Voltage controlled negative differential resistance (NDR) and electron emission (EE) have been observed in thin metal films, subsequent to the application of a forming voltage. The effect of a post-forming deposition of a thin insulating overlayer using the Langmuir-Blodgett (LB) technique is reported. Significant enhancements of the magnitudes of both the conduction current and emission current are observed. Furthermore, the voltage at which the NDR occurs and the sharpness of the current-voltage (I-V) characteristics are increased. The effect on the peak current of a change in the thermal conductivity of the sample is discussed. It is suggested that this and the intrinsic film resistance are responsible for the increased sharpness of the I-V characteristics and the change in peak position.