Carbon nanotube (CNT) emitters are of interest for inclusion in cold cathodes and field emission ... more Carbon nanotube (CNT) emitters are of interest for inclusion in cold cathodes and field emission displays. CNT field electron emitters self-organized on substrates with an Fe/Al 2 O 3 catalytic/supporting layer, which accelerates CNT growth, are characterized using combinatorial libraries. A variety of morphologies are formed on single substrates by C 2 H 2 thermal chemical vapor deposition for 10 s at ambient pressure. Degradation of field emission decreases upon prolonged operation. Raman signals from thinner single-walled CNTs predominantly degrade during operation. Controlling the number of protruding thin CNTs is crucial to extracting current and ensuring sustainability. Thin CNTs protruding from CNT ensembles formed on a substrate with a multimodal distribution of catalyst particles show good field emission (FE) properties with practical sustainability. A potential design for self-organized thin CNTs fabricated by the current process is discussed on the basis of the combinatorial evaluation for field emission and 3D electric field simulations.
Our group recently reproduced the water-assisted growth method, so-called "super growth", of mill... more Our group recently reproduced the water-assisted growth method, so-called "super growth", of millimeter-thick single-walled carbon nanotube (SWNT) forests by using C2H4/ H2/ H2O/ Ar reactant gas and Fe/ Al2O3 catalyst. In this current work, a parametric study was carried out on both reaction and catalyst conditions. Results revealed that a thin Fe catalyst layer (about 0.5 nm) yielded rapid growth of SWNTs only when supported on Al2O3, and that Al2O3 support enhanced the activity of Fe, Co, and Ni catalysts. The growth window for the rapid SWNT growth was narrow, however. Optimum amount of added H2O increased the SWNT growth rate but further addition of H2O degraded both the SWNT growth rate and quality. Addition of H2 was also essential for rapid SWNT growth, but again, further addition decreased both the SWNT growth rate and quality. Because Al2O3 catalyzes hydrocarbon reforming, Al2O3 support possibly enhances the SWNT growth rate by supplying the carbon source to the catalyst nanoparticles. The origin of the narrow window for rapid SWNT growth will also be discussed.
A parametric study of so-called “super growth” of single-walled carbon nanotubes (SWNTs) was done... more A parametric study of so-called “super growth” of single-walled carbon nanotubes (SWNTs) was done by using combinatorial libraries of iron/aluminum oxide catalysts. Millimeter-thick forests of nanotubes grew within 10 min, and those grown by using catalysts with a thin Fe layer (about 0.5 nm) were SWNTs. Although nanotube forests grew under a wide range of reaction conditions such as gas composition and temperature, the window for SWNT was narrow. Fe catalysts rapidly grew nanotubes only when supported on aluminum oxide. Aluminum oxide, which is a well-known catalyst in hydrocarbon reforming, plays an essential role in enhancing the nanotube growth rates.
Abnormal structures, such as surface protrusions, fibers, particles, and voids, sometimes appear ... more Abnormal structures, such as surface protrusions, fibers, particles, and voids, sometimes appear during materials processing, degrading the quality of the product. Much research has been done to determine growth conditions under which such abnormal structures do not appear, but in most cases only successful results are reported since unsuccessful ones are usually considered as failures. We systematically studied the conditions causing the formation of abnormal structures, proposed countermeasures, based on a fundamental understanding of their formation mechanism, to prevent their formation, and published these results on the World Wide Web. [1] Surface protrusions, including particles, cauliflowers or mushrooms, and cones, are mainly the result of one of the following three causes. First, they are caused by an irregularity in the gas phase. Particles formed by gas-phase reactions lead to the ªparticles on filmsº structures, and contaminants in the source gas sometimes lead to other surface protrusions, though these can appear even without such contaminants. A positive feedback between the protrusion size and its growth rate caused by the growth instability is the second main cause for the formation of abnormal protrusions. When it is caused by temperature gradients during solidification from undercooled melts, this phenomenon is known as the Mullins±Sekerka instability. It also appears in CVD processes due to concentration gradients in the gas phase under diffusion-limited growth. This positive feedback with moderate surface relaxation, such as surface diffusion of adsorbates, leads to the formation of cauliflower or mushroom structures. Under surface reaction-limited growth without the positive feedback, a local growth rate larger than the surrounding growth rate can be the third cause of the formation of protrusions. Examples are the Ti-rich phases in AlN/TiN composite CVD films, and the crystalline phases in amorphous phases in Pb-Ti-Nb-O films formed by MOCVD. These phases have larger growth rates than the surrounding phases with constant ratios, and cause the formation of cones with a sectoral cross-section.
Abnormal structures, such as surface protrusions, fibers, particles, and voids, sometimes appear ... more Abnormal structures, such as surface protrusions, fibers, particles, and voids, sometimes appear during materials processing, degrading the quality of the product. Much research has been done to determine growth conditions under which such abnormal structures do not appear, but in most cases only successful results are reported since unsuccessful ones are usually considered as failures. We systematically studied the conditions causing the formation of abnormal structures, proposed countermeasures, based on a fundamental understanding of their formation mechanism, to prevent their formation, and published these results on the World Wide Web. [1] Surface protrusions, including particles, cauliflowers or mushrooms, and cones, are mainly the result of one of the following three causes. First, they are caused by an irregularity in the gas phase. Particles formed by gas-phase reactions lead to the ªparticles on filmsº structures, and contaminants in the source gas sometimes lead to other surface protrusions, though these can appear even without such contaminants. A positive feedback between the protrusion size and its growth rate caused by the growth instability is the second main cause for the formation of abnormal protrusions. When it is caused by temperature gradients during solidification from undercooled melts, this phenomenon is known as the Mullins±Sekerka instability. It also appears in CVD processes due to concentration gradients in the gas phase under diffusion-limited growth. This positive feedback with moderate surface relaxation, such as surface diffusion of adsorbates, leads to the formation of cauliflower or mushroom structures. Under surface reaction-limited growth without the positive feedback, a local growth rate larger than the surrounding growth rate can be the third cause of the formation of protrusions. Examples are the Ti-rich phases in AlN/TiN composite CVD films, and the crystalline phases in amorphous phases in Pb-Ti-Nb-O films formed by MOCVD. These phases have larger growth rates than the surrounding phases with constant ratios, and cause the formation of cones with a sectoral cross-section.
In the absence of epitaxy between a film and a substrate, the preferred orientation (PO) of polyc... more In the absence of epitaxy between a film and a substrate, the preferred orientation (PO) of polycrystalline films can often be explained by the "evolutionary selection rule", which states that grains with the fastest growing direction normal to the substrate envelope the other grains and determine the final orientation of the film. However, the mechanism determining the fastest growing plane and the factors affecting the growth rates of each plane are still not well understood. We examined existing experimental results in the open literature and found a correlation between process conditions and PO for poly-Si and poly-SiC thin films. We present a model based on Langmuir-type adsorption for predicting PO, which agrees well with experimental results in the open literature for Si and SiC.
Carbon nanotube (CNT) emitters were formed on line-patterned cathodes in microtrenches through a ... more Carbon nanotube (CNT) emitters were formed on line-patterned cathodes in microtrenches through a thermal CVD process. Single-walled carbon nanotubes (SWCNTs) self-organized along the trench lines with a submicron inter-CNT spacing. Excellent field emission (FE) properties were obtained: current densities at the anode (J(a)) of 1 microA cm(-2), 10 mA cm(-2) and 100 mA cm(-2) were recorded at gate voltages (V(g)) of 16, 25 and 36 V, respectively. The required voltage difference to gain a 1:10 000 contrast of the anode current was as low as 9 V, indicating that a very low operating voltage is possible for these devices. Not only a large number of emission sites but also the optimal combination of trench structure and emitter morphology are crucial to achieve the full FE potential of thin CNTs with a practical lifetime. The FE properties of 1D arrays of CNT emitters and their optimal design are discussed. Self-organization of thin CNTs is an attractive prospect to tailor preferable emitter designs in FE devices.
Self-supporting hybrid electrodes were fabricated through the systematic combination of activated... more Self-supporting hybrid electrodes were fabricated through the systematic combination of activated carbon (AC), a low cost capacitive material, with sub-millimetre long few-wall carbon nanotubes (FWCNTs). After an easy three-step (mixing, dispersion and filtration) process, robust self-supporting films were obtained, comprising 90% AC particles wrapped in a 3-dimensional FWCNT collector. The 10% FWCNTs provide electrical conductivity and mechanical strength, and replace heavier metal collectors. The FWCNT matrix effectively improved the capacitance of the inexpensive, high surface area AC to 169 F g À1 at a slow scan rate of 5 mV s À1 , and to 131 F g À1 at a fast scan rate of 100 mV s À1 , in fairly thick ($200 mm) electrodes.
The growth mechanism of epitaxial CoSi 2 was studied using Co/Ti/Si multilayer solid phase reacti... more The growth mechanism of epitaxial CoSi 2 was studied using Co/Ti/Si multilayer solid phase reaction. Results showed that phase formation was controlled by diffusion of Co through the growing CoSi x , although at the early stage of CoSi 2 growth the diffusion of Co could be controlled by a Ti layer. A reactive deposition technique was also evaluated by using a conventional magnetron sputtering system. Results showed that an epitaxial CoSi 2 layer was formed by controlling the Co sputtering rate not to exceed the Co diffusion rate through CoSi x . However, the surface of CoSi 2 became rough when the deposition rate was much slower than the Co diffusion rate through CoSi x . The roughness was caused by the formation of CoSi 2 (111) facets at the interface between CoSi 2 and the Si substrate. Si/CoSi 2 /Si double heteroepitaxial structures were fabricated when Si and Co were sequentially sputter-deposited on a Si (100) substrate.
ABSTRACT Utilizing a combinatorial method, we used spectroscopic ellipsometry to determine the di... more ABSTRACT Utilizing a combinatorial method, we used spectroscopic ellipsometry to determine the dielectric functions of silver island films over a large range of sizes and morphologies from the percolation threshold down to average particle size smaller than 5 nm. We measured films on silicon substrates with 2 and 20 nm oxide layers and compared the surface-enhanced Raman scattering properties of the films. As expected, the films on 20-nm-thick oxide substrates showed increased Raman counts due to reduced damping of the plasmon resonance; however, the optical absorption was greater in the films on 2 nm oxide. The maximum Raman scattering was observed for average particle diameters of 13.6 and 25 nm and interparticle spacings of 3.3 and 4.1 nm for the 2 and 20 nm oxide substrates, respectively. The use of a combinatorial method resulted in significantly reduced uncertainties by avoiding multiple sample preparations and allowed unambiguous identification of optimal film parameters for the different substrates.
ABSTRACT We present a two-dimensional combinatorial investigation of resonant Raman and fluoresce... more ABSTRACT We present a two-dimensional combinatorial investigation of resonant Raman and fluorescence enhancement in silver and gold sandwich structures. Gold and silver, separated by a thin alumina spacer layer, were deposited in two orthogonal gradients, with a thickness from a few hundred to a few nanometers, covering the range from island films through percolation to continuous films. Resonant Raman spectra of Rhodamine 6G adsorbed on the substrate surface were recorded in a 13 x 13 matrix using an automated scanning stage. The most Raman-active substrates were composed of silver (8 nm)-on-alumina (7 nm)-on-gold (5 nm). They consist of both gold and silver discontinuous nanoparticle films separated by alumina, forming a labyrinthine network structure. Gold-on-alumina-on-silver substrates also displayed increased activity compared with that of goldon-alumina substrates. Maximum fluorescence intensity was observed on silver films nominally 35 nm thick covered by 8 nm of alumina. The efficacy of the combinatorial method to correlate multiple aspects of the measurements and reduce uncertainties is demonstrated.
Carbon nanotube (CNT) emitters are of interest for inclusion in cold cathodes and field emission ... more Carbon nanotube (CNT) emitters are of interest for inclusion in cold cathodes and field emission displays. CNT field electron emitters self-organized on substrates with an Fe/Al 2 O 3 catalytic/supporting layer, which accelerates CNT growth, are characterized using combinatorial libraries. A variety of morphologies are formed on single substrates by C 2 H 2 thermal chemical vapor deposition for 10 s at ambient pressure. Degradation of field emission decreases upon prolonged operation. Raman signals from thinner single-walled CNTs predominantly degrade during operation. Controlling the number of protruding thin CNTs is crucial to extracting current and ensuring sustainability. Thin CNTs protruding from CNT ensembles formed on a substrate with a multimodal distribution of catalyst particles show good field emission (FE) properties with practical sustainability. A potential design for self-organized thin CNTs fabricated by the current process is discussed on the basis of the combinatorial evaluation for field emission and 3D electric field simulations.
The pulsed laser induced phase transition of gold nanoparticles in aqueous solution was observed ... more The pulsed laser induced phase transition of gold nanoparticles in aqueous solution was observed via a transient absorption on nanosecond time scales and longer. Gold nanoparticles were excited with an intense picosecond laser pulse (355 nm, 30 ps), and the subsequent changes were monitored using two continuous wave laser wavelengths (488 and 635 nm). On the nanosecond time scale, below 6.3 mJ cm(-2), no change was observed; however, in the low fluence region between 6.3 and 17 mJ cm(-2), gold nanoparticles produced a bleach signal (488 nm) attributed to the melting of the gold nanoparticles, which decreased linearly with increasing laser fluence. Laser fluences above 17 mJ cm(-2) resulted in a strong absorption at both wavelengths, which is ascribed to vaporization of gold nanoparticles rather than solvated electrons (ejected from gold nanoparticles) or light scattering. The decay of both signals was faster than the 5 ns time resolution used in our experimental system. On the microsecond time scale, increase in absorbance at 635 nm was observed with a time constant of 1.0 micros, while no change was observed at 488 nm. It is considered that this increase is attributed to the formation of smaller gold nanoparticles resulting from pulsed laser induced size reduction of initial gold nanoparticles.
Carbon nanotube (CNT) emitters are of interest for inclusion in cold cathodes and field emission ... more Carbon nanotube (CNT) emitters are of interest for inclusion in cold cathodes and field emission displays. CNT field electron emitters self-organized on substrates with an Fe/Al 2 O 3 catalytic/supporting layer, which accelerates CNT growth, are characterized using combinatorial libraries. A variety of morphologies are formed on single substrates by C 2 H 2 thermal chemical vapor deposition for 10 s at ambient pressure. Degradation of field emission decreases upon prolonged operation. Raman signals from thinner single-walled CNTs predominantly degrade during operation. Controlling the number of protruding thin CNTs is crucial to extracting current and ensuring sustainability. Thin CNTs protruding from CNT ensembles formed on a substrate with a multimodal distribution of catalyst particles show good field emission (FE) properties with practical sustainability. A potential design for self-organized thin CNTs fabricated by the current process is discussed on the basis of the combinatorial evaluation for field emission and 3D electric field simulations.
Our group recently reproduced the water-assisted growth method, so-called "super growth", of mill... more Our group recently reproduced the water-assisted growth method, so-called "super growth", of millimeter-thick single-walled carbon nanotube (SWNT) forests by using C2H4/ H2/ H2O/ Ar reactant gas and Fe/ Al2O3 catalyst. In this current work, a parametric study was carried out on both reaction and catalyst conditions. Results revealed that a thin Fe catalyst layer (about 0.5 nm) yielded rapid growth of SWNTs only when supported on Al2O3, and that Al2O3 support enhanced the activity of Fe, Co, and Ni catalysts. The growth window for the rapid SWNT growth was narrow, however. Optimum amount of added H2O increased the SWNT growth rate but further addition of H2O degraded both the SWNT growth rate and quality. Addition of H2 was also essential for rapid SWNT growth, but again, further addition decreased both the SWNT growth rate and quality. Because Al2O3 catalyzes hydrocarbon reforming, Al2O3 support possibly enhances the SWNT growth rate by supplying the carbon source to the catalyst nanoparticles. The origin of the narrow window for rapid SWNT growth will also be discussed.
A parametric study of so-called “super growth” of single-walled carbon nanotubes (SWNTs) was done... more A parametric study of so-called “super growth” of single-walled carbon nanotubes (SWNTs) was done by using combinatorial libraries of iron/aluminum oxide catalysts. Millimeter-thick forests of nanotubes grew within 10 min, and those grown by using catalysts with a thin Fe layer (about 0.5 nm) were SWNTs. Although nanotube forests grew under a wide range of reaction conditions such as gas composition and temperature, the window for SWNT was narrow. Fe catalysts rapidly grew nanotubes only when supported on aluminum oxide. Aluminum oxide, which is a well-known catalyst in hydrocarbon reforming, plays an essential role in enhancing the nanotube growth rates.
Abnormal structures, such as surface protrusions, fibers, particles, and voids, sometimes appear ... more Abnormal structures, such as surface protrusions, fibers, particles, and voids, sometimes appear during materials processing, degrading the quality of the product. Much research has been done to determine growth conditions under which such abnormal structures do not appear, but in most cases only successful results are reported since unsuccessful ones are usually considered as failures. We systematically studied the conditions causing the formation of abnormal structures, proposed countermeasures, based on a fundamental understanding of their formation mechanism, to prevent their formation, and published these results on the World Wide Web. [1] Surface protrusions, including particles, cauliflowers or mushrooms, and cones, are mainly the result of one of the following three causes. First, they are caused by an irregularity in the gas phase. Particles formed by gas-phase reactions lead to the ªparticles on filmsº structures, and contaminants in the source gas sometimes lead to other surface protrusions, though these can appear even without such contaminants. A positive feedback between the protrusion size and its growth rate caused by the growth instability is the second main cause for the formation of abnormal protrusions. When it is caused by temperature gradients during solidification from undercooled melts, this phenomenon is known as the Mullins±Sekerka instability. It also appears in CVD processes due to concentration gradients in the gas phase under diffusion-limited growth. This positive feedback with moderate surface relaxation, such as surface diffusion of adsorbates, leads to the formation of cauliflower or mushroom structures. Under surface reaction-limited growth without the positive feedback, a local growth rate larger than the surrounding growth rate can be the third cause of the formation of protrusions. Examples are the Ti-rich phases in AlN/TiN composite CVD films, and the crystalline phases in amorphous phases in Pb-Ti-Nb-O films formed by MOCVD. These phases have larger growth rates than the surrounding phases with constant ratios, and cause the formation of cones with a sectoral cross-section.
Abnormal structures, such as surface protrusions, fibers, particles, and voids, sometimes appear ... more Abnormal structures, such as surface protrusions, fibers, particles, and voids, sometimes appear during materials processing, degrading the quality of the product. Much research has been done to determine growth conditions under which such abnormal structures do not appear, but in most cases only successful results are reported since unsuccessful ones are usually considered as failures. We systematically studied the conditions causing the formation of abnormal structures, proposed countermeasures, based on a fundamental understanding of their formation mechanism, to prevent their formation, and published these results on the World Wide Web. [1] Surface protrusions, including particles, cauliflowers or mushrooms, and cones, are mainly the result of one of the following three causes. First, they are caused by an irregularity in the gas phase. Particles formed by gas-phase reactions lead to the ªparticles on filmsº structures, and contaminants in the source gas sometimes lead to other surface protrusions, though these can appear even without such contaminants. A positive feedback between the protrusion size and its growth rate caused by the growth instability is the second main cause for the formation of abnormal protrusions. When it is caused by temperature gradients during solidification from undercooled melts, this phenomenon is known as the Mullins±Sekerka instability. It also appears in CVD processes due to concentration gradients in the gas phase under diffusion-limited growth. This positive feedback with moderate surface relaxation, such as surface diffusion of adsorbates, leads to the formation of cauliflower or mushroom structures. Under surface reaction-limited growth without the positive feedback, a local growth rate larger than the surrounding growth rate can be the third cause of the formation of protrusions. Examples are the Ti-rich phases in AlN/TiN composite CVD films, and the crystalline phases in amorphous phases in Pb-Ti-Nb-O films formed by MOCVD. These phases have larger growth rates than the surrounding phases with constant ratios, and cause the formation of cones with a sectoral cross-section.
In the absence of epitaxy between a film and a substrate, the preferred orientation (PO) of polyc... more In the absence of epitaxy between a film and a substrate, the preferred orientation (PO) of polycrystalline films can often be explained by the "evolutionary selection rule", which states that grains with the fastest growing direction normal to the substrate envelope the other grains and determine the final orientation of the film. However, the mechanism determining the fastest growing plane and the factors affecting the growth rates of each plane are still not well understood. We examined existing experimental results in the open literature and found a correlation between process conditions and PO for poly-Si and poly-SiC thin films. We present a model based on Langmuir-type adsorption for predicting PO, which agrees well with experimental results in the open literature for Si and SiC.
Carbon nanotube (CNT) emitters were formed on line-patterned cathodes in microtrenches through a ... more Carbon nanotube (CNT) emitters were formed on line-patterned cathodes in microtrenches through a thermal CVD process. Single-walled carbon nanotubes (SWCNTs) self-organized along the trench lines with a submicron inter-CNT spacing. Excellent field emission (FE) properties were obtained: current densities at the anode (J(a)) of 1 microA cm(-2), 10 mA cm(-2) and 100 mA cm(-2) were recorded at gate voltages (V(g)) of 16, 25 and 36 V, respectively. The required voltage difference to gain a 1:10 000 contrast of the anode current was as low as 9 V, indicating that a very low operating voltage is possible for these devices. Not only a large number of emission sites but also the optimal combination of trench structure and emitter morphology are crucial to achieve the full FE potential of thin CNTs with a practical lifetime. The FE properties of 1D arrays of CNT emitters and their optimal design are discussed. Self-organization of thin CNTs is an attractive prospect to tailor preferable emitter designs in FE devices.
Self-supporting hybrid electrodes were fabricated through the systematic combination of activated... more Self-supporting hybrid electrodes were fabricated through the systematic combination of activated carbon (AC), a low cost capacitive material, with sub-millimetre long few-wall carbon nanotubes (FWCNTs). After an easy three-step (mixing, dispersion and filtration) process, robust self-supporting films were obtained, comprising 90% AC particles wrapped in a 3-dimensional FWCNT collector. The 10% FWCNTs provide electrical conductivity and mechanical strength, and replace heavier metal collectors. The FWCNT matrix effectively improved the capacitance of the inexpensive, high surface area AC to 169 F g À1 at a slow scan rate of 5 mV s À1 , and to 131 F g À1 at a fast scan rate of 100 mV s À1 , in fairly thick ($200 mm) electrodes.
The growth mechanism of epitaxial CoSi 2 was studied using Co/Ti/Si multilayer solid phase reacti... more The growth mechanism of epitaxial CoSi 2 was studied using Co/Ti/Si multilayer solid phase reaction. Results showed that phase formation was controlled by diffusion of Co through the growing CoSi x , although at the early stage of CoSi 2 growth the diffusion of Co could be controlled by a Ti layer. A reactive deposition technique was also evaluated by using a conventional magnetron sputtering system. Results showed that an epitaxial CoSi 2 layer was formed by controlling the Co sputtering rate not to exceed the Co diffusion rate through CoSi x . However, the surface of CoSi 2 became rough when the deposition rate was much slower than the Co diffusion rate through CoSi x . The roughness was caused by the formation of CoSi 2 (111) facets at the interface between CoSi 2 and the Si substrate. Si/CoSi 2 /Si double heteroepitaxial structures were fabricated when Si and Co were sequentially sputter-deposited on a Si (100) substrate.
ABSTRACT Utilizing a combinatorial method, we used spectroscopic ellipsometry to determine the di... more ABSTRACT Utilizing a combinatorial method, we used spectroscopic ellipsometry to determine the dielectric functions of silver island films over a large range of sizes and morphologies from the percolation threshold down to average particle size smaller than 5 nm. We measured films on silicon substrates with 2 and 20 nm oxide layers and compared the surface-enhanced Raman scattering properties of the films. As expected, the films on 20-nm-thick oxide substrates showed increased Raman counts due to reduced damping of the plasmon resonance; however, the optical absorption was greater in the films on 2 nm oxide. The maximum Raman scattering was observed for average particle diameters of 13.6 and 25 nm and interparticle spacings of 3.3 and 4.1 nm for the 2 and 20 nm oxide substrates, respectively. The use of a combinatorial method resulted in significantly reduced uncertainties by avoiding multiple sample preparations and allowed unambiguous identification of optimal film parameters for the different substrates.
ABSTRACT We present a two-dimensional combinatorial investigation of resonant Raman and fluoresce... more ABSTRACT We present a two-dimensional combinatorial investigation of resonant Raman and fluorescence enhancement in silver and gold sandwich structures. Gold and silver, separated by a thin alumina spacer layer, were deposited in two orthogonal gradients, with a thickness from a few hundred to a few nanometers, covering the range from island films through percolation to continuous films. Resonant Raman spectra of Rhodamine 6G adsorbed on the substrate surface were recorded in a 13 x 13 matrix using an automated scanning stage. The most Raman-active substrates were composed of silver (8 nm)-on-alumina (7 nm)-on-gold (5 nm). They consist of both gold and silver discontinuous nanoparticle films separated by alumina, forming a labyrinthine network structure. Gold-on-alumina-on-silver substrates also displayed increased activity compared with that of goldon-alumina substrates. Maximum fluorescence intensity was observed on silver films nominally 35 nm thick covered by 8 nm of alumina. The efficacy of the combinatorial method to correlate multiple aspects of the measurements and reduce uncertainties is demonstrated.
Carbon nanotube (CNT) emitters are of interest for inclusion in cold cathodes and field emission ... more Carbon nanotube (CNT) emitters are of interest for inclusion in cold cathodes and field emission displays. CNT field electron emitters self-organized on substrates with an Fe/Al 2 O 3 catalytic/supporting layer, which accelerates CNT growth, are characterized using combinatorial libraries. A variety of morphologies are formed on single substrates by C 2 H 2 thermal chemical vapor deposition for 10 s at ambient pressure. Degradation of field emission decreases upon prolonged operation. Raman signals from thinner single-walled CNTs predominantly degrade during operation. Controlling the number of protruding thin CNTs is crucial to extracting current and ensuring sustainability. Thin CNTs protruding from CNT ensembles formed on a substrate with a multimodal distribution of catalyst particles show good field emission (FE) properties with practical sustainability. A potential design for self-organized thin CNTs fabricated by the current process is discussed on the basis of the combinatorial evaluation for field emission and 3D electric field simulations.
The pulsed laser induced phase transition of gold nanoparticles in aqueous solution was observed ... more The pulsed laser induced phase transition of gold nanoparticles in aqueous solution was observed via a transient absorption on nanosecond time scales and longer. Gold nanoparticles were excited with an intense picosecond laser pulse (355 nm, 30 ps), and the subsequent changes were monitored using two continuous wave laser wavelengths (488 and 635 nm). On the nanosecond time scale, below 6.3 mJ cm(-2), no change was observed; however, in the low fluence region between 6.3 and 17 mJ cm(-2), gold nanoparticles produced a bleach signal (488 nm) attributed to the melting of the gold nanoparticles, which decreased linearly with increasing laser fluence. Laser fluences above 17 mJ cm(-2) resulted in a strong absorption at both wavelengths, which is ascribed to vaporization of gold nanoparticles rather than solvated electrons (ejected from gold nanoparticles) or light scattering. The decay of both signals was faster than the 5 ns time resolution used in our experimental system. On the microsecond time scale, increase in absorbance at 635 nm was observed with a time constant of 1.0 micros, while no change was observed at 488 nm. It is considered that this increase is attributed to the formation of smaller gold nanoparticles resulting from pulsed laser induced size reduction of initial gold nanoparticles.
Uploads
Papers by Suguru Noda