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SPM Principles
I(z) Spectroscopy
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The I(z) Spectroscopy is related to LBH spectroscopy and can be used for providing an information about the zdependence of the microscopic work function of the surface. Next important use of the I(z) Spectroscopy is concerned with for testing of the STM tip quality. The tunneling current I_{T} in STM exponentially decays with the tipsample separation z as I_{T} ~ exp(2kz), where the decay constant is given by 2k = 2(2mU/h2)^{1/2} U is the average work function U_{av} = (U_{s} + U_{t })/2, where U_{t} and U_{s} are the tip and sample work functions, respectively. In the I(z) Spectroscopy, we measure the tunnel current versus tipsample separation at each pixel of an STM image. For U_{av} = 1 eV, 2k = 1.025 A^{1}eV^{1}. Sharp I(z) dependence helps in determining of tip quality. As is empirically established if tunnel current I_{T} drop to onehalf with Z < 3 A the tip is considered to be very good, if with Z < 10 A, then using this tip it is possible to have an atomic resolution on HOPG. If this takes place with Z > 20 A this tip should not be used and must be replaced. References

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