NPL's Quantum Detection Group has recently published a study in ("Carrier type inversion in quasi-free standing graphene: studies of local electronic and structural properties") that casts a new light on the electronic properties of quasi-free standing graphene (QFSG), a material that may find applications in high speed electronics, sensing and electronic applications. The study, which was conducted in collaboration with the University of Surrey, UK, and the Institute of Electronic Materials Technology, Poland, shows for the first time the nanoscale changes of graphene's electronic and structural properties upon hydrogen intercalation which decouples the material from the silicon carbide supporting substrate. The researchers showed that the insertion of hydrogen molecules between epitaxial graphene and SiC promotes a dramatic change in the electronic properties of the material, leading to the change of the carrier type and significant increase in carrier mobility. By using Kelvin probe force microscopy, the scientists were able to generate a complete map of the surface potential distribution of graphene layers both for SiC supported epitaxial graphene and QFSG on SiC. By observing a change in the surface potential distribution between the two systems, directly correlated with information from Raman spectroscopy, the scientists could detect changes in the electronic properties of the graphene layers. "While electrons are main carriers in pristine epitaxial graphene, in the QFSG the main carriers are holes," Olga Kazakova, principal research scientist, explained. By performing Hall effect-based measurements, the group also observed a three-fold increase in the conductivity of QSFG, a fundamental feature for future applications in electronics. Kazakova said that the observed increase in carrier mobility is approaching the world record for this type of materials at room temperature. Epitaxial graphene on SiC, which is obtained via chemical vapour deposition method (CVD), has three main advantages, as it can be easily scaled-up to 4 inches in size, has a very good structural quality and does not require transfer to another substrates, thus significantly simplifying the technological process. However, the interfacial layer between graphene and SiC reduces the conductivity of the material. limiting applications of pristine epitaxial graphene in high speed electronics. Once the formation of QFSG through hydrogen intercalation has occurred, the material changes its electronic properties and shows a high electrical mobility. "In our work, we showed for the first time how this process occurs on nanoscale," Kazakova said. The study also demonstrates that Kelvin probe force microscopy is a powerful technique to provide very detailed information on surface phenomena.
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Fabrication of carbon nanotube transparent conductive film with long-term stability
As nanoparticles of metal halides such as copper iodide are grown in a film, the newly developed carbon nanotube (CNT) transparent conductive film has a hybrid structure in which the nanoparticles connect CNTs to each other. The film retains 85 % of the transmittance of the base material, while sheet resistance (surface resistance rate) is 60 Ω/square. The film has sufficiently high transparency and conductivity for practical CNT transparent conductive films. The film also achieved long-term stability of sheet resistance when kept in the open air, which has been an issue with the conventional doping technology used to improve conductivity. The developed film is expected to have applications in touch panels, sensors, flexible solar cells, and more as a flexible conductive material using the flexible characteristics of CNTs. It is also expected to have applications in wearable electronics that require elasticity. Details of the results were published in . Social Background of Research Indium tin oxide (ITO) film is currently used mainly as a transparent electrode material for mobile information devices and touch panel PCs. It uses the scarce metal indium, a resource with some concern about depletion and the supply becoming unstable due to international affairs. Another problem with ITO film is that it is brittle and does not stand bending. This makes it difficult to use for developing flexible next-generation electronic devices that will be usable even when bent and folded. Therefore, an alternative transparent conductive material is needed to resolve these issues. History of Research The Nanotube Research Center of AIST developed the eDIPS method for the mass production, quality improvement, diameter control, and so on of single-wall CNTs. In addition, the Electronics and Photonics Research Institute dispersed single-wall CNTs produced by the eDIPS method in a solvent containing a cellulose-based polymer to make an ink that is used to fabricate a coating film of outstanding uniformity on a plastic substrate. The substrate was subjected to post-treatments including pulsed light firing. This resulted in producing a transparent conductive film with high conductivity. The present research has dramatically increased long-term stability of that conductivity, an issue that has been an obstacle to practical use of the CNT transparent conductive film. A part of this research and development was conducted with support from a Grant-in-Aid for Research Activity Startup Program of the Japan Society for the Promotion of Science. Details of Research CNTs are a material having a tubular structure made of curled graphene sheet(s). They are known to be flexible like polymers and very highly conductive. However, the conductivity of CNT films is much lower than that of individual CNTs. This is thought to be because the contact resistance between CNTs has a significant effect on conductivity. Doping, which involves adding a small amount of oxidizing agent such as nitric acid, is a method often used to increase the conductivity of CNT films. Nitric acid doping involves making volatile nitric acid adsorb to the CNTs, so if such films are kept in the open air for long periods, volatile molecules are gradually released from the doped film, raising sheet resistance and creating a problem of durability. In this study, a film of metal halides such as copper iodide on the top or bottom of the CNT film by vacuum deposition instead of doping the CNTs with nitric acid (Fig. 1). This was then irradiated with light of a few hundred milliseconds pulse width to rapidly raise and lower the film temperature. The process caused the metal halide to transfer to the interior of the film, producing a transparent conductive film. Using single-wall CNTs produced by the eDIPS method yielded sheet resistance of 60 Ω/square with 85 % transmittance (relative value at wavelength 550 nm when the transmittance of the base material is defined as 100 %). These are the highest levels of transparency and conductivity recorded for a CNT transparent conductive film. 
Figure 1: The developed CNT transparent conductive film production process. Atomic force microscope images of the CNT film before and after irradiation with pulsed light show that this irradiation causes nanoparticles of metal halide to grow and at the same time transfer to the interior of the CNT network. Moreover, after the irradiation with pulsed light, the nanoparticles are mainly located in places where two or more CNTs intersect with each other (Fig. 2). This indicates the possibility of enabling the CNT transparent conducting film to maintain high conductivity by the interconnecting-structured nanoparticles that reinforce the contacts between CNTs. 
Figure 2: Atomic force microscope images of CNT transparent conductive film. (a) CNT film without nanoparticles; (b) CNT film produced by the developed technology; (c) Enlarged image of (b). Measurement of change in conductivity over time when the film is kept at room temperature in the open air shows that a conventional CNT transparent conductive film treated by nitric acid doping undergoes a rapid increase in sheet resistance immediately after it is produced, and sheet resistance continues to rise gradually after that. In contrast, the developed transparent conductive film maintains over a long period the same level of sheet resistance as it had immediately after it was produced (Fig. 3). This is because nanoparticles of metal halides do not volatilize even if exposed to the open air, so the film can maintain stable performance for a long period of time. The developed material represents an improvement of long-term stability of conductivity, which had been an obstacle to practical use of transparent conductive films that use CNTs or graphene in the past. 
Figure 3: Changes in sheet resistance of the developed CNT transparent conductive film over time. Future Plans The researchers aim to further improve the conductivity and transparency of CNT transparent conductive films by optimizing the type of nanoparticle material used and the conditions of optical processing. They also aim to produce such films using wet processes, such as coating and printing, for all processes. They further aim to use processes such as large-area patterning by screen printing to develop a wide range of applications in addition to touch panels, such as sensors, solar cell electrodes, and wearable electronics.
read more "Fabrication of carbon nanotube transparent conductive film with long-term stability"
Figure 1: The developed CNT transparent conductive film production process. Atomic force microscope images of the CNT film before and after irradiation with pulsed light show that this irradiation causes nanoparticles of metal halide to grow and at the same time transfer to the interior of the CNT network. Moreover, after the irradiation with pulsed light, the nanoparticles are mainly located in places where two or more CNTs intersect with each other (Fig. 2). This indicates the possibility of enabling the CNT transparent conducting film to maintain high conductivity by the interconnecting-structured nanoparticles that reinforce the contacts between CNTs. Figure 2: Atomic force microscope images of CNT transparent conductive film. (a) CNT film without nanoparticles; (b) CNT film produced by the developed technology; (c) Enlarged image of (b). Measurement of change in conductivity over time when the film is kept at room temperature in the open air shows that a conventional CNT transparent conductive film treated by nitric acid doping undergoes a rapid increase in sheet resistance immediately after it is produced, and sheet resistance continues to rise gradually after that. In contrast, the developed transparent conductive film maintains over a long period the same level of sheet resistance as it had immediately after it was produced (Fig. 3). This is because nanoparticles of metal halides do not volatilize even if exposed to the open air, so the film can maintain stable performance for a long period of time. The developed material represents an improvement of long-term stability of conductivity, which had been an obstacle to practical use of transparent conductive films that use CNTs or graphene in the past. Figure 3: Changes in sheet resistance of the developed CNT transparent conductive film over time. Future Plans The researchers aim to further improve the conductivity and transparency of CNT transparent conductive films by optimizing the type of nanoparticle material used and the conditions of optical processing. They also aim to produce such films using wet processes, such as coating and printing, for all processes. They further aim to use processes such as large-area patterning by screen printing to develop a wide range of applications in addition to touch panels, such as sensors, solar cell electrodes, and wearable electronics.
Water near a water-repelling surface cannot dissolve salts
Researchers at the University of Tokyo have demonstrated that water near a water-repelling surface has significantly less capability to dissolve salts (, "Subnanoscale hydrophobic modulation of salt bridges in aqueous media"). 
Salt and a water-repelling surface. Water near a water-repelling surface is less likely to dissolve salts. (Image: Yoshimitsu Itoh, Takuzo Aida) Surface pollution is a problem that is found everywhere, such as on dirty clothes in everyday life and shellfish on a ship’s bottom. Since the initial step of pollution starts from adhesion of a pollutant onto a surface, designing antipollution surfaces require an in-depth understanding of surface adhesion at the nanoscale. However, scientific understanding of surface adhesion is still very limited. The research group of Dr. Yoshimitsu Itoh and Dr. Takuzo Aida at the University of Tokyo, Graduate School of Engineering, Department of Chemistry and Biotechnology discovered that water near a water-repelling surface has significantly less capability to dissolve salts. They utilized a plate where they could place a salt at a defined distance from a water-repelling surface and measured the solubility of salt in water. They found is that when the distance from the water-repelling surface decreases, the salt becomes less soluble. This phenomenon is pronounced at distances of less than one nanometer. One nanometer is the distance at which a substance sticks to a surface. “Water near a water-repelling surface is less able to dissolve salts.” This unique understanding will force a revision of the common sense regarding salt dissolution. This will pave the way not only for designing novel antipollution surfaces, but also for designing drugs, which also requires a precise understanding of interactions between water-attracting and water-repelling parts of molecules.
read more "Water near a water-repelling surface cannot dissolve salts"
Salt and a water-repelling surface. Water near a water-repelling surface is less likely to dissolve salts. (Image: Yoshimitsu Itoh, Takuzo Aida) Surface pollution is a problem that is found everywhere, such as on dirty clothes in everyday life and shellfish on a ship’s bottom. Since the initial step of pollution starts from adhesion of a pollutant onto a surface, designing antipollution surfaces require an in-depth understanding of surface adhesion at the nanoscale. However, scientific understanding of surface adhesion is still very limited. The research group of Dr. Yoshimitsu Itoh and Dr. Takuzo Aida at the University of Tokyo, Graduate School of Engineering, Department of Chemistry and Biotechnology discovered that water near a water-repelling surface has significantly less capability to dissolve salts. They utilized a plate where they could place a salt at a defined distance from a water-repelling surface and measured the solubility of salt in water. They found is that when the distance from the water-repelling surface decreases, the salt becomes less soluble. This phenomenon is pronounced at distances of less than one nanometer. One nanometer is the distance at which a substance sticks to a surface. “Water near a water-repelling surface is less able to dissolve salts.” This unique understanding will force a revision of the common sense regarding salt dissolution. This will pave the way not only for designing novel antipollution surfaces, but also for designing drugs, which also requires a precise understanding of interactions between water-attracting and water-repelling parts of molecules.
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