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With a focus on Mn based organometallic compounds with suitable physico‐chemical properties to serve as precursors for chemical vapor deposition (CVD) and atomic layer deposition (ALD) of Mn‐containing materials, systematic synthetic approaches with ligand variation, detailed characterization, and theoretical input from density functional theory (DFT) studies are presented. A series of new homoleptic all‐nitrogen and mixed oxygen/nitrogen‐coordinated Mn(II) complexes bearing the acetamidinate, formamidinate, guanidinate and ß‐ketoiminate ligands have been successfully synthesized for the first time. The specific choice of these ligand classes with changes in structure and coordination sphere and side chain variations result in significant structural differences whereby mononuclear and dinuclear complexes are formed. This was supported by density functional theory (DFT) studies. The compounds were thoroughly characterized by single crystal X‐ray diffraction, magnetic measurements, mass spectrometry and elemental analysis. To evaluate their suitability as precursors for deposition of Mn‐based materials, the thermal properties were investigated in detail. Mn(II) complexes possessing the most promising thermal properties, namely Bis(N,N'‐ditertbutylformamidinato)manganese(II) (IV) and Bis(4‐(isopropylamino)pent‐3‐en‐2‐onato)manganese(II) (ßIII) were used in reactivity studies with DFT to explore their interaction with oxidizing co‐reactants such as oxygen and water which will guide future CVD and ALD process development. [ABSTRACT FROM AUTHOR]

Thin films of Al as interconnect materials and those of AlN as wide bandgap semiconductor and piezoelectric material are of great interest for microelectronic applications. For the fabrication of these thin films via chemical vapor deposition (CVD) based routes, the available precursor library is rather limited, mostly comprising aluminium alkyls, chlorides, and few small amine-stabilized aluminium hydrides. Herein, we focused on rational precursor development for Al, their characterization and comparison to existing precursors comprising stabilized aluminium hydrides. We present and compare a series of potentially new and reported aluminium hydride precursors divided into three main groups with respect to their stabilization motive, and their systematic structural variation to evaluate the physicochemical properties. All compounds were comprehensively characterized by means of nuclear magnetic resonance spectroscopy (NMR), Fourier-transform infrared spectroscopy (FTIR), elemental analysis (EA), electron-impact ionization mass spectrometry (EI-MS) and thermogravimetric analysis (TGA). Promising representatives were further evaluated as potential single source precursors for aluminium metal formation in proof-of-concept experiments. Structure and reaction enthalpies with NH3 or H2 as co-reactants were calculated via first principles density functional theory simulations and show the great potential as atomic layer deposition (ALD) precursors for Al and AlN thin films. [ABSTRACT FROM AUTHOR]

This feature article presents insights concerning the correlation of plasma‐enhanced chemical vapor deposition and plasma‐enhanced atomic layer deposition thin film structures with their barrier or membrane properties. While in principle similar precursor gases and processes can be applied, the adjustment of deposition parameters for different polymer substrates can lead to either an effective diffusion barrier or selective permeabilities. In both cases, the understanding of the film growth and the analysis of the pore size distribution and the pore surface chemistry is of utmost importance for the understanding of the related transport properties of small molecules. In this regard, the article presents both concepts of thin film engineering and analytical as well as theoretical approaches leading to a comprehensive description of the state of the art in this field. Perspectives of future relevant research in this area, exploiting the presented correlation of film structure and molecular transport properties, are presented. [ABSTRACT FROM AUTHOR]

This feature article presents recent results on the analysis of plasma/polymer interactions and the nucleation of ultra‐thin plasma films on polymeric substrates. Because of their high importance for the understanding of such processes, in situ analytical approaches of the plasma volume as well as the plasma/substrate interfaces are introduced before the findings on plasma surface chemistry. The plasma activation of polymeric substrates is divided into the understanding of fundamental processes on model substrates and the relevance of polymer surface complexity. Concerning thin film nucleation and growth, both plasma‐enhanced chemical vapor deposition and plasma‐enhanced atomic layer deposition processes as well as the combination of both processes are considered both for model substrates and technical polymers. Based on the comprehensive presentation of recent results, selective perspectives of this research field are discussed. [ABSTRACT FROM AUTHOR]

In the present study, the effects of oxygen plasma treatment and subsequent 2 nm thin Al2O3 film deposition by atomic layer deposition on about 30 nm thick hexamethyldisilazane polymer layers are investigated by using a combination of spectroscopic and electrochemical analysis. The investigations focus on the microporosity of the corresponding films and their structural changes. Upon oxygen plasma treatment, the surface near region of the films is converted into SiOx, and the microporosity is increased. Atomic layer deposition of Al2O3 on the plasma oxidized films leads to the decrease of pore sizes and an effective sealing. A correlation between the film microporosity and the change of hydroxyl groups of the films with the adsorption of water was established by ellipsometric porosimetry and in situ Fourier transform infrared (FTIR) spectroscopy. Moreover, electrochemical analysis provided complementary information on the electrolyte up‐take in the differently conditioned thin films. [ABSTRACT FROM AUTHOR]

To implement 2D molybdenum disulfide (MoS2) in the flexible electronic industry, large, uniform, and crystalline films on flexible substrates are needed. Thermal atomic layer deposition (ALD) generates large‐area uniform MoS2 films at low temperatures directly on temperature‐sensitive substrates. But if the grown films are amorphous, a high‐temperature posttreatment of the whole sample, which may cause thermal degradation of the substrate or other layers, needs to be avoided. In this article, the crystallization of amorphous MoS2 layers deposited by thermal ALD processed with picosecond laser pulses (λ = 532 nm), in a "cold" annealing process, is reported. The laser fluence range varies from Fmin$F_{\text{min}}$ = 8.73 mJ cm−2 to Fmax$F_{\text{max}}$ = 18.25 mJ cm−2 with scanning speeds from vscan,min$v_{\text{scan,min}}$ = 240 mm s−1 to vscan,max$v_{\text{scan,max}}$ = 2640 mm s−1. The crystallization and the influence of the processing parameters on the film morphology are analyzed in detail by Raman spectroscopy and scanning electron microscopy. Furthermore, a transition of amorphous MoS2 by laser annealing to self‐organized patterns is demonstrated and a possible process mechanism for the ultrashort‐pulsed (usp)‐laser annealing is discussed. Finally, the usp laser annealed films are compared to thermally and continuous‐wave‐laser‐annealed samples. [ABSTRACT FROM AUTHOR]

HfO2 thin films are appealing for microelectronic applications such as high‐κ dielectric layers, memristors, and ferroelectric memory devices. To fulfill the different requirements of each application, the properties of the deposited material need to be tuned accordingly. In this context, plasma‐enhanced atomic layer deposition (PEALD) is a powerful processing route to tailor the properties of HfO2 thin films, especially at low temperatures. Herein, a comprehensive bottom‐up approach is presented, ranging from the synthesis of molecularly engineered Hf precursors to the development of a HfO2 PEALD process and a detailed evaluation where plasma can be exploited to tune the dielectric properties. With the example of the newly synthesized bis‐(dialkylamido)‐bis‐(formamidinato) Hf(IV) precursor, [Hf{η2‐(iPrN)2CH}2(NMe2)2] which is reactive, thermally robust and volatile, successful implementation in a PEALD process for HfO2 at low temperatures is demonstrated. The typical atomic layer deposition (ALD) characteristics of precursor saturation, linearity, and ALD temperature window are demonstrated with constant growth of 0.7 Å per cycle from 125 to 200 °C, yielding high‐purity layers. The effect of plasma pulse duration on the chemical composition alongside structural, topographical, as well as dielectric properties of the films is investigated. For the latter, the films are incorporated in metal‐insulator semiconductor (MIS) structures. [ABSTRACT FROM AUTHOR]

Volatile, reactive, and thermally stable organometallic copper and silver complexes are of significant interest as precursors for the metalorganic chemical vapor deposition (MOCVD) and atomic layer deposition (ALD) of ultra-thin metallic films. Well-established CuI and AgI precursors are commonly stabilized by halogens, phosphorous, silicon, and oxygen, potentially leading to the incorporation of these elements as impurities in the thin films. These precursors are typically stabilized by a neutral and anionic ligand. Recent advancements were established by the stabilization of these complexes using N-heterocyclic carbenes (NHCs) as neutral ligands. To further enhance the reactivity, in this study the anionic ligand is sequentially changed from β-diketonates to β-ketoiminates and β-diketiminates, yielding two new CuI and two new AgI NHC-stabilized complexes in the general form of [M(NHC) (R)] (M = Cu, Ag; R = β-ketoiminate, β-diketiminate). The synthesized complexes were comparatively analyzed in solid, dissolved, and gaseous states. Furthermore, the thermal properties were investigated to assess their potential application in MOCVD or ALD. Among the newly synthesized complexes, the β-diketiminate-based [Cu(tBuNHC) (NacNacMe)] was identified to be the most suitable candidate as a precursor for Cu thin film deposition. The resulting halogen-, oxygen-, and silicon-free CuI and AgI precursors for MOCVD and ALD applications are established for the first time and set a new baseline for coinage metal precursors. [ABSTRACT FROM AUTHOR]

The unique properties of atomic layer deposition (ALD) are mainly exploited for metal oxides, while the growth of metals, such as silver, is still in its infancy. Low growth temperatures and high growth rates are essential to achieve conductive (i.e. percolated) films. Here, a study based on the authors' recently introduced N‐heterocyclic carbene‐based Ag amide precursor [(NHC)Ag(hmds)] (1,3‐di‐tert‐butyl‐imidazolin‐2‐ylidene silver(I) 1,1,1‐trimethyl‐N‐(trimethylsilyl) silanaminide) using plasma‐enhanced spatial ALD at atmospheric pressure and at deposition temperatures as low as 60 °C, is provided. The favorable reactivity and high volatility of the [(NHC)Ag(hmds)] precursor affords high growth rates up to 3.4 × 1014 Ag atoms cm–2 per cycle, which are ≈2.5 times higher than that found with the established triethylphosphine(6,6,7,7,8,8,8‐heptafluoro‐2,2‐dimethyl‐3,5‐octanedionate) silver(I) [Ag(fod)(PEt3)] precursor. Consequently, highly conductive Ag films with resistivities as low as 2.7 µΩ cm are achieved at a deposition temperature of 100 °C with a percolation threshold of ≈2.6 × 1017 Ag atoms cm–2, which is more than 1.6 times lower compared to [Ag(fod)(PEt3)]. As a concept study, conductive Ag layers are used as bottom electrodes in organic solar cells, that achieve the same performance as those based on Ag electrodes resulting from a high vacuum process. [ABSTRACT FROM AUTHOR]

Two novel ruthenium complexes belonging to the Ru(II)(DAD)(Cym) (DAD = diazadienyl) (Cym = cymene) compound family are introduced as promising precursors. Their chemical nature, potential for chemical vapor deposition (CVD), and possibly atomic layer deposition (ALD) are demonstrated. The development of nonoxidative CVD processes yielding high‐quality Ru thin films is realized. Chemical analyses are exercised that vitiate the deceptive assumption of Ru(DAD)(Aryl) complexes being zero‐valent through clear evidence for the redox noninnocence of the DAD ligand. Two different CVD routes for the growth of Ru films are developed using Ru(tBu2DAD)(Cym). Ru thin films from both processes are subjected to thorough and comparative analyses that allowed to deduce similarities and differences in film growth. Ru thin films with a thickness of 30–35 nm grown on SiO2 yielded close‐to‐bulk resistivity values ranging from 12 to 16 µΩ cm. Catalysis evaluation of the films in the acidic oxygen evolution reaction (OER) results in promising performances based on overpotentials as low as 240 mV with Tafel slopes of 45–50 mV dec−1. Based on the degradation observed during electrochemical measurements, the impact of OER conditions on the layers is critically assessed by complementary methods. [ABSTRACT FROM AUTHOR]

Tin monoxide (SnO) is a promising oxide semiconductor which is appealing for a wide range of applications from channel materials in p-type field effect transistors (FET) to electrode materials searched for next-generation batteries. For the controlled growth of SnO films at low temperatures, atomic layer deposition (ALD) is employed in this study, where the choice of the precursor plays a significant role. A comparative thermal evaluation of four different amidinate-based tin(II) precursors and the influence of the ligand sphere on their physicochemical properties revealed that bis(N,N′-diisopropylformamidinato tin(II) (1) possesses the required volatility, good thermal stability and sufficient reactivity towards water, to be implemented as the ALD precursor. The water-assisted ALD process resulted in crystalline SnO films on Si substrates with a growth per cycle (GPC) of 0.82 Å at temperatures as low as 140 °C. By employing complementary analytical tools, namely, X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray reflectivity (XRR), Rutherford backscattering spectrometry/nuclear reaction analysis (RBS/NRA) and X-ray photoelectron spectroscopy (XPS), the formation of tin monoxide was confirmed. Finally, the optical properties of the as-deposited films were analyzed via UV-Vis spectroscopy, exhibiting a band gap of 2.74 eV, which further confirms the formation of the targeted SnO phase. [ABSTRACT FROM AUTHOR]

The microporosity, structure and permeability of SiOx thin films deposited by microwave plasma‐enhanced chemical vapour deposition (PE‐CVD) and plasma‐enhanced atomic layer deposition (PE‐ALD) on polydimethylsiloxane (PDMS) substrates were investigated by positron annihilation spectroscopy and complementary technique, such as X‐ray photoelectron spectroscopy, infrared spectroscopy, time of flight mass spectroscopy and atomic force microscopy. The SiOx films were deposited onto spin‐coated PDMS substrates, which were previously exposed to an oxygen plasma thus achieving the conversion of the top polymer layer into SiOx. The presence of this oxidised surface near the region led to an overall decrease in micropore density and to a shift towards smaller pore sizes within the deposited SiOx films. A correlation between the oxygen fluence during the oxygen plasma treatment and the microporosity of the PE‐CVD and PE‐ALD SiOx films could be established. [ABSTRACT FROM AUTHOR]

Cu and Ag precursors that are volatile, reactive, and thermally stable are currently of high interest for their application in atomic‐layer deposition (ALD) of thin metal films. In pursuit of new precursors for coinage metals, namely Cu and Ag, a series of new N‐heterocyclic carbene (NHC)‐based CuI and AgI complexes were synthesized. Modifications in the substitution pattern of diketonate‐based anionic backbones led to five monomeric Cu complexes and four closely related Ag complexes with the general formula [M(tBuNHC)(R)] (M=Cu, Ag; tBuNHC=1,3‐di‐tert‐butyl‐imidazolin‐2‐ylidene; R=diketonate). Thermal analysis indicated that most of the Cu complexes are thermally stable and volatile compared to the more fragile Ag analogs. One of the promising Cu precursors was evaluated for the ALD of nanoparticulate Cu metal deposits by using hydroquinone as the reducing agent at appreciably low deposition temperatures (145–160 °C). This study highlights the considerable impact of the employed ligand sphere on the structural and thermal properties of metal complexes that are relevant for vapor‐phase processing of thin films. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of a series of closely related Y(III) compounds comprising the formamidinate ligands (RNCHNR) (R = alkyl) is reported, with the scope of using them as prospective precursors for atomic layer deposition (ALD) of yttrium oxide (Y2O3) thin films. The influence of the side chain variation on the thermal properties of the resulting complexes is studied and benchmarked by thermal analysis and vapor pressure measurements. Density functional theory (DFT) studies give theoretical insights into the reactivity of the compounds towards water, which was targeted as a co-reactant for the deposition of Y2O3via thermal ALD in the next step. Among the four complexes analyzed, tris(N,N′-di-tert-butyl-formamidinato)yttrium(III) [Y(tBu2-famd)3] 1 was found to possess enhanced thermal stability and was selected for Y2O3 ALD process development. A broad ALD window ranging from 200 °C to 325 °C was obtained, yielding films of high compositional quality. Furthermore, with a film density of (4.95 ± 0.05) g cm−1 close to the bulk value, polycrystalline fcc Y2O3 layers with a smooth topography resulted in promising dielectric properties when implemented in metal insulator semiconductor (MIS) capacitor structures. [ABSTRACT FROM AUTHOR]

High‐quality copper metal thin films are demanded for a number of advanced technologies. Herein, a facile ALD (atomic layer deposition) process for the fabrication of Cu metal films directly from two solid readily usable precursors, copper acetylacetonate as the source of copper and hydroquinone as the reductant is reported. This process yields highly crystalline, dense, specularly reflecting, and electrically conductive Cu films with an appreciably high growth rate of 1.8 Å/cycle at deposition temperatures as low as 160 to 240 °C. [ABSTRACT FROM AUTHOR]

In order to enable the application of atomic probe tomography combinatorial processing platforms for atomic-scale investigations of phase evolution at elevated temperatures, the pre-sharpened Si tip of 10-20 nm in diameter must be protected against interdiffusion and reaction of the reactive Si with a film of interest by a conformal coating on the Si tip. It is shown that unwanted reactions can be suppressed by introducing a 20-nm-thick intermediate Al2O3 layer grown by atomic layer deposition (ALD). As a representative case, Pt is chosen as a film of interest, as it easily forms silicides. Whereas without the ALD coating diffusion/reactions occur, with the protective film, this is prevented for temperatures up to at least 600°C. The effectiveness of the Al2O3 layer serving as a diffusion barrier is not limited to a sharpened Si tip but works generally for all cases where a Si substrate is used. [ABSTRACT FROM AUTHOR]

Eight new atomic layer deposition (ALD) precursors were synthesized using a ligand that is new to the field of ALD: (tBuNH)SiMe2NMe2. Complexes containing Mg, V, Mn, Fe, Co, Ni, and Zn were found to be tetrahedral, and Li complexes form more complex structures. These compounds performed exceptionally well by thermogravimetric analysis (TGA). All compounds except for one Li species and the Fe complex left residual masses below 5%, similar or better than the analogous amidinate complexes. In particular, the Co(II) complex is very thermally robust and performs very well during a TGA stress test, surpassing temperatures above 200 °C. These compounds are the first of a family of precursors containing this type of monoanionic N–Si–N ligand and are prime candidates for ALD process development. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper demonstrates a carbene stabilized precursor [Cu(tBuNHC)(hmds)] with suitable volatility, reactivity and thermal stability, that enables the spatial plasma-enhanced atomic layer deposition (APP-ALD) of copper thin films at atmospheric pressure. The resulting conductive and pure copper layers were thoroughly analysed and a comparison of precursor and process with the previously reported silver analogue [Ag(tBuNHC)(hmds)] revealed interesting similarities and notable differences in precursor chemistry and growth characteristics. This first report of APP-ALD grown copper layers is an important starting point for high throughput, low-cost manufacturing of copper films for nano- and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide (MoS2) is known for its versatile properties and hence is promising for a wide range of applications. The fabrication of high quality MoS2 either as homogeneous films or as two-dimensional layers on large areas is thus the objective of intense research. Since industry requirements on MoS2 thin films can hardly be matched by established exfoliation fabrication methods, there is an enhanced need for developing new chemical vapor deposition (CVD) and atomic layer deposition (ALD) processes where a rational precursor selection is a crucial step. In this study, a new molybdenum precursor, namely 1,4-di-tert-butyl-1,4-diazabutadienyl-bis(tert-butylimido)molybdenum(VI) [Mo(NtBu)2(tBu2DAD)], is identified as a potential candidate. The combination of imido and chelating 1,4-diazadieneyl ligand moieties around the molybdenum metal center results in a monomeric compound possessing adequate thermal characteristics relevant for vapor phase deposition applications. Hexagonal MoS2 layers are fabricated in a metalorganic CVD (MOCVD) process with elemental sulfur as the co-reactant at temperatures between 600 °C and 800 °C. The structure and composition of the films are investigated by X-ray diffraction, high resolution transmission electron microscopy, synchrotron X-ray photoelectron spectroscopy and Raman spectroscopy revealing crystalline and stoichiometric MoS2 films. The new MOCVD process developed for MoS2 is highly promising due to its moderate process conditions, scalability and controlled targeted composition. [ABSTRACT FROM AUTHOR]

Yttrium oxide (Y2O3) thin films are implemented as a functional component in a broad field of applications such as optics, electronics or thermal barrier coatings. Atomic layer deposition (ALD) is a promising technique to fabricate high‐quality thin films with atomic level precision in which the precursor choice plays a crucial role in process development. The limited number of suitable yttrium precursors available for ALD of Y2O3 has triggered increasing research activity seeking new or modified precursors. In this study, heteroleptic compounds of yttrium bearing the cyclopentadienyl (Cp) ligand in combination with the chelating amidinate or guanidinate ligands were targeted as potential precursors for ALD. In this context, a systematic and comparative study of the structure and thermal characteristics of (bis‐cyclopentadienyl‐(N,N'‐diisopropyl‐2‐methyl‐amidinato)yttrium) [YCp2(dpamd)] 1 and (bis‐cyclopentadienyl‐(N,N'‐diisopropyl‐2‐dimethylamido‐guanidinato)yttrium) [YCp2(dpdmg)] 2 was performed. Complementary characterization tools such as 1H‐NMR, elemental analysis, electron‐impact mass spectrometry (EI‐MS) and single‐crystal X‐ray diffraction (XRD) confirmed the spectroscopic purity and the monomeric nature of the metalorganic compounds. Hirshfeld surface analysis revealed influence of the ligand choice on the intermolecular interactions of the compounds. The important figures of merit for a precursor, namely the thermal properties were investigated via thermogravimetric analysis. Thus, the volatility, transport behavior and thermal stability were examined and compared to their homoleptic counterparts [YCp3], [Y(dpamd)3] or [Y(dpdmg)3]. [ABSTRACT FROM AUTHOR]

Attempted preparation of a chelated CoII β‐silylamide resulted in the unprecedented disproportionation to Co0 and a spirocyclic cobalt(IV) bis(β‐silyldiamide): [Co[(NtBu)2SiMe2]2] (1). Compound 1 exhibited a room‐temperature magnetic moment of 1.8 B.M. and a solid‐state axial EPR spectrum diagnostic of a rare S=1/2 configuration for tetrahedral CoIV. Ab initio semicanonical coupled‐cluster calculations (DLPNO‐CCSD(T)) revealed the doublet state was clearly preferred (−27 kcal mol−1) over higher spin configurations only for the bulky tert‐butyl‐substituted analogue. Unlike other CoIV complexes, 1 had remarkable thermal stability, and was demonstrated to form a stable self‐limiting monolayer in preliminary atomic layer deposition (ALD) surface saturation experiments. The ease of synthesis and high stability make 1 an attractive starting point to investigate otherwise inaccessible CoIV intermediates and for synthesizing new materials. [ABSTRACT FROM AUTHOR]

New precursor chemistries for the atomic layer deposition (ALD) of aluminium oxide are reported as potential alternatives to the pyrophoric trimethylaluminium (TMA) which is to date a widely used Al precursor. Combining the high reactivity of aluminium alkyls employing the 3‐(dimethylamino)propyl (DMP) ligand with thermally stable amide ligands yielded three new heteroleptic, non‐pyrophoric compounds [Al(NMe2)2(DMP)] (2), [Al(NEt2)2(DMP)] (3, BDEADA) and [Al(NiPr2)2(DMP)] (4), which combine the properties of both ligand systems. The compounds were synthesized and thoroughly chemically characterized, showing the intramolecular stabilization of the DMP ligand as well as only reactive Al−C and Al−N bonds, which are the key factors for the thermal stability accompanied by a sufficient reactivity, both being crucial for ALD precursors. Upon rational variation of the amide alkyl chains, tunable and high evaporation rates accompanied by thermal stability were found, as revealed by thermal evaluation. In addition, a new and promising plasma enhanced (PE)ALD process using BDEADA and oxygen plasma in a wide temperature range from 60 to 220 °C is reported and compared to that of a modified variation of the TMA, namely [AlMe2(DMP)] (DMAD). The resulting Al2O3 layers are of high density, smooth, uniform, and of high purity. The applicability of the Al2O3 films as effective gas barrier layers (GBLs) was successfully demonstrated, considering that coating on polyethylene terephthalate (PET) substrates yielded very good oxygen transmission rates (OTR) with an improvement factor of 86 for a 15 nm film by using DMAD and a factor of 25 for a film thickness of just 5 nm by using BDEDA compared to bare PET substrates. All these film attributes are of the same quality as those obtained for the industrial precursor TMA, rendering the new precursors safe and potential alternatives to TMA. [ABSTRACT FROM AUTHOR]

A new N‐heterocyclic carbene (NHC)‐based silver amide compound, 1,3‐di‐tert‐butyl‐imidazolin‐2‐ylidene silver(I) 1,1,1‐trimethyl‐N‐(trimethylsilyl)silanaminide [(NHC)Ag(hmds)] was synthesized and analyzed by single‐crystal X‐ray diffraction, 1H and 13C NMR spectroscopy, as well as EI mass spectrometry, and subsequently evaluated for its thermal characteristics. This new halogen‐ and phosphine‐free Ag atomic layer deposition (ALD) precursor was tested successfully for silver thin film growth in atmospheric pressure plasma enhanced spatial (APP‐ALD). High‐purity conductive Ag thin films with a low sheet resistance of 0.9 Ω/sq (resistivity: 10−5 Ωcm) were deposited at 100 °C and characterized by X‐ray photoelectron spectroscopy, scanning electron microscopy, optical transmittance, and Rutherford back‐scattering techniques. The carbene‐based Ag precursor and the new APP‐ALD process are significant developments in the field of precursor chemistry as well as metal ALD processing. Without contamination: A new halogen‐ and phosphine‐free carbene‐based silver precursor was developed and successfully utilized in plasma‐enhanced spatial atomic layer deposition at atmospheric pressure, yielding low‐resistivity silver thin films. [ABSTRACT FROM AUTHOR]

Herein we describe an efficient low temperature (60–160 °C) plasma enhanced atomic layer deposition (PEALD) process for gallium oxide (Ga2O3) thin films using hexakis(dimethylamido)digallium [Ga(NMe2)3]2 with oxygen (O2) plasma on Si(100). The use of O2 plasma was found to have a significant improvement on the growth rate and deposition temperature when compared to former Ga2O3 processes. The process yielded the second highest growth rates (1.5 Å per cycle) in terms of Ga2O3 ALD and the lowest temperature to date for the ALD growth of Ga2O3 and typical ALD characteristics were determined. From in situ quartz crystal microbalance (QCM) studies and ex situ ellipsometry measurements, it was deduced that the process is initially substrate-inhibited. Complementary analytical techniques were employed to investigate the crystallinity (grazing-incidence X-ray diffraction), composition (Rutherford backscattering analysis/nuclear reaction analysis/X-ray photoelectron spectroscopy), morphology (X-ray reflectivity/atomic force microscopy) which revealed the formation of amorphous, homogeneous and nearly stoichiometric Ga2O3 thin films of high purity (carbon and nitrogen ＜2 at.%) under optimised process conditions. Tauc plots obtained via UV-Vis spectroscopy yielded a band gap of 4.9 eV and the transmittance values were more than 80%. Upon annealing at 1000 °C, the transformation to oxygen rich polycrystalline β-gallium oxide took place, which also resulted in the densification and roughening of the layer, accompanied by a slight reduction in the band gap. This work outlines a fast and efficient method for the low temperature ALD growth of Ga2O3 thin films and provides the means to deposit Ga2O3 upon thermally sensitive polymers like polyethylene terephthalate. [ABSTRACT FROM AUTHOR]

Vapor phase deposited iron oxide nanostructures are promising for fabrication of solid state chemical sensors, photoelectrodes for solar water splitting, batteries, and logic devices. The deposition of iron oxide via chemical vapor deposition (CVD) or atomic layer deposition (ALD) under mild conditions necessitates a precursor that comprises good volatility, stability, and reactivity. Here, a versatile iron precursor, namely [bis( N-isopropylketoiminate) iron(II)], which possesses ideal characteristics both for low-temperature CVD and water-assisted ALD processes, is reported. The films are thoroughly investigated toward phase, composition, and morphology. As-deposited ALD grown Fe2O3 layers are amorphous, while the CVD process in the presence of oxygen leads to polycrystalline hematite layers. The nanostructured iron oxide grown via CVD consists of nanoplatelets that are appealing for photoelectrochemical applications. Preliminary tests of the photoelectrocatalytic activity of CVD-grown Fe2O3 layers show photocurrent densities up to 0.3 mA cm−2 at 1.2 V versus reversible hydrogen electrode (RHE) and 1.2 mA cm−2 at 1.6 V versus RHE under simulated sunlight (1 sun). Surface modification by cobalt oxyhydroxide (Co-Pi) co-catalyst is found to have a highly beneficial effect on photocurrent, leading to maximum monochromatic quantum efficiencies of 10% at 400 nm and 4% at 500 nm at 1.5 V versus RHE. [ABSTRACT FROM AUTHOR]

Identification and synthesis of intramolecularly donor-stabilized aluminium(III) complexes, which contain a 3-(dimethylamino)propyl (DMP) ligand, as novel atomic layer deposition (ALD) precursors has enabled the development of new and promising ALD processes for Al2O3 thin films at low temperatures. Key for this promising outcome is the nature of the ligand combination that leads to heteroleptic Al complexes encompassing optimal volatility, thermal stability and reactivity. The first ever example of the application of this family of Al precursors for ALD is reported here. The process shows typical ALD like growth characteristics yielding homogeneous, smooth and high purity Al2O3 thin films that are comparable to Al2O3 layers grown by well-established, but highly pyrophoric, trimethylaluminium (TMA)-based ALD processes. This is a significant development based on the fact that these compounds are non-pyrophoric in nature and therefore should be considered as an alternative to the industrial TMA-based Al2O3 ALD process used in many technological fields of application. [ABSTRACT FROM AUTHOR]

Luminescent erbium-based inorganic-organic hybrid materials play an important role in many frontier nano-sized applications, such as amplifiers, detectors and OLEDs. Here, we demonstrate the possibility to fabricate high-quality thin films comprising both erbium and an appropriate organic molecule as a luminescence sensitizer utilizing the combined atomic layer deposition and molecular layer deposition (ALD/MLD) technique. We employ tris( N, N′-diisopropyl-2-dimethylamido guanidinato)erbium(III) [Er(DPDMG)] together with 3,5-pyridine dicarboxylic acid as precursors. With the appreciably high film deposition rate achieved (6.4 Å cycle), the guanidinate precursor indeed appears as an interesting new addition to the ALD/MLD precursor variety toward novel materials. Our erbium-organic thin films showed highly promising UV absorption properties and a photoluminescence at 1535 nm for a 325-nm excitation, relevant to possible future luminescence applications. [ABSTRACT FROM AUTHOR]

The influences of annealing temperature in N atmosphere on interfacial chemical properties and band alignment of AlN/Si structure deposited by atomic layer deposition have been investigated based on x-ray photoelectron spectroscopy and spectroscopic ellipsometry. It is found that more oxygen incorporated into AlN film with the increasing annealing temperature, resulting from a little residual HO in N atmosphere reacting with AlN film during the annealing treatment. Accordingly, the Si-N bonding at the interface gradually transforms to Si-O bonding with the increasing temperature due to the diffusion of oxygen from AlN film to the Si substrate. Specially, the Si-O-Al bonding state can be detected in the 900 °C-annealed sample. Furthermore, it is determined that the band gap and valence band offset increase with increasing annealing temperature. [ABSTRACT FROM AUTHOR]

In this study the atomic layer deposition (ALD) of TiO2 and ZrO2 using two heteroleptic amido-guanidinate precursors, [Ti(NEtMe)3(guan-NEtMe)] and [Zr(NEtMe)3(guan-NEtMe)], together with water or ozone as oxygen sources, are investigated. All processes exhibit self-limiting growth at a deposition temperature of 275°C. The zirconium precursor especially gives high growth rates (0.8/1.0 Å per cycle with H2O/O3). The films are also relatively smooth, as determined by atomic force microscopy (AFM). The composition of the films is examined using X-ray photoelectron spectroscopy (XPS) and time of flight elastic recoil detection analysis (TOF-ERDA). When using ozone as the oxygen source the films present very high purity. The results are compared and discussed with respect to earlier studies on guanidinate, as well as homoleptic amido precursors. [ABSTRACT FROM AUTHOR]

We report on the electrical and optical characterisation of the high-permittivity (high- κ) TiO2 thin films grown by plasma enhanced atomic layer deposition on Si (100) and glass substrates, respectively. TiO2 films were incorporated in metal-oxide semiconductor (MOS) capacitor structures with an Al metal gate electrode. The as-deposited films were amorphous; however upon annealing in the temperature range 500-900 °C, crystalline TiO2 in the anatase phase was formed. This was further confirmed by performing Raman measurements where the characteristic features corresponding to the anatase phase were observed. Transmittance and absorption spectra of the as-deposited and annealed films were performed by UV-Vis measurements showing more than 70% of transmittance. The formation of stoichiometric TiO2 was revealed by X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectroscopy (RBS) analysis performed on annealed samples (500-900 °C). The dielectric constants were calculated from capacitance-voltage ( C- V) curves of the MOS structure on the as-deposited film and annealed films revealing a significant improvement of the dielectric constants from 10 to 75 at AC frequencies of 100 kHz for the 700 °C annealed TiO2 thin films. The increase in the dielectric constant for annealed films could be attributed to the transformation of film structure from amorphous to polycrystalline (anatase). However, the transformation of amorphous to crystalline phase, leads to an increase in the leakage current which was also found best fitted with Schottky emission mechanism at moderated electric fields. [ABSTRACT FROM AUTHOR]

Highlights: [•] Progress in precursor chemistry at the Inorganic Materials Chemistry group in Bochum reported. [•] New classes of MOCVD and ALD precursors developed for group IV and rare earth oxides. [•] Promising group IV alkoxide and amide based complexes successfully evaluated as precursors. [•] Novel rare earth complexes with malonates, guanidinates and amidinates as ligands. [•] Guanidinate complexes have evolved as bench mark precursors for MOCVD and ALD. [Copyright &y& Elsevier]

Cover Feature: Role of Anionic Backbone in NHC-Stabilized Coinage Metal Complexes: New Precursors for Atomic Layer Deposition (Chem. Eur. J. 16/2022) Atomic layer deposition, carbene ligands, coinage metals, precursors, X-ray diffraction Keywords: atomic layer deposition; carbene ligands; coinage metals; precursors; X-ray diffraction EN atomic layer deposition carbene ligands coinage metals precursors X-ray diffraction 1 1 1 03/22/22 20220316 NES 220316 B A series of new N-heterocyclic carbene (NHC) b based Cu(I) and Ag(I) complexes were synthesized, analyzed, and evaluated for their potential usage in atomic layer deposition (ALD) of coinage metal thin films. [Extracted from the article]

[Display omitted] • CuO x enhances the growth per cycle of CrO x in atomic layer deposition. • Optoelectronic properties of copper-chromium-oxide ternary compounds were reported. • Addition of Cu in CrO x increases the work function of the thin film. • The work function of CuCr 2 O 4 is 5 eV. In this work, we investigate the properties of Cu x Cr y O z thin films deposited by atomic layer deposition (ALD) over a wide compositional range. A significant increase in growth rate is observed for intermediate compositions and shown to arise from an enhancement of the CrO x deposition rate on the CuO x surface. In addition to the characteristics of the deposition process, we explore the structural and optoelectronic properties of these films for compositions ranging from copper-free chromium oxide to chromium-free copper oxide, and for various post-deposition annealing temperatures (400–800 °C). The resulting composition, optical constants, band gap, valence band maximum and work function are determined and used to draw full band diagrams of the binary and ternary oxides. We report for the first time the experimental work function of the spinel phase CuCr 2 O 4 (5.0 ± 0.2 eV). Finally, the contact resistivity of the films with p-type silicon is examined to assess their potential use as hole-selective contacts for crystalline Si solar cells. The lowest contact resistivity (1.72 Ω cm2) was found for as-deposited Cu 0.05 Cr 0.30 O 0.65. [ABSTRACT FROM AUTHOR]

• Heterostructured p-CuO/n-SnO2 core-shell NWs with precisely controlled shell thickness were synthesized by ALD technique. • The p-CuO/n-SnO2 core-shell NW structured gas sensors with 24 nm SnO2 shell layer exhibited enhanced sensing performance. • The well-structured core-shell NWs also have excellent selectivity for HCHO. Highly sensitive and selective gas sensors based on heterostructured p -CuO/ n -SnO 2 core-shell nanowires (NWs) with precisely controlled shell thickness were synthesized through a sequential process combining a solution processing and atomic layer deposition. The gas sensing devices were fabricated on micro-electromechanical systems, which has triggered great research interest for low power consumption and highly integrated design. The designed p -CuO/ n -SnO 2 core-shell NW structured gas sensors exhibited superior gas sensing performance, which is closely related to the thickness of the SnO 2 shell. Specifically, p -CuO/ n -SnO 2 core-shell NWs with a 24 nm thick SnO 2 shell displayed a high sensitivity (R a /R g) of 2.42, whose rate of resistance change (i.e. 1.42) is 3 times higher than the pristine CuO NW sensor when detecting 50 ppm formaldehyde (HCHO) at 250 °C. The enhanced gas sensing performance could be attributed to the formation of p - n heterojunction which was revealed by specific band alignment and the heterojunction-depletion model. Besides, the well-structured p -CuO/ n -SnO 2 core-shell NWs achieved excellent selectivity for HCHO from commonly occurred reducing gases. In a word, such heterostructured p -CuO/ n -SnO 2 core-shell NW gas sensors demonstrate a feasible approach for enhanced sensitive and selective HCHO detection. [ABSTRACT FROM AUTHOR]

Herein, we describe a process for the low-temperature atomic layer deposition of copper using Cu(dmap)2 (dmap = dimethylamino-2-propoxide). The use of tertiary butyl hydrazine (TBH) as the reducing agent was found to have a significant improvement on the purity and the resistivity of the Cu films compared to previous processes. Our process was studied at low temperatures of 80-140 °C on native oxide terminated Si. At 120 °C, self-limiting Cu deposition was demonstrated with respect to both Cu(dmap)2 and TBH pulse lengths. During the initial stages of the deposition (125-1000 cycles), a growth rate of 0.17 Å/cycle was measured. Once the substrate surface was completely covered, deposition proceeded with a more moderate growth rate of 0.05 Å/cycle. According to X-ray diffraction, the films were crystalline cubic Cu with a slight preference toward (111) orientation. Based on scanning electron micrographs, the Cu films were relatively smooth with the roughness increasing as a function of both increasing temperature and thickness. A 54 nm film deposited at the low temperature of 120 °C exhibited a low resistivity of 1.9 μΩ·cm. Composition analysis on this film showed a remarkably high purity of approximately 99.4 at.%, with the rest being hydrogen and oxygen. The films could be deposited also on hydrogen terminated Si, glass, Al2O3, TiN, and Ru, extending the suitability of the process to a wide range of applications. [ABSTRACT FROM AUTHOR]

We have developed a low-temperature atomic layer deposition (ALD) process for depositing crystalline and phase pure spinel cobalt oxide (Co3O4) films at 120 °C using [Co(tBu2DAD)2] and ozone as coreagent. X-ray diffraction, UV-vis spectroscopy, atomic force microscopy, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, and time-of-flight elastic recoil detection analysis were performed to characterize the structure and properties of the films. The as-deposited Co3O4 films are crystalline with a low amount of impurities (<2% C and <5% H) despite low deposition temperatures. Deposition of Co3O4 onto thin TiO2 photoanodes (100 nm) for water oxidation resulted in 30% improvement of photocurrent (after 10 ALD cycles yielding small Co3O4 particles) as compared to pristine TiO2 films), and exhibited no detrimental effects on photocurrent response up to 300 deposition cycles (approximately 35 nm thick films), demonstrating the applicability of the developed ALD process for deposition of effective catalyst particles and layers in photoelectrochemical water-splitting devices. [ABSTRACT FROM AUTHOR]

Volatile metal complexes are important for chemical vapour deposition (CVD) and atomic layer deposition (ALD) to deliver metal componentsto growing thin films. Compounds that are thermally stable enoughto volatilize but that can also react with a specific substrate are uncommon and remain unknown for many metal centres. Guanidinate ligands, as discussed in this review, have proven their utility for CVD and ALD precursors for a broad range of metal centres. Guanidinate complexes have been used to deposit metal oxides, metal nitrides and pure metal films by tuning process parameters. Our review highlights use of guanidinate ligands for CVD and ALD of thin films over the past five years, design trends for precursors, promising precursor candidates and discusses the future outlook of these ligands. [ABSTRACT FROM AUTHOR]

[Zr(NEtMe)2(guan-NEtMe2)2], arecently developed compound, was investigated as a novel precursorfor the atomic layer deposition (ALD) of ZrO2. With wateras the oxygen source, the growth rate remained constant over a widetemperature range, whereas with ozone the growth rate increased steadilywith deposition temperature. Both ALD processes were successfullydeveloped: the characteristic self-limiting ALD growth mode was confirmedat 300 °C. The growth rates were exceptionally high, 0.9 and1.15 Å/cycle with water and ozone, respectively. X-ray diffraction(XRD) indicated that the films were deposited in the high-permittivitycubic phase, even when grown at temperatures as low as 250 °C.Compositional analysis performed by means of X-ray photoelectron spectroscopy(XPS) demonstrated low carbon and nitrogen contamination (<2 at.% when deposited with ozone). The films presented low root-mean-square(rms) roughness, below 5% of the film thickness, as well as excellentstep coverage and conformality on 30:1 aspect ratio trench structures.Dielectric characterization was performed on ZrO2metal–insulator–metal(MIM) capacitors and demonstrated high permittivity and low leakagecurrent, as well as good stability of the capacitance. The ALD reactionmechanism was studied in situ: adsorption of the precursor throughreaction of the two guan-NEtMe2ligands with the surface−OD groups was confirmed by the quartz crystal microbalance(QCM) and quadrupole mass spectrometric (QMS) results. [ABSTRACT FROM AUTHOR]

We studied the growth of TiO2by liquid injection atomiclayer deposition (ALD) utilizing two different amide-based titaniumsources, tetrakis-dimethylamido-titanium [(NMe2)4-Ti, TDMAT] and its recently developed derivative, tris-(dimethylamido)-mono-(N,N′-diisopropyl-dimethyl-amido-guanidinato)-titanium{[(N-iPr)2NMe2]Ti(NMe2)3, TiA3G1}, with water vapor as counterreactant.A clear saturation of growth with an increasing precursor supply wasfound for TDMAT between 150 and 300 °C and for TiA3G1between 150 and 330 °C. Representative growthper cycle (GPC) values at 250 °C were 0.041 and 0.044 nm/cycle,respectively. Compared to that of TDMAT, ALD of TiA3G1exhibited a significantly higher stability in the GPC valuesup to 300 °C coinciding with an improved temperature stabilityof the precursor. Both processes showed a minimum of the growth rateas a function of temperature. In all cases, the residual carbon andnitrogen contents of the TiO2films were <3 atom %.Conformal growth was demonstrated on three-dimensional pinhole structureswith an aspect ratio of around 1:30. Deposition temperatures of ≤200°C led to quasi-amorphous films. At higher growth temperatures,the anatase phase developed, accompanied by the brookite and/or therutile phase depending on process conditions, deposition temperature,and film thickness. [ABSTRACT FROM AUTHOR]

Gd2O3 and Dy2O3 thin films were grown by atomic layer deposition (ALD) on Si(100) substrates using the homoleptic rare earth guanidinate based precursors, namely, tris(N,N′-diisopropyl-2-dimethylamido-guanidinato)gadolinium(III) [Gd(DPDMG)3] (1) and tris(N,N′-diisopropyl-2-dimethylamido-guanidinato)dysprosium(III) [Dy(DPDMG)3] (2), respectively. Both complexes are volatile and exhibit high reactivity and good thermal stability, which are ideal characteristics of a good ALD precursor. Thin Gd2O3 and Dy2O3 layers were grown by ALD, where the precursors were used in combination with water as a reactant at reduced pressure at the substrate temperature ranging from 150 °C to 350 °C. A constant growth per cycle (GPC) of 1.1 Å was obtained at deposition temperatures between 175 and 275 °C for Gd2O3, and in the case of Dy2O3, a GPC of 1.0 Å was obtained at 200–275 °C. The self-limiting ALD growth characteristics and the saturation behavior of the precursors were confirmed at substrate temperatures of 225 and 250 °C within the ALD window for both Gd2O3 and Dy2O3. Thin films were structurally characterized by grazing incidence X-ray diffraction (GI-XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM) analyses for crystallinity and morphology. The chemical composition of the layer was examined by Rutherford backscattering (RBS) analysis and Auger electron spectroscopy (AES) depth profile measurements. The electrical properties of the ALD grown layers were analyzed by capacitance–voltage (C–V) and current–voltage (I–V) measurements. Upon subjection to a forming gas treatment, the ALD grown layers show promising dielectric behavior, with no hysteresis and reduced interface trap densities, thus revealing the potential of these layers as high-k oxide for application in complementary metal oxide semiconductor based devices. The application of the tris-guanidinates of Gd and Dy for the low-temperature water-assisted atomic layer deposition (ALD) process of their respective oxide thin films has been demonstrated. True ALD characteristics were verified for Gd2O3 and Dy2O3, with the films exhibiting high quality interface and promising electrical properties, revealing their potential as high-k gate dielectrics in future complementary metal oxide semiconductor based device applications. [ABSTRACT FROM AUTHOR]