The advancements in electron optics have made it possible to cover a wide electron energy range without significant degradation in the imaging quality of a scanning electron microscope. The secondary electron emission and the surface sensitivity are enhanced when using low voltages. The addition of an energy dispersive x-ray spectrometer with a thin window allows the detection of low energy emission lines, thus making the technique comparable, or at least complementary to surface techniques such as Auger electron and x-ray photoelectron spectroscopies. In this paper, aspects of low-voltage SEM are discussed and factors affecting the secondary electron images are examined. The surface sensitivity is evaluated and is compared to Auger electron spectroscopy. Study cases from the printed circuit board manufacturing area are presented.
The surface topography of gold electroplated as a function of current density has been studied by two topographical imaging techniques. Scanning tunneling microscopy (STM) was used to extend the magnification regime of scanning electron microscopy (SEM). STM micrographs of a 1×1-μm scan area compare well with high resolution (50 000×) SEM micrographs. The surface of the gold was found to exhibit a distinct trend from an amorphous, porous appearance to a closely packed granular structure with decreasing current density. Surface roughness values extracted from STM data indicate a logarithmic dependence of roughness on the plating density.
flllCROf COPY 101salts, the fluorescent caEcium channel ligand BODtPY FL verapamil, and the salts of the calcium indicators Fura Red, Fluo-4, and Oregon Green BAPTA-1. It should be noted that measuring solvents like methanol with a pipette can cause slightly imprecise volumes because of the high vapor pressure. In general, this method can also be used to prepare alEquots of drugs like receptor Ilgands or ion channel blockers. Water Recirculator (Chiller) Maintenance 1Owen Mills Michigan Technological institute opmills@mtu.edu In my mind two things commonly cause problems for electron microscopes. One is vacuum, and the other is cooling water. It is really not that they are trouble, but rather that extra maintenance is involved. The maintenance of water redrafting systems will be discussed in this note.A water recirculator is really a heat exchanger that operates on a basic heat transfer principle. The process cooiing water within the recirculating system is forced through the scope by a pump. Heat is transferred to the process cooEing water as it flows through the microscope lenses, power supplies, and diffusion pump. The process cooling water then flows back through a heat exchanger inside the water recirculator. The total heat is transferred through this heat exchanger into one of two cooling sources: 1. Refrigerated cooling system (evaporator) 2. Non-refrigerated cooiing system (water-to-water heat exchanger)In a refrigerated water recircuiating system, ihe total heat (heat from the microscope plus heat from the mechanical compressor) is transferred through the evaporator by refrigerant into a second heat exchanger known as a condenser A condenser may be air coofed or it may be water coded* An air cooled condenser wili transfer the totai heat into the surrounding ambient air. A water cooled condenser will transfer the total heat into an in-house source of cooling water. The typical temperature range for the condenser water circuit is 50-85In a non-refrigerated water recirculating system, the total heat is transferred through the water-to-water heat exchanger directly into an in-house source of cooling water. The typical temperature range for the water-to-water heat exchanger circuit is 40-55^.Concerning maintenance, the tank water is checked weekly to insure a proper operating level. ]t is also a good idea to check the pH tevel of the water to make sure that it remains neutral. When it becomes dirty, it is drained and refilled with clean water. This occurs about every two years. After the system is drained, the intake filter is cleaned or replaced, A large ultrasonic cleaner can be used to clean the intake filters. Since the intake is directly before the pump, and in order to prevent pump failure, the water pump should always be primed by manually filling the intake hose before installing the filter. Distilled water is used in all systems, and mineral buildup has not been a problem. Except for one scope, all the supply hoses are opaque. Algae problems in that scope chiller are treated with Chlorarnine T (Sigm...
Recently, when faced with a problem involving inhibited nickel/gold over-plating on copper surfaces, a real life example showing the advantage resulting from use of low incident electron beam voltage in the SEM became apparent. This will serve as a reminder to explore variable SEM incident beam energies during analyses to enhance specific features.During a manufacturing process, incomplete coverage of overplated metals on copper was ibund. Initial optical examination SEM image pair: left image -area of interest ax 20keV, right image -same area at 5keVof the condition suggested the presence of a residue. If true, and depending on the properties ofthe residue, it could inhibit or even prohibit proper over-plating coverage. SEM analysis was undertaken to prove or disprove the presence of a residual surface layer. Initial SEM inspection at 20keV proved inconclusive. It was noted that it was difficult to clearly focus the areas in question, which could be an indication of a thin surface film being present Lowering the SEM incident beam voltage will decrease the total specimen/beam interaction volume and, thus, dramatically increase the contrast contribution originating in any thin surface film that might be present. The incident electron beam voltage was reduced to 5keV from 20keV in this examination. That reduction in beam energy resulted in clearly showing a cracked, thin film residue on the copper surface as seen in the figures. Once this condition was observed, the issue of improper over-pkting coverage became clear. The unexpected film acts as a mask on the copper surface and inhibits or prevents the formation of viable subsequent plated layers.This example is a striking illustration of the low voltage advantage. Using a higher beam voltage might have resulted in the surface film going unnoticed. Taking the time to investigate possible surface features with a lower energy accelerating voltage allowed us to image the problem film. II hi -in
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