In Situ Thermal Decomposition of Exfoliated Two-Dimensional Black Phosphorus

With a semiconducting band gap and high charge carrier mobility, two-dimensional (2D) black phosphorus (BP), often referred to as phosphorene, holds significant promise for next generation electronics and optoelectronics. However, as a 2D material, it possesses a higher surface area to volume ratio than bulk BP, suggesting that its chemical and thermal stability will be modified. Herein, an atomic-scale microscopic and spectroscopic study is performed to characterize the thermal degradation of mechanically exfoliated 2D BP. From in situ scanning/transmission electron microscopy, decomposition of 2D BP is observed to occur at ~400 {\deg}C in vacuum, in contrast to the 550 {\deg}C bulk BP sublimation temperature. This decomposition initiates via eye-shaped cracks along the [001] direction and then continues until only a thin, amorphous red phosphorous like skeleton remains. In situ electron energy loss spectroscopy, energy-dispersive X-ray spectroscopy, and energy-loss near-edge structure changes provide quantitative insight into this chemical transformation process.Comment: In press: 4 figures in main manuscript, 27 pages with supporting informatio

Solvent Exfoliation of Electronic-Grade, Two-Dimensional Black Phosphorus

Solution dispersions of two-dimensional (2D) black phosphorus (BP), often referred to as phosphorene, are achieved by solvent exfoliation. These pristine, electronic-grade BP dispersions are produced with anhydrous, organic solvents in a sealed tip ultrasonication system, which circumvents BP degradation that would otherwise occur via solvated oxygen or water. Among conventional solvents, n-methyl-pyrrolidone (NMP) is found to provide stable, highly concentrated (~0.4 mg/mL) BP dispersions. Atomic force microscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy show that the structure and chemistry of solvent-exfoliated BP nanosheets are comparable to mechanically exfoliated BP flakes. Additionally, residual NMP from the liquid-phase processing suppresses the rate of BP oxidation in ambient conditions. Solvent-exfoliated BP nanosheet field-effect transistors (FETs) exhibit ambipolar behavior with current on/off ratios and mobilities up to ~10000 and ~50 cm^2/(V*s), respectively. Overall, this study shows that stable, highly concentrated, electronic-grade 2D BP dispersions can be realized by scalable solvent exfoliation, thereby presenting opportunities for large-area, high-performance BP device applications.Comment: 6 figures, 31 pages, including supporting informatio

High speed self-testing quantum random number generation without detection loophole

Quantum mechanics provides means of generating genuine randomness that is impossible with deterministic classical processes. Remarkably, the unpredictability of randomness can be certified in a self-testing manner that is independent of implementation devices. Here, we present an experimental demonstration of self-testing quantum random number generation based on an detection-loophole free Bell test with entangled photons. In the randomness analysis, without the assumption of independent identical distribution, we consider the worst case scenario that the adversary launches the most powerful attacks against quantum adversary. After considering statistical fluctuations and applying an 80 Gb $\times$ 45.6 Mb Toeplitz matrix hashing, we achieve a final random bit rate of 114 bits/s, with a failure probability less than $10^{-5}$. Such self-testing random number generators mark a critical step towards realistic applications in cryptography and fundamental physics tests.Comment: 34 pages, 10 figure

Detection of Target ssDNA Using a Microfabricated Hall Magnetometer with Correlated Optical Readout

Sensing biological agents at the genomic level, while enhancing the response time for biodetection over commonly used, optics-based techniques such as nucleic acid microarrays or enzyme-linked immunosorbent assays (ELISAs), is an important criterion for new biosensors. Here, we describe the successful detection of a 35-base, single-strand nucleic acid target by Hall-based magnetic transduction as a mimic for pathogenic DNA target detection. The detection platform has low background, large signal amplification following target binding and can discriminate a single, 350 nm superparamagnetic bead labeled with DNA. Detection of the target sequence was demonstrated at 364 pM (<2 target DNA strands per bead) target DNA in the presence of 36 μM nontarget (noncomplementary) DNA (<10 ppm target DNA) using optical microscopy detection on a GaAs Hall mimic. The use of Hall magnetometers as magnetic transduction biosensors holds promise for multiplexing applications that can greatly improve point-of-care (POC) diagnostics and subsequent medical care