The Microstructural And Optical Properties Of Boron Ion Implanted Microcrystalline Diamond Films

Diamond materials have acquired a great deal of attention due to their many properties,such as wide range of spectral transmission,high refractive index?2.45?,excellent optical exchange performance,light attenuation in the mid-infrared region is less than 1 dB/cm^-1,the band gap is much larger than that of the congeners?such as silicon and germanium?and the characteristic spectral(1500-1800 cm^-1)exhibits a low optical absorption rate and little loss of optical signal.Meanwhile,diamond films has its well physicochemical of light quality,biocompatibility and corrosion resistance,in which the properties allows it to work normally at extreme environment and high thermal conductivity coefficient can timely conduct high heat generated during operation of the waveguide device.Based on diamond above excellent performance,manufacturing a diamond Mach-Zehnder interferometer?MZI?is expected to be applied in a highly sensitive or food liquid phase detecting sensor device.In this paper,a series of microcrystalline diamond films?MCD?with different grain sizes were prepared by hot filament chemical vapor deposition?HFCVD?and ion implantation.The conclusions of this thesis are as following:Microcrystalline diamond?MCD?films with different grain sizes of 160-2200nm were prepared by using hot filament chemical vapor deposition?HFCVD?system,and the influences of grain size and structural features on optical properties were investigated.The results show that film with grain size in the range of 160-310 nm exhibits higher refractive index?2.77-2.92?.With grain size increasing to 620±100 nm,the refractive index shows a value of 2.39-2.47,approaching to nature diamond?2.37-2.55?,and a lower extinction coefficient value of 0.08-0.77.When the grain size increases to 2200 nm,the value of refractive index increases to 2.66-2.81,and the extinction coefficient increases to 0.22-1.28.Visible Raman spectroscopy measurements show that all samples have distinct diamond peaks located at 1331-1333 cm^-1,the content of diamond phase increases gradually as grain size increases,and the amount of trans-polyacetylene?TPA?content reduces.Meanwhile,the sp² carbon content is significantly reduced in MCD films with grain size of 620nm,which improves the optical properties of the films.The correlation between micro-structure and optical properties of boron ion implanted microcrystalline diamond?B-MCD?films was investigated to understand the effect of different annealing temperature on their complex refractive index.The optical properties of B-MCD films were investigated in a wavelength range of380-1000 nm by ellipsometry spectroscopy?SE?.Physical models and fitting results show that average film thickness of 500 nm was achieved,and the films exhibited relatively high refractive index?2.29-2.30?and low extinction coefficient values after 800?annealing.At lower annealing temperature??700??,the trans-polyacetylene?TPA?in grain boundaries began to decrease and graphite phase disorder compared with unannealed sample.The annealing temperature of 800?was found to be a transition point.At this temperature,graphite phase becomes more ordered,and diamond peak in Raman spectra shifts to 1332 cm^-1 and its full width at half maximum?FWHM?becomes smaller?7.08?,indicating diamond have better lattice structure currently.With annealing temperature increasing to 900?,the diamond peak increase from 7.08 to 9.01cm^-1,indicating that the lattice structure is destroyed at higher annealing temperatures.X-ray photoelectron spectroscopy?XPS?results show that the content of sp³ carbon content increases from 36.7%to 52.7%and then decreases to 43.9% with the annealing temperature increases from 700? to 900?,suggesting that fewer non-diamond phase on film surface in the case of 800? annealing,which dramatically improving the optical properties.The MCD films were implanted by B⁺ with different doses.The influences of ion doses on the microstructural and optical properties of MCD films were systematically studied.The results show that the content of impurity phase on the surface of the film increases with the increase of ion implantation dose in the unannealed condition.Meanwhile,when MCD films are implanted by higher ion dose,the implanting process can seriously damage the diamond grains microstructure.Therefore,we performed vacuum annealing on MCD films,which aimed at decreasing the TPA content and recover the diamond grains,increasing the diamond content in the films.The B-MCD-13 sample's refractive index is 2.28-2.30,which is closer to the natural diamond refractive index of 2.45 compared with other doping samples.The Hall coefficient is -4.18×10⁴ cm²·C^-1,and its Hall mobility is 61 cm²·V^-1·s^-1,showing a good n-type conductivity capacity.Based on the above results,the suitable ion doses have a very broad development prospect for the research of diamond waveguide devices.