AXIS Nova (XPS) Surface Analysis Spectrometer

The AXIS Nova combines XPS imaging and spectroscopic capabilities with a highly automated, large sample handling system and is the next generation of AXIS Nova spectrometer. The AXIS Nova is based on Kratos’ tried and tested AXIS technology with key features such as: magnetic and electrostatic transfer lenses; co-axial electron-only charge neutralization; spherical mirror and hemispherical electron energy analyzers. Novel technologies developed by Kratos including the delay-line detector for spectroscopy, and imaging modes and high energy X-ray excitation sources ensure the AXIS Nova is more than up to the most challenging research and development settings.

Built with simplicity in mind, the AXIS Nova has automated sample loading, orthogonal cameras for easy sample positioning and intuitive data acquisition software. Something that is unique to the AXIS Nova is the 110 mm diameter sample platen that allows unrivaled large sample handling and high sample throughput.

Even with all these features there is no concession to performance. The AXIS Nova is capable of high sensitivity, excellent energy resolution and fast, high spatial resolution imaging meeting the analysis needs of the most demanding applications.

Capabilities of the AXIS Nova

High Resolution Spectroscopy and Selected Area Spectroscopy

In spectroscopy mode the large radius hemispherical sector analyzer (HSA) ensures excellent photoelectron transmission guaranteeing high sensitivity and high energy resolution. By inserting an aperture into the electrostatic lens column and forming a virtual probe at the surface it can be used for small spot spectroscopy

This small area analysis technique eliminates sample charging problems and X-ray induced degradation seen with micro-focused X-ray sources. Small spot spectra can be acquired from areas as small as 10 µm diameter from anywhere within the field of view of the lens.

A unique electrostatic deflection system allows the position of the virtual probe to be deflected across the surface of the sample. The position for acquisition of small spot spectra can be defined by a simple mouse click from a parallel photoelectron image with the advantage that there is no need for translation of the sample; or the high resolution in-situ optical microscope image of the sample may be used to define the XPS analysis position directly.

The X-ray source on the AXIS Nova uses the large 500 mm Rowland circle geometry as a basis, which means less energy dispersion in the focused X-ray spot than systems based on smaller Rowland circles. This guarantees the highest energy resolution as demonstrated by a FWHM <0.48 eV for Ag 3d. The Al Kα X-rays are monochromated by a single toroidal backplane for ease of alignment of the X-ray spot with the analysis position. The X-ray anode is engineered to allow indexed movement of the anode surface with respect to the cathode, so that new anode surface may be exposed as required without breaking the vacuum. Being able to move the anode across 10 positions significantly increases the useful lifetime of the anode.

Quantitative Parallel Imaging

The AXIS Nova provides peerless performance for fast elemental and chemical state imaging. The spectrometer uses a 165 mm mean radius hemispherical analyzer (HSA) for spectroscopy coupled with the Kratos patented spherical mirror analyzer (SMA) for parallel imaging.

In parallel imaging mode photoelectrons at a discrete kinetic energy (binding energy) are focused on the two-dimensional photoelectron detector producing a direct image of the surface without scanning. The relative position of the photoelectrons is kept constant as they pass through the SMA allowing acquisition of parallel images in a matter of seconds in contrast to the slower pixel by pixel acquisition of XPS mapping.

By increasing the speed of parallel image acquisition it greatly reduces X-ray exposure to delicate samples, a huge benefit. Parallel XPS images of the sample surface with a spatial resolution of <3 µm can be acquired by using a 256 x 256 pixel array. Elemental or chemical differences may be easily imaged even if they are not visible by optical inspection. The properties and design of the SMA mean that the parallel images have both high spatial and high energy resolution. Data (below) show hydrocarbon and C-F chemical state images for a plasma patterned sample. Images may also be used to define the analysis position for small spot selected are spectra without translating the sample.

Charge Neutralization

The AXIS Nova charge neutralizer is based upon proven cutting edge technology used in over 250 AXIS spectrometers. The use of a coaxial low energy electron source within the field of the magnetic lens ensures that the ultimate base pressure of the spectrometer is maintained during analysis of insulating samples, as opposed to other neutralization systems which require an additional source of Ar+ ions.

The advanced design of the Kratos neutralizer ensures self-regulation of the system and works effectively on all classes of insulating materials including fibers, powders and thin films. When used in partnership with the monochromatic X-ray source, spectra with unparalleled energy resolution may be generated from electrically insulating materials as demonstrated by data showing FWHM of <0.68 eV on the ester component in polyethylene terephthalate (PET).

Large Sample Handling

The AXIS Nova sample handling and platen navigation system integrates in-situ optical microscopes with the acquisition software for quick and simple definition of sample analysis positions. Both full platen (110 mm diameter field of view) and high magnification (2 mm field of view) high resolution optical images can be saved into a dataset and recalled for sample positioning.  A large view port allows the user to see the platen in the analysis chamber giving complete confidence in sample location.

Delay-Line Detector

Kratos Analytical is still the leader in the development of imaging X-ray photoelectron spectrometers with the introduction of the delay-line detector (DLD). At the forefront of photoelectron detector technology, the DLD provides a single pulse counting detector for both spectroscopy and imaging experiments. Comprising a multi-channel plate stack above two orthogonal delay-line anodes and associated electronic control units, the DLD is at the core of the AXIS Nova.

With a large active area the DLD possesses 128 channels for photoelectron detection in spectroscopy mode. This high channel number means that, as well as collecting photoelectrons in usual energy scanning mode; the spectrometer can also be used to collect spectra with 128 data points without scanning the analyzer, also known as ‘snapshot’ spectroscopy. This mode allows an individual photoelectron peak to be collected in faster than 1 second with obvious advantages for data acquisition during depth profiling or dynamic surface characterizations.

When used in parallel imaging mode, photoelectrons with 2D spatial distribution are incident on the DLD. For every electron event the fast DLD control electronics convert the electron arrival position on each of the two delay-line anodes into an x, y co-ordinate. Integrating the signals over several seconds allows the generation of truly quantitative elemental or chemical images of the surface over a 65,500 pixel array. In the highest magnification imaging mode the spatial resolution at the surface is <3 µm. A key advantage of the digital DLD technology is that the system has inherent low noise characteristics with spike immunity assured.