The initial stages of the atomic layer deposition of metal-sulfide thin films are hindered by delayed nucleation and poor film continuity. The present work explores the nucleation of gallium sulfide (GaSx) films using hexakis(dimethylamino)digallium and H2S as precursors. Smooth amorphous GaSx layers were deposited, with their composition confirmed by XPS and their structure examined by TEM. Postdeposition annealing in H2S was attempted to induce crystallinity. To address the nucleation barrier, a novel surface functionalization strategy was developed: replacing surface hydroxyl groups with sulfur-containing species prior to deposition. Different functionalization treatments were tested, which significantly enhanced nucleation, as demonstrated by accelerated initial growth and improved film uniformity even at low cycle numbers. These results establish chemically specific surface functionalization as an effective strategy to promote controlled nucleation of sulfide thin films.

Infrared spectroscopy is a very popular measurement technique presently, especially in healthcare, agriculture, and food industry. NIR LEDs have high efficiencies, but narrow wavelengths, therefore they are suitable for measurements at a certain wavelength. GaInAsP/InP is an ideal material system for the fabrication of double heterostructure LED devices with tuneable emission wavelengths. The present study addresses the need when a broader emission-peak is preferred for spectroscopic applications. An LED structure is covered by photoluminescent layers grown epitaxially by liquid phase epitaxy. The primary light of the active layer excites the further layers which emit photoluminescent radiation. The partly transmitted primary and the secondary lights together result in a broader spectrum. This work presents NIR LEDs with wide emission spectra which cover the entire NIR range based on multiple photon-recycling photoluminescent layers. This type of NIR light source could replace the incandescent light sources on account of their small dimensions, high efficiency, and low power consumption, which is critical in small, handheld NIR spectroscopy devices.

A compact electrochemical sensor module for pH detection was developed for potential integration into specialized devices used for live cell or tissue incubation, for applications in highly parallelized cell culture analysis, by incorporating Organ-on-Chip devices. This research focuses on the deposition, structural and chemical analysis, and functional characterization of different titanium-oxide layers with various compositions as potentially sensitive materials for pH sensing applications. The titanium-oxide layers were deposited using vacuum sputtering and atomic layer deposition at 100 °C and 300 °C, respectively. Transmission electron microscopy and X-ray photoelectron spectroscopy were utilized to determine the specific composition and structure of different titanium-oxide layers. These TiOx-functionalized electrodes were connected to the application-specific analog front-end chip of the low-power readout circuit for precise evaluation. The pH sensitivity of the differently modified electrodes, employing various TiOx materials, was evaluated using pH calibration solutions ranging from pH 6 to 8. Among the various deposition solutions, such as sputtering or high-temperature atomic layer deposition, the TiOx layer deposited using low-temperature atomic layer deposition proved more suitable for pH sensing applications, with a sensitivity of 54.8–56.7 mV/pH, which closely approximates the Nernstian response.

The present paper reports on the atomic layer deposition of vanadium sulfide (VS) layers from tetrakis(ethylmethylamino)vanadium and H2S. The deposition of VS layers with these precursors has proven possible between 200 and 300 °C. The prepared layers were amorphous, but a postdeposition annealing in H2S atmosphere yielded crystalline VS layers. The use of this precursor combination has so far not been reported.

The nucleation and growth of atomic layer deposited (ALD) vanadium oxide and sulfide layers were examined on the surface of sapphire and silicon. The growth of vanadium oxide was layer by layer on sapphire, but islandlike on silicon. The stable growth rates could be derived from the steric hindrance of the precursor molecules. The nucleation of vanadium sulfide was always islandlike. The merging of the islands, and, thus, continuous film growth, could be achieved by enhancing the surface active sites by chemical pretreatments, as well as by starting the ALD growth by longer cycles. With the combination of these approaches, ultrathin continuous VO2 and VS layers could be grown. The nucleation was also modeled mathematically, and the unknown starting boundary conditions could be derived from the model fitting.

Complex biological photocatalytic heteronanostructures were produced by the integration of different multicomponent Au–Cu2O nanoparticles (NPs) into the blue-colored photonic nanoarchitectures occurring in the wings of male Polyommatus icarus butterflies. Both bare wings and wings conformally coated by 15-nm ZnO by atomic layer deposition were used as substrates. The NPs were characterized by UV–visible spectroscopy, focus stacking optical microscopy, and electron microscopy. After the deposition of the different NPs, the photocatalytic performance of the samples under visible light illumination was tested by the photodegradation of methyl orange in aqueous solution monitored continuously by an immersion probe. It was found that the components of the biological hetero-nanoarchitecture: ZnO-coated wings and wings without ZnO with deposited NPs exhibited poor catalytic performance. But the combined system: ZnO-coated wings with NPs deposited onto them exhibited sixfold to eightfold increase in their catalytic performance. This increase is attributed to the extension of the ZnO absorption into the visible range and to the formation of the heterojunction between the n-type ZnO and the p-type Cu2O NPs which resulted in the charge transfer of the photogenerated carriers. As the samples exhibited good stability under the continuous magnetic stirring, they can be used in flow-through systems suitable for wastewater remediation. The biological templates for the hetero-nanoarchitectures were produced by the controlled breeding of herbivorous insects, which does not raise any environmental concerns.

Atomic layer deposition was used to grow epitaxial iron sulfide layers on alpha-Al2O3 substrates. According to the transmission electron microscopic measurements, these Fe-sulfide films had 1C pyrrhotite structure (Fe1-xS). In the case of pyrrhotite materials, both the magnetic and electric properties depend significantly on their iron content and on the ordering of iron vacancies. By tuning the parameters of the atomic layer deposition method, the structure of epitaxial pyrrhotite films could be controlled, thus the electronic properties of the Fe1-xS films could be influenced: At deposition temperatures below 350 degrees C, the structure contained many faults, and the layers were n type semiconductors, while at higher temperatures, the resulting films were p-type with excellent crystalline structures with disordered vacancies. A post deposition annealing could further improve the crystallinity and induce p-type conductivity.

A compact pH measuring electrochemical sensor module was developed for Smart Multi-Well Plates (SMWP) applicable for highly parallelized cell culture analysis using incorporated Organ-on-Chip devices. A specific electronic architecture was designed and manufactured containing an extended gate field effect transistor as the transducer device. Electrochemical electrodes were functionalized using pH sensitive metal-oxides and applied as the gate material. The composition and the related pH sensitivity of differently deposited materials were characterized and the suitability of ALD-deposited, non-stoichiometric titanium oxide (TiOx) for sensitive pH measurement was verified showing excellent responses close to the ideal Nernstian slope (59 mV/pH).

Photonic nanoarchitectures of butterfly wings can serve as biotemplates to prepare semiconductor thin films of ZnO by atomic layer deposition. The resulting biotemplated ZnO nanoarchitecture preserves the structural and optical properties of the natural system, while it will also have the features of the functional material. The ZnO-coated wings can be used directly in heterogeneous photocatalysis to decompose pollutants dissolved in water upon visible light illumination. We used the photonic nanoarchitectures of different Morpho butterflies with different structural colors as biotemplates and examined the dependence of decomposition rates of methyl orange and rhodamine B dyes on the structural color of the biotemplates and the thickness of the ZnO coating. Using methyl orange, we measured a ten-fold increase in photodegradation rate when the 20 nm ZnO-coated wings were compared to similarly coated glass substrates. Using rhodamine B, a saturating relationship was found between the degradation rate and the thickness of the deposited ZnO on butterfly wings. We concluded that the enhancement of the catalytic efficiency can be attributed to the slow light effect due to a spectral overlap between the ZnO-coated Morpho butterfly wings reflectance with the absorption band of dyes, thus the photocatalytic performance could be changed by the tuning of the structural color of the butterfly biotemplates. The photodegradation mechanism of the dyes was investigated by liquid chromatography–mass spectroscopy.

The present work explores the atomic layer deposition (ALD) of VO2 layers for resistive switching applications. Tetrakis (ethylmethylamino)vanadium (TEMAV) precursor was used combined with different oxidants, deposition temperatures, and annealing procedures, and the structural and electrical properties of the layers were analysed. All the as-deposited layers were amorphous, but an annealing in oxygen containing atmosphere at temperatures exceeding 400 degrees C yielded pure and crystalline VO2 layers. The thus prepared films are compact with crystallite sizes between 50 and 100 nm, displaying excellent electrical switching properties, with their resistivity decreasing 3 orders of magnitude at 68 degrees C.

The photocatalytic activity of a flat surface can be increased by micro- and nanostructuring the interface to increase the area of the contact surface between the photocatalyst and the solute, and moreover, to optimize charge carrier transfer. Further enhancement can be achieved by using photonic nanostructures, which exhibit photonic band gap (PBG). Structurally coloured butterfly wings offer a rich ‘library’ of PBGs in the visible spectral range which can be used as naturally tuned sample sets for biotemplating. We used conformal atomic layer deposition of ZnO on the wings of various butterfly species ( Arhopala asopia , Hypochrysops polycletus , Morpho sulkowskyi , Polyommatus icarus ) possessing structural colour extending from the near UV to the blue wavelength range, to test the effects arising from the nanostructured surfaces and from the presence of different types of PBGs. Aqueous solutions of rhodamine B were used to test the enhancement of photocatalytic activity that was found for all ZnO-coated butterfly wings. The best reaction rate of decomposing rhodamine B when illuminated with visible light was found in 15 nm ZnO coated M. sulkowskyi wing, the reflectance of which had the highest overlap with the absorption band of the dye and had the highest reflectance intensity.

Mechanical characterization of quasi one-dimensional nanostructures is essential for the design of novel nanoelectromechanical systems. However, the results obtained on basic mechanical quantities, such as Young’s modulus and fracture strength, show significant standard deviation in the literature. This is partly because of diversity in the quality of the nanowire, and partly because of inappropriately performed mechanical tests and simplified mechanical models. Here we present orientation-controlled bending and fracture studies on wet chemically grown vertical ZnO nanowires, using lateral force microscopy. The lateral force signal of the atomic force microscope was calibrated by a diamagnetic levitation spring system. By acquiring the bending curves of 14 nanowires, and applying a two-segment mechanical model, an average bending modulus of 108 ± 17 GPa was obtained, which was 23% lower than the Young’s modulus of bulk ZnO in the [0001] direction. It was also found that the average fracture strain and stress inside the nanowire was above 3.1 ± 0.3 % and 3.3 ± 0.3 GPa, respectively. However, the fracture of the nanowires was governed by the quality of the nanowire/substrate interface. The demonstrated technique is a relatively simple and productive way for the accurate mechanical characterization of vertical nanowire arrays.

HfS2 has recently emerged as a promising 2D semiconductor, but the lack of a reliable method to produce continuous films on a large scale has hindered its spreading. The atomic layer deposition of the material with the precursor tetrakis-dimethylamino-hafnium with H2S is a relatively novel solution to this problem. This paper shows that it is a facile approach to synthesizing homogeneous and smooth HfS2 layers in a controlled and reproducible manner. The deposition is examined at different temperatures and layer thicknesses, exploring the ALD window of the deposition and the chemical, morphological and electronic properties of the films. The method yielded films with wafer-sized uniformity and controlled properties and is, thus, a promising way to prepare this important transition metal dichalcogenide material.

Solar radiation is a cheap and abundant energy for water remediation, hydrogen generation by water splitting, and CO2 reduction. Supported photocatalysts have to be tuned to the pollutants to be eliminated. Spectral engineering may be a handy tool to increase the efficiency or the selectivity of these. Photonic nanoarchitectures of biological origin with hierarchical organization from nanometers to centimeters are candidates for such applications. We used the blue wing surface of laboratory-reared male Polyommatus icarus butterflies in combination with atomic layer deposition (ALD) of conformal ZnO coating and octahedral Cu2O nanoparticles (NP) to explore the possibilities of engineering the optical and catalytic properties of hybrid photonic nanoarchitectures. The samples were characterized by UV-Vis spectroscopy and optical and scanning electron microscopy. Their photocatalytic performance was benchmarked by comparing the initial decomposition rates of rhodamine B. Cu2O NPs alone or on the butterfly wings, covered by a 5 nm thick layer of ZnO, showed poor performance. Butterfly wings, or ZnO coated butterfly wings with 15 nm ALD layer showed a 3 to 3.5 times enhancement as compared to bare glass. The best performance of almost 4.3 times increase was obtained for the wings conformally coated with 15 nm ZnO, deposited with Cu2O NPs, followed by conformal coating with an additional 5 nm of ZnO by ALD. This enhanced efficiency is associated with slow light effects on the red edge of the reflectance maximum of the photonic nanoarchitectures and with enhanced carrier separation through the n-type ZnO and the p-type Cu2O heterojunction. Properly chosen biologic photonic nanoarchitectures in combination with carefully selected photocatalyst(s) can significantly increase the photodegradation of pollutants in water under visible light illumination.

Due to its remarkable switching effect in electrical and optical properties, VO2 is a promising material for several applications. However, the stoichiometry control of multivalent vanadium oxides, especially with a rational deposition technique, is still challenging. Here, we propose and optimize a simple fabrication method for VO2 rich layers by the oxidation of metallic vanadium in atmospheric air. It was shown that a sufficiently broad annealing time window of 3.0–3.5 h can be obtained at an optimal oxidation temperature of 400 °C. The presence of VO2 was detected by selected area diffraction in a transmission electron microscope. According to the temperature dependent electrical measurements, the resistance contrast (R30 °C/R100 °C) varied between 44 and 68, whereas the optical switching was confirmed using in situ spectroscopic ellipsometric measurement by monitoring the complex refractive indices. The obtained phase transition temperature, both for the electrical resistance and for the ellipsometric angles, was found to be 49 ± 7 °C, i.e., significantly lower than that of the bulk VO2 of 68 ± 6 °C.

The modification of photonic nanoarchitectures occurring in butterfly wing scales with different nanostructures was investigated experimentally and by modeling. Single crystalline, polycrystalline, simple thin film, and pepper-pot-type photonic nanoarchitectures in the wing scales of different butterflies were investigated. By atomic layer deposition (ALD) (additive) the color of all nanoarchitectures was red shifted and by plasma etching (subtractive) the color of all nanoarchitectures was blue shifted in a controllable way. Langmuir-Blodgett multilayers of silica nanospheres were used as physical models. ALD produced color shifts similar to those for butterfly wings. In the case of a simple thin film, a theoretical calculation reproduced the spectral alterations well. For the more complex photonic nanoarchitectures, the general trends of the modifications were well reproduced by more sophisticated models, but differences in the magnitude of the alterations were found, attributed to the complex, random porous structures of the pepper-pot-type structures.

The present work focuses on the atomic layer deposition (ALD), annealing, and Zn doping of gallium oxide (Ga2O3) films using a novel Ga precursor, hexakis-dimethylamino-digallium. As ALD deposited Ga2O3 films are always amorphous, the optimal annealing procedure had to be found to achieve crystalline β-Ga2O3. The bandgaps and dielectric properties of the layers were measured and the effects of the deposition parameters and postdeposition annealing on the electrical properties were determined. The effects of Zn doping on the electrical properties were analyzed, and some crucial issues for application as a UV sensor were addressed.

In this work, the photocatalytic properties of amorphous and crystalline TiO2 deposited on oxide and polymer nanoparticles by atomic layer deposition (ALD) were studied. Beside TiO2, as reference, both ALD grown amorphous Al2O3 and crystalline ZnO layers were also examined. When choosing the carrier, the priority was that it had no effect on the photocatalytic activity of TiO2; therefore the oxide layers were deposited on SiO2 and poly(methyl-methacrylate) (PMMA) nanoparticles. The amorphous SiO2 particles were synthetized by the Stöber method, while the PMMA particles were prepared by emulsion polymerization. Both the bare and core/shell composite nanoparticles were investigated by SEM-EDX, TEM, FT-IR, and XRD. Finally, the photocatalytic activity of PMMA, SiO2 and the core/shell nanoparticles was measured by the decomposition of methylene orange, monitored by UV-Vis spectroscopy. Based on the results, the SiO2 was uniformly coated with the deposited oxide films, while in the case of the PMMA a contiguous web-like polymer/TiO2 matrix was formed. During the photocatalytic reactions, the amorphous Al2O3 was not active, while the crystalline ZnO and TiO2 showed good photocatalytic activity. The amorphous TiO2 deposited by ALD on the SiO2 and PMMA nanoparticles had smaller, but a clearly detectable photocatalytic effect on the photodegradation of methylene orange.

Ga doped ZnO films were deposited at low temperature with atomic layer deposition at different temperatures with the novel precursor, hexakis (dimethylamino)gallium. The ZnO films prepared at 300 degrees C on GaN substrates are epitaxial, but the Ga doping deteriorates the crystallinity: the doped films are oriented polycrystalline. The films deposited at lower temperatures are polycrystalline in all cases. Post deposition annealing procedures were applied which improved the crystallinity of the layer and increased the mobility of the films.

Pure MgO, 1 and 10 at% Mg-doped ZnO layers were grown by atomic layer deposition technique onto (001)-oriented alpha-Al2O3 and GaN substrates. The structure and the microstructure of the deposited layers were studied by TEM in detail. The pure MgO layer starts to grow with epitaxy with (100)-type defects that transforms to random orientation. In the 10 at% Mg-doped samples epitaxial cubic MgO buffer layer forms at the interface. This buffer layer helps the ZnO to grow epitaxially in the case of alpha-Al2O3 substrate forming a ZnO/MgO/c-plane alpha-Al2O3 hetero-structure showing higher mobility with lower carrier concentration, while in the case on GaN substrate the ZnO is strongly textured. Consequently for higher concentration Mg doping (with the formation of MgO buffer layer) alpha-Al(2)O(3 )is better choice to grow epitaxial ZnO layer. The 1 at% Mg-doping of the epitaxial ZnO layer grown onto GaN substrate was successfully implemented, while in the case of alpha-Al2O3 substrate a thin cubic MgO buffer layer forms. This shows that the success of low concentration Mg doping in ZnO largely depends on the choice of substrate material as well.