Effects of dual-pulse laser ablation

U ovome radu proučavan je efekt laserske ablacije dobivene s dva, vremenski korelirana, laserska pulsa. Kao glavni parametar javlja se vrijeme kašnjenja između laserskih pulseva τ, koje je varirano između 0 i 50 μs. Eksperiment se bazira na mjerenju vremenski ovisne apsorpcije, odnosno emisije ablacijskog oblaka titana u vakuumu u ovisnosti o τ. Mjereni su apsorpcijski i emisijski spektri atoma Ti, te emisijski spektri atoma Ti i iona Ti+, te je praćeno njihovo vremensko odvijanje. Za mjerenje apsorpcije korištena je laserska apsorpcijska spektroskopija pomoću optičkog rezonatora (laspor), a za mjerenje emisije klasična emisijska spektroskopija pomoću monokromatora. Rezultati apsorpcije i emisije pokazuju višestruko pojačanje signala prilikom dvostruke ablacije za dani τ u odnosu na jednostruku. U apsorpcijskim se mjerenjima, za određene prostorno-vremenske paremetre, javlja dopplerovo cijepane apsorpcijskih linija što je indikacija povećane paralelne brzine (u odnosu na površinu mete) ablatiranih čestica, odnosno posljedica eksplozije faze. Također je razvijen i model koji simulira apsorpcijska mjerenja, a pomoću kojega je moguće odrediti i neke dodatne parametre (npr. Raspodjela brzina, te oblik funkcije gustoće ablatiranih čestica). Mjereni su i volumeni kratera nastali na površini mete nakon ablacije, te njihova dubina i radijus, za razna vremena τ. Za najmanja vremena τ dominira efekt zasjenjenja za drugi puls pa volumen nije najveći iako je meta za drugi puls najzagrijanija (najmanji prag za ablaciju). Također se za veća vremena kašnjenja (2 μs) dobivaju napareni filmovi titana na Si substrat s najmanjom hrapavošću i najvećom debljinom.In this work the effect of laser ablation which is induced with two, time separated, laser pulses was studied. As a main parameter in dual-pulse laser ablation delay time between the laser pulses τ appeared and it was scanned within interval 0 – 50 μs. Experiment is based on measurement of time-dependent absorption and emission from plasma plume of titanium ablated in vacuum in respect to τ. Absorption and emission spectra of Ti, and emission spectra of Ti+ were also measured as well as its temporal dependence. Absorption measurements were performed by means of cavity ring-down spectroscopy while emission measuremenst were performed by means of classical monocromator. Results shows many-fold increase of measured signal in dual-pulse in comparison to single-pulse laser ablation. For given temporal and spatial parameters absorption line profiles appeared doppler-splitted. It is indication of increased velocity component parellel to the target surface, i.e. increased phase explosion. The model was developed for simulation of absorption measurements. From the model parameters such are velocity distributuin of ablated species, or anisotropy function can be assessed. Otherway those parameters cannot be obtained directly from the experiment. Volumes, radii and depths of the craters induced by laser ablation were also measured in respect to τ. It was found that largest volumes were given for shorters τ when ablation threshold is lowest, except that for the shortest τ where screening effect dominates for the second pulse hence energy delievered to the target was decreased. Ti films deposited on si depend on τ and on regime of ablation (single or dual). The thickest and smoothed layer was made with τ = 2 μs

The PlasmaArt Project – Application of Atmospheric-Pressure Plasma Jets in Conservation-Restoration of Wooden Objects

Projekt PlasmaArt realiziran je kao suradnja Instituta za fiziku (kao nositelja projekta) i Hrvatskog restauratorskog zavoda uz suradnju s Prehrambeno-biotehnološkim fakultetom i Biološkim odsjekom Prirodoslovnomatematičkog fakulteta. Projekt je poglavito financiran sredstvima Zaklade Adris grupe i manjim dijelom projektom IP-11 2013-2753 Hrvatske zaklade za znanost, a njime smo ispitali primjenu hladnog atmosferskog plazmenog mlaza na drvenim testnim pločicama koje vjerno simuliraju umjetnine od drva u svrhu dezinfekcije i uklanjanja stratigrafskih slojeva oslika. Iz etičkih razloga eksperimentalna ispitivanja nisu provedena na pravim umjetninama. Atmosferski plazmeni mlaz nastaje tako da se kroz staklenu kapilaru u kojoj je smještena elektroda propuhuje plin (Ar, He ili mješavina Ar i O2). Na elektrodu se narine visokofrekventni (20 kHz) visoki napon (7 kV). Atmosferski plazmeni mlazovi hladni su tip plazmi, temperature mlazova su oko 30 - 50 °C, dok je zagrijavanje tretiranog materijala puno manje (tek se nekoliko °C lokalno povisi temperatura tretiranog uzorka) pa nema nikakve termalne štete. Obrade plazmenim mlazovima Ar i He izvođene su tako da je mlaz bio usmjeren u jednu točku na površini testne pločice ili da je pločica pomicana u odnosu na mlaz. Obrada uzoraka plazmenim mlazom je beskontaktna (nema mehaničkog kontakta pa time ni mehaničkih oštećenja), a udaljenost plazmenog mlaza od uzorka može utjecati na jačinu međudjelovanja mlaza i površine, čime se može kontrolirati jačina, odnosno učinkovitost obrade. Beskontaktni hladni atmosferski plazmeni mlaz omogućio bi sigurniju obradu drvenih umjetnina kao alternativa uporabi metil-bromida, alkohola (etanol) i mehaničkog uklanjanja mikroorganizama. Ideja je da se plazmenim mlazom uklanjaju nečistoće s površina (procesima jetkanja s pomoću kisikovih radikala) i deaktiviraju mikroorganizmi, kao što su gljivice, budući da je plazmeni mlaz kemijski vrlo aktivan (MOUNIR LAROUSSI, 2002) (UV svjetlo, radikali, ozon, peroksid). Također se ispitivala mogućnost uklanjanja stratigrafskih slojeva oslika testnih pločica. Pri uklanjanju stratigrafskih slojeva udaljenost mlaza bila je 0,5 cm i s duljim djelovanjem na jednu točku na površini, za razliku od obrade dezinfekcije u kojoj je udaljenost bila 1 – 1,5 cm sa znatno kraćim vremenskim djelovanjem na jednu točku. U prvom dijelu projekta za ispitivanje uklanjanja stratigrafskih slojeva oslika izrađeno je 12 posrebrenih i 12 pozlaćenih pločica (dimenzija 3 cm x 3 cm x 2 cm). Metalizacija je izrađena samo na gornjoj stranici pločica. Testne pločice su dodatno višeslojno oslikane i/ili lakirane, s ciljem da se što vjernije imitiraju višestruki preslici, lakovi i naknadne intervencije koje se često nalaze na pravim umjetninama. Mikrouzorci slikanog sloja pločica uzeti prije i nakon obrade plazmenim mlazom poslužili su za precizniju analizu dobivenih rezultata uklanjanja stratigrafskih slojeva. Nakon probi uklanjanja stratigrafskih slojeva, može se zaključiti da plazmeni izvor nije učinkovit u tu svrhu. Naročito nije moguće uklanjati svaki sloj zasebno. Pri obradi na posrebrenim testnim pločicama primijećeno je da srebrni listić površinski oksidira pri kontaktu s plazmenim mlazom ako nema nikakav zaštitni sloj (npr. lak) na površini. Međutim, primjetna je morfološka promjena tretiranih slojeva na svim testnim pločicama. Te novonastale morfološke promjene laka nakon obrade potrebno je bolje istražiti zbog kemijskih promjena, a time se otvara mogućnost izvođenja novih istraživanja. Zaključeno je da tim tipom plazme nije moguće ukloniti stratigrafski sloj s površine, ali je primjetna morfološka promjena tretiranog sloja. U drugom dijelu projekta ispitivano je djelovanje hladnog plazmenog mlaza u svrhu dezinfekcije drvenih testnih pločica kontaminiranih gljivičnim micelijem. Prije ispitivanja utjecaja plazmenog mlaza na rast gljiva, uspostavljen je sustav uzgoja uzročnika truleži drva, i to vrsta Coniophora puteana i vrsta Serpula lacrymans na testnim pločicama. U tu svrhu izrađene su pozlaćene testne pločice od tri vrste drva (lipa, smreka, bukva), od kojih su najčešće izrađene drvene polikromirane skulpture na našem području. Utvrđeno je da gljivična vrsta C. puteana brže raste u eksperimentalnim uvjetima pa je ona korištena u ispitivanju učinkovitosti plazmenog mlaza na dezinfekciju testnih pločica. Sve tri vrste drva bile su podjednako dobar supstrat za rast gljiva, no u daljnjim pokusima korištena je lipa. Komadići krute hranjive podloge prorasli micelijem naneseni su na testne pločice i smješteni u zatvoreni sustav s visokim sadržajem vlage potrebnim za rast gljivičnih vrsta. Nakon sedam dana pri 18 °C micelij je dovoljno porastao, odnosno prekrio određeni postotak površine pozlaćenih testnih pločica. Taj postotak bio je referentni podatak u odnosu na koji se određivao daljnji rast gljiva nakon obrade. Uzorci su obrađeni različitim vrstama hladne plazme. Nakon obrade, uzorci su vraćeni u sustav na još osam dana kako bi se pratilo je li došlo do oporavka gljivice. Za proučavanje učinkovitosti dezinfekcije testnih pločica kontaminiranih gljivicama vrste C. puteana atmosferskim plazmenim mlazom načinjeno je više obrada s tri plina (helij, argon i mješavina 90 % argona i 10 % kisika) i s dvije duljine obrade (dvije minute i pet minuta). Testne pločice su pri obradi pomicane u odnosu na mlaz, kako bi se tretirala cijela gornja površina pločice na kojoj su bile izrasle gljive. Za usporedbu, testne pločice tretirane su alkoholom (96 %-tni etanol) i mehanički (standardna obrada u restauriranju/konzerviranju). Svaka obrada izvodila se na tri testne pločice da se dobiju statistički podaci za kvantizaciju učinkovitosti obrade plazmenim mlazom. Ispitivanje dezinfekcije testnih pločica dalo je pozitivne rezultate, što je bio i glavni cilj projekta. Rezultati ispitivanja pokazali su da je plazmeni mlaz Ar najučinkovitiji, budući da uvjetno nakon prve obrade nije bilo daljnjeg rasta gljivica. Također, plazmeni mlaz Ar/O2 znatno uspori napredovanje gljivica. Općenito se postiglo da obrada atmosferskim plazmenim mlazom, bez obzira na vrstu plina, daje bolje rezultate nego mehaničko uklanjanje gljivica. Uklanjanje alkoholom (96 %-tni etanol) također se pokazalo vrlo učinkovitim, odnosno potpuno je zaustavilo rast gljivica. Međutim, pri toj obradi pojavila su se i oštećenja na površini testne pločice, što je svakako negativan učinak. Iako bi bilo dobro nastaviti i proširiti ispitivanje, dobiveni rezultati upućuju na mogućnost korištenja atmosferskog hladnog plazmenog mlaza u svrhu dezinfekcije predmeta od drva. Na kraju se može zaključiti da je projekt otvorio nove mogućnosti istraživanja primjene hladnog atmosferskog plazmenog mlaza u konzerviranju-restauriranju umjetnina. Istraživanja se mogu provoditi, osim na drvu, i na drugim osjetljivim materijalima, kao što su papir i platno, što će biti tema naših budućih interdisciplinarnih istraživanja.The PlasmaArt project was realized as a collaboration between the Institute of Physics and the Croatian Conservation Institute. The project was funded mainly by the Funds of the Adris Group, and to a lesser extent by project IP-11-2013-2753 of the Croatian Science Foundation. The main idea of the project was to test the application of cold atmospheric plasma jets on wooden test plates that simulate wooden artwork for the purpose of disinfection and removal of stratigraphic layers of overpaint. For ethical reasons, experimental research was carried out not on real artwork, but on wooden test plates which had been prepared to simulate wooden artefacts. (The samples were silver-plated and gold-plated plates, painted and varnished to faithfully represent real artwork.) To test the efficiency of the disinfection effect, some of the test plates were contaminated with fungal mycelia, and to test the removal of stratigraphic layers, the rest of the silver-plated and gold-plated test plates were covered with several layers of paint and varnish. The prepared test plates were treated with cold atmospheric-pressure plasma jets. The results showed that the stratigraphic layers could not be removed, and it was not possible to remove each layer separately. As a result of the disinfection procedure, positive effects were obtained in comparison to standard procedures used in conservation, while the efficiency depended on the type of plasma and the length of the treatment. It was found that the cold atmospheric-pressure plasma jet was an effective source for disinfection of wooden artwork in the conditions described in this paper

Tuning the composition of plasma-activated water by a surface-wave microwave discharge and a kHz plasma jet

An atmospheric pressure surface-wave microwave discharge and a kHz plasma jet are used to activate purified water. It is shown, that by varying the treatment distance and the initial Ar/N2/O2 mixture composition of the surface-wave microwave discharge the concentration ratio of NO−3 and H2O2 radicals created in the plasma activated water (PAW) can be varied over three orders of magnitude, which can be preserved during months of storage at room temperature. At the same time, with the 5 min treatment of the 32 ml water the absolute radical concentrations are varied in the range of 0.5–85 mg l−1 for H2O2, 20–180 mg l−1 for NO−3 and 0.5–14 mg l−1 for NO−2 . In the case of the N2 kHz plasma jet this concentration ratio can be tuned within one order of magnitude by varying the treatment distance. By treating different volumes very similar concentration ratios are obtained, which evolve differently during storage, as the ageing dynamics is determined by the absolute concentration of radicals. In general, the radical most affected by ageing is NO−2 , whose recombination is found to be determined by the H2O2 radical. In order to control the H2O2 concentration and thus the NO−2 radicals recombination, the application of a Fenton type reaction is suggested, which is implied by inserting a copper surface into PAW during or after plasma treatment

Synergy of Nd:YAG Picosecond Pulsed Laser Irradiation and Electrochemical Anodization in the Formation of TiO2 Nanostructures for the Photocatalytic Degradation of Pesticide Carbofuran

This study proposes a simple and controlled method for producing TiO2 with phase junction, oxygen vacancies, and Ti3+ by combining picosecond pulsed laser irradiation and electrochemical anodization. Ti mesh was pretreated by irradiating with a picosecond pulsed laser technique using an Nd:YAG laser (1064 nm) at two fluencies, 15 J/cm2 and 30 J/cm2 . The samples were then subjected to electrochemical anodization to form TiO2 nanotube arrays on the previously laser-treated surface. This study will investigate the possibility of forming TiO2 nanotube arrays on a pre-laser-treated Ti substrate and determine their physicochemical and photocatalytic properties. The samples were characterized by FESEM, XRD, Raman, XPS, and UV-Vis DRS. UV-Vis spectroscopy was used to observe the progress of photocatalytic degradation for all samples, and degradation products were determined using GC-MS. With the synergistic effects of phase junction, oxygen vacancies, and Ti3+, the laser-treated TiO2 with 30 J/cm2 showed a higher photocatalytic degradation rate (85.1%) of the pesticide carbofuran compared to non-laser-treated TiO2 (54.8%), remaining stable during successive degradation cycles, which has promising practical applications

Enhancement of Methylene Blue Photodegradation Rate Using Laser Synthesized Ag-Doped ZnO Nanoparticles

In this work, Ag-doped ZnO nanoparticles are obtained via pulsed laser ablation of the Ag-coated ZnO target in water. The ratio of Ag dopant in ZnO nanoparticles strongly depends on the thickness of the Ag layer at the ZnO target. Synthesized nanoparticles were characterized by XRD, XPS, SEM, EDS, ICP-OES, and UV–VIS spectrophotometry to obtain their crystal structure, elemental composition, morphology and size distribution, mass concentration, and optical properties, respectively. The photocatalytic studies showed photodegradation of methylene blue (MB) under UV irradiation. Different ratios of Ag dopant in ZnO nanoparticles influence the photodegradation rate. The ZnO nanoparticles doped with 0.32% silver show the most efficient photodegradation rate, with the chemical reaction constant of 0.0233 min−1. It exhibits an almost twice as large photodegradation rate compared to pure ZnO nanoparticles, showing the doping effect on the photocatalytic activity

Photocatalytic application of laser synthesized nanoparticles

U ovom radu ispitivana je mogućnost primene nanočestica ZnO za fotokatalitičku degradaciju boje bromkrezol zeleno i komercijalno dostupne boje za bojenje tekstila. Vodena suspenzija nanočestica ZnO dobijena je laserskom ablacijom [1]. Koncentracija nanočestica određena je metodom ISP-OES. Rastvori boje sa različitim količinama nanočestica izlagani su dejstvu UVC zračenja i to u intervalima od 5 minuta u ukupnom trajanju od sat vremena. Degradacija boja u toku ozračivanja utvrđena je merenjem apsorbancije UV-VIS spektrometrijom pre, tokom i nakon ozračivanja. Preliminarni rezultati potvrdili su početnu pretpostavku da se nanočestice dobijene laserskom sintezom mogu koristiti za degradaciju boja.In this paper, the possible use of ZnO nanoparticles for photocatalytic degradation of dyes, in particular bromocresol green and commercial textile dyes, was examined. А water suspension of ZnO nanoparticles was prepared by laser ablation. Concentration of nanoparticles was measured by ICP-OES technique. Dyes solutions with different amounts of nanoparticles were exposed to UVC irradiation at 5 minute intervals for a total period of 1 hour. Degradation of dyes during irradiation was determined by UV-VIS spectroscopy by measuring solution absorbance before, during, and after exposition. Preliminary results confirmed the initial assumption that laser synthesized nanoparticles could be used for dye degradation.58th Meeting of the Serbian Chemical Society; June 9-10, 2022, Belgrade, Serbia

Laser ablation and chemical synthesis of bicomponent ZnO nanoparticles

The bicomponent nano particles draw attention of the researchers because introducing the second component into the crystal lattice of the nanoparticle we can tune physical properties of the material. One of the simplest and fastest method for synthesis of various bicomponent nanoparticles is by pulsed lasers ablation of the bulk material in water. For the synthesis of our bicomponent nanoparticles we use twostep process. The first step is to deposit a thin film of metal onto ZnO substrate using pulsed laser deposition in vacuum (PLD). The second step is to produce colloidal solution of nanoparticles by laser ablation in water (LAL) of metal coated ZnO. The ablating target was then scanned with laser beam in order to avoid heating of the target and to produce the high yield of bicomponent nanoparticles. The obtained nanoparticles were characterized using UV-VIS, XPS, SEM and XRD diagnostics. The second process that we used for synthetizing bicomponent zinc oxide nanoparticles was self-propagating room temperature reaction of zinc nitrate with sodium hydroxide with addition of (x=1; 3 and 5%) of AgNO3. The chemical composition of the produced nanoparticles is Zn1−xAgxO (x=0.01;0.05 and 0.05). After the reaction, obtained powder was calcinated at 1100 °C for 4 h in a furnace. The diffraction patterns were recorded at room temperature and atmospheric pressure in the absence of any re-heating of the samples. From the XRD spectra we found that no second phase were formed in the samples, the ions of silver are embedded into the crystal lattice of the nanoparticles. The bicomponent nanoparticles produced with these two methods are tested for the photocatalytic activity. We used UV lamp for irradiation of nanoparticle and organic dye (methylene blue – MB) mixture in a cuvette. The nanoparticles synthetized with both methods show good photocatalytic activity for degradation of organic dye

Perspective on the use of nanoparticles to improve the tea CO2 based LIBS analytical performances: copper nanoparticles for NELIBS analysis of polypropylene

In this work, signal enhancement of the original TEA CO2 LIBS setup was studied. Two different methods for copper nanoparticle synthesis were applied. Obtained nanoparticles were characterized and then used for Nanoparticle-Enhanced Laser-Induced Breakdown Spectroscopy (NELIBS) of plastic polypropylene. Preliminary results have shown that improvement in the analytical sensitivity for the detection of Cr in plastic materials was achieved.SPIG 2022 : 31st Summer School and International Symposium on the Physics of Ionized Gases : Contributed papers and abstracts of invited lectures, topical invited lectures and progress reports; September 5-9,2022, Belgrad

Influence of RF excitation during pulsed laser deposition in oxygen atmosphere on the structural properties and luminescence of nanocrystalline ZnO:Al thin films

Thin ZnO:Al layers were deposited by pulsed laser deposition in vacuum and in oxygen atmosphere at gas pressures between 10 and 70 Pa and by applying radio-frequency (RF) plasma. Grazing incidence small angle x-ray scattering and grazing incidence x-ray diffraction (GIXRD) data showed that an increase in the oxygen pressure leads to an increase in the roughness, a decrease in the sample density, and changes in the size distribution of nanovoids. The nanocrystal sizes estimated from GIXRD were around 20 nm, while the sizes of the nanovoids increased from 1 to 2 nm with the oxygen pressure. The RF plasma mainly influenced the nanostructural properties and point defects dynamics. The photoluminescence consisted of three contributions, ultraviolet (UV), blue emission due to Zn vacancies, and red emission, which are related to an excess of oxygen. The RF excitation lowered the defect level related to blue emission and narrowed the UV luminescence peak, which indicates an improvement of the structural ordering. The observed influence of the deposition conditions on the film properties is discussed as a consequence of two main effects: the variation of the energy transfer from the laser plume to the growing film and changes in the growth chemistry