Abstract
Results on stress analysis for single-crystal diamonds are presented. Isolated crystals were studied by Raman mapping and depth profiling techniques, using confocal microscopy. Diamonds were deposited on molybdenum and tantalum by hot filament and microwave CVD methods at growth rates between 10 and 30 μm·h-1. Crystals from 10 to 40 μm size were examined. Local stress was evaluated by analyzing the position, broadening and splitting of the 1332 cm-1 Raman peak in a 3D mapping. For the (001) orientation, the most stressed zone was found at the center of the crystal base, close to the interface with the substrate: a Raman peak around 1340 cm-1 was measured, corresponding to a pressure c.a. 3 GPa, according to our dynamical calculations. This peak disappears few microns out of the center, suggesting that this highly concentrated stress sector was the nucleation zone of the crystal. A shifting and slight broadening of the 1332 cm-1 band was observed in the rest of the crystal. The causes of these effects are discussed: they proved not to be due to anisotropic stress but to refractive effects. Same results were found for different crystal sizes and growth rates.
Highlights
Diamond is one of the most promising semiconductor materials because of its outstanding mechanical, thermal and electrical properties [1,2]
Diamond crystals were grown on Mo and Ta with both methods; the growth rate was higher for MPCVD (30 μm·h−1) than for HFCVD (10 μm·h−1), under similar conditions
The diamond Raman frequency increases towards the crystal-substrate interface center, indicating a raising in stress, as expected
Summary
Diamond is one of the most promising semiconductor materials because of its outstanding mechanical, thermal and electrical properties [1,2]. Due to the mismatch in refractive index between air and the studied material, depth scale is artificially compressed and depth resolution can be worsened by orders of magnitude compared with the diffraction-limited values, about 2 μm for most of the commercial instruments [13,14] Neglecting these effects could lead to misinterpretations of the results. Several solutions have been proposed to work out this problem, including the use of immersion objectives to reduce the refractive index mismatch and numerical corrections of the data collected by dry objectives [15,16] Carefully considering this effect, confocal micro-Raman spectroscopy has been used to estimate shapes and sizes of distributed particles in heterogeneous systems [17]. Local stress at different points along diamond crystals by combining the depth-profiling and x-y mapping techniques
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