Low Temperature Multi-Channel Cathodoluminescene Instrument – Allalin 4027

The Allalin 4027 is a nanometer resolution spectroscopy instrument, based on a disruptive technology known as low-temperature quantitative cathodoluminescence that securely integrates a light microscope, a scanning electron microscope, and a cryogenic stage into one tool. It is built for those who need to follow a tight technology roadmap and quickly access very precise spectroscopic information that has been unattainable using traditional methods.

In the semiconductor sector, the Allalin 4027’s 1600 color channels offer an unparalleled solution for measurement of energy transfer in second generation solar cells and band-gap energy in gallium nitride based devices such as LEDs and power transistors. It can accelerate technology development process and perform advance failure analysis (Indium clustering, band-gap shifts, etc.). In scientific and industrial research, the Allalin 4027’s ability to create spectroscopic maps with nanometer resolution at varied temperatures makes it the ultimate tool to acquire a deep understanding into the physics of nanoscale objects.

The system was constructed from the ground up to attain greater cathodoluminescence performance without sacrificing the electron microscope performance: the light microscope and the objective lens of the scanning electron microscope are carefully intricated so that their focal planes match each other; the light microscope is machined with sub-micrometer precision so as to reach ideal achromatism, high numerical aperture (N.A. 0.71) and constant and better photon collection efficiency over a field of view of 300 µm, so that quantitative cathodoluminescence benchmarking becomes conceivable for the first time; the electron microscope also works at low electron beam energy (3–10 kV) for improved cathodoluminescence resolution. The Allalin 4027 adds a six-degrees-of-freedom cryogenic stage for arbitrary positioning of the specimen with 1 nm increments and zero drift and vibration at low temperature (10–300 K).

The Allalin 4027 includes a spectrometer, a zero-drift liquid Helium cryostat, a high speed EMCCD camera, a six-degrees-of-freedom nano positioning stage and extra electronic hardware to run fast hyperspectral acquisitions.

Key Benefits

• Zero alignment: patented achromatic light microscope embedded in the column of a proprietary scanning electron microscope. Operating the Allalin 4027 is intuitive thanks to its context-based user interface, therefore it does not require an expert
• No compromise: simultaneous generation of a SEM image and a hyperspectral CL image with no degradation of the electron probe size
• Quantitative: the photon collection efficiency is constant over a large field of view of 300 µm with 0% photon loss due to vignetting in polychromatic mode; a mapping of 300 micron is performed without any displacement of the specimen: cathodoluminescence results are reproducible and comparable
• High light collection efficiency: a numerical aperture of 0.71 (f/0.5) makes low emission cathodoluminescence a reality
• Low temperature stability: obtain a hour-long map 10 K without detecting any drift
• Nanometer positioning system: nanometer scale measurements thanks to the most innovative nano positioning system ever built in an electron microscope
• Upgradable: the key components (scanning electron microscope and light microscope) of the Grammont 2172, Allalin 4027 and Rosa 4634 are the same; it is possible to upgrade anytime to another system by incorporating various modules
• Optical hub: for integration of the Attolight CL instrument in a larger spectroscopic system

Applications

• Failure analysis
• Solar cells efficiency
• GaN power transistors
• LED performance and reliability
• Threading Dislocation Density (TDD) counting
• Development of nanoscale optolectronic devices

Attolight optical microscope features constant resolution and photon collection efficiency over a field of view of 300 μm (left). Quantitative cathodoluminescence, i.e. comparison of emission intensities between various points is now possible. The traditional parabolic mirror approach is plagued by blur and vignetting (right).

Close-up of two NWs tip. Red now represent emission from the GaAs core (820 nm) of the wire, when blue regions mark the QDs emission (670 nm). Dots at less than 500 nm can be easily resolved. (Specimen temperature : 10 K)

Mapping of the QDs location with respect to the emitted wavelength. Blue, green and red correspond to 3 wavelengths between 650 and 700 nm. Some dots emit at several wavelength, resulting in composite colors (e.g. yellow).

Hyperspectral mapping of different layers in a cross section of a GaN/AlGaN hetero structure.

Product Specifications

Measurements Mode

• Ultrafast hyperspectral mapping from 180 to 1100 nm
• Cathodoluminescence mapping (polychromatic and monochromatic)
• Simultaneous SE and CL imaging
• Secondary electrons (SE) mapping

Electron Optics

• Schottky thermal field emission gun
• Acceleration voltage: 3–10 kV
• High sensitivity SE detector
• Highest spatial resolution: 2.8 nm at 10 kV
• Electron optics optimized for continuous and pulsed operation
• Electro-magnetic lenses, electrostatic deflectors and astigmatism correctors
• No loss of SE resolution in cathodoluminescence mode
• Electron probe current: 30 pA to 20 nA
• Field-upgradable to picosecond pulsed photoelectron gun
• Optimum working distance: 3 mm (matches light microscope focal plane)
• Maximum field of view: 600 µm at 3 kV

Light Optics

• Fully achromatic reflective objective from 180 nm to 1.6 µm
• Light microscope embedded within the electron optics
• Field of view: > 300 µm
• Resolution: < 5 µm
• Numerical aperture: NA 0.71 (f/0.5)
• Light collection efficiency: 30% of the photons emitted by a Lambertian emitter exit the microscope (constant over the whole field of view)

Light Detectors

• Dispersive spectrometer with two imaging exits (320 mm focal length) and a 3-grating turret (gratings to be specified by customer at time of order)
• High speed EMCCD camera for UV-Visible detection
• Ultrafast hyperspectral mode generates a 128 by 128 pixels map in 18 seconds

Chamber and Vacuum System

• Internal chamber dimensions: 208 mm (diameter) x 300 mm (height)
• Typical specimen exchange time: 20 minutes
• Ion getter pumps for electron gun and electron column
• Turbo molecular pump for the specimen chamber
• Electron beam and light microscope coincidence plane at 3 mm working distance

Nano-Positioning Stage

• Smallest increment: 1 nm
• Six degrees of freedom for arbitrary movements (compatible with the cryostat)
• Travel range: 25 mm (X and Y), 3 mm (Z), 3° tilt (X and Y), 35° rotation (Z)
• Repeatability (100 nm range): < 2 nm
• Repeatability (full travel range): 100 nm

Low Temperature Cryostat

• Minimal sample temperature range: 10 K–300 K
• Helium cold finger for low vibrations
• Advanced digital temperature controller

Sample size

• Maximum thickness: 1.5 mm
• Maximum diameter: 25.4 mm

System Control

• Hardware control and data server: 32 bit server with Windows^® 7, 7 inch touchscreen monitor for system initialization, WiFi router for connection to remote control
• User interface and remote control: wireless tablet computer with 2048 x 1536 touchscreen

Consumables (Partial List)

• Ion Getter Pumps
• Replacement electron source module
• Aperture strip for electron beam

Installation Requirements

• Power: 1 standard wall plug (230 V, 50 Hz) delivering 10 A
• Weight: 800 kg
• Dry nitrogen: (0.1–0.5 bar)
• Compressed air: 551 kPa/80 psi, clean, dry and oil free
• Environment: temperature 20 °C +/-3 °C, relative humidity below 60% RH, stray AV magnetic fields < 100 nT asynchronous < 300 nT synchronous for line times > 20 ms (50 Hz mains)
• Floor vibrations (site survey required as floor spectrum relevant)
• Preferred door width: 120 cm (100 cm possible when removing isolator posts)
• Acoustic guidelines: < 55 dBC (site survey required as floor spectrum relevant)

Common Upgrades

• Time-resolved: time-resolved cathodoluminescence measurements from 180 to 850 nm
• Infrared: hyperspectral mapping up to 1600 nm

Lay-Out

The Attolight CL Tool sits on an optical breadboard mounted on four isolator posts to attain vibration isolation. A typical recommended layout is shown below.

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