The role of Di(2-ethylhexyl)phosphoric acid as a cosurfactant on the morphology control of mesoporous silica microspheres

Synthesis of mesoporous silica microspheres larger than 10 microm via surfactant template approach has rarely been reported. According to the previous studies, particle morphologies were highly variable, depending on the synthesis conditions and impeller design such as impeller type, size, and agitation speed. A new robust surfactant-template synthesis strategy for the stable suspension of large silica microspheres was investigated by introducing an additional cosurfactant. Di(2-ethylhexyl)phosphoric acid (HDEHP) as a cosurfactant played a key role in suspension stabilization without distorting the spherical morphology as well as in the formation of uniform pore structures. High quality of mesoporous silica microspheres was obtained and compared with the Kosuge's silica under different conditions such as stirring rate, acid concentration, the amount of solvent in a mother liquor.     

Optimization of the number of quantum well pairs for high-brightness AlGaLnP-based light emitting diodes

We investigated high-brightness light emitting diodes (LEDs) appropriate for general lighting applications in terms of their temperature dependent photoluminescence characteristics and device performance according to the change of quantum well pairs (QWs). As the number of QWs was increased from 2 to 35 pairs, radiative recombination efficiency and device performances significantly improved, due to the suppression of carrier overflow by decreasing the carrier density in the active region and shortening the carrier transfer time from barrier to well. At a further increase in the number of QWs to 50 pairs, however, the optical and device performances started to degrade because of the increase in internal loss in the active region, such as the well volume itself acting as light absorbing layer and due to the aluminum oxide complexes in the barrier.     

Preparation and analysis of amorphous carbon films deposited from (C6H12)/Ar/He chemistry for application as the dry etch hard mask in the semiconductor manufacturing process

Amorphous carbon layers (ACL) were deposited on Si (100) wafers by plasma enhanced chemical vapor deposition (PECVD) by using 1-hexene (C₆H₁₂) as a carbon source for dry etch hard mask of semiconductor devices manufacturing process. The deposition characteristics and film properties were investigated by means of ellipsometry, Raman spectroscopy, X-ray photo electron spectroscopy (XPS) and stress analysis. Hardness, Young's modulus, and surface roughness of ACL deposited at 550 °C were investigated by using nano-indentation and AFM. The deposition rate was decreased from 5050 Å/min to 2160 Å/min, and dry etch rate was decreased from 2090 Å/min to 1770 Å/min, and extinction coefficient was increased from 0.1 to 0.5. Raman analysis revealed a higher shift of the G-peak and a lower shift of the D-peak and the increase of I(D)/I(G) ratio as the deposition temperature was increased from 350 °C to 550 °C. XPS results of ACL deposited at 550 °C revealed a carbon 1s binding energy of 284.4 eV. The compressive film stress was decreased from 2.95 GPa to 1.28 GPa with increasing deposition temperature. The hardness and Young's modulus of ACL deposited at 550 °C were 5.8 GPa and 48.7 GPa respectively. The surface roughness RMS of ACL deposited at 550 °C was 2.24 Å, and that after cleaning in diluted HF solution (H₂O:HF = 200:1), SC1 (NH₄OH:H₂O₂:H₂O = 1:4:20) solution, and sulfuric acid solution (H₂SO₄:H₂O₂ = 6:1) was 2.28 Å, 2.30 Å and 7.34 Å, respectively. The removal amount of ACL deposited at 550 °C in diluted HF solution, SC1 solution and sulfuric acid solution was 6 Å, 36 Å and 110 Å, respectively. These results demonstrated the viability of ACL deposited by PECVD from C₆H₁₂ at 550 °C for application as the dry etch hard mask in fabrication of semiconductor devices.     

Diversity analysis of lactic acid bacteria in Korean rice wines by culture-independent method using PCR-denaturing gradient gel electrophoresis

A polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) method was used to determine the presence and diversity of lactic acid bacteria (LAB) in takju, a traditional Korean rice wine. Bacterial DNAs were extracted from 15 commercial rice wines and amplicons of partial 16S rRNA genes were separated by DGGE and intense bands were sequenced. Lactobacillus (Lb.) paracasei, Lb. plantarum, and Leuconostoc pseudomesenteroides were detected in all samples and Lb. harbinensis and Lb. parabuchneri were found with above 80% frequency of occurrence. Unknown species of Lactobacillus were also widely detected. This result revealed that, regardless of products and raw materials, the distribution profiles of LAB in takju products have a common pattern comprising of above predominant species and, furthermore, takju can be regarded as a LAB-rich fermented food providing various probiotics.     

Sensing margin trend with technology scaling in MRAM

Magnetoresistive random access memory (MRAM) is a leading candidate for future memory applications because it may provide compelling advantages by combining desirable attributes of SRAM, DRAM, and Flash. Process technology has recently scaled down to the nano‐meter regime, which accordingly has resulted in lowering supply voltage, increasing short channel effect, and rapidly increasing process variation. MRAM is also affected by technology scaling, which significantly reduces the sensing margin. In this paper, several circuit design parameters, such as supply voltage, transistor size, and transistor gate voltage in the sensing circuit, are evaluated to discover the root causes of reduced sensing margin with technology scaling. The lowered supply voltage and lowered output resistance of the transistor, which occurs with technology scaling, are verified as the root causes of reduced sensing margin. It is also shown that increased process variation due to technology scaling aggravates the problem. A high supply voltage with power gating combined with optimized transistor size and gate voltage, and a power gating scheme using an IO device with an IO voltage are suggested as effective design solutions for reliably increasing the sensing margin in the presence of process variation. Copyright © 2010 John Wiley & Sons, Ltd.     

Mechanical Properties and Residual Stress Measurements in Anodic Aluminium Oxide Structures Using Nanoindentation

Anodic alumina has been used widely for corrosion protection of aluminum surfaces or as a dielectric material in microelectronics applications. It exhibits a homogeneous morphology of parallel pores that can easily be controlled between 10 and 400 nm. It has been applied as a template for fabrication of the nanometer-scale composite. In this study, the mechanical properties of anodic aluminum oxide (AAO) structures are measured by the nanoindentation method. The nanoindentation technique is one of the most effective methods to measure the mechanical properties of nanostructures. Using the nanoindentation method, we investigated the residual stress and mechanical properties such as the indentation modulus and hardness of the AAO structure with different-sized nanoholes. As a result, we find that the “hole effect” that changes the mechanical properties is the hole size.Original English Text Copyright © 2005 by Fizika i Khimiya Stekla, Ko, D. Lee, Jee, Park, K. Lee, Hwang.This article was submitted by the authors in English.