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Pulsed-laser epitaxy of metallic delafossite PdCrO <sub/>2</sub> films
摘要： Alternate stacking of a highly conducting metallic layer with a magnetic triangular layer found in delafossite PdCrO2 provides an excellent platform for discovering intriguing correlated quantum phenomena. Thin film growth of delafossites may enable not only the tuning of the basic physical properties beyond what bulk materials can exhibit, but also the development of novel hybrid materials by interfacing with dissimilar materials, yet this has proven to be extremely challenging. Here, we report the epitaxial growth of metallic delafossite PdCrO2 films by pulsed laser epitaxy (PLE). The fundamental role of the PLE growth conditions, epitaxial strain, and chemical and structural characteristics of the substrate is investigated by growing under various growth conditions and on various types of substrates. While strain plays a large role in improving the crystallinity, the direct growth of epitaxial PdCrO2 films without impurity phases was not successful. We attribute this difficulty to both the chemical and structural dissimilarities with the substrate and volatile nature of the PdO sublayer, which make nucleation of the right phase difficult. This difficulty was overcome by growing CuCrO2 buffer layers before PdCrO2 films were grown. Unlike PdCrO2, CuCrO2 films were readily grown with a relatively wide growth window. Only a monolayer thick buffer layer was sufficient to grow the correct PdCrO2 phase. This result indicates that the epitaxy of Pd-based delafossites is extremely sensitive to the chemistry and structure of the interface, necessitating near perfect substrate materials. The resulting films are commensurately strained and show an antiferromagnetic transition at 40 K that persists down to as thin as 3.6 nm in thickness. This work provides key insights into advancing the epitaxial growth of the broader class of metallic delafossites for both studying the basic physical properties and developing new spintronic and computing devices.
关键词： delafossite,pulsed laser epitaxy,thin film growth,antiferromagnetic transition,PdCrO2
更新于2025-09-23 15:21:01
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Vital role of Ar ambient pressure in controlled properties of nanocrystalline CdS thin films
摘要： A report on the manipulation of structural, optical, and electrical properties of nanocrystalline CdS (ncCdS) thin films in the framework of varying Ar ambient pressure in pulsed laser deposition (PLD) is presented here. Increase in Ar ambient pressure results in reduction of crystallite size which in turns increases the structural imperfections and structural phase transformation of ncCdS thin films. The most significant observation here is the bleaching of multiphonon Raman modes (MRMs) particularly LO + 2E2, 2LO + 2E2, etc. in ncCdS thin films. An acute investigation on the reason of bleaching of LO + 2E2, 2LO + 2E2, etc. modes is carried out here and concluded that it is due to the fading of E2 mode with increasing Ar pressure as confirmed by low-frequency micro-Raman measurements. UV–visible absorption and photoluminescence spectroscopies are used to examine the optical properties like bandgap and possible electronic transitions in ncCdS thin films. Further, transport properties of ncCdS thin films are investigated using Hall measurement and I–V characteristics.
关键词： electrical properties,optical properties,Ar ambient pressure,structural properties,pulsed laser deposition,nanocrystalline CdS thin films
更新于2025-09-23 15:21:01
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On the Formation of Amorphous Ge Nanoclusters and Ge Nanocrystals in GeSixOy Films on Quartz Substrates by Furnace and Pulsed Laser Annealing
摘要： Nonstoichiometric GeO0.5[SiO2]0.5 and GeO0.5[SiO]0.5 germanosilicate glassy films are produced by the high-vacuum coevaporation of GeO2 and either SiO or SiO2 powders with deposition onto a cold fused silica substrate. Then the films are subjected to furnace or laser annealing (a XeCl laser, λ = 308 nm, pulse duration of 15 ns). The properties of the samples are studied by transmittance and reflectance spectroscopy, Raman spectroscopy, and photoluminescence spectroscopy. As shown by analysis of the Raman spectra, the GeO[SiO] film deposited at a substrate temperature of 100°C contains amorphous Ge clusters, whereas no signal from Ge–Ge bond vibrations is observed in the Raman spectra of the GeO[SiO2] film deposited at the same temperature. The optical absorption edge of the as-deposited GeO[SiO2] film corresponds to ~400 nm; at the same time, in the GeO[SiO] film, absorption is observed right up to the near-infrared region, which is apparently due to absorption in Ge clusters. Annealing induces a shift of the absorption edge to longer wavelengths. After annealing of the GeO[SiO2] film at 450°C, amorphous germanium clusters are detected in the film, and after annealing at 550°C as well as after pulsed laser annealing, germanium nanocrystals are detected. The crystallization of amorphous Ge nanoclusters in the GeO[SiO] film requires annealing at a temperature of 680°C. In this case, the size of Ge nanoclusters in this film are smaller than that in the GeO[SiO2] film. It is not possible to crystallize Ge clusters in the GeO[SiO] film. It seems obvious that the smaller the semiconductor nanoclusters in an insulating matrix, the more difficult it is to crystallize them. In the low-temperature photoluminescence spectra of the annealed films, signals caused by either defects or Ge clusters are detected.
关键词： crystallization,pulsed laser annealing,germanosilicate glasses,germanium nanoclusters
更新于2025-09-23 15:21:01
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Near-infrared nanosecond-pulsed laser-activated high efficient intracellular delivery mediated by nano-corrugated mushroom-shaped gold-coated polystyrene nanoparticles
摘要： Here, efficient intracellular delivery of molecules with high cell viability is reported using nanosecond-pulsed laser-activated plasmonic photoporation mediated by high-aspect-ratio nano-corrugated mushroom-shaped gold-coated polystyrene nanoparticles (nm-AuPNPs) at near-infrared wavelength. Upon laser illumination, nm-AuPNPs exhibit greater plasmonic extinction than spherical AuPNPs, which increase their energy efficiency and reduce the necessary illumination of light, effectively controlling cell damage and improving delivery efficiency. Nm-AuPNPs exhibit surface plasmon absorption at near infrared region with peak at 945 nm. Pulsed laser illumination at this plasmon peak triggers explosive nanobubbles, which create transient membrane pores, allowing the delivery of dyes, quantum dots and plasmids into the cells. The results can be tuned by laser fluence, exposure time, molecular size and concentration of nm-AuPNPs. The best results are found for CL1-0 cells, which yielded a 94% intracellular PI dye uptake and ~100% cell viability at 35 mJ/cm2 laser fluence for 945 nm wavelength. Thus, the presented approach has proven to have an inevitable potential for biological cell research and therapeutic applications.
关键词： near-infrared wavelength,intracellular delivery,nanosecond-pulsed laser,gold-coated polystyrene nanoparticles,plasmonic photoporation
更新于2025-09-23 15:21:01
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Structural and Optical Properties of Epitaxial Iron Oxide Thin Films Deposited by Pulsed Laser Deposition
摘要： Iron oxides have been intensively studied owing to potential applications related to energy conversion and storage systems. In this paper, we investigated crystal structures and optical properties of iron oxide thin films deposited at various oxygen partial pressures and temperatures using pulsed laser deposition. The iron oxide thin films were epitaxially grown on Al2O3 (0001) substrates confirmed by X-ray diffraction measurements. With increasing the growth temperature from 450 K to 800 K, the films exhibited better crystalline hematite phase, alpha-Fe2O3. When the pressure was decreased to 0.5 mTorr, the magnetite phase, Fe3O4, was formed. We found that the optical band gaps of iron oxides mainly originated from O 2p to Fe 3d could be modulated from 2.18 eV to 2.42 eV, applicable for energy conversion systems.
关键词： Absorption,Functional devices,Pulsed laser deposition,Fe2O3,Thin films
更新于2025-09-23 15:21:01
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Color tunable upconversion luminescence and optical thermometry properties of mixed Gd2O3:Yb3+/Ho3+/Er3+ nanoparticles prepared via laser ablation in liquid
摘要： The mixtures of Gd2O3:Yb3+/Er3+ and Gd2O3:Yb3+/Ho3+ nanoparticles were successfully prepared via pulsed laser ablation in liquid followed by solution mixing. Under excitation of 980 nm diode laser, tunable color from green to red emission was achieved. Based on the thermal linked energy levels, the temperature sensitive upconversion emission was observed. The fluorescence intensity ratio (FIR) of I513–530 nm/I530–580 nm increased as the elevation of temperature. The absolute sensitivity and relative sensitivity were derived from temperature dependent FIR. The results show that the mixture of Gd2O3:Yb3+/Er3+ and Gd2O3:Yb3+/Ho3+ nanoparticles are not only potential candidates for multicolor upconversion luminescence but also promising optical materials for non-contact optical thermometry.
关键词： Gd2O3 nanoparticles,Color tunable emission,Pulsed laser ablation in liquid,Optical thermometry,Upconversion luminescence
更新于2025-09-23 15:21:01
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A low-temperature limit for growth of ZnO nanowires by using of laser ablation processes
摘要： The contribution deals with growth of ZnO nanowires on metal catalysts by using of pulsed laser deposition and with the influence of growth temperature. The process of nanowires preparation comprised two technological steps—both were based on pulsed laser ablation processes: (1) production of metal nanoparticles by laser ablation in liquids and (2) pulsed laser deposition of ZnO nanowires by ablation of ZnO target on substrate with metal nanoparticles. Nanoparticles from various metals (Au, Ag, Ni, Cu, Al, Mg, Zn, Sn and BiSn alloy) were prepared by pulsed laser ablation at 1064 nm in deionised water. Colloids contained metal nanoparticles were applied on Si (100) substrates, and after drying, nanoparticles served as catalysts of VLS crystallisation. Temperatures in interval 600—200 °C were experimentally compared for the nanowires growth with applied ablation laser working at 248 nm. The lowest achieved temperature value for growth of ZnO nanowires was 425–450 °C. However, among applied metals Cu and Al nanoparticles only successfully catalysed ZnO nanowires at this temperature. Properties of prepared samples were investigated by scanning electron microscopy and photoluminescence. Experimental results revealed that along with the growth temperature, selection of proper metal catalyst is also important factor for nanowires crystallisation.
关键词： Nanoparticles,Zinc oxide,Pulsed laser ablation,Nanowires,Directed growth
更新于2025-09-23 15:21:01
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Low-Temperature Laser Synthesis of Thin Electrochromic WO3 Films
摘要： Amorphous dielectric WO3 films with a surface roughness from 4 to 5 nm have been grown by room-temperature pulsed laser deposition on quartz and c-sapphire substrates using metallic targets. We have examined the effect of the nature of the substrates and the oxygen pressure during the growth process on the transmission spectrum of the WO3 films in the range from 400 to 2000 nm. The parameters of the films have been shown to depend on the oxygen pressure during the growth process. Raising the oxygen pressure from 20 to 60 mTorr during the film growth process increases the transmission of the WO3 films from 40 to 75% in the visible and UV spectral regions and from 10 to 70% in the IR. With increasing oxygen pressure during film growth, the band gap of the WO3 films increases from 3.01 to 3.34 eV in the case of sapphire substrates and from 2.95 to 3.42 eV in the case of quartz substrates, being only slightly dependent on the nature of the substrate. Using a WO3 film grown at room temperature, we have fabricated the first thin-film liquid-electrolyte electrochromic cell. Its transmission in the spectral range from 300 to 900 nm drops by 30% at an applied voltage of 2.5 V, with a coloration time on the order of 2 min.
关键词： electrochromic cell,room-temperature pulsed laser deposition,thin WO3 films
更新于2025-09-23 15:21:01
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Pulsed Laser Deposition Films Based on CdSe-Doped Zinc Aluminophosphate Glass
摘要： A composite material with applications in optoelectronics has been investigated. Pulsed laser deposition CdSe-doped glass film was prepared by the combinatorial deposition from two targets, namely pure CdSe and glass belonging to the 20Li2O-10Al2O3-7BaO-2La2O3-2ZnO-59P2O5 system. Exciton peaks in the Vis domain, related to electron–hole pairs transitions from the valence band to the conduction band, were revealed in the optical absorption spectra of the CdSe-doped film. CdSe quantum dots (QDs) band gap energy depends on the CdSe quantum confinement effect. CdSe-doped film photoluminescence exhibits peaks in the red domain assigned to CdSe transitions from the excited state to the ground state. The size of CdSe nanoclusters, determined from x-ray diffraction is correlated with scanning electron microscopy–energy dispersive x-ray spectroscopy and atomic force microscopy results. Vibration modes specific both to CdSe QDs and to the vitreous network have been evidenced by Fourier transform infrared and Raman spectroscopy.
关键词： quantum dots,optoelectronics,zinc aluminophosphate glass,pulsed laser deposition,CdSe
更新于2025-09-23 15:21:01
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Kinetics of graphitization of thin diamond-like carbon (DLC) films catalyzed by transition metal
摘要： In this paper, we have studied the kinetics of graphitization at 773K of thin diamond-like carbon (DLC) films coated with minute amount of Ni metallic particles. DLC films are deposited at room temperature by pulsed laser deposition (PLD) on a transparent quartz substrate, and Ni is deposited on the surface of DLC using molecular beam epitaxy technique at room temperature. The ultra-high vacuum thermal (range 573-873K with 60 min annealing treatments) and kinetic (range 30-3760 min at 773K) behaviors of the deposited films are investigated. Surface and interface characterizations indicate that the growth of graphitic sp2 clusters starts at temperatures lower than 573K. The kinetics of graphitization is recorded at 773K. Thus, the continuous growth of graphitic clusters leads to a long-range kinetics. These clusters are responsible for the increase in the electrical conductivity and carrier mobility, reaching values of 6.103 Siemens/cm and 20 V/cm2?s, respectively. This continuous change is not only explained by the nucleation and growth of graphitic clusters, but also by some reorientation of them alongside both the surface and the quartz substrate. The obtained results demonstrate that thermally post-treated catalytic metal/DLC films are promising materials for conductive electrodes and sensing applications.
关键词： Raman spectroscopy,thermal treatment,electric transport measurements,optical transmission and absorption,diamond-like carbon,thin graphite films,pulsed laser deposition,metal catalyst
更新于2025-09-23 15:21:01