Transduction of Single Nanomechanical Pillar Resonators by Scattering of Surface Acoustic Waves.

One of the challenges of nanoelectromechanical systems (NEMS) is the effective transduction of the tiny resonators. Vertical structures, such as nanomechanical pillar resonators, which are exploited in optomechanics, acoustic metamaterials, and nanomechanical sensing, are particularly challenging to transduce. Existing electromechanical transduction methods are ill-suited as they put constraints on the pillars' material and do not enable a transduction of freestanding pillars. Here, we present an electromechanical transduction method for single nanomechanical pillar resonators based on surface acoustic waves (SAWs). We demonstrate the transduction of freestanding nanomechanical platinum-carbon pillars in the first-order bending and compression mode. Since the principle of the transduction method is based on resonant scattering of a SAW by a nanomechanical resonator, our transduction method is independent of the pillar's material and not limited to pillar-shaped geometries. It represents a general method to transduce vertical mechanical resonators with nanoscale lateral dimensions.

Advancement and challenges in sample preparation for atomic force microscopy and infrared microscopy for wood-based materials.

Wood-based materials such as composites or laminates play an important role in today's furniture industry, especially in manufacturing high-quality kitchen and dining room furniture. One important aspect after fabrication is the investigation of these materials to derive quality metrics such as surface stain and scuff resistance. Current sample preparation methods are mostly straightforward and rely on cutting and grinding the materials under test, including sensitive wood substrates. To investigate cross-sections and different layer topologies, characterisation techniques such as atomic force microscopy (AFM) and infrared (IR) microscopy are of potential interest. However, a huge limitation is that current sample preparation methods lead to smeared coatings on the sample cross-sections and high surface roughness. Hence, these methods are not applicable for the sample preparation in measuring AFM and IR microscopy. Therefore, new preparation techniques need to be developed accordingly. This article presents a new approach towards coated wood-based sample preparation including embedding processes to use those samples for AFM and IR microscopy technologies. The proposed method has been evaluated by obtaining AFM, IR and microscopy measurements of more than four different wood-based samples such as (i) raw paper, (ii) impregnated paper, (iii) melamine-coated chipboards and (iv) medium-density fibreboards. The investigation results showed a significant improvement in sample preparation, as well as clear chemical and physical characterisation over whole sample construction, including coating layers, for wood-based materials.

Humidity Response of Cellulose Thin Films.

Cellulose-water interactions are crucial to understand biological processes as well as to develop tailor made cellulose-based products. However, the main challenge to study these interactions is the diversity of natural cellulose fibers and alterations in their supramolecular structure. Here, we study the humidity response of different, well-defined, ultrathin cellulose films as a function of industrially relevant treatments using different techniques. As treatments, drying at elevated temperature, swelling, and swelling followed by drying at elevated temperatures were chosen. The cellulose films were prepared by spin coating a soluble cellulose derivative, trimethylsilyl cellulose, onto solid substrates followed by conversion to cellulose by HCl vapor. For the highest investigated humidity levels (97%), the layer thickness increased by ca. 40% corresponding to the incorporation of 3.6 molecules of water per anhydroglucose unit (AGU), independent of the cellulose source used. The aforementioned treatments affected this ratio significantly with drying being the most notable procedure (2.0 and 2.6 molecules per AGU). The alterations were investigated in real time with X-ray reflectivity and quartz crystal microbalance with dissipation, equipped with a humidity module to obtain information about changes in the thickness, roughness, and electron density of the films and qualitatively confirmed using grazing incidence small angle X-ray scattering measurements using synchrotron irradiation.

How Bound and Free Fatty Acids in Cellulose Films Impact Nonspecific Protein Adsorption.

The effect of fatty acids and fatty acid esters to impair nonspecific protein adsorption on cellulose thin films is investigated. Thin films are prepared by blending trimethylsilyl cellulose solutions with either cellulose stearoyl ester or stearic acid at various ratios. After film formation by spin coating, the trimethylsilyl cellulose fraction of the films is converted to cellulose by exposure to HCl vapors. The morphologies and surface roughness of the blends were examined by atomic force microscopy revealing different feature shapes and sizes depending on the blend ratios. Nonspecific protein adsorption at the example of bovine serum albumin toward the blend thin films was tested by means of surface plasmon resonance spectroscopy in real-time. Incorporation of stearic acid into the cellulose leads to highly protein repellent surfaces regardless of the amount added. The stearic acid acts as a sacrificial compound that builds a complex with bovine serum albumin thereby inhibiting protein adsorption. For the blends where stearoyl ester is added to the cellulose films, the cellulose:cellulose stearoyl ester ratios of 3:1 and 1:1 lead to much lower nonspecific protein adsorption compared to pure cellulose, whereas for the other ratios, adsorption increases. Supplementary results were obtained from atomic force microscopy experiments performed in liquid during exposure to protein solution and surface free energy determinations.

Star-shaped Polymers through Simple Wavelength-Selective Free-Radical Photopolymerization.

Star-shaped polymers represent highly desired materials in nanotechnology and life sciences, including biomedical applications (e.g., diagnostic imaging, tissue engineering, and targeted drug delivery). Herein, we report a straightforward synthesis of wavelength-selective multifunctional photoinitiators (PIs) that contain a bisacylphosphane oxide (BAPO) group and an α-hydroxy ketone moiety within one molecule. By using three different wavelengths, these photoactive groups can be selectively addressed and activated, thereby allowing the synthesis of ABC-type miktoarm star polymers through a simple, highly selective, and robust free-radical polymerization method. The photochemistry of these new initiators and the feasibility of this concept were investigated in unprecedented detail by using various spectroscopic techniques.

Enzymes as Biodevelopers for Nano- And Micropatterned Bicomponent Biopolymer Thin Films.

The creation of nano- and micropatterned polymer films is a crucial step for innumerous applications in science and technology. However, there are several problems associated with environmental aspects concerning the polymer synthesis itself, cross-linkers to induce the patterns as well as toxic solvents used for the preparation and even more important development of the films (e.g., chlorobenzene). In this paper, we present a facile method to produce micro- and nanopatterned biopolymer thin films using enzymes as so-called biodevelopers. Instead of synthetic polymers, naturally derived ones are employed, namely, poly-3-hydroxybutyrate and a cellulose derivative, which are dissolved in a common solvent in different ratios and subjected to spin coating. Consequently, the two biopolymers undergo microphase separation and different domain sizes are formed depending on the ratio of the biopolymers. The development step proceeds via addition of the appropriate enzyme (either PHB-depolymerase or cellulase), whereas one of the two biopolymers is selectively degraded, while the other one remains on the surface. In order to highlight the enzymatic development of the films, video AFM studies have been performed in real time to image the development process in situ as well as surface plasmon resonance spectroscopy to determine the kinetics. These studies may pave the way for the use of enzymes in patterning processes, particularly for materials intended to be used in a physiological environment.

Cellulose surface degradation by a lytic polysaccharide monooxygenase and its effect on cellulase hydrolytic efficiency.

Lytic polysaccharide monooxygenase (LPMO) represents a unique principle of oxidative degradation of recalcitrant insoluble polysaccharides. Used in combination with hydrolytic enzymes, LPMO appears to constitute a significant factor of the efficiency of enzymatic biomass depolymerization. LPMO activity on different cellulose substrates has been shown from the slow release of oxidized oligosaccharides into solution, but an immediate and direct demonstration of the enzyme action on the cellulose surface is lacking. Specificity of LPMO for degrading ordered crystalline and unordered amorphous cellulose material of the substrate surface is also unknown. We show by fluorescence dye adsorption analyzed with confocal laser scanning microscopy that a LPMO (from Neurospora crassa) introduces carboxyl groups primarily in surface-exposed crystalline areas of the cellulosic substrate. Using time-resolved in situ atomic force microscopy we further demonstrate that cellulose nano-fibrils exposed on the surface are degraded into shorter and thinner insoluble fragments. Also using atomic force microscopy, we show that prior action of LPMO enables cellulases to attack otherwise highly resistant crystalline substrate areas and that it promotes an overall faster and more complete surface degradation. Overall, this study reveals key characteristics of LPMO action on the cellulose surface and suggests the effects of substrate morphology on the synergy between LPMO and hydrolytic enzymes in cellulose depolymerization.

Focused particle beam nano-machining: the next evolution step towards simulation aided process prediction.

During the last decade, focused ion beam processing has been developed from traditionally used Ga(+) liquid ion sources towards higher resolution gas field ion sources (He(+) and Ne(+)). Process simulations not only improve the fundamental understanding of the relevant ion-matter interactions, but also enable a certain predictive power to accelerate advances. The historic 'gold' standard in ion-solid simulations is the SRIM/TRIM Monte Carlo package released by Ziegler, Ziegler and Biersack 2010 Nucl. Instrum. Methods B 268 1818-23. While SRIM/TRIM is very useful for a myriad of applications, it is not applicable for the understanding of the nanoscale evolution associated with ion beam nano-machining as the substrate does not evolve with the sputtering process. As a solution for this problem, a new, adapted simulation code is briefly overviewed and finally addresses these contributions. By that, experimentally observed Ne(+) beam sputter profiles can be explained from a fundamental point of view. Due to their very good agreement, these simulations contain the potential for computer aided optimization towards predictable sputter processes for different nanotechnology applications. With these benefits in mind, the discussed simulation approach represents an enormous step towards a computer based master tool for adaptable ion beam applications in the context of industrial applications.

A combined approach to predict spatial temperature evolution and its consequences during FIB processing of soft matter.

Accessing local temperatures and their evolution during focused ion beam (FIB) processing is of particular importance in the context of polymers or biomaterials as they tend to undergo severe chemical and morphological damage due to the high temperatures arising. In this study we present a combination of ion trajectory simulations and thermal spike model based calculations, which allows predicting local temperatures, lateral distributions and evolution during FIB patterning. Simulations and calculations have been done without any approximation or correction factors and lead to results in very good agreement with experiments on polymers taking into account their thermal behaviour. Finally, the model is applied to different scanning strategies which demonstrate how classically applied patterning strategies lead to massive temperature increases which can be the knock out criteria for low melting materials.

Nanoscale, surface-confined phase separation by electron beam induced oxidation.

Electron-assisted oxidation of Co-Si-based focused electron beam induced deposition (FEBID) materials is shown to form a 2-4 nm metal oxide surface layer on top of an electrically insulating silicon oxide layer less than 10 nm thick. Differences between thermal and electron-induced oxidation on the resulting microstructure are illustrated.

Dissecting and reconstructing synergism: in situ visualization of cooperativity among cellulases.

Cellulose is the most abundant biopolymer and a major reservoir of fixed carbon on earth. Comprehension of the elusive mechanism of its enzymatic degradation represents a fundamental problem at the interface of biology, biotechnology, and materials science. The interdependence of cellulose disintegration and hydrolysis and the synergistic interplay among cellulases is yet poorly understood. Here we report evidence from in situ atomic force microscopy (AFM) that delineates degradation of a polymorphic cellulose substrate as a dynamic cycle of alternating exposure and removal of crystalline fibers. Direct observation shows that chain-end-cleaving cellobiohydrolases (CBH I, CBH II) and an internally chain-cleaving endoglucanase (EG), the major components of cellulase systems, take on distinct roles: EG and CBH II make the cellulose surface accessible for CBH I by removing amorphous-unordered substrate areas, thus exposing otherwise embedded crystalline-ordered nanofibrils of the cellulose. Subsequently, these fibrils are degraded efficiently by CBH I, thereby uncovering new amorphous areas. Without prior action of EG and CBH II, CBH I was poorly active on the cellulosic substrate. This leads to the conclusion that synergism among cellulases is morphology-dependent and governed by the cooperativity between enzymes degrading amorphous regions and those targeting primarily crystalline regions. The surface-disrupting activity of cellulases therefore strongly depends on mesoscopic structural features of the substrate: size and packing of crystalline fibers are key determinants of the overall efficiency of cellulose degradation.

Cellulases dig deep: in situ observation of the mesoscopic structural dynamics of enzymatic cellulose degradation.

Enzymatic hydrolysis of cellulose is key for the production of second generation biofuels, which represent a long-standing leading area in the field of sustainable energy. Despite the wealth of knowledge about cellulase structure and function, the elusive mechanism by which these enzymes disintegrate the complex structure of their insoluble substrate, which is the gist of cellulose saccharification, is still unclear. We herein present a time-resolved structural characterization of the action of cellulases on a nano-flat cellulose preparation, which enabled us to overcome previous limitations, using atomic force microscopy (AFM). As a first step in substrate disintegration, elongated fissures emerge which develop into coniform cracks as disintegration continues. Detailed data analysis allowed tracing the surface evolution back to the dynamics of crack morphology. This, in turn, reflects the interplay between surface degradation inside and outside of the crack. We observed how small cracks evolved and initially increased in size. At a certain point, the crack diameter stagnated and then started decreasing again. Stagnation corresponds with a decrease in the total amount of surface which is fissured and thus leads to the conclusion that the surface hydrolysis "around" the cracks is proceeding more rapidly than inside the cracks. The mesoscopic view presented here is in good agreement with various mechanistic proposals from the past and allows a novel insight into the structural dynamics occurring on the cellulosic substrate through cellulase action.

Visualizing cellulase activity.

Commercial exploitation of lignocellulose for biotechnological production of fuels and commodity chemicals requires efficient-usually enzymatic-saccharification of the highly recalcitrant insoluble substrate. A key characteristic of cellulose conversion is that the actual hydrolysis of the polysaccharide chains is intrinsically entangled with physical disruption of substrate morphology and structure. This "substrate deconstruction" by cellulase activity is a slow, yet markedly dynamic process that occurs at different length scales from and above the nanometer range. Little is currently known about the role of progressive substrate deconstruction on hydrolysis efficiency. Application of advanced visualization techniques to the characterization of enzymatic degradation of different celluloses has provided important new insights, at the requisite nano-scale resolution and down to the level of single enzyme molecules, into cellulase activity on the cellulose surface. Using true in situ imaging, dynamic features of enzyme action and substrate deconstruction were portrayed at different morphological levels of the cellulose, thus providing new suggestions and interpretations of rate-determining factors. Here, we review the milestones achieved through visualization, the methods which significantly promoted the field, compare suitable (model) substrates, and identify limiting factors, challenges and future tasks.

Chemical tuning of PtC nanostructures fabricated via focused electron beam induced deposition.

The fundamental dependence between process parameters during focused electron beam induced deposition and the chemistry of functional PtC nanostructures have been studied via a multi-technique approach using SEM, (S)TEM, EELS, AFM, and EFM. The study reveals that the highest Pt contents can only be achieved by an ideal balance between potentially dissociating electrons and available precursor molecules on the surface. For precursor regimes apart from this situation, an unwanted increase of carbon is observed which originates from completely different mechanisms: (1) an excess of electrons leads to polymerization of precursor fragments whereas (2) a lack of electrons leads to incompletely dissociated precursor molecules incorporated into the nanostructures. While the former represents an unwanted class of carbon, the latter condition maximizes the volume growth rates and allows for post-growth curing strategies which can strongly increase the functionality. Furthermore, the study gives an explanation of why growing deposits can dynamically change their chemistry and provides a straightforward guide towards more controlled fabrication conditions.

Variable tunneling barriers in FEBID based PtC metal-matrix nanocomposites as a transducing element for humidity sensing.

The development of simple gas sensing concepts is still of great interest for science and technology. The demands on an ideal device would be a single-step fabrication method providing a device which is sensitive, analyte-selective, quantitative, and reversible without special operating/reformation conditions such as high temperatures or special environments. In this study we demonstrate a new gas sensing concept based on a nanosized PtC metal-matrix system fabricated in a single step via focused electron beam induced deposition (FEBID). The sensors react selectively on polar H2O molecules quantitatively and reversibly without any special reformation conditions after detection events, whereas non-polar species (O2, CO2, N2) produce no response. The key elements are isolated Pt nanograins (2-3 nm) which are embedded in a dielectric carbon matrix. The electrical transport in such materials is based on tunneling effects in the correlated variable range hopping regime, where the dielectric carbon matrix screens the electric field between the particles, which governs the final conductivity. The specific change of these dielectric properties by the physisorption of polar gas molecules (H2O) can change the tunneling probability and thus the overall conductivity, allowing their application as a simple and straightforward sensing concept.

3D Nanoprinting Replication Enhancement Using a Simulation-Informed Analytical Model for Electron Beam Exposure Dose Compensation.

3D nanoprinting, using focused electron beam-induced deposition, is prone to a common structural artifact arising from a temperature gradient that naturally evolves during deposition, extending from the electron beam impact region (BIR) to the substrate. Inelastic electron energy loss drives the Joule heating and surface temperature variations lead to precursor surface concentration variations due, in most part, to temperature-dependent precursor surface desorption. The result is unwanted curvature when prescribing linear segments in 3D objects, and thus, complex geometries contain distortions. Here, an electron dose compensation strategy is presented to offset deleterious heating effects; the Decelerating Beam Exposure Algorithm, or DBEA, which corrects for nanowire bending a priori, during computer-aided design, uses an analytical solution derived from information gleaned from 3D nanoprinting simulations. Electron dose modulation is an ideal solution for artifact correction because variations in electron dose have no influence on temperature. Thus, the generalized compensation strategy revealed here will help advance 3D nanoscale printing fidelity for focused electron beam-induced deposition.

A Review of the Current State of Magnetic Force Microscopy to Unravel the Magnetic Properties of Nanomaterials Applied in Biological Systems and Future Directions for Quantum Technologies.

Magnetism plays a pivotal role in many biological systems. However, the intensity of the magnetic forces exerted between magnetic bodies is usually low, which demands the development of ultra-sensitivity tools for proper sensing. In this framework, magnetic force microscopy (MFM) offers excellent lateral resolution and the possibility of conducting single-molecule studies like other single-probe microscopy (SPM) techniques. This comprehensive review attempts to describe the paramount importance of magnetic forces for biological applications by highlighting MFM's main advantages but also intrinsic limitations. While the working principles are described in depth, the article also focuses on novel micro- and nanofabrication procedures for MFM tips, which enhance the magnetic response signal of tested biomaterials compared to commercial nanoprobes. This work also depicts some relevant examples where MFM can quantitatively assess the magnetic performance of nanomaterials involved in biological systems, including magnetotactic bacteria, cryptochrome flavoproteins, and magnetic nanoparticles that can interact with animal tissues. Additionally, the most promising perspectives in this field are highlighted to make the reader aware of upcoming challenges when aiming toward quantum technologies.

Additive Manufacturing of Co3Fe Nano-Probes for Magnetic Force Microscopy.

Magnetic force microscopy (MFM) is a powerful extension of atomic force microscopy (AFM), which mostly uses nano-probes with functional coatings for studying magnetic surface features. Although well established, additional layers inherently increase apex radii, which reduce lateral resolution and also contain the risk of delamination, rendering such nano-probes doubtful or even useless. To overcome these limitations, we now introduce the additive direct-write fabrication of magnetic nano-cones via focused electron beam-induced deposition (FEBID) using an HCo3Fe(CO)12 precursor. The study first identifies a proper 3D design, confines the most relevant process parameters by means of primary electron energy and beam currents, and evaluates post-growth procedures as well. That way, highly crystalline nano-tips with minimal surface contamination and apex radii in the sub-15 nm regime are fabricated and benchmarked against commercial products. The results not only reveal a very high performance during MFM operation but in particular demonstrate virtually loss-free behavior after almost 8 h of continuous operation, thanks to the all-metal character. Even after more than 12 months of storage in ambient conditions, no performance loss is observed, which underlines the high overall performance of the here-introduced FEBID-based Co3Fe MFM nano-probes.

Pillar Growth by Focused Electron Beam-Induced Deposition Using a Bimetallic Precursor as Model System: High-Energy Fragmentation vs. Low-Energy Decomposition.

Electron-induced fragmentation of the HFeCo3(CO)12 precursor allows direct-write fabrication of 3D nanostructures with metallic contents of up to >95 at %. While microstructure and composition determine the physical and functional properties of focused electron beam-induced deposits, they also provide fundamental insights into the decomposition process of precursors, as elaborated in this study based on EDX and TEM. The results provide solid information suggesting that different dominant fragmentation channels are active in single-spot growth processes for pillar formation. The use of the single source precursor provides a unique insight into high- and low-energy fragmentation channels being active in the same deposit formation process.

Substrate selected polymorphism of epitaxially aligned tetraphenyl-porphyrin thin films.

Porphyrin molecules, of interest as versatile materials for organic electronics, are highly prone to formation of significantly different polymorphic phases. To elucidate the determinants for the specific polymorphic phase formed in thin films as well as for the arrangement of the molecules on a given substrate two different anisotropic substrate surfaces have been selected: KCl(100) and the oxygen reconstructed Cu(110) surface. We observe that the crystal structure of the thin films depends on the substrate, whereas the relative molecular orientations in both cases are similar. X-Ray and transmission electron diffraction of 30 nm thick tetraphenyl-porphyrin (H(2)TPP) and platinum tetraphenyl-porphyrin (PtTPP) thin films deposited on KCl(100) surfaces reveals that both kinds of molecules crystallize in a tetragonal polymorph with the (001) lattice planes, i.e. with their macrocycles, parallel to the substrate. Films deposited on the oxygen reconstructed Cu(110)-(2 × 1)O surface exhibit in contrast the triclinic polymorph even though molecules again align nearly parallel to the substrate surface as observed by LEED and X-ray diffraction. On both substrates we identify two driving forces for the epitaxial alignment of porphyrins: (i) molecules aligning with their macrocycles (nearly) parallel to the substrate surface and (ii) the porphyrin molecules forming a commensurate unit cell with the respective substrate. The polymorphic phase meeting both requirements is the most favorable to be formed on a given substrate and due to this structural flexibility in both cases well-ordered, epitaxially aligned porphyrin thin films are achieved.