Microscopy, 2014, Vol. 63, No. S1
i10
doi: 10.1093/jmicro/dfu074
Near-infrared nano-imaging spectroscopy using a phase change mask method Yu Sato, Shohei Kanazawa, and Toshiharu Saiki Department of Electronics and Electrical Engineering, Keio University 3-14-1 Hiyoshi, Kohoku, Yokohama, Kanagawa 223-8522, Japan We propose a technique that employs an optical mask layer of a phase-change material, e.g. GeSbTe, which is widely used for rewritable optical recording media, for realizing highly sensitive near-field imaging spectroscopy of single semiconductor quantum constituents at optical telecommunication wavelengths. Semiconductor quantum dots (QDs) have shown great promise as efficient single photon emitters and entangled photon sources, making them attractive for quantum communication and quantum information processing applications. Self-assembled InAs QDs on InP substrate are promising as near-infrared (NIR) single photon and entangled photon emitters. In order to clarify and control the optical properties of QDs for telecommunication devices, photoluminescence (PL) spectroscopy studies of single QDs with high spatial resolution at NIR wavelength is necessary. The most useful technique to attain this is by using near-field scanning optical miscroscopy (NSOM). However, NSOM has a lower PL collection efficiency at NIR wavelength than at visible wavelength [1]. This problem inhibits NIR-PL spectroscopy based on NSOM to be practically realized. Therefore, we deveopled a method to overcome the low NIR-PL spectroscopy by using a nanoaperture on an optical mask layer of phase-change material (PCM) [2]. Due to the large optical contrast between the crystalline and amorphous phases of the phase-change material at visible wavelengths and its high transparency at NIR wavelengths, an amorphous nanoaperture can be used to realize imaging spectroscopy with a high spatial resolution and a high collection efficiency (Fig. 1). We demonstrate the effectiveness of the proposed method by performing numerical simulations and PL measurements of InAs/InP QDs.
Fig. 1. Schematic illustration of phase change mask method
PCM mask effect has also the potential to be applied in emission energy control of QDs. One of the main problems for realization of quantum communication applications is precise control of energy in QDs. We proposed a new approach to control the emission energy of QDs by applying a local strain using volume expansion of phasechange material [3–5]. We calculated the stress and energy shift distribution induced by volume expansion using finite element method. Simulation result reveals that redshift is obtained beneath the flat part of amorphous mark, while blueshift is obtained beneath the edge region of amorphous mark. Simulation result is accompanied by two experimental studies; two-dimensional PL intensity mapping of InAs/ InP QD sample deposited by a layer of PCM, and an analysis on the relationship between PL intensity ratio and energy shift were performed.
References 1. Tsumori N., Takahashi M., Saiki T., Sakuma Y., Appl. Opt. 50, 5710 (2011). 2. Tsumori N., Takahashi M., Kubota R., Saiki T., Regreny P., Gendry M., Appl. Phys. Lett. 100, 063111 (2012). 3. Takahashi M., Syafawati Humam Nurrul, Tsumori N., Saiki T., Regreny P., Gendry M., Appl. Phys. Lett. 102, 093120 (2013). 4. Tsumori N., Takahashi M., Syafawati Humam Nurrul, Regreny P., Gendry M., Saiki T., Journal of Physics: Conference Series 471, 012007 (2013). 5. Nurrul Syafawati Binti Humam, Sato Y., Takahashi M., Kanazawa S., Tsumori N., Regreny P., Gendry M., Saiki T., Opt. Expr. 22, 14830 (2014). doi: 10.1093/jmicro/dfu089
High-resolution Structural Analysis on Ionic-Liquid/Solid Interfaces by Frequency Modulation Atomic Force Microscopy Takashi Ichii and Hiroyuki Sugimura Department of Materials Science and Engineering, Kyoto University,
E-mail: [email protected] Ionic liquids (ILs) are salts usually consisting of sterically-hindered organic/inorganic ions with melting points below 100 ○C or room temperature. Since they have a number of distinct physical and chemical properties, such as high ionic conductivity, high electrochemical stability, non-volatility, and non-combustibility, they have attracted considerable attention as a replacement for water and organic solvent. The interfaces between ILs and solid substrates play an important role in various applications including electrochemistry, heterogeneous catalysis, and lubrication, and thus, structural analysis on IL/solid interfaces would be both academically interesting and practically important. Frequency Modulation Atomic Force Microscopy (AFM) is known to be capable of atomic-scale imaging on solid substrates in various environments such as vacuum, atmosphere, and liquid. FM-AFM can be also applicable for investigating the density distribution of liquid molecules on liquid/solid interfaces and hence, it is also expected to provide helpful information for improving the IL-based applications mentioned above. Here, we report FM-AFM studies on IL/solid interfaces. A quartz tuning fork (QTF) sensor was used as a force sensor instead of a Si cantilever because the Q factor of a Si cantilever would be heavily suppressed in ILs. The Q factor of the QTF sensor was typically 100 in ILs, which was much higher than the reported Q factor of a Si cantilever in liquid environment. Figure 1(a) shows a topographic image of a KCl(100) surface obtained in 1-butyl-1-methylpyrrolidinium tris ( pentafluoroethyl)trifluorophosphate ([Py1,4]FAP). While the viscosity of the IL was as approximately 400 times high as that of water (346 cP), the square-lattice structure with a period of ∼0.4 nm was clearly imaged. That is, atomic-resolution imaging was successfully
Downloaded from http://jmicro.oxfordjournals.org/ at University Library, University of Illinois at Chicago on February 9, 2015
4. Kawata M, Sato C (2007) A statistically harmonized alignmentclassification in image space enables accurate and robust alignment of noisy images in single particle analysis. J. Electron Microsc. 56: 83–92. 5. Kawata M, Sato C (2013) Multi-reference-based multiple alignment statistics enables accurate protein-particle pickup from noisy images. Microscopy 62: 303–315. 6. Ogura T, Tong KI, Mio K, Maruyama Y, Kurokawa H, Sato C, Yamamoto M (2010) Keap1 is a forked-stem dimer structure with two large spheres enclosing the intervening, double glycine repeat, and C-terminal domains. Proc Natl Acad Sci U S A. 107:2842–2847. 7. Yajima H, Ogura T, Nitta R, Okada Y, Sato C, Hirokawa N (2012) Conformational changes in tubulin in GMPCPP and GDP-taxol microtubules observed by cryoelectron microscopy. J Cell Biol. 198: 315–322. 8. Miyashita H, Maruyama Y, Isshiki H, Osawa S, Ogura T, Mio K, Sato C, Tomita T, Iwatsubo T (2011) Three-dimensional structure of the signal peptide peptidase. J Biol Chem. 286: 26188–26197.
i10
doi: 10.1093/jmicro/dfu074
Near-infrared nano-imaging spectroscopy using a phase change mask method Yu Sato, Shohei Kanazawa, and Toshiharu Saiki Department of Electronics and Electrical Engineering, Keio University 3-14-1 Hiyoshi, Kohoku, Yokohama, Kanagawa 223-8522, Japan We propose a technique that employs an optical mask layer of a phase-change material, e.g. GeSbTe, which is widely used for rewritable optical recording media, for realizing highly sensitive near-field imaging spectroscopy of single semiconductor quantum constituents at optical telecommunication wavelengths. Semiconductor quantum dots (QDs) have shown great promise as efficient single photon emitters and entangled photon sources, making them attractive for quantum communication and quantum information processing applications. Self-assembled InAs QDs on InP substrate are promising as near-infrared (NIR) single photon and entangled photon emitters. In order to clarify and control the optical properties of QDs for telecommunication devices, photoluminescence (PL) spectroscopy studies of single QDs with high spatial resolution at NIR wavelength is necessary. The most useful technique to attain this is by using near-field scanning optical miscroscopy (NSOM). However, NSOM has a lower PL collection efficiency at NIR wavelength than at visible wavelength [1]. This problem inhibits NIR-PL spectroscopy based on NSOM to be practically realized. Therefore, we deveopled a method to overcome the low NIR-PL spectroscopy by using a nanoaperture on an optical mask layer of phase-change material (PCM) [2]. Due to the large optical contrast between the crystalline and amorphous phases of the phase-change material at visible wavelengths and its high transparency at NIR wavelengths, an amorphous nanoaperture can be used to realize imaging spectroscopy with a high spatial resolution and a high collection efficiency (Fig. 1). We demonstrate the effectiveness of the proposed method by performing numerical simulations and PL measurements of InAs/InP QDs.
Fig. 1. Schematic illustration of phase change mask method
PCM mask effect has also the potential to be applied in emission energy control of QDs. One of the main problems for realization of quantum communication applications is precise control of energy in QDs. We proposed a new approach to control the emission energy of QDs by applying a local strain using volume expansion of phasechange material [3–5]. We calculated the stress and energy shift distribution induced by volume expansion using finite element method. Simulation result reveals that redshift is obtained beneath the flat part of amorphous mark, while blueshift is obtained beneath the edge region of amorphous mark. Simulation result is accompanied by two experimental studies; two-dimensional PL intensity mapping of InAs/ InP QD sample deposited by a layer of PCM, and an analysis on the relationship between PL intensity ratio and energy shift were performed.
References 1. Tsumori N., Takahashi M., Saiki T., Sakuma Y., Appl. Opt. 50, 5710 (2011). 2. Tsumori N., Takahashi M., Kubota R., Saiki T., Regreny P., Gendry M., Appl. Phys. Lett. 100, 063111 (2012). 3. Takahashi M., Syafawati Humam Nurrul, Tsumori N., Saiki T., Regreny P., Gendry M., Appl. Phys. Lett. 102, 093120 (2013). 4. Tsumori N., Takahashi M., Syafawati Humam Nurrul, Regreny P., Gendry M., Saiki T., Journal of Physics: Conference Series 471, 012007 (2013). 5. Nurrul Syafawati Binti Humam, Sato Y., Takahashi M., Kanazawa S., Tsumori N., Regreny P., Gendry M., Saiki T., Opt. Expr. 22, 14830 (2014). doi: 10.1093/jmicro/dfu089
High-resolution Structural Analysis on Ionic-Liquid/Solid Interfaces by Frequency Modulation Atomic Force Microscopy Takashi Ichii and Hiroyuki Sugimura Department of Materials Science and Engineering, Kyoto University,
E-mail: [email protected] Ionic liquids (ILs) are salts usually consisting of sterically-hindered organic/inorganic ions with melting points below 100 ○C or room temperature. Since they have a number of distinct physical and chemical properties, such as high ionic conductivity, high electrochemical stability, non-volatility, and non-combustibility, they have attracted considerable attention as a replacement for water and organic solvent. The interfaces between ILs and solid substrates play an important role in various applications including electrochemistry, heterogeneous catalysis, and lubrication, and thus, structural analysis on IL/solid interfaces would be both academically interesting and practically important. Frequency Modulation Atomic Force Microscopy (AFM) is known to be capable of atomic-scale imaging on solid substrates in various environments such as vacuum, atmosphere, and liquid. FM-AFM can be also applicable for investigating the density distribution of liquid molecules on liquid/solid interfaces and hence, it is also expected to provide helpful information for improving the IL-based applications mentioned above. Here, we report FM-AFM studies on IL/solid interfaces. A quartz tuning fork (QTF) sensor was used as a force sensor instead of a Si cantilever because the Q factor of a Si cantilever would be heavily suppressed in ILs. The Q factor of the QTF sensor was typically 100 in ILs, which was much higher than the reported Q factor of a Si cantilever in liquid environment. Figure 1(a) shows a topographic image of a KCl(100) surface obtained in 1-butyl-1-methylpyrrolidinium tris ( pentafluoroethyl)trifluorophosphate ([Py1,4]FAP). While the viscosity of the IL was as approximately 400 times high as that of water (346 cP), the square-lattice structure with a period of ∼0.4 nm was clearly imaged. That is, atomic-resolution imaging was successfully
Downloaded from http://jmicro.oxfordjournals.org/ at University Library, University of Illinois at Chicago on February 9, 2015
4. Kawata M, Sato C (2007) A statistically harmonized alignmentclassification in image space enables accurate and robust alignment of noisy images in single particle analysis. J. Electron Microsc. 56: 83–92. 5. Kawata M, Sato C (2013) Multi-reference-based multiple alignment statistics enables accurate protein-particle pickup from noisy images. Microscopy 62: 303–315. 6. Ogura T, Tong KI, Mio K, Maruyama Y, Kurokawa H, Sato C, Yamamoto M (2010) Keap1 is a forked-stem dimer structure with two large spheres enclosing the intervening, double glycine repeat, and C-terminal domains. Proc Natl Acad Sci U S A. 107:2842–2847. 7. Yajima H, Ogura T, Nitta R, Okada Y, Sato C, Hirokawa N (2012) Conformational changes in tubulin in GMPCPP and GDP-taxol microtubules observed by cryoelectron microscopy. J Cell Biol. 198: 315–322. 8. Miyashita H, Maruyama Y, Isshiki H, Osawa S, Ogura T, Mio K, Sato C, Tomita T, Iwatsubo T (2011) Three-dimensional structure of the signal peptide peptidase. J Biol Chem. 286: 26188–26197.
