Polyethylenimine-Modified Graphene Oxide as a Novel Antibacterial Agent and Its Synergistic Effect with Daptomycin for Methicillin-Resistant <i>Staphylococcus aureus</i>

An aqueous dispersion of polyethylenimine-modified graphene oxide (PEI-GO) was prepared via a one-step synthesis through an epoxy ring-opening reaction. PEI-GO exhibited bacterial growth inhibition activity on methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) with a minimum inhibitory concentration as low as 8 μg mL^–1. Time–kill curve assay and SYTOX Green assay showed the antibacterial activity and bacteria cell membrane permeability of PEI-GO, respectively. Most importantly, when PEI-GO was employed at 1–2 μg mL^–1, a synergistic effect with daptomycin to resensitize daptomycin-resistant MRSA was revealed. A synergistic effect between PEI-GO and daptomycin provides a possible way to increase bacterial killing and reduce the development of daptomycin resistance. The antibacterial activity of PEI-GO is attributed to the damaged cell membrane caused by the sharp edge and chain structure of the PEI-GO nanosheets as well as the high density of amine groups present in the PEI chains. Our results indicate that PEI-GO dispersion has a great potential for clinical pathogenic bacteria treatment

Omnidirectional Harvesting of Weak Light Using a Graphene Quantum Dot-Modified Organic/Silicon Hybrid Device

Despite great improvements in traditional inorganic photodetectors and photovoltaics, more progress is needed in the detection/collection of light at low-level conditions. Traditional photodetectors tend to suffer from high noise when operated at room temperature; therefore, these devices require additional cooling systems to detect weak or dim light. Conventional solar cells also face the challenge of poor light-harvesting capabilities in hazy or cloudy weather. The real world features such varying levels of light, which makes it important to develop strategies that allow optical devices to function when conditions are less than optimal. In this work, we report an organic/inorganic hybrid device that consists of graphene quantum dot-modified poly­(3,4-ethylenedioxythiophene) polystyrenesulfonate spin-coated on Si for the detection/harvest of weak light. The hybrid configuration provides the device with high responsivity and detectability, omnidirectional light trapping, and fast operation speed. To demonstrate the potential of this hybrid device in real world applications, we measured near-infrared light scattered through human tissue to demonstrate noninvasive oximetric photodetection as well as characterized the device’s photovoltaic properties in outdoor (<i>i</i>.<i>e</i>., weather-dependent) and indoor weak light conditions. This organic/inorganic device configuration demonstrates a promising strategy for developing future high-performance low-light compatible photodetectors and photovoltaics

Size and Dopant Dependent Single Particle Fluorescence Properties of Graphene Quantum Dots

The emissive properties of both doped and nondoped graphene quantum dots (GQDs) with sizes ranging from 3 to 11 nm were analyzed at the single particle level. Both doped and nondoped GQDs are a composite of particles exhibiting green, red, or NIR fluorescence on excitation at 488, 561, and 640 nm, respectively. Nitrogen-doped GQDs (N-GQDs) with diameters ranging from 3.4 to 5.2 nm show a larger proportion of particles with NIR emission as compared to nondoped particles. Doping of GQDs also resulted in changes in the photostability and the fluorescence intermittency seen in single GQD particles. While milliseconds to seconds time scale blinking was regularly observed for red-emitting nondoped GQDs, nitrogen doping significantly reduced blinking. Both doped and nondoped particles also exhibit moderate size dependent photophysical properties

Wafer-Scale Synthesis of High-Quality Semiconducting Two-Dimensional Layered InSe with Broadband Photoresponse

Large-scale synthesis of two-dimensional (2D) materials is one of the significant issues for fabricating layered materials into practical devices. As one of the typical III–VI semiconductors, InSe has attracted much attention due to its outstanding electrical transport property, attractive quantum physics characteristics, and dramatic photoresponse when it is reduced to atomic scale. However, scalable synthesis of single phase 2D InSe has not yet been achieved so far, greatly hindering further fundamental studies and device applications. Here, we demonstrate the direct growth of wafer-scale layered InSe nanosheets by pulsed laser deposition (PLD). The obtained InSe layers exhibit good uniformity, high crystallinity with macro texture feature, and stoichiometric growth by <i>in situ</i> precise control. The characterization of optical properties indicates that PLD grown InSe nanosheets have a wide range tunable band gap (1.26–2.20 eV) among the large-scale 2D crystals. The device demonstration of field-effect transistor shows the n-type channel feature with high mobility of 10 cm² V^–1 s^–1. Upon illumination, InSe-based phototransistors show a broad photoresponse to the wavelengths from ultraviolet to near-infrared. The maximum photoresponsivity attains 27 A/W, plus a response time of 0.5 s for the rise and 1.7 s for the decay, demonstrating the strong and fast photodetection ability. Our findings suggest that the PLD grown InSe would be a promising choice for future device applications in the 2D limit

Efficiency Enhancement of Silicon Heterojunction Solar Cells via Photon Management Using Graphene Quantum Dot as Downconverters

By employing graphene quantum dots (GQDs), we have achieved a high efficiency of 16.55% in n-type Si heterojunction solar cells. The efficiency enhancement is based on the photon downconversion phenomenon of GQDs to make more photons absorbed in the depletion region for effective carrier separation, leading to the enhanced photovoltaic effect. The short circuit current and the fill factor are increased from 35.31 to 37.47 mA/cm² and 70.29% to 72.51%, respectively. The work demonstrated here holds the promise for incorporating graphene-based materials in commercially available solar devices for developing ultrahigh efficiency photovoltaic cells in the future

Exceptional Tunability of Band Energy in a Compressively Strained Trilayer MoS₂ Sheet

Tuning band energies of semiconductors through strain engineering can significantly enhance their electronic, photonic, and spintronic performances. Although low-dimensional nanostructures are relatively flexible, the reported tunability of the band gap is within 100 meV per 1% strain. It is also challenging to control strains in atomically thin semiconductors precisely and monitor the optical and phonon properties simultaneously. Here, we developed an electromechanical device that can apply biaxial compressive strain to trilayer MoS₂ supported by a piezoelectric substrate and covered by a transparent graphene electrode. Photoluminescence and Raman characterizations show that the direct band gap can be blue-shifted for ∼300 meV per 1% strain. First-principles investigations confirm the blue-shift of the direct band gap and reveal a higher tunability of the indirect band gap than the direct one. The exceptionally high strain tunability of the electronic structure in MoS₂ promising a wide range of applications in functional nanodevices and the developed methodology should be generally applicable for two-dimensional semiconductors

Uncooled Mid-Infrared Sensing Enabled by Chip-Integrated Low-Temperature-Grown 2D PdTe₂ Dirac Semimetal

Next-generation mid-infrared (MIR) imaging chips demand free-cooling capability and high-level integration. The rising two-dimensional (2D) semimetals with excellent infrared (IR) photoresponses are compliant with these requirements. However, challenges remain in scalable growth and substrate-dependence for on-chip integration. Here, we demonstrate the inch-level 2D palladium ditelluride (PdTe2) Dirac semimetal using a low-temperature self-stitched epitaxy (SSE) approach. The low formation energy between two precursors facilitates low-temperature multiple-point nucleation (∼300 °C), growing up, and merging, resulting in self-stitching of PdTe2 domains into a continuous film, which is highly compatible with back-end-of-line (BEOL) technology. The uncooled on-chip PdTe2/Si Schottky junction-based photodetector exhibits an ultrabroadband photoresponse of up to 10.6 μm with a large specific detectivity. Furthermore, the highly integrated device array demonstrates high-resolution room-temperature imaging capability, and the device can serve as an optical data receiver for IR optical communication. This study paves the way toward low-temperature growth of 2D semimetals for uncooled MIR sensing

Si Hybrid Solar Cells with 13% Efficiency <i>via</i> Concurrent Improvement in Optical and Electrical Properties by Employing Graphene Quantum Dots

By employing graphene quantum dots (GQDs) in PEDOT:PSS, we have achieved an efficiency of 13.22% in Si/PEDOT:PSS hybrid solar cells. The efficiency enhancement is based on concurrent improvement in optical and electrical properties by the photon downconversion process and the improved conductivity of PEDOT:PSS via appropriate incorporation of GQDs. After introducing GQDs into PEDOT:PSS, the short circuit current and the fill factor of rear-contact optimized hybrid cells are increased from 32.11 to 36.26 mA/cm² and 62.85% to 63.87%, respectively. The organic–inorganic hybrid solar cell obtained herein holds the promise for developing photon-managing, low-cost, and highly efficient photovoltaic devices

Nonlithographic Fabrication of Crystalline Silicon Nanodots on Graphene

We report a nonlithographic fabrication method to grow uniform and large-scale crystalline silicon (Si) nanodot (c-SiNDs) arrays on single-layer graphene by an ultrathin anodic porous alumina template and Ni-induced Si crystallization technique. The lateral height of the template can be as thin as 160 nm and the crystallization of Si can be achieved at a low temperature of 400 °C. The effects of c-SiNDs on graphene were studied by Raman spectroscopy. Furthermore, the c-SiNDs/graphene based field effect transistors were demonstrated

Deep Ultraviolet Photoluminescence of Water-Soluble Self-Passivated Graphene Quantum Dots

Glucose-derived water-soluble crystalline graphene quantum dots (GQDs) with an average diameter as small as 1.65 nm (∼5 layers) were prepared by a facile microwave-assisted hydrothermal method. The GQDs exhibits deep ultraviolet (DUV) emission of 4.1 eV, which is the shortest emission wavelength among all the solution-based QDs. The GQDs exhibit typical excitation wavelength-dependent properties as expected in carbon-based quantum dots. However, the emission wavelength is independent of the size of the GQDs. The unique optical properties of the GQDs are attributed to the self-passivated layer on the surface of the GQDs as revealed by electron energy loss spectroscopy. The photoluminescence quantum yields of the GQDs were determined to be 7–11%. The GQDs are capable of converting blue light into white light when the GQDs are coated onto a blue light emitting diode