Nucleation Of Thin Films Research Articles

Structure and stability of copper nanoclusters on monolayer tungsten dichalcogenides.

Layered materials, such as tungsten dichalcogenides (TMDs), are being studied for a wide range of applications, due to their unique and varied properties. Specifically, their use as either a support for low dimensional catalysts or as an ultrathin diffusion barrier in semiconductor devices interconnect structures are particularly relevant. In order to fully realise these possible applications for TMDs, understanding the interaction between metals and the monolayer they are deposited on is of utmost importance. The morphology that arises due to given metal-substrate combinations determines their possible applications and thus is a central characteristic. Previous theoretical studies typically focus on the effects which single metal adatoms, or dopants, have on a TMDs' electronic and optical properties, thereby leaving a knowledge gap in terms of thin film nucleation on TMD monolayers. To address this, we present a density functional theory (DFT) study of the adsorption of small Cu clusters on a range of TMD monolayers, namely WS2, WSe2, and WTe2. We explore how metal-substrate and metal-metal interactions contribute to both the stability of these Cu clusters and their morphology, and investigate the role of the chalcogen in these interactions. We find that single Cu atoms adsorb most strongly to the adsorption site above the W atom, however as nanocluster size increases, Cu tends to be adsorbed atop the chalcogen atoms in the monolayer to facilitate Cu-Cu bond formation. We show that Cu-Cu interactions drive the stability of the adsorbed Cu nanoclusters, with a clear preference for 3D structures on all 3 monolayers studied. Furthermore, significant Cu migration occurs during 0 K relaxation. This, combined with the small activation barriers found for Cu migration suggest facile and dynamic cluster behaviour at finite temperature on all three monolayers. Finally, we find that Cu clusters are generally most stable on WTe2 and least stable on WSe2. This difference however is typically only in the range of 0.1 eV.

Evolution of TiAlSi thin film coatings under varying target power in DC magnetron sputtering

This study, for the first time, presents the growth, nucleation, and characteristics of TiAlSi thin films sputtered from a partially sintered Ti30Al16Si10 (at. %) composite target under controlled conditions of target power. The TiAlSi thin films were grown on soda-lime glass substrates through Direct Current (DC) sputtering at varying levels of the target power: 73.2 W, 151.2 W, and 269.5 W. The other deposition parameters: the deposition temperature, time, argon mass flow rate, substrate rotation, and deposition pressure, were kept constant at 23 °C, 150 min, 25 sccm, 5 rpm, and 10−3 mbar, respectively. The pre-sputter power, argon flow rate, and time were also kept constant at 73.2 W, 20 sccm, and 5 min, respectively. The physical properties, microstructure, crystal structure, topography, and mechanical properties of the thin film coatings were analysed. The thickness and rate of deposition of the TiAlSi thin films increased with an increase in the target power (73.2 W – 269.5 W) from 414.6 nm and 0.046 nm/s to 1358.8 nm and 0.151 nm/s, respectively. The chemical composition of all the thin films remained constant, with the formation of a uniform TiAlSi alloy with no segregation of elements. However, a thin (wetting) interlayer consisting of Si and O elements was observed between the TiAlSi layer and the glass substrate. Further, the structure sizes and roughness values of the TiAlSi thin films increased with an increase in the target power, with a maximum of 75.4 nm for the size and 4.78 nm for the RMS roughness of thin films deposited at the maximum target power (269.5 W). Lastly, mechanical analysis of the TiAlSi thin films depicted an increase in the hardness as the target power increased, with the highest hardness at maximum power (269.5 W) obtained as 4.76 GPa. Despite having the lowest elastic modulus (50.5 GPa), the coating deposited at the highest power exhibited the highest plasticity index (H/E) and plastic deformation factor (H3/E2) of 0.094 and 0.042 GPa, respectively, which indicated the high resistance to abrasive wear, cracking, and deformation, compared to thin films deposited at the lowest target power (H/E = 0.066 and H3/E2 = 0.015 GPa). This study demonstrates that target power is a significant factor in determining the growth of TiAlSi thin films during the sputtering process and can be used for better control of their physical, structural, and mechanical properties.

Nucleation, growth mechanism, and bifunctional electrochromic supercapacitive properties of NiO thin films

Bifunctional devices combining display and energy storage capabilities are crucial for next-generation optoelectronic technology. This study investigates the application of nickel oxide (NiO) thin films for bifunctional electrochromic energy storage systems. The amorphous Ni(OH)2 thin films were electrodeposited with a focus on their time-dependent properties. The Scharifker-Hills model revealed a mixed nucleation process during the electrodeposition. The deposited thin films were examined for their physicochemical properties using X-ray diffraction (XRD), micro-Raman spectroscopy, X-ray photoelectron Spectroscopy (XPS), and morphological studies. Rietveld refinement of the XRD pattern confirmed a cubic NiO polycrystalline phase, while XPS identified Ni3+ as the dominant oxidation state. Significant morphological changes were observed with the varying deposition time. The NiO electrode deposited for 120 minute exhibited optimal characteristics including the highest areal capacitance of 161.77 mF/cm2, along with excellent cyclic stability of 96.54 % even after 2000 cyclic voltammetry cycles. The electrochromic study demonstrated optical modulation ranging within 55–82 % at 532 nm, with a maximum coloration efficiency of 86.90 cm2/C. This research demonstrates the viability of NiO thin films as bifunctional electrochromic energy storage systems and the advancement of optoelectronic devices that integrate display and energy storage functionalities.

Impact of high-power impulse magnetron sputtering pulse width on the nucleation, crystallization, microstructure, and ferroelectric properties of hafnium oxide thin films

The impact of the high-power impulse magnetron sputtering (HiPIMS) pulse width on the crystallization, microstructure, and ferroelectric properties of undoped HfO2 films is investigated. HfO2 films were sputtered from a hafnium metal target in an Ar/O2 atmosphere, varying the instantaneous power density by changing the HiPIMS pulse width with fixed time-averaged power and pulse frequency. The pulse width is shown to affect the ion-to-neutral ratio in the depositing species with the shortest pulse durations leading to the highest ion fraction. In situ x-ray diffraction measurements during crystallization demonstrate that the HiPIMS pulse width impacts nucleation and phase formation, with an intermediate pulse width of 110 μs stabilizing the ferroelectric phase over the widest temperature range. Although the pulse width impacts the grain size with the lowest pulse width resulting in the largest grain size, the grain size does not strongly correlate with the phase content or ferroelectric behavior in these films. These results suggest that precise control over the energetics of the depositing species may be beneficial for forming the ferroelectric phase in this material.

PECVD and PEALD on polymer substrates (part I): Fundamentals and analysis of plasma activation and thin film growth

AbstractThis 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.

Nucleation and growth of low resistivity copper thin films on polyimide substrates by low-temperature atomic layer deposition

The metallization of polyimide (PI) remains a formidable challenge when using an atomic layer deposition of copper. The present study employs Cu(hfac)2 and Et2Zn to deposit the copper thin films that are highly conformal and continuous, and possess low resistivity (5.6 μΩ·cm), through a low-temperature atomic layer deposition (120 °C) with multi-pulse of Cu(hfac)2 process on a treated polyimide surface. The process exhibited both self-limiting ALD and CVD-like reactions with a growth rate of 0.079 nm/cycle. The findings demonstrate that an increase in functional groups and adsorption area on the surface of treated PI substrates enhances the adsorption of Cu(hfac)2. A model has been developed to describe the nucleation and growth kinetics of atomic layer deposition of copper on polyimide substrates, based on the adsorption mechanism of Cu(hfac)2 and the interface structure of ALD-Cu/treated PI onto the surface and into the near-surface region of the PI substrates. The academic developing in this work provides theoretical and experimental basis for the deposition using other copper precursors onto polymeric substrates in the future.

Two-step perovskite crystallization assisted with F-containing additives enables over 23% efficiency in perovskite solar cells

The two-step preparation of perovskite solar cells (PSCs) has attracted the interest of many researchers because this method can better control the nucleation and growth of perovskite thin films. This work proposes a crystallization management strategy to improve the quality of active layer with the assistant of F-containing additives with low boiling point. Hexafluorobenzene (HFB) is introduced into lead iodide (PbI2) precursor solutions, and HFB aggregation forms due to its low surface energies. As the result, nano porous PbI2 films are obtained after the evaporation of HFB during annealing process, leading to pinhole free perovskite films with large grain size and low defect states. As the consequence, the best power conversion efficiency (PCE) of 23.01% is obtained for the PSCs with HFB assisted perovskite films. Meanwhile HFB modified unencapsulated device maintains 88% of its initial PCE after aging for over 1440 h at 25 °C and 30% relative humidity in ambient conditions.

Numerical and experimental studies on crack nucleation and propagation in thin films

The prediction of damage and cracking patterns in ceramic thin films plays a vital role in the optimal design thereof. In this study, we focus on developing a numerical framework to predict fracture in ceramic thin films. For accurate and efficient modeling, the fracture energy and the material strength (ultimate stress) are taken into account by the cohesive phase-field damage model. Moreover, we argue that the orientation of the grain morphology induces a preferential direction for the crack which serves as a weak spot for crack initiation and propagation. A novel equivalent fracture energy is introduced into the formulation to account for the effects of microstructure on the cracking behavior of thin films. On the experimental side, tensile tests on (V,Al)N and (V,Al)(O,N) thin films deposited on ductile substrates are performed. It has been shown that this approach is a fast and efficient tracking tool for determining the mode-I fracture properties. To evaluate the accuracy of the anisotropic cohesive phase-field damage model proposed in this study, the crack patterns and crack density values of two chemically different thin films are compared for both numerical and experimental setups. This work provides new insights into the effect of different material parameters on the damage behavior of thin films. The key parameters can be summarized as the ultimate strength, fracture energy as well as the existing residual stress within the film.

Synthesis of V2AlC thin films by thermal annealing of nanoscale elemental multilayered precursors: Incorporation of layered Ar bubbles and impact on microstructure formation

Periodically stacked nanoscale V/C/Al multilayered thin film precursors were deposited by magnetron sputtering using elemental targets. Their temperature-dependent phase transformation during subsequent thermal annealing in argon towards V2AlC MAX phase formation was investigated. Compositional and microstructural analyses at the nanoscale revealed undulation growth of the nanolayers and preferential incorporation of Ar atoms into amorphous carbon nanolayers within the as-deposited multilayered precursors. Single-phase and basal-plane-oriented V2AlC films were formed at annealing temperatures above 560 °C. The incorporated Ar atoms migrated and aggregated into high-density nanoscale Ar clusters/bubbles located essentially at grain boundaries after annealing, displaying pronounced layered distribution characteristics especially adjacent to the substrate/film interface. The heterogeneous incorporation of argon atoms or clusters in heterostructured films composed of multicomponent sublayers likely represents a common phenomenon during thin film nucleation and growth, while its impact on the macroscopic properties of films remains to be explored.

Modification of Two-Dimensional Tin-Based Perovskites by Pentanoic Acid for Improved Performance of Field-Effect Transistors.

Understanding and controlling the nucleation and crystallization in solution-processed perovskite thin films are critical to achieving high in-plane charge carrier transport in field-effect transistors (FETs). This work demonstrates a simple and effective additive engineering strategy using pentanoic acid (PA). Here, PA is introduced to both modulate the crystallization process and improve the charge carrier transport in 2D 2-thiopheneethylammonium tin iodide ((TEA)2 SnI4 ) perovskite FETs. It is revealed that the carboxylic group of PA is strongly coordinated to the spacer cation TEAI and [SnI6 ]4- framework in the perovskite precursor solution, inducing heterogeneous nucleation and lowering undesired oxidation of Sn2+ during the film formation. These factors contribute to a reduced defect density and improved film morphology, including lower surface roughness and larger grain size, resulting in overall enhanced transistor performance. The reduced defect density and decreased ion migration lead to a higher p-channel charge carrier mobility of 0.7 cm2 V-1 s-1 , which is more than a threefold increase compared with the control device. Temperature-dependent charge transport studies demonstrate a mobility of 2.3 cm2 V-1 s-1 at 100 K due to the diminished ion mobility at low temperatures. This result illustrates that the additive strategy bears great potential to realize high-performance Sn-based perovskite FETs.

Advanced atomic layer deposition (ALD): controlling the reaction kinetics and nucleation of metal thin films using electric-potential-assisted ALD

Electric-potential-assisted atomic layer deposition was demonstrated for Ru film growth. Surface reaction was modified via the electric potential, which affected the nucleation and microstructure of films. Assorted film properties were improved notably.

Precursor solution chemistry via water additive enabling CZTSSe solar cells with over 12% efficiency

High-quality absorber films are imperative for highly efficient Cu2ZnSn(S,Se)4 (CZTSSe) thin-film solar cells. Precursor solution chemistry, interconnected with thin-film nucleation and the crystal growth process, should be studied insightfully. Thus, creative rationales and strategies could be proposed to improve the absorber quality, carrier characteristics, and hence device performance. However, the research on precursor solution chemistry in CZTSSe solar cells is still in its infancy. In this study, a facile eco-friendly additive strategy is reported to tailor the 2-methoxyethanol-based CZTS precursor solution chemistry. Incorporating water additives improves the homogeneity and thermogravimetric characteristics of a precursor solution by adjusting the particle sizes and coordination behavior inside the precursor solution. After the tailoring of the precursor solution chemistry, CZTSSe absorbers with high quality are fabricated. Hence, benefiting from the carrier dynamics enhancement, a CZTSSe device with a certified power conversion efficiency of 12.07% is achieved. The results open an avenue in precursor solution chemistry regulation through the use of eco-friendly additives to design highly efficient kesterite CZTSSe solar cells.

In situ characterisation for studying nucleation and growth of nanostructured materials and thin films during liquid-based synthesis

Knowledge about the nucleation, growth, and formation mechanisms during materials synthesis using sol-gel and solution-based methods is important to design a material with desired properties. We used aqueous chemical synthesis as an environmentally friendly and highly flexible route to tailored and reproducible synthesis of oxide nanomaterials and thin films. For studies of hydrothermal synthesis an in situ cell using synchrotron X-ray diffraction was used to investigate the formation mechanisms of SrxBa1-xNb2O6 piezoelectrics. Aqueous chemical solution deposition of phase pure oriented piezoelectric thin films demands strong control of processing parameters. An in situ cell for synchrotron X-ray diffraction studies of the annealing and crystallisation steps during aqueous chemical solution deposition was used to understand the nucleation and crystallisation of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT). We discuss how the knowledge about nucleation and growth obtained by in situ characterisation can be used to design the optimal procedure for fabrication of oxide materials with desired properties.Graphical abstract

An in-depth analysis of nucleation and growth mechanism of CdS thin film synthesized by chemical bath deposition (CBD) technique

The aim of this study is to acquire a deeper understanding of the response mechanism that is associated with the formation of CdS thin films. We presented an effective and new hybrid sensitisation technique, which involved the 1-step linker between the related chemical bath deposition (CBD) process and the traditional doping method during CBD for synthesising high-quality, CdS thin films. The mechanism for the combined synthesis of the films is also describes. CdS films were electrostatically bonded to soda-lime glass, causing the formation of the intermediate complexes [Cd(NH3)4]2+, which aided in the collision of these complexes with a soda-lime glass slide. In the one-step fabrication technique, 3-Mercaptopropionic Acid (MPA) was employed as a second source of sulphur ions and a linker molecule. Optical studies showed that the bandgap ranged between (2.26–2.52) eV. CdS + MPA films exhibited a uniform distribution of spherical molecules based on their morphological properties. After annealing, this approach significantly altered the electrical characteristics of CdS films. The CdS + MPA films displayed the highest carrier concentration whereas the CdS + Ag + MPA films exhibited the lowest resistivity, with a jump of 3 orders of magnitude.

Comparison of heteroepitaxial diamond nucleation and growth on roughened and flat Ir/SrTiO3 substrates

Heteroepitaxial diamond deposition on iridium substrates allows production of single crystal diamond layers on large area that is difficult to achieve with homoepitaxy. Critically important is the first stage of the process when diamond nucleates on Ir upon biasing (a voltage applied to the substrate). Here, we compared the heteroepitaxial nucleation and successive growth of diamond thin films in a microwave plasma CVD reactor on Ir/SrTiO3 substrates with different surfaces modified by bias voltage. The roughened surface consists of furrows and ridges while the flat surface is a little wrinkled. The film morphology, crystal quality and stress are characterized with SEM, AFM, TEM, X-ray diffraction and Raman spectroscopy. It is found that the film on the roughened Ir surface has a lower roughness, smaller mosaic spread, but a larger residual stress than the film deposited on the flat Ir surface, which mainly originates from the difference in the domain density. By comparing diamond (111) lattice spacings of different positions from the Ir-diamond interface, it is inferred that diamond nucleation could occur at the furrows and then overgrow the ridges for Ir-roughened sample while diamond may nucleate at the wrinkle and flat regions for Ir-flat sample. These finding are helpful in understanding of details of diamond film heteroepitaxy, and in searching the ways to improve their crystallinity.

Study of Cu, Co and Ru Nanoclusters on MoS2 to Predict Thin Film Morphology

Interfaces of 2D materials with metals are of interest for a large variety of applications, including sensors, batteries, catalysis, electronics, and semi-conductor devices. Transition metal dichalcogenides (TMDs) and specifically MoS2 are some of the most widely studied 2D materials. A detailed understanding of the interactions of metals with 2D TMDs can give useful insights into possible applications for metal-TMD systems. However, the literature focuses mainly on comparing trends in single atom adsorption and studying nanoparticles on MoS2 monolayers.In this work we aim to increase the understanding of metal-MoS2 interactions and metal nucleation on TMDs. We use density functional theory (DFT) to study the adsorption of small metal clusters with up to four atoms on MoS2 monolayers. Insights gained from this work allow us to understand the initial nucleation of metal thin films on TMDs as well as predict the likely morphology of the thin film as it grows.The metals studied are Cu, Co and Ru, which are chosen for their range of applications, particularly in electronics. Metal-substrate interactions, preferred adsorption modes and stable nanocluster geometries are presented on pristine MoS2 and in the presence of the readily formed sulfur vacancy. The strength of interaction between the metals and MoS2 is in the order Co > Ru > Cu. Metal-substrate interactions are localised to the adsorption site; however we find that both Ru and Co can induce formation of sulfur vacancies through the formation of the corresponding metal sulfide.

Impact of the processing temperature on the laser-based crystallization of chemical solution deposited lead zirconate titanate thin films on short timescales

In this work, the laser-based annealing process of sol-gel-derived piezoelectric PZT53/47 (lead zirconate titanate) thin films deposited on platinized silicon substrates is investigated. A temperature control closed loop is implemented to allow for the measurement and control of the annealing temperature. Samples are treated at temperatures of up to 900 °C and heating rates between 300 and 9000 K/s in ambient conditions. The results show that highly functional PZT thin films can be crystallized at interaction times of less than 1 s while exhibiting a remanent polarization of up to 28 μC/cm2 and a piezoelectric coefficient of up to 49 pm/V. X-ray diffraction analysis shows that an intermetallic Pt3Pb phase forms prior to the formation of phase pure PZT. With decreasing interaction time between the laser beam and the thin film, the temperature range in which this Pt3Pb phase is stable extends toward temperatures as high as 900 °C without the formation of phase pure PZT. Furthermore, a decrease in the interaction time requires higher annealing temperatures to form fully crystalline PZT thin films. Scanning electron microscope images reveal that short interaction times shift the nucleation of the PZT thin films from epitaxial to heterogeneous nucleation. Overall, it is demonstrated that the crystallization time of chemical solution deposited PZT thin films can be reduced significantly by using laser radiation.

Electrosynthesis of Biocompatible Free-Standing PEDOT Thin Films at a Polarized Liquid|Liquid Interface.

Conducting polymers (CPs) find applications in energy conversion and storage, sensors, and biomedical technologies once processed into thin films. Hydrophobic CPs, like poly(3,4-ethylenedioxythiophene) (PEDOT), typically require surfactant additives, such as poly(styrenesulfonate) (PSS), to aid their aqueous processability as thin films. However, excess PSS diminishes CP electrochemical performance, biocompatibility, and device stability. Here, we report the electrosynthesis of PEDOT thin films at a polarized liquid|liquid interface, a method nonreliant on conductive solid substrates that produces free-standing, additive-free, biocompatible, easily transferrable, and scalable 2D PEDOT thin films of any shape or size in a single step at ambient conditions. Electrochemical control of thin film nucleation and growth at the polarized liquid|liquid interface allows control over the morphology, transitioning from 2D (flat on both sides with a thickness of <50 nm) to “Janus” 3D (with flat and rough sides, each showing distinct physical properties, and a thickness of >850 nm) films. The PEDOT thin films were p-doped (approaching the theoretical limit), showed high π–π conjugation, were processed directly as thin films without insulating PSS and were thus highly conductive without post-processing. This work demonstrates that interfacial electrosynthesis directly produces PEDOT thin films with distinctive molecular architectures inaccessible in bulk solution or at solid electrode–electrolyte interfaces and emergent properties that facilitate technological advances. In this regard, we demonstrate the PEDOT thin film’s superior biocompatibility as scaffolds for cellular growth, opening immediate applications in organic electrochemical transistor (OECT) devices for monitoring cell behavior over extended time periods, bioscaffolds, and medical devices, without needing physiologically unstable and poorly biocompatible PSS.

Automated processing of environmental transmission electron microscopy images for quantification of thin film dewetting and carbon nanotube nucleation dynamics

Scalable production of carbon nanotubes (CNTs) requires catalysts and reaction conditions that provide high nucleation efficiency. In situ characterization methods such as environmental transmission electron microscopy (ETEM) can reveal fundamental mechanisms of synthesis, but to date have primarily provided qualitative observations on small sample sizes. Here, quantitative analysis is performed using high-resolution, high-rate video capture of ETEM experimentation coupled with automated image processing, involving computer vision algorithms and convolutional neural networks. By this approach, we detect distinct nanoparticle formation from an alumina-supported iron thin film and subsequent CNT nucleation from the nanoparticles. The statistical summary of particles in each video shows that, compared to a H2-only atmosphere, pretreatment of the catalyst with carbon added to the H2 atmosphere results in a smaller average particle diameter, a 2-fold increase in particle density (to 5300 particles/μm2), a 3-fold increase in CNT nucleation efficiency (to 92%), and more than a 5-fold increase in CNT density (to 4800/μm2). Addition of carbon during exposure to H2 is also more effective than NH3 at dewetting the catalyst film and increasing the CNT nucleation efficiency, in spite of NH3 being a stronger reducing agent for iron. Insights from this study are applicable to improving CNT yield and productivity in both batch-style and continuous processes.

Study of the Optimal Composition of the Bath on Nucleation and Growth of Ni-Fe Alloy Thin Films

Study of the Optimal Composition of the Bath on Nucleation and Growth of Ni-Fe Alloy Thin Films