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Thin-film deposition is about phase transition from the vapor phase to solid phase. Atoms condense on a substrate. These adsorbed atoms are subject to desorption and surface diffusion. Some adsorbed atoms bond to each other, reducing the desorption probability. More atoms aggregate and some of the bigger clusters avoid desorption. (Franssila, S., Introduction to Microfabrication, p. 78)
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Films are typically the most desirable medium for use in semiconducting devices. The hybrid perovskites are often soluble in common polar solvents and both components generally volatilize at relatively low tepmperatures. In addition, the range of interactions both within and between the organic and inorganic components structure typically strongly favors the formation of the hybrid perovskite crystals or thin films using a number of simple processes, including vacuum thermal evaporation, solution-based techniques such as spin-coating and stamping, and even melt processing. Each of these options provide advantages for selected applications, thereby enabling convenient deposition on a range of substrates, including those envisioned for flexible plastic displays and low-cost electronic devices.
(Gomez-Romero P. Sanchez C., Functional Hybrid Materials, p. 362)
4-) Photochemical Machining
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The specific steps that are involved when photochemical machining (PCM) is performed with the use of photoresists. These are as follows: 1. Clean the workpiece. 2. Coat the workpiece with a photoresist, usually by hot-roller lamination of dry-film photoresists, on both sides, although liquid photoresists may also be applied by dipping, flowing. rolling, or electrophoresis (i.e., migration of charged molecules in the presence of an electric field). For liquid photoresists, the coating is heated in an oven to remove solvents. 3. Prepare the artwork. A drawing of the workpiece is made on a computer-aided design (CAD) system. 4. Develop the phototool. The CAD file is used to derive a photographic negative workpiece. Several methods may be used. Typically, the CAD drawing is downloaded to a laser-imaging system that exposes the desired Image directly onto photograph (e.g., silver halide) film. In the past, oversized artwork was used to Increase the curacy of the phototool through photographic reduction of the artwork. 5. Expose the photoresist. Bring the phototool in contact with the workpiece, a vacuum frame to ensure good contact, and expose the workpiece to Intense violet (UV) light 6. Develop the photoresist. Exposure of the photoresist to intense UV light alters the chemistry of the photoresist, making it more resistant to dissolution in certain solvents. By placing the exposed maskant in the proper solvent, the unexposed areas of the resist are removed, exposing the underlying material for etching. All residue is rinsed away 7. Spray the workpiece with (or immerse it in) the reagent 8. Remove the remaining maskant. PCM has been widely used for the production of small, complex parts, such as printed circuit boards, and very thin parts that are too small or too thin to be blanked or milled by ordinary sheet metal forming or machining operations, respectively Refinements to the PCM process are used in the microeletronics fabrication.
(MATERIALS AND PROCESSES IN MANUFACTURING 10th edition, J. Temple Black, Ernest Paul DeGarmo, Ronald A. Kohser, p.489)
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Photochemical machining, as also known chemical blanking, involves producing parts by chemical action. It is accomplished by placing an exact image of the part to be produced on a sheet of metal and immersing them both in a chemical. The chemical action dissolves all of the metal except the desired part. Most photochemically machined parts are thin and flat.
Photochemical machining has a number of applications where in it provides unique advantages. Some of these include: working on extremely thin materials when handling difficulties and die accuracies preclude the use of normal mechanical methods; working on hardened or brittle materials when mechanical action would cause breakage or stress concentration points. Production of extremely complex parts for which die costs would be prohibitive. And producing short-run parts for which the relatively low setup costs and short time from print to production offer advantages. This is especially important in research and development projects and in model shops.
(Goetsch L.D., Technical Drawing, p. 774)
5-) Proximity Sensors
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Proximity sensing using optical or acoustic techniques is useful when a robot tool is brought into contact with a workpiece. Since the robot is designed to be very stiff and the workpiece is usually quite rigid, the contact force between them builds very rapidly when the robot contacts the workpiece with finite velocity. Even if force sensing is used, the contact force may build to damaging levels before the system can respond. Proximity sensors are short-range, noncontact sensors which allow fine control of tool velocity shortly before contact to avoid severe impacts. Optical systems based on triangulation or simply the intensity of light reflected off the workpiece have been tested. Ultrasonic rangefinders using a sonar-type principle offer an alternative technology.
(Standard Handbook of Machine Design, Robots and Smart Machines, Kenneth J. Waldron, Ph.D.,p47.20)
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Proximity Sensing is the technique of detecting the presence or absence of an object with an electronic noncontact sensor.
Mechanical limit swtiches were the first devices to detect objects in industrial applications. A mechanical arm touching the target object moves a plunger or rotates a shaft which causes an electrical contact to close or open. Subsequent signals will produce other control functions through the connecting system. The stich may be activating a simple control relay or a sophisticated programmable logic control device, or a direct interface to a computer network. This simple activity, once done successfully, will enable variaties of manufacturing operations to direct a combination of production plans according to the computer-integrated-manufacturing strategy.
Inductive proximity sensors are used in place of limit switches for noncontact sensing of metallic objects. Capacitive proximity switches are used on the same basis as inductive proximity sensors; however capacitive sensors can also detect non-metallic objects. Both inductive and capacitive sensors are limit switches with ranges up to 100 mm.
The distinct advantage of photoelectric sensors over inductive or capacitive sensors is their increased range. However dirt, oil mist, and other environmental factors will hinder operation of photoelectric sensors during the vital operation of reporting the status of a manufacturing process. This may lead to significant waste and buildup of false data.
(Soloman S., Sensors Handbook, p1.21)
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