Preparations And Properties Of Micro-nano Surface Structures Of Polycrystalline Boron Doped Diamond Films

Diamond has excellent properties such as high hardness,high thermal conductivity,excellent chemical stability and biocompatibility,which are important for basic and application research in many fields such as cutting tools,semiconductor devices,optical windows,micromotor system,and radiation detectors.Compared with intrinsic diamond,boron-doped diamond（BDD）has excellent properties such as high electrical conductivity,high oxidation resistance,high corrosion resistance,wide potential window and low background current,etc.The properties of BDD films（surface free energy,wettability,electrochemical properties,etc.）are closely related to its surface micro-structure and functional modification,which determine the application performance in various fields.The surface free energy（surface energy）of diamond,as a basic parameter of the material,determines the diffusion behavior of external molecules at the solid-liquid interface and directly affects the wettability of diamond surface.More researches have been carried out on intrinsic diamond,but the research of surface energy of BDD film and the relationship between wettability and surface energy are still lack of systematic and in-deep research.Chemical vapor deposition（CVD）diamond has a naturally hydrophobic and lipophilic hydrogen-terminated surface,while the oxygen-terminal surface is hydrophilic.The superhydrophobic hydrogen-terminated diamond surface（water contact angle>150°）and superhydrophilic oxygen-terminated diamond surface（water contact angle≈0°）can be obtained by adjusting the surface micro-nano structure.The surface energy of BDD films will change due to the introduction of doped boron atoms,and their wettability will be different from intrinsic diamond.Meanwhile,the design of micro-nano structure,using the modification effect of doped boron atoms in BDD,is also expected to improve the application properties of BDD film.To address the above issues,the thesis presents an in-depth study on the surface wettability and surface energy of BDD films,and the preparation of superhydrophobic Oxygen-terminated BDD films（O-BDD）with micro-nano porous surface,which has excellent mechanical and thermal stability.The nanocrystalline graphite-BDD composite films were prepared by a one-step method and used for the electrochemical trace detection of acetaminophen（APAP）,which showed good detection performance.The details and results of the study are as follows.1.BDD films with different boron doping concentrations were prepared by microwave plasma CVD（MPCVD）method.The contact angles measurements of deionized water,diiodomethane and glycerol on the BDD surface show that the contact angle of the three liquids gradually decreases with the increase of boron doping concentration in the BDD films,and the wettability on the BDD surface was enhanced.Based on the results,many surface energy calculation methods such as Fowkes approach,alternative formulation of Bertherot’s rule were selected from the surface tension component method and the equation of state method to calculate the surface energy of BDD films,respectively.The comparative analysis of the calculation results concluding that the Owens-Wendt-Kaelble approach,Lifshitz-van der Waals/acid-base（van Oss）approach and alternative formulation of Bertherot’s rule（two-liquid combination）were suitable for calculating the surface energy of BDD films and can achieve reasonable and credible surface energy.The surface energy of BDD films increases with the increasing of boron doping concentration from 1.50×10¹⁸ cm^-3to2.39×10²¹ cm^-3,and the surface energy varies from 43.26 to 49.66 m J/m²（Owens-Wendt-Kaelble approach）,42.89 to 52.26 m J/m²（Lifshitz-van der Waals/acid-base（van Oss）approach）,and 44.38 to 48.73 m J/m²（alternative formulation of Bertherot’s rule（two-liquid combination））.2.The catalytic etching effect of gold（Au）and copper oxide（Cu O）particles was exploited to prepare O-BDD surface with micro-nano porous structure.The BDD films with Au and Cu films deposited on the surface were treated at high temperature（800°C）in air,the hydrogen termination on the BDD surface were destroyed and transformed into oxygen termination.At the same time,the Au and Cu films were transformed into Au and Cu O particles due to the dewetting effect,and their synergistic effects result in the preferential etching at the grain boundaries where the BDD films have more defects,forming a dense micro-nano porous structure.The micro-nano porous structure was benefit to trap air and change the wettability.By modulating the etching parameters of the BDD film and Au/Cu composite film to change the micro-nano porous structure,the modulation of the surface wettability was achieved and the O-BDD surface with superhydrophobic property（water contact angle:165±5°）is obtained.As a superhard material,diamond has good mechanical and thermal properties,and the superhydrophobic O-BDD film basically maintains its original superhydrophobic properties after high pressure（5.24 MPa）,high temperature（200°C）and sandpaper scraping（66.5 k Pa,30 cycles）treatments,showing excellent mechanical and thermal stability.3.The nanocrystalline graphite-BDD composite structured films were prepared by MPCVD method with different temperature of substrate.Under high temperature conditions（950°C,1050°C）,part of the sp³ diamond phase on the（111）diamond surface with high boron-doping concentration converted into sp² graphite phase,and nanocrystalline graphite（NG）was formed on the surface of BDD（NG-BDD composite structure）.When used as an electrochemical detection electrode for acetaminophen（APAP）,the combination of the low background current property of NG-BDD and the strong adsorption effect of NG on APAP have excellent detection performance of the NG-BDD electrode.The electrode exhibits wide linear response to APAP（0.02-50μM）,low detection limit（5 n M,lower than known literature data）,good interference immunity（accurate detection of APAP in solutions mixed with dopamine,uric acid,ascorbic acid and tryptophan）and excellent stability(peak current fluctuation for 10consecutive days of testing:The NG-BDD electrode can be used for APAP detection in real samples with good reproducibility（98%-103%）for drugs containing APAP（Tylenol and Benadryl）with a relative standard deviation of less than 3.1%.In the thesis,the effects of boron doping on the surface energy,wettability and electrochemical detection properties of BDD films were systematically investigated to provide experimental data and references for basic and applied research on the surface properties of BDD films.Using the modification effect of boron doping on diamond,the robust superhydrophobic O-BDD films with micro-nano porous structures and NG-BDD electrodes with high detection sensitivity were prepared from the design of surface micro-nano structure and composite film,which provide new ideas for the design and development of new structures and devices of BDD films.This work is beneficial to expand applications in physics,chemistry,materials,bionics and other fields.