Oxford Instruments Cypher SPM, Руководство пользователя

Страница: 40 / 243

Cypher SPM
User Guide
Item Part # Item Description Qty Picture
8 448.081 Cypher ORCA 1M Resistor Assembly. A
1M Ohm Test Resistor (Dual Gain ORCA
Only). See
9.5 .
1
7.5 The ORCA Amplifier
There are a variety of ORCA cantilever holders each based on either a single or dual amplification
design. The design type and amplification gain are labeled on the top of the holder. Like all the
Cypher cantilever holders, a built-in circuit in the holder allows the software to automatically sense
the type of holder and configure the system accordingly.
The amplification range of the ORCA amplifier is expressed by its sensitivity—the ability to produce
a voltage output from a certain current flow into the tip. In terms of the full range of the ORCA amp-
lifier, the output is +/- 10 V, so multiplying the sensitivity by +/- 10 will give you the full range.
The ORCA amplifier incorporates the use of a trans-impedance amplifier which converts the input
current from the tip to an output voltage. The input potential of the amp is referenced to ground
so the tip is essentially held at 0 V potential. During the measurement, the sample can be biased
b/- 10 V using a voltage source provided by the Cypher electronics.
Each ORCA cantilever holder has a fixed gain(s) to provide the highest current measurement range
while considering the lowest noise. The following ORCA holders are currently available. Custom
holders can be configured on request.
Part number Sensitivity Current Range Typical noise 1-1 KHz
901.730 2 nA/V +/- 20 nA 1.5 pA
901.737 0.2 nA/V +/- 2 nA 750 fA
901.708 1 nA/V +/- 10 nA 3 pA
1 μA/V +/- 10 μA 75 pA
7.5.1 Single gain
Here is a conceptual block diagram of the single gain ORCA amplifier.
7 Standard scanner cantilever holders Page 40 of 243