Similarly, Honig and Ducker }55} observed drive speed dependent hysteresis inthe measurements at larger velocities (>1kHz). They suggested that this issue can beremoved by increasing the filter frequency.  Moreover, the useof none linear piezotranslators can also cause uncertainty in the force measurements.}53} It has also beenreported that the hydrodynamic boundary conditions measured with the help of AFMare sensitive to the stiffness }lo}ss,so and the shape of the force sensing cantilever.}56's'} Inthe study of Honig, and Ducker,}lo}ss} it was proposed that the stiffness of the cantilevercan affect the  force measurement and thus the sfip results. Stiffer cantilever waspreferred over the light one because the stiffer one can ensure the zero separationdistance between the probe and the surface. Rodriges et al }5}} conducted study ondifferent shaped and stiffness cantilevers and found that the rectangular light cantileversgave larger value of slip on hydrophilic silicon dioxide while the measurements withstiffer were more closer to the no一slip condition. Earlier, Henry and Craig }5}} reportedno一sfip condition on hydrophilic surfaces immersed in 60070 w/w sucrose solution usingrectangular cantilever, while found slip on the similar surface using V一shape/triangularcantilever.The effect of surface roughness on boundary slip has been extensively studiedand it has been found to be affecting the slip and the hydrodynamic drag measurement.Slip has been reported on surfaces with varying degree ofroughness.}44's2'}2-}s} However,e studies do not mutually agree on the increase or the decrease of the slip with varyingsurface roughness.  Theoretically,  it has been proved that the sparsely distributednanoasperities  can  provide  a  pressure  relief  and  thus  apparently  decrease  thhydrodynamic drag.}54'}}} In the experimental study of Guriyanova et al }28} it was foundthat the nanoasperities on rough patterned hydrophilicsurfaces considerably decreasesthe hydrodynamic drag. To compensate this decrease, additional parameter i.e. sfiplength will need  to  be  invoked.}l0}  Therefore,  surface  roughness  or presence  ofinhomogeneous nanoasperities can lead to apparent slip. Furthermore, the moleculardynamic simulation study of Chen et al }6}} showed that the sfip velocity decreases withncreasing the roughness. Similarly, experimental studies have also shown that theroughness can decrease the sfip at solid liquid interface.}44'62} Hence, the effect ofroughness on the slip and the possible mechanism is still under debate. These studiessuggest that the roughness factor should therefore be taken in to consideration beforeoncluding the magnitude of slip.      The presences of contaminants on the surfaces can give rise to the similar effectas  surface roughness.  Theoretical studies  have  shown that the contaminants  candecrease the hydrodynamic drag and thus lead to an apparently large s1ip}54}. Similarly,in two separately reported studies of Cottin-Bizonne et al}l}'40}, there was a differenceseveral order in the measured slip results. Therefore, they attributed the difference to the possible presence of contaminants. They further commented that the results of severalorder larger sfip were not reproducible. Additionally, it has also been reported that theno sfip condition changes to sfip condition in the presence of surfactants. }68'69} It wasalso found that, in the presence of surfactants, the sfip occurs of both the hydrophilic  The wettability of a certain surface by a liquid idefined by the contact angle(CA) of that liquid on the surface. Based on the tendency of the surface to attract orepel water, various surfaces are termed as hydrophilic or hydrophobic. Examples of thewater attraction and repellence is shown in Fig. 1-5(a,-d). Studies have shown that thatthe sfip has a relation with the wettability of the surface.}ls'}o'}1} The theoretical studiessuggest very small slip lenghts (b<_Snm) on smooth hydrophobic surfac  contrary,with exception of few studies }1o}24}ss}，  most of the experimental studies have reportedsfip lengths that are larger than 20 nm up to 1 gym. }"''9'ZO'3'-33'40'42'44''2] This urges thatthe sfip has relation with the hydropobicity. The contradiction, on the magnitude of slip,among various studies is still an open question. Furthermore, larger slip lengths havebeen reported on the superhydrophobic surfaces.  }2}'}}-}5} The slip lengths on the superhydrophobic  surfaces  range  from  several  hundred  nanometers  to  severalmicrometers. X2'''3-'6} The increasing slip length with enhanced none-wetting nature of the surface suggests dependence of the sfip on the wetability of the surface.}}l}Similarly the study of Sendner and Janecek }34} et al }35}also suggested that thedepletion layer can cause slippage. Furthermore, Doshi et al }}}} found a depletion layerof 0.5 nm thickness at heavy water- octadecyltrichlorosilane (D20一OTS) interface usingdirect none invasive neutron reflectivity measurements. They suggested that the slip on OTS surface can be attributed to the proposed depletion layer.  However, the thicknessof the depletion layer suggested by Doshi et al is larger than that suggested by themolecular dynamic simulation (<0.2nm) of Huang and Chinappi et al. }'3''s} Therefore,the difference in the experimentally measured slip }1}n9,ao,3o-33,4o,4a,44} and that obtainedfrom molecular dynamic simulation }13'ls} studies is still an open question. Based on theexperimental studies, the magnitude of slippage of water on the hydrophobic OTS likesurface is at least 20 nm while the theoreticalssuggested 0.2 to 5 nm on similarsurfaces. Furthermore, theoretically, it has been idealized that the nanobubbles can leadto boundary slip.  }}}} However,  it has not been proved, experimentally,  that thenanobubbles can enhance slip and needs further study.