TEM Images from me. -DSJ

 

 

So I've been telling people for a while that i would make a little page so that they could see what sorts of images (pictures) i'm taking. Here's a few of the more interesting ones, most of which do not have scale bars (Sorry!)

 

Many of these images were taken for my TEM lab, though the research related images are at the bottom, and will grow over time. Amorphous plan views aren't very interesting ... without statistical analysis, and the films I've been making lately are doped amorphous silicon layers.  I'd fistfight a yeti to have a quasicrystal to get diffraction patterns off of, but you can't always get what you want.

 

 

Many images are taken on a Phillips 420 @ 120kV, especially if there aren't any scale bars on them. The rest are on a Jeol 2010 w/ Lab6 emitter & GIF.  I've now also trained on the 2010F shown below, thought it is a different beast from the others, and requires a bit more care to operate (for me, right now).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 The Tranmission Electron Microscopes (TEM)

 

 

 

 

 

Avove is a lowsy photo of the Phillips 420 in our lab.  Below is the Jeol 2010F, which I don't use often, but it looks somewhat similar to our Jeol LaB6 which produces many of the images seen below.

 

 

 

 

 

GaN film epitaxially grown on Si substrate:

 

*epitaxy is the process by which single crystal layers are (attempted to be) grown. It is a slow, layer by layer process, which sometimes still produces material with defects. Imaging these defects can be achieved through a momentum selection process accomplished with judicious application of the objective aperture and dark field tilt mechanism. 

Sooo.... anyway, this is a series of images of a crystal with defects, imaged with the 420.

 

 

Bright Field, WB Dark Field, and DF images of a particular diffraction spot. This GaN film is deposited on a Si substrate (bottom left), with some layers of buffer material. In addition to the criminal absense of scale bars, the dark field images don't include their vector directions, which are (if i recall correctly, hey - this isn't a paper) are normal to the film. The dislocation cores light up in the center image because they distory the local lattice into a scattering (Bragg) condition.

 

 

 

 

This is a diffraction pattern of the above film, at a tilt that is close to the110 Silicon Zone axis.  The 001 Silicon and the 0001 GaN zone axes have diffraction patterns are overlaid ontop of one another, they are the 'horizontal' spots that are in line with each other, with the closer spacings. This image is rotated with respect to the other GaN/c-Si images above.

 

Diffraction patterns don't make sense to those who aren't familiar, but the link below has some cool java applets that illustrate how a diffraction pattern changes with respect to the orientation of the crystal that is scattering.  Long story short:  you build a 'reciprocal lattice' whose points correspond to reflections from planes of atoms, where this lattice interesects something called the Ewald Sphere, those interesection points appear as spots on the diffraction pattern.  This phenomenon allows crystallographic information to be gleaned from a suitable sample.

http://newton.umsl.edu/run//nano/known.html

 

 

 

Au Nanoparticle

 

 

 

Out of many images of many different gold nanoparticles, I decided to show this one, which is very close to zone axis for several grains. Those fringes you see are actual planes of atoms, stacked together. It's hard to say if the attoms are the light spots, or the dark spots, as this changes as a function of illumination.  The carbon support can be seen as the noise in the background.

 

The microscope beam is slightly astigmated here, possibly from sample drift, or poor alignment.

It is approximately 8.8nm in diameter from this perspective. (It may spherical in the projection diretion, or not)

 

Taken on the LaB6.

 

 

 

 

Poly Au

 

A Polycrystalline Gold film, taken with the LaB6, along with the corresponding diffraction pattern. Bright spots on the circle may represent particularly well represented orientations of microcrystals. If you center a Dark Field image on these spots, sometimes you can selectively image these grains.

 

An enhanced view.

 

 

 

Amorphous Si Ge mystery blend:

 

 

So this is a bright field view of the first sample that I successfully polished, milled, and otherwise avoided destroying. I inherited it from N.P. through a group he's in touch with, who didn't pass on what the composition of the film might have been, though some of the deposition parameters were sugesting that microcrystalites might form. Instead, We see an amorphous film with nanovoids.

 

 

Selected Area Diffraction pattern and Dark field views of an amorphous silicon germanium film grown on some kind of oxide on c-Si. Difficult to interpret as the thickness toward the bottom is such that the electron transparency becomes an issue.

 

 

Here's a higher resolution image from the LaB6, along with a reoriented image that has an intensity integral from left to right across the interface. The brightest line is an ~25nm Oxide on crystal silicon. A keen eye notices the thin layer of amorphous silicon (~7-10nm) to help ensure less crystallinity. After this, the SiGe film (of unknown composition) begins growing in the amorphous regime without voids for ~45nm, then with a series of columnar filimentary voids with thicknesses betwen 1-4 nm. Probably not device quality material.

 

 

 

Other Newer things-

 

Amorphous to Microcrystalline Germanium cross sections:

 

 

   

Bright and dark field images of Ge:H on native c-Si.  The difference in scattering between the amorphous areas and the microcrystalline domains can be seen clearly, along withe the cone growth structure. 

 

 

 

Diffraction pattern for Above.  Notice the streaky lines.  I'm not sure about this, but that may have to do with a series of nano-twins, as twin phenomena tend to exhibit particular distortions that include such lines.  The source of this is that the nanotwins are a series of stacking faults whose ordering and symmetry create additional features in the diffraction pattern.

 

 

Reducing the size of this image for the web really washed out a lot of the better details, but you can still see the prominant fringes from at least one obvious grain here.  The image is ~167x111 nm in real space.

 

 

NiMnO Sol-Gel Films:

 

 So a friend of mine made some films, and I wanted to see what they looked like.  The undoped film was rather interesting, illustrating that there's some effect of the layer-by-layer growth method. 

 

 

 

 

 

 

 

 

 

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Because this is page has gained an excessive number of pictures, further updates will be included on TEM images page 2.