Chemical Vapor Deposited Monolayer Graphene Research Articles

Functionalized CVD monolayer graphene for label-free impedimetric biosensing

Recent advances in large area graphene growth have led to many applications in different areas. In the present study, chemical vapor deposited (CVD) monolayer graphene supported on glass substrate was examined as electrode material for electrochemical biosensing applications. We report a facile strategy for covalent functionalization of CVD monolayer graphene by electrochemical reduction of carboxyphenyl diazonium salt prepared in situ in acidic aqueous solution. The carboxyphenyl-modified graphene is characterized using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM), as well as electrochemical impedance spectroscopy (EIS). We also show that the number of grafted carboxyphenyl groups on the graphene surface can be controlled by the number of cyclic voltammetry (CV) scans used for electrografting. We further present the fabrication and characterization of an immunosensor based on immobilization of ovalbumin antibody on the graphene surface after the activation of the grafted carboxylic groups via EDC/NHS chemistry. The binding between the surface-immobilized antibodies and ovalbumin was then monitored using Faradaic EIS in [Fe(CN)6]3−/4− solution. The percentage change of charge transfer resistance (R ct) after binding exhibited a linear dependence for ovalbumin concentrations ranging from 1.0 pg·mL−1 to 100 ng·mL−1, with a detection limit of 0.9 pg·mL−1. Our results indicate good sensitivity of the developed functionalized CVD graphene platform, paving the way for using CVD monolayer graphene in a variety of electrochemical biosensing devices.

Graphene field effect transistors with mica as gate dielectric layers.

Chemical vapor deposited monolayer graphene is transferred onto atomically flat and ultra-thin muscovite mica to study the transport characteristics of graphene with a test structure of mica-based graphene field effect transistor (GFET). The transfer curve of the 24 nm mica-based GFET shows an effective carrier mobility of 2748 cm(2)/Vs and a transconductance of 3.36 μS, a factor of 2 and 7 larger than those values obtained from 40 nm SiO2 based GFET, respectively. The results demonstrate that mica is an excellent gate dielectric material due to its high dielectric constant, high dielectric strength, and atomically flat surface.

Large-energy, wavelength-tunable, all-fiber passively Q-switched Er:Yb-codoped double-clad fiber laser with mono-layer chemical vapor deposition graphene.

We demonstrate a large-energy, wavelength-tunable, all-fiber passively Q-switched Er:Yb-codoped laser using a mono-layer chemical vapor deposition (CVD) graphene saturable absorber (SA). By exploiting the large laser gain of Er:Yb double-clad fiber and optimizing the coupling ratio of the output coupler, not only can the mono-layer CVD graphene SA be protected from oversaturation and thermal damage, but also a large pulse energy up to 1.05μJ (corresponding to the average output power of 25.6mW) is thus achieved. Using a tunable fiber Fabry-Perot filter, stable Q-switched pulses can operate with a tunable range from 1530.97 to 1546.92nm, covering a wavelength range of ∼16 nm. The Q-switching states at the different lasing wavelengths have been observed and recorded. The Q-switched repetition rate and the pulse duration (with the minimum one of 2.6μs) have been characterized as well. This is, to the best of our knowledge, the largest pulse energy from an all-fiber graphene Q-switched laser.

Ultrafast relaxation of hot optical phonons in monolayer and multilayer graphene on different substrates

Hot carrier cooling in few-layer and multilayer epitaxial graphene on SiC, and chemical vapor deposition (CVD) grown graphene transferred onto a glass substrate was investigated by transient absorption spectroscopy and imaging. Coupling to the substrate was found to play a critical role in charge carrier cooling. For both multilayer epitaxial graphene and monolayer CVD graphene, charge carriers transfer heat predominantly to intrinsic in-plane optical phonons of graphene. At high pump intensity, a significant number of optical phonons are accumulated, and the optical phonon lifetime presents a bottleneck for charge carrier cooling. This hot phonon effect did not occur in few-layer epitaxial graphene because of strong coupling to the substrate, which provided additional cooling channels. The limiting charge carrier lifetimes at high excitation densities were 1.8 ± 0.1 ps and 1.4 ± 0.1 ps for multilayer epitaxial graphene and monolayer CVD graphene, respectively. These values represent lower limits on the optical phonon lifetime for the graphene samples.