Surface Topography And Optical Properties Of Crystals Induced By Low Energy Ion Beam

Low energy ion beam erosion to generate self-organizing nano-structure on solidsurfaces is a simple, effective, and inexpensive method for production of orderlynano-structure with a large area. This method has the features of higher manufacturingprecision, realization of control over nano-structure dimensions by changing ion beamparameters, and aptness for automation. Therefore, it has been a research focus inEurope and the USA in recent years. This paper researches the critical techniques ofnano-structure formation with various ion beam parameters, for experimental materialsof monocrystalline silicon and sapphire, which makes the major research achievementsas following:1. The analyses and simulations of the theoretical models for nano-strucureformation by ion beam erosion are conducted. BH model and MCB model, both ofwhich are based on Sigmund spurting theory, are analyzed. And the introduction of ionbeam inducing term and non-linear term to MCB model improves the shortcoming ofBH mode, failure to explain nano-structure formation at low temperatures and long-timeerosion saturation. This paper makes the detailed analyses and simulations of MCBmodel, provides erosion term, dispersion term and diffusion term, and accounts for theformation and evolution of self-organizing nano-structure.2. This paper establishes a mathematical model to describe formation ofself-organizing spot nano-structure with sample rotations, confirms that amorphouslayer thermal diffusion is the main diffusion mechanism for monocrystalline silicon andobtains nono-stucture of monocrystalline silicon. When ion flux density is265A/cm2and ion beam energy1000eV, without sample rotations, ribbon pattern nano-structuresappear on the surfaces of samples, spurted by ion beams with a small angle (540).Increase in the incident angle(4050) leads to the tendency to be smoother for thesample surfaces; further increase in the incident angle up to65, columnarnano-structures begin to emerge on sample surfaces. While samples are rotating, withthe identical ion beam parameters, dot nano-structures can be obtained no matter theincident angle is smaller（540） or larger（>65）, with a dimension range of5085nanometer. The erosion results confirm the validity of the mathematical model.3. After obtaining sapphire nano-structure and confirming that ion beam inducingdiffusion is sapphire’s main surface diffusion mechanism, a3+1dimensionmathematical model is established to describe the evolution of sapphire surfacetopographies by ion beam erosion. When Ar+ion beams are employed to erode sapphire, with an ion beam energy of1200eV and an ion flux density of265A cm2, dotnano-structures of smaller vertical dimensions can form, with lower orderliness, at anincident angle of520and3545; if the incident angle lies in30about, samplesurfaces tend to be smother; if the incident angle is up to45, orderly ribbon patternstructures appear on sample surfaces, perpendicular to ion beams; if the incident angle isfurther raised, columnar structures turn up in the incident direction of ion beams andorderly ribbon pattern structures remain in the vertical direction, with a rapidenhancement of sample surface roughness. Different from monocrystalline silicon,sapphire has an anisotropic ion beam energy distribution, and sapphire surfacerelaxation mainly depends on ion beam inducing mechanism. The establishedmathematical model is employed to simulate and analyze the erosion results.4. The relationship is established between surface topographies of erodedsapphire and different Ar+ion beam energies, and the formation mechanism of surfacetopographies is displayed. The experiments find that various energies with the sameincident angles can produce different nano-structures on sapphire surfaces after eroding.At the incident angle of65, lower energy (600750eV) results in dot structures onsample surfaces; higher energy(900eV) produces regular ribbon pattern structures; andeven higher energy(>900eV) generates columnar structures in the incident direction ofion beams and orderly ribbon pattern structures in the vertical direction. Depositiondepth and anisotropic energy distribution are chief causes for evolution ofnano-structures.5. A method is raised to improve sample transmittance with formation of orderlynano-structure by employing ion beam erosion. Within the wavelength range of1100nm2000nm，Ar+ion beams are employed to erode monocrystalline silicon，whenincident angle is at15with ion flux density265A/cm2and ion beam energy1000eV,without samples rotation, ribbon pattern nano-structures appear on the surfaces ofsamples, transmittance of samples increased by8%approximately; when incident angleis at65with the same ion flux density and ion beam energy, with samples rotation, dotpattern nano-structures emerge, transmittance of samples increased by20%approximately. Enhancement of surface orderliness and height of nano-structures resultsin the increase of transmittance, which accounts for sample surface antireflections, withthe introduction of equivalent refractive index theory.6. The effects of eroding time on monocrystalline silicon and sapphire erosions arestudied. The results find that time extension is unable to change nano-struturetopographies, but able to increase the vertical nano-structure dimensions and enhance the orderliness. When saturation is achieved after long-time erosion, non-linear termsof model function principally.