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In this study, an electrolytic micro-machining tester is employed to investigate the effects of supply voltage,electrode gap and initial machining position on the geometry of the tungsten needle. The tungsten needle to be electrolyzed is dipped in an aqueous electrolyte of 2wt % sodium hydroxide as the anode, and the stainless steel needle with a diameter of 50 £gm as the cathode(tool electrode), and the electrode gap is set to be 30 £gm.Morever,the tungsten needle can be allowed to be fixed or in the reciprocating motion. Experimental results show that when the tip diameter of stainless steel needle is less than 50 £gm, a great quantity of current density and power are generated to cause the temperature failure of the tool electrode. At a certain gap between the electrodes, the electric field is focused on the narrow range to improve its processing efficiency. Under the higher supply voltage condition, it is difficult to control the size because the diameter of tungsten rod is reduced very quickly. Under the lower supply voltage condition, the diameter of tungsten rod can be processed to smaller sizes, but it takes a long time. Therefore, in the beginning of the experiment, the tungsten rod is electrolyzed under a higher voltage to the small size, and then the supply vltage is switched to lower value to conduct the electrolysis process. Consequently, a finer and more even tungsten needle can be obtained. Experimental results show that a more even tungsten needle with the length of 600 £gm and the diameter of 4 £gm can be manufactured.

No description available.

Tungsten disulfide is a proven material as a low friction solid coating. The material is well characterized and has proven its capabilities the last century. Graphene is this centurys most promising material with electrical and mechanical properties. With it the 2D material revolution have started. In this thesis I present a feasible way to sputter tungsten disulfide on graphene as a substrate with little damage to the graphene from energetic particles and a straight forward method to quantize the damage before and after deposition. Further I investigate compositional changes in the sputtered films depending on processing pressure and how tungsten disulfide film thickness and the amount of graphene damage affects the materials low friction capabilities. It is shown that graphene is not a viable substrate for a low friction tungsten disulfide film and that tungsten disulfide is an excellent material for low friction coatings even down too a few nanometers and that the films behavior during load in the friction testing significantly depends on the processing pressure during sputtering.

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published_or_final_version / abstract / Physics / Master / Master of Philosophy

No description available.

En esta tesis doctoral, se ha investigado y desarrollado un nuevo método de CVD asistido por aerosol (AACVD), que permite el crecimiento de nanoestructuras de WO3 intrínsecas y funcionalizadas con Au. Así mismo se han depositado capas policristalinas de SnO2 para aplicaciones de detección de gases. La síntesis de materiales nanoestructurados, la fabricación de dispositivos y sus propiedades de detección de gases, han sido estudiadas. El método AACVD fue utilizado para la síntesis y la deposición directa de capas activas encima de sustratos de alúmina y también sobre substratos micromecanizados (microhotplates), lo que demuestra la compatibilidad entre la tecnología de silicio y la deposición de la capas activas nanoestructuradas. En la tesis se ha demostrado que las capas nanoestructuradas de WO3 funcionalizadas con oro tienen una sensibilidad mejor que las intrínsecas frente a algunos gases relevantes y al mismo tiempo se ha producido un cambio de selectividad. / In this doctoral thesis, it has been investigated and developed the Aerosol Assisted Chemical Vapour Deposition (AACVD) method for direct in-situ growth of intrinsic and Au-functionalised nanostructured WO3, as well as SnO2-based devices for gas sensing applications. The nanostructured material synthesis, device fabrication and their gas sensing properties have been studied. AACVD method was used for synthesis and direct deposition of sensing films onto classical alumina and microhotplate gas sensor substrates, demonstrating the compatibility between the microhotplate fabrication process and the sensing nanostructured layer deposition. The effect of Au nanoparticles on the gas sensor’s response was measured and presented in this thesis. The test results revealed that the addition of Au nanoparticles to the WO3 nanoneedles has increased the sensor’s response towards the tested gases (i.e. EtOH). It was therefore demonstrated that the Au-functionalisation has an enhancing effect on the gas sensing properties of WO3 nanoneedles

No description available.

Buvo tiriama Co(II) ir Ni(II) įvairių kompleksų elektroredukcija chloridiniuose, sulfatiniuose, citratiniuose, pirofosfatiniuose bei pirofosfatiniouose-amoniakiniuose tirpaluose, Ni ir Co lydinių su W ir Mo elektronusodinimas, gautų dangų sudėtis ir paviršiaus morfologija, struktūra bei korozinės savybės. W ir Mo lydiniai buvo nusodinami iš citratinių - boratinių ir pirofosfatinių – amoniakinių elektrolitų, o koroziniai tyrimai atlikti sulfatiniuose tirpaluose. Tiriant Co(II) ir Ni(II) elektroredukciją nustatyta, kad voltamperinių kreivių forma primena būdingas mišriai kinetikai voltamperines kreives, jose yra ryškus persilenkimas. Tačiau tyrimai EIS metodu parodė, kad šio persilenkimo negalima sieti su difuziniais apribojimais. Padaryta prielaida apie elektrochemiškai aktyvaus Co arba Ni komplekso lėtą adsorbciją ant elektrodo. Nustatyta, kad Ni elektonusodinimo greitis iš pirofosfatinių tirpalų be amonio jonų yra labai mažas. Pridėjus (NH4)2SO4 ir taip formuojant amoniakinius nikelio kompleksus tirpale, labai pagreitėja Ni elektronusodinimas. Šis efektas labai gerai koreliuoja su didėjančia apskaičiuotų įvairių Ni (II) kompleksų su amonio jonais frakcija. Tačiau amonio jonų buvimas praktiškai neturi įtakos Co elektronusodinimo greičiui. Iš gautų duomenų daroma išvada, kad elektrochemiškai aktyvus Ni ir Co kompleksai yra skirtingi, t.y. CoOH+ ir Ni(NH3)162+ yra krūvį pernešančios dalelės pirofosfatiniuose – amoniakiniuose tirpaluose. Tiriant Co-Mo ir Co-Mo-P lydinius... [toliau žr. visą tekstą] / Electroreduction of various Ni(II) and Co(II) complexes in chloride, sulfate, citrate, pyrophosphate and pyrophosphate –ammonia solutions, electrodeposition of Ni and Co and their alloys with W and Mo and composition of obtained coatings and surface morphology, structure and corrosion properties have been studied. W and Mo alloys were electrodeposited from citrate – borate and pyrophosphate –ammonia solutions, and the corrosion behavior of obtained alloys was investigated in sulfate solutions. The shapes of voltammetric curves obtained for Co(II) and Ni(II) electroreduction are similar to the typical shapes of curves for processes occurring under mixed kinetics, and clear plateau presences in voltammogram. However, based on the data obtained by the electrochemical impedance spectroscopy was confirmed that the obtained plateau does not attribute to the diffusion limitations. A slow adsorption stage of electrochemicaly active complex of Co and Ni on the electrode was assumed. It was determined that Ni electrodeposition rate from pyrophosphate baths without ammonia is relatively small. Adding of (NH4)2SO4 and further forming of Ni(II) complexes with ammonia in the solution accelerates sufficiently the rate of Ni electrodeposition. The effect well correlates with increasing the calculated molar fraction of various ammonia complexes with Ni(II). Based on the received data we conclude that electrochemicaly active Ni and Co complexes are different, i.e. CoOH+ and Ni(NH3)162+... [to full text]