Ab Initio Study Of The Hydrogen-covered Diamond (001) Surface

Diamond is an ideal material for many applications because of itsoutstanding optical, electrical, thermal and mechanical properties. In1954,W. Eversole reported the synthesis of diamond by chemicalvapor deposition (CVD). From then on many research work has beendone in this field. In the CVD growth of diamond, the surface is mostly hydrogenterminated because abundant hydrogen exists in the growthenvironment. Therefore, understanding the structure and the propertiesof this surface becomes quite important for both fundamental researchand application. In this dissertation the structures and the properties of thediamond(001) surface are investigated from the atomic to electroniclevel by means of first principles total-energy calculations withingeneralized gradient approximation. Six different structures were investigated in our calculation.These are the (2×1): H surface, the (3×1): 1.33H surface, the (2×1):1.5H surface, the (2×2): 1.5H trough surface, the symmetric (1×1): 2Hsurface, and the canted (1×1): 2H surface. There are two danglingbonds per surface carbon atom for the bulk-truncated bare surface, areconstruction takes place in which two adjacent surface atoms movecloser toward each other to form rows of symmetric dimmers. Uponadsorption of hydrogen atoms, possible configurations include themonohydride (one hydrogen atom attached to a carbon atom) anddihydride (two hydrogen atoms attached to the same carbon atom) 75吉林大学硕士学位论文arrangements and others with hydrogen coverage between them. The formation energy of different phases has been analysed as afunction of the hydrogen chemical potential. As theμH increases, the(2×1):H phase, (2×2): 1.5H trough phase and the canted (1×1):2Hphase successively become the most stable phase. The (2x2):1.5Htrough surface phase, with all the dangling bonds saturated and thelarge distance between neighbour hydrogen atoms, is a well-foundedstable phase existing over a narrow chemical potential range, althoughhas not been observed so far. The hydrogen terminated diamond surface has a unique feature, afairly high p-type surface conductivity, which has attracted a lot ofinterest since a number of electronic applications proposed fordiamond are based on the effect. It is observed that the p-typeconduction has great relation with the surrounding ambience. Here theinteraction of the adsorbate molecules (HCl, NH3 and H2O) and thehydrogen-covered diamond (001) surface is studied by ab initiosimulation. Both the energy and the geometry indicate the existence ofa dihydrogen bonding between the HCl and H2O molecule (electronacceptor) and the surface H atoms (electron donor). The formation ofthe dihydrogen bond leads to electron transfer electron donor to theacceptor in the bonding region. This kind of electron transformationcan cause the p-type surface conduction found in experiments.