ALD Method Research Articles

Tuning the Optical and Electrical Properties of ALD-Grown ZnO Films by Germanium Doping.

In this work, we report on the fabrication of ZnO thin films doped with Ge via the ALD method. With an optimized amount of Ge doping, there was an improvement in the conductivity of the films owing to an increase in the carrier concentration. The optical properties of the films doped with Ge show improved transmittance and reduced reflectance, making them more attractive for opto-electronic applications. The band gap of the films exhibits a blue shift with Ge doping due to the Burstein-Moss effect. The variations in the band gap and the work function of ZnO depend strongly on the carrier density of the films. From the surface studies carried out using XPS, we could confirm that Ge replaces some of the Zn in the wurtzite structure. In the films containing Ge, the concentration of oxygen vacancies is also high, which is somehow related to the poor electrical properties of the films at higher Ge concentrations.

The Al2O3/TiO2 double antireflection coating deposited by ALD method

The Al2O3/TiO2 double antireflection coating deposited by ALD method

Molecular Mechanism of Selective Al2O3 Atomic Layer Deposition on Self-Assembled Monolayers.

Area-selective atomic layer deposition (AS-ALD) of insulating metallic oxide layers could be a useful nanopatterning technique for making increasingly complex semiconductor circuits. Although the alkanethiol self-assembled monolayer (SAM) has been considered promising as an ALD inhibitor, the low inhibition efficiency of the SAM during ALD processes makes its wide application difficult. We investigated the deposition mechanism of Al2O3 on alkanethiol-SAMs using temperature-dependent vibrational sum-frequency-generation spectroscopy. We found that the thermally induced formation of gauche defects in the SAMs is the main causative factor deteriorating the inhibition efficiency. Here, we demonstrate that a discontinuously temperature-controlled ALD technique involving self-healing and dissipation of thermally induced stress on the structure of SAM substantially enhances the SAM's inhibition efficiency and enables us to achieve 60 ALD cycles (6.6 nm). We anticipate that the present experimental results on the ALD mechanism on the SAM surface and the proposed ALD method will provide clues to improve the efficiency of AS-ALD, a promising nanoscale patterning and manufacturing technique.

Investigation of Ti/Al2O3 + TiO2 and Ti + TiO2/Al2O3 + TiO2 hybrid coatings as protection of ultra-light Mg–(Li)–Al–RE alloys against corrosion

Low corrosion resistance is a significant problem of magnesium alloys, particularly ultra-light magnesium-lithium alloys. Surface treatment is one way to improve their corrosion resistance. The paper presents the results of tests of Ti/Al2O3 + TiO2 and Ti + TiO2/Al2O3 + TiO2 coatings obtained in a hybrid process combining PVD and ALD methods and ALD coating of Al2O3 + TiO2 type obtained on AE42 (Mg–4Li–2RE) and LAE442 (Mg–4Li–4Al–2RE). Structural studies were performed using scanning and transmission electron microscopy (SEM and TEM), atomic force microscopy and EDS and XPS spectroscopic methods. Potentiodynamic tests and electrochemical impedance spectroscopy EIS in 0.05 M NaCl solution were performed to determine the electrochemical properties of the tested materials. Moreover, tests of surface wettability and tribological properties using the ball-on-disc method were performed. Based on the analysis of anodic polarisation curves and Tafel analysis, it was found that the Ti + TiO2/Al2O3 + TiO2 coating showed the best potentiodynamic properties on both substrates. In particular, on the magnesium-lithium substrate, the value of the polarisation resistance of this hybrid coating is Rpol = 14 × 103 Ω × cm2, and the value of the corrosion current is jcorr = 0.4 µA/cm2. For the uncoated LAE442 substrate, the polarisation resistance is Rpol = 1.05 × 103 Ω × cm2, and the corrosion current value is jcorr = 5.49 µA/cm2. This improvement is due to the synergistic effect of the combined PVD and ALD technologies. The study confirmed the impact of hybrid coatings on improving the anti-corrosion and tribological properties of ultra-light magnesium alloys.

Incorporating ALD Based Pt Alloy Catalysts into Gas Diffusion Electrodes for Proton Exchange Membrane Fuel Cells

Atom layer deposition is a promising method to fabricate gas diffusion electrodes (GDE) with platinum catalysts for high-power-density Proton Exchange Membrane Fuel Cells (PEMFCs). Alloying Pt with transition metals can further improve the intrinsic activity for oxygen reduction reaction due to the ligand and strain effects. Nevertheless, incorporating alloy catalysts into GDE posts more challenges.In this study, we systematically explore and optimize alloy-based catalysts via ALD deposition on gas diffusion layers (GDL). While GDE tolerates 200 oC annealing for alloys that can form under low temperature (e.g.PtxZny) and present high ORR performance, GDE for PtxTiy alloy presents inferior performance after high-temperature annealing.To circumvent this temperature compatibility issue, we successfully developed a modified high-temperature ALD method for PtxTiy alloy by taking advantage of a porous metal felt. With this, ALD-based high temperature annealed PtxTiy series alloy can maintain its atomic structure, and the GDL can keep its high hydrophobicity. Further Membrane Electrode Assembly (MEA) testing results and insights into active site areas and activation energy for different alloys and fabrication methods provide the in-depth elucidation of the relationship between reaction kinetics and GDE structures.

The Electrochemical Impedance Spectroscopy and Wettability Analysis of Ti6Al4V Alloy Modified by Atomic Layer Deposition ALD Method

The Electrochemical Impedance Spectroscopy and Wettability Analysis of Ti6Al4V Alloy Modified by Atomic Layer Deposition ALD Method

INFLUENCE OF THIN COATINGS FORMED BY ALD TECHNIQUES ON THE PROPERTIES OF Ti13Nb13Zr TITANIUM ALLOY

The article evaluates the properties of oxide films: Al2O3 and TiO2, deposited using the ALD method on the Ti13Nb13Zr alloy. It presents the results of examining the geometrical structure of the surface, nanohardness and tribological tests. The surface’s geometrical structure was tested through optical microscopy, and nanohardness was determined using the instrumental indentation method with a Berkovich indenter. The modelling tribological tests were performed in a reciprocating motion under the conditions of technically dry friction and with lubrication using Ringer's solution. An analysis of the results of tribological tests indicates that the films were characterised by lower motion resistances and wear with respect to the Ti13Nb13Zr alloy. Hardness measurements indicate that, as a result of deposition of the films, the hardness increased by approximately 51% in the case of the Al2O3 film and by approximately 44% in the case of the TiO2 coating. The produced test results constitute a source of knowledge about the Ti13Nb13Zr alloy, oxide films and the possibilities of their potential application to low-load biotribological systems.

Preparation of antistatic AZO/Al2O3-ZnO-Y2O3 composite thermal control coating and its study on electron-resistance radiation performance

As space exploration moves further and further into deep space, it is a big challenge to develop antistatic inorganic thermal control coating with lightweight and strong adhesion to substrates. Herein, this work reported an inorganic antistatic AZO/Al2O3-ZnO-Y2O3 composite coating fabricated by PEO combined with ALD methods. The results show that when the Zn/Al ratio of deposited AZO film is 24:1, its overall performance is the optimal, and the emissivity, absorptivity and resistivity are 0.892, 0.409 and 1.15 × 10–3 Ω·cm, respectively, which can meet thermal control application requirements of spacecraft. Furthermore, the AZO/Al2O3-ZnO-Y2O3 composite coating shows a good electron-resistance irradiation performance, which is because AZO conductive film is easy to generate free carriers, speed up some electron transport and make electrons better disperse and conduct, thus reducing the penetration depth of electron irradiation. This work provides a material basis for thermal control system of spacecraft with long life and high reliability.

Unoccupied electronic states of ultrathin phenolphthalein films on the ZnO surface formed by atomic layer deposition

The results of a study of the unoccupied electronic states of ultrathin films of phenolphthalein molecules on a ZnO surface formed by atomic layer deposition technique are presented. The atomic composition of the ZnO layer was determined by X-ray photoelectron spectroscopy (XPS) and its crystallinity was characterized using X-ray diffraction. The predominance of the content of O atoms by 5-10%, compared with the content of Zn atoms, was found. The electronic characteristics of the ZnO/phenolphthalein structure were studied using total current spectroscopy (TCS) in the energy range from 5 eV to 20 eV above EF during thermal vacuum deposition of phenolphthalein films up to 8 nm thick. Phenolphthalein molecules contain two hydroxyl functional groups. The TCS results on the phenolphthalein films are compared with the TCS results obtained from films of molecules that represent the backbone of phenolphthalein molecules without hydroxyl groups. The TCS fine structure maxima of phenolphthalein films located in the energy range from 5 eV to 8 eV above EF can be associated with the boundaries of the π* bands of electronic states. The work function of the ZnO surface formed by the ALD method were 4.2±0.1 eV. The deposition of a phenolphthalein film led to a decrease in the work function of the surface by 0.1 eV. Keywords: Phenolphthalein, ultrathin films, ZnO, atomic layer deposition, electronic properties, low-energy electron spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy.

A study on the physicochemical properties of surface modified Ti13Nb13Zr alloy for skeletal implants

As it is widely stated in the literature, biofilms are responsible for most chronic infections, which have grown exponentially over the past three decades. The use of so-called alloys, as a new generation of materials, enables us to find the golden mean in the arena widely known as implantology. The use of the surface layer, using the chosen Atomic Layer Deposition method, is to be the basis for minimizing the risk of an organism reactions. Therefore, the primary objective of this study was to observe the impact of physicochemical properties of the surface layers (bactericidal) on the processes that occur on the implants surface made of titanium biomaterials used in bone structures. The study also attempted to evaluate the physicochemical properties of the ZnO coatings, deposited on the substrate of one of the new generation Ti13Nb13Zr alloys, using the ALD method. Included in the assessment of the physicochemical properties of the surface layers formed in this manner, we perform pitting corrosion resistance tests, scratch tests, tribological tests and surface wettability tests. Based on the obtained data, the differing physicochemical properties of the alloy with ZnO coatings are found to be dependent on the applied surface modification. For the conducted tests, differences are determined for the tests on the corrosion resistance, surface wettability and the abrasion resistance for samples with and without the ZnO coating. In addition, tests show that the coating applied to the alloy, which is previously subjected to the sand-blasted process, is characterized by improved adhesion.

Незаполненные электронные состояния ультратонких пленок фенолфталеина на поверхности ZnO, сформированного методом молекулярного наслаивания

The results of a study of the unoccupied electronic states of ultrathin films of phenolphthalein molecules on a ZnO surface formed by atomic layer deposition technique are presented. The atomic composition of the ZnO layer was determined by X-ray photoelectron spectroscopy (XPS) and its crystallinity was characterized using X-ray diffraction. The predominance of the content of O atoms by 5-10%, compared with the content of Zn atoms, was found. The electronic characteristics of the ZnO/phenolphthalein structure were studied using total current spectroscopy (TCS) in the energy range from 5 eV to 20 eV above EF during thermal vacuum deposition of phenolphthalein films up to 8 nm thick. Phenolphthalein molecules contain two hydroxyl functional groups. The TCS results on the phenolphthalein films are compared with the TCS results obtained from films of molecules that represent the backbone of phenolphthalein molecules without hydroxyl groups. The TCS fine structure maxima of phenolphthalein films located in the energy range from 5 eV to 8 eV above EF can be associated with the boundaries of the p* bands of electronic states. The work function of the ZnO surface formed by the ALD method were 4.2±0.1 eV. The deposition of a phenolphthalein film led to a decrease in the work function of the surface by 0.1 eV.

Fabrication of TiN/CNTs on carbon cloth substrates via a CVD–ALD method as free-standing electrodes for zinc ion hybrid capacitors

A novel fabrication of TiN/CNTs@CC was presented and can be used as electrodes with good flexibility and conductivity in ZIHCs.

Surface Modification and Stabilization of Photoluminescence Perovskite Nanocrystals Via Atomic Layer Deposition

Photoluminescence perovskite nanocrystals (NCs) have shown significant potential in optoelectronic applications in view of their narrow band emission with high photoluminescence quantum yields (PLQYs) and color tunability. However, their poor stability in light, heat and water environments still hinders practical applications in optoelectronic and bioimaging fields due to their ionic character.Atomic layer deposition (ALD) has been developed as an attractive method to stabilize the crystal structure of perovskite NCs through encapsulation and surface passivation. In this presentation, several stabilization methods through ALD are introduced. First, a low-temperature Al2O3 ALD process was developed to enhance the stability of CsPbBr3 quantum dots-silica sphere in light, water and heat, which originated from the crystal structure stabilization after ALD coating. Nonetheless, a significant photoluminescence (PL) quenching of NCs was typically observed upon Al2O3 ALD. Accordingly, a specially designed ALD reactor integrated a FTIR spectrometer was exploited, which enabled in-situ characterizations to investigate ligands exchange and evolution during deposition after each precursor dosing. It was found that the surface chemical reaction between ALD precursor and capping oleic acid (OA) ligands led to reorganization of OA ligands that increased surface trap sites, leading to PL quenching. Based on the reaction mechanisms observed, a hybrid passivation strategy was developed to simultaneously enhance the photoluminescence quantum yield and the stability of perovskite NCs by two-step modification with surface halogen replenishment and ALD. Consequently, the PL quenching was avoided and the perovskite NCs/Al2O3 nanocomposites exhibited exceptional stability against water, light and heat. Our work provides a versatile method for preparing ultrastable perovskite NCs through ALD method and significantly improves their potential in LED illumination and backlight displays.

Application Properties of ZnO and AZO Thin Films Obtained by the ALD Method

The thin layers of ZnO and ZnO: Al (Al doped zinc oxide—AZO) were deposited by the atomic deposition layer (ALD) method on silicon and glass substrates. The structures were deposited using diethylzinc (DEZ) and deionized water as zinc and oxygen precursors. A precursor of trimethylaluminum (TMA) was used to introduce the aluminum dopant. The present study of ALD-deposited ZnO and AZO films was motivated by their applications in photovoltaics. We attempted to expose several properties of such films. Structural, optical (including ellipsometric measurements) and electrical investigations were performed. We discussed the relations between samples doped with different Al fractions and their properties.

Impact of GaAs(100) surface preparation on EQE of AZO/Al2O3/p-GaAs photovoltaic structures.

In order to effectively utilize the photovoltaic properties of gallium arsenide, its surface/interface needs to be properly prepared. In the experiments described here we examined eight different paths of GaAs surface treatment (cleaning, etching, passivation) which resulted in different external quantum efficiency (EQE) values of the tested photovoltaic (PV) cells. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) examinations were conducted to obtain structural details of the devices. X-ray photoelectron spectroscopy (XPS) with depth profiling was used to examine interface structure and changes in the elemental content and chemical bonds. The photoluminescence (PL) properties and bandgap measurements of the deposited layers were also reported. The highest EQE value was obtained for the samples initially etched with a citric acid-based etchant and, in the last preparation step, either passivated with ammonium sulfide aqueous solution or treated with ammonium hydroxide solution with no final passivation. Subsequent I–V measurements, however, confirmed that from these samples, only the sulfur-passivated ones provided the highest current density. The tested devices were fabricated by using the ALD method.

Investigations of TiO₂, Ti/TiO₂, and Ti/TiO₂/Ti/TiO₂ coatings produced by ALD and PVD methods on Mg-(Li)-Al-RE alloys substrates

Investigations of TiO₂, Ti/TiO₂, and Ti/TiO₂/Ti/TiO₂ coatings produced by ALD and PVD methods on Mg-(Li)-Al-RE alloys substrates

Atomic Layer Deposition of a Nanometer-Thick Li3PO4 Protective Layer on LiNi0.5Mn1.5O4 Films: Dream or Reality for Long-Term Cycling?

LiNi0.5Mn1.5O4 (LNMO) is a promising 5V-class electrode for Li-ion batteries but suffers from manganese dissolution and electrolyte decomposition owing to the high working potential. An attractive solution to stabilize the surface chemistry consists in mastering the interface between the LNMO electrode and the liquid electrolyte with a surface protective layer made from the powerful surface deposition method. Here, we show that a 7400 nm thick sputtered LNMO film coated with a nanometer-thick lithium-ion-conductive Li3PO4 layer was deposited by the atomic layer deposition method. We demonstrate that this "material model system" can deliver a remarkable surface capacity (∼0.4 mAh cm-2 at 1C) and exhibits improved cycling lifetime (×650%) compared to the nonprotected electrode. Nevertheless, we observe that mechanical failure occurs within the LNMO and Li3PO4 films when long-term cycling is performed. This in-depth study gives new insights regarding the mechanical degradation of LNMO electrodes upon charge/discharge cycling and reveals for the first time that the surface protective layer made from the ALD method is not sufficient for long-term stability applications.

Large enhancement of photocatalytic activity in ZnO thin films grown by plasma-enhanced atomic layer deposition

In this work, we present a large, tenfold enhancement in the photocatalytic activity of thin ZnO films grown by plasma-enhanced atomic layer deposition (PE-ALD) at 100 °C, compared to values obtained for thin ZnO films deposited by a conventional thermal ALD method at the same temperature. Thus, we have demonstrated that we can deposit thin ZnO films using the PE-ALD method both at low temperatures and with a high photocatalytic ability. A number of structural (SEM, EDX, HRTEM, GIXRD, XRR, XPS, SIMS) and optical (UV-Vis, PL) experimental techniques have been employed to elucidate a possible physical origin of the observed remarkable difference in the photocatalytic activity of thin ZnO films grown by the PE-ALD method compared to those grown by the thermal ALD method.

The Technique of thin Zinc Oxide Films Synthesis by ALD Method

Article shows experimental results of thin ZnO films synthesis with required structure and thickness produced by different atomic layer deposition methods (normal temperature, thermal and photo-assisted deposition). The influence of the synthesis temperature and UV-irradiation on the characteristics of ZnO films was analyzed. Both amorphous and polycrystalline films were synthesized by changing the deposition parameters. Film optical properties were examined in UV, visible and IR range. The bandgap was determined using absorption spectra. Morphological parameters of the films were valued using the atomic force microscopy. Suppositions on film growth mechanisms were made, preliminary results of friction wear tests are quoted.

Atomic layer deposited ZnO films on stainless steel for biomedical applications

The main goal of carried out tests were the impact of physicochemical properties of surface layers on the course of processes taking place on the surface of implants made of metallic biomaterials used in the bone system. As a precursor of ZnO, diethylzinc (DEZ) has been used, which reacted with water enabling the deposition of thin films. The chamber temperature was as follows—T = 200°–300 °C. The number of cycles was 500, 1000, and 1500. In the first stage, pitting corrosion test was carried out. Corrosion resistance has been tested under conditions simulating tissue environment. Moreover, the created layers were tested using electrochemical impedance spectroscopy (EIS). The conducted electrochemical tests showed the beneficial effect of the ZnO layer on the substrate made of 316 LVM steel, as evidenced by the obtained parameters describing the corrosion resistance. Furthermore, tests were performed on mechanical properties (scratch test), surface morphology (SEM and AFM method), and physical properties (wettability and thickness layers) for samples with different surface treatments. The investigations of the surface morphology of the applied ZnO layer using the ALD method showed a tendency to inherit the substrate independently of the used application parameters. On the other hand, the tests of adhesion to the substrate showed that the number of cycles of the application process has a fundamental impact on the adhesion of the applied layer to the substrate. Summarizing tests have clearly shown that the number of cycles and temperature in the case of the ZnO coating is significant and positively influences the increase of electrochemical, mechanical, and physical properties of layers.