Agilent Technologies E5500 Series User's Guide download pdf (Page 101)

Contact Mode Imaging 5

Agilent 5500 SPM User’s Guide 101

tip. Higher force can place undue wear on the tip and, in the extreme,

can damage the tip or sample.

The optimal Setpoint value, which will vary per sample and per probe,

places enough force on the tip to accurately trace the topography

without placing unnecessary force on the tip. A good method for setting

the Setpoint is as follows:

1 With your cursor still in the Setpoint box, press the Down arrow on

your keyboard to make the Setpoint more negative. At some point,

the Setpoint voltage will drop so low that the tip will leave contact

with the sample—when it breaks free, the indicator in the Servo

window will change from green to red.

2 Pressing the Up arrow on your keyboard, raise the Setpoint again

until the tip just regains contact with the sample. This is the lowest

possible force that will keep the tip and sample in contact.

3 During the scan, you may choose to raise the Setpoint to improve

tracking of the topography. Some iteration may be required to reach

the optimal value.

Gains

The I and P gains in the Servo window dictate how quickly the feedback

system reacts to changes in deflection. Typically the I (Integral) and P

(Proportional) gains are set to the same value; the I gain setting has a

much greater effect on imaging than the P gain.

When the gains are set too high, the system will overcompensate to

correct changes in tip deflection which will lead to “ringing” at the

leading and trailing edges of features. When the gains are too low, the

system will not adjust the tip quickly enough for that scan speed,

blurring the topography.

Gain settings of 5-10 % are typical, though some iteration will most

often be required to optimize the gains for a particular sample.

Scan Settings

In the Scan and Motor window, the scan Speed and Resolution (X) will

all affect image quality.

A faster scan speed decreases imaging time but may not allow the

system sufficient time to accurately track the topography. A typical scan

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Agilent Technologies E5500 Series User's Guide Page 101