Basic Research Of Surface State Control And Related Applications Of Diamond

The excellent properties of diamond enable it to be widely used in various fields of machinery,heat transfer,optics and semiconductor.Precision surface control including the smooth surface,controllable surface/subsurface defects and surface bonds state are the basic prerequisites for the application of diamond.However,the excellent physicochemical stability of diamond leads to its poor surface machining and remanufacturability.Therefore,the basic research of diamond surface state control and its related applications are of great significance.In this dissertation,high speed three-dimensional dynamic friction polishing(3DM-DFP),oxygen based inductively coupled plasma(ICP)and hydrogen plasma etching were used to control the surface state of diamond.The surface roughness of polycrystalline diamond(PCD)and single crystal diamond(SCD)could be<5 nm or even 1 nm,resulting from the evolution of surface catalytic oxidation by optimized 3DM-DFP.Fatigue effect and continuous energy input lead to subsurface cleavage of diamond(111)facet.This damage of nearly 10μm beneath the surface conmprises cleavage layer,transition layer and compression zone.And the generated new Raman characteristic peaks,i.e.,1425 cm-1,2200 cm-1,1750 cm-1 and 2100 cm-1,are associated with the quasi sp2+sp3 amorphous structure,local defects of carbon-vacancy and.sp1 phase.At the same time,the intrinsic absorption and scattering effects of the non-diamond phase in the diamond for terahertz window applicaiton give rise to a significant decrease of dielectric constant.Plasma etching technique is considered to be an effective way to realize the surface control of diamond.For the oxygen based ICP etching process,the addition of auxiliary gases as well as different plasma power and radio-frequence(RF)power control play a decisive role in distinct diamond etching rate and surface state.The lowest surface roughness of the PCD black film was obtained at a rate of 4.6 μm/min with the addition of 10%CHF3,corresponding to the highest ratio of C-O-C symmetric ether bonding structure.At the same time,the SCD was etched at a rate of 0.23 μm/min to obtain a surface roughness<0.5 nm and a uniform surface microstructure.While the evolution of needle-like surface morphology is owing to the selective etching of diamond(111)crystal plane and preferential etching of defect and twin boundary,etc.In addition,the trans-polyacetylene produced by oxidation would disappear under the condition of containing Cl or H,while the formation of chloride and the absence of fluoride can also lead to the difference of etching rate and morphology.Meanwhile,hydrogen plasma can effectively control the surface morphology of diamond and,furthermore,form surface p-type hole conduction.The structure of solution gate field effect transistor(SGFET)based on hydrogenated smooth diamond film shows different I-V responses in different aqueous solutions.With the rising of voltage,the surface C-H bonds in KHP mixed solution with the addition of NaOH and H2SO4 can be damaged by surface reaction,and thereupon the surface resistance was increased from 13.57 kΩ to 95.78 kΩ,electric current from the saturated 1 x 10-4 A/V dropped to 5 x 10-5A/V.However,after the treatment of this SGFET structure by linear negative potential sweep(NPS)as electrode in inorganic acid to recover surface hydrogen bonds,the resistance shows a decline from 94.33 kΩ to 30.46 kΩ,and electric current was rised from 6 x 10-6 A to 1.6 x 10-5 A.It also exhibits more sensitive I-V response in aqueous environment,and without any damage of flatness or reaction products at the same time.