(2011!04!08) electrical measure techniques in atomic force microscopy

7/31/2019 (2011!04!08) Electrical Measure Techniques in Atomic Force Microscopy

1/14

Weekly ReportName: Tran Ngoc Cuong

Date: April 8th, 2011Last week:

Principle of electrical measurement techniques in atomic force microscopy.

- Scanning surface potential microscopy (SSPM).

- Scanning impedance microscopy (SIM).

- Scanning capacitance microscopy (SCM).

- Conductive atomic force microscopy (CAFM).

- Scanning Spreading Resistance Microscopy (SSRM).

Next week:

- Photoluminescence in analysis of surfaces and interfaces.

- Study about PL measurement of ZnO growth on LNO.


2/14

PFM Review

1. PFM is based on the deflection of an induced strain by a voltage. This technique was

introduced for detecting polarized regions in ferroelectric films.2. PFMs original application was focused on imaging domain structure and local

hysteresis loops in ferroelectric materials.

Domain imaging and Dynamic Piezoresponse

Field induced strain: Sj = dij Ei

Under the modulation voltage: V= V0cos(t),surface vibrates as Z=Z0cos(t+)

Vibration amplitude : Z0 = d33V0

EE E

For P+ ( ), = 00

For P- ( ), = 1800


3/14

Electrical measurement Techniques in

Atomic Force MicroscopyPresentation: Tran Ngoc Cuong

2011/04/08


4/14

The general terms used for electrical technique


5/14

SSPM Technique

SSPM is used to measure the surface potential in NCM mode. It is based on the Kelvin

probe principle.

Where is the surface potential

correlated to the difference in tip and sample

work functions ( ).

(a) Electrostatic potential and interaction force between a conducting tip and a sample.

(b) External DC voltage applied to nullify the force.

(c) External AC voltage with adjustable DC offset is applied to the tip, which leads to its

vibration.


6/14

Principle of SSPM

There are two ac-contributions to the force, one at the modulation frequency

, and one at 2 mode.

Sample bias


7/14

Principle of SSPM

Surface height information is recorded in the

standard tapping mode where the oscillatingcantilever lightly taps the surface.

The second pass in lift mode monitors the

variations of electrostatic force at a constantheight

An extra feedback loop is used to adjust the DC bias on the tip to compensate the F1

force component as explained above. By running in lift mode, SSPM separates the

surface features and the electrostatic force on the tip.


8/14

Example

The change of the work function was

simulated by a periodically switched

voltage, applied to the sample. The

voltage changes were 0.1V.

Channel 1 (Error signal) Feed back

Example for -measurement


9/14

Scanning Capacitance Microscopy (SCM)

SCM is used to measure capacitance and capacitance gradients.

Principle of SCM

- The signal in the SCM images is the output voltage of the lock-in amplifier, which is

related to the tip-sample gradient capacitances.

- The magnitude of the SCM output ( dC/dV) signal is a function of carrier

concentration.


10/14

Capacitance signal indicate high interface trap

Topography SCM differential capacitance image

A dual section recorded along the line AB

the AFM topography and SCM

(dC/dV) images concurrentlyacquired with a Vtip of 2 V.

Higher dC/dV signal levelhigher density of interfacetraps lower freecarrier concentration.

Liu at al Threading dislocations in domain-

matching epitaxial films of ZnO J. Appl. Cryst.

(2007). 40, 924

930


11/14

Scanning Impendence Microscopy (SIM)

SIM is used to measure the frequency dependence of potential distribution along the

sample in NCM.

Principle of SIM

The lateral voltage is applied across the sample , induces

oscillations in the surface potential .The surface

potential result in an oscillating tip-sample force.

SIM amplitude image indicates the local voltage on the sample.

The phase is related to the voltage phase variations across the surface.


12/14

Conductive Atomic Force microscopy(CAFM)

CAFM is based on the detection of current passing through the cantilever tip and a

sample.

Principle of CAFM

Tunneling current sensitivities are 1 pA/V and 10 pA/V

CAFM current sensitivities are 1 nA/V and 100 nA/V


13/14

Scanning Spreading Resistance Microscopy (SSRM)

SSRM is used for resistance measurement in contact mode.

Principle of SSRM

Load force typically 15-20 N.

The main application of the SSRM technique can be found in the mapping of carrier

concentration inside a semiconductor device.


14/14

Summary

(2011!04!08) electrical measure techniques in atomic force microscopy

Documents