Kelvin Probe Force Microscopy (KPFM)An advanced package for higher resolution and complementary characterization

KPFM is a dynamic AFM mode that uses the changes in the oscillations of a conductive tip to probe the local electrostatic properties of the sample. These properties originate from the differences in work functions or surface potentials, presence of trapped charges, dipoles, or any change of a structural or chemical nature on the sample. On all Bruker AFM systems, KPFM operates in the conventional Amplitude Modulation (AM) mode in conjunction with Tapping™ mode for topography measurement. In this configuration, the surface topography and phase are acquired in a first scan and then the tip is lifted away from the surface (lift mode) for KPFM measurements. On the Dimension Icon, FastScan and Multimode 8 systems, KPFM can additionally operate in the Frequency Modulation (FM) mode. FM-KPFM mode has a higher spatial resolution and accuracy for surface potential measurements. It can operate either in a single-scan mode along with the topography measurement in Tapping™ mode or using lift mode in conjunction with PeakForce Tapping™.

PeakForce KPFMTM leverages PeakForce Tapping Mode with Quantitative Nano-mechanical Mapping (QNM) to enable a simultaneous characterization of the local

Atomic Force Microscopy

Innovation with Integrity

Figure 1. Portrait of young Albert Einstein (1912) produced by charge

writing on SiO2. Surface potential images in (a) single-scan FM KPFM

mode, (b) Lift mode AM KPFM at 35 nm lift height and (c) lift mode

AM KPFM at 100 nm. Profile sections over the same line on the three

images showing the drastic increase in spatial resolution and accuracy of

FM KPFM imaging. Scan size 20 microns.

AFM Nanoelectrical CharacterisationNew advances in quantification, resolution and multimodal analysis

Peak Force Tunnelling AFM (PF TUNA)The highest resolution current mapping on the most fragile samples

The term TUNA stands for Tunnelling AFM, The principle of TUNA is based on an Ohmic contact formed between the conductive AFM tip and the sample surface. By applying a bias voltage in between tip and sample, the resulting current through the sample is measured with a current amplifier. This is the same principle as conductive AFM (C-AFM). This mode operates in contact mode where the control of lateral shear forces is very difficult to achieve. This renders the use of TUNA or C-AFM very challenging if not impossible for very fragile samples and soft materials. Peak Force TUNA

mechanical (adhesion, Young’s modulus and deformation) and electrical (surface potential) properties of surfaces. The accurate control of the force in Peak Force Tapping to very low levels preserves tip integrity (sharpness and coating). This provides a remarkable repeatability of KPFM measurements as well as a prolonged lifetime of the AFM probe. KPFM finds its place in a large spectrum of applications such as semiconductors industry, 2D materials research such as graphene, molecular electronics, charge transport, organic photovoltaics, corrosion studies.

builds on the Peak Force Tapping (PFT) mode principle to measure the current at each time the tip gets in contact with the surface during the continuous acquisition of force curves in Peak Force Tapping.

As a result of the extremely sensitive force control in PFT mode and dramatic reduction of shear forces, very fragile samples and challenging configurations are addressed with Peak Force TUNA mode. In addition to current conductivity maps, the local mechanical properties are simultaneously obtained in PF QNM. This enables the direct correlation between a sample’s electrical and mechanical properties. Figure 2 (a,b) shows the topography and adhesion maps respectively of a bundle of P3HT organic conductive nanowires. The conductivity maps of the peak current (measured at a peak force value < 100 pN) and the TUNA current (over the entire force cycle) are shown in figure 2 (c,d) respectively. The electrical characterization of such sample would have been impossible in contact mode based methods because of its fragility and delicateness. Peak Force TUNA finds its applications in the fields of soft conductive polymers, CNTs, Semiconductors and semiconducting nanowires, Li-Ion Battery research, Graphene and 2D dimensional materials, molecular electronics and molecular junctions.

Bruker Nano Surfaceswww.bruker.com/AFM - productinfo.europe@bruker-nano.comMore information about PeakForce Tapping available hereApplication Note about PeakForce TUNA available here Application Note for PeakForce KPFM available here For more information contact the author: Khaled Kaja (Khaled.Kaja@bruker.com) - Bruker Nano UK, Coventry Laboratories

Figure 3. Imaging of a SRAM sample in SCM mode. (a) shows the surface topography. (b) dC/dV amplitude map which depends on the variation of the doping concentrations. (c) dC/dV phase map which indicates the nature of the doping. (d) SCM data map (channel b times c). Scan size 25 microns.

Figure 2. Example of a challenging fragile organic nanowires sample imaged with PF TUNA. (a) Topography of a bundle of P3HT organic NWs, (b) Adhesion map, (c) Map of the Peak current measured at the peak force. (d) Current map averaged over the entire force cycle. Scan size 3 microns.

Scanning Capacitance Microscopy (SCM)Mapping carrier concentration at the nanoscale

Scanning Capacitance Microscopy (SCM) is a contact mode based measurement. Here the conductive tip and sample form a capacitor. Its capacitance depends on the carrier density in the sample. SCM enables a qualitative mapping of carrier density in semiconducting devices. The metalized tip and the semiconductor sample (covered with a thin - often native - oxide layer) form a MIS (metal-insulator-semiconductor) capacitor. The shape of the C-V curve of this capacitor is strongly dependent on the dopant concentration of the semiconductor. High dopant levels result in a small variation in the C-V curve, whereas low dopant levels result in a large variation in the C-V curve. In SCM an AC bias (typically 0.5V, 90 kHz) is applied to the sample, and the resulting change in capacitance is monitored using a high-frequency (about 1 GHz) resonant circuit with an extremely high sensitivity (10-22F/√Hz). High dC/dV signal are measured in low level doped areas and a low dC/dV signal in highly doped areas. On the dielectric or metal regions of the sample, the C-V curve is flat and therefore results in a zero dC/dV signal. One of the main applications of SCM is 2D carrier profiling inside semiconductor devices such as MOSFETs, diodes, and laser-structures.

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