Vacuum

Germanium–antimony–telluride (GST) and selenium-doped GST (GSST) alloys are widely investigated as phase-change materials for photonic and memory applications due to their tunable crystallization and optical properties. While encapsulation is commonly employed to mitigate degradation, the chemical and structural instability of uncapped GST and GSST thin films, particularly at high temperatures, remains poorly quantified. In this work, we investigate the thermal stability, crystallization behavior, and optical response of thermal evaporated GST and GSST films with different selenium contents annealed at 200 °C and 350 °C under low-vacuum (LV) and high-vacuum (HV) conditions. Thickness measurements, energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and optical transmittance were used to decouple thermal effects from oxygen-assisted degradation mechanisms. LV annealing promotes significant thickness loss, stoichiometric drift—dominated by tellurium depletion, and disrupted crystallization, especially at 350 °C. In contrast, HV annealing strongly suppresses chemical instability, preserves film thickness within densification limits, and restores crystallization behavior consistent with intrinsic phase evolution. Although GSST films exhibit higher optical transmittance than GST after crystallization, selenium incorporation does not prevent degradation under oxygen-accessible conditions at high-temperature. These results highlight the critical role of the annealing environment in controlling the stability and performance of uncapped GST-based films at high temperatures.

In this study, the precipitation behavior and strengthening mechanism of a vacuum-cast CuCrSnZnSiY alloy were investigated. The results showed that after multi-pass thermomechanical treatment, the CuCrSnZnSiY alloy strip exhibited excellent comprehensive properties, with microhardness of 170.9 HV0.2, electrical conductivity of 73.49% of the international annealed copper standard, tensile strength of 531 MPa, yield strength of 507 MPa, and elongation after fracture of 8%. In the early stages of aging treatment, Cr and Sn showed relatively fast diffusion, which led to preferential formation of nucleation sites, promoted Cr enrichment, and resulted in formation of nanoscale Cr phases. As aging proceeded, Sn migrated to the outer layer of the nanoscale Cr phases and formed a shell-like structure that retarded the growth and coarsening of the nanoscale Cr phases. After cold rolling and annealing, strong Goss and Copper textures were present within the alloy microstructure, which were beneficial to the mechanical properties of the alloy. The interaction between dislocations introduced by large deformation and nanophases formed during aging treatment, together with the solid solution strengthening arising from dispersed microalloying elements, constituted the primary strengthening mechanisms of the alloy.

Laser Chemical Vapor Deposition (LCVD) is a high precision, direct-write technique that utilizes beam-stimulated chemical reactions to deposit metals such as Pt or Cu on a micron scale at high speeds. Prior work utilizing a continuous wave (CW) laser has successfully deposited high purity, low resistivity Cu on a multitude of substrates. Unfortunately, CW lasers introduce a significant amount of heat to the substrate, altering interfacial structure and physical properties. Pulsed lasers provide opportunities to minimize heating, but the mechanisms underlying deposition are not well understood. This work compares CW and nanosecond-pulsed LCVD of Cu on Si(100) wherein the laser wavelength is set to 532 nm and copper(I) hexafluoroacetylacetonate trimethylvinylsilane (Cu(hfac) tmvs) is utilized as a precursor gas. Energy-dispersive X-ray spectroscopy and four-point probe methods show low resistivity Cu is produced by both LCVD methods. Finite Element modeling of the laser-induced surface heating that occurs during processing further reveals that LCVD can be accomplished at temperatures well below the Si melt temperature. A new mechanism is proposed for nanosecond-pulsed LCVD whereby the enhanced excitation of conduction electrons near the surface promotes chemical reactions at lower temperatures than that required for CW LCVD.

The Ti-6Al-4V alloy exhibits exceptional specific strength, excellent corrosion resistance, and high thermal stability but suffers from poor wear resistance. To enhance the service life of titanium alloys under frictional wear, this study examines an improved surface-strengthening method. While traditional nitriding increases surface hardness, the effect of the treatment atmosphere, especially the role of trace oxygen, remains poorly explored. This paper investigates the effects of varying treatment temperatures on the surface properties of titanium alloys when a small amount of oxygen (0.5%) is added to the nitriding gas. Titanium alloy specimens were processed via ion nitriding at 650 °C and 850 °C, and the resulting layers were analysed through various experiments. The findings indicate that treatment temperature significantly influences the properties of the enhanced layer. Elevated temperatures yield a thicker and denser composite layer consisting of nitrides, oxides and their compounds. Specimens treated at 850 °C exhibit significantly increased surface hardness, and there were signs of improvement in wear resistance. These specimens also exhibit lower and more stable friction coefficients during testing. Electrochemical tests further confirm that the dense composite layer provides effective protection against corrosion, thus substantially improving the corrosion resistance of the alloy.

RF sputtering was employed to grow BaTiO3 thin films on c-sapphire substrates. Thin-film deposition was conducted under two thermal conditions: ambient temperature (at 25oC) and an elevated substrate temperature (at 100oC). The optical characterization revealed that films deposited under elevated temperature conditions exhibited a slightly larger band gap of 3.6 eV compared to 3.52 eV for room temperature films. Atomic force microscopy and FESEM analyses showed an increase in surface roughness from 13.26 nm to 25 nm at 100oC substrate temperature, which correlated well with the observed particle size evolution. X-ray diffraction (XRD) analysis revealed that high-temperature deposition improved crystallinity with a size of 15 nm. The films also exhibited a strong (110) orientation compared to the weaker crystallinity size of 8 nm at room temperature. Cross-sectional TEM and SAED analyses further confirmed the polycrystalline nature of the BaTiO3 thin films, with an interplanar spacing of 0.2669 nm that is in good agreement with the XRD results. These results demonstrate that substrate heating during sputtering plays a crucial role in tuning the optical band gap, surface morphology, and crystalline quality of BaTiO3 thin films. XPS confirmed the chemical stability of BaTiO3 thin films on sapphire substrates. The spectra showed the presence of Ba, Ti, and O elements with characteristic electronic states. FTIR and Raman analyses further validate these results, confirming the reduction of defect-related vibrational modes and the presence of characteristic BaTiO3 phonon features at 100oC substrate temperature. BaTiO3 films grown at room temperature showed high resistance and loss, while films grown with substrate heating at 100oC exhibited lower loss and enhanced crystallinity. It indicates that substrate heating is a promising approach for high performance capacitors, sensors, and optoelectronic devices.

Irradiation-induced swelling mismatch at the fiber/matrix interface is a critical factor affecting the structural stability of C/SiC composites in nuclear environments. In this work, a carbon nanotube (CNT)-modified interphase is designed to alleviate the irradiation-induced swelling mismatch in C/SiC composites. The swelling behavior and interfacial response of the CNT-modified pyrolytic carbon (PyC) interphase are systematically investigated and compared with those of a conventional PyC interphase following 5 MeV Xe ion irradiation at room and elevated temperatures using atomic force microscopy, Raman spectroscopy, and transmission electron microscopy. The results demonstrate that carbon fibers undergo significantly greater irradiation-induced swelling than the SiC matrix, leading to a pronounced swelling mismatch at the fiber/matrix interface. The introduction of in situ grown CNTs effectively mitigates this mismatch by constructing a three-dimensional compliant interphase that enhances interfacial strain accommodation. As a result, the radial stress developed within the CNT-modified PyC interphase is substantially lower than that in the conventional PyC interphase. These findings provide new insights into the interphase design of radiation-tolerant C/SiC composites for advanced nuclear energy applications.

I would like to comment on the optical analysis reported by Lemziouka et al. [Vacuum 182 (2020) 109780]. Several quantities presented therein as optical and electrical properties are obtained through equations that appear internally or dimensionally inconsistent. In particular, the reconstruction of reflectance from absorbance and transmittance is difficult to reconcile with the authors’ definition of absorbance, while the cited source therein does not contain the reflectance relation attributed to it. In addition, the expression used for “electrical conductivity” therein does not have the dimensions of electrical conductivity, yet this derived quantity is subsequently used to infer a hopping activation energy. I discuss the propagation of these problems into several reported optical and dispersion parameters.