In article number 2007864, Bettina V. Lotsch and co-workers report a facile transfer of 1D photonic crystals and patterns thereof to arbitrary substrates by applying a sacrificial layer approach combined with spatially resolved amine intercalation for hydrophobization. Post-transfer modification such as amine exchange or heat treatment allow an adaptive control of the sensing properties of the photonic crystals thus enlarging application possibilities.

1D photonic crystals (1DPCs) are well known from a variety of applications ranging from medical diagnostics to optical fibers and optoelectronics. However, large-scale application is still limited due to complex fabrication processes and bottlenecks in transferring 1DPCs to arbitrary substrates and pattern creation. These challenges were addressed by demonstrating the transfer of millimeter- to centimeter-scale 1DPC sensors comprised of alternating layers of H3 Sb3 P2 O14 nanosheets and TiO2 nanoparticles based on a non-invasive chemical approach. By depositing the 1DPC on a sacrificial layer of lithium tin sulfide nanosheets and hydrophobizing only the 1DPC by intercalation of n-octylamine via the vapor phase the 1DPC can be detached from the substrate by immersing the sample in water. Upon exfoliation of the hydrophilic sacrificial layer, the freestanding 1DPC remains at the water-air interface. In a second step, it can be transferred to arbitrary surfaces such as curved glass. In addition, the transfer of patterned 1DPCs is demonstrated by combining the sacrificial layer approach with area-resolved intercalation and etching. The fact that the sensing capability of the 1DPC is not impaired and can be modified after transfer renders this method a generic platform for the fabrication of photonic devices.

Reversible post-synthetic modification of H3Sb3P2O14 nanosheet-based thin films by applying a facile two-step amine intercalation over the vapor phase.

The development of novel, intrinsic two-dimensional (2D) antiferromagnets presents the opportunity to vastly improve the efficiency of spintronic devices and sensors. The strong intrinsic antiferromagnetism and van der Waals layered structure exhibited by the bulk transition-metal oxychlorides provide a convenient system for the synthesis of such materials. In this work, we report the exfoliation of bulk FeOCl into and subsequent characterization of intrinsically antiferromagnetic thin layer FeOCl nanosheets. The magnetic properties of bulk FeOCl, its lithium intercalate, and its nanosheet pellet are measured to determine the evolution of magnetic properties from the three-dimensional to the quasi-two-dimensional system. This work establishes FeOCl and isostructural compounds as a source for the development of two-dimensional intrinsic antiferromagnets.

The emerging field of photonic nanoarchitectonics based on stimuli responsive 2D materials is highlighted with a focus on applications in colorimetric sensing.

The development of vapor sensors with tunable sensitivity and selectivity is highly desirable because of the manifold applications ranging from air quality monitoring to food control. The design of such sensors remains, however, a great challenge. Here, we address this challenge by intercalating primary and tertiary alkylamines with varying alkyl chain lengths into H3Sb3P2O14 nanosheet-based Fabry-Perot interference sensors. As the sensors are photonic in nature, the different amines can be distinguished based on their intercalation time and optical shift. Since the amines are protonated during intercalation and therefore trapped, this allows us to use amine modification as the basis for creating optical sensors. Intercalation of different amines gradually and widely tunes the sensor's sensitivity and selectivity to various analytes. This adjustment of sensing properties allows us to construct a sensor array on a single chip, which can distinguish different volatile organic compounds. The color change of this sensor array upon exposure to solvent vapors can be tracked with the naked eye, making this system a promising platform for the high-fidelity identification of volatile compounds. The sensor design protocol presented herein is straightforward and robust and can be transferred to other nanosheet-based devices for the rational tuning of their vapor-sensing properties and beyond.

This paper presents the design and fabrication of system-in-foil for relative humidity sensing. The sensors are based on electrochemical and capacitive principles. They are fabricated on flexible polymer substrates, which are used for ultrathin chip embedding. Microcontrollers and sensor readout ICs are embedded in polymer package using a foil assembly technology called ChipFilm Patch. A method for the verification of the chip embedding process is presented herein.The measured electrochemical sensor relative conductance sensitivity on the flexible substrate is about 368%. In addition, a 30-mm thick conventional capacitive sensor is fabricated on the polymer substrate, together with a humidity-insensitive reference capacitor. The measured sensor relative sensitivity is about 75% with a response time of about 6s. Finally, a sensor system-in-foil is demonstrated using discrete components of the ultra-thin capacitive sensor and a 30-mm thick capacitance-to-digital readout chip.

This paper presents relative humidity sensors based on electrochemical and capacitive principles. The sensors are fabricated on flexible polymer substrates, which are used for ultra-thin chip embedding. The electrochemical sensor consists of spin-coated nanosheets, which shown huge range (about 5 orders of magnitude) and fast response (<; 2 s). The sensor film thickness as well as ionic conductivity change upon moisture absorption. The measured sensor relative conductance change on the flexible substrate is 368%. In addition, a 3-pm thick conventional capacitive sensor is fabricated on the polymer substrate, together with a humidity-insensitive reference capacitor. The measured sensor relative sensitivity is about 75% with a response time of about 6 s. Finally, a sensor system-in-foil is demonstrated using discrete components of the ultra-thin capacitive sensor and a 30-pm thick capacitance-to-digital readout chip.

Harvesting the properties of nanosheets is not only crucial from a fundamental perspective, but also for the development of novel functional devices based on 2D nanosheets. Herein, we demonstrate the processing of organically modified TBAx H1-x Ca2 Nb3 O10 nanosheets into photonic thin films and study their colorimetric sensing properties in response to various aqueous and organic solvent vapors. Building on the enhanced solvent accessibility of TBA-containing nanosheets and their photocatalytic activity under UV irradiation, we develop a new concept for photocatalytic lithography using TBAx H1-x Ca2 Nb3 O10 nanosheets as a negative photoresist to obtain high-fidelity micron-scale patterns of robust inorganic nanosheets. Photocatalytic nanosheet lithography (PNL) therefore adds a new resist-free, resource efficient direct patterning technique to the toolbox of photolithography.

The discovery of 2D forms of matter, pioneered by graphene, has not only triggered new insights into fundamental physics but also pushed the limits of miniaturization. To process nanosheets into ultrathin functional devices, the development of scalable exfoliation routes is of key interest. Here, we demonstrate for the first time a mild, yet highly effective silver-ion-based exfoliation route for layered transition metal oxides. Single layer transition metal oxide nanosheets were obtained by applying silver ion exchange and subsequent treatment of the silver-intercalated phases with an aqueous suspension containing organic iodides. This generic exfoliation route can be widely applied also to acid-sensitive materials and allows the modification of the nanosheets with non-conventional organic ligands, which owing to their chemical functionality may be used to tailor the optoelectronic and surface properties of the nanosheet-ligand hybrid.

A new way towards single-layer nanosheets: The novel silver-assisted exfoliation route described in this work utilizes the formation of highly insoluble silver iodide as driving force for the exfoliation of silver transition metal oxides with organic iodides. This method not only broadens the scope of organic exfoliation agents but allows for the judicious introduction of functional ligands which can be used to tailor the properties of the nanosheets. Moreover, the silver-assisted route is exceptionally mild and hence may be used to exfoliate acid-sensitive systems, which are not accessible by conventional acid-assisted exfoliation protocols, thus enlarging the portfolio of existing nanosheets. More information can be found in the Communication by B. V. Lotsch et al. on page 411 in Issue 6, 2017 (DOI: 10.1002/cnma.201700067).

Rapid progress in the synthesis of nanostructures with tailor-made morphologies necessitates adequate analytical tools to unravel their physical properties. In our study, we investigate, on the nanometer scale, the band gap of individual [TBA(x)H(1-x)](+)[Ca2Nb3O10](-) nanosheets obtained through intercalation exfoliation of the layered bulk phase KCa2Nb3O10 with tetra-n-butylammonium hydroxide (TBAOH) using valence electron energy loss spectroscopy (VEELS) in the scanning transmission electron microscope (STEM). The nanosheets consist of an anionically charged perovskite layer with cationic organic ligands surrounding it. Because of the hybrid nature, a careful acquisition and analysis protocol is required since the nanosheets disintegrate easily under electron beam irradiation. The VEELS data reveal a fundamental band gap of an individual freely suspended perovskite nanosheet to be 2.9 +/- 0.2 eV and optically allowed transitions above 3.8 +/- 0.2 eV (optical band gap). The spatial resolution of the measurements is about 9 nm, taking into account 50% of the excitations when illuminating with an incident electron beam of 1 nm diameter. Our investigations reveal that the band gap of an individual nanosheet is not changed significantly compared to the bulk phase, which is confirmed by UV-vis data. This is rationalized by the quasi-2D electronic structure of the bulk material being preserved upon delamination.

We report on the humidity-induced swelling behavior of thin film devices composed of 2D phosphatoantimonate nanosheets and study their water uptake mechanism by means of ellipsometric porosimetry. Ambient humidity changes cause significant swelling in thin films composed of turbostratically disordered H3Sb3P2O14 nanosheets through water uptake between the nanosheet layers. This phenomenon is exploited to construct humidity responsive colorimetric sensors based on 1D Photonic Crystals. We demonstrate the ultrahigh sensitivity of H3Sb3P2O14/SiO2 Bragg stacks to ambient humidity, as well as reversible transparency switching as a consequence of refractive index matching at high relative humidities. The Photonic Crystals show substantially higher sensitivity to humidity as compared to ethanol vapor, reflecting the less favorable interaction of ethanol with the nanosheet layers as compared to water. Based on their ultrahigh sensitivity to humidity, phosphatoantimonate nanosheet based Bragg stacks can be used to track the motion of a finger by responding to its humidity sheath, without the finger touching the sensor surface. The cycling stability of such optical touchless positioning interfaces as well as the reversibility of the sensing event was demonstrated for more than 100 cycles. While the dew point presents an inherent lower limit to the sensor performance, the sensing ability remains essentially unaffected at elevated temperatures up to 40 degrees C.

A 2D nanosheet-based photonic nose for vapor identification is presented. A HSbP2 O8 nanosheet thin-film sensor with resistive readout is developed for the tracking of trace amounts of water, and a photonic HSbP2 O8 /TiO2 multilayer structure is effective at optically distinguishing between chemically similar solvent vapors through analyte-specific host-guest interactions.

An approach toward intercalant tunable nanosheet-based Fabry-Pérot sensors is presented. The intercalant tetrabutylammonium significantly increases the sensitivity of the photonic nose sensor to volatile organic compounds with increasing polarity, enabling polarity-driven color-coded vapor differentiation. Paired with the improved millisecond response times for polar vapors, vapor imaging with spatio-temporal resolution is within reach.

A new optical touchless positioning interface based on ultrasensitive humidity responsive 1D photonic crystals utilizing the giant moisture dependent swelling capacity of 2D phosphatoantimonate nanosheets is presented. The spatially confined, full spectral color change combined with reversible transparency switching induced by the humidity sheath of a human finger allows for real time, true color lateral finger motion tracking under touchless conditions.

Nanocrystalline cellulose (NCC) is an abundant biogenic nanomaterial with unique properties that enables the efficient synthesis of mesoporous crystalline titania. We significantly enhance the photocatalytic activity of titania thin films by introducing solvothermally synthesized preformed anatase nanoparticles into a sol-gel based biotemplated titania scaffold. The resulting dual source titania thin films containing different amounts of preformed crystalline species were investigated by time-resolved microwave conductivity (TRMC) measurements and tested in the photocatalytic conversion of 4-chlorophenol. The gradual addition of preformed nanopartides leads to a consistent increase of the mean size of titania crystalline domains, whereas the porosity of the composite is well-preserved due to the shapepersistent nature of the NCC template. Microwave conductivity studies establish increased photoconductivity of the films containing preformed anatase nanoparticles in comparison to that of films made without the nanoparticles. The synergistic features of the dual source titania, namely the improved crystalline properties brought by the preformed nanocrystals in combination with the high surface area provided by the NCC-templated sol-gel titania, result in a very high photocatalytic activity of the films in the photocatalytic decomposition of 4-chlorophenol. In quantitative terms, the dual source titania films prepared with 75% nanoparticles exhibit a first order degradation rate constant of 0.53 h(-1) (1.47 x 10(-4) sec(-1)), which strongly outperforms the activity of commercial P90 nanopowder showing a rate constant of 0.17 h(-1) (0.47 x 10(-4) sec(-1)) under the same conditions.

Solid solutions (Ge1−xSnxTe)nSb2Te3 (n=4, 7, 12; 0≤x≤1) represent stable high-temperature phases and can be obtained as metastable compounds by quenching. High-resolution transmission electron microscopy reveals that the quenched (pseudo-)cubic materials exhibit parquet-like nanostructures comparable to, but especially for n=4 more pronounced than in (GeTe)nSb2Te3 (GST materials). The temperature-dependent phase transitions are comparable; however, substitution with Sn significantly lowers the transition temperatures between cubic high-temperature phase and the long range ordered layered phases that are stable at ambient conditions. In addition, the metrics of the quenched Sn-containing materials remains closer to cubic, especially for samples with n=7 or 12. For samples with high defect concentrations (n=4, 7), Sn-substituted samples exhibit electrical conductivities up to 3 times higher than those of corresponding GST materials. Since the difference in thermal conductivity is much less pronounced, this results in a doubling of the thermoelectric figure of merit (ZT) at high temperatures for (Ge0.5Sn0.5Te)4Sb2Te3 as compared to (GeTe)4Sb2Te3. Sn doping in (GeTe)7Sb2Te3 increases the ZT value by a factor of up to 4 which is also due to an increased Seebeck coefficient.

AbstractLow‐ and high‐temperature (lt, ht) modifications of AlPS4 are prepared by solid state reaction of AlP and 10% excess S (evacuated silica tubes, 923 K, 30 d for the lt modification, 1023 K, 30 d, for the ht modification).