Search

Amorphous diamond-like and carbon nitride films deposited by pulsed laser deposition were studied.

During the sliding of an atomic force microscope (AFM) tip on the hydrophilic rough surface, water capillary bridges can form between the tip and the asperities of the surface. The total capillary force due to these bridges increases with the normal load following a 2/3 power law and an analytical relationship is derived to explain the interplay between humidity, velocity, and normal load in nanoscopic friction.

Studies intersubband relaxation time for InGaAs/AlAs quantum wells with large transition energy. Differential transmission decays; Intersubband transitions in optoelectronic devices.

Emergent electronic phenomena, from superconductivity to ferroelectricity, magnetism, and correlated many-body band gaps, have been observed in domains created by stacking and twisting atomic layers of Van der Waals materials. In graphene, emergent properties have been observed in ABC stacking domains obtained by exfoliation followed by expert mechanical twisting and alignment with the desired orientation, a process very challenging and nonscalable. Here, conductive atomic force microscopy shows in untwisted epitaxial graphene grown on SiC the surprising presence of striped domains with dissimilar conductance, a contrast that demonstrates the presence of ABA and ABC domains since it matches exactly the conductivity difference observed in ABA/ABC domains in twisted exfoliated graphene and calculated by density functional theory. The size and geometry of the stacking domains depend on the interplay between strain, solitons crossing, and shape of the three-layer regions. Interestingly, we demonstrate the growth of three-layer regions in which the ABA/ABC stacking domains self-organize in stable stripes of a few tens of nanometers. The growth-controlled production of isolated and stripe-shaped ABA/ABC domains open the path to fabricate quantum devices on these domains. These findings on self-assembly formation of ABA/ABC epitaxial graphene stripes on SiC without the need of time-consuming and nonscalable graphene exfoliation, alignment, and twisting provide different potential applications of graphene in electronic devices., Competing Interests: Competing interests statement:The authors declare no competing interest.

The rise in antibiotic-resistant pathogens, highly infectious viruses, and chronic diseases has prompted the search for rapid and versatile medical tests that can be performed by the patient. Field-effect transistor (FET)-based electronic biosensing platforms are particularly attractive due to their sensitivity, fast turn-around time, potential for parallel detection of multiple pathogens, and compatibility with semiconductor manufacturing. However, an unmet critical need is a scalable, site-selective multiplexed biofunctionalization method with nanoscale precision for immobilizing different types of pathogen-specific bioreceptors on individual FETs, preventing parallel detection of multiple targets. Here, we propose a paradigm shift in FET biofunctionalization using thermal scanning probe lithography (tSPL) with a thermochemically sensitive polymer. This polymer can be spin-coated on fully-fabricated FET chips, making this approach applicable to any FET sensor material and technology. Crucially, we demonstrate the spatially selective multiplexed functionalization capability of this method by immobilizing different types of bioreceptors at prescribed locations on a chip with sub-20 nm resolution, paving the way for massively parallel FET detection of multiple pathogens. Antibody- and aptamer-modified graphene FET sensors are then realized, achieving ultra-sensitive detection of a minimum measured concentrations of 3 aM of SARS-CoV-2 spike proteins and 10 human SARS-CoV-2 infectious live virus particles per ml, and selectivity against human influenza A (H1N1) live virus.

In the field of hydrogen production, MoS 2 demonstrates good catalytic properties for the hydrogen evolution reaction (HER) which improve when doped with metal cations. However, while the role of sulfur atoms as active sites in the HER is largely reported, the role of metal atoms ( i.e. molybdenum or the dopant cations) has yet to be studied in depth. To understand the role of the metal dopant, we study MoS 2 thin films doped with Co and Mn ions. We identify the contribution of the electronic bands of the Mn and Co dopants to the integral valence band of the material using in situ resonant photoemission measurements. We demonstrate that Mn and Co dopants act differently: Mn doping favors the shift of the S-Mo hybridized band towards the Fermi level, while in the case of Co doping it is the less hybridized Co band that shifts closer to the Fermi level. Doping with Mn increases the effectiveness of S as the active site, thus improving the HER, while doping with Co introduces the metallic site of Co as the active site, which is less effective in improving HER properties. We therefore clarify the role of the dopant cation in the electronic structure determining the active site for hydrogen adsorption/desorption. Our results pave the way for the design of efficient materials for hydrogen production via the doping route, which can be extended to different catalytic reactions in the field of energy applications.

Silicon carbide has excellent mechanical properties such as high hardness and strength, but its applications for body armor and protective coating solutions are limited by its poor toughness. It has been demonstrated that epitaxial graphene-coated SiC can enhance SiC mechanical properties due to the pressure-activated phase transition into a sp 3 diamond structure. Here, we show that atomically thin graphene coatings increase the hardness of SiC even for indentation depths of ∼10 μm. Very importantly, the graphene coating also causes an increase of the fracture toughness by 11% compared to bare SiC, which is in contradiction with the general indirect variation of hardness and fracture toughness. This is explained in terms of the presence of a diamond phase under the indenter while the rest of the coating remains in the ultra-tough graphene phase. This study opens new venues for understanding hardness and toughness in metastable systems and for the applications of graphene-coatings.

Colloidal quantum dot (CQD) infrared (IR) photodetectors can be fabricated and operated with larger spectral tunability, fewer limitations in terms of cooling requirements and substrate lattice matching, and at a potentially lower cost than detectors based on traditional bulk materials. Silver selenide (Ag 2 Se) has emerged as a promising sustainable alternative to current state-of-the-art toxic semiconductors based on lead, cadmium, and mercury operating in the IR. However, an impeding gap in available absorption bandwidth for Ag 2 Se CQDs exists in the short-wave infrared (SWIR) region due to degenerate doping by the environment, switching the CQDs from intrinsic interband semiconductors in the near-infrared (NIR) to intraband absorbing CQDs in the mid-wave infrared (MWIR). Herein, we show that the small molecular p-type dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) can be used to extract electrons from the 1S e state of MWIR active Ag 2 Se CQDs to activate their intrinsic energy gap in the SWIR window. We demonstrate quenching of the MWIR Ag 2 Se absorbance peak, shifting of nitrile vibrational peaks characteristic of charge-neutral F4-TCNQ, as well as enhanced CQD absorption around ∼2500 nm after doping both in ambient and under air-free conditions. We elucidate the doping mechanism to be one that involves an integer charge transfer akin to doping in semiconducting polymers. These indications of charge transfer are promising milestones on the path to achieving sustainable SWIR Ag 2 Se CQD photodetectors., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Tailoring nanoscale catalysts to targeted applications is a vital component in reducing the carbon footprint of industrial processes; however, understanding and controlling the nanostructure influence on catalysts is challenging. Molybdenum disulfide (MoS 2 ), a transition metal dichalcogenide (TMD) material, is a popular example of a nonplatinum-group-metal catalyst with tunable nanoscale properties. Doping with transition metal atoms, such as cobalt, is one method of enhancing its catalytic properties. However, the location and influence of dopant atoms on catalyst behavior are poorly understood. To investigate this knowledge gap, we studied the influence of Co dopants in MoS 2 nanosheets on catalytic hydrodesulfurization (HDS) through a well-controlled, ligand-directed, tunable colloidal doping approach. X-ray absorption spectroscopy and density functional theory calculations revealed the nonmonotonous relationship between dopant concentration, location, and activity in HDS. Catalyst activity peaked at 21% Co:Mo as Co saturates the edge sites and begins basal plane doping. While Co prefers to dope the edges over basal sites, basal Co atoms are demonstrably more catalytically active than edge Co. These findings provide insight into the hydrogenolysis behavior of doped TMDs and can be extended to other TMD materials., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

As the field of low-dimensional materials (1D or 2D) grows and more complex and intriguing structures are continuing to be found, there is an emerging need for techniques to characterize the nanoscale mechanical properties of all kinds of 1D/2D materials, in particular in their most practical state: sitting on an underlying substrate. While traditional nanoindentation techniques cannot accurately determine the transverse Young's modulus at the necessary scale without large indentations depths and effects to and from the substrate, herein an atomic-force-microscopy-based modulated nanomechanical measurement technique with Angstrom-level resolution (MoNI/ÅI) is presented. This technique enables non-destructive measurements of the out-of-plane elasticity of ultra-thin materials with resolution sufficient to eliminate any contributions from the substrate. This method is used to elucidate the multi-layer stiffness dependence of graphene deposited via chemical vapor deposition and discover a peak transverse modulus in two-layer graphene. While MoNI/ÅI has been used toward great findings in the recent past, here all aspects of the implementation of the technique as well as the unique challenges in performing measurements at such small resolutions are encompassed., (© 2023 The Authors. Small Methods published by Wiley-VCH GmbH.)

Reproducing in vitro the complex multiscale physical features of human tissues creates novel biomedical opportunities and fundamental understanding of cell-environment interfaces and interactions. While stiffness has been recognized as a key driver of cell behavior, systematic studies on the role of stiffness have been limited to values in the KPa-MPa range, significantly below the stiffness of bone. Here, a platform enabling the tuning of the stiffness of a biocompatible polymeric interface up to values characteristic of human bone is reported, which are in the GPa range, by using extremely thin polymer films on glass and cross-linking the films using ultraviolet (UV) light irradiation. It is shown that a higher stiffness is related to better adhesion, proliferation, and osteogenic differentiation, and that it is possible to switch on/off cell attachment and growth by solely tuning the stiffness of the interface, without any surface chemistry or topography modification. Since the stiffness is tuned directly by UV irradiation, this platform is ideal for rapid and simple fabrication of stiffness patterns and gradients, thus representing an innovative tool for combinatorial studies of the synergistic effect of tissue environmental cues on cell behavior, and creates new opportunities for next-generation biosensors, single-cell patterning, and lab-on-a-chip devices., (© 2023 Wiley-VCH GmbH.)

Silicon carbide (SiC) is one of the hardest known materials. Its exceptional mechanical properties combined with its high thermal conductivity make it a very attractive material for a variety of technological applications. Recently, it is discovered that two-layer epitaxial graphene films on SiC can undergo a pressure activated phase transition into a sp 3 diamene structure at room temperature. Here, it is shown that epitaxial graphene films grown on SiC can increase the hardness of SiC up to 100% at low loads (up to 900 µN), and up to 30% at high loads (10 mN). By using a Berkovich diamond indenter and nanoindentation experiments, it is demonstrated that the 30% increase in hardness is present even for indentations depths of 175 nm, almost three hundred times larger than the graphene film thickness. The experiments also show that the yield point of SiC increases up to 77% when the SiC surface is coated with epitaxial graphene. These improved mechanical properties are explained with the formation of diamene under the indenter's pressure., (© 2023 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Understanding the interfacial properties between an atomic layer and its substrate is of key interest at both the fundamental and technological levels. From Fermi level pinning to strain engineering and superlubricity, the interaction between a single atomic layer and its substrate governs electronic, mechanical and chemical properties. Here, we measure the hardly accessible interfacial transverse shear modulus of an atomic layer on a substrate. By performing measurements on bulk graphite, and on epitaxial graphene films on SiC with different stacking orders and twisting, as well as in the presence of intercalated hydrogen, we find that the interfacial transverse shear modulus is critically controlled by the stacking order and the atomic layer-substrate interaction. Importantly, we demonstrate that this modulus is a pivotal measurable property to control and predict sliding friction in supported two-dimensional materials. The experiments demonstrate a reciprocal relationship between friction force per unit contact area and interfacial shear modulus. The same relationship emerges from simulations with simple friction models, where the atomic layer-substrate interaction controls the shear stiffness and therefore the resulting friction dissipation., (© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)

Background: Hemolytic blood samples are the number one cause for specimen rejection at emergency departments. Triggered by unsuitable blood sampling material or incorrect handling and a related strong vacuum force, hemolytic samples often must be retaken. The objective of this study was to assess whether correct manual aspiration using S-Monovette® could reduce the number of hemolytic samples., Methods: Between January and April 2019, a head-to-head study was conducted. Whereas in the first eight weeks, all specimens were collected using Vacutainer®, in the second eight weeks, blood was taken using S-Monovette® in aspiration mode. Specimens were categorized into five classes (0-30, 31-50, 51-75, 76-100, and 101+ mg/dl of cell-free hemoglobin) and for the statistical analyses, all samples exceeding 30 mg/dl were classified as hemolytic., Results: Data were collected on 4794 blood specimens (Vacutainer®: 2634 samples, S-Monovette®: 2160 samples). While the percentage of non-hemolytic samples (HI of 0-30 mg/dl) was substantially higher for specimens drawn by S-Monovette® (95.7 %) than Vacutainer® (83.0 %), the opposite was true for all HI categories above 30 mg/dl. Importantly, the reduction of hemolytic samples took place immediately following the imposition of S-Monovette® and remained stable at a low level until the end of the study., Conclusions: Based on our results, we conclude that switching to S-Monovette® in manual aspiration mode in the blood sampling process could be highly beneficial, not only from a financial point of view, but also with regards to reducing unnecessary tasks and stress for nursing staff and improving patient outcome overall., Competing Interests: The funding organization played no role in the study design; in the collection, analysis, and interpretation of data; in the writing of the report; or in the decision to submit the report for publication., (© 2021 Published by Elsevier B.V.)

Understanding phase transformations in 2D materials can unlock unprecedented developments in nanotechnology, since their unique properties can be dramatically modified by external fields that control the phase change. Here, experiments and simulations are used to investigate the mechanical properties of a 2D diamond boron nitride (BN) phase induced by applying local pressure on atomically thin h-BN on a SiO 2 substrate, at room temperature, and without chemical functionalization. Molecular dynamics (MD) simulations show a metastable local rearrangement of the h-BN atoms into diamond crystal clusters when increasing the indentation pressure. Raman spectroscopy experiments confirm the presence of a pressure-induced cubic BN phase, and its metastability upon release of pressure. Å-indentation experiments and simulations show that at pressures of 2-4 GPa, the indentation stiffness of monolayer h-BN on SiO 2 is the same of bare SiO 2 , whereas for two- and three-layer-thick h-BN on SiO 2 the stiffness increases of up to 50% compared to bare SiO 2 , and then it decreases when increasing the number of layers. Up to 4 GPa, the reduced strain in the layers closer to the substrate decreases the probability of the sp 2 -to-sp 3 phase transition, explaining the lower stiffness observed in thicker h-BN., Competing Interests: The authors declare no conflict of interest., (© 2020 The Authors. Advanced Science published by Wiley‐VCH GmbH.)

Understanding the atomistic origin of defects in two-dimensional transition metal dichalcogenides, their impact on the electronic properties, and how to control them is critical for future electronics and optoelectronics. Here, we demonstrate the integration of thermochemical scanning probe lithography (tc-SPL) with a flow-through reactive gas cell to achieve nanoscale control of defects in monolayer MoS 2 . The tc-SPL produced defects can present either p- or n-type doping on demand, depending on the used gasses, allowing the realization of field effect transistors, and p-n junctions with precise sub-μm spatial control, and a rectification ratio of over 10 4 . Doping and defects formation are elucidated by means of X-Ray photoelectron spectroscopy, scanning transmission electron microscopy, and density functional theory. We find that p-type doping in HCl/H 2 O atmosphere is related to the rearrangement of sulfur atoms, and the formation of protruding covalent S-S bonds on the surface. Alternatively, local heating MoS 2 in N 2 produces n-character.

Transient self-assembly of dipeptide nanofibers with lifetimes that are predictably variable through dipeptide sequence design are presented. This was achieved using 1,8-naphthalimide (NI) amino acid methyl-esters (Phe, Tyr, Leu) that are biocatalytically coupled to amino acid-amides (Phe, Tyr, Leu, Val, Ala, Ser) to form self-assembling NI-dipeptides. However, competing hydrolysis of the dipeptides results in disassembly. It was demonstrated that the kinetic parameters like lifetimes of these nanofibers can be predictably regulated by the thermodynamic parameter, namely the self-assembly propensity of the constituent dipeptide sequence. These lifetimes could vary from minutes, to hours, to permanent gels that do not degrade. Moreover, the in-built NI fluorophore was utilized to image the transient nanostructures in solution with stimulated emission depletion (STED) based super-resolution fluorescence microscopy., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Integrated optically inspired wave-based processing is envisioned to outperform digital architectures in specific tasks, such as image processing and speech recognition. In this view, spin waves represent a promising route due to their nanoscale wavelength in the gigahertz frequency range and rich phenomenology. Here, a versatile, optically inspired platform using spin waves is realized, demonstrating the wavefront engineering, focusing, and robust interference of spin waves with nanoscale wavelength. In particular, magnonic nanoantennas based on tailored spin textures are used for launching spatially shaped coherent wavefronts, diffraction-limited spin-wave beams, and generating robust multi-beam interference patterns, which spatially extend for several times the spin-wave wavelength. Furthermore, it is shown that intriguing features, such as resilience to back reflection, naturally arise from the spin-wave nonreciprocity in synthetic antiferromagnets, preserving the high quality of the interference patterns from spurious counterpropagating modes. This work represents a fundamental step toward the realization of nanoscale optically inspired devices based on spin waves., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The ability to precisely control the localization of enzymes on a surface is critical for several applications including biosensing, bionanoreactors, and single molecule studies. Despite recent advances, fabrication of enzyme patterns with resolution at the single enzyme level is limited by the lack of lithography methods that combine high resolution, compatibility with soft, polymeric structures, ease of fabrication, and high throughput. Here, a method to generate enzyme nanopatterns (using thermolysin as a model system) on a polymer surface is demonstrated using thermochemical scanning probe lithography (tc-SPL). Electrostatic immobilization of negatively charged sulfonated enzymes occurs selectively at positively charged amine nanopatterns produced by thermal deprotection of amines along the side-chain of a methacrylate-based copolymer film via tc-SPL. This process occurs simultaneously with local thermal quasi-3D topographical patterning of the same polymer, offering lateral sub-10 nm resolution, and vertical 1 nm resolution, as well as high throughput (5.2 × 10 4 μm 2 /h). The obtained single-enzyme resolution patterns are characterized by atomic force microscopy (AFM) and fluorescence microscopy. The enzyme density, the surface passivation, and the quasi-3D arbitrary geometry of these patterned pockets are directly controlled during the tc-SPL process in a single step without the need of markers or masks. Other unique features of this patterning approach include the combined single-enzyme resolution over mm 2 areas and the possibility of fabricating enzymes nanogradients.

High-throughput and large-scale patterning of enzymes with sub-10 nm resolution, the size range of individual protein molecules, is crucial for propelling advancement in a variety of areas, from the development of chip-based biomolecular nano-devices to molecular-level studies of cell biology. Despite recent developments in bio-nanofabrication technology, combining 10 nm resolution with high-throughput and large-scale patterning of enzymes is still an open challenge. Here, we demonstrate a high resolution and high-throughput patterning method to generate enzyme nanopatterns with sub-10 nm resolution by using thermochemical scanning probe lithography (tc-SPL). First, tc-SPL is used to generate amine patterns on a methacrylate copolymer film. Thermolysin enzymes functionalized with sulfonate-containing fluorescent labels (Alexa-488) are then directly immobilized onto the amine patterns through electrostatic interaction. Enzyme patterns with sub-10 nm line width are obtained as evidenced by atomic force microscopy (AFM) and fluorescence microscopy. Moreover, we demonstrate large-scale and high throughput (0.13 × 0.1 mm2 at a throughput of 5.2 × 104 μm2 h-1) patterning of enzymes incorporating 10 nm detailed pattern features. This straightforward and high-throughput method of fabricating enzyme nanopatterns will have a significant impact on future bio-nanotechnology applications and molecular-level biological studies. By scaling up using parallel probes, tc-SPL is promising for implementation to scale up the fabrication of nano-biodevices.