Nanoparticles which selectively bind to the atherosclerotic lesion can be used in diagnostic imaging and efficient drug delivery. We have developed peptides conjugated polymer nanoparticles which selectively bind to the atherosclerotic plaque. Hydrophobically modified glycol chitosan (HGC) nanoparticles were used as carriers, and the peptide which showed selective binding to the atherosclerotic plaque was screened using phage display. We synthesized peptides conjugated HGC-Cy5.5 nanoparticles and examined their binding characteristics on the activated endothelial cells in vitro under static and flow conditions. In static condition, the peptide tagged nanoparticles more avidly bound to the activated endothelial cells comparing to the unactivated endothelial cells. In laminar flow condition, selective binding of peptide tagged nanoparticles to the activated endothelial cells was more prominent.

Growth mechanism of In-rich InGaN∕GaN quantum wells (QWs) was investigated. First, we examined the initial stage of InN growth on GaN template considering strain-relieving mechanisms such as defect generation, islanding, and alloy formation at 730 °C. It was found that, instead of formation of InN layer, defective In-rich InGaN layer with thickness fluctuations was formed to relieve large lattice mismatch over 10% between InN and GaN. By introducing growth interruption (GI) before GaN capping at the same temperature, however, atomically flat InGaN∕GaN interfaces were observed, and the quality of In-rich InGaN layer was greatly improved. We found that decomposition and mass transport processes during GI in InGaN layer are responsible for this phenomenon. There exists severe decomposition in InGaN layer during GI, and a 1-nm-thick InGaN layer remained after GI due to stronger bond strength near the InGaN∕GaN interface. It was observed that the mass transport processes actively occurred during GI in InGaN layer above 730 °C so that defect annihilation in InGaN layer was greatly enhanced. Finally, based on these experimental results, we propose the growth mechanism of In-rich InGaN∕GaN QWs using GI.

In-rich InGaN/GaN nanostructures such as quantum wells (QWs) and quantum dots (QDs) were successfully grown by metal-organic chemical vapor deposition and their optical properties were investigated. Introduction of a relatively high growth temperature made it possible to grow In-rich InGaN/GaN QWs and growth interruption (GI) was effectively used to control their structural and optical properties. From In-rich InGaN/GaN QW structures grown without GI, enhanced thermal stability appeared in optical properties and thickness fluctuation in In-rich InGaN QWs could give intrinsic QD-like carrier localization centers. To enhance thermal characteristics, artificial formation of In-rich TnGaN/GaN QDs was done at a relatively lower growth temperature than that of QWs. From In-rich InGaN/GaN QDs, we could obtain high efficiency ultraviolet emission at room temperature.

In-rich InGaN quantum dot structures were grown by metalorganic chemical vapor deposition. Growth at low temperature made possible the growth of InGaN layers of high In content (over 70 InN%) with negligible formation of In metal droplets. The density, average diameter and height of typical InGaN quantum dots (QDs) were estimated at 8×109/cm2, 80 and 1.2 nm, respectively. The emission wavelength from the QDs could be controlled to the near ultraviolet (UV) region by variation of the growth conditions. This work demonstrates that In-rich InGaN QD active layers are very promising device structures for application as UV light-emitting diodes.

20 nm GaNAs epilayers were grown on GaN/sapphire by metalorganic chemical vapor deposition. As growth temperature decreased from 720 to 565 °C, it was found that As concentration was increased from 1.3 × 1020 and saturated at about 5–6 × 1020 cm–3. GaAs-like GaNAs islands were formed on GaN at 530 °C. In case of GaNAs epilayers grown at 565 and 600 °C, GaN-like GaNAs phases were observed by high-resolution X-ray diffraction (XRD) and low angle XRD. By low angle XRD and high-resolution TEM with electron nano-beam diffraction patterns, the FCC-stacked region in wurtzite matrix was clearly observed in thin GaNAs layers. We propose that this structural nonuniformity in GaNAs might be caused by the nonuniform distribution of As concentration. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We grew high quality In-rich InGaN/GaN single quantum well (SQW) structures by metal-organic chemical vapor deposition using growth interruption and obtained a sharp photoluminescence peak in near-ultraviolet (UV) region. During In-rich InGaN well layer growth, only TMIn and ammonia were supplied, however, atomic interdiffusion as well as defect generation occurred to relieve large lattice mismatch over 10% between InN and GaN. From medium-energy ion scattering measurement and subsequent fitting of the spectrum, we could find that the InGaN well layer was In-rich and it has 60-70% indium content. We also found the compositional grading of indium at top and bottom InGaN/GaN interfaces. The Fourier series method was used to calculate the energy levels and envelope functions in In-rich InGaN/GaN SQW with compositional grading and we could quantitatively explain the near-UV emission observed from the SQW.

In-rich InGaN/GaN single quantum wells were grown by metalorganic chemical vapor deposition for the first time to the best of our knowledge. The structures consist of a 2-mum thick GaN buffer layer, a 2-nm thick In-rich InGaN single quantum well, and a 20 nm thick GaN capping layer. Single quantum well structures were examined by transmission electron microscopy. Photoluminescence emissions from the single quantum well samples were observed at wavelengths ranged from 400 nm to 500 nm depending upon the growth conditions of the InN layer. From a simple energy level calculation, we found the possibility of extremely large emission peak shift with well thickness. (C) 2003 WILEYNCH Verlag GmbH & Co. KGaA, Weinheim.

The use of ammonia preheater reduces the Ga vacancy (VGa) concentration in GaN. The epilayers grown with or without preheated ammonia had little differences in structural properties from X-ray diffraction and transmission electron microscopy. It was found, however, that the GaN epilayers grown with unheated ammonia had more charge compensation centers. The intensities of yellow luminescence (YL) in GaN epilayers grown with preheated ammonia decreased with Si doping, whereas those grown with unheated ammonia increased with Si doping. It is suggested that the use of preheated ammonia reduced the VGa concentration in GaN without altering structural properties.

An in-situ, real-time spectral reflectance (SR) technique was used to monitor the GaN growth during metalorganic chemical-vapor deposition. A series of SR spectra from 190 similar to 861 nm were obtained using p-polarized light with an incident angle of 75 degrees. The SR spectra could he nicely fitted with the known refractive indices of GaN and sapphire and with the GaN thickness as a fitting variable. The fitted thickness was in good agreement with the thickness measured by scanning electron microscopy. Furthermore, the peak positions of SR spectra increased linearly to longer wavelength with thickness. This strongly implies that thickness information can be obtained in real-time by measuring the peak shift of SR spectra. not by fitting the whole spectrum at that moment.