Microstructure Evolution Of Films Research Articles

Origin of vertical slab orientation in blade-coated layered hybrid perovskite films revealed with in-situ synchrotron X-ray scattering

Controlling the vertical orientation of perovskite slabs in layered hybrid perovskite films is key for enabling further optimization of photovoltaic device performance. However, the mechanism explaining vertical orientation control in such films remains under debate. Here, we present an in-situ grazing-incidence wide-angle X-ray scattering (GIWAXS) study on the formation of BA2MAn-1PbnI3n+1 perovskite films during blade-coating. The evolution of grazing-incidence transmission wide-angle X-ray scattering (GTWAXS) signal is also monitored to reveal the specific vertically-oriented low-n phases formed in such films. We find that the blade-coating temperature greatly influences the crystallization dynamics of BA2MAn-1PbnI3n+1 perovskite films and perovskite slab orientation via intermediate phase and low-n phase formation. For the perovskite film with targeted dimensionality of n = 4, blade-coating films at higher temperatures suppresses the formation of the 2MAI∙3PbI2∙2DMF intermediate phase. This in turn suppresses the formation of the n = 2 phase that adopts an undesired horizontal perovskite slab orientation, instead favouring the formation of the n = 3 phase that adopts the desired vertical perovskite slab orientation. Further analysis on the microstructural evolution of films with near-perfect vertical orientation reveals that the formation mechanism proceeds through several stages: (i) sol-gel, (ii) weakly-texture 3D-like perovskite, (iii) n = 3 phase, and finally, (iv) crystallite reorientation into the near-perfect texture. The findings from this in-situ simultaneous GIWAXS and GTWAXS study provide improved understanding of the film formation mechanism for layered hybrid perovskite films with near-perfect vertical orientation.

Mapping of the electronic work function anisotropy of RF sputtered molybdenum thin film electrodes for piezoelectric devices

Amplitude modulated Kelvin probe force microscopy was performed on molybdenum (Mo)-thin films deposited on Si(001) substrates by RF magnetron sputtering. Evolution of film microstructure from amorphous to crystalline was observed with increasing RF power from 25 W to 200 W. Spatial mapping of work function across the film surface revealed that the Mo-thin film deposited at 200 W possesses an average work function ~4.94 ± 0.06 eV while higher values were observed at lower RF powers. The genesis of distinct periodic changes in work function is attributed to the formation of the surface dipole layer associated with the adsorbates of different polarities (O2−/OH− or H+). A phenomenological model is also presented to elucidate their effect.

RETRACTED: Influence of sputtering parameters on the structural and mechanical properties of TiC thin film coating

Abstract Titanium carbide (TiC) nanostructured thin films coating were deposited on a commercially pure titanium (CpTi) substrate to enhance the surface properties using Radio Frequency (RF) Magnetron Sputtering coating technique. The sputtering time, power and temperature were varied during the process to study the influence of the sputtering parameters on the evolving properties of the thin films. The surface morphology of the films was studied using Field emission scanning electron microscope FESEM. Atomic force microscope was used to analyse the surface topography. The mechanical properties of the film were measured using nanoindentation. The structural properties were characterized using Grazing incidence X-ray diffraction, X-ray Photoelectron spectroscopy and Raman spectroscopy. The microstructure results of the planar view revealed the film microstructural evolution with varying sputtering parameters. The XRD analyses confirmed the presence of nanostructured TiC film with (1 1 0) preferential growth diffractogram. Absence of Raman active vibrational diffraction peaks was noticed for films with continuous and defect-free microstructure produced at RF power of 200 W. The Young modulus and hardness varied with the sputtering parameters with the highest hardness value attained at 250 W.

Input power effect on microstructure and mechanical properties of Mo[sbnd]Si[sbnd]N multilayer coatings

The MoSiN single layer and multilayer films were fabricated by a reactive radio frequency, r.f., magnetron sputtering system with pure Mo and Si targets. The Ar/N2 flow ratio was fixed at 12/8, while r.f. input powers for Mo and Si were 135 W and 0 to 150 W, respectively. The corresponding Si contents in the coating ranged from 0 to approximately 20 at.%. The microstructure of the MoSiN single layers evolved from Mo2N (111) crystalline to amorphous feature with input powers and related Si doping amounts. The MoSiN multilayer coatings were fabricated with crystalline MoN, crystalline and amorphous MoSiN layers with sequential stacking of any two building layers. The multilayer film made of MoN and crystalline MoSiN layers showed an obvious crystalline microstructure, while the amorphous MoSiN layer incorporated multilayer MoSiN systems effectively suppressed the continuity of the columnar growth. The correlation between mechanical properties, including hardness, Young's modulus, indentation cracking, and scratch behavior, were investigated and discussed in terms of film microstructure evolution.

The role of the annealing temperature on the microstructural evolution of CuSbS2 thin films prepared by cationic exchange

Currently, the research in absorber films for solar cells is focused on the development of non-toxic, low-cost, and high-available materials. Thus, the CuSbS2 phase of the Cu-Sb-S system is promising due to its attractive optoelectronic properties. Chalcostibite thin films have been deposited by several approaches, however, their synthesis, as a predominant phase, is still challenging. In this work, CuSbS2 films were prepared by a simple immersion of amorphous Sb2S3 into a Cu solution. The effect of the annealing on their microstructure was assessed, too. From energy dispersive, X-ray photoelectron, inductively coupled plasma atomic emission, and Raman spectroscopies results, the formation of CuSbS2 was verified to occur through simultaneous dissolution and cationic exchange reactions. The microstructural evolution of the films goes from amorphous, passing by a chalcostibite phase, which enhances its crystallinity with further temperature increment, and finally, it undergoes a phase transition to tetrahedrite. These transitions have a strong impact on the charge carrier concentration, which generates important changes in their optoelectronic performance. The simplicity together with the demonstrated strong impact of the annealing make this methodology versatile and a powerful tool to prepare high-quality Cu-Sb-S films, as interesting candidates as absorber layers in solar cells and other optoelectronic devices.

Metal Composition and Polyethylenimine Doping Capacity Effects on Semiconducting Metal Oxide-Polymer Blend Charge Transport.

Charge transport and film microstructure evolution are investigated in a series of polyethylenimine (PEI)-doped (0.0-6.0 wt%) amorphous metal oxide (MO) semiconductor thin film blends. Here, PEI doping generality is broadened from binary In2O3 to ternary (e.g., In+Zn in IZO, In+Ga in IGO) and quaternary (e.g., In+Zn+Ga in IGZO) systems, demonstrating the universality of this approach for polymer electron doping of MO matrices. Systematic comparison of the effects of various metal ions on the electronic transport and film microstructure of these blends are investigated by combined thin-film transistor (TFT) response, AFM, XPS, XRD, X-ray reflectivity, and cross-sectional TEM. Morphological analysis reveals that layered MO film microstructures predominate in PEI-In2O3, but become less distinct in IGO and are not detectable in IZO and IGZO. TFT charge transport measurements indicate a general coincidence of a peak in carrier mobility (μpeak) and overall TFT performance at optimal PEI doping concentrations. Optimal PEI loadings that yield μpeak values depend not only on the MO elemental composition but also, equally important, on the metal atomic ratios. By investigating the relationship between the MO energy levels and PEI doping by UPS, it is concluded that the efficiency of PEI electron-donation is highly dependent on the metal oxide matrix work function in cases where film morphology is optimal, as in the IGO compositions. The results of this investigation demonstrate the broad generality and efficacy of PEI electron doping applied to electronically functional metal oxide systems and that the resulting film microstructure, morphology, and energy level modifications are all vital to understanding charge transport in these amorphous oxide blends.

Microstructural evolution of nanochannel CrN films under ion irradiation at elevated temperature and post-irradiation annealing

High-performance radiation tolerance materials are crucial for the success of future advanced nuclear reactors. In this paper, we present a further investigation that the “vein-like” nanochannel films can enhance radiation tolerance under ion irradiation at high temperature and post-irradiation annealing. The chromium nitride (CrN) nanochannel films with different nanochannel densities and the compact CrN film are chosen as a model system for these studies. Microstructural evolution of these films were investigated using Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Elastic Recoil Detection (ERD) and Grazing Incidence X-ray Diffraction (GIXRD). Under the high fluence He+ ion irradiation at 500 °C, small He bubbles with low bubble densities are observed in the irradiated nanochannel CrN films, while the aligned large He bubbles, blistering and texture reconstruction are found in the irradiated compact CrN film. For the heavy Ar2+ ion irradiation at 500 °C, the microstructure of the nanochannel CrN RT film is more stable than that of the compact CrN film due to the effective releasing of defects via the nanochannel structure. Under the He+ ion irradiation and subsequent annealing, compared with the compact film, the nanochannel films have excellent performance for the suppression of He bubble growth and possess the strong microstructural stability. Basing on the analysis on the sizes and number densities of bubbles as well as the concentrations of He retained in the nanochannel CrN films and the compact CrN film under different experimental conditions, potential mechanism for the enhanced radiation tolerance are discussed. Nanochannels play a crucial role on the release of He/defects under ion irradiation. We conclude that the tailored “vein-like” nanochannel structure may be used as advanced radiation tolerance materials for future nuclear reactors.

Elucidating doping driven microstructure evolution and optical properties of lead sulfide thin films grown from a chemical bath

Doping driven remarkable microstructural evolution of PbS thin films grown by a single-step chemical bath deposition process at 60 °C is reported. The undoped films were discontinuous with octahedral-shaped crystallites after 30 min of deposition, whereas Cu doping led to a distinctly different surface microstructure characterized by densely packed elongated crystallites. A mechanism, based on the time sequence study of microstructural evolution of the films, and detailed XRD and Raman measurements, has been proposed to explain the contrasting microstructure of the doped films. The incorporation of Cu forms an interface layer, which is devoid of Pb. The excess Cu ions in this interface layer at the initial stages of film growth strongly interact and selectively stabilize the charged {111} faces containing either Pb or S compared to the uncharged {100} faces that contain both Pb and S. This interaction interferes with the natural growth habit resulting in the observed surface features of the doped films. Concurrently, the Cu-doping potentially changed the optical properties of the films: A significant widening of the bandgap from 1.52 eV to 1.74 eV for increase in Cu concentration from 0 to 20% was observed, making it a highly potential absorber layer in thin film solar cells.

In Situ GIWAXS Analysis of Solvent and Additive Effects on PTB7 Thin Film Microstructure Evolution during Spin Coating.

The influence of solvent and processing additives on the pathways and rates of crystalline morphology formation for spin-coated semiconducting PTB7 (poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)-carbonyl]-thieno[3,4-b]thiophenediyl]]) thin films is investigated by in situ grazing incidence wide-angle X-ray scattering (GIWAXS) and optical reflectance, to better understand polymer solar cell (PSC) optimization approaches. In situ characterization of PTB7 film formation from chloroform (CF), chlorobenzene (CB), and 1,2-dichlorobenzene (DCB) solutions, as well as CB solutions with 1% and 3% v/v of the processing additives 1-chloronapthalene (CN), diphenylether (DPE), and 1,8-diiodooctane (DIO), reveals multiple crystallization pathways with: (i) single-solvent systems exhibiting rapid (<3 s) crystallization after a solvent boiling point-dependent film thinning transition, (ii) solvent + additive systems exhibiting different crystallization pathways and crystallite formation times from minutes (CN, DPE) to 1.5 h (DIO). Identifying crystalline intermediates has implications for bulk-heterojunction PSC morphology optimization via optimized spin-casting processes.

An in-situ real time study of the perovskite film micro-structural evolution in a humid environment by using synchrotron based characterization technique

Humid environment plays a vital role in affecting the performance stability of the organic metal halide perovskite solar cells. Therefore, in situ monitoring the micro-structural evolution of perovskite film in real time will help to reveal the micro-mechanism for the device performance decay induced by humidity. A device providing a controllable humid environment has been set up at X-ray diffraction beamline of Shanghai Synchrotron Radiation Facility, which is used to monitor in situ the perovskite film micro-structural evolution in real time in a humid environment by using grazing incidence X-ray diffraction(GIXRD). After a perovskite film is exposed to the environment with a relative humidity of 60%±2%, a new component emerges near the perovskite(110) diffraction peak in the early stage of the exposure, which is observed for the first time. This new component is attributed to the perovskite intermediate phase structure transformed from the gradual degradation of the perovskite crystalline. Meanwhile, UV-Vis absorption measurements show that humidity causes the absorption of the film to decrease slightly with the blue shift of the absorption edge at ~770 nm, which indicates a reduced amount of perovskite crystalline or a decrease of perovskite crystallinity. Scan electron microscope further demonstrates that the film after the humid exposure presents a worse morphology with a lower coverage, bigger pores, and larger voids between crystalline than the pristine film. The current-voltage(J-V) measurements of the solar cells fabricated on the perovskite films before and after the humid exposure show that both the filling factor and the power conversion efficiencydecrease by over 30% due to the humidity. The present work demonstrates that the close relationship between the device performance and the perovskite film microstructure as well as their morphologies can be studied very well by in-situ synchrotron based characterization technique. The present study could lay a good foundation for the understanding of the degradation mechanism for the organic metal halide perovskites.

(Invited) Role of Charges in Non-Classical Crystallization of Thin Films and Nanostructures in the Plasma CVD Process

Extensive studies have been made on non-classical crystallization, which refers to the crystal growth by the building unit of nanoparticles. In parallel with the non-classical crystallization in the crystal growth in solution, the non-classical crystallization in the gas phase synthesis of thin films and nanostructures by chemical vapor deposition (CVD) and some physical vapor deposition (PVD) has been studied extensively. Here, the charged nanoparticles (CNPs) are spontaneously generated in the gas phase and become the building block of thin films and nanostructures. Charged nanoparticle-based crystallization appears to be very general, including the growth of diamond, Si, ZrO2, GaN, ZnO films as well as nanowires. The generation of CNPs in the gas phase was experimentally confirmed in many systems and their mass distribution was shown to play a decisive role in the microstructure evolution of films, nanowires, and nanotubes. The fact that CNPs can be a building block of crystals without leaving any void behind and of nanowires with smooth surface indicates that CNPs are quasi-solid, having a liquid-like property in diffusion. This means that the charge enhances the atomic diffusion, which is a newly discovered physical phenomenon. This means again that charge weakens the bond strength. Small nanoparticles can be liquid-like even if singly charged but large nanoparticles should be multiply charged to be liquid-like. Based on this understanding, the microcrystalline silicon without an amorphous incubation layer could be deposited on a glass substrate at 320oC and on a polymer substrate at 200oC. Using the liquid-like property of CNPs, the epitaxial growth of silicon was successfully achieved at 550oC by the plasma CVD process. Weakening of bond strength by charges would enhance chemical reactions at low temperature, which can explain the low temperature decomposition in the plasma CVD process. Charge-enhanced diffusion would favor the crystallization and produce charged crystalline nanoparticles at low temperature in the plasma, which explain the low temperature deposition of crystalline films by the plasma CVD process. References N.M. Hwang and D.K. Lee, J. Phys. D: Appl. Phys. 43, 483001 (2010) (Topical Review).A. Badzian and N.M. Hwang, Diamond: Low-Pressure Synthesis, Ref. Module of Mater. Sci. & Mater. Eng. (2016).

Structural and optical properties of magnetron-sputtered Er-doped AlN films grown under negative substrate bias

Abstract In seeking suitable host-microstructures enhancing photoluminescent (PL) efficiency of reactively sputtered Er-doped AlN films deposited under varying negative substrate bias, we observed that the films’ Er-emitted PL intensity at the wavelength of 1.54 μm builds up with bias up 50 V, before falling sharply and collapsing for U above 90 V. We studied for further insight the bias-induced effects on the film microstructural and optical properties. The transmission electron microscope images of these films biased up to ∼50 V showed improved film crystallographic quality with wide and long columnar microstructures. The columnar crystallized volumes therein are maximized around a particular bias value around 90 V, above which they have finely grained nano-granular microstructures. This film-microstructural evolution concurs well with the film refractive index n and extinction coefficient k obtained from ellipsometry. Both surge for films biased from ∼50 V to ∼90 V. These correlating evidences point out that adequate adatom mobility gained under low-energy ion bombardment with bias up to 50 V properly configures the AlN Wurzite planes while leaving behind fewer sites for PL-quenching defects. Meanwhile, Urbach tail states associated with other visible-light absorbing defects created by some material disorder in appropriate locations within the columns should have absorb the exciting photon energy and transfer it efficiently to the emitting Er3+ ions. These evidences further indicate that the newer defects created under bias above 100 V act as non-radiative centers in putting out the PL. We suggest that these latter defects would be located with a high density, at the numerous grain boundaries of the nano-crystallized volumes.

Effect of annealing on microstructure evolution in CoFeB/MgO/CoFeB heterostructures by positron annihilation

As one of the most powerful tools for investigation of defects of materials, positron annihilation spectroscopy was employed to explore the thermal effects on the film microstructure evolution in CoFeB/MgO/CoFeB heterostructures. It is found that high annealing temperature can drive vacancy defects agglomeration and ordering acceleration in the MgO barrier. Meanwhile, another important type of defects, vacancy clusters, which are formed via the agglomeration of vacancy defects in the MgO barrier after annealing, still exists inside the MgO barrier. All these behaviors in the MgO barrier could potentially impact the overall performance in MgO based magnetic tunnel junctions.

Selective ion-induced grain growth: Thermal spike modeling and its experimental validation

Ion-bombardment-induced selective grain growth is a process that allows for full control of the orientation of vapor-deposited thin films, which can be converted from fiber-textured polycrystalline to single-crystal films. The main mechanisms behind this phenomenon are explained by a new thermal spike model, which takes into account and compares the different driving forces governing the film microstructure evolution upon irradiation and emphasizes the importance of the thermal spike shape and volume. The strong agreement between model and experimental data confirms that selective grain growth is driven by the minimization of the volume free energy.

Microstructure evolution of copper doped beryllium thin films

Copper (Cu) doped beryllium (Be) thin films were deposited on silicon substrates by using a simple ion beam sputtering method, which can also realize the varying of Cu doping concentration. Detailed morphological and structural characterizations of the samples clearly disclose a microstructure evolution of films upon doping Cu. Doping Cu can effectively suppress film grain growth, causing a small grain size as well as uniform size distribution. Furthermore, doping Cu affects the crystallographic texture of film, which leads to the formation of more compact film structure. In particular, the surface smoothness of the doped films is significantly improved, which makes them promising candidates for various applications.

Inkjet printable silver dispersions: Effect of bimodal particle-size distribution on film formation and electrical conductivity

Inks containing silver nanoparticles of 12 nm, 80 nm, and a 15%/85% mixture of the two sizes were used to evaluate the effect of particle size and size distribution on the electrical properties of sintered films. The silver layers deposited with a “drop-on-demand” inkjet printer were heated at temperatures ranging from 125 to 200 °C. The small particles formed less resistive films at 125 °C, while the larger ones provided better electrical conductivity above 150 °C. The inks containing mixed small and large particles yielded the most conductive silver films over the entire investigated temperature range. A mechanism explaining these results is proposed based on the evolution of film microstructure with temperature.

Broad band optical characterization of sol–gel TiO 2 thin film microstructure evolution with temperature

Titanium dioxide (TiO 2) thin films have been produced by spin coating a titanium isopropoxide sol on silicon wafer substrates. The structural evolution of the thin films in terms of decomposition, crystallization and densification has been monitored as a function of annealing temperature from 100 to 700 °C using optical characterization and other techniques. The effect of annealing temperature on the refractive index and extinction coefficient of these TiO 2 thin films was studied in the range of 0.62 to 4.96 eV photon energy (250–2000 nm wavelength) using spectroscopic ellipsometry. Thermal gravimetric analysis and atomic force microscopy support the ellipsometry data and provide information about structural transformations in the titania thin films with respect to different annealing temperatures. These data help construct a coherent picture of the decomposition of the sol–gel precursors and the creation of dense layers of TiO 2. It was observed that the refractive index increased from 2.02 to 2.45 at 2.48 eV (500 nm) in sol–gel spin coated titania films for annealing temperatures from 100 °C to 700 °C.

Crystallization and Grain Growth Kinetics for Precipitation‐Based Ceramics: A Case Study on Amorphous Ceria Thin Films from Spray Pyrolysis

AbstractThe introductory part reviews the impact of thin film fabrication, precipitation versus vacuum‐based methods, on the initial defect state of the material and microstructure evolution to amorphous, biphasic amorphous‐nanocrystalline, and fully nanocrystalline metal oxides. In this study, general rules for the kinetics of nucleation, crystallization, and grain growth of a pure single‐phase metal oxide thin film made by a precipitation‐based technique from a precursor with one single organic solvent are discussed. For this a complete case study on the isothermal and non‐isothermal microstructure evolution of dense amorphous ceria thin films fabricated by spray pyrolysis is conducted. A general model is established and comparison of these thin film microstructure evolution to kinetics of classical glass‐ceramics or metallic glasses is presented. Knowledge on thermal microstructure evolution of originally amorphous precipitation‐based metal oxide thin films allows for their introduction and distinctive microstructure engineering in devices‐based on microelectromechanical (MEMS) technology such as solar cells, capacitors, sensors, micro‐solid oxide fuel cells, or oxygen separation membranes on Si‐chips.

Substrate-plasma interaction during amorphous silicon thin films growth by sputtering technique

The present paper deals with the investigation of Argon ions – substrate interactions during film growth and their influence on sputtered hydrogenated amorphous silicon (a-Si:H) thin films structural properties. These interactions are characterized by mean of the calculation of the energy distribution of Ar ions striking the substrate and their striking force measurement in the case of Rf diode sputtering. The influence of the Ar ions bombardment on structural and physical properties of amorphous silicon thin properties is discussed. The ion bombardment affects the film growth processes and consequently, it causes films densification and evolution of film microstructure from amorphous state at low power towards a microcrystalline material with increasing the Rf power.

Thin Film Growth Related Adsorption Study of Al and O Ions on an α-Al2O3 Surface

The surface reactivity of α-Al2O3 (0001) has been investigated theoretically using density functional theory. The adsorption process of Al+, Al2+, Al3+, and O+ were studied to identify possible preferential adsorption sites during thin film growth. Differences in near surface atomic displacements (e.g., adsorption-induced surface reconstructions), energies, and bonding character have been evaluated. The adsorption energies for the metallic ions showed a strong dependence on both initial charge and adsorption site. The O+ ions showed no site dependence, but adsorption energies similar to those calculated for Al+. The results indicate that the adsorption of O+ and Al3+ may favor the formation of an amorphous structure, which is consistent with experimental observations. The results are of fundamental importance for the understanding of thin film microstructure evolution.