Atomic Layer Deposition Growth Research Articles

H2O-based atomic layer deposition mechanism of aluminum oxide using trimethylaluminum

As a nanofabrication technology, atomic layer deposition (ALD) has been widely used in the fields of displays, microelectronics, nanotechnology, catalysis, energy and coatings. It demonstrates excellent conformality, large-area uniformity and precise control of the sub-monolayer film. Al2O3 ALD using trimethylaluminum (TMA) and water (H2O) as precursors is the most ideal ALD model system. In this work, the reactions of TMA and H2O with the surface have been investigated using density functional theory (DFT) calculations in order to obtain more information on the reaction mechanism of the complicated H2O-based ALD of Al2O3. In the TMA reaction, the methyl ligands can be eliminated and new Al-O bonds can be formed via ligand exchange reactions. In the H2O reaction, the methyl ligand on the surface can be further eliminated and new AlO bonds can be formed. Meanwhile, the coupling reactions between the surface methyl and hydroxyl groups can further form new AlO bonds and release CH4 or H2O to densify the Al2O3 film. These complicated reaction mechanisms of Al2O3 H2O-based ALD can provide theoretical guidance for the precursor design and ALD growth of other oxides and aluminum-based compounds.

Atomic Layer Growth of Rutile TiO2 Films with Ultrahigh Dielectric Constants via Crystal Orientation Engineering.

In general, the electronic and optical properties of oxide films can significantly benefit from highly textured crystallinity. However, oxide films grown by atomic layer deposition (ALD), a powerful technique for the synthesis of high-quality, nanoscale thin films, usually exhibit amorphous or randomly oriented polycrystalline phases. Here, we demonstrate the growth of highly textured rutile phase ALD TiO2 films through rational substrate design. Both a- and c-axis preferentially oriented TiO2 films are obtained by varying the lattice parameters of the initial ALD growth surface. Under optimized conditions, we find that it is possible to deposit high-quality, c-axis preferentially aligned TiO2 films with a bulk dielectric constant approaching 185, rivaling the single crystal limit. These films display a remarkably high dielectric constant of 117 despite thin thickness of 5.2 nm. Moreover, the addition of a single doping sequence of Al2O3 successfully suppresses leakage currents to levels compatible with modern dynamic random access memory cells, all the while maintaining the high bulk dielectric constant of 137. These results clearly highlight the prospect of utilizing crystal orientation engineering in ALD thin films for emerging semiconductor devices.

Atomic Layer Deposition Growth and Characterization of Al2O3 Layers on Cu-Supported CVD Graphene

The deposition of thin uniform dielectric layers on graphene is important for its successful integration into electronic devices. We report on the atomic layer deposition (ALD) of Al2O3 nanofilms onto graphene grown by chemical vapor deposition onto copper foil. A pretreatment with deionized water (DI H2O) for graphene functionalization was carried out, and, subsequently, trimethylaluminum and DI H2O were used as precursors for the Al2O3 deposition process. The proper temperature regime for this process was adjusted by means of the ALD temperature window for Al2O3 deposition onto a Si substrate. The obtained Al2O3/graphene heterostructures were characterized by Raman and X-ray photoelectron spectroscopy, ellipsometry and atomic force and scanning electron microscopy. Samples of these heterostructures were transferred onto glass substrates by standard methods, with the Al2O3 coating serving as a protective layer during the transfer. Raman monitoring at every stage of the sample preparation and after the transfer enabled us to characterize the influence of the Al2O3 coating on the graphene film.

Precursor design and cascade mechanism of RuO2·xH2O atomic layer deposition

As the unique nanofabrication technique, atomic layer deposition (ALD) can be used to deposit high-quality, uniform, and conformal nanoparticle coatings. Ru and its oxides (RuOx) are important materials in the fields of microelectronics and catalysis. In this work, the reaction of Ru precursors with different ligands on the hydroxylated surfaces were explored. The elimination of the pyrrolyl (Py) ligand is easier than that of the cyclopentadienyl (Py) ligand on the hydroxylated surface. The reaction involved in RuO2·xH2O ALD using RuPy2 and H2O as precursors was further investigated. During the RuPy2 reaction, the pyrrolyl ligand is eliminated by the substitution reaction with a surface hydroxyl group. However, the desorption of the pyrrole molecule is difficult due to the strong adsorption between the pyrrole molecule and Ru surface. During the H2O reaction, the H2O molecules further help the elimination of pyrrolyl ligands from the surface and the dissociative desorption of pyrrole molecules This unique reaction mechanism involved in the ALD of RuO2 with the assistance of H2O can be termed new cascade mechanism. These findings provide theoretical guidance for precursor design and ALD growth of metal oxides.

Area-selective atomic layer deposition of palladium

We report area-selective deposition of palladium using sequential area-blocking and area-activation ALD processes. Thermal atomic layer deposition (ALD) of palladium is investigated at 100 °C using palladium (II) hexafluoroacetylacetonate and hydrogen. Palladium deposition does not proceed at such a low temperature unless catalytic sites are present to dissociate hydrogen during Pd film nucleation and before sufficient Pd has accumulated to serve as the catalyst for hydrogen dissociation. Ultrathin (<2 nm) nickel metal surfaces served as the initial catalytic sites and are prepared via low temperature (100 °C) reduction of NiO ALD films using a H-atom doser operating at 3 × 10−5 Torr. The Ni0 films are shown to seed the ALD of Pd, demonstrating a route to Pd ALD by area activation. Blanket NiO films are used to study Pd ALD growth and patterned NiO films, formed by area-blocking ALD, are used to demonstrate a bottom-up approach to patterned Pd films.

Role of a cyclopentadienyl ligand in a heteroleptic alkoxide precursor in atomic layer deposition.

Alkoxide precursors have been highlighted for depositing carbon-free films, but their use in Atomic Layer Deposition (ALD) often exhibits a non-saturated growth. This indicates no self-limiting growth due to the chain reaction of hydrolysis or ligand decomposition caused by β-hydride elimination. In the previous study, we demonstrated that self-limiting growth of ALD can be achieved using our newly developed precursor, hafnium cyclopentadienyl tris(N-ethoxy-2,2-dimethyl propanamido) [HfCp(edpa)3]. To elucidate the growth mechanism and the role of cyclopentadienyl (Cp) ligand in a heteroleptic alkoxide precursor, herein, we compare homoleptic and heteroleptic Hf precursors consisting of N-ethoxy-2,2-dimethyl propanamido (edpa) ligands with and without cyclopentadienyl ligand-hafnium tetrakis(N-ethoxy-2,2-dimethyl propanamido) [Hf(edpa)4] and HfCp(edpa)3. We also investigate the role of a Cp ligand in growth characteristics. By substituting an alkoxide ligand with a Cp ligand, we could modify the surface reaction during ALD, preventing undesired reactions. The last remaining edpa after Hf(edpa)4 adsorption can undergo a hydride elimination reaction, resulting in surface O-H generation. In contrast, Cp remains after the HfCp(edpa)3 adsorption. Accordingly, we observe proper ALD growth with self-limiting properties. Thus, a comparative study of different ligands of the precursors can provide critical clues to the design of alkoxide precursors for obtaining typical ALD growth with a saturation behavior.

Electronic properties of ZrO2 films fabricated via atomic layer deposition on 4H-SiC and Si substrates

Being an important semiconductor material for high power applications, silicon carbide (SiC) faces the problems while used as a gate oxygen layer in traditional Si MOS devices. In view of this, an innovative approach was adopted in the present work to replace the conventional SiO2 with a high-k material (ZrO2) as the gate oxygen layer to investigate its effect on the electrical characteristics of the devices. In particular ZrO2 films were deposited on Si and SiC substrates by atomic layer deposition (ALD), and Al was used as the electrode. The atomic force microscopy (AFM) microregion scan revealed a highly flat surface with Rq < 1 nm after the ALD growth of ZrO2 layer. The sample surface analysis via x-ray photoelectron spectroscopy (XPS) suggested the presence of a small amount of ZrOx components. According to the electron energy loss spectrum (EELS), the band gap width (Eg) of this ALD ZrO2 dielectric was 5.45 eV, which met the requirements for high-quality 4H-SiC-related MOS devices. The electrical properties of the samples were then studied, and the maximum breakdown voltage of the Al/ZrO2/SiC/Al MOS structure was obtained to be 23 V, i.e., nearly twice that of the Si substrate. As for the oxide layer, the interface defect density (Dit) near the conduction band of the Al/ZrO2/SiC/Al MOS structure was only 1012 eV−1 cm−2 orders of magnitude. The Neff value (the movable charge) of the structure was also controlled at 1012 cm−2. Therefore, the overall performance of the ZrO2/SiC structure in terms of electrical properties exceeded that of the ZrO2/Si structure and previously reported counterparts. In this respect, the ZrO2/SiC MOS capacitor structure has great research potential.

Atomic layer deposition and application of group III nitrides semiconductor and their alloys

Group III nitride semiconductors, such as GaN, AlN, and InN, are an important class of compound semiconductor material, and have attracted much attention, because of their unique physicochemical properties. These semiconductors possess excellent characteristics, such as wide direct bandgap, high breakdown field strength, high electron mobility, and good stability, and thus are called third-generation semiconductors. Their alloy materials can adjust their bandgaps by changing the type or proportion of group III elements, covering a wide wavelength range from near-ultraviolet to infrared, thereby achieving wavelength selectivity in optoelectronic devices. Atomic layer deposition (ALD) is a unique technique that produces high-quality group III nitride films at low temperatures. The ALD has become an important method of preparing group III nitrides and their alloys. The alloy composition can be easily controlled by adjusting the ALD cycle ratio. This review highlights recent work on the growth and application of group III nitride semiconductors and their alloys by using ALD. The work is summarized according to similarities so as to make it easier to understand the progress and focus of related research. Firstly, this review summarizes binary nitrides with a focus on their mechanism and application. In the section on mechanism investigation, the review categorizes and summarizes the effects of ALD precursor material, substrate, temperature, ALD type, and other conditions on film quality. This demonstrates the effects of different conditions on film growth behavior and quality. The section on application exploration primarily introduces the use of group III nitride films in various devices through ALD, analyzes the enhancing effects of group III nitrides on these devices, and explores the underlying mechanisms. Additionally, this section discusses the growth of group III nitride alloys through ALD, summarizing different deposition methods and conditions. Regarding the ALD growth of group III nitride semiconductors, there is more research on the ALD growth of AlN and GaN, and less research on InN and its alloys. Additionally, there is less research on the ALD growth of GaN for applications, as it is still in the exploratory stage, while there is more research on the ALD growth of AlN for applications. Finally, this review points out the prospects and challenges of ALD in preparation of group III nitride semiconductors and their alloys.

Nucleation Behavior and Growth Characteristics of Atomic-Layer Deposited Iridium Thin Films with Ticp and Oxygen

Platinum group elements (Pt, Ru, Pd, Rh, Ag, Au, and Ir) have excellent properties of high thermal and chemical stability, and low electrical resistivity. Due to the attractive characteristics, these materials are also expected for applications in the semiconductor industries. In particular, iridium (Ir) has attracted interests as a potential electrode for memory devices because of its high work function and low resistivity (bulk: 4.7 μΩ cm).Despite the advantages of Ir, the deposition of Ir thin films for the next-generation memory applications faces critical challenges. Since metal has a high surface energy, it is difficult to adsorb on a surface with a lower surface energy. So, formation of metal nuclei is delayed in the initial growth of atomic layer deposition (ALD), and island growth is preferred. During the ALD, sparsely grown nuclei cause an increase in surface roughness which deteriorates the leakage current properties of capacitors.In this study, we attempted ALD of Ir films from newly synthesized tricarbonyl (1,2,3-η)-1,2,3-tri(tert-butyl)-cyclopropenyl iridium and oxygen. The growth behavior and film properties of impurity contents and bulk resistivity were investigated in terms of the growth temperature. Also, we examined the changes in the surface morphology of the iridium film with the film thickness. Consequently, we achieved the growth of continuous and smooth Ir films even below 4 nm by forming nucleation-promoting layer at high temperature and followed by ALD of Ir at low temperature. In addition, the capacitor device characteristics were also investigated using Ir as a bottom electrode.

Strontium Vanadate Deposited by ALD: Toward a New Synthesis Approach

Transparent conductive oxides (TCOs) have a wide range of potential applications in fields such as photovoltaics, touch screens, and smart windows. The challenging task when developing conventional TCOs like tin-doped indium oxide (ITO) by the traditional method is to make them more conducting by increasing the concentration of charge carriers without compromising the optical transparency [1]. Another novel approach involves increasing the plasma energy to widen the transparency window by increasing the charge carriers' effective mass. This approach has led to growing interest in perovskite transition metal oxides such as CaVO3 and SrVO3 due to their strong electronic correlation, which results in plasma energy shifting to higher energies than classical TCOs [2,3]. However, obtaining a crystallized film in the perovskite SrVO3 phase for optimal electrical conduction and optical transparency is challenging, particularly at low growth temperatures and when deposited on amorphous substrates like glasses [2, 4].As a result, atomic layer deposition (ALD) has emerged as a promising technique for depositing conformal layers on large surfaces with high aspect ratios and low thermal budgets. In this study, we investigated the deposition of strontium vanadium oxide films by ALD using vanadium tri-isopropoxide (VTIP) as the vanadium precursor, strontium bis(isopropylcyclopentadienyl) (Sr(iPr3Cp)2) from Air Liquide company as the strontium precursor, and water as a reagent, respectively. We deposited SrVO3 films on (100) Silicon and glass substrates at 240°C and annealed them under forming gas (95% Ar, 5% H2) at 500°C for one hour. We paid particular attention to the deposition of an anatase TiO2 buffer layer to promote the crystallization of SVO.The unannealed films were found to be completely amorphous whatever the substrate, and regardless of the presence or not of the TiO2 crystallized buffer. The EDX, STEM-HAADF and SIMS analyses revealed that the buffer is a key element to avoid the Si diffusion in SVO layer, before, and even more upon annealing. The annealed samples with a buffer layer deposited on both substrates were crystallized into various SrxVyOz phases according to the Sr amount, controlled by the Sr cycles ratio (RSR) (figure). The XRD data allowed the identification of the Sr3VO8 and Sr2VO4 phases, where the last one favors the higher Sr amount. The influence of the substrate is significant and discussed. Furthermore, we characterized the films' optical properties using spectroscopic ellipsometry in the UV-visible range. We analyzed the refractive index and extinction coefficient behavior according to the Sr amount and evaluated the effect of annealing. We estimated the band gap energy using Tauc-Lorentz and Tauc plot models and discussed it in relation to the Sr amount and the obtained phases.Our study provides not only valuable insights into the deposition and characterization of SrVO3 thin films for potential TCO applications, but also on Sr3VO8 and Sr2VO4 phases, which may be of interest for their transparent oxide optical properties. New ALD growth strategies to improve the SrVO3 phases will be presented as a perspective of this study and as an example of using different V precursor or reactive atmospheres during ALD process.[1] S.C. Dixon, D.O. Scanlon, C.J. Carmalt, I.P. Parkin, "n-Type doped transparent conducting binary oxides: an overview", Journal of Materials Chemistry C, 4, 29 (2016), pp. 6946-6961[2] Zhang, Lei, et al. "Correlated metals as transparent conductors." Nature materials 15.2 (2016): 204-210.[3] Boileau, Alexis, et al. "Highly Transparent and Conductive Indium‐Free Vanadates Crystallized at Reduced Temperature on Glass Using a 2D Transparent Nanosheet Seed Layer." Advanced Functional Materials 32.5 (2022): 2108047.[4] A. Boileau, A. Cheikh, A. Fouchet, A. David, C. Labbé, P. Marie, F. Gourbilleau, U. Lüders, "Tuning of the optical properties of the transparent conducting oxide SrVO3 by electronic correlations", Advanced Optical Materials, 7, 7 (2019), pp. 1801516 Figure 1

Structure and strain of CdS nanofilms on Au(111) during electrochemical atomic layer deposition growth

X-ray scattering is used to characterise the initial stages of the growth of CdS on Au(111) surfaces via electrochemical atomic layer deposition (E-ALD). This work characterises E-ALD films using a unique in-situ setup, allowing for X-ray reflectivity and diffraction data to be obtained to characterise the growth process of the CdS film. Structural information, as well as information concerning growth rates, roughness and strain as a function of the stage in the growth process, are obtained to provide a unique perspective of the early stages of deposition for this methodology. The results show the self-limiting, linear growth rate of CdS films that are wurtzite in structure, are highly epitaxial with the underlying Au substrate, and exhibit little to no chemical impurities during the deposition procedure.

Combination of Multiple Operando and In-Situ Characterization Techniques in a Single Cluster System for Atomic Layer Deposition: Unraveling the Early Stages of Growth of Ultrathin Al2O3 Films on Metallic Ti Substrates

This work presents a new ultra-high vacuum cluster tool to perform systematic studies of the early growth stages of atomic layer deposited (ALD) ultrathin films following a surface science approach. By combining operando (spectroscopic ellipsometry and quadrupole mass spectrometry) and in situ (X-ray photoelectron spectroscopy) characterization techniques, the cluster allows us to follow the evolution of substrate, film, and reaction intermediates as a function of the total number of ALD cycles, as well as perform a constant diagnosis and evaluation of the ALD process, detecting possible malfunctions that could affect the growth, reproducibility, and conclusions derived from data analysis. The homemade ALD reactor allows the use of multiple precursors and oxidants and its operation under pump and flow-type modes. To illustrate our experimental approach, we revisit the well-known thermal ALD growth of Al2O3 using trimethylaluminum and water. We deeply discuss the role of the metallic Ti thin film substrate at room temperature and 200 °C, highlighting the differences between the heterodeposition (&lt;10 cycles) and the homodeposition (&gt;10 cycles) growth regimes at both conditions. This surface science approach will benefit our understanding of the ALD process, paving the way toward more efficient and controllable manufacturing processes.

Atomic layer deposited RuO2 with controlled crystallinity and thickness for oxygen evolution reaction catalysis

The effective production of hydrogen as an attractive alternative energy source requires efficient electrocatalysis of the oxygen evolution reaction (OER), the rate-determining step in water splitting. Ruthenium oxide has been investigated as a representative OER catalyst; however, additional research is required for practical applications because of its low stability and varied performance depending on the fabrication method. In this study, RuO2 was prepared via atomic layer deposition (ALD). The crystallinity of the film was controlled by adjusting the ALD growth temperature, and its influence on the OER performance was examined. In addition, ALD cycles were controlled to study the influence of film thickness on the OER performance, allowing for a comparative analysis. The RuO2 film was deposited onto carbon fiber paper (CFP) to enhance its active surface area for the OER. The as-obtained samples were analyzed using various techniques, including X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that the crystalline RuO2 grown at 400 °C performed better catalytic performance than amorphous RuO2 grown at 350 °C, and adjusting the film thickness enhanced the electrochemical performance and stability of the catalyst film.

Constructing tin oxides Interfacial Layer with Gradient Compositions for Efficient Perovskite/Silicon Tandem Solar Cells with Efficiency Exceeding 28.

Atomic layer deposition (ALD) growth of conformal thin SnOx films on perovskite absorbers offers a promising method to improve carrier-selective contacts, enable sputter processing, and prevent humidity ingress toward high-performance tandem perovskite solar cells. However, the interaction between perovskite materials and reactive ALD precursor limits the process parameters of ALD-SnOx film and requires an additional fullerene layer. Here, it demonstrates that reducing the water dose to deposit SnOx can reduce the degradation effect upon the perovskite underlayer while increasing the water dose to promote the oxidization can improve the electrical properties. Accordingly, a SnOx buffer layer with a gradient composition structure is designed, in which the compositionally varying are achieved by gradually increasing the oxygen source during the vapor deposition from the bottom to the top layer. In addition, the gradient SnOx structure with favorable energy funnels significantly enhances carrier extraction, further minimizing its dependence on the fullerene layer. Its broad applicability for different perovskite compositions and various textured morphology is demonstrated. Notably, the design boosts the efficiencies of perovskite/silicon tandem cells (1.0cm2) on industrially textured Czochralski (CZ) silicon to a certified efficiency of 28.0%.

Synergistic Combination of Reductive Covalent Functionalization and Atomic Layer Deposition—Towards Spatially Defined Graphene‐Organic‐Inorganic Heterostructures

AbstractThree‐dimensionally (3D) well‐ordered and highly integrated graphene hybrid architectures are considered to be next‐generation multifunctional graphene materials but still remain elusive. Here, we report the first realization of unprecedented 3D‐patterned graphene nano‐ensembles composed of a graphene monolayer, a tailor‐made structured organophenyl layer, and three metal oxide films, providing the first example of such a hybrid nano‐architecture. These spatially resolved and hierarchically structured quinary hybrids are generated via a two‐dimensional (2D)‐functionalization‐mediated atomic layer deposition growth process, involving an initial lateral molecular programming of the graphene lattice via lithography‐assisted 2D functionalization and a subsequent stepwise molecular assembly in these regions in the z‐direction. Our breakthrough lays the foundation for the construction of emerging 3D‐patterned graphene heterostructures.

Synergistic Combination of Reductive Covalent Functionalization and Atomic Layer Deposition-Towards Spatially Defined Graphene-Organic-Inorganic Heterostructures.

Three-dimensionally (3D) well-ordered and highly integrated graphene hybrid architectures are considered to be next-generation multifunctional graphene materials but still remain elusive. Here, we report the first realization of unprecedented 3D-patterned graphene nano-ensembles composed of a graphene monolayer, a tailor-made structured organophenyl layer, and three metal oxide films, providing the first example of such a hybrid nano-architecture. These spatially resolved and hierarchically structured quinary hybrids are generated via a two-dimensional (2D)-functionalization-mediated atomic layer deposition growth process, involving an initial lateral molecular programming of the graphene lattice via lithography-assisted 2D functionalization and a subsequent stepwise molecular assembly in these regions in the z-direction. Our breakthrough lays the foundation for the construction of emerging 3D-patterned graphene heterostructures.

Tailoring crystallisation of anatase TiO2 ultra-thin films grown by atomic layer deposition using 2D oxides as growth template

TiO2 ultrathin films are required in many material research areas. The anatase phase was found to be more stable in case of atomic layer deposition growth, nevertheless a critical thickness of around 10 nm appears necessary to obtain crystallization on native silicon oxide on Si (001). This work focuses on direct liquid injection Atomic Layer Deposition (ALD) of TiO2 films with thicknesses about some nanometers, using titanium tetra-isopropoxide as precursor and H2O as oxidant. A particular care to the treatment of ellipsometric measurements is employed. Below the threshold value, films remain amorphous unless the growth starts onto a crystalized surface, a thick TiO2 layer in our case. Here we propose and show the efficiency of 2-dimensional (2D) [Ca2Nb3O10]− and [Ti0.865O2]0.54− nanosheets as seeds at the surface for the crystallization and epitaxy of ultra-thin films of TiO2 below the critical thickness. Furthermore, we show that the structure of the 2D nanosheets determines the growth orientation of the epitaxial anatase, namely (010) for [Ti0.865O2]0.54−, and (100) for [Ca2Nb3O10]−. These results, based on the tailoring of crystal anisotropy via adapted 2D seed nanosheets and low temperature ALD, opens the way for opto-electronics applications of titanium oxide layers of a few unit cells.

Nanomechanical resonators fabricated by atomic layer deposition on suspended 2D materials

Atomic layer deposition (ALD), a layer-by-layer controlled method to synthesize ultrathin materials, provides various merits over other techniques such as precise thickness control, large area scalability and excellent conformality. Here we demonstrate the possibility of using ALD growth on top of suspended 2D materials to fabricate nanomechanical resonators. We fabricate ALD nanomechanical resonators consisting of a graphene/MoS2 heterostructure. Using atomic force microscope indentation and optothermal drive, we measure their mechanical properties including Young’s modulus, resonance frequency and quality factor, showing a lower energy dissipation compared to their exfoliated counterparts. We also demonstrate the fabrication of nanomechanical resonators by exfoliating an ALD grown NbS2 layer. This study exemplifies the potential of ALD techniques to produce high-quality suspended nanomechanical membranes, providing a promising route towards high-volume fabrication of future multilayer nanodevices and nanoelectromechanical systems.

The growth mechanisms of TiO2 film onto PET surfaces by atomic layer deposition

Atomic layer deposition (ALD) was used to coat a polyethylene terephthalate (PET) polymer substrate with TiO2 film. The TiO2 was grown onto the surface with better film coverage by using thicker ALD deposition. Further evaluation on the coated substrates indicated that the reactive sites of –C=O that existed on PET surface played a significant contribution to facilitating the initial ALD growth of the TiO2 thin film. The chemical composition of the coated substrates was characterised using energy dispersive X-ray spectroscopy, which showed that increasing the TiO2 film thickness increased the Ti element content. Two growth mechanisms, namely, diffusion growth and direct coordination through the precursor coordination with surface reactive sites of –C=O with product release occurred simultaneously in the initial growth of TiO2 coating onto PET polymer by ALD. The surface alteration of the coated ALD was characterised by Fourier transform infrared spectroscopy, which showed that the hydroxyl –OH groups emerged in the TiO2 ALD film.

Large enhancement of visible light photocatalytic efficiency of ZnO films doped in-situ by copper during atomic layer deposition growth

In the present study, we investigate the photocatalytic activity of ZnO thin films doped by copper atoms in successive steps during the film growth by the atomic layer deposition method. Scanning electron microscopy and x-ray diffraction measurements reveal a polycrystalline structure of samples with degrading crystallinity for films with higher Cu content. X-ray photoelectron spectroscopy analysis is consistent with the presence of copper in the Cu+ state for samples with a relative Cu content lower than 1 at.%. Those samples exhibit p-type conductivity indicating that copper ions occupy substitutional, CuZn, acceptor sites in ZnO. As established from UV–vis measurements, Cu-doped ZnO films also show enhanced optical absorption in the visible region. A reduced electron-hole recombination rate, due to much lower intrinsic free charge carrier concentrations in the doped samples, and the increased light absorption in the visible region, lead to a large enhancement of photocatalytic efficiency observed in doped films under simulated sunlight irradiation.