A large mechanical sensitivity can be achieved by a mechanically tunable quantum tunneling barrier. The tunneling resistance across the nanometer-sized gap can be changed by several orders of magnitude through a sub-angstrom-scale displacement. Here, we demonstrate the performance of a strain sensor formed from pre-stretched Platinum (Pt) on PDMS, where perturbation of the thickness of the nanogap cracks due to strain change the resistance of the device. A gauge factor >500 is realized in a device that is mechanically stabilized by self-assembled monolayer (SAM). Then, we extend the application of the nanogap based strain sensor to temperature and infrared detection. Fabricated proof-of-concept metal/SAM/metal suspended bolometers yield a temperature coefficient of resistance (TCR) between -0.006 K-1 and - 0.085 K-1, and theoretical predictions show that with further optimization the TCRs could be improve to as much as -2.7 K-1, which is more than one order of magnitude better than the state-of-the-art VOx bolometers. Furthermore, this work quantifies the 50 Hz to 10 kHz noise performance of suspended metal/nanogap/metal bolometers and compares the noise spectrum of devices with and without SAM, as well as 10 nm Pt channel vs. 30 nm Pt channel devices. Finally, early stage 830 nm optical measurements show that the device sensitivity of a 10nm Pt / air nanogap / 10 nm Pt peaks at low bias (< 1V, <20 pA) and that the 3dB point of the sensor extends past 10 kHz. The experimental results of this work suggest that nanogap-based sensor architectures exhibit a high sensitivity and may also enable fast response time detectors.
Acoustic-graphene-plasmons (AGPs) are highly confined electromagnetic modes, which carry extreme momentum and low loss in the Mid-infrared (MIR) to Terahertz (THz) spectra. They are therefore enablers of extremely strong light-matter interactions at these long wavelengths. However, owing to their large momentum they are also challenging to excite and detect. Here, we demonstrate a new way to excite AGPs that are confined to nanometric-scale cavities directly from the far-field, via localized graphene-plasmon-magnetic-resonators (GPMRs). This approach enables the efficient excitation of single AGP cavities, which are able to confine MIR light to record-breaking ultra-small mode-volumes, which are over a billion times smaller than their free-space volume.
Acoustic-graphene-plasmons (AGPs) are highly confined electromagnetic modes, which carry extreme momentum and low loss in the Mid-infrared (MIR) to Terahertz (THz) spectra. They are therefore enablers of extremely strong light-matter interactions at these long wavelengths. However, owing to their large momentum they are also challenging to excite and detect. Here, we demonstrate a new way to excite AGPs that are confined to nanometric-scale cavities directly from the far-field, via localized graphene-plasmon-magnetic-resonators (GPMRs). This approach enables the efficient excitation of single AGP cavities, which are able to confine MIR light to record-breaking ultra-small mode-volumes, which are over a billion times smaller than their free-space volume.
MoS2 has attracted substantial attention due to its atomic thickness and outstanding electronic and mechanical properties. As one of the thinnest semiconductors in the world, MoS2 is promising to build flexible electronics that can be integrated with objects with arbitrary shapes and inspires a vision of distributed ubiquitous electronics. Despite recent advances in two-dimensional materials-based electronics (e.g. 2D materials-based transistors, memory devices and sensors), an efficient and flexible energy harvesting solution is necessary, but still missing, to enable a self-powered system. At the same time, the electromagnetic (EM) radiation in the Wi-Fi band (2.4 GHz and 5.9 GHz) is becoming increasingly ubiquitous and it would be beneficial to be able to wirelessly harvest it to power future distributed electronics. However, the rectennas (i.e. RF energy harvesters) based on flexible semiconductors have not been fast enough to cover the Wi-Fi band due to their limited transport properties. Here we present a unique MoS2 semiconducting-metallic phase heterojunction, which enables a flexible and high-speed Schottky diode with a cutoff frequency of 10 GHz. Due to a novel lateral architecture and self-aligned phase engineering, our MoS2 Schottky diode exhibits significantly reduced parasitic capacitance and series resistance. By integrating the MoS2 rectifier with a flexible Wi-Fi band antenna, we successfully fabricate a fully flexible rectenna that demonstrates direct energy harvesting of EM radiation in the Wi-Fi band with zero external bias (battery-free). Moreover, taking advantage of the nonlinearity of the MoS2 Schottky diode, a frequency mixing in the gigahertz range is also successfully demonstrated on flexible substrates.
Two-dimensional (2-D) materials are of tremendous interest to silicon photonics given their singular optical characteristics spanning light emission, modulation, saturable absorption, and nonlinear optics. To harness their optical properties, these atomically thin materials are usually attached onto prefabricated devices via a transfer process. Here we present a new route for 2-D material integration with silicon photonics. Central to this approach is the use of chalcogenide glass, a multifunctional material which can be directly deposited and patterned on a wide variety of 2-D materials and can simultaneously function as the light guiding medium, a gate dielectric, and a passivation layer for 2-D materials. Besides achieving improved fabrication yield and throughput compared to the traditional transfer process, our technique also enables unconventional multilayer device geometries optimally designed for enhancing light-matter interactions in the 2-D layers. Capitalizing on this facile integration method, we demonstrate a series of high-performance glass-on-graphene devices including ultra-broadband on-chip polarizers, energy-efficient thermo-optic switches, as well as mid-infrared (mid-IR) waveguide-integrated photodetectors and modulators based on graphene and black phosphorus.
Semiconductors that are atomically thin can exhibit novel optical properties beyond those encountered in the bulk compounds. Monolayer transition-metal dichalcogenides (TMDs) are leading examples of such semiconductors that possess remarkable optical properties. They obey unique selection rules where light with different circular polarization can be used for selective photoexcitation at two different valleys in the momentum space. These valleys constitute bandgaps that are normally locked in the same energy. Selectively varying their energies is of great interest for applications because it unlocks the potential to control valley degree of freedom, and offers a new promising way to carry information in next-generation valleytronics. In this proceeding paper, we show that the energy gaps at the two valleys can be shifted relative to each other by means of the optical Stark effect in a controllable valley-selective manner. We discuss the physics of the optical Stark effect, and we describe the mechanism that leads to its valleyselectivity in monolayer TMD tungsten disulfide (WS2).
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