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The principle cause of cracks in laser-welded, Au-coated, optoelectronic materials with a phosphorus (P)-containing underlayer is studied experimentally and numerically modeled. Experimental results find that the crack formation is due to the existence of a P-containing underlayer and is not due to the thickness of the Au plating layer. The P-containing underlayer introduced by a electroless plating process may generate a low melting, P-rich segregation layer during solidification. A finite-element method analysis is performed to evaluate the residual stresses variation of the low melting P-rich segregation layer. Results show that the high residual tensile stresses of the P-rich segregation layer are generated by solidification shrinkage. A crack may be initiated by this residual stress. Both experimental observations and numerical calculations indicate that the crack formation mechanism in laser-welded Au-coated optoelectronic materials is directly related to the low melting P-rich segregation layer and its associated high tensile stresses. Based on these results, a Ni underlayer with Pfree electroplating, instead of P-containing electroless plating, should be used prior to plating Au on optoelectronic materials to prevent crack formation in laser welded Au-coated optoelectronic materials.

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Eu2O3 (0.5 mol%) nanoparticles have been synthesized in a silica glass matrix by the sol-gel method at calcination temperatures of 700 • C and above. Compared with the parent material SiO2, this nano-glass composite system shows enhancement of dielectric constant and diffuse phase transition along with magnetodielectric effect around room temperature (∼ 270 K). The observed conduction mechanism is found to be closely related to the thermally activated oxygen vacancies. Magnetodielectric behavior is strongly associated with magnetoresistance changes, depending on the nanoparticle size and separation. Such a material might be treated as a potential candidate for device miniaturization.