Effect of laser pulsing on the composition measurement of an Al-Mg-Si-Cu alloy using three-dimensional atom probe

The effect of laser pulse energy on the composition measurement of an Al-Mg-Si-Cu alloy (AA6111) specimen has been investigated over a base temperature range of 20-80K and a voltage range of 2.5-5 W. Laser pulse energy must be sufficiently higher to achieve pulse-controlled field evaporation, which is at least 0.9 nJ with a beam spot size of about 5 mu m, providing an equivalent voltage pulse fraction, similar to 14% at 80K for the alloy specimen. In contrast to the cluster composition, the measured specimen composition is sensitive to base temperature and laser energy changes. The exchange charge state under the influence of laser pulsing makes the detection of Si better at low base temperature, but detection of Cr and Mn is better at a higher temperature and using higher laser energy. No such effect occurs for detection of Mg and Cu under laser pulsing, although Mg concentration is sensitive to the analysis temperature under voltage pulsing. Mass resolution at full-width half-maximum is sensitive to local taper angle near the apex, but has little effect on composition measurement. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.