Dell 3100 Especificações descarregar pdf (Página 164)

TappingMode AFM

Advanced TappingMode AFM Operation

144 Dimension 3100 Manual Rev. D

more rapidly. The feedback system senses the error caused by going off of the step and responds

more rapidly. Unfortunately, more energy transfers to the sample surface while scanning at this

operating point.

The nature of the sample inﬂuences the decision between response time and contact force. For

example, harder samples can withstand higher contact forces, so the response time improves by

lowering the Setpoint amplitude. Soft samples that are relatively ﬂat should run with higher

Setpoint values to reduce the energy imparted to the sample. In general, the solution to the problem

is to decrease the scan rate and increase the feedback gains. In some situations, the feedback gains

cannot increase without causing piezo oscillations; in such cases there is no choice but to reduce

the scan rate.

Inadequate response time typically occurs when the tip encounters a low point in the sample. The

amplitude of the cantilever oscillation decreases very quickly when taller portions of the sample are

encountered. As a result, the system response is markedly different depending on whether the tip is

climbing or descending a feature in the sample. For this reason, Scope Mode is very useful when

setting scan parameters. As the tip descends, features are evaluated by comparing the Trace and

Retrace in Scope Mode. Figure 9.4b illustrates the effects of poorly selected scan parameters on a

calibration standard that includes a series of sharp-walled pits. Regardless of the scan direction, the

tip does not track the wall of the pit when the tip encounters a pit. However, it does track the surface

closely when moving out of the pit.

Figure 9.4b Scope Trace with High Scan Rate

Figure 9.4c depicts the same sample with a slight increase in the Integral gain and a twofold

decrease in the Scan rate. The tip now tracks the surface when it descends into the pit as well as

when it exits. The Trace and Retrace lines now coincide closely.

Z Range

50.00 nm/div

Scan Size - 2.50 µm/div

Trace

Retrace

1 2 ... 159 160 161 162 163 164 165 166 167 168 169 ... 375 376

Sem comentários

Dell 3100 Especificações Página 164