The infrared-active (IR) vibrational mode of ethanol (EtOH) associated with the asymmetrical stretching of the C-C-O bond in pico-liter volumes of EtOH-water binary mixtures is calorimetrically measured using photothermal microfluidic cantilever deflection spectroscopy (PMCDS). IR absorption by the confined liquid results in wavelength dependent cantilever deflections, thus providing a complementary response to IR absorption revealing a complex dipole moment dependence on mixture concentration. Solvent-induced blue shifts of the C-C-O asymmetric vibrational stretch for both anti and gauche conformers of EtOH were precisely monitored for EtOH concentrations ranging from 20–100% w/w. Variations in IR absorption peak maxima show an inverse dependence on induced EtOH dipole moment (μ) and is attributed to the complex clustering mechanism of EtOH-water mixtures.

A method of power transmission is proposed that delivers power through the resonance of a helical receiver with its surrounding stray capacitance. The system operates in a quasi-wireless state where power is transferred over a single connection to a surface much larger than the dimensions of the receiver. This ensures high-efficiency energy transfer over large areas without the need of strong coupling electromagnetic fields. Standard power connectors such as tracks, plugs, and cords may be easily replaced with conductive surfaces or objects such as foil sheets, desks, and cabinets. Presently, the method is experimentally demonstrated at the small scale using loads of up to 50 W at an efficiency of 83% with both bare and insulated surfaces. Simple circuit modeling of the system is presented which shows close agreement with experimental results.

features give MOFs great potential in different applications, such as gas storage, separation, catalysis, and sensors. [4][5][6] Many studies have investigated the design of bulk MOFs. Recently, the preparation of nanoscale MOF crystals with controlled size, shape, and morphology has become an important area of research because conventional methods for bulk MOFs synthesis do not meet desired requirements for many applications. [7,8] Nanoscale MOFs provide a higher specific surface area than bulk MOFs, resulting in performance enhancement in various applications such as gas storage, separation, catalysis, and sensing. [7,9,10] Thus, the synthesis and functionalization of nanoscale MOFs are crucial for achieving specific goals in various applications.Recently, 2D nanomaterials have received increasing research interest due to their unique properties when compared to other types of nanomaterials including, 0D nanoparticles, 1D nanowires, or 3D nano networks. [11] The exceptional properties of 2D nanomaterials include charge transport, large field-effect, and unique light-matter interaction modalities, which have promises in addressing present challenges in healthcare, energy conversion, storage, and electronics. [12] These exclusive properties have inspired the synthesis of 2D MOFs nanosheets. [13] Two methods have been used so far, the top-down and the bottom-up method. The chemical tunability of MOFs from bottom-up approach yields good results, especially for sensors. [14] Active sites on the surface of 2D MOFs are highly accessible, even more than their pores or channels, which allow more interactions that enhance the performance in gas sensing, catalysis, and separation applications. [15] Furthermore, the ultra-thin nature of 2D MOFs allows for rapid mass and electron transfer for chemical sensors. [16] Therefore, manipulating the surface-active sites of 2D MOFs can be exploited to enhance the performance of selective chemical sensing.Ammonia is a hazardous gas commonly produced in chemical manufacturing, petroleum refining, pesticide production, fertilizer factories, textile factories, refrigeration systems, food processing plants, livestock buildings, and many other industries. [17] It also occurs naturally during the decomposition of 2D metal-organic frameworks (MOFs) offer high surface area and unique accessibility to active adsorption sites making them appealing for gas sensing applications. 2D MOFs-based sensors are gaining traction for detecting hazardous flu-gases such as ammonia selectively at low concentrations. Fluorescent and colorimetric sensing are promising techniques offering high sensitivity, selectivity, and rapid response in simple applications. In this work, Zn-BTC is synthesized as 2D-MOFs nanosheet with approximate thickness of 2.52 nm via a fast, facile, direct synthesis technique. The introduction of 8-hydroxyquinoline during synthesis forms fluorescent compounds with zinc (ZnQ) which is encapsulated and decorated onto Zn-BTC. Inherent charges on ZnQ lead to the agglomeration of multiple ...

Here we demonstrate wireless energy transfer that exploits the conductivity and permittivity of soil to create a potential gradient on the surface around an earthed electrode, distributing electrical energy over the area. This generated surface potential can be amplified using a special standing-wave receiver for harnessing the distributed energy. We have experimentally mapped the surface potential around the electrode and plotted the received energy covering an area of 1200 m 2 . Key operating parameters are determined with a discussion on optimizing the system efficiency. This technique could address the challenge of distributing electrical energy to many low power devices over large outdoor areas without the use of wires.

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Metal−organic frameworks (MOFs) present specific adsorption sites with varying electron affinity which are uniquely conducive to selective gas sensing but are typically large-band-gap insulators. On the contrary, multiwall carbon nanotubes (MWCNTs) exhibit superior mesoscopic transport exploiting strong electron correlations among sub-bands below and above the Fermi level at room temperature. We synergize them in a new class of nanocomposites based on zeolitic imidazolate framework-8 (ZIF-8) and report selective sensing of CH 4 in ∼10 parts-per-billion (ppb) with a determined limit of detection of ∼0.22 ppb, hitherto unprecedented. The observed selectivity to CH 4 over non-polar CO 2 , polar volatile organic compounds, and moisture has roots in competing electron-sharing mechanisms at its different adsorption sites. This important result provides a significant reference to guide future MOF-related composite research to achieve the best sensing performance. On molecular adsorption, MWCNTs facilitate electrical transport via manipulating the ZIF-8 band gap to show a p-type semiconductor behavior with lower activation energy to induce a measurable resistance change. Excellent repeatability and reversibility are shown. A carbon-engineered MOF composite has the potential to actuate similar selective response to low reactive gases via carrier manipulation in the energy band gap.

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