Conductive AFM

Wold DJ, Frisbie CD (2000) Formation of metal-molecule-metal tunnel junctions microcontacts to alkanethiol monolayers with a conducting AFM tip. J Am Chem Soc 122 (12) 2970-2971... 

Frisbie et al. [120] and Findsay et al. [28] introduced CP-AFM for conductance measurements in (single) molecular junctions. CP-AFM allows precise control of the AFM probe, employing the feedback of the force signal and the simultaneous acquisition of the molecular current response. In order to achieve a better electric contact between the conducting AFM tip and the target molecules of interest, Cui et al. proposed contacting bifunctionalized target molecules embedded in inert... 

A complementary microscopy to SECM is CAFM, in which the AFM tip is made of a metal such that current can be measured as the tip is scanned, in contact, across the surface. s Conducting-AFM offers the advantage of directly measuring local electrical... 

There are two main approaches or configurations for the AFM-assisted detection of the local piezoelectric activity (pfm) in ferroelectric thin films for ferroelectric memory applications (FeRAM). The most used one was introduced in the early 90s and uses a conductive afm-tip as both top electrode and sensor for the induced vibration [2-4]. The second and more recent one [15,16], uses a normal metallic thin top electrode to apply the electric field and the vibration signal is detected by the AFM-tip above the top electrode. Both approaches present numerous advantages and disadvantages, as widely discussed in the literature, and are quite complementary. 

AFM-assisted detection of the local piezoelectric activity with a conductive AFM-tip is obviously the ideal tool to directly verify the existence and the expected properties of such a... 

Figure 19.22 Proposed polarization configuration in a fatigued PZT thin film. The upper dark triangles represent the polarization frozen nanodomains. The averaged polarization has the bottom-to-top direction. The AC-electric field applied by a conductive AFM-tip selectively excites the upper layer of the film (left side).

Figure 19.24 Phase (left side) and amplitude (right side) maps (4x4 //,m) of the piezoelectric response of a fatigued area after removal of the top electrode (Ga drop) for increasing AC voltage on the conductive AFM-tip.

Fig. 4. Nanopatterning of alkynes using a conducting AFM tip for cathodic electrografting on H/Si(lll). The process is shown schematically at the left while representative line scans after electrografting with different alkynes are shown on the right. The observed heights in the AFM scans correlate well with the expected heights. Adapted from [39].

A second developing techniqne also nses AFM tips to nanopattem surfaces. J. Sagiv uses conductive AFM tips to oxidize CH3 end gronps of (SAMs) to COOH functions by emitting electrical pnlses. Herewith, chemical information is written into an inert methyl-snrface . Again, only the software moving the tip over the snrface decides where to inscribe the information. However, similar like in the former case, there are further chemical steps necessary to finally end np with 2D or ID patterns of metal particles. The chemical modifications nsed in this case are explained in Scheme 1. 

In the case of the oxidation of a metallic substrate the anodization depends strongly on the humidity of the adsorbed water molecules which is the working electrolyte. The anodization process is carried out in conventional configuration with the tip as the counter electrode and the metal substrate as the working electrode. The anodization takes place when the metallic substrate is biased positively with respect to the tip, which as mentioned before can be either the STM tip or the tip of a conducting AFM. 

An interesting extension of DPN is to use the meniscus formed between the tip and the substrate as an electrochemical cell, by applying a bias between the two. This is similar to the anodic oxidation using a conducting AFM tip as discussed before. An electrochemical DPN technique has been reported that can be used to... 

Figure 7-20. An illustration of the conducting AFM developed by Cui et al. for measuring single molecule conductance.

The conducting AFM method has revealed interesting details of the single molecule conductance of carotene molecules. The electronic properties of carotenoids are of interest since they play a role in their biological function, especially their optical properties which are a manifestation of their delocalised electron structure. The structure of the dithiolated carotenoid used in a study by Ramachandran et al. is shown in Fig. 7-21. A synthetic molecular wire 2,5-di(phenylethynyl-4 -thioacetyl)benzene, also appraised by conducting AFM is also shown in Fig. 7-21. The measured low bias resistance of the carotenoid molecule was found to be (4.9 0.2) GQ. After... 

Figure 7-21. Molecular structures the dithiolated carotenoid and a synthetic molecular wire 2,5-di(phenylethynyl-4 -thioacetyl)benzene whose single molecule conductance has been determined by conducting AFM. ...

This section describes a variant of SPM where condncing probes are used to measure the current-voltage (J-V) relationship and resistance (conductance) of conducting materials. Conducting probe AFM (CP-AFM) is also called conducting AFM, current-sensing AFM [11,126], or scanning resistance microscopy [127,128]. 

Chen, K.W. et al.. Characterization of nano-sized Si islands in buried oxide layer of SIMOX by conducting AFM, Chem Phys Lett 376, 748-752, 2003. 

While STM gave researchers the abifity to probe atomic scale events at metal and semiconducting surfaces, many of the materials of interest to surface scientists fall outside these classes of materials, such as the surfaces of oxides and biological materials that lack conductivity. AFM is a tool that provides similar surface mapping of materials as STM, but can be used for systems that are nonconductive as well. 

The ordered P AA back-side and structured Al surface were used to produce self-organized metal nanoparticles. We used Au or amorphous carbon as add-layer for deposition of Ti or Fe nanostmctures. Both these metals have a weak wetting of the add-layer. The deposition was performed by a laser induced plasma deposition technique. In this process the energy of ions was about 20 eV. The highly ordered curved substrate surface defined position of the deposited clusters providing formation of highly ordered arrays of metal nanoclusters. A perspective application of such structures for terabit memory was demonstrated. For example, Ti nanoclusters covered by native oxide demonstrated irreversible transformation of I-V characteristics from barrier-like to the ohmic behavior after the action of current supplied by a tip of conductive AFM. 

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