Unyong Jeong

Macroscopic 10-Terabit–per–Square-Inch Arrays from Block Copolymers with Lateral Order

Generating laterally ordered, ultradense, macroscopic arrays of nanoscopic elements will revolutionize the microelectronic and storage industries. We used faceted surfaces of commercially available sapphire wafers to guide the self-assembly of block copolymer microdomains into oriented arrays with quasi–long-range crystalline order over arbitrarily large wafer surfaces. Ordered arrays of cylindrical microdomains 3 nanometers in diameter, with areal densities in excess of 10 terabits per square inch, were produced. The sawtoothed substrate topography provides directional guidance to the self-assembly of the block copolymer, which is tolerant of surface defects, such as dislocations. The lateral ordering and lattice orientation of the single-grain arrays of microdomains are maintained over the entire surface. The approach described is parallel, applicable to different substrates and block copolymers, and opens a versatile route toward ultrahigh-density systems.

Flexible, highly efficient all-polymer solar cells.

All-polymer solar cells have shown great potential as flexible and portable power generators. These devices should offer good mechanical endurance with high power-conversion efficiency for viability in commercial applications. In this work, we develop highly efficient and mechanically robust all-polymer solar cells that are based on the PBDTTTPD polymer donor and the P(NDI2HD-T) polymer acceptor. These systems exhibit high power-conversion efficiency of 6.64%. Also, the proposed all-polymer solar cells have even better performance than the control polymer-fullerene devices with phenyl-C61-butyric acid methyl ester (PCBM) as the electron acceptor (6.12%). More importantly, our all-polymer solar cells exhibit dramatically enhanced strength and flexibility compared with polymer/PCBM devices, with 60- and 470-fold improvements in elongation at break and toughness, respectively. The superior mechanical properties of all-polymer solar cells afford greater tolerance to severe deformations than conventional polymer-fullerene solar cells, making them much better candidates for applications in flexible and portable devices.

A New Theranostic System Based on Gold Nanocages and Phase-Change Materials with Unique Features for Photoacoustic Imaging and Controlled Release

This communication reports a new theranostic system with a combination of capabilities to both enhance the contrast of photoacoustic (PA) imaging and control the release of a chemical or biological effector by high-intensity focused ultrasound (HIFU). The fabrication of this system simply involves filling the hollow interiors of gold nanocages with a phase-change material (PCM) such as 1-tetradecanol that has a melting point of 38-39 °C. The PCM can be premixed and thus loaded with a dye, as well as other chemical or biological effectors. When exposed to direct heating or HIFU, the PCM will melt and escape from the interiors of nanocages through small pores on the surface, concurrently releasing the encapsulated molecules into the surrounding medium. We can control the release profile by varying the power of HIFU, the duration of exposure to HIFU, or both.

Mesoporous CuO Particles Threaded with CNTs for High‐Performance Lithium‐Ion Battery Anodes

Mesoporous CuO particles threaded with carbon nanotubes are suggested as a novel class of nanocomposite material for a high-performance anode in the lithium-ion batteries. The nanocomposite electrode exhibits a highly reversible capacity (650 mA h g(-1) at 0.1 C rate) and an excellent C rate capability (580 mA h g(-1) at 5 C, and 500 mA h g(-1) at 10 C).

Periodic Array of Polyelectrolyte-Gated Organic Transistors from Electrospun Poly(3-hexylthiophene) Nanofibers

High-performance organic field-effect transistors (OFETs) based on polyelectrolyte gate dielectric and electrospun poly(3-hexylthiophene) (P3HT) nanofibers were fabricated on a flexible polymer substrate. The use of UV-crosslinked hydrogel including ionic liquids for the insulating layer enabled fast and large-area fabrication of transistor arrays. The P3HT nanofibers were directly deposited on the methacrylated polymer substrate. During UV irradiation through a patterned mask, the methacrylate groups formed covalent bonds with the patterned polyelectrolyte dielectric layer, which provides mechanical stability to the devices. The OFETs operate at voltages of less than 2 V. The average field-effect mobility and on/off ratio were approximately 2 cm(2)/(Vs) and 10(5), respectively.

Chemical transformations in ultrathin chalcogenide nanowires.

We have studied the chemical transformations in ultrathin chalcogenide nanowires with an aim to understand the parameters that control the morphology and crystal structure of the product. Ultrathin Te nanowires were transformed into Ag2Te nanowires with preservation of the single crystallinity. The Ag2Te nanowires were then converted into CdTe, ZnTe, and PbTe using cation-exchange reactions, and the CdTe nanowires were further transformed into PtTe2 nanotubes. On the basis of the solubility products of the ionic solids, the crystal structures of the involved solids, the reaction kinetics, and the reaction conditions for transformations, we were able to reach the following conclusions: (i) The solubility products of ionic solids can be used as a rough criterion to predict if the transformation is thermodynamically favorable or not. (ii) The morphological preservation of reactant nanowires is more sensitive to the change in length rather than the total volume in addition to the lattice matching between the reactant and product nanowires. (iii) The crystal structure resulting from a transformation should be determined by the free energy of formation and the stability of the products. (iv) The transformation involving small volume change or topotactic lattice matching is considered homogeneous along the entire length of the nanowires, preserving both the single crystallinity and the morphology of the reactant nanowires.

Asymmetric block copolymers with homopolymers: Routes to multiple length scale nanostructures

positive electrode materials on aflexible substrate such as the paper-type Teflon membrane, atlow-temperatures using soft solution processing without fir-ing/sintering or melting. The results obtained were similar toother deposition processes using fluids such as vapor, gas,plasma, and beam or vacuum processing. Supersaturation andnucleation transfer have been applied to membranes placedat the supersaturation position near the Co working electrode,forming the direct attachment of a positive electrode separa-tor for lithium batteries.

Metabolizable Bi2Se3 Nanoplates: Biodistribution, Toxicity, and Uses for Cancer Radiation Therapy and Imaging

Bi, a high atomic number element, has a high photoelectric absorption coefficient, and Se has anticancer activity. Hence, their compound chalcogenide (Bi2Se3) deserves a thorough investigation for biomedical applications. This study reveals that Bi2Se3 nanoplates (54 nm wide) protected with poly(vinylpyrollidone) (PVP) could be presumed to have low toxicity even at a high dose of 20 mg/kg in mice. This conclusion is made through studies on the biodistribution and 90-day long term in vivo clearance of the nanoplates. The liver and spleen are dominant organs for accumulation of the nanoplates, which is mainly due to RES absorption. 93% of the nanoplates are cleared after 90 days of treatment. Concentrations of Bi and Se in tumor tissue continuously increased until 72 h after intraperitoneal injection into mice. Such selective accumulation of Bi is utilized to enhance the contrast of X-ray computerized tomography (CT) images. Bi element concentrated in a tumor leads to damage on the tumor cells when exposed to gamma radiation. Growth of the tumor is significantly delayed and stopped in 16 days after the tumor is treated by radiation with Bi2Se3 nanoplates. This work clearly shows that Bi2Se3 nanoplates may be used for cancer radiation therapy and CT imaging. The nanoplates deserve further study for biological and medical applications.

Assembled Monolayers of Hydrophilic Particles on Water Surfaces

A facile and quick approach to prepare self-assembled monolayers of water-dispersible particles on the water surface is presented. Particle suspensions in alcohols were dropped on a water reservoir to form long-range ordered monolayers of various particles, including spherical solid particles, soft hydrogel particles, metal nanoparticles, quantum dots, nanowires, single-wall carbon nanotubes (SWCNTs), nanoplates, and nanosheets. A systematic study was conducted on the variables affecting the monolayer assembly: the solubility parameter of spreading solvents, particle concentration, zeta potential of the particles in the suspension, surface tension of the water phase, hardness of the particles, and addition of a salt in the suspension. This method requires no hydrophobic surface treatment of the particles, which is useful to exploit these monolayer films without changing the native properties of the particles. The study highlights a quick 2D colloidal assembly without cracks in the wafer scale as well as transparent conductive thin films made of SWCNTs and graphenes.

Surfactant‐Free Scalable Synthesis of Bi2Te3 and Bi2Se3 Nanoflakes and Enhanced Thermoelectric Properties of Their Nanocomposites

Surfactant-free nanoflakes of n-type Bi2 Te3 and Bi2 Se3 are synthesized in high yields. Their suspensions are mixed to create nanocomposites with heterostructured nanograins. A maximum ZT (0.7 at 400 K) is achieved with a broad content of 10-15% Bi2 Se3 in the nanocomposites.