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We have developed a Transition Edge Sensor (TES) – Energy Dispersive Spectroscopy (EDS) for Transmission Electron Microscope (TEM) based on a dilution refrigerator. The dilution refrigerator was cooled by liquid helium (L-He), which was supplied from an L-He container separated from the dilution refrigerator. We adopted the hybrid magnetic shields combining a permalloy shield and a NbTi/Nb/Cu superconducting shield to operate the TEM–TES system under a magnetic field of 200 mT. The permalloy shield was used to prevent the ambient magnetic field until the NbTi superconducting shield cooled from room temperature (RT) to 2 K. The critical magnetic field was 220 mT for the TES change from a superconducting state to a normal state. The SQUID – current vs. bias current curve, under the condition that the snout was inserted in the TEM, was equal to the curve of the snout that was out of the TEM. The C (0 0 2) planes could be observed at 120 kV under the condition the snout was inserted in the TEM.

The Transition Edge Sensor (TES)-Energy Dispersive Spectrometer (EDS) is an X-ray detector with high-energy resolution (12.8eV). The TES can be mounted to a scanning electron microscope (SEM). The TES-EDS is based on a cryogen-free dilution refrigerator. The high-energy resolution enables analysis of the distribution of various elements in samples under low acceleration voltage (typically under 5keV) by using K-lines of light elements and M lines of heavy elements. For example, the energy of the arsenic L line differs from the magnesium K line by 28eV. When used to analyze the spore of the Pteris vittata L plant, the TES-EDS clearly reveals a different distribution of As and Mg in the micro region of the plant. The TES-EDS with SEM yields detailed information about the distribution of multi-elements in a sample.

When a scanning electron microscope (SEM) is used for analysis, a low acceleration voltage must be used to reduce damage to the sample and to obtain information near the sample surface. Here, a microcalorimeter energy dispersive spectrometer (EDS) system without external cryogen was developed to analyze material samples under low acceleration voltages (

We show how to design the position of a Josephson junction (JJ) and holes to prevent trapping of magnetic fluxes on the JJ in the superconducting device when the strength of magnetic field is determined in cooling from normal to superconducting state. The number of magnetic fluxes ( N MF ) is determined as N = α ( B − B 0 ), where B is the external field in cooling and B 0 is the threshold of external field that one magnetic flux is trapped, α is the coefficients that might depend on the device size and structure. If the number of holes ( N H ) is larger than N MF , the magnetic fluxes are trapped into the holes. The holes should be arranged regularly so that all the magnetic fluxes are trapped into the holes. If N MF is larger than N H , the magnetic fluxes occupy the holes initially, and then, the excess magnetic fluxes are trapped around the position of the potential wells arising from the interaction among the previously trapped fluxes. The position of JJ must be designed to avoid the position of a potential well. The cooling speed from normal to superconducting state should be as slow as possible to prevent non-uniformity of temperature distribution that would cause formation of unexpected potential wells outside the designed positions.

Recently, vortices confined into micro-scale superconductors with shapes like a disk, triangle, square, etc., have attracted much attention because of the quantum phase transition of the self-organized vortex arrangement occurring within such geometrical constraints. Such a transition can be observed using a scanning SQUID microscope with high spatial resolution. We have successfully improved spatial resolution by incorporating a microfabrication technique that reduces both the size of the pick-up coil of the micro DC-SQUID and the standoff distance between the pick-up coil and the sample surface. Using this microscope, we have studied vortex arrangements in micro-scale superconductors made of Nb and YBa2Cu3O7−δ films with various sizes and geometrical shapes. A peculiar oscillating behavior of diamagnetic magnetization corresponding to the particular vortex state was observed.

We have observed vortex trapped images in the ab -plane of a HoNi 2 B 2 C single crystal in a magnetic field of 1.2 μT at 4 K using a scanning SQUID microscope. The vortex observed has a fine structure consisting of two regions with opposite signs of the magnetic field which is quantized with multiple flux quanta as a whole. The spatial size of the magnetic field distribution extends over 10 μm. Such giant vortices are also observed at T N T T C and disappear above T C where T N is the magnetic transition temperature and T C is the superconducting transition temperature.

We have investigated the magnetic properties of a triangular micro-hole lattice on Pb film (TriMHoLP) by means of a SQUID magnetometer and a SQUID microscope. A matching field H φ of TriMHoLP is 0.425 G. The zero-field-cooled magnetization curves are in accordance with those expected for typical superconductors. However, the curves taken in a field-cooling mode upon cooling are always negative irrelevant to the field polarity. Even in the zero field, we have observed an appreciable amount of vortices and anti-vortices by the SQUID microscope. These strongly suggest that there must be a spontaneous magnetization at temperatures near T c . A clear vortex density wave has been found for a half-filling state of TriMHoLP.

A micro-imaging system using a low-temperature superconductor (LTS) scanning SQUID microscope (SSM) has been developed for the study of superconducting films and devices. The system consists of a micro DC-SQUID, a cryostat, a precise scanning stage, and a control unit. The spatial resolution was improved by reducing the size of the pick-up coil of the micro DC-SQUID. A cryostat without liquid nitrogen makes the operation of the system easy and speedy. Preliminary experiments were made using the system and several magnetic images were obtained. We present observations of trapped fluxes in two types of superconducting thin film: a single-crystal-like Nb film grown epitaxially and a polycrystalline Nb film. We also present observations of a SQUID array, which consists of 50 DC-SQUIDs connected in series.

A cryogen-free energy-dispersive spectrometer (EDS) using a transition edge sensor (TES) was developed for material analysis. This system can maintain a temperature at 130 mK within 30 μK, and has good energy resolution (19 eV for Mn-Kα) for long-time measurement with a drift in the DC level of less than 0.02 eV/min. This system utilizes a dilution refrigerator (φ 272 mm×height 572 mm) and has a snout (370 mm long and φ25 mm) similar to that in a conventional EDS system. The dilution refrigerator is pre-cooled by a GM refrigerator. A flexible tube between the dilution refrigerator and GM refrigerator damps the mechanical vibration of the GM refrigerator. Two shields (4 and 80 K) thermally protect the Cu rod (φ8 mm) cooled to be 100 mK. Windows composed of polyimide+Al film allow X-ray detection above the C-Kα line. A TES (6 mm×6 mm) and array SQUID amplifier (1.5 mm×3 mm) are mounted on top of the Cu rod. For Mn-Kα, the pulse height is 5.5 μA and decay time (τeff) is 90 μs. The maximum count rate (1/20 τeff) is estimated at about 500 cps.

Penetration of magnetic fluxes into a superconducting thin film that contained holes was studied for fast and slow cooling rates (0.18 and 0.009 K/s, respectively) under an ambient magnetic field of about 3 μT. By using a scanning superconducting quantum interference device microscope, we observed trapped magnetic fluxes both inside and outside of holes prepared in a superconducting film. The trapped fluxes outside the holes appeared in a regular arrangement when the superconducting film was cooled at the slow rate. Observed arrangements of the trapped fluxes were compared with a simulation that was based on a theoretical model that considered the surface barrier and the interaction among fluxes. The simulation explained well the observed arrangements of magnetic fluxes.

A high‐energy‐resolution energy dispersive spectrometer (EDS) utilizing a TES (transition edge sensor) microcalorimeter array is developed for a transmission electron microscope (TEM). The goals of the development are (1) an energy range of 0.3–10 keV, (2) an energy resolution of FWHM

We have developed a SQUID microscope with novel cooling system. This microscope is able to observe a very weak magnetic field distribution such as a distribution generated by single flux quantum. Therefore, it is expected to be used for application and study of superconducting materials and devices. This microscope consists of a newly developed cooling system, scanning system, and controller. The cooling system is helium flow thermal conducting type which does not require pre-cooling or thermal insulation by liquid nitrogen. Consequently, the cooling time has been considerably shortened, and the sample exchange time has been shortened as well. It is possible to vary the temperature of the sample between 4K and 100K. The scanning system has wide observation area of 10mm X 10mm with a resolution of 25nm. The flux sensitivity of the micro DC-SQUID is better than 8µΦ/HZ-1/2. We present results of observing quantized flux trapped in superconducting thin film or generated in meshed superconducting thin film pattern.

It is important to design buildings and civil engineering structures to take into account earthquakes in Japan. When a big earthquake occurs, some structural members are damaged with present designs absorbing the energy of earthquakes. It is important when evaluating the seismic capability, to evaluate absorption capabilities of the structural members, but the nondestructive evaluation methods for absorption capabilities of structural members are not well understood.

We have developed a non-contact current measurement system, which converts magnetic flux distribution measured with high sensitivity using DC-SQUID into current distribution. The DC-SQUID is composed of Nb/AlOx/Nb junctions with high thermal reliability, and a pickup coil. The diameter of the pickup coil and the standoff distance between the DC-SQUID and samples, which are important parameters for the spatial resolution, are respectively 200 and 500 μm . The spatial resolution is 200 μm and the current noise density calculated from the magnetic noise is 6.8 nA / Hz . We have applied the system to a solar cell to visualize the area, which does not generate electrical power.

Magnetic flux distribution of a YBa 2 Cu 3 O 7− δ microdisk with 50 μm in diameter and 0.48 μm in thickness has been studied by scanning SQUID microscopy. All vortices observed in the microdisk with high- κ each carries flux quantum φ 0 and are loosely distributed in magnetic fields up to 30 μT. Number of the vortices increases one by one with increasing magnetic field. Average magnetic field for each increase in the number is greater than that expected from the size of the microdisk, which is probably due to expulsion of magnetic field from the rim of the microdisk. These results show that multi-vortex states are stable in the microdisk.

A magnetic imaging system with a micro-DC superconducting quantum interference device magnetometer has been developed to evaluate superconducting films and to inspect a superconducting device with a high spatial resolution. A superconducting device, i.e., a DC-SQUID made of a superconducting Nb thin film, was observed using the system. The shape of the device was identified by applying the Meissner effect. The trapped fluxes in the device were clearly visible. In addition, the input current and the shielding current flowing on the device were detected by feeding a current to the device. It was confirmed experimentally that the magnetic imaging system was effective in studying superconducting devices.

The relationship between the magnetic and structural changes induced by the application of a tensile load to a carbon steel specimen was investigated by correlating the change in the spatial second-order gradient component of the magnetic flux density d2 B z /dr 2 with the appearance of the Lüders bands on the specimen surface. The magnetic change was measured using a nondestructive evaluation (NDE) system with a concentric second-order superconducting quantum interference device (SQUID) gradiometer of low temperature superconductor. The area where peaks and folds appeared in the 3-dimensional map of d2 B z /dr 2 corresponded to the area where Lüders bands appeared on the specimen surface. The dimensions of the area where peaks and folds appeared had a strong correlation with the residual strain of the specimen. It was concluded that the magnetic NDE using SQUID has the ability to detect the area plasticized by fine deformation in ferromagnetic materials.

A Direct Current Superconducting Quantum Interference Device (DC-SQUID) gradiometer for nondestructive evaluation was developed. A pick-up coil and a DC-SQUID were integrated on a 3×3 mm2 Si chip. In order to raise the spatial resolution of the gradiometer, a coplanar concentric second-order derivative coil was adopted as a pick-up coil. The pick-up coil consisted of a one-turn outer coil and a four-turn inner coil connected in series and counterclockwise to each other. The diameters of the outer coil and the inner coil were 2 mm and 1 mm, respectively. The size of the pick-up coil was determined by calculating the spatial resolution in relation to the bottom thickness of the cryostat. The high spatial resolution of the DC-SQUID gradiometer was experimentally confirmed.