Decomposition Characteristics of the TTIP (Tetraisopropyl Orthotitanate) Precursor for Atomic Layer Deposition.

The decomposition of tetraisopropyl orthotitanate (TTIP), a representative precursor used in the atomic layer deposition (ALD) of titanium dioxide (TiO2) film, and the resulting changes in the thin film properties of the TiO2 film were investigated. TTIP was evaluated after exposure to thermal stress in an enclosed container. The vapor pressure results provide reasonable evidence that impurities are generated by the decomposition of TTIP under thermal stress. These impurities led to changes in the thermal properties of TTIP and changes in the growth rate, morphology, and composition of the thin film; in particular, these impurities increased the unstable oxidation states of Ti2+ (TiO) content in the TiO2 film. The changes in the properties of the TiO2 film resulting from the changes in the physical properties of TTIP led to a change in the properties of the device. We proved that the thermal stability of the precursor is a factor that can determine the reliability of the ALD process and the resulting thin film. Additionally, systematic evaluation of the precursor can provide useful information that can improve the development of the precursor and the consistency of the process.

Thermal Decomposition In Situ Monitoring System of the Gas Phase Cyclopentadienyl Tris(dimethylamino) Zirconium (CpZr(NMe2)3) Based on FT-IR and QMS for Atomic Layer Deposition.

We developed a newly designed system based on in situ monitoring with Fourier transform infrared (FT-IR) spectroscopy and quadrupole mass spectrometry (QMS) for understanding decomposition mechanism and by-products of vaporized Cyclopentadienyl Tris(dimethylamino) Zirconium (CpZr(NMe2)3) during the move to process chamber at various temperatures because thermal decomposition products of unwanted precursors can affect process reliability. The FT-IR data show that the -CH3 peak intensity decreases while the -CH2- and C=N peak intensities increase as the temperature is increased from 100 to 250 °C. This result is attributed to decomposition of the dimethylamido ligands. Based on the FT-IR data, it can also be assumed that a new decomposition product is formation at 250 °C. While in situ QMS analysis demonstrates that vaporized CpZr(NMe2)3 decomposes to N-ethylmethanimine rather than methylmethyleneimine. The in situ monitoring with FT-IR spectroscopy and QMS provides useful information for understanding the behavior and decomposes of CpZr(NMe2)3 in the gas phase, which was not proven before. The study to understand the decomposition of vaporized precursor is the first attempt and can be provided as useful information for improving the reliability of a high- advanced ultra-thin film deposition process using atomic layer deposition in the future.

Degradation Behaviors of NPB Molecules upon Prolonged Exposure to Various Thermal Stresses under High Vacuum below 10-4 Pa.

Understanding of the long-term thermal stabilities of organic light-emitting diode (OLED) materials during film deposition is important to accurately identifying their processing windows. The thermal stresses imposed on OLED materials in the evaporation source during the deposition process may cause phase transition and/or degradation of the source materials, which results in variations in their purity and thermal properties, such as the vapor pressure and, ultimately, the device degradation. In this work, we designed a simple and efficient apparatus to determine the long-term thermal stability of OLED materials, which allows prolonged heating of a minimal amount of the sample (∼2 g) for 50 h even under high vacuum below 10-4 Pa where the organic powder samples easily and rapidly vaporized because of exposure to temperature above their deposition temperature. We used this apparatus to evaluate the thermal degradation behaviors of N,N'-bis(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPB), which is a widely used hole-transporting material in OLEDs, upon prolonged exposure to various thermal stresses. After prolonged heating at 330 °C (380 °C) for 25 h (50 h), the change in purity, mass, vapor pressure, and phase of the heated NPB were analyzed by high-performance liquid chromatography, liquid chromatography-mass spectrometry, thermogravimetric analysis, and X-ray diffraction. The lifetime of OLEDs using the heated NPB was measured to study how the thermally induced material degradation affects the device characteristics. The results showed that the NPB degradation caused by prolonged exposure to 330 °C accelerated over time. In addition, it was confirmed that the degradation products with high molecular weight that form due to exposure to 380 °C was the main cause of device degradation.

Structural, Optical and Electrical Properties of HfO2 Thin Films Deposited at Low-Temperature Using Plasma-Enhanced Atomic Layer Deposition.

HfO2 was deposited at 80-250 °C by plasma-enhanced atomic layer deposition (PEALD), and properties were compared with those obtained by using thermal atomic layer deposition (thermal ALD). The ALD window, i.e., the region where the growth per cycle (GPC) is constant, shifted from high temperatures (150-200 °C) to lower temperatures (80-150 °C) in PEALD. HfO2 deposited at 80 °C by PEALD showed higher density (8.1 g/cm3) than those deposited by thermal ALD (5.3 g/cm3) and a smooth surface (RMS Roughness: 0.2 nm). HfO2 deposited at a low temperature by PEALD showed decreased contaminants compared to thermal ALD deposited HfO2. Values of refractive indices and optical band gap of HfO2 deposited at 80 °C by PEALD (1.9, 5.6 eV) were higher than those obtained by using thermal ALD (1.7, 5.1 eV). Transparency of HfO2 deposited at 80 °C by PEALD on polyethylene terephthalate (PET) was high (> 84%). PET deposited above 80 °C was unable to withstand heat and showed deformation. HfO2 deposited at 80 °C by PEALD showed decreased leakage current from 1.4 × 10-2 to 2.5 × 10-5 A/cm2 and increased capacitance of approximately 21% compared to HfO2 using thermal ALD. Consequently, HfO2 deposited at a low temperature by PEALD showed improved properties compared to HfO2 deposited by thermal ALD.

Glucose Sensing Materials Based on Carbon Nanotubes for Electrochemical Sensing.

There is an urgent need for in situ methods for detecting environmental pollution quickly and accurately. With the development of nanotechnology, a huge potential has been created for the design of highly sensitive sensors with low energy consumption and low costs. If a composite material constructed with carbon nanotubes is used as an electrode in contact with a contaminant, this material undergoes an oxidation-reduction reaction with the contaminant that allows the electrode to function as an electrochemical sensor. This study involved the application of multi-walled carbon nanotubes and modified working electrodes constructed with multi-walled carbon nanotube composites (Ag- and ZnO-multi-walled carbon nanotubes) as electrochemical sensors. These electrodes have good response speed and sensitivity at low concentrations, and they are reusable. To lower the price of these sensors, our goal was to maximize their sensitivity by using the low-cost multiwalled carbon nanotubes in conjunction with silver electroless plating of the multi-walled carbon nanotubes and multi-walled carbon nanotube composites.

Selective Deposition of Al2O3 on the Upper Side-Photoelectrode to Improve Dye-Sensitized Solar Cell Efficiency.

Charge recombination at the photoelectrode/dye/electrolyte interface decreases the energy conversion efficiency of dye-sensitized solar cells (DSSCs). To suppress charge recombination at this interface in DSSCs, an aluminum oxide (Al2O3) film can be deposited as an insulating metal oxide layer on the photoelectrode to form an energy barrier. However, the Al2O3 energy barrier can also disturb the transport of injected electrons to the working electrode through the titanium dioxide (TiO2) photoelectrode. In this study, Al2O3 was selectively deposited as an insulating metal oxide layer on the upper side of a TiO2 photoelectrode, which has a high probability of charge recombination, using plasma-enhanced atomic layer deposition. Deposition of the Al2O3 layer by this method helped to minimize the transport rate deterioration of injected electrons. This resulted in an increase of the efficiency of DSSCs containing the Al2O3 layer by 42.3% compared with that of a reference DSSC without the insulating metal oxide layer.

Characteristics of Metal-Metal Nano-Area Contact Resistance for Less Than 5 nm Technology Node.

Recently, better understanding of nano-area is required for 5 nm or less technology node. In particular, the high contact resistance generated in a nano-area significantly degrades the device performance. In this study, we propose a direct contact resistance measurement method without a test structure by separate processes to improve the nano-area contact resistance. The nano-area contact resistance of Ti-Ti and Cu-Cu decreased from 6.46 MΩ to 1.08 MΩ and from 3.78 MΩ to 1.48 MΩ, respectively, when the metal line and native layer formed on the surface were removed. In addition, it is confirmed that the contact resistance decreased with an increase in bonding strength in the case of nano-area homo-metal contact. However, the contact resistance is affected by the tunneling effect and bond energy according to the distance between the first layers of atoms in the case of nano-area hetero-metal contact.

Effect of Growth Temperature on the Structural and Electrical Properties of ZrO2 Films Fabricated by Atomic Layer Deposition Using a CpZr[N(CH3)2]3/C7H8 Cocktail Precursor.

The effect of growth temperature on the atomic layer deposition of zirconium oxide (ZrO2) dielectric thin films that were fabricated using a CpZr[N(CH3)2]3/C7H8 cocktail precursor with ozone was investigated. The chemical, structural, and electrical properties of ZrO2 films grown at temperatures from 250 to 350 °C were characterized. Stoichiometric ZrO2 films formed at 250-350 °C with an atomic ratio of O to Zr of 1.8-1.9 and a low content of carbon impurities. The film formed at 300 °C was predominantly the tetragonal crystalline phase, whereas that formed at 350 °C was a mixture of tetragonal and monoclinic phases. Electrical properties, such as capacitance, leakage current, and voltage linearity of TiN/ZrO2/TiN capacitors fabricated using the thin ZrO2 films grown at different temperatures were compared capacitor applications. The ZrO2 film grown at 300 °C exhibited low impurity content, predominantly tetragonal crystalline structure, a high dielectric permittivity of 38.3, a low leakage current of below 10-7 A/cm² at 2 V, and low-voltage linearity.

Development of particle characteristics diagnosis system for nanoparticle analysis in vacuum.

A particle characteristics diagnosis system (PCDS) was developed to measure nano-sized particle properties by a combination of particle beam mass spectrometry, scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS). It allows us to measure the size distributions of nano-sized particles in real time, and the shape and composition can be determined by in situ SEM imaging and EDS scanning. PCDS was calibrated by measuring the size-classified nano-sized NaCl particles generated using an aqueous solution of NaCl by an atomizer. After the calibration, the characteristics of nano-sized particles sampled from the exhaust line of the plasma-enhanced chemical vapor deposition process were determined using PCDS.

Designed synthesis of SiO2/TiO2 core/shell structure as light scattering material for highly efficient dye-sensitized solar cells.

SiO2/TiO2 core/shell nanoparticles (STCS-NPs) with diameters of 110, 240, and 530 nm were fabricated to investigate the influence of the size and refractive index of light-scattering particles on light-scattering properties. The optical properties of STCS-NPs were evaluated and compared with SiO2-NPs and TiO2-NPs. The structure of STCS-NPs, consisting of a low refractive index core and high refractive index shell, provides efficient light scattering. The optimized anode film with STCS-NPs had ca. 20% improved power conversion efficiency (PCE).

Development and calibration of differential mobility analyzer for 20 to 80 nm particles under low pressure conditions.

The vienna-type differential mobility analyzer (DMA) was developed for the measurement of wide-range nm-sized particles under low-pressure conditions (2.9-8 kPa) with the faraday cup electrometer (FCE). The length, inner and outer diameter of DMA are calculated as a function of flow rate, applied voltage, pressure, and particle diameter to avoide breakdown in DMA. The algorithm for the diffusion transfer function of the DMA was successfully developed and verified by comparing the numerical and experimental results. The DMA was calibrated via the tandem DMA (TDMA) method which using two DMA in parallel. The inversion algorithm was applied to the size distribution obtained from the current of the FCE. The calibration experiment was performed with 1% NaCl particles under atmospheric and low-pressure conditions. The calibration result showed that the development of the DMA was successful as it was able to measure 20- to 80-nm paricles under low-pressure conditions with various flow rates (0.1-0.5 l/min).

Prognostic factor analysis of third-line chemotherapy in patients with advanced gastric cancer.

BACKGROUND: Almost all patients with advanced gastric cancer will eventually develop progressive disease after first-line chemotherapy. However, the role of subsequent salvage chemotherapy remains controversial. The purpose of this study was to evaluate prognostic factors for the survival of patients with advanced gastric cancer who received third-line chemotherapy. METHODS: We reviewed 502 patients with advanced gastric cancer who received palliative chemotherapy at the Onocology Department of Hwasun Chonnam National University Hospital (2004-2008). Among them, 174 received third-line chemotherapy. To evaluate the clinicopathologic factors that affected overall survival, univariate and multivariate analyses were performed on the baseline factors before beginning third-line chemotherapy. RESULTS: Multivariate analysis found 4 prognostic factors affecting poor survival following third-line chemotherapy: performance status of 2-3 (hazard ratio [HR] 1.46, 95% confidence interval [CI] 1.06-2.02; P = 0.022), serum albumin level < 4 mg/dL (HR 1.82, 95% CI 1.32-2.53; P < 0.00), poor histologic type (HR 1.77, 95% CI 1.27-2.47; P = 0.001), and progression-free survival of <2.7 months following second-line chemotherapy (HR 1.51, 95% CI 1.09-2.08; P = 0.012). A prognostic index was constructed, dividing patients into low- (0-1 factor), intermediate- (2 or 3 risk factors), or high- (4 risk factors) risk groups. Median survival times for each group were 11.8, 6.7, and 3.3 months, respectively (P < 0.00). CONCLUSIONS: This analysis suggests that some clinicopathologic factors might be helpful in identifying the subgroup of patients most likely to benefit from third-line chemotherapy for advanced gastric cancer.