Zhihua Su

Growth of Single Crystal Graphene Arrays by Locally Controlling Nucleation on Polycrystalline Cu Using Chemical Vapor Deposition

Graphene, a single atomic layer of hexagonally packed carbon atoms, has drawn signifi cant attention with its outstanding electrical, [ 1 ] mechanical, [ 2 , 3 ] and chemical properties. [ 4 , 5 ] Various promising applications based on graphene have been demonstrated, such as in electronics, [ 6 , 7 ] optoelectronics, [ 8 , 9 ] and chemical and biological sensing. [ 10–12 ] To further envision graphene technology, it is critical to synthesize high-quality graphene on a large scale. Since the fi rst mechanical isolation of graphene from graphite crystal in 2004, [ 13 ] intense efforts have been made to develop methods for graphene synthesis, including reduction of graphene oxide, [ 14 ] thermal decomposition of SiC, [ 15 , 16 ]

Resonance Raman spectroscopy of G-line and folded phonons in twisted bilayer graphene with large rotation angles

We report the synthesis and systematic Raman study of twisted bilayer graphene (tBLG) with rotation angles from below 10° to nearly 30°. Chemical vapor deposition was used to grow hexagon-shaped tBLG with a rotation angle that can be conveniently determined by relative edge misalignment. Rotation dependent G-line resonances and folded phonons were observed by selecting suitable energies of excitation lasers. The observed phonon frequencies of the tBLG superlattices agree well with our ab initio calculation.

Four-fold Raman enhancement of 2D band in twisted bilayer graphene: evidence for a doubly degenerate Dirac band and quantum interference.

We report the observation of a strong 2D band Raman in twisted bilayer graphene (tBLG) with large rotation angles under 638 nm and 532 nm visible laser excitations. The 2D band Raman intensity increased four-fold as opposed to the two-fold increase observed in single-layer graphene. The same tBLG samples also exhibited rotation-dependent G-line resonances and folded phonons under 364 nm UV laser excitation. We attribute this 2D band Raman enhancement to the constructive interference between two double-resonance Raman pathways, which were enabled by a nearly degenerate Dirac band in the tBLG Moiré superlattices.

High-resolution fiber optic temperature sensors using nonlinear spectral curve fitting technique

A generic new data processing method is developed to accurately calculate the absolute optical path difference of a low-finesse Fabry-Perot cavity from its broadband interference fringes. The method combines Fast Fourier Transformation with nonlinear curve fitting of the entire spectrum. Modular functions of LabVIEW are employed for fast implementation of the data processing algorithm. The advantages of this technique are demonstrated through high performance fiber optic temperature sensors consisting of an infrared superluminescent diode and an infrared spectrometer. A high resolution of 0.01 °C is achieved over a large dynamic range from room temperature to 800 °C, limited only by the silica fiber used for the sensor.