Transport properties of semiconductor detectors

Silicij-karbid (SiC) je poluvodički materijal koji posjeduje niz svojstava koja ga čine pogodnim za detekciju zračenja. Široki zabranjeni pojas, mala intrinzična koncentracija naboja, mala struja curenja, veliki napon proboja, dobra toplinska vodljivost, čvrstoća te otpornost na visoke temperature i razine zračenja samo su neka od obilježja po kojima je bolji od silicija (Si), najkorištenijeg materijala u poluvodičkim detektorima. U ovom radu su najprije uspoređena transportna svojstva Schottky dioda od Si i 4H-SiC podjednakih dimenzija i dopiranosti. Korištena su temperaturno ovisna strujno-naponska (I-V) i kapacitivno-naponska (C-V) mjerenja kako bi se dobili važni parametri za rad detektora i prepoznali dominantni transportni mehanizmi. 4H-SiC dioda je pokazala puno manju struju curenja, manju ovisnost širine područja osiromašenja i koncentracije slobodnih nosilaca naboja o temperaturi, manji serijski otpor, a struja koja dolazi od generacijsko-rekombinacijskih (RG) procesa u području osiromašenja je zanemariva. To sve ukazuje na bolju energijsku i vremensku rezoluciju te na veću temperaturnu stabilnost 4H-SiC detektora. Dvije 4H-SiC diode su zatim podvrgnute zračenju termalnih i brzih reaktorskih neutrona kako bi se vidjelo hoće li to promijeniti njihova transportna svojstva. Sve promjene upućuju na to da su u međupovršinu metal-poluvodič uvedeni defekti koji lokalno snižavaju Schottky barijeru, a koncentracija takvih defekata je puno veća kod ozračivanja brzim neutronima. Ostali parametri koji direktno utječu na detektorska svojstva pokazali su zanemarivu promjenu nakon zračenja. Na kraju, proučena je drugačija detektorska struktura – MOS („metal-oxide-semiconductor“). C-V karakterizacija je napravljena na neozračenom Si/SiO2 MOS i uzorku ozračenom brzim neutronima. Uočeno je da su ozračivanjem uvedeni defekti u oksid i međupovršinu oksid-poluvodič.Silicon-carbide (SiC) is the semiconductor material with properties which make it suitable for radiation detection. Wide band gap, small intrinsic carrier concentration, small leakage current, large breakdown voltage, good thermal conductivity, hardness, excellent resistance to large temperatures and high radiation tolerance are all properties which make it better than silicon - the most widely used material in semiconductor detectors. First of all, in this paper is made the comparison between transport properties of Si and 4H-SiC, which have similar dopance and dimensions. The experimental methods which are used are temperature dependent current-voltage (I-V) and capacitance-voltage (C-V) measurements, with the purpose to get the parameters which are important for detectors, and to recognize dominant transport mechanisms. 4H-SiC SBD has shown much less leakage current, the smaller temperature dependence of depletion region width and of free carrier concentration, the smaller series resistance and also recombination-generation (RG) current in depletion region is negligible. All this is the indicator of a better energy resolution and time resolution, but also of the higher temperature stability in 4H-SiC detector. Two 4H-SiC diodes are irradiated with thermal and fast reactor neutrons to see their effect on transport properties. All of the observed changes point to the introduced interface states that locally influence Schottky barrier height. Fast neutrons have introduced much more concentration of such defects than thermal neutrons. Other paramethers that directly affect the detection properties have shown negligible change after the irradiation. Finnaly, a different detector structure has been studied – MOS (metal-oxide-semiconductor), where I-V and C-V characterisation have been made on the unirradiated Si/SiO2 MOS and on the sample irradiated with fast neutrons. In the irradiated sample defects introduced to the oxide and the oxide-semiconductor interface have been observed

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

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

Structural, magnetic and photocatalytic properties of ZnOnanopowder

Removal of organic pollutants from the waste water will bethemost challenging objective in the future. The photodegradation using the zinc oxide (ZnO)is one of the bestpromising material due to low price and high efficiency. Zinc oxide nanoparticles were synthetized by self propagatingroom temperature reaction of zincnitratewith sodium hydroxide.After reaction powder wascalcinated at 1100°C for 4 h in furnace. The diffraction patterns were recorded at room temperature and atmospheric pressure in the absence of any re-heating of the samples. The temperature dependence of magnetization was measured in the field of 1000 Oe and temperature range from 2 to 300 K using MPMS5 SQUID magnetometer. Photocatalytic properties were determined using the degradation of organic dye Methylene Blue (MB). Hg UV lap was used for irradiating the solution of MB and ZnOnanopowder. The photodegradation of MB was monitored by decreasing 664 nm peak during 120 min, after this period of time we observed 95% of reduction from the starting dye concentration. Nanopowder of ZnO show strong photocatalytic performance and can be used for further investigation and applications.IX Serbian Ceramic Society Conference - Advanced Ceramics and Application : new frontiers in multifunctional material science and processing : program and the book of abstracts; September 20-21, 2021; Belgrad

Laser synthesis of nanoparticles and applications in photocatalysis

U ovoj doktorskoj disertaciji pulsna laserska ablacija u vodi korištena je za sintezu nanočestica titanovog dioksida i cinkovog oksida koje imaju jaka fotokatalitička svojstva. U tu svrhu korišten je nanosekundni laser Nd:YAG osnovne valne duljine 1064 nm. Razne eksperimentalne tehnike (XRD, XPS, TEM/SEM, UV-Vis, Raman) su primijenjene za karakterizaciju dobivenih nanočestica kako bi se odredila njihova kristalna struktura, optička svojstva, oblik i distribucija po veličini. Razvijena je jednostavna metoda za određivanje koncentracije laserski sintetiziranih nanočestica u vodi, a u njoj se koriste podaci o volumenu ablacijskog kratera i raspodjela nanočestica po veličini. Metoda je testirana na nanočesticama titanovog dioksida i provjerena pomoću Beer-Lambertovog zakona. Pulsnom laserskom ablacijom titana su dobivene načestice titanovog dioksida, koje su, nakon zagrijavanja u vodi na 90°C, kristalizirale i pokazale jaču fotokatalitičku aktivnost s obzirom na UV i vidljivo zračenje nego P25 čestice. Fotokataličnost nanočestica određivana je mjerenjem brzine fotodegradacije raznih organskih otapala (Methylene Blue, Rhodamine B) pod UV ili vidljivim zračenjem u njihovoj prisutnosti. Mjerena je ovisnost fotokatalitičke aktivnosti nanočestica cinkovog oksida o njihovoj koncentraciji, početnoj koncentraciji i vrsti organskog bojila, a dobivene ovisnosti su teorijski objašnjene. Razvijena je metoda za sintezu dopiranih nanočestica pulsnom laserskom ablacijom u vodi, na način da se u njoj ablatira meta na koju je prethodno u pulsnoj laserskoj depoziciji naparen film materijala za dopiranje. Na taj način su dobivene nanočestice cinkovog oksida s različitim udjelima srebra i pojačanom fotokatalitičkom aktivnošću koja je najveća na izmjerenom optimalnom masenom udjelu srebra 0.32%.In this PhD thesis pulsed laser ablation in water is used for synthesis of titanium dioxide and zinc oxide nanoparticles with strong photocatalytic properties. For that purpose the nanosecond laser ND:Yag with basic wavelength at 1064 nm is used. Various experimental techniques (XRD, XPS, TEM/SEM, UV-Vis, Raman) are performed for the purpose of characterization of synthesized nanoparticles in order to determine their crystal structure, optical properties, shape and size distribution. The simple method for determination of laser synthesized nanoparticles concentration in water is developed, in which the ablation crater volume and nanoparticles size-distribution data are used. The method is tested for titanium dioxide nanoparticles and verified by using Beer-Lambert law. Titanium dioxide nanoparticles are synthesized by pulsed laser ablation of titanium target and it is shown that they crystallized after heating in water at 90°C and developed large photocatalytic activity in the presence of UV and visible light when compared with P25. Photocatalytic efficiency of nanoparticles was calculated by measuring the photodegradation rate of different dyes (Methylene Blue, Rhodamine B) under UV or visible light and in their presence. A dependence of zinc oxide nanoparticles photocatalytic efficiency on their concentration, initial dye concentration and dye type was measured, and obtained relations are theoretically explained. The method for laser synthesis of doped nanoparticles is developed, in which pulsed laser ablation in water is used for ablation of target that is previously coated by dopant material using pulsed laser deposition. In this way the zinc oxide nanoparticles with different silver ratios are synthesized, and they are shown to have improved photocatalytic efficiency, which is the largest at the measured optimal silver ratio 0.32 wt %

Laser synthesis of nanoparticles and applications in photocatalysis

U ovoj doktorskoj disertaciji pulsna laserska ablacija u vodi korištena je za sintezu nanočestica titanovog dioksida i cinkovog oksida koje imaju jaka fotokatalitička svojstva. U tu svrhu korišten je nanosekundni laser Nd:YAG osnovne valne duljine 1064 nm. Razne eksperimentalne tehnike (XRD, XPS, TEM/SEM, UV-Vis, Raman) su primijenjene za karakterizaciju dobivenih nanočestica kako bi se odredila njihova kristalna struktura, optička svojstva, oblik i distribucija po veličini. Razvijena je jednostavna metoda za određivanje koncentracije laserski sintetiziranih nanočestica u vodi, a u njoj se koriste podaci o volumenu ablacijskog kratera i raspodjela nanočestica po veličini. Metoda je testirana na nanočesticama titanovog dioksida i provjerena pomoću Beer-Lambertovog zakona. Pulsnom laserskom ablacijom titana su dobivene načestice titanovog dioksida, koje su, nakon zagrijavanja u vodi na 90°C, kristalizirale i pokazale jaču fotokatalitičku aktivnost s obzirom na UV i vidljivo zračenje nego P25 čestice. Fotokataličnost nanočestica određivana je mjerenjem brzine fotodegradacije raznih organskih otapala (Methylene Blue, Rhodamine B) pod UV ili vidljivim zračenjem u njihovoj prisutnosti. Mjerena je ovisnost fotokatalitičke aktivnosti nanočestica cinkovog oksida o njihovoj koncentraciji, početnoj koncentraciji i vrsti organskog bojila, a dobivene ovisnosti su teorijski objašnjene. Razvijena je metoda za sintezu dopiranih nanočestica pulsnom laserskom ablacijom u vodi, na način da se u njoj ablatira meta na koju je prethodno u pulsnoj laserskoj depoziciji naparen film materijala za dopiranje. Na taj način su dobivene nanočestice cinkovog oksida s različitim udjelima srebra i pojačanom fotokatalitičkom aktivnošću koja je najveća na izmjerenom optimalnom masenom udjelu srebra 0.32%.In this PhD thesis pulsed laser ablation in water is used for synthesis of titanium dioxide and zinc oxide nanoparticles with strong photocatalytic properties. For that purpose the nanosecond laser ND:Yag with basic wavelength at 1064 nm is used. Various experimental techniques (XRD, XPS, TEM/SEM, UV-Vis, Raman) are performed for the purpose of characterization of synthesized nanoparticles in order to determine their crystal structure, optical properties, shape and size distribution. The simple method for determination of laser synthesized nanoparticles concentration in water is developed, in which the ablation crater volume and nanoparticles size-distribution data are used. The method is tested for titanium dioxide nanoparticles and verified by using Beer-Lambert law. Titanium dioxide nanoparticles are synthesized by pulsed laser ablation of titanium target and it is shown that they crystallized after heating in water at 90°C and developed large photocatalytic activity in the presence of UV and visible light when compared with P25. Photocatalytic efficiency of nanoparticles was calculated by measuring the photodegradation rate of different dyes (Methylene Blue, Rhodamine B) under UV or visible light and in their presence. A dependence of zinc oxide nanoparticles photocatalytic efficiency on their concentration, initial dye concentration and dye type was measured, and obtained relations are theoretically explained. The method for laser synthesis of doped nanoparticles is developed, in which pulsed laser ablation in water is used for ablation of target that is previously coated by dopant material using pulsed laser deposition. In this way the zinc oxide nanoparticles with different silver ratios are synthesized, and they are shown to have improved photocatalytic efficiency, which is the largest at the measured optimal silver ratio 0.32 wt %

Laser synthesis of nanoparticles and applications in photocatalysis

U ovoj doktorskoj disertaciji pulsna laserska ablacija u vodi korištena je za sintezu nanočestica titanovog dioksida i cinkovog oksida koje imaju jaka fotokatalitička svojstva. U tu svrhu korišten je nanosekundni laser Nd:YAG osnovne valne duljine 1064 nm. Razne eksperimentalne tehnike (XRD, XPS, TEM/SEM, UV-Vis, Raman) su primijenjene za karakterizaciju dobivenih nanočestica kako bi se odredila njihova kristalna struktura, optička svojstva, oblik i distribucija po veličini. Razvijena je jednostavna metoda za određivanje koncentracije laserski sintetiziranih nanočestica u vodi, a u njoj se koriste podaci o volumenu ablacijskog kratera i raspodjela nanočestica po veličini. Metoda je testirana na nanočesticama titanovog dioksida i provjerena pomoću Beer-Lambertovog zakona. Pulsnom laserskom ablacijom titana su dobivene načestice titanovog dioksida, koje su, nakon zagrijavanja u vodi na 90°C, kristalizirale i pokazale jaču fotokatalitičku aktivnost s obzirom na UV i vidljivo zračenje nego P25 čestice. Fotokataličnost nanočestica određivana je mjerenjem brzine fotodegradacije raznih organskih otapala (Methylene Blue, Rhodamine B) pod UV ili vidljivim zračenjem u njihovoj prisutnosti. Mjerena je ovisnost fotokatalitičke aktivnosti nanočestica cinkovog oksida o njihovoj koncentraciji, početnoj koncentraciji i vrsti organskog bojila, a dobivene ovisnosti su teorijski objašnjene. Razvijena je metoda za sintezu dopiranih nanočestica pulsnom laserskom ablacijom u vodi, na način da se u njoj ablatira meta na koju je prethodno u pulsnoj laserskoj depoziciji naparen film materijala za dopiranje. Na taj način su dobivene nanočestice cinkovog oksida s različitim udjelima srebra i pojačanom fotokatalitičkom aktivnošću koja je najveća na izmjerenom optimalnom masenom udjelu srebra 0.32%.In this PhD thesis pulsed laser ablation in water is used for synthesis of titanium dioxide and zinc oxide nanoparticles with strong photocatalytic properties. For that purpose the nanosecond laser ND:Yag with basic wavelength at 1064 nm is used. Various experimental techniques (XRD, XPS, TEM/SEM, UV-Vis, Raman) are performed for the purpose of characterization of synthesized nanoparticles in order to determine their crystal structure, optical properties, shape and size distribution. The simple method for determination of laser synthesized nanoparticles concentration in water is developed, in which the ablation crater volume and nanoparticles size-distribution data are used. The method is tested for titanium dioxide nanoparticles and verified by using Beer-Lambert law. Titanium dioxide nanoparticles are synthesized by pulsed laser ablation of titanium target and it is shown that they crystallized after heating in water at 90°C and developed large photocatalytic activity in the presence of UV and visible light when compared with P25. Photocatalytic efficiency of nanoparticles was calculated by measuring the photodegradation rate of different dyes (Methylene Blue, Rhodamine B) under UV or visible light and in their presence. A dependence of zinc oxide nanoparticles photocatalytic efficiency on their concentration, initial dye concentration and dye type was measured, and obtained relations are theoretically explained. The method for laser synthesis of doped nanoparticles is developed, in which pulsed laser ablation in water is used for ablation of target that is previously coated by dopant material using pulsed laser deposition. In this way the zinc oxide nanoparticles with different silver ratios are synthesized, and they are shown to have improved photocatalytic efficiency, which is the largest at the measured optimal silver ratio 0.32 wt %

Concentration Quantification of TiO₂ Nanoparticles Synthesized by Laser Ablation of a Ti Target in Water

In this work, we present a quantitative method for determining the concentration of metal oxide nanoparticles (NP) synthesized by laser ablation in liquid. The case study was performed with titanium dioxide nanoparticles (TiO2 NP), which were synthesized by laser ablation of a Ti target in water. After synthesis, a colloidal solution was analyzed with UV-Vis spectroscopy. At the same time, the craters that remained on the Ti target after ablation were evaluated with an optical microscope to determine the volume of the ablated material. SEM microscopy was used to determine the TiO2 NP size distribution. It was found that synthesized TiO2 NP followed a Log-Normal diameter distribution with a maximum at about 64 nm. From the volume of ablated material and NP size distribution, under the assumption that most of the ablated material is consumed to form nanoparticles, a concentration of nanoparticles can be determined. The proposed method is verified by comparing the calculated concentrations to the values obtained from the Beer–Lambert law using the Mie scattering theory for the NP cross-section calculation

Synthesis of Silver, Gold, and Platinum Doped Zinc Oxide Nanoparticles by Pulsed Laser Ablation in Water

In this paper, we propose a simple two-step method for the synthesis of Ag, Au, and Pt-doped ZnO nanoparticles. The method is based on the fabrication of targets using the pulsed laser deposition (PLD) technique where thin layers of metals (Ag, Pt, Au) have been deposited on a metal-oxide bulk substrate (ZnO). Such formed structures were used as a target for the production of doped nanoparticles (ZnO: Ag, ZnO: Au, and ZnO: Pt) by laser ablation in water. The influence of Ag, Au, and Pt doping on the optical properties, structure and composition, sizing, and morphology was studied using UV-Visible (UV-Vis) and photoluminescence (PL) spectroscopies, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), respectively. The band-gap energy decreased to 3.06, 3.08, and 3.15 for silver, gold, and platinum-doped ZnO compared to the pure ZnO (3.2 eV). PL spectra showed a decrease in the recombination rate of the electrons and holes in the case of doped ZnO. SEM, TEM, and AFM images showed spherical-shaped nanoparticles with a relatively smooth surface. The XRD patterns confirm that Ag, Au, and Pt were well incorporated inside the ZnO lattice and maintained a hexagonal wurtzite structure. This work could provide a new way for synthesizing various doped materials