Low Temperature Scanning Synchrotron Microscope · Uptec LTSSM 1D scan 146!m R. Cristiano et al.,...
Transcript of Low Temperature Scanning Synchrotron Microscope · Uptec LTSSM 1D scan 146!m R. Cristiano et al.,...
Uptec
Low Temperature Scanning Synchrotron Microscope!
1!
Uptec
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.
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Uptec
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
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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
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LTSSM 1D scan 146!m
R. Cristiano et al., J. Appl. Phys. 86, 4580 (1999).!
Al 30nm
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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).
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Energy linearity!
Nb(200)
Al(?)
Al(?)
Nb(200)
200!m
How about practical soft x-ray range?
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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)
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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 ?
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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
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Energy linearity and FWHM!
100!m square, Al 30nm
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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
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Energy linearity and FWHM
100!m square, Al 70nm
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200!m-square junction with 70nm Al!
200!m square, Al 70nm
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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!