The SGM Beamline has a number of capabilities available to both general and advanced users. Although there is considerable overlap between categories, these capabilities can be divided into Experiment Techniques, Available Detectors and Detection Methods, and Experimental Support Features.

Experimental Techniques

Near Edge X-Ray Absorption Fine Structure (NEXAFS)

NEXAFS is a technique used to study the structure near to the absorption edge. Used to study the region within 10's of eV of the edge, the technique is also known as X-Ray Absorption Near Edge Structure (XANES) although NEXAFS is used to refer specifically to the Soft X-Ray regime. With sufficient resolution, NEXAFS is a spectroscopic technique that is not only element specific, but also offers information regarding bond length and bond angle. This technique is normally used in the SSA Endstation at the SGM Beamline, and utilizes both Total Electron Yield (TEY) and Fluorescence Yield (FLY) methods. Below is a sample spectrum from a broad NEXAFS scan.

Extended X-Ray Absorption Fine Structure (EXAFS)

When absorption edges are sufficiently far apart, the EXAFS technique can be used to probe the local coordination of a sample. Since EXAFS is also element specific, this combination allows the technique to determine chemical state and is very useful for environmental chemistry in particular. As the SGM is a Soft X-Ray beamline, only higher energy edges can be studied in this fashion. Like NEXAFS, EXAFS is an absorption spectroscopy and uses similar detection methods such as TEY and FLY. The EXAFS spectrum for MgO is shown below.

[Time Resolved] X-Ray Excited Optical Luminescence (XEOL/TRXEOL)

Under certain conditions, X-Ray excitation causes samples to fluoresce strongly enough in the visible light range for the light to be seen. Using an optical spectrometer, the XEOL technique can give information about the decay processes in a sample. Furthermore, the CLS can be operated in a single-bunch mode and a streak camera can be added to the experimental set-up to allow for time resolved studies to take place. The TRXEOL technique can offer further information about the source of the luminescence, particularly whether emissions are likely due to surface states, defects, or quantum confinement effects. Below are XEOL and TRXEOL spectra.

X-Ray Photoemission Spectroscopy (XPS)

SGM has an endstation area devoted to XPS studies. This technique measures the energy of electrons ejected from a sample and is useful for studying the binding energies of sample systems. XPS is also highly surface sensitive - only capable of probing the first 10nm of a sample. Thus, the technique can be used either to characterize surface structures or to determine surface contamination. Additionally, the binding energy information gives the XPS technique the ability to identify the electronic or chemical state of the surface of a sample. As the SGM's XPS chamber is a UHV chamber, cleaving a sample can allow for bulk properties to be measured as well. Below are XPS spectra taken on the SGM Beamline.

Gas Phase Spectroscopy

The second endstation area can also be equipped to study Gas Phase Spectroscopy on the SGM Beamline. By filling an isolated section with the sample gas, a direct absorption spectrum can be collected via a transmission measurement. The resolution of the SGM Beamline was experimentally determined using this technique on known standards; however, the technique is still a valuable experimental tool. The Low Energy Grating (LEG) of the SGM was used to collect the Argon spectrum below.

Detectors and Detection Methods

Total Electron Yield (TEY) [Method]

Samples studied in both endstations on the SGM Beamline can use TEY as a detection method.  When samples that have been excited by x-rays decay back to the ground state, they shed electrons, leaving a small positively charge on the sample. As long as the sample is attached properly to the sample plate, the drain current required to neutralize this charge can be measured. This magnitude of this drain current can often be used as a measurement of the x-ray absorption cross section.

Total Fluorescence Yield (FLY) [Method]

After an electron is excited, decay processes occur to "vent" the excess energy. Many of these decay processes result in a photon being released by the sample. The SGM Beamline is capable of detecting these emitted photons, and a proportional current can be measured. Unlike TEY, which is surface sensitive, FLY measurements tend to be bulk sensitive (~100nm). This type of measurement is generally taken using the MCP Detector.

Energy-Discriminant Fluorescence Yield (FLY) [Method]

Beyond traditional Total FLY measurement capabilities, the SGM Beamline can also analyze the energy of the emitted photons using a 30 mm^2 silicon drift detector (SDD).  The resolution of this detector is sufficient to separate the fluorescence from many elements (~150 eV).  Using this method, the partial FLY, or PLY, can be monitored, often resulting in an improved sensitivity over the FLY method.  Fluorescence from other, non-resonant elements can also be monitored, which can provide additional information about the x-ray absorption cross section.

Micro-Channel Plate Detector (MCP) [Detector]

The SGM Beamline has a dedicated detector (the MCP Detector) for Total FLY measurements. The MCP acts as a photon amplifier - it takes a small photon signal in and gives a proportionally greater electrical signal out. This signal can be measured and recorded on the beamline. Since the MCP does not discriminate based on energy, the output is the total incoming photon signal. To stop electrons from creating a signal on the MCP, a bias voltage is applied.

PGT-Sahara Silicon Drift Detector (PGT/SDD) [Detector]

The PGT Detector allows users to monitor many energy regions simultaneously. The detector has a range from about 200eV up to the maximum beamline energy (2000eV) with a resolution of ~150eV. Additionally, the CLS has developed a software interface for the detector, so the data acquisition can be handled through EPICS on the beamline (rather than through the proprietary control software).

Ocean Optics QE65000 Spectrometer [Detector]

Connected with a fiber-optic feedthrough, the Ocean Optics Spectrometer is used to measure XEOL spectra on the SGM Beamline. The spectrometer has a linear CCD sensitive to photons between 200 and 1100nm. This range allows for the detection of photons in the visible range (400 to 700nm) as well as the near infrared and the near ultra violet. The CLS has also developed software to run this detector and collect data using the EPICS system, rather than the proprietary control software. This allows the Ocean Optics Spectrometer to be controlled and collected along with the rest of the beamline.

Streak Camera [Detector]

For time resolved XEOL measurements, a Hamamatsu C5680 streak camera is used. Optical photons coming from the sample pass through a Bruker IS200 spectrograph and illuminate the entrance slit of the streak camera.  In the streak camera, the temporal information on the incident photons is converted to spacial information.  The result is a streak image with wavelength on the horizontal axis and time on the vertical axis.  The temporal resolution of this system is limited by the duration of the photon pulse from the storage ring (nominally 35 ps r.m.s).

Scienta SES100 Photoemission Spectrometer [Detector]

The SES100 is the SGM's dedicated XPS detector. Built by VG Scienta, the system contains a hemispheric analyzer, a high voltage supply, and a CCD detector. While the system is optimized to service the 250eV to 1500eV range, measurements up to 2000eV are possible.  The detector resolution is ~100 meV. Considerable work has been done by the CLS to bring the Scienta into the fold at the beamline, so the detector can be run in three different modes: stand-alone, beamline triggered, or beamline-controlling. Stand-alone scans work by fixing the beamline settings (energy, undulator, exit slit) and scanning using the SES100 software. The second mode involves using the beamline software to trigger the current scan on the SES100 software. The final mode has been recently developed, which allows partial control of the beamline settings from the SES100 software.

Residual Gas Analyzer (RGA) [Detector]

The partial pressures of gases with masses of up to 200 AMU can be monitored in either endstation.

Experimental Support Features

Manipulator Arm

The SSA Endstation boasts a Thermionics high precision XYZ stage which controls the position of the manipulator in the chamber. In addition to scanning position (on a sample), the manipulator has been integrated into the IDAV interface to allow for position saving and recalling. This capability also allows for easier transitions between the transfer position and the general measurement position.

Heating and Cooling

Both the Scienta Endstation and the SSA Endstation offer the ability to cool samples using a liquid Helium cryostat (if liquid Helium temperatures are not required, liquid Nitrogen can be used). Additionally, the SSA Endstation is equipped with a ceramic button heater. While extra care is required, this gives the endstation an effective temperature range of ~15K to ~1500K.

Sample Garage

Both endstations on the SGM Beamline also offer a sample garage to make sample transfers easier and less frequent. The sample garages allow for three different sample plates to be placed into the load lock at a time.

Glovebox

We have developed a glovebox system for the preparation and loading of reactive samples in an inert environment.