Lab report 4 Very important: if you raise the sample to the 10 mm line during pumpdown, the working distance will be approximately 10 mm. (How do you know what the WD is?) There is no “elephant” (pink or otherwise) for the Quanta. Some people still aren’t getting the hint about attaching a copy of their lab notes Nobody reminded me to upload images!

Nanowires, 1 MP

Nanowires, 512x442

High resolution imaging Why? –To see really tiny stuff! Soot particles (Combustion research) Gold nanoparticles and nanorods (Jennifer Shumaker-Parry) –To get really sharp images of “fairly small” stuff Gold nanoparticles and nanorods (Marc Porter…) –Same considerations should apply to e-beam lithography

Tin balls 2.4 Mx!

Soot on TEM Grid

High resolution imaging How? –FEG Why? d p 2 = 4i p /( π 2 * β * α p 2 ) –To see small stuff, you need a small spot. –Small spot requires Low probe current (small “spot size”) High brightness Large aperture angle – α p = d A /2*WD –Short working distance –Large aperture? We’re still arguing over that one, but nobody believes it!

Contributions to actual beam diameter

Optimum convergence angle The previous equation can be differentiated and the derivative set equal to zero Result is quadratic in α 4

Optimum convergence angle If chromatic aberrations can be neglected: –α opt = [2/3C s 2 )(8i p /βπ λ 2 )] 1/8 –At 10 kV, λ = 0.01 nm, 100 pA, and β = 10 8 A/cm 2 sr C s = 2 mm, then α opt = 6.4*10 -3 rad –α p = d A /2*WD If d A = 30 microns: WD = 2.4 mm –At 1 kv λ increases by a factor of 10 α p increases to 9 mrad WD decreases to 1.7 mm Much shorter for W-filament! Note that α opt was 4 mrad for W-filament (C s = 10 mm), 20 kV in Fig 2.22.

High resolution imaging What’s the point of all this math for high resolution imaging? Short WD is important! ETD is out of the game Other options –TLD –vCD –Helix Immersion mode increases resolution about another order of magnitude

High resolution imaging Minimize emi (Ian’s lecture of last Friday!) Minimize floor vibrations –Each lab in INSCC is on an individually poured slab of concrete Minimize acoustic vibrations (audio noise) Minimize temperature fluctuations Try “Mains lock” Replace carbon tape with silver or carbon paste Use single sample mount

Minimize Acoustic vibrations!

DCJ - High Resolution 14 When do we run out of resolution? SE1 have a range of a few nm and create the ‘edge bright line’ effect As a result when the feature size is close to the SE escape range  the object is not resolved. This occurs at ~ 5-10nm for low Z materials

DCJ - High Resolution 15 In other samples...  When an object gets small enough to be comparable with the SE1 generation volume then it becomes bright all over and the defining edges disappear.  For low Z, low density materials this can happen at a scale of 5-10nm Carbon nanotubes 5nm and 10nm wide edge brightness no edges

DCJ - High Resolution 16 SE image of Single Wall NanoTube

DCJ - High Resolution 17..but how wide is this nanotube? ?  The image does not have defined edges - its width is indeterminate and equal to carbon If these are the edges then width = 5.8nm If these are the edges then width = 1.5nm C =5.5nm

DCJ - High Resolution 18 Bypassing the SE1 limit  Metals have lower than carbon, and a higher SE yield  A thin metal film on a low Z, low density sample localizes all SE production within itself. The resolution now is a function of the film thickness only  Works even with very thin metal films (a few atoms thick)  We can exploit this effect to give interpretable contrast beyond the theoretical limit Low SE yield High SE yield width ~ film thickness even when < 

DCJ - High Resolution 19 Mass thickness contrast  The SE1 yield varies with the thickness of the metal  SE1 yield reaches the bulk value at a film thickness equal to about 3  The conformation of the film to surface topography provides contrast 1nm2nm3nm Film thickness SEYieldSEYield bulk value mass thickness variation

DCJ - High Resolution 20 Metal builds contrast  The SE localization in the film provides edge definition  The mass thickness effect gives extra contrast enhancement  The feature is now ‘resolved’ since its size and shape are visible 5nm low Z object 2nm metal film Beam position SE profile with metal film SE profile without metal SESE

DCJ - High Resolution 21 courtesy of Martin Müller and Rene Herrmann, ETH Zürich T4 Phage coated with Cr Cr coatings  Cr films are smooth and without structure even as thin as 1nm  The mass thickness contrast resolves edges and make the detail visible down to a nanometer scale  The high SE yield of the Cr improves the S/N ratio  However these coatings are not stable - so use Cr coated samples immediately after they have been made T4 Phage + Cr

DCJ - High Resolution 22 Coating Summary  Coatings are an essential part of the technique of high resolution SEM because they generate interpretable contrast, improve resolution, and enhance the S/N ratio  Thin coatings are better than thick coatings - do not make your sample a piece of jewelry  Below 100kx particulate coatings are useful because of their higher SE yields and better S/N ratios  Above 100kx can use chromium or titanium or particulate coatings of W,Pt or Ir  Carbon is a contaminant not a coating

Helix Detector Looks just like the LowVac detector Mounts just like the LowVac detector Costs $28.5k “You break it, you bought it.” Runs in Immersion Mode, like the TLD Gives super images in LowVac Aperture is 62 microns

Helix Detector page

Helix detector settings 1- why and when should Helix detector voltage be changed? Helix detector voltage should be optimized after every parameter change. This just means, from the previous Helix sweet spot, needing to bump it up or down a 1% or 2% after changing a parameter like water, FWD, beam current, kV, dwell. I believe Helix needs to be running at full current, just prior to arcing, at all times. A typical Helix session may run like this; 78.5% voltage = arcing, 77.5% voltage = no arcing and good signal contrast, 76.5% voltage = no arcing and poor contrast. I don’t expect you to see identical numbers as these but I’d expect you to experience a similar “narrow window” of good zone. For me, Helix sweet spots are 1%-1.5% off saturation, 3.2-mm FWD, 4kV- 7kV, as much as 30% less water than what was needed for LVD. Reducing Spot size just means increasing dwell times but I typically work between spots 2.0 and 3.0

Gold on glass, LowVac, Helix Detector

vCD Detector Backscatter detector Mounts on pole piece Has small aperture; will work in LowVac Works with beam deceleration Works in immersion mode

Landing Energy Page

Gold Nanoparticles, TLD

Gold Nanoparticles, vCD

Worm cross-section, vCD

Virus, vCD