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Space-borne astronomical instruments require extensive characterization on the ground before launch. In the hard X-ray region however, it is difficult for a laboratory-based beamline using a conventional X-ray source to provide a capability sufficient for pre-flight high-precision calibration. In this paper, we describe an experiment to characterize a hard X-ray telescope at a synchrotron facility, mainly on the basis of experimental setup and examples of measured results. We have developed hard X-ray telescopes consisting of Wolter-I grazing incidence optics and platinum-carbon multilayer supermirror coatings. The telescopes have been characterized at the synchrotron facility SPring-8 beamline BL20B2. The measurements at BL20B2 have great advantages such as extremely high flux, large-sized and less-divergent beam, and monochromatic beam covering the entire hard X-ray region from 8 to over 100 keV. The telescope was illuminated by monochromatic hard X-rays, and the focused image was measured by high resolution hard X-ray imagers. The entire telescope aperture was mapped by a small beam, and the effective area and the point spread function were obtained as well as local optical properties for further diagnostics of the characteristics of the telescope.

We developed a multi-probe atomic force microscopy (AFM) system using piezoelectric thin film (PZT) cantilevers. The use of self-sensing cantilevers with integrated deflection sensors as probes markedly reduced complexity in the ordinary AFM setup. Address-patterned samples having microfabricated x–y coordinate patterns, fabricated by electron beam lithography, were developed as well. These samples allow us to evaluate the relative distance between the probes by the comparison of the images obtained. Although the minimum distance between these probes was 126 µm using the original cantilevers, it was reduced to 9.2 µm by using the PZT cantilevers modified by a focused ion beam. Furthermore, we found that the interaction forces between the cantilevers were detected by determining the change in the amplitude of each cantilever.

The X-ray imaging of materials with low atomic number elements is difficult through a conventional photoabsorption contrast method whereas much higher contrast can be achieved by phase-contrast imaging. We have constructed a compact size imaging system using a microfocus X-ray generator with a few µm spot size. We present here the evaluation of basic characteristics and sample results, as well as future prospects.

We report on a new type of a photon-counting device, scintillator directly coupled charge-coupled device (SD-CCD), possessing a high spatial resolution and a moderate spectral resolution for 0.3–100 keV X-rays. The SD-CCD consists of an X-ray charge-coupled device (CCD) and CsI(Tl) as the scintillator. The CsI(Tl) is directly coupled to the surface of the CCD wafer. Soft X-rays incident to the SD-CCD are absorbed in the CCD, whereas hard X-rays are absorbed in the CsI(Tl) and generate visible photons that are also detected by the CCD. The CsI(Tl) employed in the SD-CCD has a needlelike structure with a diameter of about 5 µm, which reduces the lateral spread of visible photons. Because previous SD-CCDs employed a needlelike CsI(Tl) of 100 µm thickness, we developed an SD-CCD that has a needlelike CsI(Tl) of 300 µm thickness directly deposited on a CCD. We measured the spectral resolution of the SD-CCD, to be (68±4)% at 59.5 keV, which was a factor of 2.3 worse than that of the previous best SD-CCD. To ascertain the problem of degradation of spectral capability, we ran a Monte-Carlo simulation using DETECT2000 software. We found that visible photons in the needlelike CsI(Tl) reflect diffusely on the surface of the needle and the number of visible photons detected varies according to the X-ray point of interaction, resulting in the degradation of spectral capability. We discuss a count-measure to this problem.

The mesh experiment enables us to specify the X-ray point of interaction with a subpixel resolution. Miyata et al. [Jpn. J. Appl. Phys. 41 (2002) 5827] measured the charge cloud shape produced in a back-illuminated (BI) charge-coupled device (CCD). They found that there are two components of the charge cloud shape: a narrow component and a broad component. The size of the narrow component is 2.8–5.7 µm in units of standard deviation and strongly depends on the attenuation length of incident X-rays in Si, suggesting that it originates in the depletion region. On the other hand, the size of the broad component is roughly constant at 13 µm and does not depend on X-ray energies, suggesting that it originates in the field-free region. We applied the mesh experiment with the fully depleted BI CCD and found that there is a single component of the charge cloud with a size similar to that of the narrow component in Miyata et al.'s. We thus confirmed that the narrow and broad components originate in the depletion region and the field-free region, respectively.

We have investigated the radiation damage effects on a charge-coupled device (CCD) to be used for the Japanese X-ray mission, the monitor of all-sky X-ray image (MAXI), onboard the international space station (ISS). A temperature dependence of the dark current as a function of incremental dose is studied. We found that the protons having energy of >292 keV seriously increased the dark current of the devices. In order to improve the radiation tolerance of the devices, we have developed various device architectures to minimize the radiation damage in orbit. Among them, nitride oxide enables us to reduce the dark current significantly and therefore we adopted nitride oxide for the flight devices. We also compared the dark current of a device in operation and that out of operation during the proton irradiation. The dark current of the device in operation became twofold that out of operation, and we thus determined that devices would be turned off during the passage of the radiation belt. The temperature dependence of the dark current enables us to determine the electron trap level that generates the dark current. We fitted dark current as a function of temperature by the thoretical models and found that the dark current increase after proton irradiations is caused by, at least, two kinds of electron trap levels. The shallow trap level (Ec-Et 210 K. On the other hand, another trap level is located roughly at the center of the silicon bandgap which might be associated with divacancies or P–V traps. We finally investigated the spatial distribution of the low-energy protons in the orbit of the ISS. Their density has a peak around l ~20° and b ~-55° independent of the altitude. The peak value is roughly two orders of magnitude higher than that at the South Atlantic Anomaly.

We have employed a mesh experiment for back-illuminated (BI) CCDs. BI CCDs possess the same structure to those of FI CCDs. Since X-ray photons enter from the back surface of the CCD, a primary charge cloud is formed far from the electrodes. The primary charge cloud expands through diffusion process until it reaches the potential well that is just below the electrodes. Therefore, the diffusion time for the charge cloud produced is longer than that in the FI CCD, resulting a larger charge cloud shape expected. The mesh experiment enables us to specify the X-ray point of interaction with a subpixel resolution. We then have measured a charge cloud shape produced in the BI CCD. We found that there are two components of the charge cloud shape having different size: a narrow component and a broad component. The size of the narrow component is $2.8-5.7 \mu$m in unit of a standard deviation and strongly depends on the attenuation length in Si of incident X-rays. The shorter the attenuation length of X-rays is, the larger the charge cloud becomes. This result is qualitatively consistent with a diffusion model inside the CCD. On the other hand, the size of the broad component is roughly constant of $\simeq 13 \mu$m and does not depend on X-ray energies. Judging from the design value of the CCD and the fraction of each component, we conclude that the narrow component is originated in the depletion region whereas the broad component is in the field-free region.

We developed a multi-probe atomic force microscope (AFM) having two AFM cantilevers independently controlled using the optical beam deflection method. We succeeded in simultaneously obtaining images with two independent probes by frequency modulation (FM) detection method. To evaluate the distance between the AFM tips of the cantilevers, we used a new the address-patterned sample, which was also developed for this study. The images obtained show that the distance between the probes was 2 µm. The development of the multi-probe AFM opens a wide variety of applications in the present nanoscience and engineering field.

Microfocus X-ray generators have been extensively used for magnification radiography. In these applications, the sharpness of an image depends on the X-ray source size. Therefore, it is important to evaluate and optimize the X-ray spot quantitatively. Although several methods have been devised to date, some require complicated systems whereas others are not fully quantitative. Here, we introduce a simple, practical, and quantitative method that makes use of the penumbra of a knife edge. Because the method is very simple, it can be readily integrated as an auto focusing system of a focal spot.

We have measured the soft X-ray responsivities of a fully depleted back-illuminated (BI) charge-coupled device (CCD). We constructed a soft X-ray beam line for this purpose and confirmed that we irradiated K lines of carbon, oxygen, and aluminum. We operated the BI CCD in a photon-counting mode with a low-noise condition sufficient to resolve these K lines. We clearly resolved the carbon K line with the BI CCD. Because the mean absorption length of carbon K X-rays is 0.11 µm in silicon, we confirmed that our BI CCD operates in a fully depleted condition. We obtained a good linear relationship between peak pulse height and incident X-ray energy. The energy resolution can be explained by the Fano factor, the readout noise, and a small number of additional unknown noise components.

We have recently developed a dual-probe atomic force microscopy (DP-AFM) system having two AFM cantilever probes whose positions can be independently controlled with a precision on the order of ten nanometers. In this study, we visualized charge injection processes in polydiacetylene thin film grains using the DP-AFM system. One of the two probes was used to apply bias voltages to the grains while the other probe was used to obtain surface potential images of the grains. The surface potential of the polymerized grain changed according to the applied bias voltages. The potential profiles at the edge of the grain were not sharp when negative voltages were applied to the grain, which suggests the existence of an electron injection barrier at the interface. Moreover, it is suggested from the same experiment conducted in vacuum that the p-type semiconductor characteristics of the polydiacetylene is due to the O2 hole doping.

A charge-coupled device (CCD) is a standard imager in optical region in which the image quality is limited by its pixel size. CCDs also function in X-ray region but with substantial differences in performance. An optical photon generates only one electron while an X-ray photon generates many electrons at a time. We developed a method to precisely determine the X-ray point of interaction with subpixel resolution. In particular, we found that a back-illuminated CCD efficiently functions as a fine imager. We present here the validity of our method through an actual imaging experiment.

We performed local electrical transport measurement on single grains of a pentacene thin film using a lab-built dual-probe atomic force microscopy (DP-AFM) system. We brought two conducting cantilever tips in contact with a single grain and successfully measured the p-type field-effect characteristics. Moreover, we investigated the effect of contact resistance on the measured characteristics by performing a series of transport measurements while varying tip distance. The contact resistance and hole mobility of the channel region were estimated as 3.1 GΩ and 2.7×10-2 cm2 V-1 s-1, respectively. The results demonstrate the applicability of the DP-AFM system to the nanometer-scale transport measurement of molecules.

We are developing an X-ray charge-coupled device (CCD) for the next Japanese X-ray astronomical satellite mission, NeXT (New X-ray Telescope/Nonthermal energy eXploration Telescope). We developed a trial product of the p-channel CCD fabricated on an n-type silicon wafer. It is possible to have a thick depletion layer of ∼300 µm with a p-channel CCD because it is easy to obtain high resistivity using an n-type silicon wafer compared with a p-type silicon wafer. We evaluated the performance of the p-channel CCD. The imaging area of the CCD consists of 512×512 pixels with a pixel size of 24×24 µm2. The horizontal charge transfer inefficiency (CTI) of the CCD can be improved by reducing the operating temperature and increasing the readout frequency. We obtained the best horizontal CTI of (0.98±0.09)×10-5 with an energy resolution of (202±6) eV full width at half maximum (FWHM) for 5.9 keV X-rays and a readout noise of 18 e- (rms) when the CCD was operated at a temperature of -110 °C and a readout frequency of 67 kHz. We measured the thickness of the depletion layer to be (290±33) µm from the detection efficiency of the 22.4 and 24.9 keV emission lines from 109Cd.

Spectroscopy of hard X-rays generated by focusing a femtosecond laser (42 fs at 780 nm) onto metal targets consisting elements of various atomic number (Z) is carried out in the energy range between 2 and 15 keV using a direct-detection charge-coupled-device camera.Sharp K-shell line emissions are observed for X-rays generated from medium-Z targets (Ti, Fe, Ni, Cu and Zn), which can be used for X-ray diffraction without further monochromization. A broad continuum and a weak trace of L-shell line emissions are observed for X-rays from high-Z targets (Mo, Nb and W). The energies of the characteristic X-rays agree well with that of X-rays from neutral atoms or slightly ionized ions.

The numerical simulation of a nuclear pumped 3He–Ne–Ar gas laser (λ=585.3 nm) has been made to estimate the optimal gas mixtures. The calculation shows that the optimization is established under a condition of He pressure of 2280 Torr, Ne pressure of 24 Torr, and Ar pressure of 8 Torr. The oscillation is expected to occur at a thermal neutron flux density of 3.3×1014 cm-2 s-1 when the cavity length is 50 cm and the mirror reflection coefficient is 99%. On the other hands, the energy efficiency does not exceed 0.33% under the same condition.

We report here the charge cloud shape produced by an X-ray photon inside the charge-coupled device (CCD) as well as a method to measure it. The measurement is carried out by using a multi-pitch mesh which enables us to specify the interaction position of X-rays with subpixel resolution not only for single events but also for split events. Split events are generated when the X-ray interaction position is close to the pixel boundary. The width of this area depends on the apparent charge size. Finally, we measured the signal output from the pixel according to the interaction position of X-rays. By differentiating this function, we obtain, in detail, the charge cloud shape which can be well represented by an asymmetric Gaussian function. The charge cloud size for Al-K X-rays is 0.7×1.4 µm2 while that for Mo-L X-rays is 0.8×1.4 µm2. The size of the photoelectron in Si produced by these X-rays is about 0.04 µm. Taking into account the mean absorption length for these X-rays in Si, diffusion process in the depletion region cannot explain the charge cloud size. The asymmetry of the charge cloud probably arises from the asymmetry of the electric field in the CCD.

We report the measurement result of the degree to which X-rays from a conventional X-ray generator in the energy range up to 60 keV are linearly polarized. The X-ray generator we used in which the accelerated electrons hit the water-cooled metal head is widely used commercially. We measured the degree of linear polarization by employing a Thomson scattering process. We found that the degree of linear polarization depends only on the ratio between the X-ray energy from 20 keV to 60 keV and the applied voltage to the electron. The higher the ratio is, the higher the degree of linear polarization we obtain, whereas the weaker the X-ray intensity is. By selecting an appropriate combination between the applied voltage and the X-ray energy, we confirmed that we would obtain a mono-energetic highly linear polarized X-ray beam with enough intensity for practical use.

We report the use of a new technique to measure the X-ray detection efficiency of a charge-coupled device (CCD) with subpixel resolution. The new technique makes use of a parallel X-ray beam and metal mesh placed just in front of the CCD. The CCD camera we used is a conventional system using the TC213 (Texas Instrument Japan (TIJ)) whose pixel size is 12 µ m ×12 µ m with one million pixels. The mesh has 4 µm diameter holes spaced at 12 µm intervals. We produced an efficiency map within a typical pixel showing the gate structure in detail: a virtual gate, a clock gate and an antiblooming gate. The gate structure we measured is consistent with the manufacturer's design value. By selecting single pixel events, we detected a pixel boundary. Additional plans for application will also be discussed.

Photoablation of synthetic fused quartz by simultaneous irradiation of multi-wavelength beams of a vacuum-ultraviolet (VUV) laser using high-order anti-Stokes Raman scattering is described. The VUV laser, which emits widely spread Raman-shifted lines from 133 nm to 594 nm, is ideal for effective laser ablation of the fused quartz. The well-defined patterns with a cross-sectional profile of a rectangular shape are formed by using a contact mask at an ablation rate as high as 13 nm/s. An effective absorption coefficient of 3.4×10-5 cm-1, which indicates that the multi-wavelength irradiation effect has an important role in the process, is obtained.