The invention relates to unsaturated polyester resins and more particularly polyester resin compositions curable at room temperature and comprising divinyl ethers. The method includes the following steps. In order to review a semiconductor specimen, an entire semiconductor wafer or a sub-region of a wafer is flooded with electrons from the flood gun so that the wafer surface is charged to a certain voltage level. Each quartz-crystal piece has a respective excitation portion that vibrates when electrically energized and a respective frame portion surrounding the excitation portion.