This linear TOF MS instrument was designed to permit studies of the kinetic energy distributions of ions and electrons emitted from the surface of samples using femto- and atto-second laser pulses. For such a system it is required that the sample be raised up to the flight potential during ion measurement experiments. This is typically 1–3 kV, and is quite standard in techniques such as SIMS. A 25mm diameter dual microchannelplate detector (DMCP) and flange- mounted floating pre-amplifier is used to detect the ions and electrons, and a fast, multi-hit TDC with 250 pico second resolution is used to record the flight times of the ions/electrons. Kore has written a program that integrates the fast TDC hardware and software, and also uses the general spectroscopy software known as "Grams AI", from Thermo Galactic Corporation in the USA. This programme is particularly useful in research projects since Grams comes with an internal, high-level programming language that is accessible by the end user. This allows custom tools to be developed by the user for any specific task (such as the display of kinetic energy distributions).
The linear TOF MS instrument is designed to achieve 250 milli-electron volt energy step resolution (or better) on all ions (including hydrogen) when extracted and accelerated to a nominal 1 keV i.e. the spectrometer flight energy is the sum of the start energy being measured and an additional 1kV acceleration used to ensure collection of a large solid angle of emitted ions. With the exception of light ions such as hydrogen, this energy step resolution will also be obtainable at up to 2 keV of acceleration. For the one metre flight length, the plots below show energy step resolution achievable with a 250 pico second TDC over the range of 0–100 eV start energy for mass 28 ions with 1 keV acceleration (dotted Blue Line) and 2keV acceleration (redline). The second plot shows the worst case scenario for hydrogen. Thus, at 2 keV acceleration, mass 28 ions will have approximately 120 milli electron volts energy step resolution across the starting energy range 0 to 100 eV. The performance is much better at 1 keV acceleration, but this will inevitably be accompanied by loss of transmission compared to 2 keV. With a 25 mm diameter DMCP detector at one metre from the sample, the flight time differences due to path differences between central ray and outer ray is a minimal 0.0078 per cent
The instrument is designed primarily for ion spectroscopy measurements. Nevertheless, it is the case that with the ion lens set to zero volts, it is possible to make electron energy resolution measurements, provided the analyzer and indeed the client apparatus are constructed so as to minimise the effect of both inherent magnetism and also the earth's magnetic field. The best energy step resolution performance for electron spectroscopy that can be expected for the TOF analyser is that given by the equations of electron time-of-flight for a given emission energy, coupled with the 250 pico second time resolution of the TDC. For electron spectroscopy measurements a Mu metal shield is required. Kore manufactures the main flight tube from 316 stainless steel and the ion extraction lens components either de-gaussed 310 stainless steel and from "Colsibro"- a specialised nonmagnetic silica-bronze material.
The instrument is supplied with a cable set and a 19 inch rack mounted controller that incorporates:
- Detector power supply with enable and standby logic control
- Post acceleration facility (for low energy electrons)
- HV power supplies (for sample and extraction lens volts)
- Interlock facility
- ±5V pre-amplifier power supply
Last updated: 11:28 12/01/2012
© Kore Technology Limited 2005