a combination of these. Even if only the SE signal is desirable to use alone, at least one additional concentric electrode is recommended to employ in order to help in the separation from interference of BSE and also from other noise sources such as the skirt electrons scattered out of the primary beam by the gas. This addition may act as a “guard” electrode, and by varying its bias independently from the SE electrode, the image contrast can be controlled purposefully. Alternative control electrodes are used such as a mesh between anode and cathode. A multipurpose array of electrodes below and above the specimen and above the pressure limiting aperture of the ESEM has also been described elsewhere. The development of this detector has required devoted electronics circuitry, especially when the signal is picked up by the anode at high bias, because the floating current amplified must be coupled at full bandwidth to the ground amplifier and video display circuits (developed by ElectroScan). An alternative is to bias the cathode with a negative potential and pickup the signal from the anode at floating ground without the need for coupling between amplifier stages. However, this would require extra precaution to protect users from exposure to a high potential at the specimen stage. A further alternative that has been implemented at the laboratory stage is by the application of a high bias at the anode but by pickup of the signals from the cathode at floating ground, as shown in the accompanying diagram. Concentric electrodes (E2, E3, E4) are made on a copper-coated fiberglass printed circuit board (PCB) and a copper wire (E1) is added at the center of the disk. The anode is made again from the same PCB with a conical hole (400 micrometres) to act as a pressure limiting aperture in the ESEM. The exposed fiberglass material inside the aperture cone together with its surface above are coated with silver paint in continuity with the copper material of the anode electrode (E0), which is held at high potential. The cathode electrodes are independently connected to ground amplifiers, which, in fact, can be biased with low voltage directly from the amplifier power supplies in the range of ±15 volts without any further coupling required. On account of the induction mechanism operating behind the GDD, this configuration is equivalent to the previous diagram, except for the inverted signal that is electronically