Mesoporous and large mesoporous SnO2 powders were prepared by self-assembly of surfactants as a template and then their potentials as semiconductor gas sensor materials have been examined. Phosphoric acid treatment of as-prepared powders was found to be effective for suppressing the crystallite growth and then maintaining their ordered mesoporous and large mesoporous structure as well as large specific surface area up to elevated temperatures. Owing to their thermally stable ordered porous structure, mesoporous and large mesoporous SnO2 sensors showed larger gas response than the sensors fabricated with conventionally prepared powder. Furthermore, simultaneous surface modification of conventional SnO2 powder with Ru loading and subsequent coating with a mesoporous SnO2 layer was proved to be an effective approach to improve the gas sensing properties. The improved response was considered to arise from a synergistic effect of the diffusion control by the mesoporous SnO2 layer and the chemical sensitization by the Ru loaded.
Metal-oxide semiconductor gas sensors are effective to air environment monitoring and indoor gas leakage detection, etc., because of the high sensitivity property. The principle of the sensor operation is the oxidation or the reductive reaction caused by gas molecules with the film surface heated to a high temperature. The electrical resistance of the sensor changes by this reaction. It is possible to operate as a sensor of the impedance change type by adopting Interdigital Electrodes (IDEs) for the electrode that measures the electric characteristics of the Metal-oxide semiconductor film. The equivalent circuit of the sensor with IDEs depend on the heater voltage. When the general heater voltage is given (Drive at a high temperature), the sensor almost becomes pure resistance. On the other hand, it operates as a parallel equivalent circuit of R-C when the voltage is set low (Drive at the vicinity of room temperature). In the case of high temperature driving mode, the sensor functions as a sensor of the change in resistance type by the oxidation and the reductive reaction of the old model. In the case of low temperature driving mode, the sensor functions as impedance changeable sensor by a conductivity change and a permittivity change of the film. Those changes are caused by the physical adsorption of gas molecules. In this report, the principle of impedance changeable semiconductor gas sensor and the response characteristic of the sensor are described.
A new concept of genetic field effect transistors (FET) is proposed for detection of specific binding of bio-molecules, which is in principle based on charge density change at the gate insulator. The electrical signals of the genetic FET were found to change after allele specific oligonucleotide hybridization, intercalation and primer extension. We demonstrated experimentally that the SNP genotyping could be achieved by the use of the genetic FETs in combination with allele specific extension reaction. Single base extension on the gate could be detected by the use of FET, which indicated possibility toward DNA sequencing. The genetic FET platform based on the direct transduction of oligonucleotide extension into electrical signal is suitable for a simple, accurate and inexpensive system for SNP typing in clinical diagnostics.
We have developed a new methodology to fabricate high resolution DNA microarray (2,500-104 dots/cm2) in combination with micro contact printing (μ-CP) and SPR imaging. Novel COOH-terminated PEG-disulfides with p-carborane were synthesized to fabricate the first layer on gold substrates to achieve surface coupling reaction with amino-terminated DNA in high yield. The hybridization of the target-DNA modified gold nanoparticles on probe-DNA patterned surfaces was successfully demonstrated by the SPR imaging, where nonspecific adsorption was not observed to the array background. The gold nanoparticle arrays provide quite high contrast even at low surface coverage (∼10%) by the enhancement effect of optical signals based on nano-scale phenomena in the near field. This enhancement effect can be well demonstrated by the simulation based on Maxwell-Garnett (MG) theory and Fresnel's equation.
We describe herein the concept, principle, and experimental findings of the molecular tips for chemically selective STM. It has been shown that molecular tips allow chemically selective imaging based upon the hydrogen bond, metal coordination, and charge-transfer interactions between sample and tip molecules. The chemical interactions result in facilitated electron tunneling through overlapped wave functions between the sample and tip molecules. The molecular tips were successfully applied to differentiate nucleobases, metal ions, or frontier orbitals of porphyrins. The selectivity can be tailored upon designing functional groups of the tip molecules. In addition, the molecular tips enabled the conformational analysis and detection of intermolecular electron transmission from a single molecule to another adjacent single molecule.
A taste sensor is composed of several kinds of lipid/polymer membranes for transforming information of taste substances into electric signal. The sensor output shows different patterns for chemical substances which have different taste qualities such as saltiness and sourness. Taste interactions such as suppression effect, which occurs between bitterness and sweetness, can be detected and quantified using the taste sensor. The taste and also smell of foodstuffs such as beer, coffee, tea, mineral water, soup and milk can be discussed quantitatively. The taste sensor provides the objective scale for the human sensory expression. We are now standing at the beginning of a new age of communication using digitized taste.
The odor sensing system consisting of a chemosensor array and a micro computer has been called as an Electronic-Nose (e-Nose) system. Several types of chemosensors such as a conductometric-type sensor utilizing conductivity change of metal oxide semiconductor by means of chemical reaction of gases, a gravimetric-type sensor utilizing quartz crystal microbalance, resonant frequency change, where the mass change is converted into an optical-type sensor utilizing surface plasmon resonance phenomenon and others have been used for the fabrication of the e-Nose system. In this paper, the principle of chemosensors, key technologies to prepare the intelligent e-Nose system, commercially-available e-Nose system reported so far and applications of e-Nose system are described.
RHEED patterns have been observed for vicinal surfaces of Si(001) and Si(111) polished into vicinal angle α = 2.5o and 3.1o, respectively. It was confirmed that both the glancing angle θ and the vicinal angle α can be estimated by the geometric relation between the diffraction spots and Kikuchi lines. For the step down incidence, bulk information such as Kikuchi lines and diffraction spots arisen from the three dimensional crystal lattices is mainly obtained. For the step up incidence, on the contrary, surface properties such as fractional order spots arisen from surface super structure is mainly obtained. In this study, features of the RHEED patterns taken from the vicinal surface are summarized and compared with calculated ones. It is concluded that these features can be explained by the escape length of electrons and the shadow effect by the step edges.
Frictional anisotropy is observed with crystallographic planes and sliding orientations of ice. Availing this phenomenon, a high speed skating rink was made by use of a large-single crystal ice and its lowest frictional plane. Moreover, new rinks will be made using anisotropy in plastic deformation of ice. The lower friction of curling rinks and oriented snow grains at surface came in sight. These high speed rinks were derived from the basis adhesion theory, and self-inconsistency in frictional melting theory as classical frictional mechanism was revealed.