Meet your demands for increased analytical performance and flexibility with the Thermo Scientific™ ESCALAB™ 250Xi X-ray Photoelectron Spectrometer (XPS) Microprobe, which combines high sensitivity with high resolution quantitative imaging and multi-technique capability.

Expandable, optimized, and multi-technique instrumentation with unparalleled flexibility and configurability, the ESCALAB 250Xi is extremely sensitive, producing high-quality survey scans in seconds. System control, data acquisition, processing and reporting are seamlessly integrated by the powerful Themro Scientific™ Avantage Data System. The cutting-edge technology, driven by intuitive software and hardware, provides world class results and productivity. The ESCALAB 250Xi provides the capability for ‘signature-free’ parallel imaging with a resolution of < 3 µm.

For small-area spectroscopy, the instrument uses three methods to define the analysis area:

• Source-defined area selection - The monochromated X-ray beam can be focused to spot sizes ranging from 900 µm to 200 µm.
• Lens-defined area selection - Computer-controlled irises in the transfer lens can be set to provide a lateral resolution down to 20 µm.
• Retrospective spectroscopy from images - Using the high-resolution parallel imaging, spectra from areas down to ~5 µm can be obtained.

X-ray Source

The ESCALAB 250Xi is equipped with a monochromatic X-ray source. The twin-crystal, microfocusing monochromator has a 500 mm Rowland circle and uses an Al anode. You can select any sample spot size ranging from 200 µm to 900 µm. Advantages of a microfocusing monochromator:

• Small-area XPS measurements can be made without reducing spectrometer sensitivity, which reduces the analysis time.
• Only the part of the sample being analyzed is exposed to X-rays, and therefore, areas remote from the analysis position are safe from potential damage.
• In angle-resolved measurements, the entire X-ray spot is always within the analysis area.

For any X-ray source, the aluminium coating on the anode will wear with use, affecting the intensity of the X-rays and the instrument’s sensitivity; however, the anode on the ESCALAB 250Xi can be moved to expose a new area to the electron beam, significantly increasing its lifetime. The total anode movement of 25 mm can be achieved without breaking the vacuum. An optional twin-anode source is also available. Typically, aluminium and magnesium anodes are supplied, but other materials such as gold, zirconium, or titanium are available on request.

Lens and Analyzer

The lens/analyzer/detector combination on the ESCALAB 250Xi makes the instrument ideal for spectroscopy, where a large dynamic range is essential, and for parallel imaging, where a two-dimensional detector is required.

The system consists of the following components:

• A set of input lenses, including a magnetic immersion lens.
• The input lenses incorporate a pair of motor-driven, computer-controlled iris mechanisms to set the analyzed area and the angular acceptance of the lens.
• A 180° hemispherical energy analyzer with a mean radius of 150 mm and energy range 0 to 5,000 eV.
• An output lens to reform the parallel image. The image-forming lenses in the ESCALAB 250Xi were designed to optimize the quality of the parallel images.
• A pair of channel plate detectors for imaging XPS.
• A continuous, two-dimensional, position-sensitive detector to read the output from the channel plates without applying a detector signature.

Detectors

The ESCALAB 250Xi is fitted with two detector systems: one is optimized for spectroscopy, and one is for parallel imaging. The detector for spectroscopy is an array of six-channel electron multipliers. These are situated in the output plane of the analyzer and provide a wide dynamic range. High count rates are obtained when using optional components, such as the twin-anode X-ray source, the FEG and the UV lamp. Channel electron multipliers are also the optimum type of detector for REELS and ISS, which are available on ESCALAB 250Xi instruments.

The parallel imaging detector for the ESCALAB 250Xi consists of a pair of channel plates and a continuous position-sensitive detector. The detector provides parallel images with pixel resolutions up to 256 x 256 pixels.

Because this detector is never used for high count rate spectroscopy applications, it has a long life-time, and is not prone to variable sensitivity across its surface caused by localized exposure to high count rates. High dynamic range in the detector electronics coupled with true pulse counting and uniform surface results in a detector that can easily cope with the natural variation of sensitivity over the surface, producing a ‘signature-free’ image.

Small-area XPS

From 900 μm to 200 μm, the analysis area may be defined by the size of the X-ray spot (i.e., source-defined small-area XPS). Below 200 μm, the analysis area can be defined using a pair of irises in the lens (lens-defined small-area XPS) and extends the lateral resolution for spectroscopy down to < 20 μm. The irises used for lens-defined small-area XPS are motor driven and computer controlled for maximum repeatability and remote control. Irises enable the analyst to choose an analysis area that closely matches the size of the feature being analyzed, which maximizes the signal. Small-area spectra with a lateral resolution better than 20 μm can be obtained by deriving spectra from a stack of parallel images.

The Flood Electron Source

An electron source, co-axial with the analyzer input lens, is provided with the instrument and is used for charge compensation when analyzing non-conducting samples using the monochromatic X-ray source. A second flood source produces low-energy ions, which assist in providing effective charge compensation and low-energy electrons when the magnetic lens is not in use, or for experiments where the co-axial source is not appropriate such as UPS. In addition to charge compensation, the co-axial source can be used at higher energies for physical imaging and REELS.

Ion Gun

The ESCALAB 250Xi is fitted with the MAGCIS ion gun for rapid, high-resolution depth profiling. The MAGCIS ion gun is fully computer controlled and operates at an energy range from 100 eV to 4 keV and has a maximum beam current of > 6 μA at 3 keV and a minimum spot size of 200 μm at 2.5 μA and 4 keV.

Digital Control

All analytical functions for the ESCALAB 250Xi are controlled from the Windows™-based Avantage data system. This means that the entire analysis process can be performed remotely, if required.

Instrument Alignment and Calibration

Alignment and calibration of the ESCALAB 250Xi is achieved using a standards block, which has samples of copper, silver and gold that can be used for assessing sensitivity, setting the linearity of the analyzer energy scale and determining the transmission function of the analyzer. A phosphor sample enables the analyst to examine the size and quality of the X-ray spot. A set of apertures are used to align and focus the ion beam from the EX06 ion gun. The positions of the samples and apertures are programmed into the data system so that many of the alignment and calibration procedures can be automated.

Sample Manipulation

Sample Size

The range of motion for the ESCALAB 250Xi is 50 mm in X and 20 mm in Y with 1 μm resolution, which is the area that can be used for analysis. The sample tilt range is -90° to +60° from horizontal. This range of angles makes the instrument ideal for angle-resolved XPS. The motorized, azimuthal rotation is continuous.

Sample Alignment

All axes of movement on the sample stage are controlled by the Avantage data system. A high-resolution digital video camera is fitted to the instrument and is accurately aligned with the analysis position. The field of view range from the optical system is from 300 μm to ~2.5 mm. To align a feature for analysis, it must be visible at the center of the graticule and in focus.

Alternatively, the fast-parallel imaging on the ESCALAB 250Xi can be used to align the sample in real time, either using an XPS peak or using electrons from the flood gun elastically backscattered from the sample.

Sample Manipulator

There are five axes of movement available in the base system. The manipulator is configured to enable sample heating and cooling. The motors do not require removal to bake the instrument, and the rotation and tilt motors are internal to the vacuum chamber, providing a direct drive to the sample. This feature is particularly important for the tilt axis because accuracy in setting the tilt angle is essential when performing angle-resolved XPS.

For heating and cooling, two types of sample holders are available: the posigrip specimen holder with integral heater and thermocouple for regulated cooling and heating to 600 K, and the high-temperature specimen holder with integral resistive heater and thermocouple for regulated heating to 1000 K. The power supply for heating the sample has an integral temperature controller. On a suitable sample holder, cooling to < 170 K is possible.

Vacuum System

The analysis chamber is constructed from 5 mm thick mu-metal to maximize the efficiency of the magnetic shielding. The chamber is pumped using both a turbomolecular pump and a titanium sublimation pump. This arrangement allows the analysis chamber to achieve a vacuum better than 5 x 10-10 mbar.

In addition to the ports for the energy analyzer and X-ray source, the chamber has ports for other sources, such as a twin-anode X-ray source, a field-emission electron gun and a UV lamp. These ports enable the system to be used as a true, multi-technique facility.

The Preploc is pumped using a turbo molecular pump backed by a rotary pump. The Preploc pump is also used to provide differential pumping for the ion gun. The operation of all of the pumps and valves is through the data system via a schematic diagram on the user interface. Valves are operated by pointing at the appropriate symbol on the schematic and clicking the mouse. The valve will then change its state, if allowed by the safety interlocks built into the system.

Multi-technique Capability

The ESCALAB 250Xi is designed to accommodate other analytical techniques without compromising XPS performance. Because of its large dynamic range, the multi-channel electron multiplier detector is ideal for the following spectroscopic techniques.

Ion Scattering Spectroscopy (ISS)

Reversible polarity lens and analyzer power supplies make ISS a standard feature. Channel electron multipliers provide maximum dynamic range while avoide image detector damage. Used with either the EX06 ion gun for MAGCIS is used as the primary source for ISS.

Reflection Electron Energy Loss Spectroscopy (REELS)

REELS is available from the ESCALAB 250Xi without the need for additional components. The electron source for REELS is located close to the axis of the transfer lens and can be operated at any energy up to 1 keV. This allows detection and quantification of hydrogen, the only element not detectable with XPS alone.

XPS with a Non-monochromatic X-ray Source

A twin-anode, X-ray source is available as an option. The standard source has aluminium and magnesium anodes, but other materials are available (e.g., silver and zirconium).

Auger Electron Spectroscopy (AES)

An optional Schottky field-emission electron gun (FEG 1000) is available for the ESCALAB 250Xi. At the beam energy of 10 keV, this electron gun provides a spot size of 95 nm at a beam current of 5 nA, which is ample current for AES.

Ultra-violet Photoelectron Spectroscopy (UPS)

The ESCALAB 250Xi spectrometer is ideal for UPS because of the efficient magnetic shielding provided by the instrument’s mu-metal chamber and the excellent low-energy performance of the electronics driving the lens and analyzer.

Preparation Chambers

The ESCALAB 250Xi base system has a standard Preploc chamber, which is a combined sample entry lock and preparation chamber. This chamber has ports that will accommodate a variety of sample preparation devices such as the following:

• Heating/cooling probe
• Ion gun
• High pressure gas cell
• Sample parking
• Gas admission

Other arrangements of preparation chambers are available as options. For example, a dedicated UHV preparation chamber, which remains under vacuum when samples are being introduced, adjacent to the analysis chamber and a second Preploc. Alternatively, samples can be introduced using the Preploc to which a UHV preparation chamber is also attached.