Contains report on one research project.Joint Services Electronics Program (Contract DAAG29-78-C-0020)National Institutes of Health (Grant 1 RO1 GM23597

Coleman, John W.

Contains report on one research project.National Institutes of Health (Grant 1 R01 GM23597)M.I.T. Sloan Fund for Basic Researc

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II. DEVELOPMENTAL ELECTRON OPTICS LABORATORYAcademic and Research StaffDr. J.W. Coleman1. THE AUGER ELECTRON MICROSCOPENational Institutes of Health (Grant 1 R01 GM23597)M.I.T. Sloan Fund for Basic ResearchJohn W. ColemanDuring the past year, the Auger Electron Microscope was moved to a new loca-tion, which proved to offer a better magnetic environment for the instrument.Optical misalignment of the system, which at present is the main limitation toresolution in the AEM, still remains, however, due to the lack of facility totraverse the optical elements with respect to each other while images are beingobserved. A complete design change to allow optical alignment in terms of fiveoptical column packages has now been accomplished, and the instrument will bemodified accordingly when funds become available (see Alignment Program below).In fact, five research programs, aimed at calibrating and testing the instru-ment, have been planned in detail and are being undertaken as follows.1. Contamination Program. In this program the species and amounts of back-ground gas are characterized and contamination rates are studied.2. Alignment Program. In this program the optical elements are made align-able during operation, and the energy analyzer is made independentlyalignable upon the optical system.3. Auger Emitting Sample Program. In this program simple known systemsare studied for both quantitative and qualitative characteristics ofthe output signal.4. Sample Support Program. In this program the effect of spectrum supportsis studied with respect to the signal-to-noise for a given specimen.5. Comparative Microscopies Program. In this program well-known andcharacterized specimens are examined both by AEM and SEM and/or TEM and/orlight microscopy.PR No. 123

Developmental Electron Optics Laboratory

Contains report on one research project.Joint Services Electronics Program (Contract DAAG29-78-C-0020)National Institutes of Health (Grant 1 ROI GM23597

II. DEVELOPMENTAL ELECTRON OPTICS LABORATORYAcademic and Research StaffDr. J.W. Coleman1. THE AUGER ELECTRON MICROSCOPEJoint Services Electronics Program (Contract DAAG29-78-C-0020)National Institutes of Health (Grant 1 ROI GM23597)John W. ColemanThe Auger Electron Microscope has yielded Auger + secondary dark-field imagesof carbon on tungsten, with spatial resolutions of %0.8 p and energy resolution of<20 eV. A typical AEM micrograph is shown in Fig. II-1. The main limitations atpresent to better resolution of either type are1. the lack of a facility for alignment of the optical column elements whileimages are being observed;2. the influence of slowly varying residual stray fields; and3. the lack of highly regulated power supplies.The total electron-optics package (minus the chevron electron multiplier arrayused as output) is shown in Fig. 11-2, and the overall instrument is seen in Fig.11-3.With the elimination of the problems listed above, the instrument should con-verge on its theoretical performance level, whereby eventually we expect spatialresolutions of a few angstroms and energy resolutions of a few eV to be demon-strated.PR No. 122Fig. II-i. AEM micrograph of butt end of 3-mil diam tungsten wire which has beenrubbed on graphite. (Low-mag image (330X) taken with Polaroid cameradirectly from Chevron Electron Multiplier Array phosphor screen, asseen through vacuum window (see-Fig. II-3). The CEMA current gain is1.5 x 106.) The parts of the figure are as follows:A - Periphery of CEMA phosphor screenB - A CEMA defect (burnout point)C - Scattered electrons of no interest (eventually to be aper-tured out when alignment permits)D - Support portion of L-shaped tungsten wire, seen as shadowimageE - Dark-field background due to on-axis portion of tungsten wireF - Auger + secondary image of carbon embedment.It should be noted that the butt end or specimen end of the wire ispointing away from the phosphor screen, and that the primary dark-fieldimage appears between the specimen end of the wire and the phosphorscreen. The situation is analogous to seeing a person's face againstthe background of the back of his head, and is a consequence of themirror optics necessary for a high-efficiency collection of Augerelectrons.PR No. 122Fig. 11-2. AEM electron-optics package.A - Electron gun for excitationof Augers in specimenB - Auger mirror-objective lensC - Specimen-holder drawerD - AcceleratorE - Set-up lens for energy analyzerF - Deflector ringG - Spherical-aberration-correctorfoilH - Magnetic-prism winding assemblyI - Analyzer-mirror cathodeJ - Magnetic prismK - Energy-analyzer assemblyL - Projector-discriminatorM - Deflector ring andstigmatorN - Projector #20 - Deflector ringP - Projector #3.PR No. 122Fig. 11-3.PR No. 122E~:E~:8 i,~ --' ~- --6$ ig"i~

Contains reports on one research project.Joint Services Electronics Program (Contract DAAB07-76-C-1400

II. DEVELOPMENTAL ELECTRON OPTICS LABORATORYAcademic and Research StaffDr. John W. ColemanGraduate StudentsMichael R. Graham1. ULTRAHIGH-SENSITIVITY ELECTRON OPTICAL DETERMINATIONAND LOCATION OF IMPURITY ATOMS IN Si AND GaAsJoint Services Electronics Program (Contract DAAB07-76-C-1400)John W. ColemanDuring the past year we have used specimens of gold-on-carbon substrates to cali-brate our instrumentation. We have obtained images of these specimens due to second-ary electrons, and at present we are trying to photograph them. We also have specimenson hand of Si-A1 on Si, Si-A on Ta, and P glass on Si. A chronic major problem hasbeen vacuum, which has precluded until now the predominant usage of Auger electronsfor producing the images. Plans are now under way to change over to an oil-free sys-tem; when this is complete, we will be able not only to produce Augers but also to installour channeltron-array image intensifier, which will help us to see and photograph thelow-level intensity images.PR No. 120

II. DEVELOPMENTAL ELECTRON OPTICS LABORATORYAcademic and Research StaffDr. John W. ColemanDr. Edward H. JacobsenGraduate StudentsMichael R. Graham1. ULTRAHIGH-SENSITIVITY ELECTRON OPTICAL DETERMINATIONAND LOCATION OF IMPURITY ATOMS IN Si AND GaAsJoint Services Electronics Program (Contract DAAG29-78-C-0020)National Institutes of Health (Grant 1 RO1 GM23597)John W. ColemanThe ultimate goal of the proposed research is the simultaneous species identificationand spatial resolution of atoms of low atomic number in electron micrographs. Thebasis for the research is Auger electron spectroscopy coupled to high-resolution elec-tron optics. The apparatus to accomplish this is the fixed-beam Auger electron micro-scope, which is now being made operationally dependable. The goal for the currentyear, which has been met, included final instrumental buildup, with a correction in theoptical system and reengineering of the vacuum system.The correction in the optical system was in order to bypass the undesirable focus-ing effects due to the structure of the specimen support (Davisson-Calbick Effect). Theoptics were redesigned to allow the specimen to rest at the center of a cylindrical metalelectrode. Preliminary indications are that this has made focusing far less critical.The following vacuum problems necessitated complete redesign of the housing andpumping systems of the Auger microscope:1. Oil residues in the old vacuum system (although cryotrapped) were sufficientto cause continual microdischarges between electrodes several kV apart but spacedonly millimeters away from each other.2. These microdischarges constituted erratic changes in the optical properties ofthe electrostatic lenses, thus only by chance and fleetingly would all the lenses be atsuch value that designed-for trajectories would occur.3. Further intolerable vacuum conditions (leaks in electrical feed-throughs andunclear diffusion pumping systems) limited vacuum to 10 minus 7 Torr, which precludedthe use of the CEMA image intensifier (guarantee void for use at such values) and alsomade illogical the attempt to use Auger electrons to the exclusion of other secondaries(even the cleanest surface - necessary for Augers - contaminates too rapidly at 10 minus7 Torr).PR No. 121(II. DEVELOPMENTAL ELECTRON OPTICS LABORATORY)4. With the old system, the foil lens was de facto impracticable since the electron-transparent foil contaminated rapidly, i. e., within a matter of a few minutes becameelectron-opaque with the accelerating voltage (20 kV) used in the AEM. Without thefoil lens, of course, correction of spherical aberration is impossible, and it is justthis correction which must be applied to realize the high spatial resolution which thedesign will allow.A new vacuum system was designed, therefore, to enable the following:1. Use of the CEMA image intensifier.2. Use of the foil lens to correct spherical aberration.3. Use of the magnetic prism energy analyzer without contaminating the faces.4. Photography of the images.5. Use of Augers mainly for imaging.BYPASSVALVELN TRAP T E e HERMOCOUPLE GAUGEO ION GAUGEGATE ELECTRICALVALVE FEED-THRUTURBOPUMP VIEWPORT TABLE TOPSPECIMENPORT CAMERALEGCASTORFig. II-1. Auger electron-microscope vacuum-pumpingand vacuum-housing systems.The new vacuum system uses a copper-gasketed housing with a 100% oil-free air-suspended air-driven turbomolecular pump made by ALCATEL. This pump was ninemonths in delivery. A schematic of the instrument is shown in Fig. II-1.PR No. 121

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Developmental Electron Optics Laboratory

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