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Abstract
It is well known that a metal tip blunts if it is heated in vacuum. Sharpening may occur in the case of an evaporation of the tip material. To test this, molybdenum tips were heated in vacuum. A typical result: at 2400K, the tip radius decreases from 8 mu m to 0.3 mu m thus confirming the hypothesis. Measured and calculated final radii agree roughly. The pure material evaporation can be replaced by a surface reaction followed by the evaporation of the reaction products. This is shown on tungsten tips heated (1750K) in the presence of oxygen (0.5 mTorr). The evaporation of tungsten oxides results in a sharpening to a radius to 0.05 mu m. Under special conditions, in connection with the formation of solid drops, radii down to 0.01 mu m are obtained.
... Finally, this part of the wire becomes so thin that can not hold the lower end of the wire, so the latter breaks off and a sharp tip is left behind as shown in figure 2. In practice, the etching is performed in several steps: @BULLET apply AC 30 V for initial fast etching to make the neck of the wire more thin; @BULLET adjust voltage to 20 V just before drop-off stage; @BULLET lower voltage to 5-10 V to perform an accurate final drop-off step. With this protocol, conic tools with a diameter of 1-10 µm, are obtained in a few minutes as shown infigure 3. It is known that 300 nm tips can be obtained [10]. Tools with cylindrical form can be prepared by drawing the metal wire during etching (for a detailed discussion see [11]). ...
Potential applications of micro and nano EDM in the research in micro nanotechnology and microfluidics are first discussed.
Milling EDM, one variation of EDM, is proposed as a flexible tool for such applications. In practice EDM milling is a process
rarely used because it is difficult to prepare thin electrode tools. Therefore the use of electrochemically etched Pt-Ir electrode
tool for EDM machining is demonstrated. In addition a compact micro EDM machine is described. Preliminary results concerning
the micromachining of silicon are also shown.
Artificial intelligence has major role for promoting 5G network system. Artificial intelligence solved those problems which have no proper solution at all. Including artificial intelligence all form of life with one consolidate property is their ability to sense, recognize and react to different environmental conditions. There are many sensing devices in which artificial intelligence involved. Some sensing devices have an ability to sense and recognize temperature, light, humidity, pressure, etc., changes more precisely. But all these types of sensors need some input voltage or power to start the sensing process. World already faces energy crises and, in this situation, we have to need those sensing devices which harvest the environmental energy and convert it into electrical energy. Such devices are termed as self-powered sensors. When the material used in that type of devices within nano range then that devices are termed as self-powered nanosensors. In this chapter, focus is on the self-powered nanosensors and their extraordinary applications in different fields.
The evolution towards the world of the nanotechnologies currently increases very quickly. These technologies are in many industry domains but some of them are unknown for their fundamental aspects by the industrial and scientific field. Many of the industrial processes need the temperature information: heating, cooking, heat treatment, fusion, etc. The processes for controlling and regulating temperature are included in the thermal measuring equipment. In first case, in the middle of the process, the sensor constitutes the sensitive element of this chain. For half a century, the microscopy techniques develop to characterize the material and understand the local phenomena. In order to manage this understanding, the thermal microscopies have emerged to determine at the nano-scale the temperature to know the energy level. The probe is also at the heart of the problem. The design until the development of this new probe is based on the hybrid technologies based on deposit techniques in clean rooms, and on traditional techniques of making of thermocouples. The produced probe, certainly intrusive, makes it possible to combine the temperature measurement with contact various materials, and making it possible to be an active probe. In particular, it (this probe) will be able to supplement the probes currently proposed in near field microscopy
Detailed knowledge of the tip apex structure is necessary for quantitative comparison between theory-based simulations and experimental observations of tip-substrate interactions in scanning probe microscopy SPM. Here, we discuss field ion microscopy FIM techniques to characterize and atomically define SPM tungsten tips. The tip radius can be estimated from field emission data, while FIM imaging allows the full atomic characterization of the tip apex. We find that when FIM is applied to tips with a radius of a few nanometers as is desirable for high-resolution atomic force microscopy imaging, limitations not apparent with less sharp tips arise; successful resolution of these limitations will extend the utility of FIM. Field evaporation can be used to atomically engineer the apex into a desired atomic configuration. Starting from a W111 wire, a tip terminating in three atoms can reproducibly be fabricated; due to its geometry and stability, this apex configuration is well suited for application as an atomically defined electrical contact in SPM experiments aimed at understanding contact mechanics at the atomic scale.
Nanosensors are gaining increasing attention due to the need to detect and measure chemical and physical properties in difficult to reach biological and industrial systems that are in the nano-scale region. This conceptual review surveys various nanosensors, which are categorized into three broad types: optical, electromagnetic and mechanical nanosensors. The sensing concepts and their corre-sponding advantages are discussed with reference to their applications.
To determine the temperature of a heated crystal in a field electron or ion microscope, not only the temperature of the heated loop, but also the temperature gradient along the emitter tip due to heat conduction and radiation must be considered. A method is described to calculate the temperature distribution along the tip. Typical numerical results are given for tips of tungsten and some other metals at temperatures between 1000 and 2900 °K. Considered are conical tips of different length (half cone angle between 0.5° and 6°) and some non-conical tips. The temperature gradient near the apex (which influences the shape change by surface diffusion) has a maximum for a particular angle of the conical tip. Very high gradients occur at tip constrictions.
Zusammenfassung Unter besonders guten Entgasungsverhältnissen wurde die Feldemission von thoriertem Wolfram untersucht. Es zeigte sich, daß sowohl durch Aktivieren von ThO2-haltigen Drähten wie durch Aufdampfen aus einer äußeren Thoriumquelle Oberflächen erhalten werden konnten, deren Feldemission im hohen Maße vom Bedeckungsgrad abhängig war. Das an Bariumaufdampfkathoden früher gefundene empirische ?3- Gesetz ließ sich für die Thoriumbedeckung bestätigen. — Durch Bombardieren mit Argon-, Wasserstoff- und Stickstoffionen ließ sich der Thoriumfilm gleichförmig abbauen. Dabei zeigte sich, daß Stickstoffionen auf dem Thoriumfilm adsorbiert werden können, nicht aber auf der reinen Wolframoberfläche. — Die aus der Glühemission bekannte Entaktivierung des Thoriumfilms durch Sauerstoff konnte auch hier beobachtet werden. Die Austrittsarbeit der vergifteten Kathoden stieg auf 6 e-Volt an. — Endlich ließen Beobachtungen der Aufrauhung von Wolframoberflächen durch die Kathodenzerstäubung den Schluß zu, daß bei den hier benutzten Kathoden die für die Feldemission maßgebliche Feinfeldstärke nicht wesentlich größer war als die aus der geometrischen Gestalt berechenbare Grobfeldstärke.
If a conical metal tip is annealed in vacuum, the radius at the apex increases with time by surface diffusion. This was calculated by Nichols and Mullins and recently verified by the authors. This phenomenon is now calculated in case of a simultaneous action of evaporation and surface diffusion. By evaporation the blunting rate should be lowered until it becomes zero for a critical value of the curvature radius. Numerical data for different temperatures and cone angles are calculated for some metals (W, Mo, Pt, Ni, Cu). Measured are profile changes of Mo tips during annealing. The lowering of the blunting rate and the existence of a limit radius are confirmed. An evaporation can also occur as a consequence of a surface reaction. The measured radius changes of tungsten tips annealled in 1.5 × 10−5 torr and 2.5 × 10−5 torr of oxygen agree fairly well with the predictions. Surface self-diffusion measurements at high temperatures may be erroneous if evaporation is not considered, an example for Mo at 2150°K is given.
The morphological evolution of conical tungsten tips of cone angles between 1 and 15° at temperatures between 1800° and 3000°K is studied inside a scanning electron microscope. The experimental results confirm the theory of Nichols and Mullins: existence of a critical cone angle α = 3°, formation of solid drops for α < 3°, formation of characteristic steady-state shapes for α > 3°. For a temperature in the order of 2900 °K (clean surface) the curvature radius at the tip apex increases with time according to the law. For temperatures below 2700°K discrepancies are found, which are due to an evaporation of tungsten compounds produced at the surface by a chemical reaction with the residual gas (10−5 torr). The measurements at 2900°K have enabled the determination of the surface diffusion coefficient of tungsten: D = 2.4 ×106cm2/sec.
A determination of the surface tension and surface migration constants of metals in the solid phase, based on the use of pulsed field emission microscopy, is discussed. The experimental technique is described. An application to field emission cathodes of Herring's theory of transport phenomena in solids is given, which yields the necessary relations required for the determination of the basic physical constants from the experimental data. Results are presented and discussed for the case of tungsten. The method is applicable to a number of other metals, several of which are currently under investigation.
An apparatus is described to transform the end of a wire (tungsten in the vacuum into a fine tip by electron bombardment. Curvature radii at the tip apex down to 103 × are obtained. The tips are controlled by (I) an optical microscope (2) an electron microscope and (3) a field electron microscope. The interpretation of the process of tip sharpening is based on evaporation, surface diffusion and surface energy in the presence of a temperature gradient caused by the electron bombardment. It seems possible to use the method for the production and the regeneration of point cathodes in electron microscopes as well as a field emitter in field emission microscopes.
Interaction of oxygen with a polycrystalline tungsten surface has been mass-spectrometrically studied both under transient (flash filament with single flight detection) and steady-state (constant flow) conditions at temperatures T between 1000 K and 2500 and at oxygen pressures po2 from 10−9 to 10−6 torr. Only one binding state each for atomic oxygen, WO2 and WO3 as surface species has been observed. Quantitative measurements of the respective surface concentrations show that only up to 0.4 % of the total adsorbed oxygen undergoes chemical reactions with the surface tungsten atoms to produce oxides. From the experimentally obtained stationary values of the surface coverage θ(T,po2) together with a coverage dependency of the sticking probability s(θ) = 0.7(1− θ)2, the mean residence time τ(T,θ) of oxygen atoms has been calculated. The desorption energies of atomic oxygen, WO2 and WO3 are determined as functions of coverage and have maximum values for a clean surface as 6.5, 5.0 and 4.5 eV respectively.
Auf Grund verschiedener Beobachtungen mit dem Feldelektronenmikroskop wird geschlossen, da\ die emittierende einkristalline Metallspitze eine vollkommen glatte, nahezu kugelige Kalotte besitzt und somit ihre Anwendung zur Abbildung gerechtfertigt ist. Durch seitliches Aufdampfen von Barium l\t sich die Spitzengestalt direkt erkennen. Die Ausbreitung des Bariums ber die Wolframoberflche ist auf dem Leuchtschirm zu verfolgen, wobei mit bis zu 106-facher linearer Vergr\erung einzelne adsorbierte Ionen sichtbar werden. Die Bestimmung der wirklichen Feldstrke bei der Feldemission des reinen Wolframs ergibt den von der Theorie des Tunneleffektes geforderten Wert.
The partial differential equation describing morphological changes of a surface of revolution due to capillarity‐induced surface diffusion has been derived under the assumption of isotropy of surface tension and surface self‐diffusion coefficient. A stable, convergent finite‐difference method has been developed for the general case of an arbitrary surface of revolution and solutions have been obtained for the specific problems of the blunting of field‐emission tips and the sintering of spheres. Spheroidization of cylindrical rods, as well as field‐emission tips with taper below a certain critical value, is predicted; for tapers above the critical value, steady‐state shapes are predicted and equations describing the blunting and recession of the tips are presented. If the sintering results for spheres are represented by a plot of log x/a vs log t, it is found that the inverse slope varies from approximately 5.5 to approximately 6.5 for the range 0.05≤x/a≤0.3, in contrast with the constant value of 7 found by Kuczynski from an order‐of‐magnitude analysis. At higher values of x/a, n increases steadily and without bound.
Progressive blunting of tungsten needles heated in vacuum is made continuously or intermittently visible by a technique permitting needles to be heated while mounted in a conventional electron microscope. This technique permits the study of surfaces having small radii of curvature where detectable geometric changes due to diffusion occur in conveniently short periods of time. When the needle shape remains similar to its original geometry as its radius increases, a theory of Herring is applicable for distinguishing whether the transport process involved is volume or surface diffusion. Evidence is presented which indicates that surface diffusion predominates in the conditions of these experiments, i.e., for temperatures from 2600°K to 2900°K and radii from 3×10-6 cm to 3×10-5 cm.