Atomic Layer Deposition of the Metal Pyrites FeS2, CoS2, and NiS2

Atomic layer deposition (ALD) of the pyrite‐type metal disulfides FeS₂, CoS₂, and NiS₂ is reported for the first time. The deposition processes use iron, cobalt, and nickel amidinate compounds as the corresponding metal precursors and the H₂S plasma as the sulfur source. All the processes are demonstrated to follow ideal self‐limiting ALD growth behavior to produce fairly pure, smooth, well‐crystallized, stoichiometric pyrite FeS₂, CoS₂, and NiS₂ films. By these processes, the FeS₂, CoS₂, and NiS₂ films can also be uniformly and conformally deposited into deep narrow trenches with aspect ratios as high as 10:1, which thereby highlights the broad and promising applicability of these ALD processes for conformal film coatings on complex high‐aspect‐ratio 3D architectures in general.     

Atomic Layer Deposition of Cobalt Phosphide for Efficient Water Splitting

Transition‐metal phosphides (TMP) prepared by atomic layer deposition (ALD) are reported for the first time. Ultrathin Co‐P films were deposited by using PH₃ plasma as the phosphorus source and an extra H₂ plasma step to remove excess P in the growing films. The optimized ALD process proceeded by self‐limited layer‐by‐layer growth, and the deposited Co‐P films were highly pure and smooth. The Co‐P films deposited via ALD exhibited better electrochemical and photoelectrochemical hydrogen evolution reaction (HER) activities than similar Co‐P films prepared by the traditional post‐phosphorization method. Moreover, the deposition of ultrathin Co‐P films on periodic trenches was demonstrated, which highlights the broad and promising potential application of this ALD process for a conformal coating of TMP films on complex three‐dimensional (3D) architectures.     

Optimizing the Atomic Layer Deposition of Alumina on Perovskite Nanocrystal Films by Using O2 As a Molecular Probe

Encapsulation methods have shown to be effective in imparting improved stability to metal-halide perovskite nanocrystals (NCs). Atomic layer deposition (ALD) of metal oxides is one of the promising approaches for such encapsulation, yet better control on the process parameters are required to achieve viable lifetimes for several optoelectronic and photocatalytic applications. Herein, we optimize the ALD process of amorphous aluminum oxide (AlO_x) as an encapsulating layer for CsPbBr₃ NC thin films by using oxygen (O₂) as a molecular diffusion probe to assess the uniformity of the deposited AlO_x layer. When O₂ reaches the NC surface, it extracts the photogenerated electrons, thus quenching the PL of the CsPbBr₃ NCs. As the quality of the ALD layer improves, less quenching is expected. We compare three different ALD deposition modes. We find that the low temperature/high temperature and the exposure modes improve the quality of the alumina as a gas barrier when compared with the low temperature mode. We attribute this result to a better diffusion of the ALD precursor throughout the NC film. We propose the low temperature/high temperature as the most suitable mode for future implementation of multilayered coatings.     

In situ — High Temperature Mössbauer Spectroscopy of Iron Nitrides and Nitridoferrates

The stoichiometric iron nitrides γ′‐Fe₄N, ε‐Fe₃N and ζ‐Fe₂N were characterized by Mössbauer spectroscopy. The thermal decomposition of ε‐Fe₃N was studied in‐situ by means of a specially developed Mössbauer furnace. We found ε‐Fe₃N to γ′‐Fe₄N and ε‐Fe₃N_x (x ≥ 1.3) as decomposition products and determined the border of γ′/ε transformation at T ? 930 K. Mössbauer spectroscopy was applied to study in‐situ the thermal decomposition of the nitridometalate Li₃[Fe^IIIN₂] and the formation of Li₂[(Li_1‐xFe^I_x)N], the compound with the largest local magnetic field ever observed in an iron containing material. The kinetics of formation and the stability of Li₂[(Li_1‐xFe^I_x)N] was of particular interest in the present study.     

Gallium-containing sulfide binary and ternary materials by atomic layer deposition: precursor reactivities and growth fine chemistries

Gallium sulfide (Ga_xS) and copper gallium sulfide (Cu_xGa_yS_z) were synthetized by atomic layer deposition (ALD), using copper acetylacetonate Cu(acac)₂, hexakis(dimethylamino)digallium [Ga(NMe₂)₃]₂ and hydrogen sulfide (H₂S). Thanks to the compatibility of the Cu_xS and Ga_xS ALD windows, a supercycle strategy that combines single growth cycles of the two binary compounds was used to generate the ternary material. A wide range of compositions and properties can be obtained from Ga-rich to Cu-rich via copper gallium sulfide thin films. Structural, morphological, and optoelectronic characterizations were performed on all films. Surface and in-depth chemical compositions were determined by X-ray photoelectron spectroscopy profiling, allowing a better understanding of the chemical reactions involved during the growth process. In the case of Ga_xS films, other Ga precursors have been tested. Our experimental observations, combined with reported ones and density functional theory calculation results have highlighted the specific reactivity of alkylamido precursor in ALD chemistry. Compositional studies revealed a significant O content which origin is discussed and represents an important challenge to address in ALD of sulfide materials in general.     

Structural,compositional and hardness properties of hydrogenated amorphous carbon nitride thin films synthesized by dense plasma focus device

The hydrogenated amorphous carbon nitride (a‐CN_x:H) thin films were synthesized on the SS‐304 substrates using a dense plasma focus device. The a‐CN_x:H thin films were synthesized using CH₄/N₂ admixture gas and 20 focus deposition shots on substrates placed at different distances from the anode top. X‐ray photoelectron spectroscopy and Raman analysis confirmed different C–N bonding in the a‐CN_x:H thin films. A decrease in the N/C ratio as well as the sp³/sp² ratio with an increase in the substrate distance has been observed. The higher amount of C–N formation for the film synthesized at 10 cm is observed which decreases with increasing distance. The X‐ray photoelectron spectroscopy and Raman analysis affirmed the C ≡ N presence in all the thin films synthesized at different distances. The morphology of the synthesized a‐CN_x:H thin films showed nanoparticles and nanoparticle clusters formation at the surface. The hardness results showed comparatively lower hardness of the a‐CN_x:H thin films due to the presence of C ≡ N. The C–N formation with lower amount of C ≡ N and a higher N/C ratio as well as a higher sp³/sp² ratio for the films synthesized at 10 cm show reasonably higher hardness. Copyright © 2016 John Wiley & Sons, Ltd.     

Deposition of copper‐doped iron sulfide (CuxFe1−xS) thin films using aerosol‐assisted chemical vapor deposition technique

Copper‐doped iron sulfide (Cu_xFe_1?xS, x = 0.010–0.180) thin films were deposited using a single‐source precursor, Cu(LH)₂Cl₂ (LH = monoacetylferrocene thiosemicarbazone), by aerosol‐assisted chemical vapor deposition technique. The Cu‐doped FeS thin films were deposited at different substrate temperatures, i.e. 250, 300, 350, 400 and 450 °C. The deposited thin films were characterized by X‐ray diffraction (XRD) patterns, Raman spectra, scanning electron microscopy, energy dispersive X‐ray analysis (EDX) and atomic force microscopy. XRD studies of Cu‐doped FeS thin films at all the temperatures revealed formation of single‐phase FeS structure. With increasing substrate temperature from 250 to 450 °C, there was change in morphology from wafer‐like to cylindrical plate‐like. EDX analysis showed that the doping percentage of copper increased as the substrate temperature increased from 250 to 450 °C. Raman data supports the doping of copper in FeS films. Copyright © 2010 John Wiley & Sons, Ltd.     

Rational Development of Guanidinate and Amidinate Based Cerium and Ytterbium Complexes as Atomic Layer Deposition Precursors: Synthesis,Modeling, and Application

Owing to the limited availability of suitable precursors for vapor phase deposition of rare-earth containing thin-film materials, new or improved precursors are sought after. In this study, we explored new precursors for atomic layer deposition (ALD) of cerium (Ce) and ytterbium (Yb) containing thin films. A series of homoleptic tris-guanidinate and tris-amidinate complexes of cerium (Ce) and ytterbium (Yb) were synthesized and thoroughly characterized. The C-substituents on the N-C-N backbone (Me, NMe₂, NEt₂, where Me=methyl, Et=ethyl) and the N-substituents from symmetrical iso-propyl (iPr) to asymmetrical tertiary-butyl (tBu) and Et were systematically varied to study the influence of the substituents on the physicochemical properties of the resulting compounds. Single crystal structures of [Ce(dpdmg)₃] 1 and [Yb(dpdmg)₃] 6 (dpdmg=N,N'-diisopropyl-2-dimethylamido-guanidinate) highlight a monomeric nature in the solid-state with a distorted trigonal prismatic geometry. The thermogravimetric analysis shows that the complexes are volatile and emphasize that increasing asymmetry in the complexes lowers their melting points while reducing their thermal stability. Density functional theory (DFT) was used to study the reactivity of amidinates and guanidinates of Ce and Yb complexes towards oxygen (O₂) and water (H₂O). Signified by the DFT calculations, the guanidinates show an increased reactivity toward water compared to the amidinate complexes. Furthermore, the Ce complexes are more reactive compared to the Yb complexes, indicating even a reactivity towards oxygen potentially exploitable for ALD purposes. As a representative precursor, the highly reactive [Ce(dpdmg)₃] 1 was used for proof-of-principle ALD depositions of CeO₂ thin films using water as co-reactant. The self-limited ALD growth process could be confirmed at 160 °C with polycrystalline cubic CeO₂ films formed on Si(100) substrates. This study confirms that moving towards nitrogen-coordinated rare-earth complexes bearing the guanidinate and amidinate ligands can indeed be very appealing in terms of new precursors for ALD of rare earth based materials.     

CsPbBr3 QD/AlOx Inorganic Nanocomposites with Exceptional Stability in Water,Light, and Heat

Herein, the assembly of CsPbBr₃ QD/AlO_x inorganic nanocomposites, by using atomic layer deposition (ALD) for the growth of the amorphous alumina matrix (AlO_x ), is described as a novel protection scheme for such QDs. The nucleation and growth of AlO_x on the QD surface was thoroughly investigated by miscellaneous techniques, which highlighted the importance of the interaction between the ALD precursors and the QD surface to uniformly coat the QDs while preserving the optoelectronic properties. These nanocomposites show exceptional stability towards exposure to air (for at least 45 days), irradiation under simulated solar spectrum conditions (for at least 8 h), and heat (up to 200 °C in air), and finally upon immersion in water. This method was extended to the assembly of CsPbBr_x I_3−x QD/AlO_x and CsPbI₃ QD/AlO_x nanocomposites, which were more stable than the pristine QD films.     

CsPbBr3 QD/AlOx Inorganic Nanocomposites with Exceptional Stability in Water,Light, and Heat

Herein, the assembly of CsPbBr₃ QD/AlO_x inorganic nanocomposites, by using atomic layer deposition (ALD) for the growth of the amorphous alumina matrix (AlO_x ), is described as a novel protection scheme for such QDs. The nucleation and growth of AlO_x on the QD surface was thoroughly investigated by miscellaneous techniques, which highlighted the importance of the interaction between the ALD precursors and the QD surface to uniformly coat the QDs while preserving the optoelectronic properties. These nanocomposites show exceptional stability towards exposure to air (for at least 45 days), irradiation under simulated solar spectrum conditions (for at least 8 h), and heat (up to 200 °C in air), and finally upon immersion in water. This method was extended to the assembly of CsPbBr_x I_3−x QD/AlO_x and CsPbI₃ QD/AlO_x nanocomposites, which were more stable than the pristine QD films.     

Electropolymerization of DBSA‐doped polypyrrole films on PTFE via an electroless copper interlayer

We report on the electroless deposition of thin films of copper on poly(tetrafluoroethylene) (PTFE) and their use as substrates for electropolymerization of polypyrrole. Argon plasma‐treated PTFE films were modified by silanization using N‐[3(trimethoxysilyl)propyl]diethylenetriamine (TMS). The TMS‐modified PTFE films were subsequently activated by PdCl₂ for the electroless deposition of copper. The omission of the commonly used SnCl₂ sensitization step represents a significant process enhancement with environmental and cost benefits. The surface composition of the substrate (before and after surface treatments) and overlayer films was studied using high‐resolution x‐ray photoelectron spectroscopy. A combination of time‐of‐flight secondary ion mass spectrometry and water contact‐angle measurements was also used to study the PTFE surface after argon plasma treatment. The Cu/PTFE films were used as substrates for subsequent pyrrole electropolymerization in aqueous dodecylbenzene sulphonic acid (DBSA) solution. The DBSA‐doped polypyrrole overlayers were successfully deposited on the Cu/PTFE surface using a constant applied potential of 1.5 V. The resulting material exhibited a doping level of 39%, determined using chemical component analysis of the N 1s photoelectron peak. Copyright © 2003 John Wiley & Sons, Ltd.     

Nanostructured ZrO2 and Zr‐C‐N Coatings from Chemical Vapor Deposition of Metal‐Organic Precursors

Nanocrystalline zirconium carbonitride (Zr‐C‐N) and zirconium oxide (ZrO₂) films were deposited by chemical vapor deposition (CVD) of zirconium‐tetrakis‐diethylamide (Zr(NEt₂)₄) and ‐tert‐butyloxide (Zr(OBu^t)₄), respectively. The films were deposited on iron substrates and characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS). The Zr‐C‐N films show blue, golden brown or bronze colours, with colour stability depending upon the precursor composition (pure metal amide or mixed with Et₂NH). The deposition temperature showed no pronounced effect on the granular morphology of the Zr‐C‐N films. The XRD data of the films correspond to the formation of carbonitride phase whereas the XPS analyses revealed a strong surface oxidation and incorporation of oxygen in the film. The films deposited using a mixture of Zr(NEt₂)₄ and Et₂NH showed higher N content, better adhesion and scratch resistance when compared to films obtained from the CVD of pure Zr(NEt₂)₄. Subject to the precursor composition and deposition temperature (550‐750 °C), the microhardness values of Zr‐C‐N films were found to be in the range 2.11‐5.65 GPa. For ZrO₂ films, morphology and phase composition strongly depend on the deposition temperature. The CVD deposits obtained at 350 °C show tetragonal ZrO₂ to be the only crystalline phase. Upon increasing the deposition temperature to 450 °C, a mixture of tetragonal and monoclinic modifications was formed with morphology made up of interwoven elongated grains. At higher temperatures (550 and 650 °C), pure monoclinic phase was obtained with facetted grains and developed texture.     

Microstructural and physicochemical study of the buried Fe/AlGaAs(100) interface by transmission electron microscopy and x‐ray emission spectroscopy

Among the magnetic metal/semiconductor contacts, the Fe/GaAs system has been widely studied owing to its potential applications in electronic devices. In contrast, there are not many studies concerning the Fe/Al_xGa_1?xAs contact, and in particular there are no reports concerning the changes induced in the interfacial zone by the presence of Al. In this work, thin polycrystalline iron films were deposited by ion beam sputtering at room temperature on a 300 nm thick Al_0.25Ga_0.75As layer grown by molecular beam epitaxy onto GaAs(001). X‐ray diffraction analysis showed that the iron films are polycrystalline, and indications of a (002) texture of the film were observed. The fine scale analysis of the interface was achieved by high‐resolution transmission electron microscopy (HRTEM) observations, the results of which are compared with the physicochemical information obtained from electron‐induced x‐ray emission spectroscopy, by analysing the Al 3p valence states at the Fe/Al_xGa_1?xAs interface. The HRTEM experiments on cross‐section samples indicate that the interfacial zone between iron and AlGaAs is limited to <1.5 nm in thickness. X‐ray emission spectroscopy showed the presence of Al atoms in an FeAl‐like environment at the interface, and the existence of wrong bonds and point defects. The estimated width of the perturbed interface (2.0 ± 0.5 nm) is in agreement with the HRTEM results. Copyright © 2003 John Wiley & Sons, Ltd.     

FeOx Coating on Pd/C Catalyst by Atomic Layer Deposition Enhances the Catalytic Activity in Dehydrogenation of Formic Acid

Hydrogen generation from formic acid (FA) has received significant attention.The challenge is to obtain a highly active catalyst under mild conditions for practical applications.Here atomic layer deposition (ALD) of FeO_x was performed to deposit an ultrathin oxide coating layer to a Pd/C catalyst,therein the FeO_x coverage was precisely controlled by ALD cycles.Transmission electron microscopy and powder X-ray diffraction measurements suggest that the FeO_x coating layer improved the thermal stability of Pd nanoparticles (NPs).X-ray photoelectron spectroscopy measurement showed that deposition of FeO_x on the Pd NPs caused a positive shift of Pd3d binding energy.In the FA dehydrogenation reaction,the ultrathin FeO_x layer on the Pd/C could considerably improve the catalytic activity,and Pd/C coated with 8 cycles of FeO_x showed an optimized activity with turnover frequency being about 2 times higher than the uncoated one.The improved activities were in a volcanoshape as a function of the number of FeO_x ALD cycles,indicating the coverage of FeO_x is critical for the optimized activity.In summary,simultaneous improvements of activity and thermal stability of Pd/C catalyst by ultra-thin FeO_x overlayer suggest to be an effective way to design active catalysts for the FA dehydrogenation reaction.     

Surface characterization of the SiOx films prepared by a remote atmospheric pressure plasma jet

The deposition rate and surface properties of SiO_x films were prepared and investigated using remote atmospheric pressure plasma (APP) jet. The APP, generated with low frequency power at 16 kHz, was fed with tetraethoxysilane (TEOS)/air gas mixture. After deposition, the SiO_x films were analyzed for chemical characteristics, elemental composition, surface morphology, and hardness. It was found that the deposition substrate temperature is the key factor to affect the deposition rate of remote APP chemical vapor deposition process. Fourier transform infrared (FTIR) spectra indicated that APP deposited SiO_x films are an inorganic feature. XPS examination revealed that the SiO_x films contained approximately 30% silicon, 58% oxygen and 12% carbon. Atomic forced microscopy (AFM) analysis results indicated a smooth surface of SiO_x films in deposition under higher substrate temperature. Also, pencil hardness tests indicated that the hardness of APP deposited SiO_x films was greatly improved with increasing substrate temperatures. Copyright © 2008 John Wiley & Sons, Ltd.     

Inherently Area-Selective Atomic Layer Deposition of Manganese Oxide through Electronegativity-Induced Adsorption

Manganese oxide (MnO_x) shows great potential in the areas of nano-electronics, magnetic devices and so on. Since the characteristics of precise thickness control at the atomic level and self-align lateral patterning, area-selective deposition (ASD) of the MnO_x films can be used in some key steps of nanomanufacturing. In this work, MnO_x films are deposited on Pt, Cu and SiO₂ substrates using Mn(EtCp)₂ and H₂O over a temperature range of 80–215 °C. Inherently area-selective atomic layer deposition (ALD) of MnO_x is successfully achieved on metal/SiO₂ patterns. The selectivity improves with increasing deposition temperature within the ALD window. Moreover, it is demonstrated that with the decrease of electronegativity differences between M (M = Si, Cu and Pt) and O, the chemisorption energy barrier decreases, which affects the initial nucleation rate. The inherent ASD aroused by the electronegativity differences shows a possible method for further development and prediction of ASD processes.     

Ion‐Exchange‐Induced 2D–3D Conversion of HMA1−xFAxPbI3Cl Perovskite into a High‐Quality MA1−xFAxPbI3 Perovskite

High‐quality phase‐pure MA_1?xFA_xPbI₃ planar films (MA=methylammonium, FA=formamidinium) with extended absorption and enhanced thermal stability are difficult to deposit by regular simple solution chemistry approaches owing to crystallization competition between the easy‐to‐crystallize but unwanted δ‐FAPbI₃/MAPbI₃ and FA_xMA_1?xPbI₃ requiring rigid crystallization conditions. Here A 2D–3D conversion to transform compact 2D mixed composition HMA_1?xFA_xPbI₃Cl perovskite precursor films into 3D MA_1?xFA_xPbI₃ (x=0.1–0.9) perovskites is presented. The designed Cl/I and H/FA(MA) ion exchange reaction induced fast transformation of compact 2D perovskite film, helping to form the phase‐pure and high quality MA_1?xFA_xPbI₃ without δ‐FAPbI₃ and MAPbI₃ impurity. In all, we successfully developed a facile one‐step method to fabricate high quality phase‐pure MA_1?xFA_xPbI₃ (x=0.1–0.9) perovskite films by 2D–3D conversion of HMA_1?xFA_xPbI₃Cl perovskite. This 2D–3D conversion is a promising strategy for lead halide perovskite fabrication.     

Pentacoordinated Al3+‐Stabilized Active Pd Structures on Al2O3‐Coated Palladium Catalysts for Methane Combustion

Supported Pd catalysts are active in catalyzing the highly exothermic methane combustion reaction but tend to be deactivated owing to local hyperthermal environments. Herein we report an effective approach to stabilize Pd/SiO₂ catalysts with porous Al₂O₃ overlayers coated by atomic layer deposition (ALD). ²⁷Al magic angle spinning NMR analysis showed that Al₂O₃ overlayers on Pd particles coated by the ALD method are rich in pentacoordinated Al³⁺ sites capable of strongly interacting with adjacent surface PdO_x phases on supported Pd particles. Consequently, Al₂O₃‐decorated Pd/SiO₂ catalysts exhibit active and stable PdO_x and Pd–PdO_x structures to efficiently catalyze methane combustion between 200 and 850 °C. These results reveal the unique structural characteristics of Al₂O₃ overlayers on metal surfaces coated by the ALD method and provide a practical strategy to explore stable and efficient supported Pd catalysts for methane combustion.     

Chemischer Transport von Eisensulfid. II. Experimentelle Ergebnisse beim Transport von FeSx mit Jod

Chemical Transport of Iron Sulphide. II. Experimental Results on the Transport of FeS_x with Iodine It is possible to deposite monocrystals of iron sulphide FeS_x by means of CTR method using iodine as transport agent. The presence of sufficient, high sulfur partial pressures is the most important condition for the FeS_x being transported, in other words: x must be equal or greater than approximately 1.04. The transport velocity and the shape of the deposited crystals depend on temperature, amount of iodine, and composition of the original material. The expected differences between the composition of the deposited solid and that of the residue can be verified experimentally.     

An iron (II) guanidinate compound: Synthesis,characterization, thermal properties and its application as a CVD precursor for iron oxide film

An iron compound containing guanidinate ligand [Fe((SiMe₃)₂NC(ⁱPrN)₂)₂] was synthesized using a conventional lithium‐salt‐elimination reaction, and its chemical structure was characterized through elemental analysis, ¹H‐NMR and single‐crystal X‐ray diffraction, respectively. The thermal properties of the compound were examined through thermogravimetric analysis (TGA), and the TGA results demonstrated that the compound possessed sufficient volatility and suitable thermal stability for the CVD process. Moreover, the deposition experiments were conducted using the synthesized compound as a precursor and O₂ as an oxygen source to confirm its applicability as a CVD precursor, and α‐Fe₂O₃ films were successfully deposited at a relatively low deposition temperature (300°C).