Chemical Etching of Silicon Assisted by Graphene Oxide in an HF–HNO₃ Solution and Its Catalytic Mechanism

Chemical etching of silicon assisted by various types of carbon materials is drawing much attention for the fabrication of silicon micro/nanostructures. We developed a method of chemical etching of silicon that utilizes graphene oxide (GO) sheets to promote the etching reaction in a hydrofluoric acid–nitric acid (HF–HNO₃) etchant. By using an optimized composition of the HF–HNO₃ etchant, the etching rate under the GO sheets was 100 times faster than that of our HF–H₂O₂ system used in a previous report. Kinetic analyses showed that the activation energy of the etching reaction was almost the same at both the bare silicon and GO-covered areas. We propose that adsorption sites for the reactant in the GO sheets enhance the reaction frequency, leading to a deeper etching in the GO areas than the bare areas. Furthermore, GO sheets with more defects were found to have higher catalytic activities. This suggests that defects in the GO sheets function as adsorption sites for the reactant, thereby enhancing the etching rate under the sheets

Formation of submicron-sized silica patterns on flexible polymer substrates based on vacuum ultraviolet photooxidation

Formation of precise and high-resolution silica micropatterns on polymer substrates is of importance in surface structuring for flexible device fabrication of optics, microelectronic, and biotechnology. To achieve that, substrates modified with affinity-patterns serve as a strategy for site-selective deposition. In the present paper, vacuum ultraviolet (VUV) treatment is utilized to achieve spatially-controlled surface functionalization on a cyclo-olefin polymer (COP) substrate. An organosilane, 2, 4, 6, 8-tetramethylcyclotetrasiloxane (TMCTS), preferentially deposits on the functionalized regions. Well-defined patterns of TMCTS are formed with a minimum feature of ∼500 nm. The secondary VUV/(O)-treatment converts TMCTS into SiOx, meanwhile etches the bare COP surface, forming patterned SiOx/COP microstructures with an average height of ∼150 nm. The resulting SiOx patterns retain a good copy of TMCTS patterns, which are also consistent with the patterns of photomask used in polymer affinity-patterning. The high quality SiOx patterns are of interests in microdevice fabrication, and the hydrophilicity contrast and adjustable heights reveal their potential application as a “stamp” for microcontact printing (μCP) techniques

Fundamental and higher eigenmodes of qPlus sensors with a long probe for vertical-lateral bimodal atomic force microscopy

The detection of vertical and lateral forces at the nanoscale by atomic force microscopy (AFM) reveals various mechanical properties on surfaces. The qPlus sensor is a widely used force sensor, which is built from a quartz tuning fork (QTF) and a sharpened metal probe, capable of high-resolution imaging in viscous liquids such as lubricant oils. Although a simultaneous detection technique of vertical and lateral forces by using a qPlus sensor is required in the field of nanotribology, it has still been difficult because the torsional oscillations of QTFs cannot be detected. In this paper, we propose a method to simultaneously detect vertical and lateral force components by using a qPlus sensor with a long probe. The first three eigenmodes of the qPlus sensor with a long probe are theoretically studied by solving a set of equations of motion for the QTF prong and probe. The calculation results were in good agreement with the experimental results. It was found that the tip oscillates laterally in the second and third modes. Finally, we performed friction anisotropy measurements on a polymer film by using a bimodal AFM utilizing the qPlus sensor with a long probe to confirm the lateral force detection

Molecular packing density of a self-assembled monolayer formed from N-(2-aminoethyl)-3-aminopropyltriethoxysilane by a vapor phase process.

The molecular density of an aminosilane self-assembled monolayer formed from N-(2-aminoethyl)-3-aminopropyltriethoxysilane (AEAPS) by a vapor phase method has been estimated to be about 3 AEAPS molecules per nm(2) based on chemical labeling, optical absorption spectroscopy and X-ray photoelectron spectroscopy

Submolecular-scale investigations on metal-phthalocyanine monolayers by frequency modulation atomic force microscopy

金沢大学フロンティアサイエンス機構Copper-phthalocyanine (CuPc) monolayers and cobalt-phthalocyanine monolayers deposited on Au(111) surfaces were investigated by frequency modulation atomic force microscopy (FM-AFM). Submolecular-resolution topographic images were successfully obtained for both samples. Despite the similar molecular geometry of the two molecules, they showed clearly different contrasts in the topographic images. The origin of the contrast is discussed in terms of the relationship of the molecular orbitals and the chemical interaction between the tip and the molecules. In addition, a molecular-resolution surface potential (SP) image was obtained on CuPc monolayers using Kelvin probe force microscopy (KFM) utilizing FM-AFM. The molecular-scale SP contrast was explained by the electric dipole moment at the organic/metal interface. This result suggested the possibility of the detection of the single molecular dipole moment by KFM. © 2010 American Institute of Physics

The Orbiting Carbon Observatory (OCO-2) Tracks 2-3 Peta-Gram Increase in Carbon Release to the Atmosphere During the 2014-2016 El Nino

The powerful El Nio event of 2015-2016 - the third most intense since the 1950s - has exerted a large impact on the Earth's natural climate system. The column-averaged CO2 dry-air mole fraction (XCO2) observations from satellites and ground based networks are analyzed together with in situ observations for the period of September 2014 to October 2016. From the differences between satellite (OCO-2) observations and simulations using an atmospheric chemistry-transport model, we estimate that, relative to the mean annual fluxes for 2014, the most recent El Nio has contributed to an excess CO2 emission from the Earth's surface (land+ocean) to the atmosphere in the range of 2.4+/-0.2 PgC (1 Pg = 10(exp 15) g) over the period of July 2015 to June 2016. The excess CO2 flux is resulted primarily from reduction in vegetation uptake due to drought, and to a lesser degree from increased biomass burning. It is about the half of the CO2 flux anomaly (range: 4.4-6.7 PgC) estimated for the 1997/1998 El Nio. The annual total sink is estimated to be 3.9+/-0.2 PgC for the assumed fossil fuel emission of 10.1 PgC. The major uncertainty in attribution arise from error in anthropogenic emission trends, satellite data and atmospheric transport

The Orbiting Carbon Observatory (OCO-2) tracks 2–3 peta-gram increase in carbon release to the atmosphere during the 2014–2016 El Niño

The powerful El Niño event of 2015–2016 – the third most intense since the 1950s – has exerted a large impact on the Earth’s natural climate system. The column-averaged CO_2 dry-air mole fraction (XCO_2) observations from satellites and ground-based networks are analyzed together with in situ observations for the period of September 2014 to October 2016. From the differences between satellite (OCO-2) observations and simulations using an atmospheric chemistry-transport model, we estimate that, relative to the mean annual fluxes for 2014, the most recent El Niño has contributed to an excess CO_2 emission from the Earth’s surface (land + ocean) to the atmosphere in the range of 2.4 ± 0.2 PgC (1 Pg = 10^(15) g) over the period of July 2015 to June 2016. The excess CO_2 flux is resulted primarily from reduction in vegetation uptake due to drought, and to a lesser degree from increased biomass burning. It is about the half of the CO_2 flux anomaly (range: 4.4–6.7 PgC) estimated for the 1997/1998 El Niño. The annual total sink is estimated to be 3.9 ± 0.2 PgC for the assumed fossil fuel emission of 10.1 PgC. The major uncertainty in attribution arise from error in anthropogenic emission trends, satellite data and atmospheric transport