File:U.S. Department of Energy - Science - 276 003 003 (16625682631).jpg

VIEW OF THE SCANNING TRANSMISSION ELECTRON MICROSCOPE IN BNL'S INSTRUMENTATION DIVISION.

THE SCANNING TRANSMISSION ELECTRON MICROSCOPE (STEM) WAS CONSTRUCTED BY RESEARCHERS IN BNL'S BIOLOGY DEPARTMENT TO IMAGE SPECIMENS AND MEASURE THE MASSES OF PROTEINS, NUCLEIC ACIDS AND COMPLEXES OF THE TWO. THE SCANNING TRANSMISSION ELECTRON MICROSCOPE DIFFERS FROM A CONVENTIONAL ELECTRON MICROSCOPE DUE TO ITS ABILITY TO MINIMIZE RADIATION DAMAGE. WITH A SCANNING TRANSMISSION ELECTRON MICROSCOPE, A SPECIMEN IS COOLED TO LIQUID NITROGEN TEMPERATURE AND SCANNED, RATHER THAN BEING IRRADIATED ALL AT ONCE. WHILE PASSING THROUGH THE SPECIMEN, SOME OF THE ELECTRONS INTERACT WITH IT, LOSING ENERGY TO WHATEVER THEY HIT OR CHANGING THEIR COURSE. DETECTORS COUNT EVERY TRANSMITTED ELECTRON, AND EACH ELECTRON CONTRIBUTES TO THE FINAL PICTURE. AS A RESULT,FEWER ELECTRONS ARE NEEDED TO RECORD AN IMAGE THAN WITH OTHER ELECTRON MICROSCOPES, SO RADIATION DAMAGE TO THE SAMPLE IS MINIMIZED. THE PROCESS PERMITS SCIENTISTS TO SCRUTINIZE BIOLOGICAL SPECIMENS AT A RESOLUTION OF 2.5 ANGSTROMS. STEM CAN ALSO DETERMINE MOLECULAR WEIGHT AND MASS DISTRIBUTION WITHIN SINGLE MACROMOLECULES AND COMPLEXES.