Miroslav Valtr

Atomic force microscopy analysis of nanoparticles in non-ideal conditions

Nanoparticles are often measured using atomic force microscopy or other scanning probe microscopy methods. For isolated nanoparticles on flat substrates, this is a relatively easy task. However, in real situations, we often need to analyze nanoparticles on rough substrates or nanoparticles that are not isolated. In this article, we present a simple model for realistic simulations of nanoparticle deposition and we employ this model for modeling nanoparticles on rough substrates. Different modeling conditions (coverage, relaxation after deposition) and convolution with different tip shapes are used to obtain a wide spectrum of virtual AFM nanoparticle images similar to those known from practice. Statistical parameters of nanoparticles are then analyzed using different data processing algorithms in order to show their systematic errors and to estimate uncertainties for atomic force microscopy analysis of nanoparticles under non-ideal conditions. It is shown that the elimination of user influence on the data processing algorithm is a key step for obtaining accurate results while analyzing nanoparticles measured in non-ideal conditions.

Study of plasma polymerization from acetylene in pulsed r.f. discharges

Plasma polymer films were deposited from an argon and acetylene mixture by plasma enhanced chemical vapor deposition in pulsed radio frequency discharges. The discharge on-time varied from 50 to 150 ms and the off-time was kept constant at 1900 ms. The kinetics of the film growth was studied by in-situ reflectance measurements. The films were further investigated ex-situ by spectroscopic ellipsometry, %in the ultraviolet and the visible (UV/VIS) atomic force microscopy, scanning and transmission electron microscopes. Damages in the films caused by residual stress were investigated with an optical microscope. The hydrogen content and film densities were measured by nuclear resonance reaction analyses. Some film properties namely the residual stress, deposition rate, optical properties and surface roughness were significantly influenced by the duration of the discharge pulses. We found refractive indices of the films in the visible in the range 1.60-1.73. The hydrogen-to-carbon ratio in the films and the film density were about 3:2 and 0.6 g/cm3, respectively.

Large area high-speed metrology SPM system

We present a large area high-speed measuring system capable of rapidly generating nanometre resolution scanning probe microscopy data over mm(2) regions. The system combines a slow moving but accurate large area XYZ scanner with a very fast but less accurate small area XY scanner. This arrangement enables very large areas to be scanned by stitching together the small, rapidly acquired, images from the fast XY scanner while simultaneously moving the slow XYZ scanner across the region of interest. In order to successfully merge the image sequences together two software approaches for calibrating the data from the fast scanner are described. The first utilizes the low uncertainty interferometric sensors of the XYZ scanner while the second implements a genetic algorithm with multiple parameter fitting during the data merging step of the image stitching process. The basic uncertainty components related to these high-speed measurements are also discussed. Both techniques are shown to successfully enable high-resolution, large area images to be generated at least an order of magnitude faster than with a conventional atomic force microscope.

Influence of substrate material on plasma in deposition/sputtering reactor: experiment and computer simulation

The aim of this work was to investigate the influence of the substrate material on the plasma enhanced chemical vapour deposition and the plasma sputtering of thin films in low pressure (3–20 Pa) parallel-plate radio frequency (rf) discharges. It was observed that the deposition or sputtering rates differed above different materials, e.g. above a substrate and substrate electrode. Moreover, the substrates placed on the bottom rf electrode seemed to be mirrored in the thickness of a thin film deposited or sputtered on the upper grounded electrode. The influence of the substrate material on the plasma parameters was studied via particle in cell/Monte Carlo computer simulation. According to our finding the mirroring of the substrate was caused by different secondary electron emission yields of the substrate material and material of the substrate electrode. This difference in the secondary electron yield affected plasma density above the substrate leading to higher or lower deposition or sputtering rates on the grounded electrode. Therefore, the role of secondary electrons in the discharge was studied. Spatial distributions of impact positions on the grounded electrode for electrons and ions emitted from the rf electrode and created in the ionization avalanche of the secondary electrons were calculated in order to simulate the mirroring of the substrates.

Traceable measurements of small forces and local mechanical properties

Measurement of local mechanical properties is an important topic in the fields of nanoscale device fabrication, thin film deposition and composite material development. Nanoindentation instruments are commonly used to study hardness and related mechanical properties at the nanoscale. However, traceability and uncertainty aspects of the measurement process often remain left aside. In this contribution, the use of a commercial nanoindentation instrument for metrology purposes will be discussed. Full instrument traceability, provided using atomic force microscope cantilevers and a mass comparator (normal force), interferometer (depth) and atomic force microscope (area function) is described. The uncertainty of the loading/unloading curve measurements will be analyzed and the resulting uncertainties for quantities, that are computed from loading curves such as hardness or elastic modulus, are studied. For this calculation a combination of uncertainty propagation law and Monte Carlo uncertainty evaluations are used.

Short-Range Six-Axis Interferometer Controlled Positioning for Scanning Probe Microscopy

We present a design of a nanometrology measuring setup which is a part of the national standard instrumentation for nanometrology operated by the Czech Metrology Institute (CMI) in Brno, Czech Republic. The system employs a full six-axis interferometric position measurement of the sample holder consisting of six independent interferometers. Here we report on description of alignment issues and accurate adjustment of orthogonality of the measuring axes. Consequently, suppression of cosine errors and reduction of sensitivity to Abbe offset is achieved through full control in all six degrees of freedom. Due to the geometric configuration including a wide basis of the two units measuring in y-direction and the three measuring in z-direction the angle resolution of the whole setup is minimize to tens of nanoradians. Moreover, the servo-control of all six degrees of freedom allows to keep guidance errors below 100 nrad. This small range system is based on a commercial nanopositioning stage driven by piezoelectric transducers with the range (200 × 200 × 10) μm. Thermally compensated miniature interferometric units with fiber-optic light delivery and integrated homodyne detection system were developed especially for this system and serve as sensors for othogonality alignment.

Thermal conductivity analysis of delaminated thin films by scanning thermal microscopy

Scanning thermal microscopy (SThM) is a scanning probe microscopy technique for mapping temperature and thermal properties of solid surfaces with very high resolution. It has been used for the determination of various thermophysical properties in the past and it delivers better lateral resolution than any other thermal technique. Absolute determination of thermal conductivity using SThM, however, is still problematic due to the complex nature of the heat exchange between the probe and sample. In this paper we present a method for thin film thermal conductivity determination based on the use of thin film defects—delaminations. We show that, using a combination of bonded and debonded film measurements together with numerical analysis, we can use a single SThM measurement to determine the isotropic thermal conductivity of the film, without a priori knowledge of probe–sample junction properties.

Voice coil-based scanning probe microscopy.

We present a novel system for large-area scanning probe microscopy (SPM) measurements based on minimum counter-force linear guidance mechanisms, voice coils, interferometers and fuzzy logic-based feedback loop electronics. It is shown that voice coil-based actuation combined with interferometry can be a good alternative to piezoceramic positioning systems, providing fast and still sufficient, precise displacements which range from nanometers to millimeters. Using fuzzy logic feedback control, it can be actuated even with only a few low-cost components, like a cheap single-chip microcontroller. As the final positioning resolution can be made independent on the electronics output resolution, the system can reach high positioning resolution even on very large scan sizes. This is a key prerequisite for developing novel generations of SPMs that would combine, in a very large range, with high-speed imaging.

Non-equidistant scanning approach for millimetre-sized SPM measurements

Long-range scanning probe microscope (SPM) measurements are usually extremely time consuming as many data need to be collected, and the microscope probe speed is limited. In this article, we present an adaptive measurement method for a large-area SPM. In contrast to the typically used line by line scanning with constant pixel spacing, we use an algorithm based on several levels of local refinement in order to minimize the amount of information that would be useless in the data processing phase. The data obtained from the measurement are in general formed by xyz data sets that are triangulated back with a desired local resolution. This enables storing more relevant information from a single measurement as the data are interpolated and regularized in the data processing phase instead of during the measurement. In this article, we also discuss the influence of thermal drifts on the measured data and compare the presented algorithm to the standard matrix-based measuring approach.

Tip–sample relaxation as a source of uncertainty in nanoscale scanning probe microscopy measurements

Nanoscale dimensional measurements are very often focused on small objects formed by only a few atomic layers in one or more dimensions. The classical convolution approach to tip–sample artifacts cannot be valid for these specimens due to the quantum-mechanical nature of small objects. As interatomic forces act on the sample and the tip of the microscope, the atoms of both relax in order to reach equilibrium positions. This leads to changes in those quantities that are finally interpreted as the atomic force microscope (AFM) tip position and influences the resultant dimensional measurements. In this paper, sources of uncertainty connected with tip–surface relaxation at the atomic level are discussed. Results of both density functional theory modeling and of classical molecular dynamics of AFM scans on typical systems used in nanometrology, e.g., fullerenes and carbon nanotubes, on highly oriented pyrolytic graphite substrates are presented. We study also the effects of tip–surface relaxation on critical measurements of the dimensions of these objects.