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Infrared spectroscopic study of carrier scattering in gated CVD graphene
Yu, Kwangnam,Kim, Jiho,Kim, Joo Youn,Lee, Wonki,Hwang, Jun Yeon,Hwang, E. H.,Choi, E. J. American Physical Society 2016 Physical Review B Vol.94 No.23
<P>We measured Drude absorption of gated CVD graphene using far-infrared transmission spectroscopy and determined the carrier scattering rate (gamma) as a function of the varied carrier density (n). The n-dependent gamma(n) was obtained for a series of conditions systematically changed as (10 K, vacuum) -> (300 K, vacuum) -> (300 K, ambient pressure), which reveals that (1) at low-T, charged impurity (= A/root n) and short-range defect (= B root n) are the major scattering sources which constitute the total scattering gamma = A/root n + B root n, (2) among various kinds of phonons populated at room-T, surface polar phonon of the SiO2 substrate is the dominantly scattering source, and (3) in air, the gas molecules adsorbed on graphene play a dual role in carrier scattering as charged impurity center and resonant scattering center. We present the absolute scattering strengths of those individual scattering sources, which provides the complete map of scattering mechanism of CVD graphene. This scattering map allows us to find out practical measures to suppress the individual scatterings, the mobility gains accompanied by them, and finally the ultimate attainable carrier mobility for CVD graphene.</P>
Machine learning analysis of broadband optical reflectivity of semiconductor thin film
이병주,Yu Kwangnam,Jeon Jiwon,Choi E. J. 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.80 No.4
Broadband reflection spectroscopy is a non-invasive and non-contact tool widely used to measure optical dielectric constants and thickness of thin films. However, a lot of time and effort are consumed to analyze data before the results can be attained. Here we construct an artificial neural network (ANN) using scattering matrix formalism and U-net architecture, and apply it to analyze infrared reflection of SiO2 thin film grown on Si substrate. The ANN returns multiple outputs—frequencydependent optical refractive index (n), absorption coefficient( ), and thickness of the film (d)—with high precision with 0.6 nm thickness difference. Furthermore, the ANN can fit large number of reflection data taken at numerous positions (500) of the thin film in short time less than 150 ms, and creates fine-scale thickness map with 0.6 nm thickness resolution. This work demonstrates that U-net-based ANN is a powerful method of reflectivity analysis and can be applied to other thin-film materials.
Infrared Conductivity of PED-grown (La,Ba)SnO3 Thin Films
Dongmin Seo,Kwangnam Yu,최은지 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.5
We have synthesized La-doped BaSnO3 thin films on SrTiO3 substrates by using the pulsedelectron deposition technique. By performing reflection/transmission measurements on the filmsand a Drude model analysis of the data, we determined the carrier density n = 6.7 × 1019 cm−3and the room-temperature mobility μ = 17 cm2V−1s−1 of the conducting electrons. The standardDrude optical conductivity of the films demonstrates that the electron correlation effect is minimalin the present transparent conducting oxide material.
Jang, A-Rang,Hong, Seokmo,Hyun, Chohee,Yoon, Seong In,Kim, Gwangwoo,Jeong, Hu Young,Shin, Tae Joo,Park, Sung O.,Wong, Kester,Kwak, Sang Kyu,Park, Noejung,Yu, Kwangnam,Choi, Eunjip,Mishchenko, Artem,Wi American Chemical Society 2016 Nano letters Vol.16 No.5
<P>Large-scale growth of high-quality hexagonal boron nitride has been a challenge in two-dimensional-material-based electronics. Herein, we present wafer-scale and wrinkle-free epitaxial growth of multilayer hexagonal boron nitride on a sapphire substrate by using high-temperature and low-pressure chemical vapor deposition. Microscopic and spectroscopic investigations and theoretical calculations reveal that synthesized hexagonal boron nitride has a single rotational orientation with AA' stacking order. A facile method for transferring hexagonal boron nitride onto other target substrates was developed, which provides the opportunity for using hexagonal boron nitride as a substrate in practical electronic circuits. A graphene field effect transistor fabricated on our hexagonal boron nitride sheets shows clear quantum oscillation and highly improved carrier mobility because the ultraflatness of the hexagonal boron nitride surface can reduce the substrate-induced degradation of the carrier mobility of two-dimensional materials.</P>