Jun-Kyu Yang

Magnetic PECA nanoparticles as drug carriers for targeted delivery: Synthesis and release characteristics

Magnetic poly(ethyl-2-cyanoacrylate) (PECA) nanoparticles containing anti-cancer drugs (Cisplatin and Gemcitabine) were prepared by inter-facial polymerization. The spherical nanoparticles (d = 250 ± 15 nm) with smooth surfaces and moderately uniform size distributions were obtained. The amount of magnetite encapsulated inside the polymer matrix was increased up to 14.26% (w/w) by controlling the initial weight ratio of monomer/magnetite. It was found that the amount of Cisplatin encapsulated in the magnetic nanoparticle is much higher than that of Gemcitabine because Cisplatin (hydrophobic) is highly soluble in the oil phase and encapsulated easier inside nanoparticles compared to Gemcitabine (hydrophilic). The presence of magnetite and its super-paramagnetic characteristic were confirmed by FTIR spectra and VSM. In-vitro experiments of drug release and magnetic mobility under external magnetic field demonstrated that magnetic poly(ethyl-2-cyanoacrylate) (PECA) nanoparticles can be a highly versatile magnetic drug carrier with sustained release behaviour and sufficient magnetic susceptibility.

Chemical and electrical characterization of Gd2O3∕GaAs interface improved by sulfur passivation

We report the formation of a gate dielectric film on the sulfur passivated GaAs(001). The Gd2O3 films were deposited on the n-GaAs substrates using the electron-beam evaporation. The sulfur passivated GaAs metal-oxide-semiconductor diode exhibited the improved electrical properties compared to a similar GaAs diode that was cleaned with HCl including an enhanced conduction-band barrier and a reduced-leakage current. We investigated the relation between the interfacial bonds and the electrical properties by a systematic characterization using the photoemission spectroscopy. Sulfidation was shown to preserve a stable Gd2O3∕GaAs interface and to prevent an interfacial GaAs oxide formation. The stable interface and the passivated surface were caused by the bonding transition from As–S to Ga–S. The As-oxide was dissociated to form the interfacial Ga2O3 and to volatilize the elemental As in the Gd2O3 deposition, conducted without sulfidation. The interfacial oxides and excess As degraded the electrical propertie...

The effect of excess Pb content on the crystallization and electrical properties in sol–gel derived Pb (Zr0.4Ti0.6)O3 thin films

Abstract The crystallization behavior and electrical properties are closely related to the excess Pb content in PZT (Zr/Ti=40/60) thin films. However, the role of excess Pb in the crystalline growth has not been precisely defined. In this work, the effect of excess Pb content on the crystallization and ferroelectric properties of these films was investigated. To analyze the effect, PZT films containing various amounts of excess Pb, but with same grain size and film orientation, were prepared. In the case of films derived from PZT solutions with a high excess-Pb content, more nuclei formed, but grew into smaller-sized grains than in the case of films with a low Pb content. On the other hand, a conversion from (100)- to (111)-preferred orientation was observed as a result of time-dependent bi-orientational growth. A depth profile analysis using Auger electron spectroscopy revealed that excess Pb enhanced the formation of Ti-rich PZT at the Pt/PZT interface. This Ti-rich PZT seemed to be the origin of the (111) orientation in the film with high excess Pb content. As higher excess Pb was included, the films showed a higher permittivity, a lower distribution of the space charge layer and better resistance against repeating fatigue cycles, due to the inhibition of movement of vacancies. These phenomena could be applied to the formation of a space charge layer via oxygen vacancy accumulation in the case of films with a low Pb content.

Ferroelectric-gate field effect transistors using Nd2Ti2O7/Y2O3/Si structures

Abstract Ferroelectric field effect devices offer the possibility of non-volatile active memory elements. In the metal–ferroelectric–semiconductor field effect transistor, it is important for a ferroelectric material to have a low dielectric constant to enable the application of sufficient electric field to a ferroelectric film. In this work, we report the fabrication and characterization of a ferroelectric-gate field effect transistor using Nd2Ti2O7(NTO)/Y2O3/Si structures. The crystalline property of the film as a function of annealing temperature was characterized by X-ray diffraction. C–V characteristics were measured to investigate the ferroelectric memory effects at 1 MHz with a bias sweep rate of 0.18 V/s. As a result, the memory windows were in the range of 0.98–3.31 V when the applied voltage varied from 3 to 9 V. Specifically, we confirmed the ferroelectricity of crystallized NTO films.

Energy band structure and electrical properties of (La2O3)1−x(SiO2)x(0⩽x⩽1)∕n-GaAs(001) system

This letter investigates the chemical bonding state and energy band structure of (La2O3)1−x(SiO2)x(0⩽x⩽1) films grown on sulfur-passivated n-GaAs (001). The dielectric bandgap and interfacial band alignment were modified by compounding the La2O3 films with SiO2. A shift in binding energy of the core level was observed by comparing the electronegativities of the second nearest-neighbor element. The controlled parameters of energy band structure were systematically monitored by valence band and absorption spectra. Band offset values were almost linearly related to the concentration of SiO2 when no Fermi level pinning in the midgap of n-GaAs was assumed. The correlation between band parameter and electrical properties, as probed by capacitance and leakage current measurements, is discussed.

Controlled band offset in (Gd2O3)1−x(SiO2)x(0⩽x⩽1)∕n–GaAs (001) structure

This letter investigates the chemistry and energy band structure of (Gd2O3)1−x(SiO2)x(0⩽x⩽1) films grown on n-GaAs (001). Dielectric band gap and interfacial band alignment of Gd2O3 films were modified by compounding with SiO2. Binding energy shift of core level was observed from different electronegativity of second nearest-neighbor element. Controlled parameters of energy band structure were systematically characterized by valence band, absorption, and energy loss spectra. Assuming no Fermi level pinning in the midgap of n-GaAs, band offset values represent almost linear dependency on the concentration of SiO2. The correlation of band offset with the electrical properties, as probed by capacitance and leakage current measurements, was also discussed.

Interface control of Gd2O3/GaAs system using pre-deposition of Gd metal on GaAs substrate with native oxides

Ultrathin Gd metal was evaporated on GaAs surface covered with native oxides. X-Ray photoelectron spectroscopic studies revealed that GaAs-native oxides could be reduced during the deposition of Gd metal. However, the elemental forms of Ga and As were not observed but the oxidation of Gd metal was confirmed from LMM Auger electron spectra, Gd 3d 5/2, and O 1s photoelectron spectra. The Gd coated GaAs substrates were heated at 400 °C and Gd2O3 films were successively deposited with a well developed crystalline state. This reductive metal deposition prior to oxide formation improved interfacial quality of GaAs without previous chemical etching or passivation. Capacitance–voltage (C–V) measurements at 1 MHz indicated that a good interfacial state between Gd2O3 and GaAs could be obtained appropriate for metal-oxide-semiconductor (MOS) applications through a two step deposition of Gd and Gd2O3.

Enhanced Fatigue Property through the Control of Interfacial Layer in Pt/PZT/Pt Structure

Ferroelectric Pb(ZrxTi1-x)O3 PZT thin film capacitors with Pt(111)/SiO2/Si substrate were fabricated by sol-gel method. Ultrathin PZT layer containing various contents of excess Pb was adopted as an interfacial layer to investigate the role of excess Pb on the formation of interfacial region between PZT film and Pt bottom electrode. An improvement of electrical properties was observed according to the content of excess Pb in interfacial PZT layer due to the inhibition of inter-diffusion at film-substrate interface as well as defect formation. The formation of Ti-rich PZT at the initial stage of anneal due to excess Pb was responsible for the excellent ferroelectric characteristic. This implied that the role of excess Pb in film-substrate interface was of significance to the long-term reliability.

Characteristics of interfacial bonding distribution of Gd2O3–GaAs structure

Abstract Gd 2 O 3 films are electron beam (e-beam) evaporated on GaAs at room temperature. The bonding natures of the Gd 2 O 3 /GaAs interface are characterized using Auger electron spectroscopy and X-ray photoelectron spectroscopy. LMM Auger lines clearly demonstrate the oxide-related chemical state. After the deposition of Gd 2 O 3 on S-passivated GaAs, GaAs oxides were not formed at the interface but the generation of interfacial excess As is observed. The generation of elemental excess As can be explained by the dissociation of As–S bonds. However, interfacial modification could be minimized through in situ thermal hydrogenation of S-passivated GaAs before Gd 2 O 3 deposition. The high-frequency capacitance–voltage ( C–V ) measurements showed an effective decrease of the interface state. The characteristics of deposition-induced interfacial modification and bonding distribution in Gd 2 O 3 /GaAs interface are discussed.

Fabrication and Characterization of La 2 Ti 2 O 7 Films for Ferroelectric-Gate Field Effect Transistor Applications

For applying ferroelectric material to nonvolatile active memory element in ferroelectric field effect devices, La 2 Ti 2 O 7 films on CeO 2 /Si (100) were attained at 650°C using rapid thermal annealing process followed by each coating step. The crystalline property of the film as annealing temperature was characterized by X-ray diffraction C-V characteristics were measured to investigate the ferroelectric memory. As a result, the memory windows were in the range of 0.4V to 2.1V when the applied voltage varied from 3V to 9V. However, the final annealing temperature increased, the memory window decreases due to the formation of complex oxide layer underneath CeO 2 .