Cross-stacked single-crystal organic nanowire p-n nanojunction arrays by nanotransfer printing.

We fabricated cross-stacked organic p-n nanojunction arrays made of single-crystal 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-PEN) and fullerene (C60) nanowires as p-type and n-type semiconductors, respectively, by using a nanotransfer printing technique. Single-crystal C60 nanowires were synthesized inside nanoscale channels of a mold and directly transferred onto a desired position of a flexible substrate by a lubricant liquid layer. In the consecutive printing process, single-crystal TIPS-PEN nanowires were grown in the same way and then perpendicularly aligned and placed onto the C60 nanowire arrays, resulting in a cross-stacked single-crystal organic p-n nanojunction array. The cross-stacked single-crystal TIPS-PEN/C60 nanowire p-n nanojunction devices show rectifying behavior with on/off ratio of ∼ 13 as well as photodiode characteristic with photogain of ∼ 2 under a light intensity of 12.2 mW/cm(2). Our study provides a facile, solution-processed approach to fabricate a large-area array of organic crystal nanojunction devices in a desired arrangement for future nanoscale electronics.

Highly ordered and vertically oriented TiO2/Al2O3 nanotube electrodes for application in dye-sensitized solar cells.

The surface of long TiO2 nanotube (NT) electrodes in dye-sensitized solar cells (DSSCs) was modified without post-annealing by using atomic layer deposition (ALD) for the enhancement of photovoltage. Vertically oriented TiO2 NT electrodes with highly ordered and crack-free surface structures over large areas were prepared by a two-step anodization method. The prepared TiO2 NTs had a pore size of 80 nm, and a length of 23 µm. Onto these TiO2 NTs, an Al2O3 shell of a precisely controlled thickness was deposited by ALD. The conformally coated shell layer was confirmed by high-resolution transmission electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy. The open-circuit voltage (V(oc)) of the DSSCs was gradually enhanced as the thickness of the Al2O3 shell of the TiO2/Al2O3 NT electrodes was increased, which resulted from the enhanced electron lifetime. The enhanced electron lifetime caused by the energy barrier effect of the shell layer was measured quantitatively by the open-circuit voltage decay technique. As a result, 1- and 2-cycle-coated samples showed enhanced conversion efficiencies compared to the bare sample.

Extremely High Barrier Performance of Organic-Inorganic Nanolaminated Thin Films for Organic Light-Emitting Diodes.

This work presents a novel barrier thin film based on an organic-inorganic nanolaminate, which consists of alternating nanolayers of self-assembled organic layers (SAOLs) and Al2O3. The SAOLs-Al2O3 nanolaminated films were deposited using a combination of molecular layer deposition and atomic layer deposition techniques at 80 °C. Modulation of the relative thickness ratio of the SAOLs and Al2O3 enabled control over the elastic modulus and stress in the films. Furthermore, the SAOLs-Al2O3 thin film achieved a high degree of mechanical flexibility, excellent transmittance (>95%), and an ultralow water-vapor transmission rate (2.99 × 10-7 g m-2 day-1), which represents one of the lowest permeability levels ever achieved by thin film encapsulation. On the basis of its outstanding barrier properties with high flexibility and transparency, the nanolaminated film was applied to a commercial OLEDs panel as a gas-diffusion barrier film. The results showed defect propagation could be significantly inhibited by incorporating the SAOLs layers, which enhanced the durability of the panel.

A non-destructive n-doping method for graphene with precise control of electronic properties via atomic layer deposition.

Graphene applications require high precision control of the Fermi level and carrier concentration via a nondestructive doping method. Here, we develop an effective n-doping technique using atomic layer deposition (ALD) of ZnO thin films on graphene through a reactive molecular layer. This ALD doping method is nondestructive, simple, and precise. The ZnO thin films on graphene are uniform, conformal, of good quality with a low density of pinholes, and finely tunable in thickness with 1 Å resolution. We demonstrate graphene transistor control in terms of the Dirac point, carrier density, and doping state as a function of the ZnO thickness. Moreover, ZnO functions as an effective thin-film barrier against air-borne water and oxygen on the graphene, resulting in extraordinary stability in air for graphene devices. ZnO ALD was also applied to other two-dimensional materials including MoS2 and WSe2, which substantially enhanced electron mobility.

Fabrication of a new type of organic-inorganic hybrid superlattice films combined with titanium oxide and polydiacetylene.

We fabricated a new organic-inorganic hybrid superlattice film using molecular layer deposition [MLD] combined with atomic layer deposition [ALD]. In the molecular layer deposition process, polydiacetylene [PDA] layers were grown by repeated sequential adsorption of titanium tetrachloride and 2,4-hexadiyne-1,6-diol with ultraviolet polymerization under a substrate temperature of 100°C. Titanium oxide [TiO2] inorganic layers were deposited at the same temperatures with alternating surface-saturating reactions of titanium tetrachloride and water. Ellipsometry analysis showed a self-limiting surface reaction process and linear growth of the nanohybrid films. The transmission electron microscopy analysis of the titanium oxide cross-linked polydiacetylene [TiOPDA]-TiO2 thin films confirmed the MLD growth rate and showed that the films are amorphous superlattices. Composition and polymerization of the films were confirmed by infrared spectroscopy. The TiOPDA-TiO2 nanohybrid superlattice films exhibited good thermal and mechanical stabilities.PACS: 81.07.Pr, organic-inorganic hybrid nanostructures; 82.35.-x, polymerization; 81.15.-z, film deposition; 81.15.Gh, chemical vapor deposition (including plasma enhanced CVD, MOCVD, ALD, etc.).