Beamline description

The X-Ray Fluorescence beamline is a multipurpose instrument run under the joint supervision of Elettra and IAEA.
 

The sample environment is a vacuum chamber, project of the IAEA, based on a prototype designed and built by the PTB and TU Berlin, Germany.

The general layout of the beamline is the following:

End Station

1. Main and load-lock ultra-high vacuum (UHV) chambers with a sample holder transfer mechanism;
2. A base system including three motorized stages for the alignment of the chamber with respect to the SR beam;
3. A seven-axis motorized manipulator controlled by a Stepping Motor Controller (SMC) for positioning the sample and the detectors regarding the synchrotron beam direction, with thermocouples to prevent overheating of the motors and different types of sample holders;
4. Two Silicon Drift Detectors (SDDs) for XRF and one for XRR measurements;
5. Several GaAs and Si photodiodes of various thicknesses as X-ray monitoring detectors connected to a picoammeter;
6. Two video cameras for inspecting a large (macro-camera) and small (micro-camera) field of view on the sample surface (see below for details);
7. UHV pumping system composed of turbomolecular and rotation pumps, vacuum gauges, gate valves controlled by a Gate Valve Controller (GVC);
8. A Tango-based command and data acquisition server coupled with a user-friendly Graphical User Interface to operate the instruments.

External (left) and internal (right) view of the IAEAXspe end station components.
(schematic drawings prepared by PTB, Berlin)



The IAEAXspe end station installed at the XRF beamline of the Elettra Sincrotrone Trieste

 

Video Cameras

The end station is equipped with two (2) cameras for visual inspection of the sample, one providing overall view (macro-camera) and another for detailed visualization (micro-camera) of a given area of the sample.
 
Specifications - Macro camera:
Lumenera Lw235C 2.0 megapixel USB colour camera with 1/1.8” CCD sensor, 55mm Telecentric C-mount Lens. It provides a field of view of approx. 5 x 5 cm² giving the possibility to preview the sample holder (i.e. sample versus X-ray detector position)
 
Specifications - Micro camera:
PCO.pixelfy, 1.3 megapixel USB colour camera with 2/3” CCD sensor, Infinity K2/SC DistaMax long distance microscope, LED illumination system
 
The microscope together with camera is mounted on the plane defined by the synchrotron beam and the X-ray detector axis. The angle between the microscope axis and synchrotron beam / detector axis is 45°. This system provides a field of view of approx. 5 x 4 mm².

The two video cameras installed on the end station: the macro-camera (left)
and the micro-camera with the microscope (right).

Motorized manipulator

The motorized seven-axis manipulator (Huber, Germany) is composed of four linear and three rotational stages used to provide proper orientation of the analyzed sample surface and X-ray monitoring detectors, as required by the experiment to be conducted. In particular, the sample manipulation allows three translations (‘X’, ‘Y’, ‘Z’) in the Cartesian geometry and rotation around two axes (‘Theta’ and ‘Phi’). One additional rotational axis (‘2Theta’) and one linear stage (‘Diode’) are used for the movement/translation of X-ray monitoring detectors with respect to the direction of the SR beam or/and sample surface.
In order to achieve a high-precision positioning for GIXRF and XRR measurements, the two main axes (‘Theta’ and ‘2Theta’) of the two-circle goniometer of the seven-axis manipulator are equipped with absolute encoders (Renishaw, UK). 
 

Layout of the seven-axis manipulator (position: ‘Theta’=0, ‘2Theta’=0 and ‘Phi’=0).
Schematic drawing prepared for the IAEA by Huber Diffraktionstechnik GmbH &Co 




Specifications of the seven (7) axis manipulator

Specification	Units	‘’Theta’’	‘’2Theta’’	‘’Phi’’	‘’Diode’’	‘’Z’’	‘’X’’	‘’Y’’
Repeatability	[“]1	2.3	7.0	2.5
Reversal error	[“]1	4.2	9.4	3.1
Optimal backlash distance	[°]	0.1	0.1	0.3
Pitch	[“]					32.52	27.53	9.93
Yaw	[“]					1.92	14.23	313
Roll	[“]					1.82	11.94	31.34
Motor resolution	[°]	0.00005	0.00005	0.00025
	mm				0.00025	0.0005	0.00025	0.00025
Motor maximum velocity	[°]	0.3	0.3	0.5
	mm				0.5	0.5	0.5	0.5
Motor base velocity	[°]	0.015	0.015	0.025
	mm				0.05	0.05	0.025	0.025

 

---

¹ 1” = 4.85 µrad
² Measured for 50 mm translation
³ Measured for 110 mm translation
4 Measured for 90 mm translation
 

Base System

The UHV chamber is mounted on a frame that allows its translational and rotational positioning using three (two linear and one rotational) stages, whereas the frame is movable via wheels. It consists of:

• Support frame that it is a welded steel frame with six adjustable feet and four jacking castors;
• Lifting stage (base-Y) placed on top of the frame allows motorized positioning of the other two stages and the chamber within +/- 50 mm;
• Linear horizontal stage (base-X) placed on top of the lifting stage allows movement of the rotational stage including the chamber within +/- 12 mm; the movement is perpendicular to the beam direction;
• Rotational stage (base-rot) that performs the rotary adjustment of the chamber within a range of +/- 5°.

Specifications of the motor stages for the base system

Degrees of freedom	Resolution	Reproducibility	Adjusting range
base-X	< 0.05 mm	< 0.1mm	+/- 12 mm
base-Y	< 0.05 mm	< 0.1mm	+/- 50 mm
base-rot	<0.005°	<0.01°	+/- 5°

 

X-Ray Fluorescence Detectors

The fluorescence measurements are performed using a Silicon Drift Detector (SDD) (XFlash 5030, Bruker Nano GmbH, Germany). This SDD has a 30 mm² nominal crystal area, a thickness of 450 µm and resolution equal to 131 eV (@MnKa). It is equipped with a Super Light Element Window (SLEW) of the type AP 3.3.
A Zr collimator is placed in front of the detector chip to prevent the detection of photons at the edges of the crystal and to improve the energy resolution and the peak to background ratio. The presence of the collimator limits the effective active area to about 25 mm².

To prevent the detection of photo- or Auger electrons emitted from the sample surface, the SDD is coupled with an electron trap (permanent magnet) placed in front of the end cup. Two Al apertures with respective diameters of 2.25 mm and 4.7 mm inserted at both sides of the photoelectron trap (length 4.2 mm) ensure that no parasitic line from the magnet elements will be detected, whereas the incoming X-rays are detected within the central region of the SDD sensor (3.98 mm²).

When the optimum detection of light elements (Z<14) is not necessary, the electron trap can be replaced by a 8.5 µm Be window.

The positioning of the detector-sample distance is performed using one motorized linear stage, connected to the SMC for the 7-axis manipulator and the base system.

The SDD output signal is processed by a Digital Signal Processing unit (by Bruker Nano GmbH) providing detector bias supply, pile up rejection, input/output rate meter, dead time correction using an internal “zero” peak and selectable shaping time constants in the range (0.89 – 6.1 µs). For more details see the User’s Manual of the IAEA control software.
 

In order to improve detection sensitivity for experiments in grazing incidence geometry, a three-element SDD (SGX Sensortech, UK) is currently under commissioning. The three crystals of 50 mm² active area and 450 µm thickness each are arranged vertically along an arc with a 34 mm radius. The energy resolution is 131 eV (@MnKa). All three elements have 12.5 µm DuraBe-plus window. A long and a short collimator can be used optionally, with optimum sample-detector distance of 34 mm and 14.6 mm, respectively, considering the central sensor. The detector system is water cooled. The SDD output signal of each element is processed individually by a four-channel Digital Signal Processing unit (DXP-XMAP, XIA LLC, USA).
 

X-Ray Monitoring Detectors

The vertical arm - attached to the “2theta” rotational axis - can accommodate up to six slots for photodiodes and miniaturized detectors.

A miniaturized SDD (Amptek, USA) is available for XRR measurements. This SDD has a crystal area of 25 mm², a Be window with 8.5 µm thickness, 131 eV resolution @MnKa, thickness 500 µm and internal multilayer as collimator. The chip is mounted on a special UHV assembly with the preamplifier placed outside the vacuum. This SDD is currently under commissioning.

Currently the following four detectors (three photodiodes and one miniaturized SDD) are installed.

1. Hamamatsu Si-photodiode S3590-09 (10x10 mm², 300µm thickness, no slit);
2. Hamamatsu Si-photodiode S3590-09 (vertical slit of 100 µm, 300 µm thickness);
3. Hamamatsu Si-photodiode S3590-09 (vertical slit of 200 µm, 300 µm thickness);
4. Miniaturized SDD (Amptek, USA) with vertical slit of 200 µm.

The incoming beam is monitored by a Beam Monitoring System (BMS) developed by the detector group of Elettra Sincrotrone Trieste. The system is based on a 4-channel solid state sensor composed of a 12-μm thick free standing polycrystalline Chemical Vapour Deposit (pVCD) diamond plate (Dectris, Rigi). Its total active area is 9mm x 3mm subdivided into four electrodes of 4.5 mm x 1.5 mm area each (separated by a gap of about 20 µm) connected with individual UHV feedthroughs to the signal processing and acquisition system. The BMS allows good transmission at low energies (67.4% at 3.0 keV). It can be inserted or retracted from the beam path using a manually controlled linear stage. The individual currents from the four sensors are registered by a 4-channel picoammeter (Elettra, AH501B). 

 

Acquisition and control software

The acquisition software has been designed on the needs of XRF users.

Currently two systems are operating:

• one developed by IAEA devoted mostly to XRF maps and XRR acquisition (based on LabView and operating on Windows);
• a second one developed by Elettra mostly dedicated to XANES/EXAFS acquisition and for optics optimisation (based on Python and operating on Linux).

LabView GUI

A Tango-based command and data acquisition server coupled with a LabView GUI was specially developed to facilitate the control and operation of the instruments and X-ray detectors installed in the IAEAXspe end-station.

The User’s Manual relates the steps required to set the operational parameters for the various X-ray detectors and to customize single or multi-dimensional scan measurements with real-time visualization of the selected signals. 

 

Main GUI appearance in No Scan Mode


 

Visualization of measurement results by GUI in Scan Mode of operation

EXAFS scan tool

The software devoted to the XANES/EXAFS allows the users to choose between a constant or a variable energy step.

More details are available for users under the "Users procedures" tab.

 

Vacuum system

The vacuum system of the IAEAXspe end station is controlled by a custom made Gate Valve Controller (GVC, ENZ, Germany). It manages the vacuum system and gate valves used in the main and load lock chambers. In particular, the GVC can control 8 gate valves and delivers the mains for two rotational and two turbomolecular pumps. It also reads the status of six gauges through a controller (MaxiGauge, Pfeiffer Vacuum, Germany) and the readings of the switches of each valve.  

In order to allow investigation of samples not requiring UHV conditions, a manual double gate valve (DGV) is installed between the beamline and the main chamber. Both valves have openings where windows of different materials can be installed. Currently 20 µm and 50 µm thick Be windows are available. In order to keep the section between the DGV and the last valve of the beamline under UHV conditions when (Be) windows are installed, an ion pump is used (VacIon, Agilent Technologies).

The following abbreviations will help to understand the operation of the GVC and interconnection of pumps and gate valves in the Vacuum Logical Diagram (VLD), as presented in two graphs shown below: 

• Turbo pumps: TP1:Turbo Pump 1, TP2: Turbo Pump 2;
• Maxi-Gauge channels and gauge: G1: High vacuum, DGV section , G2: High vacuum- Load lock, G3: Low pressure- Chamber, G4: Low pressure- Load Lock, G5: Low pressure in rough pump, G6: High vacuum- Chamber, P3: Rough pump, P4: Pre-Vacuum Pump (bypass softpump).

 

The front panel of IAEA Gate Valve Controller (produced by ENZ Ingenieurbüro für Umweltelektronik & Automatisierung, Germany)



The Vacuum Logical Diagram (VLD) for the main and load-lock chambers of the IAEAXspe endstation.

 

• APPLYING VACUUM IN THE UHVC.pdf (Air atmosphere in both the Main and Load Lock chambers)
• EXCHANGING SAMPLES IN THE UHVC.pdf(Main and Load Lock chamber have High Vacuum conditions)

 

Sample Transfer System

The sample transfer system helps to exchange samples without breaking the UHV condition in the main experimental chamber. The sample holder can be transferred between the main and the load lock chambers using a magnetically coupled transporter. It is possible to connect the transporter to the sample holder only if the sample holder has been placed at a specific position (inside the chamber). The orientation of the seven-axis manipulator at the sample replacement position is given below.



The sample holder system in the position to retract the sample holder
from the main chamber.