Ryoko Watanabe

Self-organized formation and self-repair of a two-dimensional nanoarray of Ge quantum dots epitaxially grown on ultrathin SiO2-covered Si substrates

Two-dimensional nanoarrays of Ge quantum dots (QDs) with the ability to self-repair were epitaxially grown by self-organization on Si substrates using an ultrathin SiO(2) film technique. Nanometer-sized voids were patterned on ultrathin SiO(2) films by transcription of the pattern of block copolymer films using a selective etching method and worked as nucleation sites for QD growth. The epitaxial QDs were elastically strain-relaxed without misfit dislocations and of uniform size. The epitaxial structures of Si-capped QD nanoarrays exhibited strong photoluminescence near 1.5 microm.

Smart block copolymer masks with molecule-transport channels for total wet nanopatterning

Total wet nanopatterning on silicon wafer surface by using liquid-crystalline (LC) integrated amphiphilic block copolymer (BC) masks with perpendicularly aligned poly(ethylene oxide) (PEO) cylindrical domains as molecule-transport channels is demonstrated. This smart BC mask enables us to fabricate hexagonally arranged nanohole arrays, by nanopatterning of silicon wafer surfaces, with tunable periodicity in a range of 16–40 nm and precise transcription with an accuracy of a few nanometers. Blending poly(ethylene glycol) monomethyl ether into the PEO cylinders to be nanochannels is a key trick to induce effective transportation of both etching reagents and products in the successful wet nanopatterning. The BC lithography with our smart BC masks and wet etching processes may be evaluated as a low-cost and mass-productive wet nanopatterning of silicon wafers, and may be applied to wide variety of substrates such as metals, semiconductors, glasses, and polymers by choosing appropriate etching reagents.

Nanodimple Arrays Fabricated on SiO2 Surfaces by Wet Etching through Block Copolymer Thin Films

Block copolymer thin films are promising nanotemplates because highly ordered periodic structures are spontaneously formed through microphase separation on a deca-nanometer scale and over a large area. An amphiphilic block copolymer, which consists of poly(ethylene oxide) (PEO) and poly(methacrylate) (PMA) with azobenzene mesogens and is denoted by PEOm-b-PMA(Az)n, indicates a strong chemical contrast between the corresponding microdomains, which offer structurally reliable nanotemplates for fabricating nanostructured materials. Thermally annealing a PEOm-b-PMA(Az)n thin film provides hexagonally arranged, perpendicularly oriented PEO cylinders, which perform as ion-conductive nanochannels. In this study, a SiO2 layer on a silicon wafer substrate is etched by NH4F through a PEO114-b-PMA(Az)54 thin film as a nanomask. The SiO2 layer is patterned with a 24-nm-periodic hexagonally arranged nanodimple array. Atomic force microscope (AFM), field emission scanning electron microscope (FESEM), and cross-sectional transmission electron microscope (TEM) observations reveal that the nanodimple array has a 2-nm depth and is spread over the entire SiO2 surface on centimeter scale.

Nanohole Arrays Fabricated on Gold Surfaces by Total Wet Nanopatterning through Block Copolymer Masks

Well-ordered nanohole arrays on atomically flat gold (111) surfaces were fabricated by wet etching through block copolymer (BC) masks using ferri/ferrocyanide etchant. Amphiphilic BCs consisting of poly(ethylene oxide) (PEO) and liquid crystalline poly(methacrylate) with azobenzene mesogens [PMA(Az)], PEOm-b-PMA(Az)n, blended with poly(ethylene glycol) monomethylether (EO) form hexagonally arranged ion-transporting nanocylinders of EO-blended PEO microdomains in the BC masks. Atomic force microscopy (AFM) revealed a hexagonally arranged nanohole array on each terrace of the gold surface after the total wet nanopattering including a 5 min etching. The diameter (d) and distance between neighboring nanoholes (D) were controlled by the degree of polymerization of the BC. Two kinds of nanohole arrays with (d, D) = (12 nm, 25 nm) and (20 nm, 41 nm) were obtained in good agreement with the d and D of the EO-blended PEO microdomains of the masks. Scanning tunneling microscopy (STM) indicated that the depth of nanoholes was 3.5 A, corresponding to the thickness of a single atomic layer of gold, and the flatness of the bottom of the holes was confirmed.

Roll-to-Roll Processable PEO-LC Block Copolymer Template Films with Normally Oriented Nanocylinder Array Structures

This paper reports the first demonstration of roll-to-roll coating of a series of poly(ethylene oxide) (PEO)-liquid crystalline (LC) block copolymers by using microgravure coating. Highly ordered hexagonal dot structure was revealed on the whole surface of the coated surface by AFM imaging. Cross sectional TEM observation of the microtomed specimen of the film exclusively exhibited normally oriented PEO nanocylinder array structure, consistent with those prepared in a conventional laboratory procedure by spin-coating, bar coating, and cast.

Nanopatterning of Si wafer surface using microphase-separated structure of block copolymer as wet etching mask

This report presents a new lithographic process utilizing the microphase-separated structures as an etching mask for wet chemical etching of Si wafer. The process demonstrated in this study could open easy tuning of pattern size by changing molecular weight of block copolymers and large area nanopattern transcription with high throughput.