RESUMEN

The ability to manipulate the dimensions, areal density, and form of substrate-supported Au and Ag nanoparticles (NPs) is highly desirable for utilizing their plasmonic properties in biosensing, photovoltaics, and nanophotonic applications. The transformation of thin films into the substrate-supported nanostructures by solid-state dewetting (SSD), provides an avenue to manipulate the dimensional aspects of nanostructures simply and cost-effectively on a large scale. However, spontaneous agglomeration of the film produces randomly distributed and non-uniform nanostructures that must be controlled. Here, we have systematically studied the effect of annealing temperature, between 200 °C and 750 °C, on the dewetting morphology evolution of Au, Ag, and Au-Ag bilayer ultrathin films sputter deposited on thec-plane (0001) sapphire substrates. Regardless of the film thickness, Ag films dewet faster than Au films and produce spherical NPs, compared to faceted Au NPs, with broader size distribution. Whereas, by the SSD of Au-Ag bilayer ultrathin films, highly spherical and monodisperse AuAg bimetallic NPs can be fabricated. Furthermore, we have shown the possibility of fabricating the AuAg bimetallic NPs of varying compositions by adjusting the thickness of individual layers, thus enabling us to smoothly tune the spectral location of plasmonic resonance within the visible range.

RESUMEN

Fracture toughness, which is the resistance of a material to crack propagation, is a critical material property for ensuring the mechanical reliability of damage-tolerant design. Recently, damage-tolerant design is introduced to flexible electronics by adopting micro-cracked ultra-thin nanocrystalline (NC) gold films as stretchable electrodes in a plane stress state. However, experimental investigation of the plane stress fracture toughness of those films remains challenging due to the intrinsic fragility from their sub-100 nm thicknesses. Here, a quantitative method for systematically evaluating the plane stress fracture toughness of freestanding ultra-thin NC gold film on water surface platform is presented. After effectively fabricating single-edge-notched-tension samples with femtosecond laser, mode I stress intensity factors are measured in the plane stress state on water surface. Moreover, investigation regarding the effect of notch length, notch sharpness, and notch tip plasticity validates this method based on linear elastic fracture mechanics theory. As a demonstration, the thickness-dependent plane stress fracture toughness of ultra-thin NC gold films is qualitatively unveiled. It is revealed that the thickness confinement effect on grain boundary sliding induces a transition in fracture behavior. This method is expected to further clarify the fracture-related properties of various ultra-thin films for next-generation electronics.

RESUMEN

Membrane-based gas separations are crucial for an energy-efficient future. However, it is difficult to develop membrane materials that are high-performing, scalable, and processable. Microporous organic polymers (MOPs) combine benefits for gas sieving and solution processability. Herein, we report membrane performance for a new family of microporous poly(arylene ether)s (PAEs) synthesized via Pd-catalyzed C-O coupling reactions. The scaffold of these microporous polymers consists of rigid three-dimensional triptycene and stereocontorted spirobifluorene, endowing these polymers with micropore dimensions attractive for gas separations. This robust PAE synthesis method allows for the facile incorporation of functionalities and branched linkers for control of permeation and mechanical properties. A solution-processable branched polymer was formed into a submicron film and characterized for permeance and selectivity, revealing lab data that rivals property sets of commercially available membranes already optimized for much thinner configurations. Moreover, the branching motif endows these materials with outstanding plasticization resistance, and their microporous structure and stability enables benefits from competitive sorption, increasing CO2 /CH4 and (H2 S+CO2 )/CH4 selectivity in mixture tests as predicted by the dual-mode sorption model. The structural tunability, stability, and ease-of-processing suggest that this new platform of microporous polymers provides generalizable design strategies to form MOPs at scale for demanding gas separations in industry.

RESUMEN

Recently, polyether ether ketone has raised increasing interest in research and industry as an alternative material for bone implants. This polymer also has some shortcomings, as it is bioinert and its surface is relatively hydrophobic, causing poor cell adhesion and therefore slow integration with bone tissue. In order to improve biocompatibility, the surface of polyether ether ketone-based implants should be modified. Therefore, polished disc-shaped polyether ether ketone samples were surface-modified by direct current magnetron sputtering with ultrathin titanium and zirconium coatings (thickness < 100 nm). The investigation results show a uniform distribution of both types of coatings on the sample surfaces, where the coatings mostly consist of titanium dioxide and zirconium dioxide. Differential scanning calorimetry revealed that the crystalline structure of the polyether ether ketone substrates was not changed by the coating deposition. Both coatings are amorphous, as shown by X-ray diffraction investigations. The roughness of both coating types increases with increasing coating thickness, which is beneficial for cell colonization. The coatings presented and investigated in this study improve wettability, increasing surface energies, in particular the polar component of the surface energies, which, in turn, are important for cell adhesion.

RESUMEN

We investigated the adsorption, surface enrichment, ion exchange, and on-surface metathesis of ultrathin mixed IL films on Ag(111). We stepwise deposited 0.5 ML of the protic IL diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]) and 1.0 ML of the aprotic IL 1-methyl-3-octylimidazolium hexafluorophosphate ([C8 C1 Im][PF6 ]) at around 90 K. Thereafter, the resulting layered frozen film was heated to 550 K, and the thermally induced phenomena were monitored in situ by angle-resolved X-ray photoelectron spectroscopy. Between 135 and 200 K, [TfO]- anions at the Ag(111) surface are exchanged by [PF6 ]- anions and enriched together with [C8 C1 Im]+ cations at the IL/vacuum interface. Upon further heating, [dema][PF6 ] and [OMIm][PF6 ] desorb selectively at ∼235 and ∼380 K, respectively. Hereby, a wetting layer of pure [C8 C1 Im][TfO] is formed by on-surface metathesis at the IL/metal interface, which completely desorbs at ∼480 K. For comparison, ion enrichment at the vacuum/IL interface was also studied in macroscopic IL mixtures, where no influence of the solid support is expected.

RESUMEN

The possibility of producing stable thin films, only a few atomic layers thick, from a variety of materials beyond graphene has led to two-dimensional (2D) materials being studied intensively in recent years. By reducing the layer thickness and approaching the crystallographic monolayer limit, a variety of unexpected and technologically relevant property phenomena were observed, which also depend on the subsequent arrangement and possible combination of individual layers to form heterostructures. These properties can be specifically used for the development of multifunctional devices, meeting the requirements of the advancing miniaturization of modern manufacturing technologies and the associated need to stabilize physical states even below critical layer thicknesses of conventional materials in the fields of electronics, magnetism and energy conversion. Differences in the structure of potential two-dimensional materials result in decisive influences on possible growth methods and possibilities for subsequent transfer of the thin films. In this review, we focus on recent advances in the rapidly growing field of two-dimensional materials, highlighting those with oxidic crystal structure like perovskites, garnets and spinels. In addition to a selection of well-established growth techniques and approaches for thin film transfer, we evaluate in detail their application potential as free-standing monolayers, bilayers and multilayers in a wide range of advanced technological applications. Finally, we provide suggestions for future developments of this promising research field in consideration of current challenges regarding scalability and structural stability of ultra-thin films.

RESUMEN

Ultrathin ferroelectrics are of great technological interest for high-density electronics, particularly non-volatile memories and field-effect transistors. With the rapid development of micro-electronics technology, there is an urgent requirement for higher density electronic devices, which need ultra-thin ferroelectric materials films. However, as ferroelectric films have becomes thinner and thinner, electrical spontaneous polarization signals have been found in a few atomic layers or even monolayer structures. The mechanisms of detection and formation of these signals are not well understood and various controversial interpretations have emerged. In this review, we summarized the recent research progress in the ultra-thin film ferroelectric material, such as HfO2, CuInP2S6, In2Se3, MoTe2and BaTiO3. Various key aspects of ferroelectric materials are discussed, including crystal structure, ferroelectric mechanism, characterization, fabrication methods, applications, and future outlooks. We hope this review will offer ideas for further improvement of ferroelectric properties of ultra-thin films and promotes practical applications.

RESUMEN

Sub-10 nm ferroelectric and multiferroic materials are attracting increased scientific and technological interest, owing to their exciting physical phenomena and prospects in miniaturized electronic devices, neuromorphic computing, and ultra-compact data storage. The Bi6Ti2.9Fe1.5Mn0.6O18 (B6TFMO) Aurivillius system is a rare example of a multiferroic that operates at room temperature. Since the formation of magnetic impurity phases can complicate attempts to measure ferromagnetic signal intrinsic to the B6TFMO multiferroic phase and thus limits its use, herein we minimize this by utilizing relatively large (49%) bismuth excess to counteract its volatility during sub-10 nm growth. X-ray diffraction, electron microscopy, and atomic force microscopy show sample crystallinity and purity are substantially improved on increasing bismuth excess from 5 to 49%, with the volume fraction of surface impurities decreasing from 2.95­3.97 vol% down to 0.02­0.31 vol%. Piezoresponse force microscopy reveals 8 nm B6TFMO films are ferroelectric, with an isotropic random distribution of stable in-plane domains and weaker out-of-plane piezoresponse. By reducing the volume fraction of magnetic impurities, this work demonstrates the recent progress in the optimization of ultra-thin B6TFMO for future multiferroic technologies. We show how the orientation of the ferroelectric polarization can be switched in 8 nm B6TFMO and arrays can be "written" and "read" to express states permitting anti-parallel information storage.

RESUMEN

This work reports about a novel approach for investigating surface processes during the early stages of galvanic corrosion of stainless steelin situby employing ultra-thin films and synchrotron x-radiation. Characterized by x-ray techniques and voltammetry, such films, sputter deposited from austenitic steel, were found representing useful replicas of the target material. Typical for stainless steel, the surface consists of a passivation layer of Fe- and Cr-oxides, a couple of nm thick, that is depleted of Ni. Films of ≈4 nm thickness were studiedin situin an electrochemical cell under potential control (-0.6 to +0.8 V vs Ag/AgCl) during exposure to 0.1 M KCl. Material transport was recorded with better than 1/10 monolayer sensitivity by x-ray spectroscopy. Leaching of Fe was observed in the cathodic range and the therefor necessary reduction of Fe-oxide appears to be accelerated by atomic hydrogen. Except for minor leaching, reduction of Ni, while expected from Pourbaix diagram, was not observed until at a potential of about +0.8 V Cr-oxide was removed from the steel film. After couple of minutes exposure at +0.8 V, the current in the electrochemical cell revealed a rapid pitting event that was simultaneously monitored by x-ray spectroscopy. Continuous loss of Cr and Ni was observed during the induction time leading to the pitting, suggesting a causal connection with the event. Finally, a spectroscopic image of a pit was recordedex situwith 50 nm lateral and 1 nm depth resolution by soft x-ray scanning absorption microscopy at the Fe L2,3-edges by using a 80 nm film on a SiN membrane, which is further demonstrating the usefulness of thin films for corrosion studies.

RESUMEN

We describe a bottom-up surface functionalization to design hybrid molecular coatings that tether biomembranes using wet chemistry. First, a monolayer was formed by immersion in a NH2-Ar-SO3H solution, allowing aryldiazonium salt radicals to spontaneously bind to it via strong C bonding. After formation of the air-stable and dense molecular monolayer (-Ar-SO3H), a subsequent activation was used to form highly reactive -Ar-SO2Cl groups nearly perpendicular to the monolayer. These can bind commercial surfactants, PEGylated oligomers and other inexpensive molecules via their -OH, -COOH, or -NH2 chain end-moieties, to build hybrid coatings. Metal and oxidized chromium, semi-conductor n-doped silicon (111), are the substrates tested for this protocol and the aromatic organic monolayers formed at their surface are characterized by X-ray photoelectron spectroscopy (XPS). XPS reveals unambiguously the presence of C-Cr and C-Si bonds, ensuring robustness of the coatings. Functional sulfur groups (-SO3H) cover up to 6.5×10-10 mol cm-2 of the silicon interface and 4.7×10-10 mol cm-2 of the oxidized chromium interface. These surface concentrations are comparable to the classic values obtained when the prefunctionalisation is driven by electrochemistry on conductors. Tethered lipid membranes formed on these coatings were analyzed by neutron reflectivity at the interface of functionalized n-doped silicon substrates after immersion in a solution of lipid vesicles and subsequent fusion. Results indicate a rather compact hybrid coating of Brij anchor-harpoon molecules that maintain a single lipid bilayer above the substrate, on top of a hydrated PEO cushion.

Asunto(s)

RESUMEN

Porous, high-surface-area electrode architectures are described that allow structural characterization of interfacial amorphous thin films with high spatial resolution under device-relevant functional electrochemical conditions using high-energy X-ray (>50 keV) scattering and pair distribution function (PDF) analysis. Porous electrodes were fabricated from glass-capillary array membranes coated with conformal transparent conductive oxide layers, consisting of either a 40 nm-50 nm crystalline indium tin oxide or a 100 nm-150 nm-thick amorphous indium zinc oxide deposited by atomic layer deposition. These porous electrodes solve the problem of insufficient interaction volumes for catalyst thin films in two-dimensional working electrode designs and provide sufficiently low scattering backgrounds to enable high-resolution signal collection from interfacial thin-film catalysts. For example, PDF measurements were readily obtained with 0.2 Šspatial resolution for amorphous cobalt oxide films with thicknesses down to 60 nm when deposited on a porous electrode with 40 µm-diameter pores. This level of resolution resolves the cobaltate domain size and structure, the presence of defect sites assigned to the domain edges, and the changes in fine structure upon redox state change that are relevant to quantitative structure-function modeling. The results suggest the opportunity to leverage the porous, electrode architectures for PDF analysis of nanometre-scale surface-supported molecular catalysts. In addition, a compact 3D-printed electrochemical cell in a three-electrode configuration is described which is designed to allow for simultaneous X-ray transmission and electrolyte flow through the porous working electrode.

RESUMEN

Pectin polysaccharides have significant potential as all-natural, non-toxic "green" coatings that exhibit thermally-cued swelling behavior. Herein, ultra-thin coatings of highly-esterified pectin polysaccharides were cross-linked with calcium chloride (CaCl2) and their swelling in water was investigated with ellipsometry. At low temperatures, the coatings swell to 2-3 times their dry layer thickness. As the temperature is increased, the coatings show a pronounced decrease in swollen thickness, reminiscent of the hydrophilic-hydrophobic transition observed in lower critical solution temperature (LCST) polymers. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy establishes that this transition is driven by dehydration of the esterified galacturonic acid residues along the pectin backbone. By adjusting both the CaCl2 concentration used to crosslink the pectin coatings as well as pH of swelling medium, the pectin coatings could be judiciously tuned for a desired swelling response as a function of temperature. Due to their non-toxic and responsive nature, it was further demonstrated that such coatings could be used in applications to control cell adhesion.

Asunto(s)

RESUMEN

Bacterial cellulose (BC) derived materials represents major advances to the current regenerative and diagnostic medicine. BC is a highly pure, biocompatible and versatile material that can be utilized in several applications - individually or in the combination with different components (e.g. biopolymers and nanoparticles) - to provide structural organization and flexible matrixes to distinct finalities. The wide application and importance of BC is described by its common utilization as skin repair treatments in cases of burns, wounds and ulcers. BC membranes accelerate the process of epithelialization and avoid infections. Furthermore, BC biocomposites exhibit the potential to regulate cell adhesion, an important characteristic to scaffolds and grafts; ultra-thin films of BC might be also utilized in the development of diagnostic sensors for its capability in immobilizing several antigens. Therefore, the growing interest in BC derived materials establishes it as a great promise to enhance the quality and functionalities of the current generation of biomedical materials.

Asunto(s)

RESUMEN

Non-stoichiometric ceria nanoparticles (NPs) were obtained by a gas aggregation source with a magnetron and were mass-selected with a quadrupole mass filter. By varying magnetron power, Ar gas flow, and the length of the aggregation tube, NPs with an average diameter of 6, 9, and 14 nm were synthesized and deposited onto a substrate, thus obtaining NP films. The morphology of the films was studied with scanning electron microscopy, while high resolution transmission electron microscopy was used to gain a deeper insight into the atomic structure of individual NPs. By using X-ray photoelectron spectroscopy we analyzed the degree of reduction of the NPs of different diameters, before and after thermal treatments in vacuum (reduction cycle) and in O2 atmosphere (oxidation cycle) at different temperatures. From this analysis we inferred that the size is an important parameter only at intermediate temperatures. As a comparison, we evaluated the reducibility of an ultra-thin ceria film with the same surface to volume ratio as the 9 nm diameter NPs film, observing that NPs are more reducible than the ceria film.

RESUMEN

We have proposed free-standing centimeter-sized ultra-thin films (nanosheets) for biomedical applications. Such nanosheets exhibit unique properties such as transparency, flexibility, and good adhesiveness. However, they are only easily adhered to broad and flat surfaces due to their dimensions. To this end, we recently proposed an innovative nanomaterial: the nanosheets fragmented into submillimeter-size pieces. Intriguingly, such fragmented nanosheets could be adhered to uneven and irregular surfaces in addition to flat surfaces in a spread-out "patchwork" manner. We herein review the fabrication procedure and characterization of fragmented nanosheets composed of biodegradable polyesters and thermostable bio-friendly polymers, and their biomedical applications in burn therapy and antithrombotic coating using a "patchwork coating".

RESUMEN

Polymeric materials are widely employed to build up tunable nanomasks for nano-patterning technologies. Ultrathin polymer layers are involved in this process. A Thermo Gravimetric Analysis-Mass Spectrometry (TGA-GC-MS) method was optimised, validated and successfully applied to investigate the thermal behavior of ultrathin poly(styrene-r-methylmethacrylate) random copolymer layers P(S-r-MMA) grafted to a silicon wafer surface. The interface between TGA and MS is highly versatile since many instrumental parameters (i.e. loop volumes, pulsed sampling frequencies, acquisition modalities, carrier gases, flow rates) can be easily tuned. Samples featuring substantial scale difference, i.e. bulk materials, thick films (few µm thickness), thin and ultrathin films (few nm thickness) can be analyzed without any instrumental modification or sample pretreatments. The TGA-GC-MS analysis was used to highlight subtle differences in samples featuring different thicknesses, in the 2-6 nm range, and subjected to various thermal treatments, thus indicating that this hyphenated technique could be successfully applied to the investigation of ultrathin polymer films.

Asunto(s)

RESUMEN

Using a high density polyethylene thin film over gold layer, a Surface PlasmonResonance sensor for detecting n-dodecane vapor is developed. Preliminary results will bepresented, showing that samples in the range of a few hundred ppm(V) of n-dodecanevapor in butane gas can be sensed. Also, studying the response as a function of time, it isdemonstrated that the sensing process is quickly reversible.