There is a contour level option, I　�ｄｊｕｓｔ　ｔｈｅ　contour ｖ�ｌｕｅ　�ｆ　ｔｈｅ　ｎｅｇ�ｔｉｖｅ　�ｅ�ｋ　to ｖｅｒｙ　ｌ�ｗ，　ｌｉｋｅ　10^ -9, the negative peaks will not show in the spectra. hope it is what you what to know. thank you

Jenny