Glass Thin Films Research Articles

PHOTOELECTRICAL PROPERTIES OF CdMnSe THIN FILMS

The studied semiconductor structure for photovoltaic cells is composed of SnO2-coated glass and CdMnSe thin film. A study is made by examining the photoluminescence from the surface of the CdMnSe thin film with laser power and sample temperature for an as-grown, then an air-annealed thin film and undergone CdCl2 treatment. Thin films of Cd1-xMnxSe (x=0.02) were grown on a glass substrate. The lifetime of charge carriers under pulsed illumination was determined from the kinetic decay of the photocurrent. The study of relaxation curves of nonequilibrium photoconductivity under the influence of laser radiation confirmed the presence of two recombination channels - intrinsic and impurity. Photocurrent relaxation occurs through fast and slow recombination channels. The fast relaxation time τ = 6 μs associated with the intrinsic transition and the slow relaxation time is due to impurity excitation and τ = 22 μs. The photoluminescence spectra of thin films of Cd1-xMnxSe (x=0.02) were studied. In the photoluminescence study, two maxima are observed due to donor-acceptor recombination and intracenter transition of Mn atom.

Nanoscale View of Alignment and Domain Growth in a Hexagonal Columnar Liquid Crystal.

Highly ordered liquid crystalline (LC) phases have important potential for organic electronics. We studied the molecular alignment and domain structure in a columnar LC thin film with nanometer resolution during in situ heating using four-dimensional scanning transmission electron microscopy (4D STEM). The initial disordered vapor-deposited LC glass thin film rapidly ordered at its glass transition temperature into a hexagonal columnar phase with small (<10 nm), well-aligned, planar domains (columns oriented parallel to the surface). Upon further heating, the domains coarsen via bulk diffusion, then the film crystallizes, then finally transforms back to an LC phase at an even higher temperature. The LC phase at high temperature shows straight columns of molecules, which we attribute to structure inherited from the intermediate crystalline phase. Nanoscale 4D STEM offers direct insight into the mechanisms of domain reorganization, and intermediate crystallization is a potential approach to manipulate orientational order and texture at the nano- to mesoscale in LC thin films.

Remarkable difference in structural relaxation dynamics of conventionally prepared bulk glass and vapor-deposited thin films.

The structural relaxation dynamics of conventionally prepared bulk glass of N,N'-bis(3-methylphenyl)-N,N'-diphenyl-benzidine (TPD) was measured by differential scanning calorimetry. The calorimetric data were quantitatively described in terms of the Tool-Narayanaswamy-Moynihan (TNM) model. The TNM parameters were evaluated using a combination of linearization and non-linear optimization methodologies: h*/R = 109.5 kK, ln(A/s) = -321, β = 0.37, x = 0.64. In addition, the TNM phenomenology was used to describe recently reported normalized thickness data of stable and aged thin TPD films measured by ellipsometry. The structural relaxation was found to proceed at a markedly higher rate in these thin films prepared by the physical vapor deposition compared to that of conventional bulk glass. This feature appears to be associated with the significantly narrower distribution of relaxation times (β ≅ 0.8) observed for stable thin film in "as-deposited" form with uniquely dense molecular packing. Interestingly, very similar attributes of the relaxation kinetics were also found in the aged thin film with a previously erased thermal history associated with the deposition.

Ultrafast laser-induced topochemistry on metallic glass surfaces

Manufacturing multifunctional nanocomposite materials and engineered surface nanopatterns involves a strategic blend of topography, crystal structures, and chemistry. Here, we report the controllable formation of crystalline nanoparticles and intermetallic compounds on thin films of metallic glasses (Zr50Cu50, Ti50Cu50, and Zr67Ag33) irradiated by ultrafast laser beams. Mapping the structural modification of the photoexcited and subsequently heated alloys reveals previously neglected chemical reactions with air, offering a direct solution for incorporating nanoparticles into an amorphous oxide matrix and broadening the range of laser-induced surface self-organization features. Our findings are attributed to the occurrence and enrichment of oxygen surface contamination that reacts with selected elements of the metallic glasses. Additionally, the growth of the crystalline phase from undercooled liquid may originate from the dissolution of oxides. Finally, our results establish that the combination of crystalline nanoparticles on amorphous periodic patterns can be universally obtained in a wide range of binary systems of irradiated metallic glasses.

Characterizing oxidation, thickness, and composition of metallic glass thin films with combined electron probe microanalysis and X-ray photoelectron spectroscopy

Metallic glass thin films (MGTFs) are a recently developed class of alloy coatings with potential applications ranging from biomedical devices to electrical components. Their tribological performance in service conditions is dictated by MGTF bulk composition but can be limited by the native oxide surface that inevitably forms upon exposure to atmosphere. Surface oxidation, thickness, and composition of ZrCuNiAl MGTFs were characterized using a combination of X-ray photoelectron microscopy (XPS) and electron probe microanalysis (EPMA). MGTF samples with nominal thicknesses of 50, 500, and 1500 nm were sputtered onto Si and SiN wafer substrates within a high vacuum deposition chamber and their amorphicity was confirmed by X-ray diffraction. XPS depth profiling identified the thin film composition and showed that the surface oxide was dominated by a mixed layer of mostly ZrO2, a little oxidized Al, and some metallic Zr. EPMA X-ray intensities were acquired as a function of beam energy to excite characteristic X-rays from different depths of the MGTFs and reconstructed using open-source thin film analysis software BadgerFilm, to determine the composition and thickness of sample layers. EPMA results constrain the composition to be Zr54Cu29Al10Ni7 within 0.7 at. % variation and total thicknesses to be 49, 470, and 1546 nm. Using the oxide composition identified from XPS depth profiling as an input for BadgerFilm analysis, EPMA results indicate the surface oxidation layer on each of the thin film samples was 6.5 ± 1.1 nm thick and uniform across a 0.25 mm region of the film.

Mechanical responses and plastic rheological behavior of Ti–Zr-Hf-Co-Ni-Cu metallic glass thin films deposited with different substrate temperatures during nanoindentation and nanoscratch process

Ti–Zr-Hf-Co-Ni-Cu metallic glass thin films were deposited by magnetron sputtering at different substrate temperatures of 293 K, 373 K, and 473 K. All the thin films were indicated to be amorphous. The roughness was decreased from 0.71 ± 0.02 nm (293 K) to 0.65 ± 0.01 nm (473 K) and the thin film became more densified with fewer voids and defects. Consequently, the mechanical properties, plastic rheological behavior, and nanoscratch properties varied regularly with the microstructure at different substrate temperatures. The hardness and elastic modulus showed increasing trends with the elevated substrate temperature. The strain-rate strengthening effect occurred, causing the gradual disappearance of the pop-in event with the increasing strain rate. The cut-off value of strain burst size showed an increasing trend with the elevating strain rate. This trend was weakened with the elevated substrate temperature due to the decreased chaos of the interaction between atoms. The cut-off value also increased with the elevating substrate temperature. During the nanoscratch measurement, the elastic recovery ratio increased with the elevating substrate temperature. The critical stress for interface separation of the Ti–Zr-Hf-Co-Ni-Cu metallic glass thin film was improved from 1.9 N to 2.7 N with the substrate temperature rising from 293 K to 473 K.

High-Q two-dimensional photonic crystal nanocavity on glass with an upper glass thin film.

We numerically analyze two-dimensional photonic crystal (PhC) nanocavities on glass with a thin glass film on top of the structure. We investigated a multistep heterostructure GaAs PhC nanocavity located on glass. We found that covering the structure even with a very thin glass film efficiently suppresses unwanted polarization mode conversion occurring due to the asymmetric refractive index environment around the PhC. We also uncovered that the glass-covered structure can exhibit a higher Q factor than that observed in the structure symmetrically cladded with thick glass. We point out that the mode mismatch between the PhC nanocavity and modes in the upper glass film largely contributed to the observed Q-factor enhancement. These observations were further analyzed through the comparison among different types of on-glass PhC nanocavities covered with thin glass films. We also discuss that the in-plane structure of the upper glass film is important for additionally enhancing the Q factor of the nanocavity.

Thermal Stability and Crystallization Processes of Pd78Au4Si18 Thin Films Visualized via In Situ TEM.

Amorphous alloys or metallic glasses (MGs) thin films have attracted extensive attention in various fields due to their unique functional properties. Here, we use in situ heating transmission electron microscopy (TEM) to investigate the thermal stability and crystallization behavior of Pd-Au-Si thin films prepared by a pulsed laser deposition (PLD) method. Upon heating treatment inside a TEM, we trace the structural changes in the Pd-Au-Si thin films through directly recording high-resolution images and diffraction patterns at different temperatures. TEM observations reveal that the Pd-Au-Si thin films started to nucleate with small crystalline embryos uniformly distributed in the glassy matrix upon approaching the glass transition temperature Tg=625K, and subsequently, the growth of crystalline nuclei into sub-10 nm Pd-Si nanocrystals commenced. Upon further increasing the temperature to 673K, the thin films transformed to micro-sized patches of stacking-faulty lamellae that further crystallized into Pd9Si2 and Pd3Si intermetallic compounds. Interestingly, with prolonged thermal heating at elevated temperatures, the Pd9Si2 transformed to Pd3Si. Simultaneously, the solute Au atoms initially dissolved in glassy alloys and eventually precipitated out of the Pd9Si2 and Pd3Si intermetallics, forming nearly spherical Au nanocrystals. Our TEM results reveal the unique thermal stability and crystallization processes of the PLD-prepared Pd-Au-Si thin films as well as demonstrate a possibility of producing a large quantity of pure nanocrystals out of amorphous solids for various applications.

High-temperature Mo-based metallic glass thin films with tunable microstructure and mechanical behaviors

Developing high-temperature metallic glass thin films (MGTFs) with excellent combination properties is crucial for extending the practical applications of metallic glasses. A high-temperature multicomponent Mo-based MGTF with tunable microstructure prepared by single-target magnetron sputtering was presented in this study. Corresponding mechanical behaviors and thermal stability of MGTFs related to microstructure are systemically explored. By adjusting deposition parameters (pressure and power), the microstructure of as-deposited MGTFs can be altered from the dense homogeneous type to the loose nanoglass type. Such structure evolution can be explained by the competition between the surface diffusion and geometric shadowing effect. MGTFs with dense microstructure possess smaller surface roughness, higher hardness, higher Young’s modulus, and better wear resistance. Moreover, they also possess higher thermal stability where the fully amorphous structure and smooth surface can be well maintained after vacuum annealing at 1123 K for 30 min. By contrast, the MGTF with nanoglass microstructure shows inferior mechanical properties and thermal stability due to plentiful loose interface regions, providing abundant free volumes during deformation and acting as favorable crystal nucleation sites during annealing. The correlation between the microstructure and properties of as-deposited MGTFs is clarified with the universal scaling law of glasses. The annealing treatment distinctly increases the hardness and Young’s modulus of MGTFs. Meanwhile, after annealing, pop-in behaviors occur in the as-annealed MGTFs with dense microstructure but not in the as-annealed MGTF with nanoglass microstructure during the nanoindentation. These phenomena can be rationalized by the annihilation of free volumes during annealing and the evolution of the dynamical variable, shear transition zone, for the plastic deformation in MGTFs.

Femtosecond laser induced damage threshold incubation and oxidation in AS2S3 and AS2Se3 thin films

Laser surface structuring has emerged as a versatile technology for precise and localized material processing. When dealing with femtosecond lasers, thermal effects and collateral damage are reduced due to nonlinear light-matter interaction, improving the processing. This study explores the fabrication of microstructures using femtosecond pulses on thin films of chalcogenide glasses, which can be used for photonics applications, such as waveguides, fiber lasers, and photonic crystals. Moreover, the photoinduced changes in chalcogenide glasses have opened up new possibilities in optoelectronics, data storage, and other applications. Femtosecond laser machining of amorphous thin films of As2S3 and As2Se3 using femtosecond laser pulses is investigated through various microscopy techniques and spectroscopy tools, focusing on the impact of incubation effects and controlled photo-oxidation. This research contributes to a deeper understanding of the interaction of ultrafast pulses with chalcogenide glasses, promoting further advancements in photonics and optoelectronic applications.

Self-Aligned InGaZnO Thin-Film Transistors and Circuits on Transparent Thin Glass and FEP Film

Self-Aligned InGaZnO Thin-Film Transistors and Circuits on Transparent Thin Glass and FEP Film

Effect of nanoheterogeneities on the fracture toughness and tensile ductility of CuTa metallic glass thin films

Nanoheterogenenous metallic glasses (MG) can offer improved ductility through a nanoscale modulation in their mechanical properties. However, the relationship between the modulation parameters and the mechanical behavior is not well understood. Physical vapor deposition can directly control the compositional and morphological parameters of nanoheterogeneous MGs and enables the systematic investigation of this problem. This work explores the microstructure and mechanical properties of a range of CuTa-based nanolayered amorphous/amorphous (A/A) and amorphous/semi-crystalline (A/SC) nanoheterogeneous MGs and MG composites. The first step was the identification of three microstructural regimes in CuTa, namely, a fully amorphous form (23–65 at.% Ta), a Ta-rich amorphous-crystalline composite (65–75 at.% Ta), and a Cu-rich amorphous-crystalline composite (16–23 at.% Ta). The hardness of the films increased from 6 GPa to 17 GPa with increasing Ta content. Next, a range of CuxTa1−x/CuyTa1−y nanolayers composed of A/A and A/SC nanolayers were investigated. The hardness of all nanolayers follows the rule of mixture. A/A structures do not provide a significant increase in fracture toughness and only a minor increase in tensile ductility despite the high amplitude modulation of hardness between layers. A/SC nanolayers’ hardness and toughness was higher than A/A nanolayers as well as monolithic amorphous films, but still remained below the monolithic Cu25Ta75 SC film. The results show that the design of nanoheterogeneities in MGs requires careful optimization to achieve a useful improvement in mechanical properties.

Enhanced diffusion in thin-film Cu-Zr nanoglasses

Tracer measurements with both radioactive, 55Fe, as well as natural, mainly 56Fe, isotopes are used to investigate Fe diffusion in a Cu-Zr nanoglass in comparison to their diffusion rates in a homogeneous amorphous counterpart. The columnar-structured nanoglass and the homogeneous amorphous films are synthesized using radio-frequency magnetron sputtering. Ion beam sputtering (with the 55Fe radioisotope) and time-of-flight secondary ion mass spectroscopy (with natural Fe) are used for the diffusion experiments. Remarkably, faster Fe diffusion is observed in the columnar nanoglasses, supporting the concept of glass–glass interfaces. The relative diffusion enhancement is explained within the excess free volume concept that is supported by structural investigations using transmission electron microscopy. For the first time, the relaxation dynamics in a nanoglass as well as in a homogeneous thin-film glass of identical composition are evaluated via time-dependent diffusion measurements.

The advantages of methanol-amine solvent mixtures in solution processing of Ge-Sb-S chalcogenide glass thin films

We report on the substantial influence of methanol presence on the dissolution mechanism of Ge20Sb5S75 bulk glass with subsequent superior properties of thin films deposited from such solutions. Raman spectroscopy confirmed significant differences in structural features present in glass solutions prepared from pure amines (n-propylamine and n-butylamine) and their mixtures with methanol. The experiments with dissolved elemental sulfur and Ge25S75 glass analog proved that both antimony and methanol presence induce further splitting of the Ge4S104− cluster structure, which fundamentally affects the properties of deposited thin films. Significant structural and compositional differences were found not only in solutions and as-prepared samples, but also after thin films’ thermal treatment (hard baking up to 210 °C). The as-prepared thin films deposited from amine-methanol mixtures possessed the exact composition of source bulk glass while thin films of other solvent formulations exhibited sulfur deficiency. The annealing up to 210 °C only highlighted this difference. As a result of the different structure of the thin films prepared in this way, the other benefits of methanol addition were found, namely an increase in the refractive index by approx. 0.1 independent of the annealing temperature, or a lower thermally induced thickness contraction (up to 7.5 %).

Plasmon enhancement of photosensitivity of Ag–chalcogenide glass thin film structures

In this paper, we present the results of studying the features of plasmon- enhanced photostimulated diffusion of silver into thin films of chalcogenide glasses (ChG), in particular, As 2 S 3 and GeSe 2 . To ensure excitation of surface plasmon-polaritons (SPPs) at the interface between silver and ChG films, silver diffraction gratings with periods of 899 and 694 nm were used as substrates. The samples were exposed to the p-polarized radiation of a He-Ne laser (λ = 632.8 nm). The radiation of the same laser, attenuated by two orders of magnitude, was used to detect SPP, which enabled to study the kinetics of photostimulated processes in the thin-layer structure of Ag–ChG. It has been established that in the initial period of exposure, the SPP electromagnetic field significantly enhances the photostimulated flux of silver ions in ChG (by 2-3 times). The photodissolution kinetics of Ag in ChG is defined by the features of the granular structure of the investigated thin chalcogenide films. For the GeSe 2 film with the effective thickness 8 nm, the kinetics of the film refractive index increase caused by silver photodoping is well approximated by a logarithmic dependence. For the Ag–As 2 S 3 structure (the effective thickness of the As 2 S 3 film is 14.8 nm), this kinetics is closer to the linear one; moreover, for photodoping without SPP excitation, the kinetics is somewhat superlinear, while with plasmon excitation, it is sublinear. The main physical mechanism responsible for the acceleration of the process of photostimulated diffusion in the structure under study appears to be an accelerated generation of electron-hole pairs, which takes place in the ChG layer near the interface with the metal, where the SPP electromagnetic field strength is maximum, and/or plasmon- assisted hot carrier generation due to plasmon scattering on the surface of the metal film and subsequent internal photoemission of electrons from silver into chalcogenide.

Visualization of latent and depleted fingermarks on CDs and DVDs using columnar thin films

CDs and DVDs are forensically important substrates for latent fingermarks. To enhance the visualization of fingermarks on CDs and DVDs, columnar thin films (CTFs) of either nickel or chalcogenide glass were deposited. The CTFs were deposited by directing a collimated vapor flux towards the substrate placed at an angle and made to rotate rapidly. The resulting CTFs of upright columnar morphology were grown conformally over these substrates. This process was shown to significantly enhance the visual quality of fingermarks. The fingermarks were aged for either 24 h or 72 h prior to the deposition of the CTF and both the latent and depleted fingermarks were used. Enhancement to maximum possible grade for visual quality occurred, even for the samples that were developed three days after the fingermarks were placed on them.

Real-Time Imaging of Plasmonic Concentric Circular Gratings Fabricated by Lens-Axicon Laser Interference Lithography.

Concentric circular gratings are diffractive optical elements useful for polarization-independent applications in photonics and plasmonics. They are usually fabricated using a low-throughput and expensive electron beam lithography technique. In this paper, concentric circular gratings with selectable pitch values were successfully manufactured on thin films of azobenzene molecular glass using a novel laser interference lithography technique utilizing Bessel beams generated by a combined lens-axicon configuration. This innovative approach offers enhanced scalability and a simplified manufacturing process on larger surface areas compared to the previously reported techniques. Furthermore, the plasmonic characteristics of these concentric circular gratings were investigated using conventional spectrometric techniques after transferring the nanostructured patterns from azobenzene to transparent gold/epoxy thin films. In addition, the real-time imaging of surface plasmon resonance colors transmitted from the concentric circular gratings was obtained using a 45-megapixel digital camera. The results demonstrated a strong correlation between the real-time photographic technique and the spectroscopy measurements, validating the efficacy and accuracy of this approach for the colorimetric studying of surface plasmon resonance responses in thin film photonics.

Structural, optical, and electrical characteristics of Ge18Bi4Se78 chalcogenide glass for optoelectronic applications

The melt quenching and thermal evaporation techniques were used to produce the chalcogenide glass Ge18Bi4Se78 powder and thin film samples, respectively. The as-deposited and annealed thin films at (180, 200, 300, 320 °C) are characterized by X-ray diffractometer and scanning electron microscopy. The Urbach tail energy Eu and the optical energy gap Eop are investigated. As well, the Swanepoel method revealed that the refractive index exhibited normal dispersion behavior. In addition, the single oscillator, dispersion energies, the lattice dielectric constant, εL, plasma frequency, ωp, and optical conductivity, σop were all examined. The electrical conductivity and the activation energies for as-deposited and annealed thin films were calculated. Whereas the J-E properties of the as-deposited and annealed films indicated varied ranges of negative differential conductance NDC depending on the annealing temperatures.

Solution processed multi-layered thin films of Ge20Sb5S75 and Ge20Sb5Se75 chalcogenide glasses

Solution processed non-toxic Ge20Sb5Se75 chalcogenide glass thin films were deposited using spin-coating method from n-propylamine—methanol solvent mixture in specular optical quality. Optical properties, composition, structure, and chemical resistance were studied in dependence on the annealing temperature. Significant increase of refractive index and chemical resistance caused by thermoinduced structural polymerization and release of organic residua were observed. The high chemical resistance of hard-baked thin films allowed repeated direct depositions by spin-coating, increasing total thickness. Multilayered thin films of amorphous Ge20Sb5Se75 and Ge20Sb5S75 were also successfully prepared by direct deposition for the first time. Solution based deposition of non-toxic Ge20Sb5Se75 thin films in specular optical quality significantly widens the applicability of solution processed chalcogenide glass thin films. Moreover, solution based direct deposition of different glasses on hard-baked thin films opens the way to simple and cost-effective preparation of more sophisticated optical elements (e.g. beam splitters, photonic mirrors).

Annealing-induced changes in wear resistance and nanomechanical properties of CuZr metallic glass thin films

Over recent years, metallic glass thin films (MGTFs) have found extensive applications in advanced micro-engineering systems. Consequently, there is a need to thoroughly assess the nanomechanical and tribological behaviors of MGTFs to optimize the design of efficient components. In this study, we employed the nanoindentation technique in various modes to investigate the elastic heterogeneity, tribological response, and mechanical properties of CuZr amorphous films. Before conducting the mechanical tests, annealing treatments at 500 K and 600 K were performed to create samples with different stored energies. The thermal history analysis revealed that the annealing process reduced the stored energy in the microstructure. Furthermore, the pre-annealing treatment resulted in increased hardness and Young’s modulus of the thin films. Additionally, higher annealing temperatures significantly improved the wear resistance of the MGTFs. Observing the serration dynamics in the scratching test, we noticed that the annealing treatment induced larger shear bands on the wear track side. Moreover, the increase in annealing temperature led to a reduction in elastic heterogeneity, which was consistent with the enthalpy relaxation values in the samples. This suggests that the annealing temperature enhanced the densely packed atomic structure, leading to the stabilization of the thin films.