THE HEBREW UNIVERSITY CENTER FOR NANOSCIENCE AND NANOTECHNOLOGY

Extra High Resolution Scnning Electron Microsopy MagellanTM 400L


Overview of Technique

The MagellanT XHR SEM enables scientists and engineers to quickly see things they could not see before: highly-sensitive surface images, looking top-down or at an angle, and at resolutions below one nanometer. This made possible thanks to the monochromatized Schottky-type field emission gun, allowing association of high spatial resolution with very shallow beam penetration. The MagellanT XHR SEM is equipped with new high sensitive and ultrafast electron detectors (including scanning-transmission 14-segments BF/DF/HAADF detector), newly implemented beam deceleration mode, high precision ultra-stable piezo-ceramic stage, built-in plasma cleaner and oil-free vacuum system. Microanalysis is available with the brand new large area EDS silicon drift detector Oxford X-Max (Oxford Instruments, UK) working on INCA 450 platform.

Basics and Tutorials

The scanning electron microscope (SEM) generates a beam of electrons in a vacuum. That beam is collimated and focused by electromagnetic lenses and scanned across the surface of the sample by electromagnetic deflection coils. Interaction of primary electron beam with the material of the sample in SEM causes excitation of secondary, backscattered, Auger electrons, characteristic X-ray radiation and photons of light. The primary imaging method is by collecting electrons that are released by the sample. Depending on their energy, angular distribution and the excitation energy of the primary beam, the electrons emitted by a sample are detected by different electron detectors mounted in the microscope chamber up to a sample surface. Detection of the electron signals is done either through solid state silicon-based detectors, or via photomultiplier-type detector involving double-conversion of a signal through light photons. By correlating the sample scan position with the detected signal, an image of a sample is formed. This image could be strikingly similar to what would be seen through an optical microscope and is, therefore, more or less intuitively understood by a human brain. Generally, each detected signal provides specific type of imaging in SEM. Imaging in secondary electrons (former samples' electrons leaving its surface with up to 250 eV excessive energy) provides mainly topographic information. Imaging in back-scattered electrons uses high energy electrons that emerge nearly 180 degrees from the illuminating beam direction. The backscatter electron yield is a function of the average atomic number of each point on the sample, and thus can give compositional information. Basically, a resolution of SEM image depends on a spot size produced by illuminating beam on a sample surface, and on a subsurface volume in which a detected signal is generated. Therefore, improved resolution in SEM is achieved through improvement of its source-optical part as well via proper choice of beam-specimen interaction conditions.

Our Magellan system is equipped with unique UNICUP electron source enabling monochromated highly coherent electron beam producing sub-nanometer spot on a sample surface. For better beam confinement and higher singal collection efficiency optical system of the microscope includes magnetic immersion lens. Beam decelerator (negative bias at microscope stage) is included for flexible handling of beam-specimen interaction volume that allows beam landing energy as low as 50 V only. At such low excitation energy, the interaction volume is confined to a few nanometers thus enabling surface sensitive imaging and accurate acquisition of tiny topography.

One more new feature of our Magellan system is imaging in scanning-transmission mode with the special bright field (BF)/dark field (DF)/high angular annular dark field (HAADF) STEM detector. Very likely to STEM imaging in our Tecnai F20 G2 system, this imaging mode allows upmost resolution of 0.5 nm, but achieved at much lower accelerating voltage of 30 kV. Therefore, high resolution structural and chemical imaging of beam-sensitive materials is now available with STEM mode in Magellan.

Scanning electron microscopes are often coupled with X-ray analyzers. The energetic electron beam - sample interactions generate X-rays that are characteristic of the elements presenting in the sample and are used to identify local chemical composition of the samples (energy dispersive X-ray spectroscopy (EDS)).

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Equipment Specifications

Resolution

* 0.8 nm at 15kV in SE mode
* 0.9 nm at 1kV in SE mode
* 1.5 nm at 200V in SE mode
* 0.5 nm at 30 kV in STEM mode

Horizontal field width (eq. Magnification)

From 100nm to 1.5mm {Mag~ x25- 1,000,000}

Landing energy

50V to 30kV

Beam current

1 pA to 22 nA

Electron source

Schottky FEG with UC (unicolor) technology
(<0.2eV energy spread - min Cc - chromatic aberration)

Detection

* Secondary electron detector (ETD)
* Through-lens SE and BSE detector (TLD)
* High contrast retractable solid state detector (vCD)
* Retractable Annular BF/DF/HAADF STEM detector
* IR camera
* Optical Nav-Cam+ camera for navigation

Beam decelerator

Optional stage bias to enhance low-kV performance, especially at ultra-low landing energies

Scanning

* 16-bit digital scanning
* Scanning range 512x442 - 4096x3536 pixels
*
25 ns/pixel min dwell time

Stage

5 axes high precision and stability piezoceramic stage:
XY: 100mm, Z: max 20 mm, T: -10 ° to +60°, R: 360° continuous

Vacuum system and anti-contamination accessories

* Entirely oil-free, includes Edwards XDS10 scroll pump, TMP and IGPs
* Automated Loadlock
* Built-in FEI plasma cleaner
* Special LN2 FEI cryo cleaner

Chamber

Large analytical chamber with 21 ports