Thin Film Samples Research Articles

Creating bulk ultrastable glasses by random particle bonding

A recent breakthrough in glass science has been the synthesis of ultrastable glasses via physical vapor deposition techniques. These samples display enhanced thermodynamic, kinetic and mechanical stability, with important implications for fundamental science and technological applications. However, the vapor deposition technique is limited to atomic, polymer and organic glass-formers and is only able to produce thin film samples. Here, we propose a novel approach to generate ultrastable glassy configurations in the bulk, via random particle bonding, and using computer simulations we show that this method does indeed allow for the production of ultrastable glasses. Our technique is in principle applicable to any molecular or soft matter system, such as colloidal particles with tunable bonding interactions, thus opening the way to the design of a large class of ultrastable glasses.

AlN Thin Films Grown on Different Substrates by Metal Nitride Vapor Phase Epitaxy

AbstractIn this paper, AlN thin films are fabricated by green and efficient metal nitride vapor phase epitaxy (MNVPE). First, AlN films are grown on c‐plane sapphire substrates at different molar flow ratios (V/III ratios) of the source material, and the effects of V/III on the crystal quality and surface morphology of the films are investigated. The growth conditions are kept constant (growth temperature of 1550 °C, growth pressure of 10 kPa, V/III ratio of 4420), and the AlN thin films are prepared by heterogeneous epitaxial growth on c‐plane sapphire, silicon (111), and GaN substrates. The crystal quality, residual stress, and luminescence properties of epitaxial AlN thin films on the three substrates are investigated using X‐ray diffraction, scanning electron microscopy, Raman spectroscopy, photoluminescence, and UV spectrophotometer. Among them, the FWHM value of the sample AlN/GaN (002) plane can reach 338 arcsec. The residual stress in samples AlN/Sapphire, AlN/GaN and AlN/Si are 1027, −81, and −541 MPa, respectively, and the sample AlN/GaN has fewer point defects. At the same time, a 50‐nanometer‐thick void layer appears in the AlN thin film samples prepared on GaN substrates, which provides a new technical idea for realizing large‐scale and high‐quality self‐supporting AlN thin films.

Evidence of defect-induced broadband light emission from 2D Ag-Bi double perovskites grown at liquid-liquid interfaces.

Controlling the light emission spectra of low-dimensional hybrid organic-inorganic materials remains an important goal toward the implementation of these materials into real-world optoelectronic devices. In this study, we present evidence that the self-assembly of two-dimensional (2D) silver bismuth iodide double perovskite derivatives at the interface of aqueous and organic solutions leads to the formation of defects capable of modulating the light emission spectra of these materials. Through an analysis of the structural parameters used to explain the photoluminescence (PL) spectra of 2D perovskites, we show the light spectra emitted by (4-ammonium methyl)piperidinium (4-AMP) and (3-ammonium methyl)pyridinium (3-AMPy)-spaced AgBiI8 double perovskites formed through interfacial solution-phase chemistry differ qualitatively and quantitatively from thin film samples. We use previous results to propose the differences observed in the PL spectra of different material morphologies stem from equatorial iodide vacancy formation driven by the kinetics of self-assembly at the liquid-liquid interface. These results show the generality of these chemical physics principles in the formation of defect sites in solution-processed semiconducting nanomaterials, which could help enable their broad use in optoelectronic technologies.

Cu-Au core-shell nanostructures induced by ArF excimer laser irradiation

In this paper, Cu-Au nanospherical structures were formed on glass surfaces by nanosecond UV laser irradiation. ArF laser pulses (193 nm wavelength, 15 ns time duration) were used for the experiments. Cu-Au bimetallic thin-film sample surfaces are structured under ArF excimer laser irradiation during the ablation process. Laser irradiation experiments were carried out using different laser fluences, the number of pulses, and focusing optics. Morphology of the irradiated surfaces and images of the nanostructures were obtained by the scanning electron microscopy method. Also, the optical and plasmonic behaviors of the nanostructures were collected by UV-Vis spectroscopy. Elemental composition and its spatial distribution were obtained using energy-dispersive x-ray spectroscopy (EDS) and mapping. EDS mapping shows that bimetallic nanospheres have a core-shell structure. Our results show that different laser irradiation parameters change the nanostructures’ composition, size, distribution, morphology, and optical properties. Cu-Au nanospherical structures can be used for nano-biosensing, catalysis, and enhanced spectroscopy applications.

Experimental Band Structure of Pb(Zr,Ti)O3 : Mechanism of Ferroelectric Stabilization.

Pb(Zr,Ti)O3 (PZT) is the most common ferroelectric (FE) material widely used in solid-state technology. Despite intense studies of PZT over decades, its intrinsic band structure, electron energy depending on 3D momentum k, is still unknown. Here, Pb(Zr0.2 Ti0.8 )O3 using soft-X-ray angle-resolved photoelectron spectroscopy (ARPES) is explored. The enhanced photoelectron escape depth in this photon energy range allows sharp intrinsic definition of the out-of-plane momentum k and thereby of the full 3D band structure. Furthermore, the problem of sample charging due to the inherently insulating nature of PZT is solved by using thin-film PZT samples, where a thickness-induced self-doping results in their heavy doping. For the first time, the soft-X-ray ARPES experiments deliver the intrinsic 3D band structure of PZT as well as the FE-polarization dependent electrostatic potential profile across the PZT film deposited on SrTiO3 and Lax SrMn1- x O3 substrates. The negative charges near the surface, required to stabilize the FE state pointing away from the sample (P+), are identified as oxygen vacancies creating localized in-gap states below the Fermi energy. For the opposite polarization state (P-), the positive charges near the surface are identified as cation vacancies resulting from non-ideal stoichiometry of the PZT film as deduced from quantitative XPS measurements.

Development of highly sensitive Al, Ga, and In-doped ZnO films by the drop casting method for NH3 gas sensing

This article proposes 2 wt% of aluminum, indium, and gallium-doped ZnO thin film samples for ammonia gas sensors.

Effect of Er/Y addition on the growth and superconductivity of Bi2212 films.

In order to increase the critical current density of Bi2212 superconducting films to broaden their application areas. A series of Bi2Sr2CaCu2O8+δ-xRE2O3 (RE = Er/Y) (x = 0, 0.04, 0.08, 0.12, 0.16, 0.20) thin films were prepared by the sol-gel method. The structure, morphology and superconductivity of the RE2O3 doping films were characterized in detail. The effect of RE2O3 on the superconductivity of Bi2212 superconducting films was investigated. It was shown that the Bi2212 films were (00l) epitaxially grown. The in-plane orientation relationship between the Bi2212-xRE2O3 and the SrTiO3 was Bi2212[100](001)//SrTiO3[011](100). The grain size in the out-of-plane direction of Bi2212 tends to increase with the amount of RE2O3 doping. Doping with RE2O3 had no significant effect on the anisotropy of Bi2212 crystal growth, but inhibited the agglomerative growth of the precipitated phase on the surface to a certain extent. Furthermore, the conclusion was that the superconducting transition temperature (Tc,onset) was almost unaffected, while the zero resistance transition temperature (Tc,zero) continued to decrease with increasing doping level. The thin film samples Er2 (x = 0.04) and Y3 (x = 0.08) exhibited the best current-carrying capacity in magnetic fields.

Magnetotransport and magnetic properties of Cr-modified Mn2Sb epitaxial thin films.

High-quality Mn2-xCrxSb (x = 0.01, 0.04, and 0.1) epitaxial thin films were grown on SrTiO3 (STO) (001) single-crystal substrates using molecular beam epitaxy. Magnetotransport and magnetic measurements reveal that the x = 0.01 sample undergoes a quasi-ferrimagnetic (I) [Q-FIM(I)]-to-ferrimagnetic (II) [FIM(II)] spin reorientation (SR) transition and a giant magnetoresistance (MR) associated first-order ferrimagnetic(II)-to-antiferromagnetic (AFM) phase transition upon cooling, resulting in the AFM ground state with a weak in-plane net moment. Upon increasing the doping level from x = 0.01 to 0.1, both the SR transition and the first-order magnetic transition are suppressed. For x = 0.1, the former transition is suppressed, leaving only the Q-FIM(I)-to-AFM transition within the whole temperature region. TAFM-FIM shows almost similar changes upon the application of either in-plane or out-of-plane magnetic fields. TAFM-FIM values of the x = 0.01 and 0.04 samples are much higher than those of the Mn2-xCrxSb bulk with similar doping levels, which can be understood by the clamping effect from STO substrates. For each thin-film sample, the MR effect is observed near TAFM-FIM and disappears in the high temperature Q-FIM(I) phase and low temperature AFM phase, indicating that MR is related to the spin-dependent electron scattering during the first-order magnetic phase transition. Based on the magnetotransport and magnetic data, a magnetic phase diagram is established for the Mn2-xCrxSb films in the low doping level region.

Rapid Fabrication of Fe and Pd Thin Films as SERS-Active Substrates via Dynamic Hydrogen Bubble Template Method

Fe and Pd thin film samples have been fabricated in a rapid fashion utilizing the versatile technique of dynamic hydrogen bubble template (DHBT) method via potentiostatic electrodeposition over a copper substrate. The morphology of the samples is dendritic, with the composition being directly proportional to the deposition time. All the samples have been tested as SERS substrates for the detection of Rhodamine 6G (R6G) dye. The samples perform very well, with the best performance shown by the Pd samples. The lowest detectable R6G concentration was found to be 10-6 M (479 μgL-1) by one of the Pd samples with the deposition time of 180 s. The highest enhancement of signals noticed in this sample can be attributed to its morphology, which is more nanostructured compared to other samples, which is extremely conducive to the phenomenon of localized surface plasmon resonance (LSPR). Overall, these samples are cheaper, easy to prepare with a rapid fabrication method, and show appreciable SERS performance.

The effect of polyvinyl alcohol (PVA) on the optical, electrical and solid state properties of copper zinc tin sulfide (CZTS) deposited by sensitive spray pyrolysis (SSP)

Recently, the use of CZTS as the basis for other generation of low cost thin films solar cells has stimulated further researches. Its excellent p-type absorber nature, relatively high absorption coefficient and ideal energy band-gap of 1.5eV motivated these efforts. Additionally, CZTS consist of earth-abundant, cheap and non-toxic elements with very low manufacturing cost. Initially, copper indium gallium selenide (CIGS) solar cell device emerged but suffered limitations in further development because of rare indium and gallium in the device structure therefore, CZTS is recently preferred as an alternative to CIGS commercial solar cell absorber layer. In this work, solution mixture of CZTS and PVA was deposited on a substrate at temperature of 150 °C. Sensitive spray pyrolysis was used to grow the thin films where calculated amount of the precursor mixture was allowed to fall and be deposited on a heated substrate to form CZTS/PVA thin films. Subsequently, the thin film samples were annealed at a temperature of 200oCfor 1 h to achieving pure crystalline thin film formation. SEM, XRD analysis, Optical, Solid State properties and Raman analysis were studied. The XRD analysis showed that the thin films fell into the pure kesterite structure of CZTS. Results show that produced thin films exhibited higher absorption coefficient and optical conductivity than pure CZTS, 106 m−1 and 1014(S−1) against 104cm−1 and 1012(S−1) respectively. The band-gap is between 1.53eV and 1.73eV. Using a PVA concentration of 0.05 M yielded highest absorbance and optical conductivity with lowest real dielectric constant and transmittance. These improved optical, electrical and solid state properties suitably qualify these thin films as absorber layer material for solar cell applications.

Flow cell for operando X-ray photon-in-photon-out studies on photo-electrochemical thin film devices.

Background: Photo-electro-chemical (PEC) water splitting represents a promising technology towards an artificial photosynthetic device but many fundamental electronic processes, which govern long-term stability and energetics, are not yet fully understood. X-ray absorption spectroscopy (XAS), and particularly its high energy resolution fluorescence-detected (HERFD) mode, emerges as a powerful tool to study photo-excited charge carrier behavior under operating conditions. The established thin film device architecture of PEC cells provides a well-defined measurement geometry, but it puts many constraints on conducting operando XAS experiments. It remains a challenge to establish a standardized thin film exchange procedure and concurrently record high-quality photoelectrochemical and X‑ray absorption spectroscopy data that is unperturbed by bubble formation. Here we address and overcome these instrumental limitations for photoelectrochemical operando HERFD-XAS. Methods: We constructed a novel operando photo-electro-chemical cell by computer numerical control milling, guided by the materials' X‑ray and visible light absorption properties to optimize signal detection. To test the cell's functionality, semiconducting thin film photoelectrodes have been fabricated via solution deposition and their photoelectrochemical responses under simulated solar light were studied using a commercial potentiostat in a three-electrode configuration during HERFD-XAS experiments at a synchrotron. Results: We demonstrate the cell's capabilities to measure and control potentiostatically and in open‑circuit, to detect X‑ray signals unperturbed by bubbles and to fluently exchange different thin film samples by collecting high-resolution Fe K-edge spectra of hematite ( α -Fe 2O 3) and ferrite thin film ( MFe 2O 4, M= Zn, Ni) photoelectrodes during water oxidation. Conclusions: Our cell establishes a measurement routine that will provide experimental access of photo-electro-chemical operando HERFD-XAS experiments to a broader scientific community, particularly due to the ease of sample exchange. We believe to enable a broad range of experiments which acquired fundamental insights will spur further photoelectrochemical research and commercialization of water splitting technologies.

Effect of deposition parameters on optical and electrical properties of ZnO–In2O3–SnO2 thin films

A combinatorial study was carried out using a magnetron sputtering system to determine suitable ternary compositions of ZnO–In2O3–SnO2 (ZITO) thin films for optoelectronic applications. Samples were obtained on glass substrates via the co-sputtering of high purity oxide targets. Parameters such as the sputtering gas pressure, deposition time and substrate temperature were studied as the process variables and their effects on the composition, optical, and electrical properties of the thin films were examined in detail. The results have revealed that the samples deposited under a sputtering gas pressure of 10 mTorr and deposition time of 45 min in the Zn-rich region presented the best optical properties (max. 84%), whereas In-rich compositions exhibited better electrical properties (min. 14 Ω/□). More specifically, 61.7 at.% Zn, 31.4 at.% In, and 6.9 at.% Sn was determined as the most suitable ZITO composition for various optoelectronic applications. In addition, the increase in deposition temperature enhanced the optoelectronic properties of the thin film samples as well as their crystal quality.

Enhancing the optoelectronic properties of low-cost nebulizer spray pyrolysis (NSP) prepared ZnS thin film through praseodymium doping for photodetector applications

In this report, ZnS and ZnS:Pr (1, 3, and 5 wt% of Pr) thin films were coated onto the glass substrates by using the low-cost nebulizer spray pyrolysis (NSP) technique. Various characterization techniques were employed to analyze the structural, morphological, optical, and photosensing properties of the prepared samples. The X-ray diffraction results show that the ZnS and ZnS:Pr samples exhibit hexagonal wurtzite structure having preferential growth along the (002) plane which belongs to the P63mc space group. No secondary phases were detected in all the coated thin film samples. The maximum crystallite size of 36 nm was observed for ZnS:Pr1% sample. The SEM analysis revealed that the samples exhibit agglomerated grains and the EDX spectrum of the ZnS:Pr(1 %) sample showed the presence of Zn, S, and Pr elements. The UV–vis absorption spectrum of the ZnS:Pr1% sample revealed that it has higher absorption in the UV region and a decrease in bandgap is noticed among the fabricated samples. The PL spectra showed a highly intense emission line of around 489 nm and a weak UV emission of around 385 nm for all the films. The I-V characteristics of the prepared thin films show that the ZnS:Pr1% sample has higher photosensing properties of responsivity, photoresponse, External Quantum Efficiency (EQE), and the detectivity values of 5.30 × 10-3 AW−1, 5.27, 1.70 %, and 3.76 × 109 Jones, respectively suggesting the sample might be well suited for the UV photodetector applications.

Strongly overdoped La2−xSrxCuO4 : Evidence for Josephson-coupled grains of strongly correlated superconductor

The interpretation of how superconductivity disappears in cuprates at large hole doping has been controversial. To address this issue, we present an experimental study of single-crystal and thin film samples of ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$ (LSCO) with $x\ensuremath{\ge}0.25$. In particular, measurements of bulk susceptibility on LSCO crystals with $x=0.25$ indicate an onset of diamagnetism at ${T}_{c1}=38.5$ K, with a sharp transition to a phase with full bulk shielding at ${T}_{c2}=18$ K, independent of field direction. Strikingly, the in-plane resistivity only goes to zero at ${T}_{c2}$. Inelastic neutron scattering on $x=0.25$ crystals confirms the presence of low-energy incommensurate magnetic excitations with reduced strength compared to lower doping levels. The ratio of the spin gap to ${T}_{c2}$ is anomalously large. Our results are consistent with a theoretical prediction for strongly overdoped cuprates by Spivak, Oreto, and Kivelson, in which superconductivity initially develops within disconnected self-organized grains characterized by a reduced hole concentration, with bulk superconductivity occurring only after superconductivity is induced by proximity effect in the surrounding medium of higher hole concentration. Beyond the superconducting-to-metal transition, local differential conductance measurements on an LSCO thin film suggest that regions with pairing correlations survive, but are too dilute to support superconducting order. Future experiments will be needed to test the degree to which these results apply to overdoped cuprates in general.

Characterization of CdTe Thin Films Using Orthogonal Double-Pulse Laser-Induced Breakdown Spectroscopy

Orthogonal reheating double-pulse laser-induced breakdown spectroscopy (LIBS) was applied to the elemental analysis of CdTe thin film samples. Films were grown through nanosecond pulsed laser ablation over silicon and glass substrates. The analysis was performed by applying a 266 nm pulsed laser devised to minimize sample damage. Re-excitation was conducted using a nanosecond laser emitting at 1064 nm that induced air breakdown 1 mm above the target. Emission enhancement was investigated as a function of both time acquisition delay and inter-pulse delay. The plasma temperature and electron density calculations made showed that the double-pulse scheme produced higher temperature values and a longer plasma duration than single-pulse LIBS. The self-absorption coefficient of the lines was determined from the measured ablated matter, plasma volume and collected spectra. The results of the double-pulse LIBS configuration showed a significant increase in emission intensity, reducing the self-absorption effect. In addition, the relative concentration of the thin films was determined for both experimental schemes. The calculated elemental values for the double-pulse configuration coincide with those expected and are more accurate than those obtained using a single laser.

Size and shape dependent rotation characteristics of thin film ultrasonic rotors

The controlled rotation of acoustically levitated samples is beneficial for analyzing sample properties, e.g., in a recently reported room temperature x-ray diffraction experiment, wherein thin film sample holders comprising thin film disks with short blades attached around their circumference were utilized. However, the mechanism of producing the torque and the determinant factor of the rotation direction for these planar ultrasonic rotors have been elusive. We, therefore, study the impact of the size and shape on the rotation characteristics of these ultrasonic rotors in air and further study the influence of the viscosity of fluid. Theory and experiment demonstrate the essential role of the short blades in producing the acoustic torque both in air and water. In the airborne case, the shape and arrangement of the blades are found to determine the rotation direction. In water, with a dynamic viscosity 55 times higher than that of air, we demonstrate that ultrasonic rotors down to 25-μm-disk-diameter function in an optimized experimental geometry with approximately the same actuation efficiency as in air. Our results will be beneficial to further improve the applicability of the ultrasonic rotors as sample holders for airborne experiments and to explore the micrometer-scale ultrasonic rotors in liquid.

Versatile Confocal Raman Imaging Microscope Built from Off-the-Shelf Opto-Mechanical Components.

Confocal Raman microscopic (CRM) imaging has evolved to become a key tool for spatially resolved, compositional analysis and imaging, down to the μm-scale, and nowadays one may choose between numerous commercial instruments. That notwithstanding, situations may arise which exclude the use of a commercial instrument, e.g., if the analysis involves toxic or radioactive samples/environments; one may not wish to render an expensive instrument unusable for other uses, due to contamination. Therefore, custom-designed CRM instrumentation-being adaptable to hazardous conditions and providing operational flexibility-may be beneficial. Here, we describe a CRM setup, which is constructed nearly in its entirety from off-the-shelf optomechanical and optical components. The original aim was to develop a CRM suitable for the investigation of samples exposed to tritium. For increased flexibility, the CRM system incorporates optical fiber coupling to both the Raman excitation laser and the spectrometer. Lateral raster scans and axial profiling of samples are facilitated by the use of a motorized xyz-translation assembly. Besides the description of the construction and alignment of the CRM system, we also provide (i) the experimental evaluation of system performance (such as, e.g., spatial resolution) and (ii) examples of Raman raster maps and axial profiles of selected thin-film samples (such as, e.g., graphene sheets).

Aluminum Doped Titanium Dioxide Thin Film for Perovskite Electron Transport Layer

Aluminum (Al) doped titanium dioxide thin film with different Al doping concentration (Al = 0 mol%, 1 mol%, 3 mol%, 5 mol% and 7 mol%) were deposited using solution spin coating technique and the effect of Al concentration on the structural, morphological and optical properties were examine. All samples were annealed at 450°C for 1 hour. XRD reveal that the films exhibits anatase crystal phase at (101) peak orientation. Based on the FESEM and AFM image it is found that, surface morphology of the film was significantly affected with different doping concentration. Al doped titanium dioxide with 3 mol% Al concentration shows the highest transmittance compared to others samples. Consequently, it is shown that different Al doping concentration plays vital roles in producing an optimum Al doped titanium dioxide thin films samples.

Efficient pump-probe sampling with a single-cavity dual-comb laser: Application in ultrafast photoacoustics

Ultrafast pump-probe measurements are used to characterize various samples, such as biological cells, bulk, and thin-film structures. However, typical implementations of the pump-probe apparatus are either slow or complex and costly hindering wide deployment. Here we combine a single-cavity dual-comb laser with a simple experimental setup to obtain pump-probe measurements with ultra-high sensitivity, fast acquisition, and high timing precision over long optical delay scan ranges of 12.5 ns that would correspond to a mechanical delay of about 3.75 m. We employ digital signal balancing to obtain shot-noise-limited detection compatible with pump-probe microscopy deployment. Here we demonstrate ultrafast photoacoustics for thin-film sample characterization. We measured a tungsten layer thickness of (700 ± 4) Å with shot-noise-limited detection. Such single-cavity dual-comb lasers can be used for any pump-probe measurements and are especially well-suited for ultrafast photoacoustic studies such as involving ultrasonic echoes, Brillouin oscillations, surface acoustic waves and thermal dynamics.

Monolithic multi-wavelength lasing from multi-sized microdisk lasers.

This paper demonstrates monolithic multi-wavelength lasing through fabrication of multi-sized microdisks on a green-emitting thin film sample. The different dimensions of the microdisks incur different extent of strain relaxation, thus changing the emission/gain spectra due to the reduction of the quantum confined Stark effect. Under room-temperature optical pumping, lasing thresholds of 15.1 mJ/cm2, 2.9 mJ/cm2, and 5.3 mJ/cm2 with Q factors of 2370, 2060, and 4308 are realized, respectively, for fabricated microdisks with diameters of 950 nm, 6 μm, and 10 μm. By exciting the microdisks with a pump laser spot diameter of 2 mm, simultaneous multi-wavelength lasing action is thus observed. The strain relaxation effect is confirmed by the shift of the E2 (high) Raman peak from 563.2 cm-1 to 561.5 cm-1 as the diameter of the fabricated microdisk reduces.