Рентгеновский фотоэлектронный спектрометр, объединяющий в себе передовые характеристики и легкость в работе, обеспеченную новым программным обеспечением ESCApe и автоматизированным трансфером образцов. AXIS Supra является улучшенной и дополненной моделью, которая полностью заменила известный спектрометр AXIS Ultra.
Рентгеновский фотоэлектронный спектрометр AXIS Supra представляет собой полноценную систему для реализации метода РФЭС высокого разрешения, более того наличие запатентованного анализатора дает возможность проводить методику рентгеновской фотоэлектронной микроскопии с латеральным разрешением в 1 мкм. Тем самым позволяя строить карты распределения элементов и их химических состояний по поверхности за считанные минуты. Благодаря тому, что камера спектрометра оснащена большим количеством фланцев, AXIS Supra становится многофункциональным прибором и способен совместить в себе такие методы анализа, как: ультрафиолетовая фотоэлектронная спектроскопия (УФЭС), Оже-электронная спектро- и микроскопия (ОЭС, ОЭМ), сканирующая электронная микроскопия (СЭМ), спектроскопия ионного рассеяния (ISS), а также другие необходимые методы.
Parallel imaging and spectra from images
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.
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.
Sample Analysis Chamber
Mu-metal chamber, 400 l/sec Turbomolecular pump, Auxiliary pumping by titanium sublimation pump.
Flexible sample load lock, Sample magazine (up to 3 sample holders), Turbomolecular pump (240 l/sec) with oil-free scroll pump.
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)
Multichannel plate array with delay-line detector
Scanned & snapshot spectroscopic acquisition
2D parallel imaging
Co-axial electron only
Sample Mounting & Handling
Standard sample holder
Combination sample holder with 15mm stub
Rotation sample (for rotation during profiling)
ESCApe integrated acquisition and processing software for automated acquisition and instrument control.
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 poly-aromatic hydrocarbon ion source (Minibeam 5) is a dual mode ion source, using either coronene (C24H12+ ) or monatomic Ar+ions for sputter profiling. Using the ion source in coronene mode allows the depth profiling of organic samples whilst the ability to switch to Ar+ ions retains the capability of successfully profiling inorganic and metallic samples. The ions are extracted from the source region, accelerated to maximum energy of 20 keV (coronene) or 5 keV (Ar) focussed using standard ion optics.
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.
Analysis area (spot size)
Slot mode: 700 x 300 μm
Small spot modes (diameter):110 μm, 55 μm, 27 μm and 15 μm
The spherical mirror analyser used for parallel imaging in combination with the magnetic and electrostatic lenses provides a range of predetermined analysis areas of ca. 800 x 800 μm, 400 x 400 μm and 200 x 200 μm fields of view.
Guaranteed spatial resolution in imaging mode: 1 μm
XPS Specifications – Al Monochromator
Resolution – 0.48 eV
Intensity – 400 000 cps
Performance on insulators
X-ray Photoelectron Spectroscopy (XPS)
X-ray photoelectron spectroscopy (XPS), also known as ESCA (electron spectroscopy for chemical analysis) provides both elemental and chemical state information virtually without restriction on the type of material which can be analysed. The sample is illuminated with x-rays – monochromatic or unfiltered Al Kα or Mg Kα – and photoelectrons are emitted from the surface. The kinetic energy of these emitted electrons is characteristic of the element from which the photoelectron originated. The position and intensity of the peaks in an energy spectrum provide the desired chemical state and quantitative information.
The chemical state of an atom alters the binding energy (BE) of a photoelectron which results in a change in the measured kinetic energy (KE). The BE is related to the measured photoelectron KE by the simple equation; BE = hν – KE where hv is the photon (x-ray) energy. The chemical or bonding information of the element is derived from these chemical shifts.
In modern spectrometers the x-rays are energy filtered or monochromatised using a quartz crystal to give x-rays with very little energy spread. This monochromatic x-ray illumination of the sample enables high energy resolution of chemical shifts as well as detailed study of line profiles and subtle bonding changes evident in the valence band.
Photoelectrons may also be collected from the surface in two dimensions to generate elemental or chemical state images of the surface.
Ultraviolet Photoemission Spectroscopy (UPS)
Ultra violet photoemission spectroscopy (UPS) is analogous to XPS but the excitation source is a helium discharge source. Depending on the operating conditions of the source the photon energy can be optimised for He I = 21.22eV or He II = 44.8eV which is significantly lower energy than Al or Mg Kα used in XPS. As with XPS the BE is related to the measured photoelectron KE by the simple equation; BE = hν – KE where hv is the photon (x-ray) energy. The consequence of this lower photon energy is that only the low binding energy valence electrons may be excited using the He source. A further consequence of the low photon energy is UPS is more surface sensitive than XPS and thus very sensitive to surface contamination.
UPS is very useful as a technique to determine the work function of the material being analysed and is finding increasing application in characterisation of organic and inorganic photovoltaics, organic LEDs.
Auger Electron Spectroscopy (AES)
AES employs a beam of electrons as surface a probe. As a result of electronic rearrangements within the atoms, Auger electrons characteristic of each element present at the surface are emitted from the surface. Only those electrons that emerge from the topmost atomic layers contribute to the spectrum so giving rise to the high surface specificity of this technique. Auger electron spectroscopy (AES) detects all elements except hydrogen and helium usually to a sensitivity better than 1 atom percent of a monolayer. Since the probe electrons can be focused to diameters <0.5μm high spatial resolution analysis (scanning Auger microprobe, SAM) can be performed. Rastering the focused electron beam synchronously with a video display, using scanning electron microscope (SEM) techniques, produces physical images and element distribution maps of the surface. The ability to pinpoint exact areas for analysis makes AES especially suited to investigations of the small features of microelectronic circuits or very fine surface particles.
Ion Scattering Spectroscopy (ISS)
A beam of positive ions frequently derived from He or Ar is directed at the surface. Some of these ions are reflected with the loss of energy appropriate to the simple binary elastic collision of the ion beam with a particular surface atom. At any fixed scattering angle, defined by the angle between the ion source and the analyser, the energy loss of the ion is dependent only on the mass of the surface atom causing the scattering. An ISS spectrum is easily obtained by recording the number of scattered primary ions collected per second as a function of their energy from zero to the energy of the primary beam. The technique is uniquely sensitive to the outermost layer of the surface and is complementary to SIMS (secondary ion mass spectrometry).