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Low Temperature Scanning Synchrotron Microscope!

1!

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Bad junction!

Nb(200)

Al(30)

Al(30)

Nb(200)

200!m

Full illumination with 55Fe X-ray source (5.9keV, 6.4keV)

0.4K!

200!m

Bias:0.7mV, 300nA

(b) Nose level!

Bias:0.3mV, 16nA

A

Charge! (a)

92eV

71eV

fd21-06.-16nA!

The answer is spatial nonuniformity.

2!

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Low Temperature Scanning Synchrotron Microscope

LTSSM

PF@KEK, TERAS@AIST

6 keV - 20 keV, Multipole Wiggler + Si(111)

70 - 1900 eV, Bending magnet + Grating

Scanning has not been available by LTD.

5 - 10!m x-ray microbeam

3!

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LTSSM 3D images, 200!m, Vbias=!/e

top bottom

(a)

Integration

+! =!

Photo

n y

ield

[k c

ounts

]!

Charge [106 electrons]!

(b)

200!m STJ

Charge [a.u.]!

55Fe full illumination (c)

6keV, Al 30nm

4!

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LTSSM 1D scan 146!m

R. Cristiano et al., J. Appl. Phys. 86, 4580 (1999).!

Al 30nm

5!

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The spatial profile depends on!

! " bias point,

! " junction size,

! " strength of magnetic field,

! " thickness of Al layers (vist J11, M. Ukibe et al.), and

! " photon energy (this study).

6!

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Energy linearity!

Nb(200)

Al(?)

Al(?)

Nb(200)

200!m

How about practical soft x-ray range?

7!

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6keV

Nb L escape

Si K"

Total absorption

Spatial profiles at 6 keV and 1.74 keV!

200!m square, Al 30nm

SiK" (1.74keV)

8!

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How about further lower energies (< 1.74keV)?!

The spectrum for 520 eV and 1040 eV shows the same

large spatial nonuniformity as for 1.74 keV and 6keV.

200!m square, Al 30nm

6keV

Hopeless ?

9!

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100!m square, Al 30nm

The spectrum of the 100!m-square junction for 520

eV shows that the spatial nonuniformity is small.

Smaller junctions help us.!

#=1.3!s

10!

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Energy linearity and FWHM!

100!m square, Al 30nm

11!

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Junctions with thicker Al!

100!m square, Al 70nm #=1.9!s

Nb(150)

Al(70)

Al(70)

Nb(200)

100!m

12!

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Energy linearity and FWHM

100!m square, Al 70nm

13!

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200!m-square junction with 70nm Al!

200!m square, Al 70nm

14!

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Conclusions!

! " Spatial profile strongly depends on photon energy.

! " Response to low energies (< ~1 keV) may be within

conventional quasiparticle diffusion model. The uniformity

and E-linearity is improved by increasing the Al thickness.

! " Response to high energies (> ~1 keV) requires new signal

creation framework

(high density of excitation, too far from equilibrium state).

! " Full understanding of STJ operation requires an

advanced nonequilibrium theory and further LTSSM

studies.

! " Stephan’s favorite 50nm Al may be good for energy

resolution, response time, and detector size in < 2 keV.

! " Junctions have a high energy resolution, a high count rate,

and a reasonable detector size for soft X-ray spectroscopy.

15!