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Items of interest for the JEOL community


Imaging a Spider Web with the SEM

The challenge was to image the spider’s web without causing any induced stress or deformation of the structure as collected. The web was collected between two glass plates to protect the structure. The top glass plate was removed and the sample was transferred to an SEM holder that was configured as in the Photos.


Top reference holder with cap removed.


Top reference holder with carbon tape on the cap and with cap reinserted.


Top reference holder with tape pressed onto the web.

For illustration purposes a piece of window screen was used to demonstrate this technique, as spider silk would be too small to show up in the macro photos. A strip of conductive C tape was applied to completely surround the removable cap of a holder designed to hold polished metallographic mounts. This was then pressed onto the web and lifted off. This allowed the intact web inside the tape to be ripped away from the rest of the web outside of the tape without any stress or strain. The cap was then placed onto the specimen holder for insertion into the SEM. This type of mounting allows the microscopist to have nothing in the background of the image.


Top reference holder with tape pressed onto the web.


Top reference holder with tape lifted from the web.


Top reference holder with web firmly attached showing the remaining web left behind.

In addition to preserving the structure the goal was to create a publishable image. This is often as much art as it is science. One of the main components of such an image is a very clean, featureless, completely black background. The second attribute of a high quality image is to have as little artifact in the image as possible. Two of the most common artifacts in SEM images, especially on organic or other low atomic number materials are edge effect and charging. Edge effect is a washing out of edges, corners or small surface structures due to electron emission from a large volume of excitation between the electron beam and the sample that greatly reduces true surface morphology. This is easily overcome by lowering the accelerating voltage. With older SEMs, this meant loss of resolution, but with today’s FEG SEMs there is effectively no loss in resolution when operating at low kV.

The other artifact is charging which is a buildup of primary beam electrons on the surface of a nonconductive sample. In the past a conductive coating (either evaporated carbon or sputtered metal, typically Au, Pd, or Pt) had to be applied to make the sample conductive. Today’s FEG SEMs, with ultra-high resolution, are capable of imaging the grain structure of any metal film which has a subtle surface morphology that is not really present in the real sample. A charging sample prohibits low energy electrons, which carry surface morphology information, from escaping from the surface. This too can be eliminated at low accelerating voltages without the need to apply a coating thereby simplifying and speeding up the analysis process. The resulting images were used for the presentation at M&M 2016 and one was chosen as the cover photo for the journal BioNanoScience Vol.6, No.2, June 2016.


Students Investigate Mechanical Properties of Spider Web

It isn't often that 8th graders inspire scientists with their class project. When a group of scientists at the Massachusetts Institute of Technology found that a spider's web from the basement had an unusual pattern, they invited a small team of middle school students to investigate its mechanical properties. Their work caught the attention of the MIT researchers and also landed a talk at M&M 2016.


With the poster at M&M 2016: 8th grader Nicholas Moy, teacher Douglas Shattuck, and Vern Robertson of JEOL.

Doug Shattuck, an 8th grade Concord Middle School teacher, has successfully dovetailed his classroom projects with his summer work at MIT in the Civil and Environmental Engineering department (headed by Prof. Markus Buehler, Ph.D.) where the focus is development of novel composite materials. He has also had a long-time affiliation with JEOL USA, specifically Vern Robertson, who has on occasion imaged samples of balsa wood and 3D printed models of synthetic materials for the Laboratory for Atomistic and Molecular Mechanics using a SEM at JEOL's Peabody, Mass. headquarters. During a previous school year, when balsa wood properties were being investigated in the Lab, Shattuck had his students design balsa wood bridges capable of bearing a hundred times their own weight. This was in conjunction with the atomistic modeling of how the wood fails at the atomic bonding level.

More recently, the lab had done 3D printing of spider webs to study mechanical strength and reported their findings in 2015 publications. After observing the weaving process and reviewing the micrographs, Dr. Zhao Qin, a Research Scientist, found that the structural features of the sheet web produced by an Araneidae spider were too difficult to be duplicated with synthetic materials in the similar manner as spiders. The web construction proved even more interesting because of the unusual complexities that the SEM images revealed are connected to how the spider constructs the web, a tedious work performed in an elegant way.


SEM images show the unique pattern in the junctions between the rays of this particular spider's web and the chords that helically wrap each ray.

The researchers were surprised to see an "odd crossover that hadn't been seen before" - a unique pattern in the junctions between the rays of this particular spider's web and the chords that helically wrap each ray. With the goal of determining if the helically wrapped chords (shown in frames 2,3, and 4) provided any mechanical advantage when it comes to managing normal tensile forces acting on the web, the students utilized the SEM images and evaluated ways of reconstructing an analog of the web design using sewing thread and trying different designs for a 3D printed loom with which to make them. The results of their findings were originally slated for a poster at M&M as part of the Microscopy Outreach program which promotes microscopy in education as an important learning tool for inspiring future STEM professionals. When it was learned that the research had shown some unusual properties of the spider web, the poster was elevated to a platform talk.


Concord Middle School students formed a good relationship with MIT researchers during their work. Standing in the middle are MIT Prof. Markus Buehler, Ph.D., and Concord Middle School 8th grade teacher Douglas Shattuck.

The talk was given by 8th grader Nicholas Moy, whose parents were pleased to be able to make the trip to Columbus, Ohio for the opportunity. Shattuck accompanied him and was able to see not only how well his students were able to thoroughly investigate the challenge they were given, but also experience the other side of being a scientist, writing and presenting a paper.

This research per se helps to reveal the secret of web architecture by providing the relation between the complex web structure and its advanced mechanical function. It will also shed light on the design of strong and light synthetic composite materials with their reinforced fibers arranged in the similar way as the spider web. Shattuck's students receive a certificate for their work, and have had the unique experience of being part of a real world science lab and following real procedures to solve scientific problems. It's an experience that surely will give them a leg up in the future should they decide to pursue science in their careers.

Read how to prepare the spider web for imaging in the SEM.

Complex Web Construction: A Possible Clue to Mechanical Properties 

Abstract
Poster


Some Thoughts on Low kV Imaging

What makes the difference between a good SEM image and a stellar one? Imaging samples at the appropriate conditions, and that often means at very low accelerating voltage (low kV). It's time to give it a try!

Every modern day scanning electron microscope (SEM) from the top of the line, ultra-high resolution field emission SEMs to the most economical entry level tungsten (W) thermionic SEMs has the capability of imaging samples at very low accelerating voltage (Low kV ). While it is true that low kV requires a little more effort, the benefits are enormous and worth the effort. Click here to read the full technical note and see examples and comparisons.

pdf: Some Thoughts on Low kV Imaging


Why is the Sand Purple at Plum Island Beach?

Typical New England beach sand differs in color from light and dark grey to medium tan based on its common mineralogy, but at Plum Island Beach there are swatches of purple sand that appear haphazardly as one walks along the shore. The beach spans much of the length of Plum Island, an 8-mile long barrier island that takes a beating from the Atlantic Ocean in stormy weather. Tall dunes separate the beach from thickets, marshes, and a river that comprises the Parker River Wildlife Refuge established in 1942. At any given time, visitors can see seals on the beach, raptors, now including bald eagles, waterfowl, shore and song birds. In spring the beach is closed to allow Piping Plovers to nest. And in the mid-summer bravery is required to withstand the onslaught of the fierce biting green head flies.

When three coworkers from JEOL walked Plum Island Beach early in January they were hoping to spot a Snowy Owl perched high in the dunes where they have been known to appear in recent winters. Walking along the beach they noticed numerous bands of purple in the sand and wondered what had caused them: were they man made, pollution, rotting or decaying organic material or something in the sand's composition? They appeared randomly and yet frequently at the base of the dunes above the normal high tide line. One of the walkers gathered a handful of the purple sand and put it in his pocket to bring back to ask the company's geological experts for their opinion, and to have it analyzed using one of the JEOL scanning electron microscopes (SEM) and energy dispersive X-Ray spectrometers (EDS) with a little bit of optical microscopy prior to introduction into the SEM/EDS. JEOL USA, Inc. located in Peabody, MA, supplies much of the research world with SEMs that make it possible to see things at extremely high magnifications and also analyze them for their chemical composition.

At first look under the optical microscope, the granules of sand appeared like scattered jewels of many colors; predominantly glassy pink angular grains, with smaller quantities of milky white rounded grains, clear angular grains, black grains (some magnetic and some not), and even the occasional green.

What could be the cause of the purple color? The answer was one that came as no surprise to the scientist, but was exciting for the beach walkers because they had an exact answer to a question that no doubt is one that many people have when they visit Plum Island - which was actually named for its beach plum bushes, not the plum-colored sand.

When large amounts of fine grained pink is intermixed with a smaller number of darker grains and dampened by rain or sea water the human eye will “see” the sand as a much darker pink to almost purple. The two most common pink minerals are rose quartz (while quartz is one of the two most common minerals on earth, the pink rose quartz variety is not so common ,especially in the New England geology, and is found only in a few isolated pegmatite deposits in NH & southern Maine which are where most gemstones originate) and the solid solution series of almandine and pyrope garnet which is also a very common mineral (and is quite common in the Seacoast area from the abundance of metamorphic rocks called mica schist and from contact metamorphism. This is also why many commercial sandpaper products have a pink color as the angular hard gains of almandine / pyrope garnet are the perfect abrasive. The most likely candidates for the white and clear are any of the feldspars and or quartz. The green is most likely epidote. Just based on the optical examination these are no more than educated logical guesses (but still guesses).

Vern Robertson, JEOL’s SEM Technical Sales Manager, originally examined the grains under a low power optical stereo microscope with the above conclusions. In addition to providing technical and scientific support to JEOL SEM customers for a multitude of applications, Vern holds a degree in Geology. After a cursory look optically, it was time to get down to some spectroscopic analysis to determine the actual mineral species present in the sand.

Individual grains of various colors were selected and mounted for examination with the JSM-6010LA+ InTouchScope SEM and for analysis using EDS. The SEM allows much higher magnification imaging with greater depth of field than a traditional OM and the low vacuum capability allows examination of the sample without the traditional conductive coating that needs to be applied for SEM imaging. However, it generates images in only black & white (electrons have no color!). One specialized detector in the SEM, the Backscatter Electron Detector, yields images with the gray level intensity directly proportional to the average atomic number (or density). This means that minerals containing only lighter elements like O, Si are darker in appearance to minerals that contain heavier elements like Fe or any of the metallic or rare earth elements.


View Data -

Once located, each grain can be analyzed with the EDS. When an electron beam hits a sample it creates not only an image from the emitted electrons but creates X-rays, which when collected in a spectrum, indicate what elements are present and at what concentrations. This allows not only the elemental composition of the individual grains to be determined but the concentrations can be compared to known stoichiometry of the suspected mineral grains. The combination of color and magnetic properties from OM examination and the chemical makeup of the individual grains yield the answer.

The purple color (or more appropriately, pink color) comes from the abundance of almandine-pyrope garnet with a nominal solid solution composition of Fe3+2Al2Si3O12 to Mg3+2Al2Si3O12. As expected, the white grains are a mix of feldspars but mostly K-feldspar (potassium alumino-silicates) and quartz SiO2. The black nonmagnetic grains were a mix of a pyroxene called augite which showed its characteristic strong cleavage, (Ca,Na)(Mg,Fe,Al)(Si,Al)2O6 , and a mix of ilmenite FeTiO3 and hematite Fe2O3 which are the magnetic components. The green was confirmed to be epidote Ca2(Al,Fe)3(SiO4) 3(OH). With the exception of the high concentration of garnets the rest are common minerals one would expect to find in sands.

While analyzing loose, irregular, as-received grains is not optimal for quantitative elemental analysis (high precision and accuracy quantitative analysis requires the samples be: clean, flat , polished, homogeneous at the scale being analyzed, and compared element by element to known similar matrix standards) the resulting standardless EDS analysis produced results that matched the known stoichiometry for these minerals nearly exactly.

The other item of note is that the sand is very angular and not rounded like one would expect in surf-tossed, coastal, oceanic beaches where the constant grinding of the grains by the tides would remove all sharp edges over time producing a “frosted” appearance like sea glass. Plum Island is a barrier island. This purple sand is high above the high tide high water mark and is a remnant of the its initial deposition when the last glacial ice age began to recede and melt and dropped the sediments it had accumulated and pushed forward during its advance. These sediments likely come from tens to hundreds of kilometers away from their current resting place. 

The Seacoast area is full of evidence of glaciation if you know what to look for like: HUGE boulders in a seemingly odd place pushed & dropped there by the massive ice sheets, shiny, striated, polished rock faces from the immense rubbing pressures as the glaciers overtook the land, barrier islands like Plum Island and even Boars Head at Hampton Beach, NH which is a terminal moraine or the farthest point the glacier reached on its southward march before retreating and leaving a pile of debris much like the snow plows of this winter would have done.

The Scanning Electron Microscope with an Energy Dispersive X-ray spectrometer (SEM/EDS) is a powerful tool not only in academia and industry but also in answering the vexing questions of: who, what ,where, when & how of items encountered in everyday life.