AXIS Supra (XPS) surface analysis instrument

The spectroscopic and imaging performance of an X-ray photoelectron spectrometer define its ability to perform in the most demanding research and development laboratories. The AXIS Supra excels at both and combines the highest level of automation currently available with the flexibility to incorporate complementary surface analytical techniques. Designed for ease of use with automated sample loading and exchange, integrated camera system, easy to use ESCApe data acquisition and processing software, the AXIS Supra really is made to measure.


Based on patented AXIS technology the AXIS Supra is an instrument with unrivalled spectroscopic and imaging performance. The mu-metal analysis chamber is designed to accommodate optional excitation sources such as an achromatic Al/Mg X-ray source, UV He discharge lamp for ultra-violet photoelectron spectroscopy (UPS) and field-emission electron source for scanning Auger electron spectroscopy (AES) and secondary electron microscopy (SEM). Sample preparation and surface modification options are easily fitted to the sample introduction chamber, also referred to as the Flexi-lock. Options available for this chamber include sample heating and cooling, air sensitive sample transporter, broad spot ion source, crystal cleaver and glove box. An optional third chamber, the surface science station, provides a dedicated UHV chamber which can be configured with a manual sample stage and a range of options for surface science studies and in-situ sample preparation.

CAPABILITIES OF THE AXIS Supra

LARGE AREA, HIGH SENSITIVITY XPS
The AXIS Supra is first and foremost a high performance X-ray photoelectron spectrometer. Efficient collection of photoelectrons by the magnetic and electrostatic lenses combined with the high transmission 165 mm mean radius hemispherical analyser ensures that the AXIS Supra has unrivalled sensitivity and resolution.Spectra are collected in traditional scanned mode or fast, unscanned snap-shot mode where spectra may be acquired in less than a second using the delay-line detector (DLD).
Key attributes include:
• Easy detection of light elements.
• Excellent signal-to-noise, even at low concentrations.
• Fast data acquisition

SMALL SPOT, SELECTED AREA SPECTROSCOPY
Selected area spectroscopy is achieved by inserting a motorised aperture into the electrostatic lens column, forming a virtual probe at the sample surface. This approach means that selected area spectroscopy can be performed with either the monochromatic or achromatic dual anode X-ray source. Spectra are acquired from pre-defined analysis areas as small as 15 μm diameter from any position within the field of view of the lens. Key attributes include;
• Pre-defined small spot analysis areas.
• Optimised x-ray illumination for selected area performance.
• Click and analyse multipoint spectroscopy without sample movement.

HIGH ENERGY RESOLUTION
The primary application of the AXIS Supra is as a photoelectron spectrometer for chemical statecharacterisation of the surface. The 500 mm Rowland circle monochromated Al Ka X-ray source and optimised electron optics contribute to the excellent energy resolution performance.
• Unambiguous identification of chemical shifts.
• Guaranteed energy resolution on insulating and conducting samples.

FAST PARALLEL IMAGING
Parallel imaging, where an image of the sample surface is projected via the unique spherical mirror analyser (SMA) onto the 2D delay-line detector, allows the lateral distribution on surface chemistry to be investigated. Fast parallel imaging produces images with higher spatial resolution than the more traditional mapping approach.
• Ultimate spatial resolution of 1 μm at the highest magnification.
• Simple mouse click on image to define area of interest for selected area spectroscopy.
• Stitched imaging - combining parallel images with stage movements allows high spatial resolution images to be acquired over areas of several millimetres.
• Quantitative imaging – the unique SMA operates in fixed analyser transmission which ensures that energy resolution is constant as a function of kinetic energy allowing quantitative chemical state imaging.
• Spectromicroscopy – easy acquisition of spectra from images where a series of images are acquired over a defined energy range to produce a spectrum at each pixel.

UNRIVALLED INSTRUMENT AUTOMATION
Complete automation sets the AXIS Supra apart from any other X-ray photoelectron spectrometer currently available. Unattended sample transfer and exchange during analysis is realised through coordination of the Flexi-lock sample magazine and autostage in the sample analysis chamber. Auto exchange of sample holders during analysis ensures extremely high sample throughput removing the rate-limiting step previously associated with sample loading. Motorisation of both X-ray source and X-ray mirror automates calibration. Switching between monochromated Al Ka and the optional Ag La excitation sources is under full computer control. Where gas introduction to the vacuum system is required such as ion etching or UPS, gas handling and pressure regulation is fully automated. Automation extends to data interpretation with auto-peak ID integrated into the ESCApe processing software.
• Automated sample introduction and exchange.
• Computer controlled X-ray source and mirror.
• Automated gas introduction and pressure regulation for ion sources and UV lamp.

The AXIS Supra offers a choice of ion sources, the Minibeam 4 high flux Ar+ ion source or the Minibeam 6 gas cluster ion source (GCIS). Both ion sources are fully integrated and controlled through the ESCApe acquisition software which provides an easy user interface for depth profiling and sample cleaning. Azimuthal rotation during depth profiling helps to improve interface resolution of depth profiles. Gas handling is fully automated including pump/purge sequences to facilitate changing to He gas for ion scattering spectroscopy (ISS). The Minibeam 4 monatomic Ar+ ion source operates with continuously variable beam energies between 4 keV and 500 eV. The precision ion column incorporates a bend for neutral suppression as well as the ability to operate in column float mode producing a high ion flux at low energies for improved interface resolution whilst retaining high etch rates.

The multi-mode Arn+ GCIS is as close to a universal ion source as is currently available. The use of Arn+ clusters for sputter depth profiling organic materials has allowed the successful concentration depth profiles of many complex multi-layer materials including organic LEDs and organic photovoltaics. 20 keV Arn+ cluster modes have also been successfully used to minimise ion induced chemical changes while sputter profiling inorganic materials such as titanium dioxide. The GCIS may also be operated in monatomic Ar+ mode for depth profiling metals or inorganic materials and used with He, generation He+ primary ions for the optional technique of ion scattering spectrometry (ISS).

The Surface Science Station is a dedicated chamber interfaces directly with the sample analysis chamber and is designed to house a number of optional surface characterisation techniques including quadrupole secondary ion mass spectrometry (SIMS), low energy electron diffraction (LEED) or inverse photoemission electron spectroscopy (IPES).  In-situ surface preparation and modification options may be added to the SSS including heating and cooling; thin film deposition; crystal cleavers, low pressure gas doser etc.  The surface science station (SSS) has two experimental locations, the first at the centre of a cluster of flanges and a second at the end of the linear transfer mechanism.  The SSS is typically configured with a manual stage for use with 15mm diameter stubs.  Up to 3 sample stubs may be stored in the SSS. 

The SSS is separated from the sample analysis chamber by an automatic gate valve controlled by the ESCApe data-system.  The operation of the valve is interlocked with vacuum and position of the linear transfer mechanism.

High resolution XPS and imaging analysis can be complemented with additional surface characterisation techniques in the sample analysis chamber including: UV discharge source for ultraviolet photoelectron spectroscopy (UPS), Schottky field emission electron source for Auger electron spectroscopy (AES), scanning Auger microscopy (SAM) and secondary electron microscopy (SEM), reflected electron energy loss spectroscopy (REELS) and ion scattering spectrometry (ISS). Control of these additional analytical techniques is integrated seamlessly into ESCApe acquisition software so that a truly multi-technique approach can be taken to materials surface characterisation using the AXIS Supra.


Genuine multi-technique capability ensures that addition of optional analytical techniques will not compromise the performance of XPS modes of acquisition, even if added as an upgrade in the future. For dedicated surface science experiments an optional surface science station may be configured with additional techniques such as: low energy electron diffraction (LEED), quadrupole secondary ion mass spectrometry (SIMS) or inverse photoemission spectroscopy (IPES).

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