Conductive AFM Tip Research Articles

Scanning Probes of Nonlinear Properties in Complex Materials

Nonlinear materials have found wide applications in electronic devices. Of special importance and interest are those with varistor-type grain boundaries and those displaying large piezoelectric and electrostrictive responses to external fields. To access the local properties of these materials, we have designed two new contact mode scanning probe techniques. The first technique referred to as nanoimpedance microscopy/spectroscopy, which incorporates impedance spectroscopy with a conducting AFM tip as an electrode, has been demonstrated on measuring local grain boundary properties of a ZnO varistor, as well as the contact quality between AFM tip and a ferroelectric sample. The other technique referred to as second harmonic piezoresponse force microscopy developed to measure the electrosctriction has been demonstrated on ferroelectric polymer thin film. A theoretical model has been presented to describe the contrast formation of the second harmonic as well as the first harmonic (piezoresponse) images and to explain the observed hysteretic field dependence of the second harmonic amplitude signal.

AFM-induced amine deprotection: triggering localized bond cleavage by application of tip/substrate voltage bias for the surface self-assembly of nanosized dendritic objects.

An alpha,alpha-dimethyl-3,5-dimethoxybenzyloxycarbonyl (DDZ)-protected amine monolayer can be selectively deprotected by the application of a voltage bias from a conducting AFM tip to afford localized nanoscale patterns that can be visualized by self-assembly of dendritic molecular objects with terminal carboxylic acid groups and different aspect ratios.

Investigation of Transversal Conductance in Semiconductor CdTe Nanowires with and without a Coaxial Silica Shell

Semiconductor CdTe nanowires were coated with a coaxial layer of silica in aqueous solutions by the hydrolysis of tetraethyl orthosilicate. The structure and morphology of the nanowires before and after coating were studied by UV−vis spectroscopy, atomic force microscopy, and transmission electron microscopy. Interestingly, silica deposition on the nanowire ends was retarded. For sufficiently thin layers, this effect makes possible the preparation of coaxial insulated nanowires with electrical access to the semiconductor core. Insulating properties of the silica layer were tested by applying voltage to a conductive AFM tip placed directly on the sidewall surface of the nanowires. These experiments demonstrated that the silica layers had strong insulating properties for coatings as thin as 10 nm. Similar measurements done with naked nanowires showed that transversal conductance took place through the middle band-gap states.

Electrical Force Microscopy measurements on nanoconductors deposited by electropulsed SPM

The reduced dimensions of novel integrated devices and systems stresses the need for new nanopatterning techniques. We showed that metallic pixels of about 30 nm can be deposited by electropulsed SPM. Deposition is obtained by applying −12 to −17 V pulses to a tip coated with a CoCr metallic film while scanning in tapping mode AFM. By assembling arrays of these pixels it is possible to obtain custom-shaped conductors. We deposited rectangular conductors with dimensions from 50×100 nm up to 2000×400 nm and thickness between 2 and 3 nm. A typical conductor line of 2000×400 nm deposited at 40 Hz pulse frequency, 800 nm/s tip velocity and at a line density of 0.64 nm −1 shows a thickness of approximately 3 nm. For electrical measurements this line is deposited perpendicularly and welded from the edge of a conventional Al pad used for microelectronics. The opposite end of the nanoconductor line is located by AFM and the electrical conductivity is then asserted using the conductive AFM tip in Electrical Force Microscopy (EFM) mode.

Actuators of individual carbon nanotubes

Abstract In this paper, actuation properties of carbon nanotubes are discussed. Samples of freestanding nanotubes on nanostructured metallic blocks have been prepared. Using a conducting AFM tip, electrons can be injected into the nanotubes. As a consequence, the nanotube expands in a similar way as buckypaper does in an electrolyte. From experimental data, the relative length change is estimated to be less than 1%. These findings are taken as a demonstration of an electromechanical actuator based on individual single walled carbon nanotubes.

Conductance Microscopy for Electric Conduction Study of Bio-Inspired Hybrid Nanostructures under Ambient Conditions

ABSTRACTElectrical conductance of single stranded DNA (5′-TTT TTT TTT T/3 Thio MC3-D/-3′) monolayer patterns on Au surface is compared with those of various organic molecular patterns via the conductance microscope (CM) technique that allows one to take nanoscale conductance images utilizing a conducting AFM tip in contact mode AFM. In the experiment, reference molecules and ssDNA are patterned on the same substrate via direct deposition methods such as dip-pen nanolithography and microcontact printing. Then, conductance microscope image is recorded revealing the relative conductivity of ssDNA patterns relative to various reference molecules. 16-mercaptohexadecanoic acid and 2-mercaptobenzimidazole patterns are found conducting better than the ssDNA patterns. This result indicates that the ssDNA with 10T bases is a relatively poor electrical conductor. The capabilities of CM technique are also tested on various nanostructures including the single wall carbon nanotube junction.

Conductance Microscopy for Electric Conduction Study of Bio-Inspired Hybrid Nanostructures under Ambient Conditions

ABSTRACTElectrical conductance of single stranded DNA (5′-TTT TTT TTT T/3 Thio MC3-D/-3′) monolayer patterns on Au surface is compared with those of various organic molecular patterns via the conductance microscope (CM) technique that allows one to take nanoscale conductance images utilizing a conducting AFM tip in contact mode AFM. In the experiment, reference molecules and ssDNA are patterned on the same substrate via direct deposition methods such as dip-pen nanolithography and microcontact printing. Then, conductance microscope image is recorded revealing the relative conductivity of ssDNA patterns relative to various reference molecules. 16-mercaptohexadecanoic acid and 2-mercaptobenzimidazole patterns are found conducting better than the ssDNA patterns. This result indicates that the ssDNA with 10T bases is a relatively poor electrical conductor. The capabilities of CM technique are also tested on various nanostructures including the single wall carbon nanotube junction.

Electrical conduction in layer silicates investigated by combined scanning tunnelling microscopy and atomic force microscopy

AbstractLayer silicates are generally assumed to be insulators, but electron transport may take place in nm thick particles. A combined scanning tunnelling-atomic force (STM-AFM) instrument using a conducting AFM tip has been constructed to investigate this conduction. Some layer silicates, e.g. micas (muscovite and biotite), are in fact semiconductors, conduction taking place through free electrons in the tetrahedral sheet (n-type semiconductivity) and probably through polaron hopping in the octahedral sheet. This implies that these minerals can be investigated by STM. Furthermore, micas show negative differential resistance (decreasing current with increasing voltage) at 2 – 5 V.

An application of polarized domains in ferroelectric thin films using scanning probe microscope

The feasibility of utilizing PZT films as future data storage media was investigated using a modified AFM. Applying voltages between a conductive AFM tip and the PZT films causes the switching of ferroelectric domains. The domains are observed using an EFM imaging technique. The experimental results and calculations revealed that the electrostatic force generated between the polarized area and the tip is a main contributor for the imaging of the polarized domains. The written features on ferroelectric films were less than 100 nm in diameter, implying the possibility of realizing data storage devices with ultra-high area density. The disappearance of the polarized images without any applied voltage was observed, which is a drawback in this application of PZT thin films.

Formation of Metal−Molecule−Metal Tunnel Junctions: Microcontacts to Alkanethiol Monolayers with a Conducting AFM Tip

Formation of Metal−Molecule−Metal Tunnel Junctions: Microcontacts to Alkanethiol Monolayers with a Conducting AFM Tip

Fabrication of PdIr-Coated Conductive Atomic Force Microscope Tip and its Application in Nanofabrication

We report a new conductive AFM tip, which is fabricated by thermal evaporation of 20–30nm PdIr alloy onto commercial silicon nitride cantilevers. With well-controlled evaporation conditions, a tip with nice electrical conductivity, good mechanical and chemical stabilities has been prepared. Thus fabricated AFM tips were used to measure electrical properties of materials with spatial resolution higher than 2nm, and to fabricate nanostructures on Zn-doped p-type GaAs (100) and chromium surfaces via field-induced oxidation.

KELVIN PROBE FORCE MICROSCOPY OF MOLECULAR SURFACES

▪ Abstract The electrostatic force microscope is one of many specialized tip sensors used in near-field microscopy. This type of microscope is realized by applying a voltage on a conducting AFM tip. It can be used to image samples that present a distribution of electrical properties on inhomogeneous materials as well as on nanostructures. This microscopy technique has been used to probe phase separation, chemical recognition, molecular orientation, and photo-induced charge separation in molecular photodiodes in Langmuir-Blodgett films.

Nanofabrication with proximal probes

We report the fabrication of nanometer-scale Si structures using an atomic force microscope. A conducting AFM tip was used to write nanometer-scale oxide patterns by the local anodic oxidation of a passivated Si(100) surface. These oxide patterns were used as masks for selective etching of the silicon to form the completed structures. Side-gated Si field effect transistors with critical features as small as 30 nm have been fabricated by this method.

Atomic Force Microscope Chemically Induced Direct Processing

AbstractInterest in room-temperature operable quantum effect devices has created a need for simple and inexpensive nanofabrication techniques. By applying a bias to a conductive AFM tip, we have succeeded in fabricating narrow (˜30 nm) oxide lines on a variety of metal and III-V semiconductor substrates. The effects of different drawing parameters such as tip bias, translation speed, ambient atmosphere, and substrate doping on line quality were explored.