Lim Daeyoung

We describe an in situ method for measuring the band bending of Si substrates in complex metal-oxide-semiconductor systems using femtosecond pump-probe photoelectron spectroscopy. Following deposition of metal layers (Pt, Re, or Re oxide) on the high-k dielectric HfO2, measurement of the band bending in the underlying Si provides a direct determination of the location of the Fermi level within the Si band gap at the Si-dielectric interface. Changes in the Fermi level with post-deposition anneals

We show that optical second-harmonic generation (SHG) from few-layer MoSe2 can sensitivelyprobe external symmetry perturbations such as chemical doping. The SHGs from few-layer MoSe2are enhanced after AuCl3 chemical doping, especially more so for the thicker MoSe2 samples. Thisenhancement is due to an electric-field-induced SHG contribution originating from the charge transferbetween the adsorbed chemical dopants and the MoSe2. By using this sensitivity, we demonstratean in-situ monitoring of th

ZnO doped with non-magnetic C has been reported to exhibit room-temperature ferromagnetism (RTF). The theoretical explanations of the RTF in ZnO:C are based on the incorporation of C at the O site and on the p-p exchange interaction between the localized C2p spins and valenceband holes. Here, we investigated the incorporation site of C and the electrical properties of Cdoped ZnO films grown by using pulsed laser deposition (PLD) under oxygen-rich and oxygen-poor conditions. Contrary to the theor

We report in situ photovoltage measurements of metal-oxide-semiconductor (MOS) structures using femtosecond pump-probe photoelectron spectroscopy. This technique, which employs a single femtosecond laser, is a noncontact noninvasive measurement method for extracting the magnitude and direction of the band bending in Si substrates covered with high-k dielectric stacks and thin metal layers. We studied MOS structures consisting of thin metal layers of both high and low work functions deposited ato

Abstract We describe experiments using 100 femtosecond pulses of 266 nm light to ablate Cr defects from photomasks with resolution below 100 nm. In addition to the ablative removal of Cr, experiments were carried out to deposit Cr metal onto fused silica substrates using 100 fs, 400 nm light at atmospheric pressure. Multiphoton dissociation of Cr(CO)6 adsorbed on fused silica substrates initiates Cr deposition. The mechanisms for deposition on both transparent (fused silica) and absorbing (Cr me

We describe experiments using ultrashort pulses of laser light to ablatively remove opaque and partially transmitting materials from transparent substrates. Pulses of 100 femtosecond duration at a wavelength of 266 nm were used to repair defects on photomasks used in lithographic printing of integrated circuits, with better than 100 nm spatial resolution. Details of the development and implementation of a photomask repair tool, presently operating in manufacturing, which exploits the advantages

We investigated ferroelectric characteristics of BiFeO3 (BFO) thin films on SrRuO3 (SRO)/yttria-stabilized zirconia (YSZ)/glass substrates grown by pulsed laser deposition. YSZ buffer layers were employed to grow highly crystallized BFO thin films as well as SRO bottom electrodes on glass substrates. The BFO thin films exhibited good ferroelectric properties with a remanent polarization of 2Pr = 59.6 μC/cm2 and fast switching behavior within about 125 ns. Piezoelectric force microscopy (PFM) stu

We investigated the charge trapping properties of rare-earth(RE)-Yb-doped Al2 O3 in view of their potential application to nonvolatile memories. The as-grown, low-temperature annealed Yb-doped Al2 O3 film showed a dominant hole trapping behavior, but it changed to mostly electron trapping after high temperature annealing. No correlation was found between the Yb charge state and the reduction of hole traps, excluding the Yb ion itself as the hole trap. As-grown annealed Yb-doped Al2 O3 showed a d

We study the excitonic valley polarization and coherence in few-layer MoS2 by using circularandlinear-polarization-resolved photoluminescence. The valley polarization is largest in monolayerMoS2 and decreases with increasing number of layers or temperature. Contrary to the valleypolarization, the linear polarization is negligibly small in monolayer MoS2 and increases with increasingnumber of layers or temperature. The temperature-dependent valley depolarization canbe explained by the exciton cen

We studied the electrical, optical and valley properties of monolayer MoSe2. The measured PL circular polarization of monolayer MoSe2 was negligibly small, compared with the more-than 60% circular polarization of monolayer MoS2. Doping-dependent PL measurement and Kelvin probe microscopy show that the small circular polarization because of its longer exciton lifetime in monolayer MoSe2. Furthermore, it is found that the longer exciton lifetime is due to the nearly intrinsic electrical property o

Highly strained BiFeO<SUB>3</SUB> thin films have been found to exhibit a 'tetragonal-like monoclinic' crystal structure different from the bulk rhombohedral structure. Here, we report our second harmonic generation (SHG) study of epitaxially strained tetragonal-like BiFeO<SUB>3</SUB> films as a function of temperature and film thickness. We observed a strong SHG peak at ~370 K, corresponding to the structural phase transition between two T-like BFO phases. Our SHG symmetry analysis revealed tha

We study the effects of charged defects and impurities on the optical properties and the valley polarization in monolayer MoS2. Both the defects generated by vacuum annealing and the impurities introduced by AuCl3 chemical doping dramatically increase the photoluminescence (PL) intensity. This is due to a p-doping effect, which increases the exciton lifetime by suppressing the non-radiative trionic decay in the n-type, as-exfoliated monolayer MoS2. The PL from vacuum-annealed MoS2 can be control