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43 

Manual V2.docx  |  Status 10.12.2015  |  Version 1 

 

Dynamic range 

6.3

Thermally excited electrons in the silicon lattice of the CCD chip are counted as a signal. 
Thermal noise charges, again expressed as electrons, are generated in a CCD camera 
regardless as to whether it is exposed to light or complete darkness. Thermal noise is 
temperature dependent. The higher the temperature of the CCD, the higher the thermal 
noise. The lower the temperature, the lower the thermal noise. For this reason, many CCD 
cameras have some type of cooling device (e.g. Peltier cooling). 
  
 The total noise σ

N

 is the root mean square of the thermal noise D

τ

 and the read out noise σ

R

 

 

"

#

$"

%

&

'

 

  
The thermal noise increases linearly with the dwell time τ. 
  
The dynamic range of a camera is defined as the full well capacity divided by the total noise. 
Since the thermal noise is dwell time dependent, the dynamic range is a function of the dwell 
time as well. To be able to fully exploit the dynamic range, the ADC has to have sufficient bit 
depth (the number of bits in each pixel). 
  
Cameras with a high dynamic range are more expensive. Thus, it is necessary to carefully 
consider which dynamic range is necessary for the experiment. The dynamic range of the 2D 
CCD detector is limited by the dynamic range of the camera.  
 

 

Flat field correction 

6.4

A CCD imager consists of a two dimensional array of pixels (i.e. light sensitive detectors). The 
CCD array is mechanically stable with the pixels retaining a rigidly fixed geometric 
relationship. However, each pixel in the array has its own unique light sensitivity 
characteristics. These characteristics affect camera performance, so they need to be 
removed by calibration. Calibrating a CCD camera is known as "flat fielding" or "shading 
correction". Flat fielding can be illustrated by the following equation 
 

(

) *

!

+

 

  
where 

•

 

IC is the calibrated image 

•

 

IR is the non-calibrated object exposure 

•

 

IB is the bias or dark frame 

Содержание 2D-CCD

Страница 1: ...User Manual Status 10 12 2015 Version 1 0 User Manual V1 0 October 19 2015...

Страница 2: ...m SPECS User Manual 2D CCD 3D VLEED Detector Version 1 0 October 16 2015 SPECS order number reference 2100000201 2015 All rights reserved No part of this manual may be reproduced without the prior per...

Страница 3: ...Conditioning the spin detector 13 3 Operation 14 3 1 Using templates to set up experiments 14 Templates for the 2D CCD 3D VLEED detector 17 3 1 3 1 1 PHOIBOS 1D Adjustment 17 3 1 2 PHOIBOS 1D DVS 17 3...

Страница 4: ...range 43 6 3 Flat field correction 43 6 4 6 4 1 Bias frame or dark frame IB 44 6 4 2 Flat field frame IF 44 6 4 3 Non calibrated object exposure IR 44 Full well capacity 44 6 5 Hot pixels 45 6 6 Camer...

Страница 5: ...am position of the electron gun 66 A 3 2 Adjusting the deflector rotator lens 67 A 3 3 Adjusting the beam alignment for the total intensity channel 70 A 3 4 Adjusting the beam alignment with the spin...

Страница 6: ...also an Appendix that describes the initial installation of the detector This is performed by SPECS service personnel and is not a normal user task Information 1 2 The 2D CCD 3D VLEED Detector is int...

Страница 7: ...t This will ensure safe transportation and speedy processing Safety 1 3 The document Safety Instructions is contained with this instrument This contains important warnings and procedures that you shou...

Страница 8: ...you should ensure the following The chamber is leak free with a pressure of 10 7 mbar or lower All connection cables are removed The cameras are removed Switch off any power supplies before removing...

Страница 9: ...operate the detector without a vacuum interlock If high voltage is applied to the detector while the chamber vents all CEMs and MCPs will be irreparably destroyed Electrical connections 2 3 The wirin...

Страница 10: ...cus Note Exactly one of the two HSA 3500 plus units should have the 24 V switch set to on Figure 1 Connection of SPECS power supplies 2 3 2 Connecting the Focus power supplies In addition to the SPECS...

Страница 11: ...me for these supplies in the context of the SPECS 2D CCD 3D VLEED Detector Caution Make sure the connectors on the rear of the spin controller power supply are all fitted to the correct outputs The ca...

Страница 12: ...r 2 5 For degassing the electron multiplier in the spin detector please refer to the Focus Ferrum Spin Detector manual The following describes the procedure for degassing the CCD detector The CCD dete...

Страница 13: ...e PHOIBOS CCD device and select the Calib Voltages tab 6 Open the Live Image View to observe the output from the camera during degassing Select Views Live Image View from the menu bar Click Activate i...

Страница 14: ...ual V Udet target V Uscrn actual V Uscrn target V 600 0 0 0 1000 1800 0 1000 1000 0 4000 1000 1000 0 2000 4000 1000 1500 2000 2500 2 4 Conditioning the spin detector Following the bakeout you need to...

Страница 15: ...other is simply a matter of selecting the analyzer in the software Note Before taking measurements you need to be sure that SpecsLab Prodigy is correctly configured to use your excitation source e g...

Страница 16: ...in the Load Template section The following example shows the UPS Spin Step Profile template Figure 4 Selecting a template 8 Most of the settings in the template do not need to be changed before you st...

Страница 17: ...just below the Description field and select Save As Template A dialog will open so that you can give the template a suitable name The template will appear in the main screen when you start SpecsLab P...

Страница 18: ...you need to increase the detector voltage to compensate See the Focus Ferrum spin detector manual for more information about life time and ageing of the CEMs Caution Do not set the detector voltage t...

Страница 19: ...vices 1 UV Dummy Provides the operating parameters for the excitation source 11 PHOIBOS Spin Controls the analyzer This includes the setting for the rotator 1 or 1 12 Magnetic Pulse Control Allows you...

Страница 20: ...he Ferrum spin detector Sleep When you start the experiment the devices are initialized In particular charging the magnetic pulse controller and magnetizing the target takes some time The sleep item m...

Страница 21: ...offers the means to change the appearance of the data as well as a number of data operations to process the data The following sections contain information about some features that are relevant to th...

Страница 22: ...This is the same as the name shown in the Experiment Editor Summation Cycle You can leave this setting as Loop If a loop is used for a number of iterations of the experiment this is taken into accoun...

Страница 23: ...u bar The Image View will open 2 Double click the spectrum in the data browser to select it A tick will appear next to the name of the spectrum 3 Click the label in the Y axis and select a parameter S...

Страница 24: ...300 works correctly any problems with the channel are likely to come from the CEM To check the operation of the PCU 300 1 Disconnect the two BNC signal cables from the PCU 300 2 Start a scan in Specs...

Страница 25: ...es between channels Note that the total intensity channel 1 of the Ferrum detector is read by the PHOIBOS 1D analyzer and that the spin channel 2 is read by the PHOIBOS Spin analyzer To set the discri...

Страница 26: ...hat the preamplifier is working correctly as described in section 4 1 Check the grounding of the analyzer If the checks above do not solve the problem you can set a higher discriminator threshold sett...

Страница 27: ...in Table 3 7 Select the Calib Settings tab 8 Set the remaining values in Table 3 9 Click Activate 10 Expand the view to see the set and actual voltages Check that the set and actual voltages agree The...

Страница 28: ...ent There should flow 178 6 mA from pin 1 to pin 2 with RotL set to 1 and 178 6 mA with RotL set to 1 4 5 Capacitances In order to check the integrity of the lens system the capacitances to ground vac...

Страница 29: ...tances for the 2D CCD 3D VLEED detector Pin Spin Lens Spin Adapter Spin Deflector Use Capacitance pF Use Capacitance pF Use Capacitance pF 1 SL1 58 SL4E 40 SL4B C 68 2 SL2Xp 28 SL6Xm 32 3 SL2Xm 28 SL6...

Страница 30: ...zer lens and hemispherical analyzer for energy resolution At the exit of the hemispherical analyzer the electrons enter a lens system which contains a magnetic rotator lens This lens rotates the trans...

Страница 31: ...hich started with different kinetic energies at the sample The software compensates for this effect so that the energy scale for each detector is correct 5 1 2 Acceleration lens The acceleration lens...

Страница 32: ...g the z axis Bz is the z component of the magnetic field and g the gyromagnetic ratio g 2 00232 v is the relativistic velocity of the electrons e the electron charge and m the electron mass The kineti...

Страница 33: ...al trajectories are equivalent for both 45 and 45 degrees spin rotation 90 deflector 5 2 The spin polarization vector S does not change in an electrostatic field An electrostatic 90 deflector can thus...

Страница 34: ...the scattering target If the Ferrum detector is oriented as shown in Figure 13 this means that by magnetizing with coil 1 it will detect the spin polarization component normal to the sample surface T...

Страница 35: ...CCD detector and the total intensity channel of the FERRUM detector The active area of the CCD detector was set to 38 48 mm2 so that it is equal to the area of the 7 mm diameter entrance of the spin...

Страница 36: ...losses It serves as a counter and preamplifier The PCU 300 is a SPECS design The Focus Ferrum Spin Detector manual describes a different design You should bear this in mind when reading the Focus Fer...

Страница 37: ...art of the valence band region Figure 17 The surface states of graphene on Ir 111 The sample is positioned at close to normal emission in the energy dispersion direction and about 3 6 off normal in th...

Страница 38: ...mode LAD pass energy 20 eV The spin detector integrates the signal over the angle range indicated in Figure 18 By using a circular hole as entrance aperture or by using the iris aperture of the PHOIBO...

Страница 39: ...plane normal to the PHOIBOS lens as seen from the hemispherical analyzer towards the sample In order to increase the separation between the bands the sample was rotated 2 around an axis parallel to t...

Страница 40: ...and a pass energy of 20 eV The entrance aperture was 3 mm diameter The acquisition dwell time was 0 2 s and 10 scans were measured for each polarization direction The total acquisition time was 12 min...

Страница 41: ...Figure 21 The asymmetry calculated from the spectra shown in Figure 20 The polarization P is calculated as where S is the Sherman function For the FERRUM detector S 0 29 is a typical value The compone...

Страница 42: ...41 Manual V2 docx Status 10 12 2015 Version 1 Figure 22 The component spectra...

Страница 43: ...e a convenient method for comparing images and data generated by different cameras This is also referred to as count and digital number Pixel voltages numbers of electrons stored during CCD integratio...

Страница 44: ...the dynamic range is a function of the dwell time as well To be able to fully exploit the dynamic range the ADC has to have sufficient bit depth the number of bits in each pixel Cameras with a high dy...

Страница 45: ...t for any variation in illumination over the field of the array The optical system most likely introduces some variation in the illumination pattern over the field of the array The flat fielding proce...

Страница 46: ...t star like points There might be a few bright hot pixels more intermediate pixels and lots of very faint ones though an entire spectrum of brightness Faint hot pixels contribute to the noise in a pic...

Страница 47: ...other radiation including UV VUV and soft X ray photons and even neutrons The MCP offers many advantages over conventional detectors compact and lightweight good timing properties due to short length...

Страница 48: ...vacuum obtained from a roughing pump 10 3 mbar is sufficient The vacuum must be oil free 6 10 2 Operating voltage The test report supplied with the detector includes the correct operating voltage Exc...

Страница 49: ...he MCPs Shipping containers should be opened only under class 100 laminar flow cleanroom conditions When handling MCPs always wear clean talc free class 100 clean room compatible vinyl gloves No physi...

Страница 50: ...after glow the emission of photons after operating at brightness levels suitable for human vision After glow effects are reduced due to the selection of the standard phosphor type P 43 Gd2O2S Tb This...

Страница 51: ...s the two photon photoemission signal of the image potential states n 1 2 and n 3 from Cu 100 at 300 K The surface was analyzed using a PHOIBOS 150 analyzer Frequency tripled pulses from a Ti Sapphire...

Страница 52: ...6 shows the quantum well state of 12 monolayers of Pb on Cu 111 evaporated at 110 K and annealed afterwards The surface was measured using a PHOIBOS 100 analyzer and the TGM 4 monochromator at the BES...

Страница 53: ...52 Manual V2 docx Status 10 12 2015 Version 1 Figure 26 Quantum well state of 12 ML Pb Cu 111...

Страница 54: ...section describes the features on the rear panel of the HSA 3500plus Spin 7 1 1 Filter box connectors There are three large connectors that lead to the filter boxes for the lens adapter and deflector...

Страница 55: ...ply is required If the 24 V switch on the other HSA 3500plus is already set to On you should set this switch to Off 7 1 4 Interlock The pinout of the connector is shown in Figure 28 The interlock is s...

Страница 56: ...onfig 0_101_156 hsa if the HSA 3500plus for the PHOIBOS is hardware type 101 The table below lists the modules installed in the power supply Figure 29 shows the internal wiring of the unit For further...

Страница 57: ...56 Manual V2 docx Status 10 12 2015 Version 1 Figure 29 Wiring diagram for hardware type 156...

Страница 58: ...lens Power supply for the camera CCD diode box Alignment camera in camera holder Power supply HSA 3500plus PCU 300 Ferrum pulse counting unit FOCUS Ferrum spin detector control unit FOCUS magnetic pul...

Страница 59: ...detector supplied by the FOCUS company A 2 Assembling the detector The detector is split into two parts for transportation as shown in Figure 30 Figure 30 The detector separated in its two parts Left...

Страница 60: ...l damage the detector Caution Do not open the smaller flange which holds the Ferrum detector to the adapter flange the flange is labeled Do not open If this flange is opened rewiring of the detector i...

Страница 61: ...he CCD deflector rotator part supported from the crane Check that the multi channel plate MCP is free from dust see Figure 33 Any dust must be removed with the air brush delivered with the detector Ca...

Страница 62: ...top disc with its pin is in the correct position Mount a new CF 150 gasket Also note that it is necessary to put in some of the stud bolts before the detector is inserted into the detector port of th...

Страница 63: ...CF 200 flange Before tightening the bolts check that the CF 200 flange is parallel with the plane defined by the detector and lens of the PHOIBOS see Figure 35 Figure 35 Checking the alignment of the...

Страница 64: ...on the protective cap as shown in Figure 31 Check that the Mu metal screen in the pump port is in place It should look as in Figure 36 Figure 36 The Mu metal shield in the pump port of the Ferrum det...

Страница 65: ...mponent hangs horizontally Check that the fingers of the Mu metal shield fits tightly into the housing of the CCD rotator deflector part The fingers can be bent slightly outwards if necessary The spri...

Страница 66: ...m the crane Mount a fresh CF 200 gasket and carefully slide the adapter lens into the CF 200 flange of the CCD rotator deflector part Check that the pumping port is aligned correctly and tighten the b...

Страница 67: ...ers used when the detector was tested at SPECS These factory optimized parameter values are stated in the Test Report Once the correct position of the excitation source relative to the PHOIBOS lens an...

Страница 68: ...that the beam of the electron gun hits the sample on the electron optical axis of the PHOIBOS lens A 3 2 Adjusting the deflector rotator lens When you have aligned the electron gun correctly you can...

Страница 69: ...tector Control in SpecsLab Prodigy Table 11 Typical parameter values for the Ferrum Detector when operated in total intensity mode Parameter Value V Scattering Energy 400 Lens 1 200 Lens 2 50 Lens 3 4...

Страница 70: ...Also change the setting RotL from 1 to 1 and back The intensity should change at most 5 when changing rotation direction see Figure 43 Figure 43 The signal from the total intensity channel when Rot L...

Страница 71: ...h measures the total intensity see the Ferrum Spin Detektor manual the beam alignment must also be done for the spin channel The procedure is similar to the beam alignment for the total intensity chan...

Страница 72: ...nergy 6 5 Lens 1 220 Lens 2 21 5 Lens 3 415 Lens 4 49 5 Lens1DeflectorX 0 Lens1DeflectorY 0 Lens1Stigmator 0 Lens3DeflectorX 0 Lens3DeflectorX 0 Lens3Stigmator 0 Due to the geometry of the Ferrum dete...

Страница 73: ...en With the RotL setting 0 a round blue spot should be visible as shown in Figure 45 Center this spot with SDefl1X and SDefl1Y It may be necessary to fine adjust the position of the electron beam on t...

Страница 74: ...he image should rotate 45 as shown in Figure 47 This corresponds to a rotation of the spin polarization by 2x45 90 around the lens axis The blue stripe does not go exactly through the center of rotati...

Страница 75: ...lectrons are deflected by 90 Use Ekin 20 eV Ep 160 eV and set RotL to 1 Set the aperture wheel to Slit5 open Use SDefl2X and SDefl2Y to center the beam on the screen at the exit of the 90 deflector Th...

Страница 76: ...re difficult The overall procedure involves the following steps Rough adjustment of the camera angular setting Changing the Z setting for the focus Correcting the X Y position Fine tuning of the angle...

Страница 77: ...camera holder 2 Hold the main body of the camera and rotate it gently The camera should be oriented so that the mounting plate is parallel to the angular adjustment screw Figure 50 shows PCO Pixelfly...

Страница 78: ...he detector 4 Set the exit slits on the analyzer to B open 5 Switch on the HSA 3500plus 6 Switch on the electron gun and make sure that the sample is correctly aligned so that electrons find their way...

Страница 79: ...sition A slits The image will show a number of lines 9 Turn the camera to get the position as good as possible The lines should be vertical It is sufficient to get the camera image nearly right you ca...

Страница 80: ...ou need to make the following corrections Adjusting the focus in order to obtain a sharp image Centering the image in the x direction The line to the left should be at 0 mm Centering the image in the...

Страница 81: ...s the optimum distance of the camera 5 Tighten the four hex bolts A 5 3 Set X Y The four hex adjustment bolts allow you to tilt the camera in the X Y directions until you see the correct alignment Thi...

Страница 82: ...m scale For the Y position set entrance slit 6 1 mm diameter hole and exit slit open Adjust the Y hex bolts until the stripe is at 0 mm see Figure 54 Figure 54 Setting the Y position 4 Tighten the fou...

Страница 83: ...the lines in the image are vertical You can only move a limited amount in each direction this is determined by elongated holes around the fixing bolts 4 Tighten the locking nuts 5 Tighten the fixing b...

Страница 84: ...between the slits should be 8 mm If the slit slit distance is not correct the camera magnification needs to be changed See the Manual Software 2D 3D detectors for information on how to set the camera...

Страница 85: ...84 Manual V2 docx Status 10 12 2015 Version 1 0...

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