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Dielectric function, critical points, and Rydberg exciton series of WSe<sub>2</sub> monolayer
Diware, M S,Ganorkar, S P,Park, K,Chegal, W,Cho, H M,Cho, Y J,Kim, Y D,Kim, H IOP 2018 Journal of Physics, Condensed Matter Vol.30 No.23
<P>The complex dielectric function (<img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/0953-8984/30/23/235701/cmaac187ieqn001.gif'/>) of WSe<SUB>2</SUB> monolayer grown by atomic layer deposition is investigated using spectroscopic ellipsometry. Band structure parameters are obtained by standard line-shape analysis of the second-energy-derivative of <img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/0953-8984/30/23/235701/cmaac187ieqn002.gif'/> spectra. The fundamental band gap is observed at 2.26 eV, corresponds to transition between valence band (VB) maximum at the <I>K</I> point and conduction band (CB) minimum at <I>Q</I> point in the Brillouin zone (BZ). Two strong so-called <I>A</I> and <I>B</I> excitonic peaks in <img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/0953-8984/30/23/235701/cmaac187ieqn003.gif'/> spectra originate from vertical transitions from spin–orbit split (0.43 eV) VB to CB at K point of the BZ. Binding energies of <I>A</I> and <I>B</I> exactions are 0.71 and 0.28 eV, respectively. Well resolved five excited excitons states has been detected within the spectral region between <I>A</I> and <I>B</I>. Energy profile of the Rydberg series shows significant deviation from the hydrogenic behavior, discussed in connection with the 2D hydrogen model. Results presented here will improve our understanding about the optical response of 2D materials and will help to design better optoelectronic applications and validate theoretical considerations.</P>
Solution immersed silicon (SIS)-based biosensors: a new approach in biosensing
Diware, M. S.,Cho, H. M.,Chegal, W.,Cho, Y. J.,Jo, J. H.,O, S. W.,Paek, S. H.,Yoon, Y. H.,Kim, D. The Royal Society of Chemistry 2015 The Analyst Vol.140 No.3
<P>A novel, solution immersed silicon (SIS)-based sensor has been developed which employs the non-reflecting condition (NRC) for a p-polarized wave. The SIS sensor's response is almost independent of change in the refractive index (RI) of a buffer solution (BS) which makes it capable of measuring low-concentration and/or low-molecular-weight compounds.</P> <P>Graphic Abstract</P><P>The non-reflecting condition for p-polarized waves is effectively utilized for biomolecular detection through the measurement of thickness change. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4an01584c'> </P>
Diware, M.S.,Park, K.,Mun, J.,Park, H.G.,Chegal, W.,Cho, Y.J.,Cho, H.M.,Park, J.,Kim, H.,Kang, S.W.,Kim, Y.D. Elsevier 2017 CURRENT APPLIED PHYSICS Vol.17 No.10
<P>Here, we present the spectroscopic ellipsometry investigation of synthetically grown wafer-scale two-dimensional (2D) MoS2 and WSe2 films to access quality and thickness uniformity. MoS2 and WSe2 samples were grown by chemical vapor deposition and atomic layer deposition, respectively. Complex dielectric function (epsilon =epsilon(1) + i epsilon(2)) and thickness information of these 2D films were extracted from the measured data using multilayer optical calculations. Broad spectral range (1.2-6 eV) and multiple angles of incidence were used to reduce correlations among fitting parameter. Lineshape of epsilon of MoS2 and WSe2 monolayer films are consistent with literature but shows higher values, suggests better quality of our samples. Eight-inch wafer size MoS2 monolayer sample shows similar to 70% uniformity with an average thickness of 0.65 +/- 0.2 nm, and three-layer WSe2 sample of 8 x 1 cm(2) area shows similar to 80% uniformity with an average thickness of 2.5 +/- 0.4 nm. Our results will be helpful to accelerate commercialization process of 2D devices. (C) 2017 Elsevier B.V. All rights reserved.</P>
Characterization of wafer-scale MoS2 and WSe2 2D films by spectroscopic ellipsometry
Mangesh S. Diware,박규남,문지훈,박한결,Won Chegal,조용재,조현모,박주상,김형준,강상우,김영동 한국물리학회 2017 Current Applied Physics Vol.17 No.10
Here, we present the spectroscopic ellipsometry investigation of synthetically grown wafer-scale twodimensional (2D) MoS2 and WSe2 films to access quality and thickness uniformity. MoS2 and WSe2 samples were grown by chemical vapor deposition and atomic layer deposition, respectively. Complex dielectric function (ε ¼ ε1 þ iε2) and thickness information of these 2D films were extracted from the measured data using multilayer optical calculations. Broad spectral range (1.2e6 eV) and multiple angles of incidence were used to reduce correlations among fitting parameter. Lineshape of ε of MoS2 and WSe2 monolayer films are consistent with literature but shows higher values, suggests better quality of our samples. Eight-inch wafer size MoS2 monolayer sample shows ~ 70% uniformity with an average thickness of 0.65 ± 0.2 nm, and three-layer WSe2 sample of 8 『 1 cm2 area shows ~ 80% uniformity with an average thickness of 2.5 ± 0.4 nm. Our results will be helpful to accelerate commercialization process of 2D devices.
Investigation of InSb Critical-point Energies at 25 K by Using Spectroscopic Ellipsometry
김태중,황순용,최준호,변준석,Mangesh S. Diware,Han Gyeol Park,김영동 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.3
We report dielectric function data from 0.74 to 6.6 eV for InSb at 25 K obtained using spectroscopic ellipsometry. The values of the critical-point (CP) energies were determined from numerically calculated second energy derivatives of the data. The CP structures are blue shifted and significantly sharpened relative to those at room temperature (RT). The <i>E<i>1, <i>E<i><sub>1</sub> +Δ<sub>1</sub>, <i>E<i>'<sub>0</sub>, Δ<sub>5</sub><sup>cu</sup> −Δ<sub>5</sub><sup>vu</sup>, <i>E<i>'<sub>0</sub> +Δ'<sub>0</sub>, and Δ<sub>5</sub><sup>cl</sup>-Δ<sub>5</sub><sp>vu</sup> CP structures are clearly observed at energies below 4 eV. We also report the <i>E<i><sub>2</sub>, <i>E<i>'<sub>2</sub> , <i>E<i><sub>2</sub> + Δ<sub>2</sub>, <i>E<i>'<sub>2</sub> + Δ<sub>2</sub>, <i>E<i>'<sub>1</sub>, <i>E<i>'<sub>1</sub> + Δ'<sub>1</sub>, and <i>E<i>'<sub>1</sub> + Δ'<sub>1</sub> + Δ<sub>1</sub> features in the <i>E<i><sub>2</sub> − <i>E<i>'<sub>1</sub> energy range of 4 to 6 eV. These cannot be resolved at RT, but are clearly separated at 25 K. In particular, several CPs in the E02 and the E01 + 01 + 1 transitions have not previously been observed.
Parametric Model Dielectric Functions of InAs for Temperatures from 22 to 675 K
김태중,황순용,변준석,Mangesh S. Diware,Jun Young Kim,김영동 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.11
Dielectric functions as a continuous function of temperature are useful for nondestructive in-situ monitoring of deposition and device design. Here, we present an analytic expression that accurately represents the dielectric function ε = ε<SUB>1</SUB> + <i>i</i>ε<SUB>2</SUB> of InAs from 0.74 to 6.54 eV for temperatures from 22 to 675 K. We use the parametric model, which is known to accurately portray ε without unphysical assumptions. The parameters are obtained from ε spectra obtained on an InAs substrate by spectroscopic ellipsometry. The dielectric function is parameterized successfully by seven Gaussian-broadened polynomials.