Strong Enhancement of Light–Matter Interaction in Graphene Coupled to a Photonic Crystal Nanocavity

We demonstrate a large enhancement in the interaction of light with graphene through coupling with localized modes in a photonic crystal nanocavity. Spectroscopic studies show that a single atomic layer of graphene reduces the cavity reflection by more than a factor of one hundred, while also sharply reducing the cavity quality factor. The strong interaction allows for cavity-enhanced Raman spectroscopy on subwavelength regions of a graphene sample. A coupled-mode theory model matches experimental observations and indicates significantly increased light absorption in the graphene layer. The coupled graphene–cavity system also enables precise measurements of graphene’s complex refractive index

Terahertz Nanofocusing with Cantilevered Terahertz-Resonant Antenna Tips

We developed THz-resonant scanning probe tips, yielding strongly enhanced and nanoscale confined THz near fields at their tip apex. The tips with length in the order of the THz wavelength (λ = 96.5 μm) were fabricated by focused ion beam (FIB) machining and attached to standard atomic force microscopy (AFM) cantilevers. Measurements of the near-field intensity at the very tip apex (25 nm radius) as a function of tip length, via graphene-based (thermoelectric) near-field detection, indicate their first and second order geometrical antenna resonances for tip length of 33 and 78 μm, respectively. On resonance, we find that the near-field intensity is enhanced by one order of magnitude compared to tips of 17 μm length (standard AFM tip length), which is corroborated by numerical simulations that further predict remarkable intensity enhancements of about 10⁷ relative to the incident field. Because of the strong field enhancement and standard AFM operation of our tips, we envision manifold and straightforward future application in scattering-type THz near-field nanoscopy and THz photocurrent nanoimaging, nanoscale nonlinear THz imaging, or nanoscale control and manipulation of matter employing ultrastrong and ultrashort THz pulses

High-Speed Electro-Optic Modulator Integrated with Graphene-Boron Nitride Heterostructure and Photonic Crystal Nanocavity

Nanoscale and power-efficient electro-optic (EO) modulators are essential components for optical interconnects that are beginning to replace electrical wiring for intra- and interchip communications.− Silicon-based EO modulators show sufficient figures of merits regarding device footprint, speed, power consumption, and modulation depth.− However, the weak electro-optic effect of silicon still sets a technical bottleneck for these devices, motivating the development of modulators based on new materials. Graphene, a two-dimensional carbon allotrope, has emerged as an alternative active material for optoelectronic applications owing to its exceptional optical and electronic properties.− Here, we demonstrate a high-speed graphene electro-optic modulator based on a graphene-boron nitride (BN) heterostructure integrated with a silicon photonic crystal nanocavity. Strongly enhanced light-matter interaction of graphene in a submicron cavity enables efficient electrical tuning of the cavity reflection. We observe a modulation depth of 3.2 dB and a cutoff frequency of 1.2 GHz

High-Contrast Electrooptic Modulation of a Photonic Crystal Nanocavity by Electrical Gating of Graphene

We demonstrate high-contrast electro-optic modulation of a photonic crystal nanocavity integrated with an electrically gated monolayer graphene. A silicon air-slot nanocavity provides strong overlap between the resonant optical field and graphene. Tuning the Fermi energy of the graphene layer to 0.85 eV enables strong control of its optical conductivity at telecom wavelengths, which allows modulation of cavity reflection in excess of 10 dB for a swing voltage of only 1.5 V. The cavity resonance at 1570 nm is found to undergo a shift in wavelength of nearly 2 nm, together with a 3-fold increase in quality factor. These observations enable a cavity-enhanced determination of graphene’s complex optical sheet conductivity at different doping levels. Our simple device demonstrates the feasibility of high-contrast, low-power, and frequency-selective electro-optic modulators in graphene-integrated silicon photonic integrated circuits

Physical Adsorption and Charge Transfer of Molecular Br₂ on Graphene

We present a detailed study of gaseous Br₂ adsorption and charge transfer on graphene, combining <i>in situ</i> Raman spectroscopy and density functional theory (DFT). When graphene is encapsulated by hexagonal boron nitride (h-BN) layers on both sides, in a h-BN/graphene/h-BN sandwich structure, it is protected from doping by strongly oxidizing Br₂. Graphene supported on only one side by h-BN shows strong hole doping by adsorbed Br₂. Using Raman spectroscopy, we determine the graphene charge density as a function of pressure. DFT calculations reveal the variation in charge transfer per adsorbed molecule as a function of coverage. The molecular adsorption isotherm (coverage <i>versus</i> pressure) is obtained by combining Raman spectra with DFT calculations. The Fowler–Guggenheim isotherm fits better than the Langmuir isotherm. The fitting yields the adsorption equilibrium constant (∼0.31 Torr^–1) and repulsive lateral interaction (∼20 meV) between adsorbed Br₂ molecules. The Br₂ molecule binding energy is ∼0.35 eV. We estimate that at monolayer coverage each Br₂ molecule accepts 0.09 e^– from single-layer graphene. If graphene is supported on SiO₂ instead of h-BN, a threshold pressure is observed for diffusion of Br₂ along the (somewhat rough) SiO₂/graphene interface. At high pressure, graphene supported on SiO₂ is doped by adsorbed Br₂ on both sides

Comparison of serum viral Loads and HBsAg levels.

<p>COI, cutoff index</p><p>Comparison of serum viral Loads and HBsAg levels.</p

Demographic and clinical characteristics of the Patient cohort.

<p>HCV viral genotype was not available for 357 individuals in the HCV mono-infection group and 74 individuals in the HCV-HBV co-infection group; however, those with undetermined genotype results were not among the treated patients.</p><p>^▲P<0.05, HBV versus HCV group</p><p>*P<0.05, HCV versus HBV-HCV group</p><p>^#P<0.05, HBV versus HBV-HCV group</p><p>Quantitative variables are displayed as interquartile range (range), except age.APRI and FIB-4 level which are displayed as mean±SD BMI, body mass index; ALT, alanine aminotransferase, Normal value: 8–50.00 U/L; AST, aspartate aminotransferase, Normal value: 8–40.00 U/L; ALP, alkaline phosphatase, Normal value: 15–112.00 U/L; GGT, glutamyl transpeptidase, Normal value: 5–54.00 U/L; TP, total protein, Normal value: 60–83.00 g/l; ALB, albumin, Normal value: 35–55.00 g/l; GLB, globulin, Normal value: 20–30.00 g/L; TBIL, total bilirubin, Normal value: 6.8–30.00 μmol/L; DBIL, direct bilirubin, Normal value: 0–8.60 μmol/L; IBIL, indirect bilirubin, Normal value: 5.1–21.40 umol/L; CHE, cholinesterase, Normal value: 4300–12000.00 U/L; BUN, blood urea nitrogen, Normal value: 3.2–7.00 mmol/L; Cr, creatinine, Normal value: 44–115.00 μmol/L; TG, triglycerides, Normal value: 0.28–1.80 mmol/L; TC, total cholesterol,Normal value: 2.6–6.00 mmol/L; GLU, glucose,Normal value: 3.9–6.10 mmol/L; PLT, platelet,Normal value: 100–300.00 10^9/L; APRI, aspartate aminotransferase to platelet ratio index; FIB-4, fibrosis index based on the four factors score</p><p>Demographic and clinical characteristics of the Patient cohort.</p

Baseline characteristics of HBV/HCV replication with HBV-HCV co-infection.

<p>Quantitative variables are displayed as interquartile range (range), and HBsAg, HCV core Ag,HCV-RNA and HBV-DNA which are displayed as interquartile range (IQR), except age and BMI are displayed as interquartile mean±SD</p><p>BMI, body mass index; ALT, alanine aminotransferase, Normal value: 8–50.00 U/L; AST, aspartate aminotransferase, Normal value: 8–40.00 U/L; ALP, alkaline phosphatase, Normal value: 15–112.00 U/L; GGT, glutamyl transpeptidase, Normal value: 5–54.00 U/L; TP, total protein, Normal value: 60–83.00 g/l; ALB, albumin, Normal value: 35–55.00 g/l; GLB, globulin, Normal value: 20–30.00 g/L; TBIL, total bilirubin, Normal value: 6.8–30.00 μmol/L; DBIL, direct bilirubin, Normal value: 0–8.60 μmol/L; IBIL, indirect bilirubin, Normal value: 5.1–21.40 umol/L; CHE, cholinesterase, Normal value: 4300–12000.00 U/L; BUN, blood urea nitrogen, Normal value: 3.2–7.00 mmol/L; Cr, creatinine, Normal value: 44–115.00 μmol/L; TG, triglycerides, Normal value: 0.28–1.80 mmol/L; TC, total cholesterol,Normal value: 2.6–6.00 mmol/L; GLU, glucose,Normal value: 3.9–6.10 mmol/L; PLT, platelet,Normal value: 100–300.00 10^9/L; APRI, aspartate aminotransferase to platelet ratio index; FIB-4, fibrosis index based on the four factors score</p><p>Baseline characteristics of HBV/HCV replication with HBV-HCV co-infection.</p

Comparison of serum HCV core Ag levels and scores of the HBV-HCV co-infection and matched HCV controls.

<p>Comparison of serum HCV core Ag levels and scores of the HBV-HCV co-infection and matched HCV controls.</p

Comparison of serum HCV core Ag levels in HBV- HCV co-infection patients.

<p>Comparison of serum HCV core Ag levels in HBV- HCV co-infection patients.</p