Resolving the Subsurface Structure and Elastic Modulus of Layered Films via Contact Resonance Atomic Force Microscopy.

Since its discovery, atomic force microscopy (AFM) has become widely used for surface characterization, evolving from a tool for probing surface topography to a versatile method for characterizing mechanical, electrical, chemical, magnetic, and electro-optical properties of surfaces at the nanoscale. Developments of several AFM-based techniques have enabled even subsurface imaging, which is routinely being carried out at the qualitative level of feature detection for localized subsurface inhomogeneities. We surmise, however, that a quantitative three-dimensional (3D) subsurface characterization can emerge from the AFM mechanical response of flat buried interfaces, and present here a methodology for determining the depth of a film and its mechanical properties.

Open-loop amplitude-modulation Kelvin probe force microscopy operated in single-pass PeakForce tapping mode.

The open-loop (OL) variant of Kelvin probe force microscopy (KPFM) provides access to the voltage response of the electrostatic interaction between a conductive atomic force microscopy (AFM) probe and the investigated sample. The measured response can be analyzed a posteriori, modeled, and interpreted to include various contributions from the probe geometry and imaged features of the sample. In contrast to this, the currently implemented closed-loop (CL) variants of KPFM, either amplitude-modulation (AM) or frequency-modulation (FM), solely report on their final product in terms of the tip-sample contact potential difference.

High-speed digitization of the amplitude and frequency in open-loop sideband frequency-modulation Kelvin probe force microscopy.

A more inclusive and detailed measurement of various physical interactions is enabled by the advance of high-speed data digitization. For surface potential characterization, this was demonstrated recently in terms of open-loop amplitude modulation Kelvin probe force microscopy (OL AM-KPFM). Its counterpart, namely open-loop frequency modulation Kelvin probe force microscopy (OL FM-KPFM), is examined here across different materials and under various bias voltages in the form of OL sideband FM-KPFM.

Doping of MoTe via Surface Charge Transfer in Air.

Doping is a key process by which the concentration and type of majority carriers can be tuned to achieve desired conduction properties. The common way of doping is via bulk impurities, as in the case of silicon. For van der Waals bonded semiconductors, control over bulk impurities is not as well developed, because they may either migrate between the layers or bond with the surfaces or interfaces becoming undesired scattering centers for carriers.

Thelazia callipaeda in mustelids from Romania with the European badger, Meles meles, as a new host for this parasite.

Background: Thelazia callipaeda (Spirurida, Thelaziidae) is a vector-borne zoonotic eye worm with a broad host spectrum. In Europe, it is an emerging threat, having greatly expanded its geographical distribution during the past two decades. In Romania, T.

The effect of edge compliance on the adhesive contact between a spherical indenter and a quarter-space.

In this work, the effect of the edge compliance on the adhesive, frictionless contacts near the edge of a quarter-space is analyzed in terms of stress, deformation, and contact stiffness. The study relies on the numerical implementation of the conjugate gradient method (CGM) to adhesive contacts near the edge of a quarter-space. It extends the previous CGM developed for contact analysis of non-adhesive and adhesive contacts on half-space to the matrix formulation of the quarter-space problem.

Charge-Induced Disorder Controls the Thermal Conductivity of Entropy-Stabilized Oxides.

Manipulating a crystalline material's configurational entropy through the introduction of unique atomic species can produce novel materials with desirable mechanical and electrical properties. From a thermal transport perspective, large differences between elemental properties such as mass and interatomic force can reduce the rate at which phonons carry heat and thus reduce the thermal conductivity. Recent advances in materials synthesis are enabling the fabrication of entropy-stabilized ceramics, opening the door for understanding the implications of extreme disorder on thermal transport.

Nanoparticle separation based on size-dependent aggregation of nanoparticles due to the critical Casimir effect.

Nanoparticles typically have an inherent wide size distribution that may affect the performance and reliability of many nanomaterials. Because the synthesis and purification of nanoparticles with desirable sizes are crucial to the applications of nanoparticles in various fields including medicine, biology, health care, and energy, there is a great need to search for more efficient and generic methods for size-selective nanoparticle purification/separation. Here we propose and conclusively demonstrate the effectiveness of a size-selective particle purification/separation method based on the critical Casimir force.

The effect of edge compliance on the contact between a spherical indenter and a high-aspect-ratio rectangular fin.

In the last two decades, significant progress has been made on developing new nanoscale mechanical property measurement techniques including instrumented indentation and atomic force microscopy based techniques. The changes in the tip-sample contact mechanics during measurements uniquely modify the displacement and force sensed by a measurement sensor and much effort is dedicated to correctly retrieve the sample mechanical properties from the measured signal. It turns out that in many cases, for the sake of simplicity, a simple contact mechanics model is adopted by overlooking the complexity of the actual contact geometry.

PEGylation of zinc nanoparticles amplifies their ability to enhance olfactory responses to odorant.

Olfactory responses are intensely enhanced with the addition of endogenous and engineered primarily-elemental small zinc nanoparticles (NPs). With aging, oxidation of these Zn nanoparticles eliminated the observed enhancement. The design of a polyethylene glycol coating to meet storage requirements of engineered zinc nanoparticles is evaluated to achieve maximal olfactory benefit.

Relationships between chemical structure, mechanical properties and materials processing in nanopatterned organosilicate fins.

The exploitation of nanoscale size effects to create new nanostructured materials necessitates the development of an understanding of relationships between molecular structure, physical properties and material processing at the nanoscale. Numerous metrologies capable of thermal, mechanical, and electrical characterization at the nanoscale have been demonstrated over the past two decades. However, the ability to perform nanoscale molecular/chemical structure characterization has only been recently demonstrated with the advent of atomic-force-microscopy-based infrared spectroscopy (AFM-IR) and related techniques.

Nanoscale tomographic reconstruction of the subsurface mechanical properties of low-k high-aspect ratio patterns.

In this work, intermittent contact resonance atomic force microscopy (ICR-AFM) was performed on high-aspect ratio a-SiOC:H patterned fins (100 nm in height and width from 20 to 90 nm) to map the depth and width dependencies of the material stiffness. The spatial resolution and depth sensitivity of the measurements were assessed from tomographic cross-sections over various regions of interest within the 3D space of the measurements. Furthermore, the depth-dependence of the measured contact stiffness over the scanned area was used to determine the sub-surface variation of the elastic modulus at each point in the scan.

After oxidation, zinc nanoparticles lose their ability to enhance responses to odorants.

Electrical responses of olfactory sensory neurons to odorants were examined in the presence of zinc nanoparticles of various sizes and degrees of oxidation. The zinc nanoparticles were prepared by the underwater electrical discharge method and analyzed by atomic force microscopy and X-ray photoelectron spectroscopy. Small (1.

Adhesive contact between a rigid spherical indenter and an elastic multi-layer coated substrate.

In this work the frictionless, adhesive contact between a rigid spherical indenter and an elastic multi-layer coated half-space was investigated by means of an integral transform formulation. The indented multi-layer coats were considered as made of isotropic layers that are perfectly bonded to each other and to an isotropic substrate. The adhesive interaction between indenter and contacting surface was treated as Maugis-type adhesion to provide general applicability within the entire range of adhesive interactions.

Silicon epitaxy on H-terminated Si (100) surfaces at 250 °C.

Low temperature Si epitaxy has become increasingly important due to its critical role in the encapsulation and performance of buried nanoscale dopant devices. We demonstrate epitaxial growth up to nominally 25 nm, at 250°C, with analysis at successive growth steps using STM and cross section TEM to reveal the nature and quality of the epitaxial growth. STM images indicate that growth morphology of both Si on Si and Si on H-terminated Si (H: Si) is epitaxial in nature at temperatures as low as 250 °C.

Engineered metal nanoparticles in the sub-nanomolar levels kill cancer cells.

Background: Small metal nanoparticles obtained from animal blood were observed to be toxic to cultured cancer cells, whereas noncancerous cells were much less affected. In this work, engineered zinc and copper metal nanoparticles were produced from bulk metal rods by an underwater high-voltage discharge method. The metal nanoparticles were characterized by atomic force microscopy and X-ray photoelectron spectroscopy.

Assessing strain mapping by electron backscatter diffraction and confocal Raman microscopy using wedge-indented Si.

The accuracy of electron backscatter diffraction (EBSD) and confocal Raman microscopy (CRM) for small-scale strain mapping are assessed using the multi-axial strain field surrounding a wedge indentation in Si as a test vehicle. The strain field is modeled using finite element analysis (FEA) that is adapted to the near-indentation surface profile measured by atomic force microscopy (AFM). The assessment consists of (1) direct experimental comparisons of strain and deformation and (2) comparisons in which the modeled strain field is used as an intermediate step.

Vertical 2D/3D Semiconductor Heterostructures Based on Epitaxial Molybdenum Disulfide and Gallium Nitride.

When designing semiconductor heterostructures, it is expected that epitaxial alignment will facilitate low-defect interfaces and efficient vertical transport. Here, we report lattice-matched epitaxial growth of molybdenum disulfide (MoS2) directly on gallium nitride (GaN), resulting in high-quality, unstrained, single-layer MoS2 with strict registry to the GaN lattice. These results present a promising path toward the implementation of high-performance electronic devices based on 2D/3D vertical heterostructures, where each of the 3D and 2D semiconductors is both a template for subsequent epitaxial growth and an active component of the device.

Nanoscale Buckling of Ultrathin Low-k Dielectric Lines during Hard-Mask Patterning.

Commonly known in macroscale mechanics, buckling phenomena are now also encountered in the nanoscale world as revealed in today's cutting-edge fabrication of microelectronics. The description of nanoscale buckling requires precise dimensional and elastic moduli measurements, as well as a thorough understanding of the relationships between stresses in the system and the ensuing morphologies. Here, we analyze quantitatively the buckling mechanics of organosilicate fins that are capped with hard masks in the process of lithographic formation of deep interconnects.

Intermittent contact resonance atomic force microscopy.

The intermittent contact resonance atomic force microscopy (ICR-AFM) mode proposed here is a new frequency modulation technique performed in scanning force controlled AFM modes like force volume or peak force tapping. It consists of tracking the change in the resonance frequency of an eigenmode of a driven AFM cantilever during scanning as the AFM probe intermittently contacts a surface at a controlled applied maximum force (setpoint). A high speed data capture was used during individual oscillations to obtain detailed contact stiffness-force curve measurements on a two-phase polystyrene/poly(methyl methacrylate) film with sub-micrometer size domains.

Frequency, amplitude, and phase measurements in contact resonance atomic force microscopies.

The resonance frequency, amplitude, and phase response of the first two eigenmodes of two contact-resonance atomic force microscopy (CR-AFM) configurations, which differ in the method used to excite the system (cantilever base vs sample excitation), are analyzed in this work. Similarities and differences in the observables of the cantilever dynamics, as well as the different effect of the tip-sample contact properties on those observables in each configuration are discussed. Finally, the expected accuracy of CR-AFM using phase-locked loop detection is investigated and quantification of the typical errors incurred during measurements is provided.

Nanoscale mechanics by tomographic contact resonance atomic force microscopy.

We report on quantifiable depth-dependent contact resonance AFM (CR-AFM) measurements over polystyrene-polypropylene (PS-PP) blends to detail surface and sub-surface features in terms of elastic modulus and mechanical dissipation. The depth-dependences of the measured parameters were analyzed to generate cross-sectional images of tomographic reconstructions. Through a suitable normalization of the measured contact stiffness and indentation depth, the depth-dependence of the contact stiffness was analyzed by linear fits to obtain the elastic moduli of the materials probed.

Nanoscale mapping of contact stiffness and damping by contact resonance atomic force microscopy.

In this work, a new procedure is demonstrated to retrieve the conservative and dissipative contributions to contact resonance atomic force microscopy (CR-AFM) measurements from the contact resonance frequency and resonance amplitude. By simultaneously tracking the CR-AFM frequency and amplitude during contact AFM scanning, the contact stiffness and damping were mapped with nanoscale resolution on copper (Cu) interconnects and low-k dielectric materials. A detailed surface mechanical characterization of the two materials and their interfaces was performed in terms of elastic moduli and contact damping coefficients by considering the system dynamics and included contact mechanics.

Nanomechanical properties of polyethylene glycol brushes on gold substrates.

A necessary step in advancing the use of polyethylene glycol (PEG) surface coatings in critical biotechnological applications such as cancer treatments is to provide direct and reliable nanoscale property characterization. Measurements for such characterization are currently provided by scanning probe methods, which are capable of assessing heterogeneity of both surface coverage and properties with nanoscale spatial resolution. In particular, atomic force microscopy (AFM) can be used to detect and quantify the heterogeneity of surface coverage, whereas atomic force spectroscopy can be used to determine mechanical properties, thereby revealing possible heterogeneity of properties within coatings.

Chaotic dynamics of driven flux drops: a superconducting "dripping faucet".

When a current is applied to a type-I superconducting strip containing a narrow channel across its width, magnetic flux spots nucleate at the edge and are then driven along the channel by the current. These flux "drops" are reminiscent of water drops dripping from a faucet, a model system for studying low-dimensional chaos. We use a novel high-bandwidth Hall probe to detect in real time the motion of individual flux spots moving along the channel.