Investigations On Preparation Of Micro-nano Structural Diamond Film And The Related Wettability Property And Application In Electrochemical Sensor

Diamond is a kind of material with a variety of excellent performance.With the development of modern science and technology,the research on diamond's high-quality growth and growth mechanism have been very mature.The current challenges faced by people are not only confined to the preparation of diamond material itself,but more is how to expand its application in the real world.The micro-nano processing and surface modification of diamond are the hotspots of research in recent years.When the material structure is at the micro-nano scale,it will show new features that don't belong to many macroscopic block materials.It is imperative to find a method that is simple,convenient,useful and efficient for the processing and modification of diamonds as its super-hard texture makes it extremely hard to be processed in the micro-structure scale via the traditional mechanical processing approach.The surface structure and immersion property of diamonds can well modulate and complement for each other.If we combine this feature with the field of biology and chemistry,we will be able to expand the research on diamonds and to enhance its performance,which is likely to become the trend in the field and is worth to be commercialized.In this paper,a micro-nano structure of the surface of diamond was obtained in a short time by processing the self-supporting chemical vapor deposition(CVD)diamond film via thermal oxidation.Research has also been done on the change and mechanism behind its immersion property(droplet contact angle).The immersion property of the diamond was modulated to transform the diamond into one with a super-hydrophilic surface so that it can be used in detecting the concentration of conductive solution.Ion sputtering and thermal oxidation were used to put goldnanoparticles evenly on the surface of the diamond.With this and the use of biomolecules,the environmental trace amount of hormone bisphenol A was detected,with the detection rate reaching the flying level,the highest in the field.Main results are as follows:(1)Diamonds whose micro-nano structure is closely related to the growth of its texture were manufactured by processing the(100)and non-(100)texture freestanding CVD diamond films via thermal oxidation at 800 o C.The growth planes and nucleation surfaces of the(100)texture diamond films then grew into micro-sized(100)diamond columns and micro-nano diamond cones respectively.For the non-(100)texture diamond films,a great number of nano-holes appeared on the growth surface,forming a diamond nano cone with a nucleation surface.The forming of this particular micro-nano structure was due to the oxidation and etching of the non-diamond crystal plane at the grain boundaries and the smaller nano-diamonds as well as the different oxidation rates of the different crystal planes of the diamond.This confirms the "V" growth mechanism behind diamond grains.The high temperature oxidation approach is user-friendly and efficient,and has provided a new method for the design and processing of the micro-nano structure.(2)The change in the immersion property of self-supporting CVD diamond films before and after oxidation and hydrogenation were also studied.Experiments showed that immersion property was affected by a variety of factors including the texture,micro structure,film composition,surface hydrogen and oxygen termination.The nucleation surface and the growth surface of the oxidized diamond film then became hydrophilic or superhydrophilic,with the contact angle of the super hydrophilic surface reaching as far as 0o.After the hydrogenation,the surface of the diamond film remained hydrophilic,but the contact angle became larger.Using the super-hydrophilic nature of the diamond film,we filled the nucleation surface with conductive solution in a short time,and then concentration of the conductive solvent in the solution was quickly detected by the I-V measurement curve.Superhydrophilic diamond films come with low background current,chemical inertness and arereusable.Furthermore,it can be used in extreme environments such as the ones with strong acid and strong alkali.(3)Au nanoparticles were made to deposit evenly on the surface of boron-doped diamond(BDD)films via ion sputtering and thermal oxidation.Also,we assembled the Aptamer and Mercaptoethano onto the Au nanoparticles via the Au-S covalent bond to invent an efficient electrochemical sensor with a composite structure of MCH/ Aptamer / Au-NPs / BDD and detected the trace environmental hormone bisphenol A(BPA)via the impedance test.The new electrochemical sensor comes with low background current,a large surface and is not subject to interference.Also,there is a strong binding between Aptamer and BPA,leading to a stable spatial conformation.The rate of detection can reach the flying level(7.2×10-15 mol/L),the highest in the field.It has been used for the trace detection of BPA in milk samples,and has brought forth a fine recycle rate.This provides justification for its use in the trace detection of pollutants in food,the environment and other fields.In this thesis,based on the CVD diamond film,the author designed and processed the micro-nano structure of the diamond via high-temperature oxidation on its surface and the use of nano-metal particles and bio-molecules,which made the control of its immersing rate and a high electrochemical sensitivity become possible.This was later used for the trace detection of conductive solution and environmental pollutants.This approach enjoys the merit of high stability,good specificity and high sensitivity,providing new ideas for the application and development of diamond-based sensors.The research has laid down the theoretical and experimental foundation for future preliminary researches on inventing better diamond-based structures and devices,stimulating their use in different fields,structure design and mechanism.