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IV - Setup

In this chapter, software features that support you to properly set up your system are described. This includes adjustment, maintenance and trouble shooting aspects, as well as customization of the user interface.

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The Software Settings form

In the Software Settings window, you can customize several global program settings such as colors, paths and specific parameters of your LEED system and data acquisition hardware. For all tabs there are the "Apply" and "Default" buttons either for applying the settings in the currently opened tab or for loading the default settings.

The user settings tab ("User")

The user settings tab contains the information of the current user, including his/her name and experience level.

Note: All other settings that can be modified in the software settings form and are saved in the config.txt file are also attributed to each specific user, e.g., paths, sample, GUI settings etc.

GUI Element	Meaning and Usage
User	Name of the current user
User Name	You may change the name of the current user here.
Desktop Layout	The default desktop layout for the current user.
Experience Level	The experience level (=amount of access rights) of the current user.

You can use the experience level of the user in order to ensure that no settings are accessible which could compromise the usability of the instrument and require intervention by more experienced users.

The graphical user interface settings tab ("GUI")

In the "GUI" tab you can customize several details of the visual appearance of WinSPA's graphical user interface.

In most cases, the pre-defined color schemes are fully sufficient to make the graphical user interface (GUI) as easy as possible to work with. Nevertheless, not only personal preferences and taste, but also ambient light conditions as well as size, resolution and brightness of the display may require individual color settings of the GUI.

GUI Element	Meaning and Usage
Color Scheme	Select one of the pre-defined color schemes.
Marker Color	Color of all markers, such as for the active scan line.
Background Color	Color of the background area of data displays.
Lines and Text Color	Color of lines and text in data displays.
Scan Data Color	Color of scan data in 1D displays.
XOR Color	Color for XOR plotting of graphic tools etc.
Help Lines Color	Color of small help lines, e.g., for intermediate ticks in 1D plots.
Additional Data Colours	Colors of additional data curves, e.g., in spot tracker or image shift form.
LED Colors	Colors of LED-like GUI elements (stop watch, voltage meters etc.)
Preset color table	Select a color table to be preset for all 2D scan displays.
User defined color table	Modify a color table for your personal requirements.

Depending on the specific nature of each diffraction image, scaling and color affect to a great degree the visibility of regions of interest, as well as the overall appearance.

Diffraction images with few, clear and sharp diffraction spots usually look best in a classical black and white color table. For diffraction images with many broad features in the diffuse background intensity, however, a color table with higher contrast over five or even more colors may be better suited.

In order to allow the user to optimize the display of each diffraction image as much as possible, WinSPA not only offers many pre-defined color tables, but also (from V2.1 on) the possibility to define a custom color table with selectable contrast/resolution and colors.

If you design your own color table, keep in mind that many journals (at least in the printed version) are not completely in color. That means, that for publications as also for printouts a conversion from colors to greyscale can become necessary. In that case, it is important that the equivalent greyscale of the defined color table is also sufficiently close to a linear greyscale color table in order to convey a 1:1 information between displayed brightness and measured intensity. Especially ambiguous brightness/intensity relationships should be avoided, instead, try to aim for a uniformly continuous brightness increase with intensity. Note that the example in the screenshot above is an example of a poorly designed color table in terms of grayscale compatibility.

Depending on gamma correction and weighting of the RGB channels, several greyscale conversion formulae are in use for different purposes.
WinSPA utilizes the following relationship for greyscale conversion:

grey = 0.299 × red + 0.587 × green + 0.114 × blue

On the top of the right hand side in the GUI settings tab, a preview of the defined GUI colors is displayed and updated based on your chosen settings.

Below this color display, some settings regarding the behavior of several forms and input elements can be changed.

GUI Element	Meaning and Usage
Color Scheme Preview	Small preview of your choice of colors. The color table is by default the grayscale.
Recalculate coordinates	Select, whether WinSPA should recalculate k space coordinates such as (x,y) center position and scan size, when you change the k space coordinates, in order to keep the scan effectively the same.
Adapt zoom factor	Select, whether the zoom factor of 2D data displays should be adapted to the window size in order to maximize the image size without truncation.
Navigator form always stay on top	Select, whether the navigator form should be on top of all other forms.
Recalculate coordinates upon units change	Select, whether the entered k-space coordinates in each scan form should be recalculated if you change the k-space units.
Load positions	Load a WinSPA desktop configuration (all window positions and sizes) from disk.
Save positions	Save a WinSPA desktop configuration (all window positions and sizes) to disk.

Loading and saving desktop configurations, i.e., the positions and sizes of all forms, can be very helpful for different measurement setups. You may want to have one desktop configurations for adjustment (with one SEM scan, one 2D scan, an RSM scan and the image shift correction form open), another one for basic scans (one 2D and one 1D scan form) and potentially one for time resolved tracking of growth experiments (spot tracker and multiple small 1D and 2D scans).

The paths settings tab ("Paths")

The paths settings tabs contains some global settings of WinSPA that are not related to SPA-LEED at all. You can set the installation and data paths and your standard printer.

GUI Element	Meaning and Usage
Program Path	Path of the WinSPA installation; config.dat, NetCDF.dll and SpaDAQ.dll are expected here.
Data Path	Default path for all file save/load operations and the logfiles.
Current Printer	The printer for all printouts.
Online Help Path	The path of the WinSPA online help files on the world wide web.
License information	Details on the individual WinSPA license.

Especially if you are using network attached storages (NAS) or mounted folders to store your data, you may want to distinguish between program path and data path.

Note: The log file is written into the folder specified by the data path. Earlier releases of WinSPA (including V1.0) used the program path for the logfile.

The SPA-LEED system settings tab ("Instrument")

In the LEED system tab you can set several (hardware) parameters of your SPA-LEED system, including geometry and beam deflection values.

GUI Element	Meaning and Usage
Internal / External geometry	Select whether you are using the internal or external geometry as described in the "hardware" section.
Internal angle between ki and kf	Angle between incoming and reflection electron beam in internal geometry. Can be calculated from the distances sample-detector and gun-detector.
External angle between ki and kf	Angle between incoming and reflection electron beam in external geometry. Can be calculated from the three distances detector-sample, sample-external gun, external gun-detector.
k Sensitivity	Deflection of beam in diffraction mode, normalized to electron energy.
R Sensitivity	Deflection of beam in real-space mode, normalized to electron energy.
Time constant for deflection voltages settling	The t90 time is meant here, i.e., the time span during which the output value reaches 90% of the final value upon a fully range jump of the input voltage (-10V..+10V). Ideally measured with a HV probe and and oscilloscope.
Time constant for electron energy voltages settling	The t90 time is meant here, i.e., the time span during which the output value reaches 90% of the final value upon a fully range jump of the input voltage (0V..+10V). Ideally measured with a HV probe and and oscilloscope.
External lens type (electrostatic/magnetic)	Select which type of auxiliary voltage output versus electron energy you need, linear or square root. These two types correspond to the control of an electrostatic or a magnetic electron lens, but the voltage can also be used for other purposes.
Electrostatic lens control parameters	The linear function of an electrostatic lens versus energy is described by two parameters.
Magnetic lens control parameters	The square-root function of a magnetic lens versus energy is described by three parameters.

Note: If you are using an Omicron third-generation SPA-LEED with a sample distance of 15 mm, then the preset settings are correct. In other cases, please take the necessary time for measuring and calculating (angles) as well as calibrating (sensitivities). Refer to the section "standard operating procedures" for further details.

Note: The R space sensitivity may be dramatically different depending on how you realized the SEM-like mode of operation: You may either change the polarity of one of the two octupole deflectors in your instrument or simply ground one of them, preferably of course the one at the sample end of the instrument, not the one at the emitter/channeltron end.

The sample settings tab ("Sample")

In the Sample Settings tab you can change the parameters describing the surface of your current sample. This is necessary for the internal calculation of reciprocal space units.

In the "Sample" tab you can enter the name, step height and lattice constant of the sample you are using. These values are used if you choose %BZ as k_par units and/or the scattering phase S as k_perp units.

GUI Element	Meaning and Usage
From Presets / User Defined (substrate)	Choose either from preset list or directly enter substrate parameters.
Preset substrates dropdown list	List of predefined substrates you can choose from.
Name of Surface	Name of substrate, for identification in list only.
Step Height	Step height of substrate, needed for scattering phase calculation.
Lattice Constant	Lattice constant of substrate, needed for %BZ calculation.

Note: Each time you use a user defined substrate, it will be automatically added to the presets list (for WinSPA V1.06 and higher).

If you frequently use other samples than the predefined ones, you may also add them to the samples list in WinSPA's config file with the standard Windows text editor.

Note: If you use a sample which has neither quadratic nor hexagonal surface symmetry then %BZ are not an appropriate k_par unit, since the k_x and k_y are then different. Use either the deflection voltages or inverse Angstroms for those samples.

Note (as of 2/2020) that an additional identification of the sample (individual sample as well as description of the batch/wafer it originates from) is planned to be added soon.
This can be a valuable information attached to all data files for future analysis of your data.

The Scan settings tab ("Scan")

In the Scan tab in the Software Settings window you can define the basic settings of your SPA-LEED system. The values of deflection and emitter high voltage amplifier gains have to be correct for proper operation of WinSPA with your hardware.

GUI Element	Meaning and Usage
Deflection Amplifier Gain	Voltage gain of your deflection amplifiers.
Emitter HV Amplifier Gain	Voltage gain of your emitter high voltage amplifier.
DAQ Hardware	Your currently used DAQ hardware. This is for your information only.
Bidirectional 2D Scans	In a Bidirectional 2D Scan, the scans lines are alternately scanned from the left to the right and from the right to the left. This avoids large deflection voltage steps during a scan.
Direct Retrace Scans	In a Direct Retrace Scan, after finishing a scan line the deflection voltages of the first point of the scan line are set. This allows the deflection voltages to settle while the display is updated etc.
Set Beam to Deflection Offset Positions	If no scan is active then the deflection voltages are set to the values defined in the "manual offset" form. Use this setting if and only if you want to visually align your system. ...not yet implemented.
Park Beam at safe Position	If no scan is active then the deflection voltages are set to the values specified as "beam park position" in order to reduce the exposure of the channeltron to electrons. This is currently the preset and only available setting. Please note that a (00) spot on a well ordered surface could lead to count rates of about 2*106 cps, resulting in channeltron lifetimes of only a few hours (lunch break, night).
Beam X,Y Park Position	Deflection voltage outputs during idle times. Select a k-space position with low electron intensity.
Timing strategy αD upon deflection voltage changes	Define, how long the scan progress should be delayed after changes of the deflection voltages.
Timing strategy αE upon energy voltage changes	Define, how long the scan progress should be delayed after changes of the electron energy.
Relay switch time	The approximate time required for one switching of the deflection voltages by the internal mechanical relay.

Note: The timing strategy of the counter can heavily influence your measured results. Please make sure you are aware of the following aspects before you change settings of the timing strategy.

The high voltages for deflection and acceleration do not change ideally synchronous to the respective software commands. After a dead time due to software execution times, hardware driver communication and loading of the values to the D/A converters, the high voltages will show an exponential creep from last stable value to the newly set one, see below.

On modern PC systems the dead time are negligible in comparison to counter gate time of 0.1ms and above. The time constants of the high voltages may, however, be significant and are therefore taken into account via the "counter timing" settings.

The finite speed of the high voltages is inherent, since HV amplifiers are usually designed to have a high output impedance (safety and power considerations) and the cables and deflection plates are electrically a capacitance. Together, output impedance and load capacitance, they form a first order low-pass circuit (RC filter). The deflection voltage may not have to drive a "large" capacitance of deflection plates, but usually several control voltages inside an electron gun are coupled via high value resistors (anode, lens, acceleration potential) in order to derive the needed voltages from only one reference voltage. The effect is comparable to the one described for the deflection voltages. For the sake of stable and low noise high voltages additional low pass filter elements may have been added by the designer of your SPA-LEED system. As a rule of thumb, the deflection voltages of an Omicron SPA-LEED are quite fast, some old Leybold systems contain much slower, heavily low-pass-filtered deflection voltage amplifiers.
The electron energy settling is comparably slow in both systems and may take up to several seconds, until all affected voltages (emitter and lenses) are fully stable at their new target values after a step-change in electron energy.

The time constants for the exponential creep is entered in the LEED system tab, since they are typical for the used hardware. The way how to deal with finite HV voltage speeds is defined in the DAQ tab.

Since reaching the exact high voltages level would take infinitely long, the idea is to define an "acceptable" deviation between set deflection or acceleration voltage and the "as is" value which is internally calculated from time constant and delay time. "Acceptable" means of course always a compromise between speed and precision.

The timing strategy parameters α_E,D define the required delay time in multiples of the t90 time of the respective signal chain (energy, deflection). Values smaller than zero denote multiples of t90 time times ΔU divided by the voltage range.

Δt_E = α_E * t90     α_E >=0
Δt_E = Abs(α_E) * t90*ΔU_E/(U_E,max-U_E,min)     α_E <0

Δt_D = α_D * t90     α_D >=0
Δt_D = Abs(α_D) * t90*ΔU_D/(U_D,max-U_D,min)     α_D <0

You may want to optimize these settings by using two different 2D scans at different energies (suggestion: 80eV, 220eV). Execute each scan first as atomic scan and store the images, the start both in parallel as non-atomic scans. Minimize artefacts by optimizing the energy voltage timing strategy settings. Then use only one of the two scans with neither bidirectional nor direct retrace settings and minimize artefacts by optimizing the deflection voltage timing strategy settings.

Note: Depending on your SPA-LEED hardware, the chosen scan type (bidirectional, direct retrace) could lead to artefacts in your acquired data. Please make sure you are fully aware of the meaning of these settings before you change them.

The finite response times of the deflection voltages as described above are the reason for the two scan types you can choose from. Both are meant for reducing artifacts caused by the finite speed of the high voltages even without delay times.

In a bidirectional scan (valid for 2D, RSM, SEM) neighboring lines are scanned in alternating directions. This minimizes the voltage differences between the last point of one scan lines and the first point of the next one and therefore reduces the absolute error of the deflection voltages at the beginning of each scan line. The drawback, however, is that the small relative deflection voltage errors may now become visible since the errors in adjacent lines have opposite signs: Comb-like distortions of diffraction spots may appear for small gate times and slow deflection amplifiers.

A direct-retrace scan (also valid for 2D, RSM, SEM) the idea is implemented to use the scan idle times for letting the deflection voltages settle: The first points of adjacent scan lines correspond to a very similar pair of x/y-deflection voltage values. Therefore the deflection voltages are set to the values of the first scan point after a scan line is finished. The time for displaying the scan data on the graphical user interface is then "used" for the settlement of the deflection voltages. No specific artefacts are caused from this setting, it is therefore the standard preset.

The "usual" scan mode of the SPA-LEED as implemented in older software packages, where each scan line is finished, the data are displayed and then the next scan line is started, could cause artefacts especially at small counter gate times and slow deflection amplifiers: It may occur that the counting at the first point of the next scan line is already started while the deflection voltages are still somewhere between last point of old scan line and first point of new one. This leads to fake intensity at the first one or few scan pixels of each scan line, since the counter acquires intensity during the creep of the deflection voltages.

The image below shows schematically the behavior of the different scan types.

The combination of direct retrace and bidirectional is allowed but does not make sense: The first scan type is based on the idea of using idle times for large scan voltage changes while the second one minimizes the scan voltage changes. The combination of both simply combines the artefacts of both without any benefit.

Hint: Take a 2D scan with a small gate time (1 ms or less) with the "bidirectional scan" setting active, and observe the inter-digital-like shifts of the scan lines. If these shifts are small, you may use the "bidirectional scan" setting and not delay timing (see next tab) for fastest possible scans. If the shifts are large, you should introduce delays to allows for high voltage settling.

Note: The beam park position is used to protect your channeltron during idle times, since the latter's lifetime at the approx. 10⁶ counts per second from a specular spot is limited to only a few hours.

Check always that your park position setting does not accidentally coincide with a diffraction spot position.

Some scan types, especially the RSM scan, rely on a "perfect" alignment of the sample. This means that the (00) spot is centered in the diffraction images solely mechanically, the sample is placed in the specified distance in front of the instrument, and no electromagnetic fields are present.

GUI Element	Meaning and Usage
Image shift compensation parameters for x direction	A compensation voltage according to this formula is added to the ideal-case x deflection voltage.
Image shift compensation parameters for y direction	A compensation voltage according to this formula is added to the ideal-case y deflection voltage.

This ideal case is hard to achieve. Especially, a perfect mechanical alignment requires to angles of rotation of the sample holder (rotation and tilt) as well as a time-consuming iterative alignment if the sample holder does to rotate around the point of incidence of the electron beam onto the sample surface. Therefore WinSPA allows a correction of angular misalignments, which cause a linear image shift upon changes of the electron energy.

The D/A converter settings tab ("DAQ-DAC")

In this tab, specific settings regarding the analog output voltages of your DAQ system can be changed.

WinSPA allows a flexible routing of the (logical) analog control voltages to the (physical) D/A channels of your system, as well as changing the overall gain specifically for your gun supply and deflection amplifier.

Please keep in mind that these settings - if not chosen correctly - may seriously compromise the data acquisition and overall system operability.

GUI Element	Meaning and Usage
D/A Signal routing	Connection of logical signals to physical outputs.
Signal gains	Amplifier gains. Transfer ratio of bip. D/A voltage (-10..10V) to deflection voltage, or Transfer ratio of unip. D/A voltage (0..10V) to electron energy.
Ramp gain / units	Gain and units for space signal "Ramp".
Aux gain / units	Gain and units for space signal "Aux".

Note: Routing several logical signals to one physical output is possible, but does not make sense.

The Counter settings tab ("DAQ-Ctr")

In this tab, specific settings regarding the TTL counter of your DAQ system can be changed.

GUI Element	Meaning and Usage
Create 8253/3 mode 2 initialization pulse	Fixed, required.
Reduce gate time at low count rates	Select, whether gate time can be reduced at low count rates. Speeds up scans on the cost of diffuse background statistics.
Lower/Upper Threshold	Range of count rates with gate time reduction.
Apply dithering noise	...not yet implemented
Correct count rates	Calculate count rate based on really available DAQ time window, excluding dead time.

Please keep in mind that these settings - if not chosen correctly - may seriously compromise the data acquisition and overall system operability.

The file I/O settings tab ("File I/O")

In the "File I/O" tab you find the settings for data import and export.

GUI Element	Meaning and Usage
NetCDF library found	This checkbox is activated if WinSPA was successful in loading the NetCDF.dll library.
Try again!	Click here to let WinSPA search again for the NetCDF library. You could place the NetCDF.dll file in the WinSPA directory.
Library Version	Here the version of your NetCDF.dll library is displayed. Note: WinSPA was developed and tested with V 3.5.0 (4th April 2001).
ASCII Export: Value Delimiter	Character that separates the individual data points. The scan data itself are stored as character separated values (CSV), sometimes incorrectly referred to as comma separated values. All scientific data analysis software packages can import this type of ASCII file, including all modern spreadsheet applications.
ASCII Export: Line Delimiter	Character that separates lines in 2D/SEM/RSM data.
ASCII Export: Comment style	Choose, how the metadata of your scan are stored in the ASCII file. All metadata are stored as comments. You can choose between the most common comment styles of several programming languages of the last decades. Use a comment style which is does not irritate the program you want to import the scan data into.
ASCII Export: Use Form Feed	A "form feed" command can optionally be put at the end of the ASCII export file. May be helpful for direct text printer compatibility, but for 99.9% of the data I/O you will probably not see any effect of this setting.

WinSPA uses the free data format NetCDF (network Common Data Format). NetCDF is a machine-independent format for representing scientific data. This format is widely used in the scientific community. NetCDF files can be handled by numerous software products such has IDL (native) and Matlab (requires a toolbox). C, Fortran, Java, etc. libraries are also available to read/write NetCDF data files.

In particular, NetCDF data are

• Self-Describing:
  A NetCDF file includes meta-information about the data it contains.
• Architecture-independent:
  A NetCDF file is represented in a form that can be accessed by computers with different ways of storing integers, characters, and floating-point numbers.
• Sharable:
  One writer and multiple readers may simultaneously access the same NetCDF file.
• Direct-access:
  A small subset of a large dataset may be accessed efficiently, without first reading through all the preceding data.

All information on how to deal with NetCDF format can be retrieved at Unidata. Free NetCDF browsers for viewing data are also available (NCbrowse and Panoply).

Note: In the NetCDF tab you can see whether the dynamic link library (DLL) for NetCDF file access has been found or not. You should check this after the installation of WinSPA. If the DLL has not been located by WinSPA, re-check the presence of the NetCDF.dll and click on the try again button.

The tab for global ranges settings ("Ranges")

In the "Ranges" tab you can modify the allowed input value ranges.
The values of many graphical user interface input elements of WinSPA are checked to be within a defined range of allowed values. Even though this patronizes the user, severe problems can be avoided this way, such as

• Memory overflow due to giant scan sizes.
• System lock due to long gate times.
• Emitter damage due to overvoltage arcs between emitter and anode.
• ...and many more.

There may be, however, situations where the user does not want the software to try to be more intelligent than the user. For example, you may want to make a 2D scan with 10,000 by 100 pixels, knowing that this costs less memory than the default 4000 by 4000 pixels. Or you might want to view a 100 by 100 pixels 2D scan in 20 times magnification, knowing that this would not be a good idea for a 4000 by 4000 pixels 2D scan since the internal graphics memory might not be sufficient.

In those cases only you might change the range settings of WinSPA. Please think twice why the preset ranges are not sufficient for your application and whether any problems could be caused by exceeding the predefined ranges. Also, please set the default values immediately after you have finished the scans for which you needed the extended settings.

Note: Since the standard settings are considered to be correct for all "normal" applications of SPA-LEED, your changed settings for input value ranges are not saved in the config.dat file - they are only valid until closing WinSPA.

GUI Element	Meaning and Usage
Electron Energy Min. / Max.	Minimum/maximum allowed values for the electron energy.
Gate Time Min. / Max.	Minimum/maximum allowed values for the counter gate time.
Points 1D Min. / Max.	Minimum/maximum number of scan points in 1D scans.
Points 2D Min. / Max.	Minimum/maximum number of scan points in each direction in 2D scans.
Threshold Min. / Max.	Minimum/maximum value of threshold intensity in spot tracker for point scans.
Wait Time Min. / Max.	Minimum/maximum value of wait time between repetetive scans.
Max. 2D Zoom	Maximum image zoom for all 2D scans (2D, SEM, RSM).
PWM duty cycle	Minimum/maximum value of PWM duty cycle.
Maximum t90 deflection	Maximum t90 time for deflection voltage changes.
Maximum t90 energy	Maximum t90 time for energy voltage changes.
Max. relay switch time	Maximum time for relay switching (real space/reciprocal space).
Counter dead time	Minimum/maximum value for overall counter dead time (pair resolution time), including RC time constant, CEM recovery time, TTL pulse length etc.

XY offset voltages

For adjustment purposes you can set offsets on the deflection voltage in the x- and y-directions. During "normal" operation the offsets should be set to zero, since a good mechanical alignment of your sample is independent of the electron energy and therefore better than electrical shifts.

GUI Element	Meaning and Usage
x voltage offset coarse/medium/fine	Three sliders with different ranges for changing the X offset voltage.
>||< ("Center") x voltage Offsets (medium/fine)	If the medium or fine slider of the X offset voltage is at one end of the range, you can transfer most of its value to the next coarser slider.
x voltage	Display of the X offset voltage.
0! (Set x voltage to zero)	Click here to center all sliders and thereby reset the X offset voltage to zero.
y voltage offset coarse/medium/fine	Three sliders with different ranges for changing the Y offset voltage.
>||< ("Center") y voltage offsets (medium/fine)	If the medium or fine slider of the Y offset voltage is at one end of the range, you can transfer most of its value to the next coarser slider.
y voltage	Display of the Y offset voltage.
0! (Set y voltage to zero)	Click here to center all sliders and thereby reset the Y offset voltage to zero.
Angle of Rotation (slider and value display)	With this slider you can comfortably define an angle of rotation between x/y coordinate system of deflection of manually set deflection voltages and the two x/y axes of your instrument.
Resulting x and y voltage	The two manual deflection voltages which are added to any deflection voltage output value. In case of no offset rotation, these values are the same as above.s

Manual energy setting ("Manual E")

In some situations, you may want to set the electron energy manually and directly , for example to find an out-of-phase condition, mainly when you are looking at the phosphor screen of your SPA-LEED. In case the SPA-LEED supply is too far away to reach the energy control while looking at the phosphor screen, "manual energy" allows you to use mouse and keyboard (extension cables may be useful) to change the electron energy quickly and observe the effect immediately.

GUI Element	Meaning and Usage
Manual Energy Coarse/Medium/Fine	Three sliders with different ranges for changing the electron energy manually.
>||< ("Center") energy voltages (medium/fine)	If the medium or fine slider of the energy voltage is at one end of the range, you can transfer most of its value to the next coarser slider.
Active	Click here to activate the manual energy setting. Consider the "note" below.

Note: WinSPA crashes if the manual energy setting is used in parallel to the execution of any scan. This is caused by the way the energy setting and scan execution are handled internally. This may be changed sometime in the future, but in fact there is really no good reason for tinkering with the electron energy during scanning!

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The rate meter

In the ratemeter and the voltage meters windows you can find some display elements for checking and controlling the I/O data of WinSPA, such as count rate, deflection voltages, electron energy and more.

All those values are displayed via a callback function from the SpaDAQ.dll. That means that they come from a very deep abstraction layer of the software. You can therefore be pretty sure that these values are correct (depending on the voltage gain of your deflection and emitter high voltage amplifier). The drawback of this callback approach is a greatly reduced system performance (bidirectional communication with data acquisition library) and lots of problems with a thread-safe and lock-proof access of the Delphi VCL (visual control library).

In order to avoid those problems, the meters are now designed (from WinSPA V1.05 on) to work asynchronously from the value changes. This means, the meters are udated a little bit more often than 10 times per second with the latest values. As known from any time discretized system, this can lead to sampling artefacts (moire, beats).

GUI Element	Meaning and Usage
Rate Meter Display	In this display field a bargraph display of the current count rate is visualized, along with lines for peak hold and moving average (if active).
Linear / Logarithmic Scaling	Linear or logarithmic scaling of the ratemeter.
CPS Max.	Upper limit of the ratemeter display range.
Peak hold	Switch display of peak hold on or off. Peak hold value is displayed as thick line in "data color".
Peak hold time range	Duration for peak hold memory.
Moving Average	Switch display of moving average on or off. Moving average value is displayed as thick line in "marker color".
Moving Average speed	Time constant for moving average.

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The voltage meters

The voltage meters allow you to monitor the output voltages of WinSPA.

GUI Element	Meaning and Usage
X Voltage	X deflection voltage Ux.
Y Voltage	Y deflection voltage Uy
Energy	Electron energy UE.
External lens	Output voltage of the auxiliary fourth analog output.
Mode of Operation (k-Space / SEM)	Status of logical output for controlling an optional external relay switch for deflection voltages.

Note: The values are updated when and only when SpaDAQ.dll updates the output values. In order to minimize hardware access, the values are only written to the hardware if and only if a value has changed. You might therefore see E=000.00eV quite some time after switching on the "show voltages", even though the electron energy is not 0 eV. This value is only updated after current electron energy is changed the first time after switching on the display (the same holds for the deflection voltages).

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The k-space calibration

The k-space calibration form is a tool that makes it very easy to perform a calibration of the reciprocal space of your SPA-LEED system.

GUI Element	Meaning and Usage
Surface lattice constant of sample	Surface lattice constant of sample. Use a well defined sample such as Si(111) for the calibration.s
Electron Energy	Electron energy used in calibration scan.
Reference Length in k-Space in V and %BZ	Length for calibration in calibration scan (via 1D tool in 2D scan).
Resulting k Sensitivity	k sensitivity as calculated from given values.
Calculate	Calculate the k sensitivity from given values.
Apply	Apply the calculated k sensitivity to the software settings form.

Note: The k-space calibration is one of the standard operating procedures. Please refer to the respective section of this help.

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The R-space calibration

The R-space calibration form is a tool that makes it very easy to perform a calibration of the real space of your SPA-LEED system.

GUI Element	Meaning and Usage
Electron Energy	Electron energy used in calibration scan.
Reference Length in R-Space in V and mm	Length for calibration in scan (via 1D tool in SEM scan) and real space. Use a known distance such as the sample width or length for calibration!
Resulting R Sensitivity	R sensitivity as calculated from given values.
Calculate	Calculate the R sensitivity from given values.
Apply	Apply the calculated R sensitivity to the software settings form.

Note: The R-space calibration is one of the standard operating procedures. Please refer to the respective section of this help.

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The Image Shift calculation

In the image shift calculation form you can enter the position of a diffraction spot (the specular spot in most cases) at different electron energies. A linear function can then be fitted to the positions, and their parameters can be copied to the software settings form.

GUI Element	Meaning and Usage
X and Y Pos.(ition) columns	Contain the x and y coordinates of the supporting points.
Energy column	Contains the electron energies of the supporting points.
Data display	Displays the data points and the fitted lines.
Calculate	Calculate the linear shift from given supporting points.
Apply	Apply the inverse of the calculated linear shift to the software settings.

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