The end stations
The transfer stage
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The insertion of samples is done through the transfer stage. The sample is inserted in the load lock chamber (pressure 5e-6 mbar). The usual time for pumping is 15-20 minutes. The sample can then be inserted with a transfer arm in the garage chamber (base pressure 8e-10 mbar), where three sample holders can be placed. The samples from this stage can then be moved or to the preparation or directly to the experimental chambers with a second transfer arm.
Picture of the insertion stage |
Layout of the insertion stage |
The experimental chamber
Specifications:
base pressure 1 x 10-10mbar;
sample manipulator with six degrees of freedom (X,Y,Z, Theta, Phi, Correction of precession) click here for further details;
sample LN2 cooling (220 K);
200 °C annealing;
availability of a remainence magnetiser;
Available detectors are:
Luminescence channel;
Fluorescence detector;
Light detectors for diffuse & specular reflectivity (Diodes IRD SXUV-100 and AXUV-100 and Channeltron SJUTS model KBL15), covering a 2pi solid angle;
Electron analyser (MCP 16 channels, 66 mm radius, 1 deg acceptance, 2pi solid angle).
The experimental chamber
The preparation chamber
The preparation chamber is an UHV chamber (base pressure 1e-10 mbar) equipped with:
- a manipulator stage with 5 degrees of freedom (X,Y,Z,Theta,Phi). The manipulator stage allows to heat (up to 1000 K) and to cool down the sample (100 K).
The control of temperature can be done through an IRCON pyrometer (T>250°C) or through a thermocouple K that can be brought in touch with the sample;
- a leed VG;
- an ion gun VG;
- a mass spectrometer (model SRS RGA-200)
- two quartz microbalance thickness monitors (one on the chamber, one on the manipulator);
- Tricon evaporators or home made evaporators; click here to have further details for surface preparation;
- a Cylindrical mirror analyzer.
Picture of the preparation chamber
The ammeters
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The current measurements (for instance, reflectivity with diodes or total electron yield from the sample) require the use of Keithley model 6517A.
Setting the BIAS
INTEGRATION AND WAITING TIME |
 Scheme for current measurement: Diagram 1: No bias; Diagram 2: Bias to the sample |
Photodiodes
The experimental chamber is equipped with 4 silicon diodes for light detection. All diodes are mounted on a aluminum frame placed on the PhiA analyzer frame, at 160 mm from the chamber center. These detectors are all at 160 mm from the chamber center. 3 diodes are SXUV-100 model and one is AXUV-100G for absolute intensity measurements. Moreover, there is also an absolute diode AXUV-300 mounted on the monitor chamber for I0. The following table summarizes the main properties of the detectors:
| model | distance from center (mm) | mask size (mm2) V X H | Acceptance (H x V) deg2 | Group/connection | Direct beam position |
| sxuv100 | 160 mm | 8 x 8 | 7.6 x 7.6 | A 2 | ThetaA -50 PhiA 0 |
| sxuv100 | 160 mm | 8 x 0.5 | 7.6 x 0.5 | B 1 | ThetaA -119.6 PhiA +2 |
| axuv100 | 160 mm | 8 x 8 | 7.6 x 7.6 | A 1 | ThetaA -129.6 PhiA -2.5 |
| sxuv100 | 160 mm | 8 x 8 | 7.6 x 7.6 | B 2 | ThetaA -59.4 PhiA +2 |
| axuv300 | monitor chamber | 20 x 20 | ------------ | A 3 | --------------------------- |
The diodes are connected through a DN63CF 8-ways feedthrough placed near the phiA motor.
Diodes mounted on PhiA frame
UHV feedthrough for photodiodes.
The sample holders
We have available 4 sample holders (XL25 VG standard) for different uses. The sample holders 1 and 4 allows to heat and cool down samples, differently sample horders 2 and 3.
Sample holder 1 (with Mo plate)
Sample holder 2
Sample holder 3
Sample holder 4 (electron bombardment)
The specifications of the standard XL 25 sample are given below. For further details, click here.
Sample Size: 25.4mm Diameter (N.B. The block sample holder + sample has to pass through a copper gasket of inner diameter 40 mm).
Sample holder 1 (heater element)
Heating: Maximum Continuous Current: 1.2 Amps. Maximum Short Term Current: 5 Amps for up to 10 minutes from a cold start. If the element is pre-heated, this must be reduced accordingly. The heater element is pyrolytic graphite (PG) encapsulated in pyrolytic boron nitride (PBN). The heating resistance is about 15 ohms.
Cooling: Minimum Temperature -170°C (100K).Time to Minimum Temperature* (about 60 minutes).
Current (Amps)
Temperature (°C)
Power (W)
1.2
500
8
1.5
600
13
2.0
700
23
2.5
800
35
3.0
900
60
3.5
1000
100
Current (Amps)
Temperature (°C)
0.1
40
0.2
90
0.3
135
0.4
180
0.5
220
0.6
260
0.7
300
0.8
320
0.9
340
1.0
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Sample holder 4 (electron bombardment)
The sample holder 4 permits to heat samples by electron bombardment. The home made filament is made in 0.2 mm annealed Goodfellow thoriated tungsten.
With a filament current of 3.4 Amps, we reached a temperature of 800°C, sample grounded.
Details of XL25
Picture of XL25 sample holder
The magnetiser
A remanence magnetiser system has been developed on a standard XL25 sample holder. The magnetiser is based on a ferromagnet with a 7 mm large air gap.
The magnetic field is applied through a kapton insulated wire. This device gives a magnetic field of about 130 Oe/Amp, with a maximum of about 600 Oe.
A picture of the magnetiser
Magnetic field as a function of the applied current
The fluorescence detector
A new large area Vacuum Silicon Drift Spectrometer by PN Detector GmbH has been installed on the spectroscopy chamber of the beam line. This detector has been conceived for light element detection from Mg down to C and B. From preliminary tests, we obtained an excellent energy resolution down to 133 eV @ Mn-K alfa and a low level noise <150 eV. The main characteristics are:
Distance from sample ≥ 20mm
Solid angle ≤ 0.075 sterad
Energy range 200 - 8000 eV
Sensor cooled by a Peltier cell(T~-15°C)
Built in electronics (integrated JFET)
Input PN integrated window (optimized detection of low energy photons)
On-chip Zr collimator
MCA with 8192 channels, calibrated with 55Fe K line (6 keV), Ga Lα line (1098 eV), As Lα line (1282 eV).
In the figure below is shown a design of the detector and of its support that allows to regulate the distance to the sample.
The Fluoresecence detector
Typical setup for fluorescence measurements
The luminescence apparatus
The experimental chamber is also equipped with a luminescence apparatus. Important applications of this apparatus are the development of scintillating detectors, biomedical markers, Organic Light Emitting Diode (OLED), Light intensifier devices (ex: YAG), and the characterization of wavelength shifters. Important perspectives are the study of the lifetime of excited energy states and transition probabilities, the study of relaxation times and the dynamics of exciting processes (pumping-probe measurements), the opening in the direction of exploitation of fast sources (FEL).
The luminescence apparatus is based on:
- a quartz UV/VIS fiber optic of diameter 1 mm that can be brought close to the sample;
- the luminescence light is recorded or without monochromatization (photodiode, PMT) or with monochromatization (spectrometer Ocean Optics HR4000 (λ= 191 – 1100 nm) or monochromator (Acton Sp-300i + CCD camera cooled with Liquid Nitrogen λ= 400 – 1100 nm).
It's also possible to perform time resolved measurements with a TAC (Time to Analog Converter).
Luminescence apparatus layout
UV-VIS fiber optics transmission
An example of luminescence measurement is shown here: the fiber optics collects the monochromatic radiation coming from sample in the experimental chamber (left figure), the radiation is taken outside the apparatus through the UHV connector (central figure), the final output is based on a CCD equipped Andor monochromator for analysis (right figure). (Courtesy of Prof. Belski, Université Lyon1) .
The electron analyzer
The electron analyzer is an hemispherical spectrometer characterized by a mean radius of 66 mm. The collecting system is based on three lenses V1, V2 and V3, while the detection system is based on a 16 channel Multi Channel Plate. The independent electrodes of the analyzer, the two spheres of the hemispherical part and are polarized by programmable power supply following calibration curves previously obtained by electron trajectories simulation, to set for each point in the analyzed energy range, the optimal working conditions. This scheme ensures a very high flexibility of the apparatus being possible to weakly change the lens characteristic by software. The curves are dependent on the retarding factor R=Ek/Ep.
Transmission
The transmission of the analyzer as a function of the kinetic energy is shown in Fig. 2. The transmission has been determined by measuring the intensity of Au 4f xps spectra, after the data have been normalized taking into the photoemission cross section. Measurement have been done with pass energy 5 eV. The data have then been normalized to the incoming intensity by measuring the flux with a silicon detector diode and taking into account its responsivity. The transmission is well fitted with a 7th degree polynomial curve
T(Ek)= p1·Ek^7+p2·Ek^6+p3·Ek^5 p4·Ek^4+p5·Ek^3+p6·Ek^2+p7·Ek^1+p8 with
p1=-7.9564e-008;p2=0.00022951;p3=-0.26007;p4=142.36; p5=-34583; p6= 5.4847e+005; p7=1.0074e+009; p8=-2.2156e+010.
Instrumental broadening-energy resolution
The spectrometer resolution has been experimentally determined by measuring the broadening of Au 4f 7/2 and 5/2 XPS spectra of a polycrystalline gold sample cleaned with one hour cycle of ion sputtering. The instrumental broadening has been calculated with a fitting procedure by using the reference ‘P.H. Citrin, “Surface-atom x-ray photoemission from clean metals: Cu, Ag, and Au”, PRB 27-6 (1983)’. The core level spectra have been fitted as the sum of 4 Voigt functions, after a linear subtraction of the background. The 2+2 components are given by the contribution of bulk and surface components, whose intensity ratio is given by the takeoff angle. Measurements have been done in normal emission. The instrumental broadening is given by the width of the Gaussian component of the 4 Voigt functions. The broadening is given by the contribution of the exciting radiation (then from resolution that is given by photon energy and vertical slit aperture) and of the spectrometer (then from the pass energy).
