AFM

The cantilever holder

The cantilever dimensions Tip position

SEM image of the AFM tip

Typical Features of our AFM indirectly, from phase information Chemical composition 3D / 2piImage information noOblique view max 3 µmSample height ~0.03 nm Lower limit resolution 64 to 1024 pixelsResolution per image up to 100 x 100 µm 2 Working area ambient temperature and pressure Working environment

mirror computer system feedback system positioning system probe tip sample piezo-electric scanner PSPD Laser diode z y x hardware components of the AFM

Inter-atomic force vs. distance curve Non-contac t contact distance tip to sample separation repulsive forces attractive forces Intermittent- contact Force

Modes of operation of an AFM Contact mode Non-contact mode ƒ’ = the force gradient between tip and sample k eff = effective spring constant ω = operational frequency m = effective mass of cantilever

Theory, inter-molecular forces Electrostatic, (magnetic) and van der Waals forces Van der Waals forces: Polarisation from permanent dipoles Induction-induced dipoles Dispersion-fluctuation of electrons as function of light

Theory, inter-molecular forces 1. Coulombic energy between ions with net charges leading to a long range attraction with u α r Energy interactions between permanent dipole u α r -6 3 energy interactions between an ion and a dipole it induced in another molecule U α r -4 4 between a permanent dipole and the dipole it induced in another molecule U α r -6 5 forces between neutral atoms/molecules U α r Overlapping energy arising from positive nuclei of one molecule and the electron cloud of another. This overlap leads to repulsion at very close intermolecular separations with α r -9 to α r -12 potential. Van der waals interactions arise from 2, 4, and 5.

Image processing Plane levelling Filtering Measuring particle sizes

2D Topography Image – Aerosol Particles Source = Topography Mode = AFM Fast Scan Direction = X X scan = left to right Y scan = bottom to top # of columns = 256 # of rows = 256 X scan size = µm Y scan size = µm µm

Particles from stage µm

(x’,y’) image i(x,y) Minimum separation Raised tip t(x-x’,y-y’)Tip Sample s(x,y) Tip Characterization