Scanning tunneling microscopy and spectroscopy studies of superconducting boron-doped diamond films

Abstract

We report on scanning tunneling microscopy/spectroscopy (STM/STS) experiments on (1 1 1)-oriented epitaxial films of heavily boron-doped diamond grown by using the microwave plasma-assisted chemical vapor deposition method. STM/STS measurements were performed by 3 He-refrigerator based STM under ultra-high vacuum. The STM topography on the film surface shows a corrugation (with a typical size of $1 mm) and grain-like microstructures ($5-20 nm). The tunneling conductance spectra do not show large spatial dependence and superconductivity is observed independent of the surface structures. The tunneling spectra are analyzed by the Dynes function and the superconducting energy gap is estimated to be D ¼ 0:87 meV at T ¼ 0.47 K, corresponding to 2D=k B T c ¼ 3:7. The relatively large value of the broadening parameter G ¼ 0:38 meV is discussed in terms of the inelastic electron scattering processes. r

Spatially correlated microstructure and superconductivity in polycrystalline boron-doped diamond

“…We have checked that tunneling spectra did not depend on the tunnel resistance set point in the range 1 -10 M⍀. In contrast to early STM measurements on similar samples, 20,21 we observe in many locations an almost fully opened gap, presumably thanks to a better sample surface morphology. Within one grain, the electronic properties change smoothly as expected for a slow variation in doping concentration ͑small Fig.…”

Laser-excited photoemission spectroscopy study of superconducting boron-doped diamond

“…This is in contrast to the previously reported scanning tunneling spectroscopy (STS) study, where a BCS-type weakcoupling superconducting gap spectrum ð2D 0 ¼ 3:5k B T c Þ with well defined quasiparticle peaks is observed in CVD (1 0 0) thin film with T c ¼ 1:9 K [21]. Very recently reported STS result on (1 1 1) thin film, on the other hand, exhibits a broad superconducting gap feature fairly alike to that of our PES measurement [22]. This discrepancy among (1 0 0) and (1 1 1) thin films may be explained by the sample inhomogeneity which is reported to become serious in (1 1 1) thin films, particularly in the heavily B-doped region [23].…”

Low-temperature STM/STS studies on boron-doped (1 1 1) diamond films

“…The superconducting transition temperature was T c ¼ 5.4 K and the boron concentration was estimated to be n$6 Â 10 21 cm À3 [5]. STM/STS measurements were performed by using 3 He-refrigerator-based STM under the ultra-high vacuum (UHV) condition [16,17]. The spatial variation of the LDOS was measured at T ¼ 0.47 and 4.2 K. In order to reduce the oxygen contamination, the film was annealed at 450 1C in the UHV chamber just before STM/STS measurements [16].…”

“…Various theoretical proposals [6][7][8][9][10][11] and experiments [12][13][14][15][16][17][18][19][20] have been performed to understand the electronic structure and the mechanism of the superconductivity in boron-doped diamond. Scanning tunneling microscopy/spectroscopy (STM/STS) is a powerful tool to detect high-energy-resolution information about the electronic state with sub-nanometer spatial resolution.…”