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Laser scanning microscopy of HTS films and devices (Review Article)
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View: Figures


Image of FIG. 1.
FIG. 1.

Schematic diagram of the LT LSM optics and cryogenics. Notation: L—lens; BS—beam splitter; —focal length; SM—single mode; f.c.—fiber coupler; PD—photodiode. The inset illustrates the reflective LSM image of the SEM grid with square-shaped through-hole cells separated by metal strips.

Image of FIG. 2.
FIG. 2.

Josephson junction array: sample cross section and scanning schematic ; half-tone response map in dc voltage mode at ; superconducting transition of an array section imaged as temperature series (vertical) of a single scan line ( in ) .

Image of FIG. 3.
FIG. 3.

Propagation of normal thermal domain (hot spot) in voltage-biased YBCO/STO film strip. The voltage bias value (indicated in figure) determines the hot spot size. Film thickness , critical temperature , critical current density , , beam modulation frequency .

Image of FIG. 4.
FIG. 4.

Half-tone dc voltage response map of polycrystalline YBCO film with percolative current flow through a maze of weak links between grains at . The arrow denotes current flow direction.

Image of FIG. 5.
FIG. 5.

LSM images showing optical image of HTS sample , thermoelectric map of its granulated structure , and resistive response at the grain boundaries .

Image of FIG. 6.
FIG. 6.

Phase slip lines in a BSCCO single crystal microstrip. curve of -wide microstrip , dc voltage response map of a single PSL , the same map taken at a higher current with multiple PSLs filling the whole strip .

Image of FIG. 7.
FIG. 7.

Phase slip lines in YBCO thin film strip. optical image of the thin film sample , single PSL in the strip center . The YBCO strip is roughly outlined by white dashed line.

Image of FIG. 8.
FIG. 8.

Microphoto of YBCO single crystal samples prepared by laser cutting and oriented in preset crystallographic directions. The electrical contacts to pads are made by conducting paste.

Image of FIG. 9.
FIG. 9.

Meissner effect in YBCO single crystal containing twin boundaries parallel to current flow direction. Half-tone voltage response map at a current slightly below before scanning, plot of response in single scan line denoted by dashed line in .

Image of FIG. 10.
FIG. 10.

Current flow in the same YBCO single crystal as in previous figure but with twin boundaries across the current direction. Temperature, K: 91.6 , 90.6 , 90.63 , 90.34 . Current , beam modulation frequency . Darker areas represent higher response.

Image of FIG. 11.
FIG. 11.

Imaging of twin boundaries (TB) in YBCO single crystal. Current flows across the TBs. Darker areas correspond to higher response voltage. Temperature , current , beam modulation frequency .

Image of FIG. 12.
FIG. 12.

LSM dc voltage response maps of fragments of superconducting filaments extracted from different sites of BSCCO/Ag tape cross section (denoted by numbers in schematic of the tape cross section).

Image of FIG. 13.
FIG. 13.

A schematic sketch of the resonator structure used in the measurements. White arrows show the longitudinal path from A to D used in Fig. 16 for plotting the profiles of the standing wave patterns.

Image of FIG. 14.
FIG. 14.

The resonator (Fig. 13) output spectrum generated as a result of the nonlinear mixing of the two primary tones and at corresponding frequencies and were centered with spacing around the resonant frequency of the device, . The signals at frequencies and were used for the LSM imaging of both inductive and resistive components of hf PR while the signals at IMD were used for imaging of NL sources. The dashed line, , is the linear characteristic measured for calculation of and insertion loss.

Image of FIG. 15.
FIG. 15.

3D surface of the distribution generated by the first: and the third: harmonic frequency at . Positions B and C correspond to that shown in Fig. 13. Positions P1 and P2 are selected for detailed LSM imaging, and P3 is the geometrical center of the YBCO stripline.

Image of FIG. 16.
FIG. 16.

Transverse averaged hf current densities vs. the distance along the length of the resonator YBCO strip-line showing the standing wave patterns at and . The arrows in positions B, C, P1–P3 indicate the particular sections selected for detailed LSM imaging.

Image of FIG. 17.
FIG. 17.

Amplitude profile of the LSM PR distribution in the middle cross section of the YBCO strip. denotes the averaged photoresponse while is its maximum amplitude. The section geometry is shown under the profile.

Image of FIG. 18.
FIG. 18.

Detailed gray-scale LSM images of the spatial variations located near C (Fig. 13) in the area of HTS structure corresponding to right-hand side and left-hand inside corners that are crossed by twin-domain blocks of different orientation. Position of LSM scans is shown by dotted boxes in reflective LSM image. Bright (dark) regions correspond to large (small) PR signal. Amplitudes of are normalized to get the best contrast.

Image of FIG. 19.
FIG. 19.

Gray scale representation of the distribution in the areas of LSM scan near section P1 and region around the position P2 of Fig. 16. The YBCO strip edges are shown by white dotted lines. The central area of is shown in the inset with enhanced contrast for clarity.

Image of FIG. 20.
FIG. 20.

The same area LSM scans obtained in different LSM imaging modes to show power-dependent redistribution of the component, optical map, the distribution, and nonlinear (IMD) responses.

Image of FIG. 21.
FIG. 21.

2D LSM dc voltage image of the resistive state in a YBCO strip fragment induced by transport current at temperature : an artificial linear defect (crack) is present near the bottom edge, the second laser beam generates additional inhomogeneity. The strip width is , it is indicated by arrows and outlined by dashed lines.

Image of FIG. 22.
FIG. 22.

LTLSM profiles of reflectance and rf photoresponse. Details are described in the text.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Laser scanning microscopy of HTS films and devices (Review Article)