Laser-assisted Atom Probe Analysis of Bulk Insulating Ceramics
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Laser-assisted Atom Probe Analysis of Bulk Insulating Ceramics T. Ohkubo1, Y. M. Chen2, M. Kodzuka2, F. Li1, K. Oh-ishi1 and K. Hono1,2 1 National Institute for Materials Science, Tsukuba 305-0047, Japan 2 Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-0047, Japan ABSTRACT A Yb:KGW femtosecond laser (400 fs) with 3rd and 4th harmonic generators (343 and 258 nm) was adopted to a locally built 3DAP instrument to assist field evaporation from ceramics tips that were bonded on tungsten wire. Using this setting, we have demonstrated that quantitative atom probe tomography is possible from Y2O3-ZrO2-MgAl2O4, (Ce,Y)O2, Li(Co,Ni,Mg,Al)O2 bulk ceramics, which are all insulators. INTRODUCTION The three-dimensional (3D) atom probe technique is now widely used to obtain atomic tomography of metals and semiconductors[1]. To perform atom probe tomography, atoms on needle like specimens of a few 100 nm in diameter must be field evaporated under the presence of ultrahigh electric field of a few 1010 V/m. In the conventional atom probe microscope, such field evaporation was triggered by the application of ns voltage pulses typically ranging from 1 to 2 kV superimposed on high standing DC voltage typically ranging from 5 to 20 kV. The presence of the electric field from the tip (D~10-7m) to the detector (D~10-1m) results in the magnification of a few million. Since the conduction of voltage pulse was not possible in insulating materials, the atom probe tomography have been limited to conductive materials, mainly metals. Recent successful implementation of pulsed laser to assist field evaporation[2,3] expanded the application areas of the atom probe tomography to a wide variety of materials including semiconductors[4] and thin film oxides [5,6]. In addition, the development of site specific specimen preparation method using the focused ion beam technique[7] broadened the application areas of the atom probe tomography to magnetic multi-layers[8] and semiconductor devices[4]. The substantially reduced frequency of specimen ruptures in the pulsed laser assisted mode has also made the analysis of these specimens practical. Despite the recent remarkable advances in the laser-assisted atom probe, little work has been carried out on the analysis of insulating materials. A few successful examples are the analyses of thin oxide films, such as MgO and Al2O3 layer in magnetic tunneling junctions[9,10], HfO2 high dielectric (high-k) ultrathin films on Si[4], and oxide films that are formed on tip surfaces[11,12]. Also, the field ion microscopy (FIM) image and the mass spectrum from bulk insulators had been shown, although the 3D atom distribution was not shown[13, 14]. Up to now, there has been few reports on successful 3D atom probe tomography of bulk insulating ceramics[15]. The main objective of this work was to show the spreading of analysis of bulk insulating ceramics by the atom probe tomography assisted with ultraviolet (UV) laser pulses. EXPERIMENTAL DETAILS All specimens for atom probe to
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