Sahara II 

Silicon Drift Detector

Silicon Drift Detector - Overview

The Sahara II Silicon Drift Detector (SDD) is PGT's latest addition to our extensive line of X-ray detectors. Evolving from the original Sahara SDD, introduced in 2001, Sahara II features high performance with no liquid nitrogen, no moving parts, no vibration and no maintenance. Sahara II is the ideal solution for people looking to relieve the burden and cost of liquid nitrogen and still maintain excellent X-ray performance. And because it's vibration-free, the Sahara is the best choice when working in challenging industrial environments where optimum resolution for lower energy X-ray spectroscopy has been impossible with traditional mechanical coolers.

Unlike LN cooled X-ray detectors, choices of detector to sample geometry are no longer dependent on liquid nitrogen dewer design. The main housing of the Sahara II is less than 200 mm long, less than 140 mm wide and less than 80 mm high. The detector end-cap can be specified for lengths of less than 100 mm to lengths greater than 300 mm. This versatility makes the Sahara II a much easier design consideration for applications ranging from tight spaced beam-line set-ups to the most demanding bench-top or on-line installations. In any configuration, you can depend on the best performance available for high rate, high throughput X-ray spectroscopy.

How it Works

Unlike a conventional Si(Li) detector, the SDD design features a unique electrical field shape and signal path, low capacitance relative to the active surface area, and a small anode and integral FET on the surface of the device (fig 1). This design results in optimum signal shaping and resolution specification at 1 microsecond, compared to 10 microseconds or longer for a conventional Si(Li). And the short shaping time yields another advantage - exceptional high-count rate performance with little compromise in energy resolution.

The Sahara detector is operated at -15°C and cools in less than 30 seconds utilizing air-cooled Peltier cooling, eliminating the need for liquid nitrogen or noisy coolant circulators. Si(Li) detectors require operation at near liquid nitrogen temperature. To reach this temperature, mechanically (or Peltier) cooled Si(Li) detectors require compressors, water chillers and other mechanical moving parts that cause vibration, require maintenance, and ultimately wear out. Cool down time for such a detector is measured in hours.

Excellence by Design

  • Unrivalled high resolution at high count rate with pulse reset preamp
  • Stable peak position with count rate and time
  • Cool down and warm up in seconds. Unique dual Peltier temperature control system for short-term and long-term stability
  • Proprietary crystal housing and window provides the best possible low energy sensitivity
  • Low energy detection down to Carbon with the 138 eV resolution Sahara
Spectrum collected at 100,000 cps

Performance

The Sahara II brings low energy performance into the realm once occupied only by Si(Li) detectors. Couple this with ultra-high count rates, and the Sahara II is clearly the performance leader. Featuring our proprietary thin window technology, the Sahara provides the best low energy sensitivity available - down to Boron with the 129 eV resolution Sahara and down to Carbon with the 138 eV resolution Sahara.

Plot of Mn peak position vs. count rate

Stability

In an EDS system, the detector is the most critical component affecting long-term performance and accuracy. In addition to excellent resolution and high count rates, peak stability directly affects the absolute accuracy of your measurements. The Sahara II detector delivers unprecedented stability over the entire count rate range. The result - reproducible results, time after time.

Versatility

Schematic of Variable Z detector motion

Variable Z (VZ) is a unique feature on PGT detectors that allows tilting the detector in the vertical direction while under vacuum. This lets you optimize count rate regardless of the microscope and sample geometry. Whether you need to make measurements at short working distances for low vacuum work, or longer working distances for lower magnification and large samples, Variable Z puts you in control. Doing EDS under variable pressure on a sample at 5mm working distanc one moment, then EDS/EBSD at 20mm the next moment…Try that with a fixed-geometry detector.

Convenience

While other detectors use Peltier cooling, they often require the addition of fluid circulators to remove the excess heat from the system, adding noise, vibration, and yet another device to maintain. Not the Sahara II. By utilizing the unique properties of the SDD, the Sahara is able to achieve peak performance at a temperature of -15° C, with a temperature cycle time of less than 30 seconds. Turn it on when you need it, off when you don't - it's that simple. Ideal for use in clean rooms and other environments where LN2 is unavailable, the Sahara offers long-term cost savings, convenience and safety benefits as well.

Sahara VS Mechanically/Peltier Cooled Si (Li)

  • 30 Second Cooldown vs hours
  • Operating Temperature -15° C vs. -200>° C
  • No moving parts vs. Mechanical compressors or water chillers
  • NO vibration vs. transfer of mechanical vibration to the electron column

Silicon Drift Detector Applications:

  • X-ray Fluorescence analysis
  • Accelerators:
    • Particle Induced X-ray Excitation
  • Synchrotrons:
    • X-ray Absorption Edge Spectroscopy
  • SEM & TEM X-ray Microanalysis
  • Electron Microprobes