E. J. Choi

Optical response of large scale single layer graphene

We have measured optical transmission and reflection spectra of large scale graphene grown by chemical vapor deposition technique over the extensive frequency range from far-IR to uv (4 meV–6.2 eV). Large scale graphene exhibits an excitonic absorption peak in the uv-region (ℏω=4.6 eV) and the constant interband absorption with σ1(ω)=e2/4ℏ in the IR-visible region, respectively. In the far-IR range, Drude peak is observed, and its strength ωp,2d2 indicates the induced carrier density N2d=1.95×1012 cm−2. These results are highly consistent with the theoretical prediction/experimental results of the single layer graphene. It proves that, contrary to the doubts about its quality due to the chemical growth process, the sample has single layer optical response over the entire photon energy; therefore, it can be applied to large scale devices such as terahertz-IR detector, solar cell material, and visible uv-transparent conductor.

Far-infrared study of substrate-effect on large scale graphene

From far-IR Drude absorption measurement we determine carrier density (N) and carrier scattering rate (Γ) of graphene deposited on buffer-layer/SiO2 composite substrate. Two types of buffer-layers, (1) polar dielectric oxide ZnO and SrTiO3 (2) organic thin film hexamethyldisilazane and polymethyl methacrylate (PMMA) were studied. N varies widely over 0.12–11.8(×1012 cm−2) range depending on the buffer-layer. In contrast Γ remains almost constant, ∼100 cm−1, irrespective of the buffer-layers. This indicates that carrier mobility (μ) of graphene depends on substrate through N, but not by Γ as commonly believed.From far-IR Drude absorption measurement we determine carrier density (N) and carrier scattering rate (Γ) of graphene deposited on buffer-layer/SiO2 composite substrate. Two types of buffer-layers, (1) polar dielectric oxide ZnO and SrTiO3 (2) organic thin film hexamethyldisilazane and polymethyl methacrylate (PMMA) were studied. N varies widely over 0.12–11.8(×1012 cm−2) range depending on the buffer-layer. In contrast Γ remains almost constant, ∼100 cm−1, irrespective of the buffer-layers. This indicates that carrier mobility (μ) of graphene depends on substrate through N, but not by Γ as commonly believed.

Melting of charge/orbital ordered states in Nd 1 / 2 Sr 1 / 2 MnO 3 : Temperature and magnetic-field-dependent optical studies

We investigated the temperature

Infrared-optical spectroscopy of transparent conducting perovskite (La,Ba)SnO3 thin films

(T=15\ensuremath{\sim}290\mathrm{K})

Photoluminescence induced by thermal annealing in SrTiO3 thin film

and the magnetic-field-dependent

Thermoelectric power of MgB 2 − x Be x

(H=0\ensuremath{\sim}17\mathrm{T})

Infrared spectroscopy of the interface charge in a ZnO field-effect transistor

optical conductivity spectra of a charge-orbital-ordered manganite

Pulsed Electron Deposition of 50-nm-thick ZnO Film at Room Temperature

{\mathrm{Nd}}_{1/2}{\mathrm{Sr}}_{1/2}{\mathrm{MnO}}_{3}.

Ferromagnetism and infrared conductivity of the homogeneous hexaboride alloy Eu1?xCaxB6

With variation of T and H, large spectral weight changes were observed up to 4.0 eV. These spectral weight changes could be explained using the polaron picture. Interestingly, our results suggested that some local ordered state might remain above the charge ordering temperature, and that the charge/orbital melted state at a high magnetic field (i.e., at

Infrared optical absorption spectra of CuO single crystals: Fermion-spinon band and dimensional crossover of the antiferromagnetic order

H=17\mathrm{T}