Nam-Hui Kim

TiNx layer as an antireflection and antistatic coating for display

Abstract In this study TiN x films were fabricated by a r.f. magnetron sputtering apparatus and the optical, electrical and structural properties were investigated. X-Ray photoelectron spectroscopy (XPS) measurements showed a Ti 2p 3/2 peak at 456 eV after etching the oxidized film surface so that the formation of TiN bonding was confirmed. As the nitrogen gas flow rate increased, the XRD analysis showed that the TiN films were polycrystalline and the ratio of (200) to (111) intensity peak increased. The sheet resistivity of the films varied with the N 2 flow rate and was influenced by the film thickness. Optical constants of TiN x films were measured by the spectroscopic ellipsometer and also calculated by fitting the measured reflectance to the Forouhi–Bloomer dispersion relation. From the measured optical constants the thickness of SiO 2 layer was calculated for broadband AR coating in the visible region. Reflectance of a two-layer coating, TiN x and SiO 2 , on glass substrate was below 0.5% in the visible wavelength and the maximum transmittance was approximately 62% at 520 nm.

Improvement of the interfacial Dzyaloshinskii-Moriya interaction by introducing a Ta buffer layer

We report systematic measurements of the interfacial Dzyaloshinskii-Moriya interaction (iDMI) by employing Brillouin light scattering in Pt/Co/AlOx and Ta/Pt/Co/AlOx structures. By introducing a tantalum buffer layer, the saturation magnetization and the interfacial perpendicular magnetic anisotropy are significantly improved due to the better interface between heavy metal and ferromagnetic layer. From the frequency shift between Stokes- and anti-Stokes spin-waves, we successively obtain considerably larger iDM energy densities (Dmax = 1.65 ± 0.13 mJ/m2 at tCo = 1.35 nm) upon adding the Ta buffer layer, despite the nominally identical interface materials. Moreover, the energy density shows an inverse proportionality with the Co layer thickness, which is the critical clue that the observed iDMI is indeed originating from the interface between the Pt and Co layers.

Role of top and bottom interfaces of a Pt/Co/AlOx system in Dzyaloshinskii-Moriya interaction, interface perpendicular magnetic anisotropy, and magneto-optical Kerr effect

We investigate the role of top and bottom interfaces in inversion symmetry-breaking Pt/Co/AlOx systems by inserting ultra-thin Cu layers. Wedge-type ultrathin Cu layers (0-0.5 nm) are introduced between Pt/Co or Co/AlOx interfaces. Interface sensitive physical quantities such as the interfacial Dzyaloshinskii-Moriya interaction (iDMI) energy density, the interfacial perpendicular magnetic anisotropy (iPMA), and the magneto-optical Kerr effects (MOKE) are systematically measured as a function of Cu-insertion layer thickness. We find that the Cu-insertion layer in the bottom interface (Pt/Co) plays a more important role in iDMI, PMA, and MOKE. In contrast, the top interface (Co/AlOx) noticeably contributes to only PMA, while its contributions to iDMI and MOKE enhancement are less significant. Although the PMA mainly comes from the bottom interface (Pt/Co), the Cu-insertion layers of all interfaces (Pt/Co, Co/AlOx) influence PMA. For iDMI, only the Cu-insertion layer in the bottom interface exerts SOC suppre...

Deposition of multi-period low-emissivity filters for display application by RF magnetron sputtering

Abstract Three types of low emissive (low-e) filters for the display application based on the structure of [TiO 2 ∣Ti∣Ag∣TiO 2 ] were deposited by the RF magnetron sputtering method. The optical and electrical performances of the filters were examined by the measurements of transmittance and reflectance with a spectrophotometer and sheet resistance with a four-point probe meter. Also, the physical and chemical states were investigated by the scanning electron microscopy (SEM) and Auger electron spectroscopy (AES). The results suggest that multiple repetition of the basic structure can be used for a display application in that the transmittance of three periods of [TiO 2 ∣Ti∣Ag∣TiO 2 ] can be drastically reduced in the near IR and the sheet resistance can be low enough to shield the electromagnetic waves.

Optical properties of Fabry–Perot microcavity with organic light emitting materials

Abstract We investigated the optical properties of the tris(8-hydroxyquinoline)aluminum (Alq 3 ) organic film with Fabry–Perot microcavity by measuring photoluminescence (PL) and transmittance. We have simulated the phase change on reflection as a function of wavelength. The Fabry–Perot microcavity structures were designed according to the simulation results and the resonant wavelength corresponding to the maximum of PL spectrum of a bare Alq 3 film. These structures were fabricated in three types of microcavities, such as type A [air|metal|Alq 3 |metal|glass], type B [air|dielectric|Alq 3 |dielectric|glass], and type C [air|metal|Alq 3 |dielectric|glass]. A bare Alq 3 layer on glass, [air|Alq 3 |glass], showed a PL peak around 514 nm and its full width at half maximum (FWHM) was about 80 nm. The broad FWHM of the bare Alq 3 film was reduced to 15–27.5, 7–10.5 and 16–16.6 nm for three types by cavity effects. Also, the control of the resonant wavelength can be achieved by the spacer length as well as the phase change on reflection on mirror.

Study of spin dynamics and damping on the magnetic nanowire arrays with various nanowire widths

Abstract We investigate the spin dynamics including Gilbert damping in the ferromagnetic nanowire arrays. We have measured the ferromagnetic resonance of ferromagnetic nanowire arrays using vector-network analyzer ferromagnetic resonance (VNA-FMR) and analyzed the results with the micromagnetic simulations. We find excellent agreement between the experimental VNA-FMR spectra and micromagnetic simulations result for various applied magnetic fields. We find that the same tendency of the demagnetization factor for longitudinal and transverse conditions, N z ( N y ) increases (decreases) as increasing the nanowire width in the micromagnetic simulations while N x is almost zero value in transverse case. We also find that the Gilbert damping constant increases from 0.018 to 0.051 as the increasing nanowire width for the transverse case, while it is almost constant as 0.021 for the longitudinal case.

Study on the Imaging Resolution of a Multiply-stacked Compton Camera

We have investigated the effect of detector parameters, such as the energy and the position resolution, on the imaging resolution and sensitivity of a multiply-stacked Compton camera by using the proof-of-principle system and the GEANT4 simulation toolkit, including Doppler broadening. The multiply-stacked Compton camera consisted of three double-sided silicon strip detectors. The proof-of-principle system shows that the three-Compton method can reconstruct the incident gamma-ray energy distributions and that it helps to illustrate the usefulness of the three-Compton method when gamma rays don’t stop completely. Reconstructed images and spectra from a Cs gamma-ray source have been obtained by using an event reconstruction algorithm. The reconstructed gamma-ray energy shows a photopeak of 661.7 keV for Cs at 607.5 keV and has a 149.8-keV FWHM. GEANT4 simulation results show the feasibility of using the proof-of-principle system in the energy range from 661.7 keV to 1400.0 keV. The image resolution was significantly affected by the position resolution of the multiply-stacked Compton camera rather than by the energy resolution of the detector.