So How does the JEM-2010F STEM work?

UIC Electron Microscopy Service

So How does So How does the JEM-2010F the JEM-2010F STEM work?STEM work?

and how do you and how do you get good data get good data

out of it?out of it?

Alan NichollsAlan NichollsResearch Resources CenterResearch Resources CenterUniversity of Illinois at ChicagoUniversity of Illinois at Chicago


Optimizing STEM performanceOptimizing STEM performance

• Specimen considerationsSpecimen considerations

•JEM-2010F JEM-2010F STEM optics & aberrations STEM optics & aberrations

• STEM Detectors STEM Detectors STEM (solid state & PMT); CCD (TEM imaging & EELS); EDXSTEM (solid state & PMT); CCD (TEM imaging & EELS); EDX

•FasTEMFasTEM and STEM and STEM


Specimen ConsiderationsSpecimen Considerations• Specimens for STEM need to be contamination free!

• Do not touch any part that is used inside a vacuum system with your bare hands (I.e. Ion Mill holders etc)

• IN PARTICULAR no part of the specimen holder, support or tools should ever be touched by ungloved hands.

• Keep use of acetone down to a minimum - this is notoriously dirty and a primary source of hydrocarbon contamination.

• Specimens that are glued will always need Plasma cleaning in the holder. 20 min Ar, 10 min O2 at 10W is recommended if the specimen is not damaged by oxygen.

• Specimens can be plasma etched at 100W BUT must be in the Gatan duomill holder supplied NOT the specimen holder. Approximately 1nm/minute is removed.

• DO NOT Plasma Clean any holder without a specimen in.

• DO NOT EVER Plasma Clean heating or cooling holders!

• Specimens on Carbon Films can be plasma cleaned or use an Infra Red Lamp with the specimen on a slide or filter paper at setting 6 for 30 minutes.


STEM - the STEM - the important partsimportant parts


Thermal emission Field emission

W LaB6 Shottky ZrO/W Thermal FEW (100)

Cold FEW (310)

Brightness (A/cm2/sr) at 200kV ~5x105 ~5x106 ~5x108 ~5x108 ~5x108

Electron Source Size 50m 10m 0.1-1m 10-100nm 10-100nm

Energy Width (ev) 2.3 1.5 0.6-0.8 0.6-0.8 0.3-0.5

Vacuum (Pa) 10-3 10-5 10-7 10-7 10-8 10-9OperatingConditions Temperature (K) 2800 1800 1800 1600 300

Current (A) ~100 ~20 ~100 20-100 5-20

Short termstability

1% 1% 1% 7% 5% 2%

Emission

Long termstability

1%/hr 3%/hr 1%/hr 6%/hr 20% 10%

Maintenance Not necessary Not necessary Start-up takestime

Build upnecessary

after change

Flash everyfew hours

Price & Operation Low & simple Low & simple High & easy High & easy High &complicated ?

Lifetime 3 months 1 year >4 years(UIC 8 years +)

? ? 1 year

UIC instruments JEM-100CX JEM-3010 JEM-2010F NA NA HB601

Characteristics of different electron sourcesCharacteristics of different electron sources


TEM>STEM

Microscope should be aligned in TEM mode before entering STEM mode. If EELS spectra to be collected this should include GIF alignment.

If you need to adjust A2 to optimize the probe this should be done before TEM alignment.

A2 adjustments are only necessary for ultimate imaging resolution and should be done slowly!


NomenclatureNomenclature

Gun

Cond

Obj

X

X

X

TEM STEM

N/A

N/A

Condenser Aperture

Condenser Stigmator

Objective Aperture

Objective Stigmator

(Virtual Objective Aperture)

(Condenser Stigmator)

Objective Aperture

Objective Stigmator

N/A

N/A

Specimen


NB Increasing Condenser lens strength increases the demagnification

Decreasing A2 increases the demagnification :- the electrostatic focussing effect is the difference between A2 and A3 (voltage applied to each stage of accelerator (~55kV))

But increasing demagnification lowers beam current as defining aperture after condenser lenses


STEM - STEM - How much demagnification do we How much demagnification do we need for atomic resolution?need for atomic resolution?

Source sizeSource size ~170nm~170nm

Beam size at specimenBeam size at specimen 0.2nm0.2nm

Total demagnificationTotal demagnification ~850 ~850

C1=6V; C2=4.7V; Demag 570C1=6V; C2=4.7V; Demag 570

C1=7.07V; C2=4.64V; Demag 860C1=7.07V; C2=4.64V; Demag 860

C1=8V; C2=4.61V; Demag 1185C1=8V; C2=4.61V; Demag 1185

OPTIMUMOPTIMUM

To get to 0.13nm use A2 to increase gun To get to 0.13nm use A2 to increase gun demagnification - reduce 7.3>6.8demagnification - reduce 7.3>6.8



TEM modeTEM mode vv STEM modeSTEM mode

TEM - Image is readout in parallel from the whole illuminated area. All pixcels in the image are exposed at the same time.

STEM - Image is read out in serial from area scanned on the specimen. Intensity from each pixcel is read out and displayed independently in order.

SpecimenSpecimen DetectorDetector


HADFHADF

EELSEELS

BFBF


Effect of CEffect of Css on Ronchigram on Ronchigram

Increasing Objective lens strength


Stigmating using the RonchigramStigmating using the Ronchigram

Ronchigram from amorphous area. Select Scan mode Spot 1 and a magnification above 100Kx.

a) underfocus astigmatic

b) underfocus stigmated

c) Gausian focus stigmated (almost!)

a bb cc

Red circle marks unaberrated part of Ronchigram that should be selected by Objective aperture


< Au contact layer on GaAs - 0.2nm probe, (C1 6.06; C2 4.65; A2 7.3)

Si dumbells resolving 0.136nm 004 spacing with 0.13nm probe > (C1 6.06; C2 4.65, A2 6.8)



JEOL HADF DetectorJEOL HADF Detector


Radiation causes photoelectrons to be generated by Radiation causes photoelectrons to be generated by cathode. These are multiplied by the dynode chain cathode. These are multiplied by the dynode chain (typically 8 elements) giving a 10(typically 8 elements) giving a 1088 amplification of the amplification of the signal.signal.

Photomultiplier TubePhotomultiplier Tube



Bright Field Annular Dark Field

Schematic of Gatan STEM Detector


So which STEM detector is better?So which STEM detector is better?

Solid stateSolid state oror PMT basedPMT based• Easy to fabricateEasy to fabricate

• Cheap to replaceCheap to replace

• Can be cut into any shapeCan be cut into any shape

BUTBUT

• Large dark currentLarge dark current

• DQE poor for low intensityDQE poor for low intensity

• Electron beam damageElectron beam damage

• Insensitive to low energy Insensitive to low energy electronselectrons

• Gain of system is high with a Gain of system is high with a DQE of 0.9DQE of 0.9

• Noise level is lowNoise level is low

• Good at TV rate or low signalGood at TV rate or low signal

BUTBUT

• scintillator not as robust as SSDscintillator not as robust as SSD

• more expensive and bulkymore expensive and bulky

For Z contrast STEM PMT is best!For Z contrast STEM PMT is best!


Gatan Imaging FilterGatan Imaging Filter


CCD detector componentsCCD detector components


Repeat until all rows are read out

Read out rates can be as fast as Read out rates can be as fast as 0.01s per frame. CCD can be re-0.01s per frame. CCD can be re-exposed once read out.exposed once read out.

CCD arrays have:-CCD arrays have:-

low noise and good DQE when low noise and good DQE when cooled.cooled.

High dynamic rangeHigh dynamic range

BUTBUT

they are expensive they are expensive

($250K for 4Kx4K CCD)($250K for 4Kx4K CCD)

CCD ReadoutCCD Readout


Electron Energy Loss Spectrum from Graphitic Carbon

EELS Spectrum from Graphitic CarbonEELS Spectrum from Graphitic Carbon

In STEM mode, with 0.2nm, probe use 0.1s for zero loss region and, as a starting point, 1s per 100eV to look at higher losses (eg O at 532eV - 5sec)



XEDS Spectrum from BSCCOXEDS Spectrum from BSCCO

Typically need a > 0.25nA to collect a statistically significant spectrum in 100sec (I.e. 0.5-1nm spot size 50-70m CA). Can collect spectra with 0.2nm probe for ID of Major (>10%) components.


EELS onlyEELS only

Spectrum ImagingSpectrum Imaging

XEDS & EELSXEDS & EELS


XEDS Spectrum ImagingXEDS Spectrum Imaging

• Acquire spectrum at each point in image typically using 1nm probe to get sufficient X-ray signal.

• Short acquisition time at each point and multiple scans. 128x128 SI usually takes 30-45 minutes to get significant data

• Data can be interrogated afterwards to generate spectra, new maps and linescans


XEDS Spectrum ImagingXEDS Spectrum Imaging

LINESCAN example.

For planar defects data can be, post acquisition, integrated parallel to the interface


FasTEMFasTEM

Start UpStart Up

Programs must be started in the order listed.

• FasTem Server and GIF are usually left running

• You MUST Login to FasTem server before opening the Client (Control window).

• FasTem Video Server does not need to be running.


Simple KnobsetSimple Knobset

Detector Select

Brightness FocusTEM

Image Shift X

TEM Image Shift Y

Image Save Q.Beam Selector Multi Function

WOB/DEF/STIGMAG/DIFF Select


FasTEM 　 GUIFasTEM 　 GUI


FasTEM ClientFasTEM Client

Selector Selector • Projector alignment settings are stored for the different detectors. Please make sure that you center the illumination in probe size 1-3 at 100Kx

• CAM TOP is not used

• MSC is not used (used for above GIF CCD camera for TEM)

• CAM BOT is the off axis camera (or other TV rate camera)

• SCRN is the fluorescent screen

• STEM is for Scanning mode

• GIF is for the Gatan Imaging Filter (EELS & Filtered TEM imaging)



STEM SelectorSTEM SelectorModeEM - TEM; AL - Alignment - center caustic figure with Condenser Def then illumination with Condenser ShiftSM - STEM monitor; DM - STEM Digital Micrograph

Active DetectorTEI - JEOL HADF DetectorEXT - Gatan STEM detector

Scan ModePIC/RDC - Full Frame/ Reduced FrameSPOT/SPOT1/SPOT2 - Spot modes, Spot1 should be used for Ronchigram



STEM SelectorSTEM Selector

Probe Size & Camera Length - choose from dropdown list.

NB Spot size on ASID unit affects probe size selected through FasTEM - Make sure Small is selected.

Alignment Function Default is “Projector” for centering beam on detector. Change to “Condenser 2 (Beam Tilt)” for electronic specimen shift - be careful miss-aligning column!


STEM set upSTEM set up

• Choose appropriate probe size

Probe Size

A2 Condenser Aperture

For

0.14nm 6.8 30mm Z Contrast HADF at highest resolution0.2nm 7.3 30mm EELS + Z Contrast (>20pA)0.5nm 7.3 50mm XEDS, EELS (>100pA)1.0nm 7.3 70mm XEDS, EELS (>500pA)

• Choose appropriate camera length

Camera Length

Inner Angle

For

2cm, 4cm EELS + HADF using Gatan detector8cm 85mrad JEOL HADF

10cm 62mrad JEOL HADF12cm 52mrad JEOL HADF15cm 40mrad JEOL HADF

15cm off axis 15cm CL centered on off-axis camera for Ronchigram


Digital Micrograph Digital Micrograph main windowmain window


Digiscan STEM controlsDigiscan STEM controls

Scan Setup• Select - 256, 512 and 1024 are set up for phase locked imaging. Use Default for fast scanning (Pixcel time can be altered)

• Waveform Monitor - Allows brightness and contrast to be optimized.

• Control Beam - Beam position tool only visible when not scanning image.

•NB Esc key stops scan immediately, Stop button only at the end of a frame. Record only acquires one frame


Z-contrast STEM - summaryZ-contrast STEM - summary

• Align microscope in TEM mode at desired A2 (inc. GIF for EELS)

• Enter STEM mode with largest CA (150m). Go to Spot1 with magnification greater than 100Kx - choose spot size and appropriate camera length for Ronchigram (NB 1nm up may be too bright for camera - for large probe sizes put aperture in, wobble Objective lens and minimize wobble using X&Y

aperture controls)

• Correct for Astigmatism (preferably on amorphous region) move to area for imaging. If fringes are visible in Ronchigram put appropriate aperture on axis. If fringes are not visible specimen is too thick, too far of axis or has too thick amorphous surface layer - choose another area.

• Choose appropriate camera length for STEM detector - insert detector change back to PIC mode.

• Increase magnification to x4M and focus to get atomic resolution image!

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So How does the JEM-2010F STEM work?