Study on excimer laser irradiation for controlled dehydrogenation and crystallization of boron doped hydrogenated amorphous/nanocrystalline silicon multilayers

We report on the excimer laser annealing (ELA) induced temperature gradients, allowing controlled crystal-lization and dehydrogenation of boron-doped a-Si:H/nc-Si:H multilayers. Depth of the dehydrogenation and crystallization process has been studied numerically and experimentally, showing that temperatures below the monohydride decomposition can be used and that significant changes of the doping profile can be avoided. Calculation of temperature profiles has been achieved through numerical modeling of the heat conduction differential equation. Increase in the amount of nano-crystals, but not in their size, has been demonstrated by Raman spectroscopy. Effective dehydrogenation and shape of the boron profile have been studied by time of flight secondary ion mass spectroscopy. The relatively low temperature threshold for dehydrogenation, below the monohydride decomposition temperature, has been attributed to both, the large hydrogen content of the original films and the partial crystallization during the ELA process. The results of this study show that UV-laser irradiation is an effective tool to improve crystallinity and dopant activation in p+-nc-Si:H films without damaging the substrate.Fundação para a Ciência e Tecnologia (FCT)CRUP Spanish–Portuguese bilateral agreement HP2006- 0122Spanish national and regional research contracts: MAT-2000-1050, MAT-2003-04908MAT-2011-24077, PGIDIT03-04908, PGIDT-01PX130301PN, XUGA- Infra 93, XUGA-Infra 94-58, SB93-A0742819D and INFRA 99-PR 405a-46

Review article laser-induced hyperthermia on graphene oxide composites

Background: Hyperthermia-based therapies have shown great potential for clinical applications such as for the antitumor and antipathogenic activities. Within all strategies, the so-called photothermal therapy proposes to induce the hyperthermia by the remote laser radiation on a photothermal conversion agent, in contact with the target tissue. Methods: This paper reviews the most relevant in vitro and in vivo studies focused on NIR laser-induced hyperthermia due to photoexcitation of graphene oxide (GO) and reduced graphene oxide (rGO). Relevant parameters such as the amount of GO/rGO, the influence of the laser wavelength and power density are considered. Moreover, the required temperature and exposure time for each antitumor/antipathogenic case are collected and unified in a thermal dose parameter: the CEM43. Results: The calculated CEM43 thermal doses revealed a great variability for the same type of tumor/strain. In order to detect potential tendencies, the values were classified into four ranges, varying from CEM4360ºC). Conclusions: The ability of GO/rGO as effective photothermal conversion agents to promote a controlled hyperthermia is proven. The variability found for the CEM43 thermal doses on the reviewed studies reveals the potentiality to evaluate, for each application, the use of lower temperatures, by modulating time and/or repetitions in the dosesMinisterio de Ciencia e Innovación del Gobierno de España | Ref. BIOHEAT (PID 2020- 115415RB-100)Xunta de Galicia | Ref. GRC (ED431C 2021/49

Pulsed 193 nm Excimer laser processing of 4H–SiC (0001) wafers with radiant exposure dependent in situ reflectivity studies for process optimization

Apoyo científico y técnico del CACTI193 nm Excimer lasers are efficient tools to process group-IV semiconductors for advanced microelectronic and photonic devices through crystallization annealing, or strain engineering. The combination of both, high photon energy and low penetration depth of the 193 nm laser pulses allow breaking most covalent bonds with a single photon, and low thermal budget treatments through a precise control of the laser processed volume. Up to now, studies using 193 nm lasers for silicon carbide (SiC) processing are mostly limited to ablation processes for micromachining purposes. This paper presents a first study to demonstrate that the optimization of other processes, like the creation or annealing of vacancies, the alloying of SiC surfaces or the selective ablation of silicon or carbon should also be feasible. To develop such laser assisted processes and optimize process parameters, a numerical simulation of the laser/material interaction is essential. This implies that the temporal evolution of the laser pulse must be well known, and that an “in-situ measurement” of the response of the material to the laser pulse should be available. This study therefore evaluates the temporal profile of a new high-power Excimer laser, and presents the results of in-situ Time Resolved Reflectivity (TRR) measurements obtained when irradiating 4H–SiC(0001) wafers with radiant exposures ranging from 0,1 J/cm2 to 3,0 J/cm2. The temporal pulse profile is determined, fitted and applied in a 1-D numerical simulation of the temperature gradients for Si(100) as reference sample, to validate the experimental findings. Radiant exposure thresholds at around 1,4 J/cm2 to locally produce molten surfaces and 1,8 J/cm2 to ablate and create carbon-rich regions with graphene, are determined in-situ and confirmed by Raman spectroscopy.Los láseres Excimer de 193 nm son herramientas eficaces para procesar semiconductores del grupo IV para dispositivos microelectrónicos y fotónicos avanzados mediante recocido de cristalización o ingeniería de deformación. La combinación de la alta energía fotónica y la baja profundidad de penetración de los pulsos láser de 193 nm permite romper la mayoría de los enlaces covalentes con un solo fotón, y tratamientos de bajo presupuesto térmico mediante un control preciso del volumen procesado por láser. Hasta ahora, los estudios que utilizan láseres de 193 nm para el procesado de carburo de silicio (SiC) se limitan principalmente a procesos de ablación con fines de micromecanizado. Este trabajo presenta un primer estudio para demostrar que la optimización de otros procesos, como la creación o recocido de vacantes, la aleación de superficies de SiC o la ablación selectiva de silicio o carbono también debería ser factible. Para desarrollar estos procesos asistidos por láser y optimizar los parámetros del proceso, es esencial realizar una simulación numérica de la interacción entre el láser y el material. Esto implica que debe conocerse bien la evolución temporal del pulso láser y que debe disponerse de una "medición in situ" de la respuesta del material al pulso láser. Por lo tanto, este estudio evalúa el perfil temporal de un nuevo láser Excimer de alta potencia, y presenta los resultados de las medidas in-situ de Reflectividad Resuelta en el Tiempo (TRR) obtenidas al irradiar obleas de 4H-SiC(0001) con exposiciones radiantes que oscilan entre 0,1 J/cm2 y 3,0 J/cm2. El perfil temporal del pulso se determina, ajusta y aplica en una simulación numérica 1-D de los gradientes de temperatura para Si(100) como muestra de referencia, para validar los resultados experimentales. Los umbrales de exposición radiante en torno a 1,4 J/cm2 para producir localmente superficies fundidas y 1,8 J/cm2 para ablacionar y crear regiones ricas en carbono con grafeno, se determinan in situ y se confirman mediante espectroscopia Raman.Xunta de Galicia | Ref. ED431C-2021/49Agencia Estatal de Investigación | Ref. TED2021-131760B-I00Universidade de Vigo/CISU

Development of robust chiroptical systems through spirobifluorenes

Chiroptical responses are valuable for the structural determination of dissymmetric molecules. However, the development of everyday applications based on chiroptical systems is yet to come. We have been earlier using axially chiral allenes for the construction of linear, cyclic, and cage‐shaped molecules that present remarkable chiroptical responses. Additionally, we have developed chiral surfaces through upstanding chiral architectures. Since the goal is to obtain robust chiroptical materials, more recently we have been studying spirobifluorenes (SBFs), a well‐established building block in optoelectronic applications. After theoretical and experimental demonstration, the suitability of chiral SBFs for the development of robust chiroptical systems was certified by the construction all‐carbon double helices, flexible shape‐persistent macrocycles, chiral frameworks for surface functionalization, and structures featuring helical or spiroconjugated molecular orbitals. Here, we give an overview of our contribution to these matters.Ministerio de Ciencia e Innovacion | Ref. TED2021-131760B-100Ministerio de UniversidadesXunta de Galicia | Ref. ED431C 2017/51Universidade de Vigo/CISU

Raman shifts in MBE‐grown SixGe1 − x − ySny alloys with large Si content

We examine the Raman shift in silicon–germanium–tin alloys with high silicon content grown on a germanium virtual substrate by molecular beam epitaxy. The Raman shifts of the three most prominent modes, Si–Si, Si–Ge, and Ge–Ge, are measured and compared with results in previous literature. We analyze and fit the dependence of the three modes on the composition and strain of the semiconductor alloys. We also demonstrate the calculation of the composition and strain of SixGe1 − x − ySny from the Raman shifts alone, based on the fitted relationships. Our analysis extends previous results to samples lattice matched on Ge and with higher Si content than in prior comprehensive Raman analyses, thus making Raman measurements as a local, fast, and nondestructive characterization technique accessible for a wider compositional range of these ternary alloys for silicon-based photonic and microelectronic devices.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Peer Reviewe

How to sterilize polylactic acid based medical devices?

How sterilization techniques accurately affect the properties of biopolymers continues to be an issue of discussion in the field of biomedical engineering, particularly now with the development of 3D-printed devices. One of the most widely used biopolymers in the manufacture of biomedical devices is the polylactic acid (PLA). Despite the large number of studies found in the literature on PLA devices, relatively few papers focus on the effects of sterilization treatments on its properties. It is well documented in the literature that conventional sterilization techniques, such as heat, gamma irradiation and ethylene oxide, can induced damages, alterations or toxic products release, due to the thermal and hydrolytical sensitivity of PLA. The purposes of this paper are, therefore, to review the published data on the most common techniques used to sterilize PLA medical devices and to analyse how they are affecting their physicochemical and biocompatible properties. Emerging and alternative sterilization methods for sensitive biomaterials are also presented.Xunta de Galicia | Ref. ED481A 2019/314Interreg Atlantic Area | Ref. EAPA_151/201

How to Sterilize Polylactic Acid Based Medical Devices?

How sterilization techniques accurately affect the properties of biopolymers continues to be an issue of discussion in the field of biomedical engineering, particularly now with the development of 3D-printed devices. One of the most widely used biopolymers in the manufacture of biomedical devices is the polylactic acid (PLA). Despite the large number of studies found in the literature on PLA devices, relatively few papers focus on the effects of sterilization treatments on its properties. It is well documented in the literature that conventional sterilization techniques, such as heat, gamma irradiation and ethylene oxide, can induced damages, alterations or toxic products release, due to the thermal and hydrolytical sensitivity of PLA. The purposes of this paper are, therefore, to review the published data on the most common techniques used to sterilize PLA medical devices and to analyse how they are affecting their physicochemical and biocompatible properties. Emerging and alternative sterilization methods for sensitive biomaterials are also presented