Ultralow Catalytic Loading for Optimised Electrocatalytic Performance of AuPt Nanoparticles to Produce Hydrogen and Ammonia.

The hydrogen evolution and nitrite reduction reactions are key to producing green hydrogen and ammonia. Antenna-reactor nanoparticles hold promise to improve the performances of these transformations under visible-light excitation, by combining plasmonic and catalytic materials. However, current materials involve compromising either on the catalytic activity or the plasmonic enhancement and also lack control of reaction selectivity. Here, we demonstrate that ultralow loadings and non-uniform surface segregation of the catalytic component optimize catalytic activity and selectivity under visible-light irradiation. Taking Pt-Au as an example we find that fine-tuning the Pt content produces a 6-fold increase in the hydrogen evolution compared to commercial Pt/C as well as a 6.5-fold increase in the nitrite reduction and a 2.5-fold increase in the selectivity for producing ammonia under visible light excitation relative to dark conditions. Density functional theory suggests that the catalytic reactions are accelerated by the intimate contact between nanoscale Pt-rich and Au-rich regions at the surface, which facilitates the formation of electron-rich hot-carrier puddles associated with the Pt-based active sites. The results provide exciting opportunities to design new materials with improved photocatalytic performance for demanding sustainable energy applications.

Atomic Layer Deposition of ScF3 and ScxAlyFz Thin Films.

In this paper, we present an ALD process for ScF3 using Sc(thd)3 and NH4F as precursors. This is the first material made by ALD that has a negative thermal expansion over a wide-temperature range. Crystalline films were obtained at the deposition temperatures of 250-375 °C, with a growth per cycle (GPC) increasing along the deposition temperature from 0.16 to 0.23 Å. Saturation of the GPC with respect to precursor pulses and purges was studied at 300 °C. Saturation was achieved with Sc(thd)3, whereas soft saturation was achieved with NH4F. The thickness of the films grows linearly with the number of applied ALD cycles. The F/Sc ratio is 2.9:3.1 as measured by ToF-ERDA. The main impurity is hydrogen with a maximum content of 3.0 at %. Also carbon and oxygen impurities were found in the films with maximum contents of 0.5 and 1.6 at %. The ScF3 process was also combined with an ALD AlF3 process to deposit ScxAlyFz films. In the AlF3 process, AlCl3 and NH4F were used as precursors. It was possible to modify the thermal expansion properties of ScF3 by Al3+ addition. The ScF3 films shrink upon annealing, whereas the ScxAlyFz films show thermal expansion, as measured with HTXRD. The thermal expansion becomes more pronounced as the Al content in the film is increased.

Reductive Thermal Atomic Layer Deposition Process for Gold.

In this work, we developed an atomic layer deposition (ALD) process for gold metal thin films from chloro(triethylphosphine)gold(I) [AuCl(PEt3)] and 1,4-bis(trimethylgermyl)-1,4-dihydropyrazine [(Me3Ge)2DHP]. High purity gold films were deposited on different substrate materials at 180 °C for the first time with thermal reductive ALD. The growth rate is 1.7 Å/cycle after the film reaches full coverage. The films have a very low resistivity close to the bulk value, and a minimal amount of impurities could be detected. The reaction mechanism of the process is studied in situ with a quartz crystal microbalance and a quadrupole mass spectrometer.

Atomic layer deposition of CoF2, NiF2 and HoF3 thin films.

The present study describes atomic layer deposition (ALD) processes and characterization of CoF2, NiF2, and HoF3 thin films. For CoF2 deposition CoCl2(TMEDA) (TMEDA = N,N,N',N'-tetramethylethylenediamine) and NH4F were used as precursors. CoF2 deposition was studied at 180-275 °C, resulting in a growth per cycle (GPC) of 0.7 to 1.2 Å. All the films consist of tetragonal CoF2 according to XRD. The impurity contents were measured with ToF-ERDA and less than 1 at% of N and Cl were detected in the films, indicating effective reactions. In addition, the F/Co ratio is close to 2 as measured by the same method. The saturation of the GPC with respect to precursor pulses and purges was verified at 250 °C. The common feature of ALD metal fluoride films - remarkable roughness - is encountered also in this process. However, the films became smoother as the deposition temperature was increased. CoF2 deposition was also demonstrated on graphite substrates. NiF2 deposition was studied at 210-250 °C by using Ni(thd)2 and TaF5 or a new fluoride source NbF5 as the precursors. Tetragonal NiF2 was obtained, but the oxygen and hydrogen contents in the films were remarkable, up to ∼11 at%, as measured by ToF-ERDA. This was observed also when the films were in situ capped with YF3. NbF5 was shown to be a potential fluoride precursor by combining it with Ho(thd)3 to deposit HoF3 films. Orthorhombic HoF3 was obtained at deposition temperatures of 200-275 °C. The films deposited at 235-275 °C are pure, and the Nb contents in films deposited at 250 and 275 °C are only 0.21 and 0.15 at%. The main impurity in both films is oxygen, but the contents are only 1.5 and 1.6 at%. The saturation of the GPC with respect to precursor pulses was verified at 250 °C. The GPC is ∼1 Å.

Inherent area-selective atomic layer deposition of ZnS.

Atomic layer deposition processes with inherent substrate selectivity are more straightforward for area-selective atomic layer deposition (AS-ALD) than approaches using surface passivation or activation with self-assembled monolayers (SAMs), small molecule inhibitors (SMIs) or seed layers. Here, ALD of ZnS using elemental zinc and sulfur as precursors is reported to have excellent inherent selectivity. At 400-500 °C for 250 cycles, substantial ZnS growth was observed on Ti and TiO2 surfaces while no growth was measured on native SiO2 and Al2O3 surfaces. On TiO2, the ZnS growth rate remains constant at 1.0 Å per cycle at temperatures of 400-500 °C. On Ti, in contrast, the initial growth rate increases significantly from 1.2 Å per cycle at 350 °C to 6.2 Å per cycle at 500 °C. The high growth rates on Ti are believed to be caused by CVD-like growth during the early ALD cycles, arising from the reservoir effect of the Ti layer for Zn atoms. After the first 100 cycles, the growth rate decreases from 3.5 to 1.0 Å per cycle, the same as the growth rate on TiO2. Selective adsorption of sulfur on TiO2 over Al2O3 and SiO2 is assumed to be the selectivity mechanism on TiO2. Self-aligned deposition of ZnS was successfully demonstrated on a micrometer-scale Ti/native SiO2 pattern and on a nanometer-scale TiO2/Al2O3 pattern at 450 °C for 250 cycles; ZnS films with a thickness of ∼80 nm were selectively deposited on Ti over native SiO2, and ZnS films with a thickness of ∼23 nm were selectively deposited on TiO2 over Al2O3.

Monocyte Differentiation on Atomic Layer-Deposited (ALD) Hydroxyapatite Coating on Titanium Substrate.

Hydroxyapatite (HA; Ca10(PO4)6(OH)2) coating of bone implants has many beneficial properties as it improves osseointegration and eventually becomes degraded and replaced with new bone. We prepared HA coating on a titanium substrate with atomic layer deposition (ALD) and compared monocyte differentiation and material resorption between ALD-HA and bone. After stimulation with macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor kappa-B ligand (RANKL), human peripheral blood monocytes differentiated into resorbing osteoclasts on bovine bone, but non-resorbing foreign body cells were observed on ALD-HA. The analysis of the topography of ALD-HA and bone showed no differences in wettability (water contact angle on ALD-HA 86.2° vs. 86.7° on the bone), but the surface roughness of ALD-HA (Ra 0.713 µm) was significantly lower compared to bone (Ra 2.30 µm). The cellular reaction observed on ALD-HA might be a consequence of the topographical properties of the coating. The absence of resorptive osteoclasts on ALD-HA might indicate inhibition of their differentiation or the need to modify the coating to induce osteoclast differentiation.

Laboratory-scale X-ray absorption spectroscopy of 3d transition metals in inorganic thin films.

In this paper we present laboratory-scale X-ray absorption spectroscopy applied to the research of nanometer-scale thin films. We demonstrate the Cu K edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) of CuI and CuO thin films grown with atomic layer deposition. Film thicknesses in the investigated samples ranged from 12 to 248 nm. Even from the thinnest films, XANES spectra can be obtained in 5-20 minutes and EXAFS in 1-4 days. In order to prove the capability of laboratory-based XAS for in situ measurements on thin films, we demonstrate an experiment on in situ oxidation of a 248 nm thick CuI film at a temperature of 240 °C. These methods have important implications for novel and enhanced possibilities for inorganic thin film research.

Toposelective vapor deposition of hybrid and inorganic materials inside nanocavities by polymeric templating and vapor phase infiltration.

Selective deposition of hybrid and inorganic materials inside nanostructures could enable major nanotechnological advances. However, inserting ready-made composites inside nanocavities may be difficult, and therefore, stepwise approaches are needed. In this paper, a poly(ethyl acrylate) template is grown selectively inside cavities via condensation-controlled toposelective vapor deposition, and the polymer is then hybridized by alumina, titania, or zinc oxide. The hybridization is carried out by infiltrating the polymer with a vapor-phase metalorganic precursor and water vapor either via a short-pulse (atomic layer deposition, ALD) or a long-pulse (vapor phase infiltration, VPI) sequence. When the polymer-MO x hybrid material is calcined at 450 °C in air, an inorganic phase is left as the residue. Various suspected confinement effects are discussed. The infiltration of inorganic materials is reduced in deeper layers of the cavity-grown polymer and is dependent on the cavity geometry. The structure of the inorganic deposition after calcination varies from scattered particles and their aggregates to cavity-capping films or cavity-filling low-density porous deposition, and the inorganic deposition is often anisotropically cracked. A large part of the infiltration is achieved already during the short-pulse experiments with a commercial ALD reactor. Furthermore, the infiltrated polymer is more resistant to dissolution in acetone whereas the inorganic component can still be heavily affected by phosphoric acid.

Atomic layer deposition of PbCl2, PbBr2 and mixed lead halide (Cl, Br, I) PbXnY2-n thin films.

Atomic layer deposition offers outstanding film uniformity and conformality on substrates with high aspect ratio features. These qualities are essential for mixed-halide perovskite films applied in tandem solar cells, transistors and light-emitting diodes. The optical and electronic properties of mixed-halide perovskites can be adjusted by adjusting the ratios of different halides. So far ALD is only capable of depositing iodine-based halide perovskites whereas other halide processes are lacking. We describe six new low temperature (≤100 °C) ALD processes for PbCl2 and PbBr2 that are crucial steps for the deposition of mixed-halide perovskites with ALD. Lead bis[bis(trimethylsilyl)amide]-GaCl3 and -TiBr4 processes yield the purest, crystalline, uniform and conformal films of PbCl2 and PbBr2 respectively. We show that these two processes in combination with a PbI2 process from the literature deposit mixed lead halide films. The four less optimal processes revealed that reaction by-products in lead halide deposition processes may cause film etching or incorporate themselves into the film.

A low-temperature thermal ALD process for nickel utilizing dichlorobis(triethylphosphine)nickel(II) and 1,4-bis(trimethylgermyl)-1,4-dihydropyrazine.

In this work, we developed a new ALD process for nickel metal from dichlorobis(triethylphosphine)nickel(II) (NiCl2(PEt3)2) and 1,4-bis(trimethylgermyl)-1,4-dihydropyrazine ((Me3Ge)2DHP). A series of phosphine adducts of nickel and cobalt halides were synthesized and characterized for their volatility and thermal stability. Also (Me3Ge)2DHP is a novel reducing agent in ALD. Smooth nickel films were deposited on different substrate materials at 110 °C, which is the lowest deposition temperature for Ni metal found in the literature. The growth rate is 0.2 Å per cycle when the film is not continuous and decreases to 0.1 Å per cycle after the film becomes pinhole-free. Besides a small amount (7 at%) of carbidic carbon, the films have only small amounts of impurities. Most notably, the chlorine content is below 0.2 at%, indicating efficient reduction. Furthermore, we think that (Me3Ge)2DHP can open new avenues for the ALD of other metals at low temperatures.

Osteoblast Attachment on Titanium Coated with Hydroxyapatite by Atomic Layer Deposition.

BACKGROUND: The increasing demand for bone implants with improved osseointegration properties has prompted researchers to develop various coating types for metal implants. Atomic layer deposition (ALD) is a method for producing nanoscale coatings conformally on complex three-dimensional surfaces. We have prepared hydroxyapatite (HA) coating on titanium (Ti) substrate with the ALD method and analyzed the biocompatibility of this coating in terms of cell adhesion and viability. METHODS: HA coatings were prepared on Ti substrates by depositing CaCO3 films by ALD and converting them to HA by wet treatment in dilute phosphate solution. MC3T3-E1 preosteoblasts were cultured on ALD-HA, glass slides and bovine bone slices. ALD-HA and glass slides were either coated or non-coated with fibronectin. After 48h culture, cells were imaged with scanning electron microscopy (SEM) and analyzed by vinculin antibody staining for focal adhesion localization. An 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) test was performed to study cell viability. RESULTS: Vinculin staining revealed similar focal adhesion-like structures on ALD-HA as on glass slides and bone, albeit on ALD-HA and bone the structures were thinner compared to glass slides. This might be due to thin and broad focal adhesions on complex three-dimensional surfaces of ALD-HA and bone. The MTT test showed comparable cell viability on ALD-HA, glass slides and bone. CONCLUSION: ALD-HA coating was shown to be biocompatible in regard to cell adhesion and viability. This leads to new opportunities in developing improved implant coatings for better osseointegration and implant survival.

Highly conductive and stable Co9S8 thin films by atomic layer deposition: from process development and film characterization to selective and epitaxial growth.

Co9S8 is an interesting sulfide material with metallic conductivity that has shown promise for various energy applications. Herein, we report a new atomic layer deposition process producing crystalline, pure, and highly conductive Co9S8 thin films using CoCl2(TMEDA) (TMEDA = N,N,N',N'-tetramethylethylenediamine) and H2S as precursors at 180-300 °C. The lowest resistivity of 80 µΩ cm, best uniformity, and highest growth rate are achieved at 275 °C. Area-selective deposition is enabled by inherent substrate-dependency of film nucleation. We show that a continuous and conductive Co9S8 film can be prepared on oxide-covered silicon without any growth on Si-H. Besides silicon, Co9S8 films can be grown on a variety of substrates. The first example of an epitaxial Co9S8 film is shown using a GaN substrate. The Co9S8 films are stable up to 750 °C in N2, 400 °C in forming gas, and 225 °C in O2 atmosphere. The reported ALD process offers a scalable and cost-effective route to high-quality Co9S8 films, which are of interest for applications ranging from electrocatalysis and rechargeable batteries to metal barrier and liner layers in microelectronics and beyond.

Synchronizing gas injections and time-resolved data acquisition for perturbation-enhanced APXPS experiments.

An experimental approach is described in which well-defined perturbations of the gas feed into an Ambient Pressure X-ray Photoelectron Spectroscopy (APXPS) cell are fully synchronized with the time-resolved x-ray photoelectron spectroscopy data acquisition. These experiments unlock new possibilities for investigating the properties of materials and chemical reactions mediated by their surfaces, such as those in heterogeneous catalysis, surface science, and coating/deposition applications. Implementation of this approach, which is termed perturbation-enhanced APXPS, at the SPECIES beamline of MAX IV Laboratory is discussed along with several experimental examples including individual pulses of N2 gas over a Au foil, a multi-pulse titration of oxygen vacancies in a pre-reduced TiO2 single crystal with O2 gas, and a sequence of alternating precursor pulses for atomic layer deposition of TiO2 on a silicon wafer substrate.

Oxidative MLD of Conductive PEDOT Thin Films with EDOT and ReCl5 as Precursors.

Because of its high conductivity and intrinsic stability, poly(3,4-ethylenedioxythiophene (PEDOT) has gained great attention both in academic research and industry over the years. In this study, we used the oxidative molecular layer deposition (oMLD) technique to deposit PEDOT from 3,4-ethylenedioxythiophene (EDOT) and a new inorganic oxidizing agent, rhenium pentachloride (ReCl5). We extensively characterized the properties of the films by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), Raman, and conductivity measurements. The oMLD of polymers is based on the sequential adsorption of the monomer and its oxidation-induced polymerization. However, oMLD has been scarcely used because of the challenge of finding a suitable combination of volatile, reactive, and stable organic monomers applicable at high temperatures. ReCl5 showed promising properties in oMLD because it has high thermal stability and high oxidizing ability for EDOT. PEDOT films were deposited at temperatures of 125-200 °C. EDS and XPS measurements showed that the as-deposited films contained residues of rhenium and chlorine, which could be removed by rinsing the films with deionized water. The polymer films were transparent in the visible region and showed relatively high electrical conductivities within the 2-2000 S cm-1 range.

Role of ALD Al2O3 Surface Passivation on the Performance of p-Type Cu2O Thin Film Transistors.

High-performance p-type oxide thin film transistors (TFTs) have great potential for many semiconductor applications. However, these devices typically suffer from low hole mobility and high off-state currents. We fabricated p-type TFTs with a phase-pure polycrystalline Cu2O semiconductor channel grown by atomic layer deposition (ALD). The TFT switching characteristics were improved by applying a thin ALD Al2O3 passivation layer on the Cu2O channel, followed by vacuum annealing at 300 °C. Detailed characterization by transmission electron microscopy-energy dispersive X-ray analysis and X-ray photoelectron spectroscopy shows that the surface of Cu2O is reduced following Al2O3 deposition and indicates the formation of a 1-2 nm thick CuAlO2 interfacial layer. This, together with field-effect passivation caused by the high negative fixed charge of the ALD Al2O3, leads to an improvement in the TFT performance by reducing the density of deep trap states as well as by reducing the accumulation of electrons in the semiconducting layer in the device off-state.

Novel electroblowing synthesis of tin dioxide and composite tin dioxide/silicon dioxide submicron fibers for cobalt(ii) uptake.

Nanoscale SnO2 has many important properties ranging from sorption of metal ions to gas sensing. Using a novel electroblowing method followed by calcination, we synthesized SnO2 and composite SnO2/SiO2 submicron fibers with a Sn : Si molar ratio of 3 : 1. Different calcination temperatures and heating rates produced fibers with varying structures and morphologies. In all the fibers SnO2 was detected by XRD indicating the SnO2/SiO2 fibers to be composite instead of complete mixtures. We studied the Co2+ separation ability of the fibers, since 60Co is a problematic contaminant in nuclear power plant wastewaters. Both SnO2 and SnO2/SiO2 fibers had an excellent Co2+ uptake with their highest uptake/K d values being 99.82%/281 000 mL g-1 and 99.79%/234 000 mL g-1, respectively. Compared to the bare SnO2 fibers, the SiO2 component improved the elasticity and mechanical strength of the composite fibers which is advantageous in dynamic column operation.

Photocatalytic and Gas Sensitive Multiwalled Carbon Nanotube/TiO2-ZnO and ZnO-TiO2 Composites Prepared by Atomic Layer Deposition.

TiO2 and ZnO single and multilayers were deposited on hydroxyl functionalized multi-walled carbon nanotubes using atomic layer deposition. The bare carbon nanotubes and the resulting heterostructures were characterized by TG/DTA, Raman, XRD, SEM-EDX, XPS, TEM-EELS-SAED and low temperature nitrogen adsorption techniques, and their photocatalytic and gas sensing activities were also studied. The carbon nanotubes (CNTs) were uniformly covered with anatase TiO2 and wurtzite ZnO layers and with their combinations. In the photocatalytic degradation of methyl orange, the most beneficial structures are those where ZnO is the external layer, both in the case of single and double oxide layer covered CNTs (CNT-ZnO and CNT-TiO2-ZnO). The samples with multilayer oxides (CNT-ZnO-TiO2 and CNT-TiO2-ZnO) have lower catalytic activity due to their larger average densities, and consequently lower surface areas, compared to single oxide layer coated CNTs (CNT-ZnO and CNT-TiO2). In contrast, in gas sensing it is advantageous to have TiO2 as the outer layer. Since ZnO has higher conductivity, its gas sensing signals are lower when reacting with NH3 gas. The double oxide layer samples have higher resistivity, and hence a larger gas sensing response than their single oxide layer counterparts.

Silicon oxide-niobium oxide mixture films and nanolaminates grown by atomic layer deposition from niobium pentaethoxide and hexakis(ethylamino) disilane.

Amorphous SiO2-Nb2O5 nanolaminates and mixture films were grown by atomic layer deposition. The films were grown at 300 °C from Nb(OC2H5)5, Si2(NHC2H5)6, and O3 to thicknesses ranging from 13 to 130 nm. The niobium to silicon atomic ratio was varied in the range of 0.11-7.20. After optimizing the composition, resistive switching properties could be observed in the form of characteristic current-voltage behavior. Switching parameters in the conventional regime were well defined only in a SiO2:Nb2O5 mixture at certain, optimized, composition with Nb:Si atomic ratio of 0.13, whereas low-reading voltage measurements allowed recording memory effects in a wider composition range.

Atomic Layer Deposition of Photoconductive Cu2O Thin Films.

Herein, we report an atomic layer deposition (ALD) process for Cu2O thin films using copper(II) acetate [Cu(OAc)2] and water vapor as precursors. This precursor combination enables the deposition of phase-pure, polycrystalline, and impurity-free Cu2O thin films at temperatures of 180-220 °C. The deposition of Cu(I) oxide films from a Cu(II) precursor without the use of a reducing agent is explained by the thermally induced reduction of Cu(OAc)2 to the volatile copper(I) acetate, CuOAc. In addition to the optimization of ALD process parameters and characterization of film properties, we studied the Cu2O films in the fabrication of photoconductor devices. Our proof-of-concept devices show that approximately 20 nm thick Cu2O films can be used for photodetection in the visible wavelength range and that the thin film photoconductors exhibit improved device characteristics in comparison to bulk Cu2O crystals.

Fully Automated Online Dynamic In-Tube Extraction for Continuous Sampling of Volatile Organic Compounds in Air.

Comprehensive and time-dependent information (e.g., chemical composition, concentration) of volatile organic compounds (VOCs) in atmospheric, indoor, and breath air is essential to understand the fundamental science of the atmosphere, air quality, and diseases diagnostic. Here, we introduced a fully automated online dynamic in-tube extraction (ITEX)-gas chromatography/mass spectrometry (GC/MS) method for continuous and quantitative monitoring of VOCs in air. In this approach, modified Cycle Composer software and a PAL autosampler controlled and operated the ITEX preconditioning, internal standard (ISTD) addition, air sampling, and ITEX desorption sequentially to enable full automation. Air flow passed through the ITEX with the help of an external pump, instead of plunger up-down strokes, to allow larger sampling volumes, exhaustive extraction, and consequently lower detection limits. Further, in order to evaluate the ITEX system stability and to develop the corresponding quantitative ITEX method, two laboratory-made permeation systems (for standard VOCs and ISTD) were constructed. The stability and suitability of the developed system was validated with a consecutive 19 day atmospheric air campaign under automation. By using an electrospun polyacrylonitrile nanofibers packed ITEX, selective extraction of some VOCs and durability of over 1500 extraction and desorption cycles were achieved. Especially, the latter step is critically important for on-site long-term application at remote regions. This ITEX method provided 2-3 magnitudes lower quantitation limits than the headspace dynamic ITEX method and other needle trap methods. Our results proved the excellence of the fully automated online dynamic ITEX-GC/MS system for tracking VOCs in the atmospheric air.