The University of Arizona

Newsletter 200906 - Seeing the Little-Big Picture

Edited by Steven Hernandez

In science and engineering there are many tools that enable us to get the job done. As trite as it may sound, most of us pursue the next step as quickly, and efficiently, as possible. Even so, we are often left with an unsatisfied feeling when we discover the limited access to such instruments.
Nevertheless, the University of Arizona is fortunate to be one of the nations leading universities in science and engineering. Therefore, access to such instruments may not be as scarce as we once thought.
Just south of Old Main (in the Marley Building), The University Spectroscopy and Imaging Facilities (USIF) is a full service lab specializing in electron microscopy (EM). Not only is it the largest and most well equipped EM facility, USIF also supports staff members who have decades of experience in the field.

As we watch an apparent exponential growth of the role nano technology plays in our world, we begin to wonder how we could dream of a future without EM.

Picture1A bundle of single walled carbon nano tubes.
-Phil Anderson (H-8100)

USIF is an EM Lab that supports the following instruments:

  1. Scanning Electron Microscopes
    • Variable Pressure
    • Field Emission
  2. Transmission Electron Microscopes
    • High Resolution
    • Biological
  3. X-ray Diffraction
  4. In-SEM: Raman spectroscopy, Photoluminescence and Cathodoluminescence

All in One SEM: Hitachi S-3400N

One of the newest and most impressive instruments at USIF is the S-3400N VPSEM. This microscope , on its own, packs a big punch when it comes to imaging. Typically, most samples are either semi-conductive, or just plain non-conductive, so thin coatings of metal are needed to make them conductive. However, the 3400’s variable pressure capability enables the user to image their sample without having to deposit a metal layer. This is highly useful for researchers in archeological and conservation sciences who could be working with ancient potteries.

The 3400 is also equipped with an energy dispersive spectrometer (EDS), and a Raman, Cathololuminescence and photoluminescence spectrometer. With all these tools the operator can easily image their sample, get elemental analysis, phase identification and conductance properties of their sample in a matter of hours.

Ultra-fast Mapping of semiconductor
-Thermo Scientific

Picture2

A New Direction for Carbon Nanotube Characterization

Binh Duong, Supapan Seraphin, Yitian Peng, Lu Wang, Hao Xin

Our project focuses on the growth and characterization of carbon nanotubes (CNTs), by chemical vapor deposition (CVD) method for, microwave testing purposes.

Simultaneously, using the SEM S-3400’s advanced Raman spectrometer system, we were able to obtain critical information on the morphology, chemical and electronic structures of the nanotubes. Our results revealed that by changing the feeding gases concentrations, we were able to produce up to 90% semiconducting double-walled nanotubes (DWCNTs).

Using the H-8100 TEM, inner diameters were determined to be approximately 1 to 3 nm. Fig 2 shows a high resolution TEM image of typical double-walled CNTs bundles. The information from this study shall pave the way to produce high quantity and quality tubes with desired properties.

Picture4 Figure 1: SEM images of carbon nano tubes. -Binh Duong

Picture3
Figure 3: One of only two of the nations In-SEM Raman systems

Picture5Figure 2: High resolution TEM image of typical double-walled CNTs bundles. -Phil Anderson

For information on specs and capabilities:
Steven Hernandez – USIF Staff
sah@email.arizona.edu

Side Stepping Charging Effects

As mentioned before, many specimens we encounter are poor conductors. Therefore, to avoid charging effects, we either use sample preparation techniques, or we might use a variable pressure system (VP).
On the other hand, lets say VP isn’t going to get you the resolution you are looking for and a field emission scope is needed. Hitachi’s S-4800 also has a scheme to avoid such situations.

The S-4800 is equipped with an energy filtration system. The main goal of this capability is to filter out different levels of secondary electron (SE) signals. The SE signal is low in energy (~5-50 eV); for this reason, the positively biased plates of the energy filter, or ExB system, can attract different energy types of SE’s and subtract them from your image. As a result, when charging prevents the incident beam from interacting with the specimen the energy filter can “block” the “corrupted” SE signal from reaching the detector and leave the operator with a pure backscattered electron (BSE) signal.

However, like most situations in life there can be some drawbacks. SE signal is best for surface resolution due to its shallow escape depth; therefore, when we are left with the pure BSE image, we have lost some resolution as a result of the BSE’s higher escape depth. Nevertheless, this technique can give you valuable information about the composition of your sample.

Below is a series of images showing the effect of using the ExB filter.

ELECTRON MICROSCOPY

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Announcements

Posted by Admin on December, 2010

***USIF Offers Custom SEM Training*** We now offer the SEM Short Course on a one-to-one basis. To inquire, email Steven Hernandez.

 

University Spectroscopy and Imaging Facilities
520-621-5097