PinPoint™ Conductive AFM obtains the best of resolution and sensitivity during current measurements

PinPoint™ Conductive AFM was developed for well defined electric contact between the tip and the sample. They XY scanner stops while measuring the electric current with contact time controlled by a user. PinPoint™ Conductive AFM allows higher spatial resolution, without lateral force, with optimized current measurement over different sample surface.

1. The XY scanner stops during acquisition
2. Approach and retract at each pixel point.
3. Record the approach height and maintain the Z distance.

The conventional contact and tapping conductive AFM have cons and pros.
PinPoint iAFM has the best of both spatial resolution and current sensitivity.

Probing the Local Electronic Structure of a Sample’s Surface

Conductive Probe AFM simultaneously images topography and conductivity of the sample surface. The local conductivity of a sample is acquired by placing a conducting cantilever on the sample surface and applying a bias between the cantilever and the sample. Conductive Probe AFM detects the resulting current flow, which can be as low as a few pA. The typically low level of current measurement requires a detection scheme with a current noise level of sub pA. Park Systems offers three current sensing options, detecting current signals from sub pA to mA.

• Ulta-Low Noise Conductive AFM(ULCA): < 0.1 pA noise level
• Variable Enhanced Conductive AFM(VECA): < 0.3 pA noise level
• Internal Conductive AFM:< 1 pA noise level

The contrast on the Conductive Probe AFM image indicates differences in the electrical property of the raised dots.
The topography of a DRAM surface and Conductive Probe AFM image with various sample bias.

Park AFMs feature the ability to conduct current voltage spectroscopy on specified point of the sample surface. The low noise of Park Systems’ conductive AFM options allows for the detection of extremely small changes in a sample’s electronic characteristics.

High Resolution and High Sensitivity Imaging of Electrostatic Force

Almost every surface property measured by AFM is acquired by the process depicted. EFM measurements follow the same procedure. For EFM, the sample surface properties would be electrical properties and the interaction force will be the electrostatic force between the biased tip and sample. However, in addition to the electrostatic force, the van der Waals forces between the tip and the sample surface are always present. The magnitude of these van der Waals forces change according to the tip-sample distance, and are therefore used to measure the surface topography.

(a) Topography (b) EFM Amplitude at -1V sample bias

High Resolution and High Sensitivity Imaging of Surface Potential

Principle of KPFM is similar to Enhanced EFM with DC bias feedback. DC bias is controlled by feedback loop to zero the ω term. The DC bias that zeros the force is a measure of the surface potential. The difference is in the way the signal obtained from the Lock-in Amplifier is processed. As presented in previous section, the ω signal from Lock-in Amplifier can be expressed as following equation. scanning-kelvin-probe-microscopy-KPFM-f3 The ω signal can be used on its own to measure the surface potential. The amplitude of the ω signal is zero when VDC = Vs, or when the DC offset bias matches the surface potential of the sample. A feedback loop can be added to the system and vary the DC offset bias such that the output of the Lock-in Amplifier that measures the ω signal is zero. This value of the DC offset bias that zeroes the ω signal is then a measure of the surface potential. An image created from this variation in the DC offset bias is given as an image representing the absolute value of the surface potential.

Surface Potential distribution on graphene

High Resolution and High Sensitivity Imaging of Electrostatic Force

DC-EFM is capable of extremely high definition EFM results. Patented by Park Systems, DC-EFM actively applies an AC voltage bias to the cantilever and detects the amplitude and the phase change of the cantilever modulation with respect to the applied bias. DC-EFM provides the ability to monitor the second harmonic of the modulation which can be compared to the capacitance of a sample and enhances the electric force signal from the background intermolecular force.

Our patented PFM mode accurately measures electric domain structures such as polarity in ferroelectric or piezoelectric samples. This mode includes independent control of an applied AC and DC bias, and local amplitude/phase vs. DC bias spectroscopy.

QuickStep™ to make faster SCM data acquisition

In order to improve the signal-to-noise ratio, conventional SCM adopts very slow scan speeds as a means of giving the detector enough time to collect the data. QuickStep™ SCM differs from the conventional methodology of slow continuous movement. Here, XY scanner stops at each pixel point to record the data and then makes a fast and rapid hop to the next measurement points. This effectively speeds up the scan rate while maintaining the same signal sensitivity of the measurements by conventional SCM at slow scan speeds.

Application note: Accurate dopant profiles of semiconductor device structures with QuickStep Scanning Capacitance Microscopy

QuickStep Scan (Scan rate 1.5Hz)

Conventional Scan (Scan rate 1Hz)

High Resolution and High Sensitivity Imaging of Charge Distribution

Our SCM mode provides doping concentration information over the sample surface by measuring the capacitance change between tip and sample. the module enables a variable resonator frequency, which allows a wide RF bandwidth capable of monitoring a large range of doping concentrations by selecting the most sensitive frequency of the resonator for a specific doping range.

The n-doped silicon sample has areas of varying dopant concentration, imaged by Park SCM.
The doping concentration of less than an order of magnitude is clearly distinguishable.

Probing the Local Electronic Structure of a Sample’s Surface

Our SSRM mode precisely measures the local resistance over a sample surface by using a conductive AFM tip to scan a small region while applying DC bias.

Probing the Local Electronic Structure of a Sample’s Surface

STM measures the tunneling current between tip and sample, giving highly accurate sub-nanometer scale images you can use to gain insights into sample properties.

STM image of YBCO super conductor

Our STS mode provides current-voltage (I/V) spectroscopy data at user-defined points which can then be used to analyze the local electronic states of the sample.

Enabling Innovation in Photosensitive Materials Research

Our Tr-PCM mode measures photoelectric response to a time-resolved illumination without interference from unwanted light sources, including the feedback laser. This mode features a laser illumination module and acquisition and analysis software.

A typical photocurrent response to a time-resolved illumination.
The current between the sample and a voltage-biased cantilever is measured before, during, and after the illumination.

 

Point-by-point mapping of photocurrent spectroscopy.
Photocurrent response in time domain is acquired in each grid point defined on a sample.