Fig.1 Schematic of air-to-vacuum transmitting system.
Fig.2 Installation in atom probe chamber.
The traditional counter electrode design with no ground connection results in significant signal reflectron and loss . We design an air-to-vacuum transmitting system illustrated in Fig 1. It is essentially composed of a microstrip circuit interconnected to UHV SMA cables. The center of the microstrip TL is pierced with a via presenting a diameter of Ø=350µm. The hole serves as a microelectrode, and the sample is directly excited by the electrical pulse, atoms are field evaporated from the sample and are projected through the hole to the position sensitive detector. The system has a large electrical bandwidth (>2GHz) allowing the signal to be applied to the microelectrode without degradation and to be observed during atom probe analyses with an oscilloscope.
Oscilloscope and attenuator
Generated electric pulses were measured by the Agilent infiniium 54855A sampling oscilloscope with a string of high voltage attenuators, as shown in Figure III‑17. The oscilloscope provides a full real-time bandwidth of up to 6 GHz and is supported on every channel by the 20 Gs/s sampling rate. The attenuation ratio of the voltage attenuators is about 1250 (-62 dB). Due to the maximum permissible voltage of the first attenuator (Barth Model: 102 series), the measurable voltage pulse is less than 2 kV.
Fig.3 High voltage pulse measurement: (a) Oscilloscope Agilent (model: infiniium 54855A) with the bandwidth 6 GHz, 20 Gs/s sample rate. (b) A series of attenuators (-62 dB).