TP de MICROSCOPIE A EFFET TUNNEL (STM) ElÃ©ments ... - CNRS

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TP STM Nano-Monde, Master 2 PRO, UJF, 2004/05sampleTipI TR_I T+V TV S = R.I TFigure 1 : simplified diagram of the current-voltage pre-amplifierb/ Control electronics moduleThis electronics module which is associated to the PC Pentium 200, is composed by:1 A 16 bits DAC and ADC card. This card converts the analogical signals to digitalsignal and vice-versa.2. Voltage amplifier +/- 12VThese amplifiers are needed to apply voltages at the different piezoelectric elements, fromdigital ramp generated by the software and converted in analogical signals by the DAC card.3. An analogical feedback loop described in figure 4.sampleTipZ-PiezoZ+∆Zcurrent-voltagePre-amplifierVoltageamplifiersV SDACADC∆ZZAbsolutevalueLogarithmComparatorFigure 2: tunneling current feedback loopThe tunneling current I T , is converted to a voltage V S at the output of the preamplifier, and V Sis digitalized by the DAC card. The analogical feedback loop compares V S to a regulationvalue fixed by the user, and deduces the error signal ∆Z, which is converted again by theDAC card in analogical signal, which is applied to the piezoelectric element in order to refindthe regulation value. This feedback loop is running continuously in imaging mode, thismode is called constant tunneling current mode. The error signal ∆Z is recorded during thescan X,Y. All the ∆Z(X,Y) points form the STM image.6
TP NanoMonde, Master 2 PRO UJF Année 2004/053/ The Easyscan software: A detailed description is available during the practical work.tracksSInertial motorsamplecylinderTip holder andpiezoelectric systemFigure 3 :Easyscan STM headFlorence Marchi, Maître de Conférence UJF7marchi@grenoble.cnrs.fr - -
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TP de MICROSCOPIE A EFFET TUNNEL (STM) ElÃ©ments ... - CNRS

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