Jihoon Park

Dielectric and piezoelectric properties of (x)Pb(Mg1/3Nb2/3)O3–(1−x)Pb(Zr1/2Ti1/2)O3 thin films prepared by the sol–gel method

The dielectric and piezoelectric properties of sol–gel derived (x)Pb(Mg1/3Nb2/3)O3–(1−x)Pb(Zr1/2Ti1/2)O3[(x)PMN–(1−x)PZT] thin films were investigated as a function of PMN content (x=0–1). For all compositions in the (x)PMN–(1−x)PZT thin films, a well-developed perovskite phase with (111) preferred orientation was obtained at the annealing temperature range of 700–800 °C. With increasing PMN content, the dielectric constant increased, while the remnant polarization and coercive field decreased. The enhanced dielectric properties were shown in the region of x=0.2. At this composition, the dielectric constant and remnant polarization were 1750 and 12.75 μC/cm2, respectively, which indicate that the morphotropic phase boundary (MPB) exists near the composition of x=0.2. The transverse piezoelectric coefficient (d31) showed a maximum value of −84 pC/N at x=0.2. These results confirmed that enhancement of the dielectric constant and remnant polarization improved the piezoelectric properties at the MPB.

Systematic Reliability Study of Top-Gate p- and n-Channel Organic Field-Effect Transistors

We report on a systematic investigation on the performance and stability of p-channel and n-channel top-gate OFETs, with a CYTOP/Al2O3 bilayer gate dielectric, exposed to controlled dry oxygen and humid atmospheres. Despite the severe conditions of environmental exposure, p-channel and n-channel top-gate OFETs show only minor changes of their performance parameters without undergoing irreversible damage. When correlated with the conditions of environmental exposure, these changes provide new insight into the possible physical mechanisms in the presence of oxygen and water. Photoexcited charge collection spectroscopy experiments provided further evidence of oxygen and water effects on OFETs. Top-gate OFETs also display outstanding durability, even when exposed to oxygen plasma and subsequent immersion in water or operated under aqueous media. These remarkable properties arise as a consequence of the use of relatively air stable organic semiconductors and proper engineering of the OFET structure.

Effect of orientation on the dielectric and piezoelectric properties of 0.2Pb(Mg1/3Nb2/3)O3–0.8Pb(Zr0.5Ti0.5)O3 thin films

0.2Pb(Mg1/3Nb2/3)O3–0.8Pb(Zr0.5Ti0.5)O3 (0.2PMN–0.8PZT) thin films were deposited on Pt(111)/Ti/SiO2/Si [Pt(111)] and Pt(200)/SiO2/Si [Pt(200)] substrates by a sol–gel method, and the effect of orientation on the piezoelectric and dielectric properties of 0.2PMN–0.8PZT thin films was investigated. The 0.2PMN–0.8PZT thin films on Pt(111) and Pt(200) showed strong (111) and (100) preferred orientations, respectively. The spontaneous polarization of the (111) oriented film was higher than that of the (100) oriented film. However, the (100) oriented film showed a higher dielectric constant (K) and transverse piezoelectric coefficients (d31) than the (111) oriented film. Because the spontaneous polarization direction of the (100) oriented film is more tilted away from the normal to the film surface than that of the (111) oriented film, the dielectric constant and the transverse piezoelectric coefficient (d31) of the (100) oriented film were enhanced.

Fabrication of a thin-layer solid optical tissue phantom by a spin-coating method: pilot study

Abstract. Solid optical tissue phantoms (OTPs) have been widely used for many purposes. This study introduces a spin-coating method (SCM) to fabricate a thin-layer solid OTP (TSOTP) with epidermal thickness. TSOTPs are fabricated by controlling the spin speed (250 to 2500 rpm), absorber concentration (0.2% to 1.0%), and the number of layers. The results show that the thicknesses of the TSOTPs are homogeneous in the region of interest. The one-layer TSOTP achieves maximum and minimum thicknesses of 65±0.28  μm (250 rpm) and 5.1±0.17  μm (2500 rpm), respectively, decreasing exponentially as a function of the spin speed. The thicknesses of the multilayer TSOTPs increases as a function of the number of layers and are correlated strongly with the spin speed (R2≥0.95). The concentration of the OTP mixture does not directly affect the thickness of the TSOTP; however, the absorption coefficients exponentially increase as a function of absorber concentration (R2≥0.98). These results suggest that the SCM can be used to fabricate homogeneous TSOTPs with various thicknesses by controlling the spin speed and number of layers. Finally, a double-layer OTP that combines epidermal TSOTP and dermal OTP is manufactured as a preliminary study to investigate the practical feasibility of TSOTPs.

Fabrication of double layer optical tissue phantom by spin coating method: mimicking epidermal and dermal layer

Methodologies to fabricate a solid optical tissue phantom (OTP) mimicking epidermal thin-layer have been developed for in vitro human skin experiment. However, there are cumbersome and time-consuming efforts in fabrication process such as a custom-made casting and calculation of solvent volume before curing process. In a previous study, we introduced a new methodology based on spin coating method (SCM) which is utilized to fabricate a thin-layer OTP analogous to epidermal thickness. In this study, a double layer solid OTP which has epidermal and dermal layers was fabricated to mimic the morphological and optical similarity of human tissue. The structural characteristic and optical properties of fabricated double layer OTP were measured using optical coherence tomography and inverse adding doubling algorithms, respectively. It is expected that the new methodology based on the SCM may be usefully used in the fabrication of double layer OTP.

Single-channel stereoscopic video imaging modality based on transparent rotating deflector.

In this study, we developed a single-channel stereoscopic video imaging modality based on a transparent rotating deflector (TRD). Sequential two-dimensional (2D) left and right images were obtained through the TRD synchronized with a camera, and the components of the imaging modality were controlled by a microcontroller unit. The imaging modality was characterized by evaluating the stereoscopic video image generation, rotation of the TRD, heat generation by the stepping motor, and image quality and its stability in terms of the structural similarity index. The degree of depth perception was estimated and subjective analysis was performed to evaluate the depth perception improvement. The results show that the single-channel stereoscopic video imaging modality may: 1) overcome some limitations of conventional stereoscopic video imaging modalities; 2) be a potential economical compact stereoscopic imaging modality if the system components can be miniaturized; 3) be easily integrated into current 2D optical imaging modalities to produce a stereoscopic image; and 4) be applied to various medical and industrial fields.

Effect of textured Pb(Zr1−xTix)O3 seed layer on fatigue properties of ferroelectric Pb0.99[(Zr0.6Sn0.4)0.85Ti0.15]0.98Nb0.02O3 thin films

Ferroelectric Pb0.99[(Zr0.6Sn0.4)0.85Ti0.15]0.98Nb0.02O3 (PZSTN) thin films with different preferred orientations were fabricated by modifying with 20 mol % excess lead that contained a Pb(ZrxTix−1)O3 seed layer (x=0,0.3,0.52,0.65). Ferroelectric properties were investigated in terms of the texturing character of the PZSTN thin film. With an increase in Zr content in the seed layer, the (100) texturing of the PZSTN film was enhanced. The highly (100) texture (∼97%) was developed by inserting a seed layer with x=1 between the Pt-coated substrate and the PZSTN thin film, whereas in the case of annealing in a reduced condition, the orientation of the film became nearly (111). The (111)-oriented PZSTN film showed relatively higher remanent polarization compared to that of the (100)-oriented film, while the (100)-oriented PZSTN film showed more fatigue behavior than the (111)-oriented film after 109 switching cycles. The (111)-oriented PZSTN film with rhombohedral structure is believed to be suspected to significant stress along applied field direction, resulting in the production of many defects, causing degradation of the polarization during switching cycles.Ferroelectric Pb0.99[(Zr0.6Sn0.4)0.85Ti0.15]0.98Nb0.02O3 (PZSTN) thin films with different preferred orientations were fabricated by modifying with 20 mol % excess lead that contained a Pb(ZrxTix−1)O3 seed layer (x=0,0.3,0.52,0.65). Ferroelectric properties were investigated in terms of the texturing character of the PZSTN thin film. With an increase in Zr content in the seed layer, the (100) texturing of the PZSTN film was enhanced. The highly (100) texture (∼97%) was developed by inserting a seed layer with x=1 between the Pt-coated substrate and the PZSTN thin film, whereas in the case of annealing in a reduced condition, the orientation of the film became nearly (111). The (111)-oriented PZSTN film showed relatively higher remanent polarization compared to that of the (100)-oriented film, while the (100)-oriented PZSTN film showed more fatigue behavior than the (111)-oriented film after 109 switching cycles. The (111)-oriented PZSTN film with rhombohedral structure is believed to be suspected to signi...

single-channel stereoscopic video imaging modality based on a transparent rotating deflector

This paper introduces a stereoscopic video imaging modality based on a transparent rotating deflector (TRD). Sequential two-dimensional (2D) left and right images were obtained by rotating the TRD on a stepping motor synchronized with a complementary metal-oxide semiconductor camera, and the components of the imaging modality were controlled through general purpose input/output ports using a microcontroller unit. In this research, live stereoscopic videos were visualized on a personal computer by both active shutter 3D and passive polarization 3D methods. The imaging modality was characterized by evaluating the stereoscopic video image generation, rotation characteristics of the TRD. The level of 3D conception was estimated in terms of simplified human stereovision. The results show that singlechannel stereoscopic video imaging modality has the potential to become an economical compact stereoscopic device as the system components are amenable to miniaturization; and could be applied in a wide variety of fields.

Development of an Optical Tissue Clearing Laser Probe System

Although low-level laser therapy (LLLT) has been a valuable therapeutic technology in the clinic, its efficacy may be reduced in deep tissue layers due to strong light scattering which limits the photon density. In order to enhance the photon density in deep tissue layers, this study developed an optical tissue clearing (OTC) laser probe (OTCLP) system which can utilize four different OTC methods: 1) tissue temperature control from 40 to

Effect of thickness and upper electrode diameter on polarization switching and electron emission of Pb(Zr0.8Ti0.2)O3 ferroelectric cathode

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