Minimum_Requirements.pdf

Requirements /Specifications for the AFIT Electron Spectrometer (Corrected)

Spectrometer:

A true 180 ° hemispherical electron energy analyzer with a 150 mm mean radius is required .

This spectrometer must be operable in an ultrahigh vacuum atmosphere at pressures of 10-10 torr, capable of a bakeout temperature of 200oC, and have a DN100CF (6 inch OD) flange for mounting to the main vacuum chamber. The spectrometer must be constructed of non-magnetic materials inside μ-metal shielding and utilize a slit mechanism providing for at least 8 entrance and 3 exit slits which can be set independently via one rotary drive from outside the vacuum. Entrance and exit slits should operate independently. For each pair of entrance slits, one slit defines the energy resolution while the other slit serves to match the angular spread for the analyzer. This arrangement allows optimum transmission for all chosen slit sizes and resolution settings. A view port is to be provided for through the lens (optical) alignment. The analyzer must provide for a 150 mm mean radius. Fringe field corrections must be provided in the entrance and exit areas to guarantee excellent energy resolution at very low kinetic energies.

A multi-element, two-stage transfer lens with well-defined optical properties must be utilized to provide ultimate transmission of electrons from the source to the analyzer. All lens modes must be able to be set electronically. In addition, a standard working distance of 40 mm and a 44° conical shape of the front part of the lens should be provided to guarantee optimum access to the sample for all types of excitation sources.

For small spot analysis, a lateral resolution down to 100 μm should be available. In addition, angular resolution must be able to be optimized down to ±0.05° to be accomplished with an Iris aperture in the diffraction plane of the lens system allowing the angular acceptance to be continuously adjusted between ±1° and ±9° while keeping the acceptance area on the sample constant.

Power Supply:

One power supply must provide for all analyzer operation modes. A modular design / architecture is desired and all detector high voltage modules should be included. The power supply should be a fully digitized, with 24 bit high-precision voltage modules, truly bipolar, with very short settle times and super low noise modes. The modular design of the unit should allow independent setting of all voltages with no voltage dividers used. Each module should be fully galvanically floating, highly stable and linear. Voltages should be controlled by high-precision 24-bit digital-to-analog converters with an overall maximum settle time of 3 ms. Each module is to be equipped with a microcontroller allowing independent setting of all voltages.

Analog-to-digital converters for output voltages and output currents should facilitate diagnosis and error localization. The complete electronics package should be contained in a single 19” standard rack housing with removable cables. In addition, the power supply should be able to be operated in FAT (Fixed Analyzer Transmission) or FRR mode (Fixed Retarding Ratio). Both pass energy and retarding ratio should be continuously adjusted to fine-tune resolution and intensity.

The power supply should provide sufficient voltage to allow for an energy span of ±3500 eV thereby giving access to the high kinetic energy lines and provide for ultra high energy resolution with step widths down to 20 μeV thus guaranteeing extraordinary stability and low-noise allowing for ultra high resolution measurements. Preferably the power supply provides the fast and reliable CAN Bus interface and an internal microprocessor for fast and reliable processing and remote control. The temperature stability of the analyzer voltage modules should be better than 1.5 ppm of the voltage span per °C. The power supply must operate on a standard 120v, 60 Hz power line.

Electron Detection:

The detection package should contain an ultra-fast, low-noise preamplifier and counter providing for single channel or multi channel detection with up to 9 channels. MCD, CCD, Spin or Delay Line Detectors should be able to be retrofitted on site. The detector should be flange-mounted with a standard detector assembly consisting of either one, five or nine single channel electron multipliers arranged as a single block providing both compactness and durability.

Channel electron multipliers with an extended dynamic range for extremely high count rate applications should be standard. Upgrades from single to multichannel detection should be capable of being performed on-site. The design of the detection electronics should take into account the need for reliable counting results even in difficult environments and for extended dynamic ranges. Other detector types should be easy to retrofit without modification to the analyzer. Specifications: Provide channels 1, 5 or 9, preamplifier 300 MHz, input Impedance of 50 Ω, threshold Level of 4 to 200 mV, dead time 6 ns to 160 ns, counter 160 MHz, 24 bit per channel, package should mount directly on detector flange with a single multi-pin feedthrough in a RF shielded housing.

Performance:

For XPS using the Ag 3d5/2 or Mg Kα spectral line ,at 15 kV, 300 W, with a distance between sample-anode <15 mm: Provides resolution of 0.85 eV with count rates (signal over noise) of at least 300,000 for SCD, 1,700,000 for MCD of 5 channels, and 3,000,000 for MCD of 9 channels.

For a resolution of 1.00 eV, these count rates are 900,000, 4,600,000, and 9,000,000 and for a resolution of 1.40 eV, these S/N count rates are 2,000,000, 12,000,000, and 26,000,000.

For UPS (Ag valence band, He I, (*) Fermi edge width (12 to 88%) at T=300 K): Provides resolution of 140 meV*with S/N count rates of 2,000,000 10,000,000 20,000,000.

For AES using Cu LMM, 20 nA sample current (+15 V bias), 5 keV: Provides resolution of 0.5 % with S/N count rates of 300,000 1,500,000 3,000,000.

For ISS Ag , 0.5 μA sample current (+90 V bias), 2 keV, He+: Provides resolution of .5 % and S/N count rates of 1,200,000 6,000,000 12,000,000.

Data Acquisition & Processing:

A software package utilizing the Windows operating system and combining ease of operation with powerful data acquisition and analysis routines must be provided. This data acquisition and data processing software must provide computer control of all analysis methods possible with the electron analyzer. Predefined sequence measurements should be limited only by computer memory and disk space. For MCD detectors, the user has online access to the separate channels and a semi-automatic dispersion calibration should ensure optimal resolution and energy calibration for all analyzer settings. An MCD ratemeter should be included. Standard data processing tools should include background subtraction (linear, Shirley and Tougaard background), satellite subtraction, smoothing, integration, differentiation, numerical operations, scaling, view options, shift, work function adjustment and much more.

Peak fitting routines and quantification with easily configurable files for peak parameters (including database for XPS and AES) result in comprehensive surface analysis software for a wide range of applications.