A unique self-actuating and self-sensing probe, which is based on a quartz tuning fork and a microfabricated cantilever, is presented for dynamic scanning probe microscopy. The probing tip can be electrically connected to an external source or measure unit. The sensitivity of the drain-source current of an ion sensitive field effect transistor (ISFET) was investigated as a function of the probe position in order to assess the potential of the probe in device testing, where its non-optical read-out mechanism may proof to be a particular advantage.

This article proposes a new application of tunneling current measurements Atomic Force Microscopy (AFM) for evaluation of silicon nitride stop-layer erosion in Shallow Trench Isolation (STI) Chemical Mechanical Planarization (CMP). Simultaneous topographical and electrical AFM measurements allow a clear identification of ‘open’ silicon surfaces on nanometer scale by enhanced tunneling currents in those areas. The measurement technique is non-destructive and can be successfully implemented for process control.

We describe a dynamic atomic force microscopy (AFM) method to map the nanoscale elastic properties of surfaces, thin films, and nanostructures. Our approach is based on atomic force acoustic microscopy (AFAM) techniques previously used for quantitative measurements of elastic properties at a fixed sample position. AFAM measurements determine the resonant frequencies of an AFM cantilever in contact mode to calculate the tip-sample contact stiffness k*. Local values for elastic properties such as the indentation modulus M can be determined from k* with the appropriate contact-mechanics models. To enable imaging at practical rates, we have developed a frequency-tracking circuit based on digital signal processor architecture to rapidly locate the contact-resonance frequencies at each image position. We present contact-resonance frequency images obtained using both flexural and torsional cantilever images as well as the corresponding vertical contact-stiffness (k*) image calculated from flexural frequency images. Methods to obtain elastic-modulus images of M from vertical contact-stiffness images are also discussed.

Scanning Probe Recognition Microscopy is a new scanning probe capability under development within our group to reliably return to and directly interact with a specific nanoscale feature of interest, without the use of a zoom box with its thermal drift and local origin difficulties. It is a recognition-driven and learning approach, made possible through combining SPM piezoelectric implementation with on-line image processing and dynamically adaptive learning algorithms. Segmentation plus a recognized pattern is implemented within a scan plan and used to guide the tip in a recognition-driven return to a specific site.

The specific application focus of our group is on the development of Scanning Probe Recognition Microscopy for nanobiological investigations. In the present work, Scanning Probe Recognition Microscopy is used in a direct investigation of the surface and elastic properties along individual tubules within a tissue scaffolding matrix. Elastic properties are indicated as important influences on actin polymerization and consequent cell pseudopodia extension and contraction.

The coalescence process of poly (ethylene-co-vinyl acetate) (EVA) and poly (ethylene-co-octene) (EO) dispersion particles was monitored in situ using tapping-mode atomic force microscopy (TMAFM) equipped with a miniature hot stage. This work describes the effect of particle size on the film formation temperature based on direct experimental observation, clarifying further the debate about particle size effect on minimum film formation temperature (MFFT). The results suggest that semicrystalline polyolefin particles have similar deformation temperature dependence. Smaller particles tend to deform faster than larger particles, which is attributed to their smaller mass. Furthermore, morphology changes and mechanical property development associated with the film formation process are also discussed. The TMAFM technique is shown to be very useful in gaining insight into the film formation mechanism, which will provide guidance in future practical applications with polyolefin dispersions.

We have developed a novel scanning near-field microwave probe capable of precise quantitative measurements of dielectric constant of thin dielectric films. The technique is noncontact and has a few-micron sampling spot-size. For dielectric films with k<7 and thickness down to 200 nm the probe provides precision and accuracy better than 1% and 5%, respectively. The probe is based on a balanced parallel-plate microwave transmission line operating at 4 GHz. Unlike the apertureless STM- or AFM-based schemes that have been previously employed, our “apertured” approach allows for truly quantitative measurements on a few-micron length scale with result that is insensitive to the material property outside this probing volume.

We will present quantitative measurements on a variety of so-called low-k dielectric films, which are of great interest to the semiconductor industry as replacements for SiO2 in interconnect wiring. When the probe is placed in close proximity to the film under test its fringe capacitance is governed by the sample permittivity, the tip geometry, and the tip-sample separation. We measure this capacitance with a resolution down to 30 zF using a microwave resonator. Extraction of the film dielectric constant is based on an original approach providing for removal of the substrate contribution. Bulk Si and a set of variable thickness thermal oxide films are employed to calibrate the probe. There is no need to know the absolute value of the tip-sample separation for either measurement or calibration procedures; this separation must only be kept nominally the same for both measurements, which is achieved by a virtually material independent shear-force distance control.

We have investigated the local electronic properties and the spatially resolved magnetoresistance of a nanostructured film of a colossal magnetoresistive (CMR) material by local conductance mapping (LCMAP) using a variable temperature Scanning Tunneling Microscope (STM) operating in a magnetic field. The nanostructured thin films (thickness ≈500nm) of the CMR material La0.67Sr0.33MnO3 (LSMO) on quartz substrates were prepared using chemical solution deposition (CSD) process. The CSD grown films were imaged by both STM and atomic force microscopy (AFM). Due to the presence of a large number of grain boundaries (GB's), these films show low field magnetoresistance (LFMR) which increases at lower temperatures.

The measurement of spatially resolved electronic properties reveal the extent of variation of the density of states (DOS) at and close to the Fermi level (EF) across the grain boundaries and its role in the electrical resistance of the GB. Measurement of the local conductance maps (LCMAP) as a function of magnetic field as well as temperature reveals that the LFMR occurs at the GB. While it was known that LFMR in CMR films originates from the GB, this is the first investigation that maps the local electronic properties at a GB in a magnetic field and traces the origin of LFMR at the GB.

This paper describes a newly developed ultra-high vacuum type scanning nonlinear dielectric microscope (UHV-SNDM) and the results from a ferroelectric LiTaO3 single crystal measured by the UHV-SNDM. In a cleaved (012) surface of LiTaO3 crystal, we can clearly observe a striped pattern with a period of about 0.3 nm and a granular pattern approximately corresponding to the sub-lattice period. From this image, we confirmed that the SNDM can be applied to lattice-level measurement in ferroelectric insulator materials.

Tip wear and its corresponding change in geometry is a major impediment for quantifying atomic force acoustic microscopy (AFAM). To better understand the process of tip wear and its influence on AFAM measurements of material elastic properties, we have performed a series of experiments and compared tip geometries calculated from experimental data with direct tip visualization in the scanning electron microscope (SEM). Using a sample with known elastic properties, the tip-sample contact stiffnesses for several different cantilevers were determined. Hertz and Derjaguin-Müller-Toporov (DMT) contact-mechanics models were applied to calculate values of the tip radius R from the experimental data. At the same time, values for R before and after each sequence of AFAM measurements were obtained from SEM images. Both methods showed that the tip radius increased with use. However, values of R calculated with the theoretical models varied indeterminately from those obtained from the SEM images. In addition, in some cases analysis of the AFAM measurements suggested a hemispherical tip, while the corresponding SEM images showed that the end of the tip was flat. We also observed other changes in tip shape, such as an increase in the tip width. By combining theoretical models for contact mechanics with visual information on the tip geometry we hope to better understand contact characteristic in AFM-based systems.

Contribution of NIST, an agency of the US government; not subject to copyright.

A technique for measuring the absolute value of the ferroelectric polarization angle using scanning nonlinear dielectric microscopy (SNDM) is proposed and demonstrated. Using the technique, periodically poled lithium niobate (PPLN) with three-dimensional domain structure is observed. The measured polarization angles agreed well with the actual polarization orientations, and allowed precise visualization of the microdomain structure in PPLN. Through this experiment, we confirmed that SNDM is a useful tool for the absolute evaluation of the three-dimensional polarization direction.

We have investigated the effect of biaxial strain on local electrical/electronic properties in thin films of La0.7Ca0.3MnO3 with varying degrees of biaxial strain in them. The local electrical properties were investigated as a function of temperature by scanning tunneling spectroscopy (STS) and scanning tunneling potentiometry (STP), along with the bulk probe like conductance fluctuations.

The results indicate a positive correlation between the lattice mismatch biaxial strain and the local electrical/electronic inhomogenities observed in the strained sample. This is plausible since the crystal structure of the manganites interfere rather strongly with the magnetic/electronic degrees of freedom. Thus even a small imbalance (biaxial strain) can induce significant changes in the electrical properties of the system.

Dynamic Atomic Force Microscopy (AFM) is typically performed at amplitudes that are quite large compared to the measured interaction range. This complicates the data interpretation as measurements become highly non-linear. A new dynamic AFM technique in which ultra-small amplitudes are used (as low as 0.15 Angstrom) is able to linearize measurements of nanomechanical phenomena in ultra-high vacuum (UHV) and in liquids. Using this new technique we have measured single atom bonding, atomic-scale dissipation and molecular ordering in liquid layers, including water.

We develop an algorithm to measure elastic properties of microcapsules with Atomic Force Microscopy (AFM). The AFM is used as an indenter and presses down on a spherical microcapsule. We study the system from an atomic point of view (considering interactions between the atoms in the system via Equivalent Crystal Theory) and calculate the force produced by the system to balance the external AFM force. We plot this force as a function of the indentation depth, and from that curve we extract the interatomic parameters of ECT that are related with elastic constants. Our calculations model measurements of force-strain curves including non-linear effects. This is relevant as classical elasticity theory breaks down in the AFM indentation regime, when atomic interactions must be considered explicitly.

Local electromechanical characterization is becoming prerequisite for the development of ferroelectric-based piezoelectric devices including multilayer actuators, micromotors, piezoelectric filters and, especially, microelectromechanical systems (MEMS), which combine piezoelectric elements and control electronics on the same chip. In this work, we present the results of local electromechanical characterization of several important ferroelectric materials including Pb(Zr, Ti)O3 (PZT) and (Pb, La)(Zr, Ti)O3 (PLZT) in both thin film and ceramic form. Local piezoelectric hysteresis measurements are performed by the piezoelectric force microscopy (PFM) that detects small electric field-induced deformation on the nanoscale e. g., within the single grain of a polycrystalline material. A number of novel phenomena is observed with increasing dc bias voltage including the jump of ferroelectric domain wall to the grain boundary, the “fingerlike” instability of domain wall, and the local phase transition into ferroelectric phase.

Scanning Kelvin probe microscopy (SKPM) is widely used to measure surface work functions and electrostatic potentials on nanoscale circuits, devices and materials. However, the accuracy of scanning Kelvin probe microscopy is reduced by a cantilever effect, which is due to a large capacitance gradient associated with the cantilever. We introduce an aperture structure to quantitatively moderate the strength of the cantilever effect. In this approach, the cantilever effect is eliminated and the true surface potential can be extracted by solving a set of linear equations. Experimental results show that this approach yields very accurate surface potentials when there is only a single potential source within the aperture. In the case of multiple potential sources, this method significantly improves accuracy as well. A mobile aperture structure mounted on a micromanipulator can make this approach more versatile.

Experimental techniques for SPM imaging and spectroscopy of low-dimensional systems have significantly progressed in recent years. At the same time, new simulation methods and computational techniques have allowed the development of a theoretical basis to the interpretation and understanding of the measurements. In this contribution, we concisely review two state-of-the-art modeling methods for scanning probe microscopy, as applied to carbon nanostructures.

Transparent Pb1-yLay(Zr1-xTix)1-y/4O3 (PLZT, y=0.0975, x=0.35) ceramics prepared via hot pressing techniques were studied via piezoelectric force microscopy (PFM). Clear piezoelectric contrast is observed in a cubic relaxor phase indicating spatial distribution of polarization with an average cluster size of about 50 nm. The irregular polarization pattern is associated with the formation of a glassy state, where random electric and stress fields are responsible for the disruption of the long-range ferroelectric order. Local poling of the ceramics resulted in the formation of a stable micron-size domain that could be continuously switched under varying dc bias (local hysteresis loop). The applied voltage of 10–12 Volts was enough to switch relaxor into the ferroelectric state. Fractal and correlation analysis of the observed images is presented. The fractal dimension close to 1.55 is consistent with the random distribution of charge defects in this material. The nature of the observed phenomena is discussed based on the current understanding of relaxor state in PLZT and possible effect of PFM instrumentation.

The imaging of nanostructural and topological variations on mechanically or chemically aged SiC materials has been performed using non-destructive Raman and Rayleigh μ-spectrometries. The case of a Hi-Nicalonf/(SiC/BN/C)m composite, corroded under alkali and oxidizing environment (modelled using molten NaNO3), is discussed. It is shown for the first time that Rayleigh imaging offers a competitive alternative to AFM measurements for un-prepared, very corrugated surface of materials containing carbon as a second phase. A comparison is made to the analysis of μ-indented areas performed on a polished section of the Ø∼140 μm SCS-6™ Textron SiC fibre. The “smart” Raman images allowed determining the strain distribution within the whole indented area.