Scanning Electron Microscope
Microscope
The Amray 1810 scanning electron microscope (SEM) uses a tungsten filament to create a focused electron beam for viewing specimen surface ultrastructure with angstrom-level resolution. This microscope produces images magnified between 20-200,000x. A universal specimen stage allows specimen movement in X, Y, Z, tilt, and continuous rotation. With accelerating voltages ranging from 0-30kV, control of beam spot size, and externally selectable objective apertures, this microscope is capable of 50 angstrom resolution. In addition to manual controls, this microscope is capable of automatic image focusing, stigmation, and contrast and brightness control. These features provide real-time adjustments of video signals for recording or continuous display viewing. The scanning and display systems enable real-time video signal processing functions including invert, filtering, gamma, and derivative functions. With seven different frame rates, users can optimize imaging for quick, initial examinations or for high signal-to-noise image capture. This microscope is maintained through a service contract provided by Electron Optics Service Inc.
Accessories
Sputter Coater. A new Cressington 108 sputter coater is available to apply a conductive coating to the surface of all SEM samples. Using Argon gas and a gold target (cathode), up to twelve specimens at a time can be covered in a gold coating. The thickness of the coating can be controlled through manipulation of current and time settings, specimen stage height, and Argon gas pressure. Desiccators are available to store dried, coated samples.
Critical Point Dryer. A new Tousimis SAMDRI-PVT-3d critical point dryer is available to dry samples safely and rapidly, avoiding the morphological changes that can accompany air drying. A brochure describing this unit is available. Samples that have been dehydrated through an ethanol series can be placed in baskets in a pressure chamber to undergo drying. Special holders are available for samples that are adhered to coverslips. Liquid CO2 is used to replace the ethanol through a continuous flush and is converted to gaseous CO2 through heat and pressure.
Funding Support.
The acquisition of this entire imaging system was made possible by funding from the National Science Foundation (Carole Browne) and Wake Forest University.
Applications
Species-Specific Characteristics of Larval Tiger Moths. During late June and early July of 2006 Dr. Lazaro Roque-Albelo, head lepidopterist from the Charles Darwin Research Station in the Galápagos Islands visited the Department of Biology at Wake Forest University. In collaboration with Dr. Bill Conner, Dr. Roque-Albelo used the scanning electron microscope to determine the species specific characters of the larvae of three endemic tiger moths of the genus Utetheisa (Lepidoptera: Arctiidae) collected in the archipelago. U. galapagensis, U. perryi, and U. devriesi are of interest because they have lost the bright aposematic coloration of their cosmopolitan congenerics. Dr. Roque-Albelo and Dr. Conner would like to know why. The attached photos are scanning electron micrographs of the third instar larva of Utetheisa galapagensis. The specimen was critical point dried and sputter coated.
Examination of Functional Characters in Erica. The plant genus Erica L. (heather plants) exhibits great diversity in the southwestern Cape Region of South Africa. Of 865 known species, only 23 occur outside of this relatively small geographic area. Historically, Erica have been classified based on their flower morphology and relative arrangement of the flowers on the branches. The laboratory of Kathy Kron has investigated the utility of functional characters, rather than the usual floral characters, for exploring the evolutionary history of these plants. Functional characters, such as particular organizations of leaf anatomy, morphology and their microstructures, are related to photosynthesis, water use efficiency and other adaptations for survival in a harsh Mediterranean climate, with hot dry summers and cold wet winters. Leaf anatomy and other fine structures were investigated on a three-dimensional, fine scale with SEM techniques. These pictures show functional characters including stomata, leaf sulcus, and branched hairs.
