Wetting Property Modification of Al2O3 by Helium Ion Irradiation: Effects of Beam Energy and Fluence on Contact Angle.

In imparting wetting properties, a fabrication process without the addition of new compounds and deposition of coating layers would be the most desirable because it does not introduce additional complexities. Hence, the ion beam irradiation technique is used as it enables the chemistry of materials to be modified through simple adjustments of irradiation parameters such as the type of accelerated particles, beam energy, and fluence. In this study, the hydrophilicity of alumina surfaces was weakened by irradiating He ion beams of different energy levels (200 keV and 20 MeV). These transitions become more pronounced as the total beam fluence increases. In low-energy irradiation, the effect of irradiation is predominant near the surface, and hydrophilicity is weakened by the increase in carbon adsorption and suppression of dissociative adsorption of water molecules owing to the introduction of oxygen vacancies. In contrast, nuclear transmutations are induced by irradiation with high-energy beams. Consequently, fluorine is generated, and hydrophobic functional groups are formed on the surface. By varying the beam conditions, the wetting properties of the target ceramic can be controlled to the desired level, which is required in various industries, via appropriate adjustments of the beam parameters. In addition, the beam irradiation technique may be applicable to all ceramic materials, including lattice oxygen and alumina.

Effects of Proton Irradiation on the Current Characteristics of SiN-Passivated AlGaN/GaN MIS-HEMTs Using a TMAH-Based Surface Pre-Treatment.

This study investigated the combined effects of proton irradiation and surface pre-treatment on the current characteristics of Gallium Nitride (GaN)-based metal-insulator-semiconductor high-electron-mobility-transistors (MIS-HEMTs) to evaluate the radiation hardness involved with the Silicon Nitride (SiN) passivation/GaN cap interface. The impact of proton irradiation on the static and dynamic current characteristics of devices with and without pre-treatment were analyzed with 5 MeV proton irradiation. In terms of transfer characteristics before and after the proton irradiation, the drain current of the devices without and with pre-treatment were reduced by an increase in sheet and contact resistances after the proton irradiation. In contrast with the static current characteristics, the gate-lag characteristics of the device with pre-treatment were significantly degenerated. In the device with pre-treatment, the hydrogen passivation for surface states of the GaN cap was formed by the pre-treatment and SiN deposition processes. Since the hydrogen passivation was removed by the proton irradiation, the newly created vacancies resulted in the degeneration of gate-lag characteristics. After nine months in an ambient atmosphere, the gate-lag characteristics of the device with pre-treatment were recovered because of the hydrogen recombination. These results demonstrated that the radiation hardness of MIS-HEMTs was affected by the SiN/GaN interface quality.

Hydrophilicity Improvement of Polymer Surfaces Induced by Simultaneous Nuclear Transmutation and Oxidation Effects Using High-Energy and Low-Fluence Helium Ion Beam Irradiation.

Two commodity polymers, polystyrene (PS) and high-density polyethylene (HDPE), were irradiated by high-energy He ion beams at low fluence to examine the wettability changes at different fluences. The water contact angles of the PS and HDPE surfaces were reduced from 78.3° to 46.7° and 81.5° to 58.5°, respectively, upon increasing the fluence from 0 to 1 × 1013 He2+/cm2 for irradiation durations ≤4 min. Surface analyses were performed to investigate these wettability changes. Surface texture evaluations via scanning electron and atomic force microscopies indicated non-remarkable changes by irradiation. However, the chemical structures of the irradiated polymer surfaces were notable. The high-energy He ions induced nuclear transmutation of C to N, leading to C-N bond formation in the polymer chains. Further, C-O and C=O bonds were formed during irradiation in air because of polymer oxidation. Finally, amide and ester groups were generated by irradiation. These polar groups improved hydrophilicity by increasing surface energies. Experiments with other polymers can further elucidate the correlation between polymer structure and surface wettability changes due to high-energy low-fluence He ion irradiation. This method can realize simple and effective utilization of commercial cyclotrons to tailor polymer surfaces without compromising surface texture and mechanical integrity.

Chitosan-TiO2 composite: A potential 68Ge/68Ga generator column material.

A durable and ready to use 68Ge-68Ga generator column material is required for its routine use in radiopharmaceutical procedures. The present work comprises preliminary studies for development and evaluation of chitosan-TiO2 based microsphere (C-TOM) composite towards its competence as a column material. The batch uptake studies showed higher distribution coefficients for 68Ge vis-à-vis 68Ga in the complete concentration range of HCl examined (0.01-1 mol.L-1). Furthermore, C-TOM showed enduring physical and chemical stability in 0.01 mol.L-1 HCl with persistent 68Ga elution profiles (>95%) and negligible 68Ge breakthrough (2 × 10-4%) for the preliminary evaluation period of ∼2 months. Overall, the studies indicated that, 68Ga with high radionuclidic purity (≥99.99%) can be eluted routinely in a small volume (∼1.5 mL) of 0.01 mol.L-1 HCl proving its potentials as a novel solid phase extractant for 68Ge/68Ge generator system.

Red Blood Cell Membrane Bioengineered Zr-89 Labelled Hollow Mesoporous Silica Nanosphere for Overcoming Phagocytosis.

Biomimetic nanoparticles (NPs) have been actively studied for their biological compatibility due to its distinguished abilities viz. long-term circulation, low toxicity, ease for surface modification, and its ability to avoid phagocytosis of NPs by macrophages. Coating the NPs with a variety of cell membranes bearing the immune control proteins increases drug efficacy while complementing the intrinsic advantages of the NPs. In this study, efforts were made to introduce oxophilic radiometal 89Zr with hollow mesoporous silica nanospheres (HMSNs) having abundant silanol groups and were bioengineered with red blood cell membrane (Rm) having cluster of differentiation 47 (CD47) protein to evaluate its long-term in vivo behavior. We were successful in demonstrating the increased in vivo stability of synthesized Rm-camouflaged, 89Zr-labelled HMSNs with the markedly reduced 89Zr release. Rm camouflaged 89Zr-HMSNs effectively accumulated in the tumor by avoiding phagocytosis of macrophages. In addition, re-injecting the Rm isolated using the blood of the same animal helped to overcome the immune barrier. This novel strategy can be applied extensively to identify the long-term in vivo behavior of nano-drugs while enhancing their biocompatibility.

Development of fluorescent probes that bind and stain amyloid plaques in Alzheimer's disease.

ß-amyloid (Aß) plaques in the brain are composed of Aß40 and Aß42 peptides, and are the defining pathological feature of Alzheimer's disease (AD). Fluorescent probes that can detect Aß plaques have gained increasing interest as potential tools for in vitro and in vivo monitoring of the progression of AD. In this study, chalcone-mimic fluorescent probe 5 was designed and prepared. Probe 5 exhibited an approximately 50-fold increase in emission intensity after mixing with Aß42 aggregates, a high affinity for Aß42 aggregates (K D = 1.59 µM), and reasonable lipophilicity (log P value = 2.55). Probe 5 also exhibited specific staining of Aß plaques in the transgenic mice (APP/PS1) brain sections. Ex vivo fluorescence imaging of the brain from normal and TG mice revealed that probe 5 was able to penetrate the BBB and stain the Aß plaques. These results suggest that chalcone-mimic probe 5 possessed the requirements of a fluorescent probe for Aß plaques and may be useful in AD research.

Micropatterning of cells on electron-irradiated poly(dimethylsiloxane) surface.

In this study, a facile route to fabricate micropatterns of cells is presented on the basis of electron irradiation of poly(dimethylsiloxane) (PDMS). PDMS films were irradiated with electron beams through a pattern mask with micrometer-sized grids. After irradiation, the changes in the chemical composition, morphology, and wettability of the PDMS surface were investigated by using an X-ray photoelectron spectrometer, an atomic force microscope, and a contact anglometer. The results of the surface analysis revealed that the hydrophobic PDMS surface was changed into a hydrophilic one by the electron irradiation. Furthermore, on the basis of cell culturing on the selectively-irradiated PDMS, cells such as NIH3T3 and L929 were selectively adhered to and proliferated on the irradiated regions of the PDMS surface, resulting in the micropatterns of the cells on the PDMS surface.

Surface morphology control of polymer films by electron irradiation and its application to superhydrophobic surfaces.

A simple and controllable one-step method to fabricate superhydrophobic surfaces on poly(tetrafluoroethylene) (PTFE) films is developed on the base of electron irradiation. When the thickness of PTFE films is higher than the penetration depth of electron beams, electrical charging occurs at the surface of the films because of the imbalance between the accumulation of incident electrons and the emission of secondary electrons. Local inhomogeneity of charge distribution due to this electrical charging results in the nonuniform decomposition of PTFE molecular bonds. As electron fluence increases, surface morphology and surface roughness of the films are dramatically changed. An extremely rough surface with micrometer-sized pores is produced on the surface of PTFE films by electron irradiation at a fluence higher than 2.5 × 10(17) cm(-2).Because of high surface roughness, the irradiated PTFE films exhibit superhydrophobic property with a water contact angle (CA) greater than 150° at fluences ranging from 4 × 10(17) to 1 × 10(18) cm(-2). The surface morphology and corresponding water CA can be controlled by simply changing the electron fluence. This electron irradiation method can be applicable to the fabrication of superhydrophobic surfaces using other low-surface-energy materials including various fluoropolymers.

Fabrication of size-controllable hexagonal non-close-packed colloidal crystals and binary colloidal crystals by pyrolysis combined with plasma-electron coirradiation of polystyrene colloidal monolayer.

We present an unprecedented and systematic route to controllably fabricate hexagonal non-close-packed (hncp) monolayer colloidal crystals and binary colloidal crystals (BCCs) based on plasma-electron coirradiation of polystyrene colloidal monolayers followed by thermal decomposition. Hncp colloidal crystals with tunable particle sizes and periods could be fabricated by changing the pristine colloidal particle size and the thermal decomposition time. In addition, BCCs and trimodal colloidal crystals that are composed of different-sized colloidal particles can also be fabricated by adding small particles on the prepared hncp colloidal crystals. Both the particle size ratio and the volume fraction of the BCCs can be widely tuned. These hncp colloidal crystals and BCCs have various potential applications as optical and photonic materials as well as in catalysis and sensors.

Fabrication of porous hierarchical polymer/ceramic composites by electron irradiation of organic/inorganic polymers: route to a highly durable, large-area superhydrophobic coating.

Polymer/ceramic composite films with micro- and nanocombined hierarchical structures are fabricated by electron irradiation of poly(methyl methacrylate) (PMMA) microspheres/silicone grease. Electron irradiation induces volume contraction of PMMA microspheres and simultaneously transforms silicone grease into a ceramic material of silicon oxycarbide with many nanobumps. As a result, highly porous structures that consist of micrometer-sized pores and microparticles decorated with nanobumps are created. The fabricated films with the porous hierarchical structure exhibit good superhydrophobicity with excellent self-cleaning and antiadhesion properties after surface treatment with fluorosilane. In addition, the porous hierarchical structures are covered with silicon oxycarbide, and thus the superhydrophobic coatings have high hardness and strong adhesion to the substrate. The presented technique provides a straightforward route to producing large-area, mechanically robust superhydrophobic films on various substrate materials.

Unconventional method for morphology-controlled carbonaceous nanoarrays based on electron irradiation of a polystyrene colloidal monolayer.

An unconventional and straightforward route to fabricate morphology-controlled 2D ordered carbonaceous nanoarrays is presented. This route is based on the electron irradiation of a polystyrene colloidal monolayer followed by thermal decomposition. This strategy has the advantages of low-cost fabrication and easy manipulation compared to conventional lithography technique and furthermore overcomes the disadvantage of the self-assembly technique that generally has the defect of irregular units in ordered arrays. Various nanoarrays with irregular units, including network-like and star-like ordered arrays as well as hexagonal non-close-packed dot arrays, were fabricated by this novel route. These ordered arrays can be used as templates or masks to fabricate other ordered structures and then can be removed completely by thermal decomposition at a high temperature. Additionally, these arrays are carbonaceous materials that have higher thermal stability and higher refractive index compared with those of the pristine polymer, which are important for real applications such as optical devices. This method might also be used for the fabrication of other unique ordered arrays if different polymer precursor materials are used.

A facile polyol route to uniform gold octahedra with tailorable size and their optical properties.

A straightforward and effective polyol route for the controllable synthesis of high-quality gold (Au) octahedra with uniform size is presented in an ethylene glycol solution. Large-scale Au octahedra with the size ranging from tens to hundreds of nanometers were selectively synthesized in high-yield. The surfaces of octahedral Au nanocrystals are smooth and correspond to {111} planes. Formation of Au nanooctahedra was attributed to the preferential adsorption of cationic surfactant poly(diallyldimethylammonium) chloride (PDDA) molecules on the {111} planes of Au nuclei that inhibited the growth rate along the <111> direction. The reduction rate of gold ions in the synthesis process can be rationally manipulated by acidic and basic solutions. This provides a facile and effective route to harvest Au octahedra with different dimensions. The synthetic strategy has the advantage of one-pot and requires no seeds, no foreign metal ions, and no pretreatment of the precursor, so that this is a practical method for controllable synthesis of Au octahedra. Size-dependent optical properties of Au octahedra were numerically and experimentally analyzed. The analysis shows that Au octahedra with sharp edges possess attractive optical properties, promising their applications to surface-enhancement spectroscopy, chemical or biological sensing, and the fabrication of nanodevices.