Takuya Mitsuoka

Silicon Nanosheets and Their Self-Assembled Regular Stacking Structure

Silicon nanomaterials are encouraging candidates for application to photonic, electronic, or biosensing devices, due to their size-quantization effects. Two-dimensional silicon nanosheets could help to realize a widespread quantum field, because of their nanoscale thickness and microscale area. However, there has been no example of a successful synthesis of two-dimensional silicon nanomaterials with large lateral size and oxygen-free surfaces. Here we report that oxygen-free silicon nanosheets covered with organic groups can be obtained by exfoliation of layered polysilane as a result of reaction with n-decylamine and dissolution in an organic solvent. The amine residues are covalently bound to the Si(111) planes. It is estimated that there is ca. 0.7 mol of residue per mole of Si atoms in the reaction product. The amine-modified layered polysilane can dissolve in chloroform and exfoliate into nanosheets that are 1-2 microm wide in the lateral direction and with thicknesses on the order of nanometers. The nanosheets have very flat and smooth surfaces due to dense coverage of n-decylamine, and they are easily self-assembled in a concentrated state to form a regularly stacked structure. The nanosheets could be useful as building blocks to create various composite materials.

Synthesis and Optical Properties of Monolayer Organosilicon Nanosheets

The synthesis of silicon nanosheets for fabricating electronic devices, without using conventional vacuum processes and vapor deposition, is challenging and is anticipated to receive significant attention for a wide range of applications. Here, we report the synthesis of oxygen-free, phenyl-modified organosilicon nanosheets with atomic thickness. In organic solvents, a consequence of this new silicon structure is its uniform dispersion and the possibility of exfoliation into unilamellar nanosheets. Light-induced photocurrent in [Si(6)H(4)Ph(2)] was observed, leading to the possibility of various organosilicon nonamaterials with useful properties.

Improving the thermal stability of organic light-emitting diodes by using a modified phthalocyanine layer

Remarkable improvement in thermal stability has been demonstrated in an organic light-emitting diode (OLED) using a metal-free phthalocyanine (H2Pc)-doped copper phthalocyanine (CuPc) layer as a hole injection layer. Compared to an OLED using a CuPc layer, approximately twice the lifetime has been achieved in the OLED using the H2Pc-doped CuPc layer at a high temperature of 85 °C, operating under a constant current and starting at a luminance of 400 cd/m2. Atomic force microscopy measurements show that the dopant of H2Pc depresses the crystallization of a CuPc layer. It is suggested that the improved thermal stability of the OLED is attributable to that of the phthalocyanine layer in morphology.

Chemical Structure of Aluminum/8-Hydroxyquinoline Aluminum Interface.

The chemical structure of interfaces between aluminum (Al) and 8-hydroxyquinoline aluminum (Alq3) has been studied by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). New subpeaks of N1s and O1s in XPS spectra were observed after the deposition of Al on Alq3. The secondary ion intensity of quinoline in TOF-SIMS spectra was found to increase with Al coverage on Alq3. We, therefore, conclude that Alq3 is decomposed by the deposition of Al on Alq3, and that quinoline is formed at the Al/Alq3 interface.

Wettability of Al2O3 Surface by Organic Molecules: Insights from Molecular Dynamics Simulation

We use molecular dynamics (MD) simulations to investigate the wettability of Al2O3 (0001) by organic molecules. Diffusion coefficients estimated for organic molecules are clearly correlated with the contact angles observed experimentally. The results of the MD simulations suggest that molecular flexibility influences wettability. In other words, wettability owing to flexible molecules, such as an epoxy tridecamer, improves with increasing temperature because the interaction between the droplet and the surface increases due to changes in molecular conformation. Conversely, for phenylene sulfide tetramer, wettability does not change with temperature because of the molecular rigidity. In addition, for epoxy monomers, we analyze the different molecular structures responsible for modifying the droplet-surface interaction. For hydrogens in aromatic rings and in methyl groups, the interaction with the surface clearly decreases with increasing temperature.