Epitaxial Growth Of Manganese Silicide Nanowires On Si(110) And (100) Surface

Manganese silicide nanowires （NWs） are promising candidates in the search formicroelectronic, opticelectronic and thermoelectric materials. A systematic study ofthe growth mechanism of these self-assembled NWs on silicon surface and synthesisof NWs by a delicate control of growth parameters is a significant step toward theirpractical applications. In this paper, manganese silicide NWs have been formed ontheSi（110）-16×2 and Si（100）-2×1 surfaces with molecular beam epitaxy method bycontrolling growth temperature, Mn deposition rate and deposition time. ScanningTunneling Microscopy was employed for the characterization of the morphology ofNWs. The composition, structure, growth mechanism, the influence of growthparameters and growth kinetics of NWs were also studied. The main results can besummarized as follows:（1） epitaxial growth of manganese silicide NWs on Si（110）-16×2 surfaceHigher growth temperature and lower deposition rate are favorable for theformationofNWswithalargeaspectratio. Intheoptimizedcondition, bydepositing1ML Mn on Si（110） surface at a deposition rate of⁰.01 ML·min-1 at ⁵75℃, thelength of NWs can reach 1700 nm, and the average width and height are ¹7nm and³ nm, respectively, showing an aspect ratio larger than 100.Manganese silicide NWs orient with the long axis along the sole [110]direction on Si（110） surface. BSE-SEM and high-resolution Scanning TunnelingMicroscopy results indicate that manganese silicide NWs are MnSi1.7. The threedimensional islands are probably Mn-rich silicide. The nucleation density ofmanganese silicide islands on Si（110） surface can be well described by the classicalnucleation theory. The growth of NWs is governed by a strain-driven energeticmechanism and the NW shape results from anisotropic lattice mismatch between the silicide and the silicon substrate. The supply of free Si atoms per unit time during thereaction with Mn plays a critical role in the growth kinetics of NWs.（2） epitaxial growth of manganese silicide NWs on Si（100）-2×1 surfaceThe growth of manganese silicide NWs with a comparatively large aspect ratioon Si（100） surface requires a demanding condition: the growth temperature, the Mndeposition rate and deposition time should be ⁴25-475℃, ⁰.2-0.5 ML·min^-1 and15-30 minutes, respectively. By depositing 4 ML Mn on Si（100） surface at adeposition rate of⁰.2 ML·min^-1 at ⁴75℃, the average length of manganese sicilideNWs can reach 500 nm, and the average width is ²0 nm, showing an aspectratioof²5.The nucleation density of manganese silicide islands on Si（100） surface can bewell described bythe classical nucleation theory. Manganese silicide NWs orient withthe long axis along the two orthogonal [ 011]and [ 011]directions on Si（100）surface. Manganese silicide NWs formed on Si（100） surface have similar charactersas those grown on Si（110） and Si（111） surfaces, so possibly they are MnSi1.7 and thethree dimensional islands are Mn5Si3. Although manganese silicide NWs can growacross surface steps, the growth of NWs with a large aspect ratio on Si （100） surface islargelyrestricted bysurface steps with high density.