AXIS Supra (XPS) surface analysis instrument

AXIS SupraTM is an X-ray photoelectron spectrometer (XPS) with unrivalled automation and ease of use for materials surface characterisation.  The patented AXIS technology ensures high electron collection efficiency in spectroscopy mode and low aberrations at high magnifications in parallel imaging mode.  XPS spectroscopy and imaging results can be complemented by additional surface analysis techniques such as: ultraviolet photoemission spectroscopy (UPS); Schottky field emission scanning Auger microscopy (SAM) and secondary electron microscopy (SEM) and ion scattering spectroscopy (ISS).  The AXIS Supra replaces the AXIS Ultra DLD as Kratos’ flagship x-ray photoelectron spectrometer.

Automated sample handling meets high performance

The AXIS Supra™ is based on the proven AXIS technology comprising: magnetic and electrostatic transfer lenses; co-axial electron only charge neutralisation; spherical mirror and hemispherical electron energy analysers.  Kratos developed innovations such as the delay-line detector for spectroscopy and imaging modes and high energy, motorised, X-ray excitation sources ensure the AXIS Supra is capable of performing in the most demanding research and development environments.  With market leading performance in both imaging and spectroscopy modes the AXIS Supra combines the highest level of automated sample handing with flexibility to incorporate complimentary analytical techniques in the analysis chamber.

The AXIS Supra is designed for ease of use with automated sample loading, optical microscopes for sample identification and positioning and intuitive data acquisition and processing software.  However, users do not need to compromise performance for ease of use and automation.  High sensitivity, excellent energy resolution and fast, high resolution imaging meet the analysis needs of the most demanding applications.

Vacuum System

The sample analysis chamber (SAC) is manufactured from mu-metal and has fifteen ports with line of sight to the sample analysis position.  The chamber has been designed to accommodate optional excitation sources such as a field emission electron source, UV He discharge lamp and achromatic Al/Mg Ka x-ray source in addition to the large 500 mm Rowland circle monochromatic Al Ka x-ray source.  Ultra high vacuum is achieved in the SAC by an oil-free scroll backed turbomolecular pump with a titanium sublimation pump providing secondary pumping.

Samples are introduced into the sample analysis chamber through the Flexi-lock.  This turbomolecular pumped chamber contains the automated sample magazine with storage for up to 3 large sample holders.  As suggested by its name, the Flexi-lock is designed to accommodate sample preparation and surface modification options including: sample heating and cooling; inert sample transporter; broad spot ion source and glove box.  The Flexi-lock also houses the large field of view optical camera for acquiring an image of the full sample holder which is the first step in the sample identification and analysis work flow.

The optional surface science station provides a dedicated UHV chamber for surface science studies and can be configured with a number of surface science techniques.  This chamber is typically fitted with a manual sample stage for samples mounted on 15 mm diameter sample stubs.  Samples may be introduced either directly from the sample analysis chamber or via a small volume load-lock.

Work flow description

Samples are mounted on the large sample holder ready for introduction to the Flexi-lock.  Up to 3 sample holders may be stored on the automated sample magazine and exchanged to the analysis chamber stage automatically.  As soon as the sample holder is loaded on the sample magazine the orthogonal camera takes an optical image of the whole sample holder during the ‘pump’ cycle.  This has the advantage that sample analysis positions may be selected from the sample holder image and the analysis work flow can be defined using the ESCApe™ acquisition software during the pump cycle.  When the Flexi-lock has reached the required pressure the automated sample holder transfer sequence starts with the holder transferred to the stage in the sample analysis chamber.  At this point the predefined analysis workflow may be started.  All aspects of analysis are defined in a simple, automated workflow environment within the ESCApe software from routine large area survey spectrum to more complex sputter depth profiles or non-destructive depth profiling by angle resolved XPS.  For samples which require complex examination the instrument is operated interactively using features such as the high lateral resolution XPS imaging and motorised zoom optical microscope helping to get the best results possible.

Efficient collection of photoelectrons by the magnetic and electrostatic lenses combined with the large 165 mm mean radius hemispherical analyser ensure that the AXIS Supra boasts unrivalled sensitivity in large area analysis mode.  The 500 mm Rowland circle monochromatic X-ray source irradiates the sample with relatively low flux of X-rays so that spectra can be collected from sensitive samples with confidence that no X-ray degradation will occur.  Outstanding spectral resolution is not limited to conducting samples.  The low energy, electron only charge neutralisation system allows photoelectron spectra to be collected from insulating, topographic samples with ease.

Survey spectrum from insulating PET acquired in 30 s in large area mode.  High resolution C 1s spectrum acquired at 10 eV pass energy demonstrating minimum guaranteed performance.

The AXIS Supra has market leading imaging spatial resolution of 1um.  Fast parallel imaging allows the lateral distribution of surface chemistry to be investigated.  Photoelectron images from the surface are projected onto the 2-dimentional delay-line detector thus collecting XPS images much faster, and at higher resolution, than the more traditional sequential rastered beam approach.  The unique spherical mirror analyser (SMA) operates in fixed analyser transmission mode ensuring that the energy resolution of photoelectron images is constant for all kinetic energies.  This is of particular importance for quantitative imaging applications.  Parallel images may also be acquired at lower pass energies to improve the energy resolution, analogous to spectroscopy mode, making chemical state imaging routine.

 

Au 4f7/2 parallel image of Au pattern on Si wafter.  10 um lines with 5 umm spcing between the lines.  The reconstructed line scan from this image demonstrates an 80:20 edge measurement of 1.1um.

The low spherical aberration of the electron optics ensures that the image of the surface can be magnified onto the detector with very little distortion resulting in high spatial resolution images.  Parallel imaging at the highest magnification gives a guaranteed spatial resolution of 1 um.

The AXIS Supra can also be used to acquire spectra from images, known as spectromicroscopy, where a series of images are acquired over an energy window.  Such data contain a spectrum at each of the 65,500 pixels.  These datasets are ideally suited to multivariate analysis which can be used to partition the data from noise and reconstruct spectra form single pixels.  These spectra may then be used to reconstruct images corresponding to fitted components thus providing a method for quantitative chemical state imaging that would not be possible in conventional parallel imaging XPS.

 

The AXIS Supra can be configured with a standard floating column monoatomic Ar+ ion source, the polyaromatic hydrocarbon (PAH) ion source or the Gas Cluster Ion Source (GCIS) depending on the type of sample to be profiled.

The monatomic Ar+ ion source (Minibeam 4) operates with continuously variable beam energies between 4 keV and 50 eV. The precision ion column incorporates a bend for neutral suppression as well as the ability to operate in floating mode producing high current densities at low ion energies for improved interface resolution and fast etch rates even at low ion acceleration voltage.

The multi-mode Ar Gas Cluster Ion Source (GCIS) (Minibeam 6) is capable of generating Arn+ clusters consisting of hundreds or even thousands of Ar atoms.  As the energy of the ion is shared by all atoms in the cluster the energy per projectile atom, or partition energy, can be as low as a few electron volts.  At these energies cluster ions only sputter material from the near-surface region leaving the subsurface layer undamaged.  The use of cluster ions for sputter depth profiling organic materials has led to successful depth profiles from many different types of multi-layer materials such as organic light emitting diodes and organic photovoltaics.  The GCIS can also be operated in the standard monatomic Ar+ mode which is better suited to conventional depth profiling inorganic materials.

All control and status read-backs are displayed in the ESCApe acquisition software with pre-defined operating conditions provided in a look-up table. Similarly the argon gas supply for the ion source can be turned on and off as required during unattended operation with pressure in monatomic mode controlled by an automatically regulated piezoelectric valve.

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.

Vacuum System   

Sample Analysis Chamber

Mu-metal chamber, 400 l/sec Turbomolecular pump, Auxiliary pumping by titanium sublimation pump.

Flexi-Lock

Flexible sample load lock, Sample magazine (up to 3 sample holders), Turbomolecular pump (240 l/sec) with oil-free scroll pump.

Excitation Sources

High power monochromatic Al Ka X-ray source

   500 mm Rowland circle

   Computer controlled, single quartz toroidal backplane

   Full computer control with read-back and interlocks

   Motorised multi-position Al or Al/Ag anode (option)

Dual Al Ka  / Mg Ka  achromatic X-ray sources (option)

Ultra Violet lamp He I / He II discharge (option)

Schottky field emission electron source (option)                          

Electron Energy Analysers

   180° hemispherical analyser (spectroscopy)

   Spherical mirror analyser (parallel imaging)

Photoelectron Detector

   Multichannel plate array with delay-line detector

     Scanned & snapshot spectroscopic acquisition

     2D parallel imaging

Charge Neutralisation

   Co-axial electron only

Sample Mounting & Handling

   Standard sample holder

   Combination sample holder with 15mm stub

   Rotation sample (for rotation during profiling)

Software

ESCApe integrated acquisition and processing software for automated acquisition and instrument control.

 

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