Browsing by Author "Evtodiev, Igor"

Now showing 1 - 20 of 49

ABSORBȚIA OPTICĂ ȘI FOTOLUMINESCENȚA COMPOZITULUI Ga2S3-Ga2O3
(Universitatea Tehnică din Moldova, 2018-05-24) Сaraman, Iuliana; Evtodiev, Igor; Untilă, Dumitru; Dmitroglo, Liliana; Caraman, Mihail; Evtodiev, Silvia; Palachi, Leonid
În această lucrare sunt studiate absorbția optică și fotoluminescența cristalelor de Ga2S3, obținute prin metoda CVT în atmosferă de I2, și a compozitului Ga2S3–Ga2O3, obținut prin tratament termic al monocristalelor de Ga2S3 în atmosferă normală, la temperatura 1073K. S-a determinat că în rezultatul tratamentului termic de lungă durată (12 ore) suprafața cristalelor de Ga2S3 se acoperă cu un strat granular de Ga2O3. Din măsurări ale reflexiei difuze, lățimea benzii interzise a stratului de Ga2O3 de pe suprafața monocristalului Ga2S3 a fost aproximată ca fiind egală cu 4,47 eV. La 300K, marginea benzii de absorbție a cristalelor de Ga2S3 este formată din trei sectoare în care au loc tranziții optice directe cu lățimea benzii interzise egală cu 3,020 eV, 3,178 eV și 3,312 eV, iar la 80K - cu 3,196 eV, 3,302 eV și 3,422 eV. Spectrul de FL a cristalelor de Ga2S3 conține doar o singură bandă în regiunea roșu a spectrului, ce se interpretează ca emisie radiativă a stratului de Ga2S3, iar spectrul de FL al compozitului Ga2S3–Ga2O3 pe lângă banda roșie conține și o bandă în regiunea violet–albastru a spectrului, ce se identifică ca emisie radiativă în cristalele de oxid din compozitul Ga2O3-Ga2S3.
ABSORPTION SPECTRA AND EXTRINSIC PHOTOCONDUCTIVITY OF Cu AND Cd DOPED GaSe SINGLE – CRYSTAL FILMS
(2006) Cuculescu, Elmira; Evtodiev, Igor; Caraman, Mihail; Rusu, George G.
GaSe single crystal films were doped during growth process with Cu or Cd atoms with concentration ranged between 0.05 and 0.50 at. %. Single crystal films (with thickness about 0.5 μm) were obtained by mechanical splitting of bulk single crystals. Impurity concentration was determined using atomic emission spectroscopy. Spectral dependences of absorption coefficient and photoconductivity were studied in the range 1.50 eV – 3.70 eV. It was experimentally established that the absorption spectra have an additional absorption band and its corresponding energy depends on the nature (Cu or Cd) and concentration of the doping atoms. Also, independently on the presence of the dopant, other two absorption bands in the IR region are present.
ANISOTROPY OF THE EXCITON PROCESSES IN GaSe CRYSTALS WITH LOW S AND TE CONCENTRATIONS
(American Scientific Publishers, 2009) Evtodiev, Igor
The anisotropy of the excitonical processes in the GaSe crystals and GaSe with small quantities of GaS(GaSe0.99S0.01) crystals has been studied through the optical specters (SO) and through the photoluminescence (PL) from the perpendicular surface on the symmetry axis C6 (E⊥C polarization) and from the flat surface parallel with the C6axis (E∥C and E⊥C polarization). The edge of the fundamental band of the GaSe crystals as well as of the GaSe0.99S0.01 and GaSe0.99Te0.01 crystals is formed at T = 78 K of the direct excitons' band. The width of the free excitons' band is determined by the processes of interaction between the excitons and optical and acoustic phonons. Phonons with energy of 17 meV and 27 meV participate to the formation of the edge towards small energies of the excitonic band in the GaSe crystals. The average energy of the phonons that participate to the formation of the excitonic absorbtion band in the GaSe crystals with small concentrations of S and Te equals 17 meV. Due to the mechanism of interaction of the excitons and phonons the integral absorption coefficient for the studied crystals (polarized E⊥C) is in small increase once with the temperature whilst the integral absorption coefficient in the maximum of the direct excitons' band. The n = 1 state is in diminution. For example, for the GaSe0.99Te0.01 crystals, α increases from 2700 at T = 78 K to 2025 cm−1 at 220 K. The edge towards small energies of the free excitons' band in the GaSe crystals and GaSe crystals with small quantities of S and Te is in a great concordance with Toyozowa's theory. The constant of interaction between the free excitons with phonons with an average energy of 135 cm−1 equals 0.9. Using the spectral characteristic of the reflection coefficient from the surface parallel to the C6 axis, there has been determined the refraction index placed in the center of the excitons n = 1 which equals 2.62 for GaSe and 2.58 and 2.55 respectively for the GaSe0.99S0.01 and GaSe0.99Te0.01 crystals. The shifting of the reflection specters towards big energies like ∼10 meV in a E⊥C polarization comparing to E∥C is determined by the difference of the oscillators' strength in these polarizations. The PL at T = 78 K specters from the surface parallel with the C6 axis (polarized E∥C) confirm the difference between the forces of the excitons' oscillators in the E∥C and E⊥C polarization. The intensity of PL bands, at the (001) surface as well as at the (100) surface depends on the excitation intensity by a function of a I = Ln force towards the emission bands of the direct and indirect free excitons the force factor is overlinear, and for the impurity nature bands it represents ∼0.5. The parameters that determine the width of the bands of excitonic PL is determined, considering the strong concentration of the structural faults at the (100) surface of the GaSe and GaSe0.99Te0.01 and GaSe0.99S0.01 GaSe crystals. Out of the spectral analysis I(L) the nature of the impurity bands has been determined, and from the PL specter structure there has been determined the energy of the accepting level which equals 93 meV from the maximum of the valence band of the GaSe crystals. Out of the analysis of the PL specter in a E∥C and E⊥C polarization (the (100) surface) it was stated that the process of emissional annihilation of the indirect excitons in the E∥C polarization takes place once with the emission of the phonons of a 38 meV energy whilst at the E⊥C polarization there are emitted phonons with an energy of 17 meV. GaSe with small concentrations of GaS and GaTe leads to the forming of a considerable concentration of localizing centers of the direct excitons and at the same time to the shifting towards small and big energies of the excitonic emission band (state n = 1) comparing to the GaSe crystals with a stoikiometric composition.
CRYSTALLINE STRUCTURE AND PHOTOLUMINESCENCE OF GaSe-CdSe NANOCOMPOSITE
(2015) Dmitroglo, Liliana; Evtodiev, Igor; Caraman, Iuliana; Kantser, Valeriu; Untila, Dumitru; Stamate, Marius; Gasin, Petru
A material consisting of CdSe and GaSe crystallites with average dimensions of 34 nm and 30 nm respectively was obtained by heat treatment at 753K and 853K of GaSe single crystal plates in Cd vapors during 24 hours. As a result of Cd atoms interaction with Se atoms CdSe layers are formed both onto outer surface and at interface of layered Se-Ga-Ga-Se packages. CdSe crystallites on the surface grow in the form of plates along C6 crystallographic axis. Photoluminescence spectra of the composite, at 78K and 300K, contain predominant bands from the luminescent emission of GaSe and CdSe components.
CRYSTALLINE STRUCTURE, SURFACE MORPHOLOGY AND OPTICAL PROPERTIES OF NANOLAMELLAR COMPOSITES OBTAINED BY INTERCALATION OF InSe WITH Cd
(2015) Untila, Dumitru; Caraman, Iuliana; Evtodiev, Igor; Canțer, Valeriu; Spalatu, Nicolae; Leontie, Liviu; Dmitroglo, Liliana; Luchian, Efimia
A material composed of InSe and CdSe crystallites was obtained by heat treatment at 753K of InSe single crystalline plates in Cd vapour for 3÷24 hours. The average diameters of CdSe and InSe crystallites determined from diffraction lines analysis are respectively equal to 20 nm and 22 nm. The photoluminescence spectra at 300K and 80K of composite decompose well into two Gaussian curves, one is in good correlation with the photoluminescence of CdSe crystals and the other is shifted to higher energies than the width of the band gap of CdSe crystals.
DISPOZITIVE FOTOELECTRONICE PE BAZĂ DE GaSe STRATIFICAT
(CEP USM, 2009) Evtodiev, Igor
In this work photosensors based on CaSe specially undoped and doped with Cu (0.05% at. – 0.50%at.) are characterized at normal temperature using the electric photoconductivity spectrums. Photoresistors based on monocrystallineGaSe fi lms are photosensible in the energy interval from 1.8eV to 5.2eV. Polarization sensibility of the GaSe, GaSe:Cu(0.5%at) photoresistors was specially investigated at every circularly polarized wave length. Are raised the curves ofrelaxation of the photocurrent through the GaSe and GaSe with 0.1%at of Cu samples with light impulses with a duration of ~1.2·10-6 s. In the absence of X radiation characteristics I-U for roentgen resistors of GaSe are virtually linear.At the growth of the X radiation dose (radiation: Cukα : λ =1.514 Å, I=1.6 mA, U=45kV ) in the GaSe,characteristics I-U are sublinear which indicates the growth of the concentration of the defects in GaSe crystals togetherwith the growth of the radiation dose. In this work is demonstrated the possibility of elaboration of the roentgen resistorsand spectral and polarization based on layered GaSe photoresistors.
ELLIPSOMETRIC STUDIES OF NANOMETRIC CdS AND CdTe FILMS
(2005) Caraman, Mihail; Evtodiev, Igor; Cuculescu, Elmira; Rusu, Marin; Salaoru, Iurie
The thickness of the layers CdS and CdTe grown on the Si, Ge, GaAs was determined from the analysis of the polarization ellipse of the reflected light from the surfaces of structures thin layers substrate. The thermal treatment of the samples CdS-CdTe in the presence of CdCl2 leads to the increasing of the crystalline phase from layers.
EMISSION SPECTRA FOR ANALYSING ELEMENTS IN CLUES USING OPTICAL METHOD
(Universitatea de Stat „Alecu Russo“ din Bălţi, 2014) Evtodiev, S.; Koss, A.; Evtodiev, Igor
The following research was dedicated to the investigation of emission spectra of different elements and their use in the analysis of clues. The used equipment was a spectrometer, the "Red Tide USB-650", and an application called "Overture". The spectrometer has a spectral range from 350 nm to 1000 nm. It’s a very lightweight and portable device,not taking up much space and weighting only 190 g. The sensitivity of the device is 75 photons at a wavelength of 400 nm. The optical resolution of the spectrometer is 2 nm, while the program can display accurate graphs with a resolution of up to 0.1 nm. The spectrometer’s integration time ranges from 3 ms to up to 65 seconds, but typically it d oesn’t exceed 15 seconds. For very precise data recording the spectrometer can also use the optic fibres. The used program has a library of emission spectra of different elements. The experiment is performed by making the substance to emit photons by exciting it. The light from this substance is received by the spectroscope and the data are transmitted to the computer. The program generates an "Intensity-Wavelength" graph right away. But to analyse and to detect elements in clues a graph is not the only required thing. Luckily, we have access to the emission spectra library built into the program. Those can be enabled and disabled to detect if the given element is present in the earlier analysed substance.Such a method can be used to detect elements in clues using spectral analisys at remarkable speeds and accuracies.
EXCITONIC ABSORPTION OF THE LIGHT IN HETEROJUNCTIONS Bi 2 O 3 -InSe
(2009) Evtodiev, Igor
The interface layer of the Bi2O3/InSe:Cd (0.10 at. %) heterojunction was investigated using optical and electroreflection spectra. The fundamental absorption edge of InSe:Cd interface layer, at 78 K, is formed by the excitonic absorption band n=1, with maximum at 1.328eV. Its direct optical band gap corresponds to electron transitions at the M point of the Brillouin zone, and is equal to 2.557 eV at 78 K.
EXCITONIC AND RADIATIVE EFFECTS IN GaSe-C 60 STRUCTURES
(2007) Evtodiev, Igor; Lozovanu, Petru; Cuculescu, E.; Caraman, Mihail
The absorption and photoluminescence spectra of GaSe intercalated in C60 fullerene has been investigated at 293 K and 78 K. C60 and C60-toluene molecules intercalated in-between GaSe stratified “packing” cause the appearance of localized levels revealed in low energy wing of n=1 excitonic of the absorption and determine the exciton-phonon interaction. It has been established that C60 and C60 -toluene molecules form new recombination levels in GaSe crystals and determine the 1.7÷1.75 eV photoluminescence band.
THE EXPERIMENTAL STUDY OF REAL AND IDEAL HARMONIC OSCILLATORS
(Universitatea de Stat „Alecu Russo“ din Bălţ, 2014) Koss, A.; Evtodiev, S.; Evtodiev, Igor
The following research was dedicated to studying and experimenting with harmonic oscillators of all kinds. The used equipment was a portable computer, the “PASCO Spark”, a force sensor, 3 different springs and weights. The portable computer is responsible for storing the data received from the force sensor, and constructing a “Force-Time” graph. The force sensor has a range of ±50 N, an accuracy of 0.1 N and a recording speed of up to 1000 Hz. It is also equipped with a reset button to automatically set it to 0 N. The springs used in the experiment differed in damping. The first spring had a very low damping coefficient, so after the weight was released they continued oscillating for a very long time, fading away only very slightly. The second spring had a medium damping coefficient, so the time it took for the oscillations to fade was much shorter, then with the first spring. The third spring however had a very high damping coefficient, so the oscillations only continued for about 6 seconds. The experiment itself was performed by hanging a weight on the spring, and starting the data recording as soon as the weight is dropped. In all 3 experiments the data was recorded at a frequency of 100 Hz. Afterwards, the computer built “Force-Time” graphs for every experiment. This allowed us to visualize the difference between the 3 springs. The computer used in the experiment has a very useful ability of generating functions for graphs. This can be done in order to study ideal harmonic oscillations. The function generated from the graph continues forever, and can be used for further research in the field of beats, which are automatically calculated and simulated by the computer. Thanks to the precise data recording equipment human errors can be minimized, which leads to very little inaccuracies in calculations.
FOTOLUMINESCENŢA STRATURILOR NANOLAMELARE DE GaSe OBŢINUTE PRIN INTERCALAREA CU Cd
(2012) Dmitroglo, Liliana; Evtodiev, Igor; Caraman, Iuliana; Nedeff, Valentin; Dafinei, Adrian
S-au analizat spectrele de emisie fotoluminescentă a lamelor monocristaline p-GaSe cu concentraţia golurilor3•1014 cm-3 şi a lamelor intercalate cu Cd în fază de vapori la temperatura 500 °C. Durata tratamentului termic a fost de 20 şi 24 ore. Spectrul de emisie al cristalelor de GaSe conţine liniile excitonilor direcţi localizaţi cu energia de legătură ~6 meV, prima repetare fononică a acestora (ħωf =20 meV) şi banda de emisie a excitonilor indirecţi cu emisia fononilor cu energia 15 meV. Spectrul de emisie a compozitelor obţinute prin intercalarea lamelor de GaSe cu Cd se obţine în rezultatul suprapunerii benzilor de emisie a compusului CdSe şi banda impuritară a monoseleniurii de galiu. Structura spectrului FL depinde de durata tratamentului termic. La majorarea timpului de tratament se amplifică subbanda corespunzătoare compusului CdSe.
GROWTH AND CHARACTERIZATION OF Eu DOPED GaSe SINGLE CRYSTALS BY X-RAY DIFFRACTION AND RAMAN SPECTROSCOPY
(CEP USM, 2017) Untila, Dumitru; Evtodiev, Igor; Caraman, Iuliana; Kantser, Valeriu; Spalatu, Nicolae; Dmitroglo, Liliana; Evtodiev, Silvia; Spoială, Dorin; Rotaru, Irina; Gașin, Petru
GaSe single crystals doped with Eu (0.025, 0.05, 0.5, 1.0 and 3.0 at%) were grown by Bridgman method using Ga, Se and Eu elementary components. The crystalline structure and vibration modes of the GaSe: Eu crystals lattice were studied by X-ray diffraction and Raman spectroscopy. Eu atoms arranged in the van der Waals space of GaSe: Eu crystals form Eu-Se valence bonds and restructure hexagonal lattice of GaSe leading to EuGa2Se4 crystallites formation. Defects generated by EuGa2Se4 crystallites lead to broadening and shifting of single phonon peaks present in Raman spectra towards shorter wavenumbers, and at the same time, activate the longitudinal optical vibrations of EuSe sublattice.
INVESTIGATION OF ENERGETIC STATES, DETERMINED BY Cu AND Cd IMPURITY ATOMS, AT SURFACE OF GaS AND GaSe MONOCRYSTALLINE LAYERS
(2007) Evtodiev, Igor; Cuculescu, E.; Postolachi, Vitalie; Caraman, Mihail
The reflection, absorption, photoconductivity, and thermally stimulated luminescence (TSL) spectra of GaS:Cu and GaSe:Cu, Cd single crystals have been studied. As a result of these investigations, the energy diagram of GaS and GaSe crystals after doping was determined.
LABORATOR DE ŞTIINŢE INTEGRATE DIDACT VEGA PENTRU ÎNVĂŢĂMÂNTUL PREUNIVERSITAR
(Tipografia "CentroGrafic" ,Cahul, 2015) Evtodiev, Silvia; Luchian, Efimia; Evtodiev, Igor; Untilă, Dumitru; Caraman, Mihail
Experimental investigations are a set of analysis techniques and methods, very important for today's society and in particularly for undergraduate and graduate education. To achieve the objectives and purpose in the most efficient way, in this paper were chosen solutions offered by the PASCO company (Didact Vega), whose equipments offers a wide range of procedures for conducting investigations. SPARKscience includes reading, data analysis and real time processing software, SPARKvue and capstone. Data acquisition system includes over a thousand PASPORT sensors for physics, chemistry, biology and environmental engineering. The SPARK mobile system can be used for experimental investigations both in laboratory and in the field. Integrated Science Laboratory contains a broad and well-structured base of labs (SPARKlab) offers to pupil/student/teacher the posibility to increase the level, volume and quality of experimental investigations in the field of Integrated Sciences .
METODE EXPERIMENTALE DE STUDIERE A STĂRILOR DE SUPRAFAȚĂ ÎN COMPUŞII STRATIFICAȚI DE TIP AIII BVI
(Tipografia Universității de Stat „Alecu Russo” din Bălți, 2005-10-05) Blaj, Octavian; Scurtu, Roman; Evtodiev, Igor
MORFOLOGIA SUPRAFEŢEI ŞI PROPRIETĂŢILE OPTICE ŞI FOTOELECTRICE ALE HETEROJONCŢIUNILOR CDTE-GATE
(CEP USM, 2014) Spalatu, Nicolae; Evtodiev, Igor; Caraman, Iuliana; Leontie, Liviu; Rotaru, Irina; Until, Dumitru; Caraman, Mihail
NANOLAMELLAR STRUCTURES OF OXIDE-AIIIBVI:Cd SEMICONDUCTORS TYPE FOR USE AS DETECTORS OF RADIATION IN THE UV SPECTRAL REGION
(Technical University of Moldova, 2011-07-07) Dmitroglo, Liliana; Untila, Dumitru; Chetruș, Petru; Evtodiev, Igor; Caraman, Iuliana; Lazăr, Gabriel; Nedeff, Valentin
In the paper, optical and photoelectrical properties of GaSe and InSe single crystal films of 10-5÷10-7 m submicron thickness and of semiconductor-native oxide structures obtained by annealing at (450÷700)°C in a normal atmosphere, are studied. The absorption spectrum of InSe lamella as well as of GaSe lamella in the energetic range from the red threshold up to 4,5 eV contains three bands with a rapid increase of the absorption coefficient which varies in the limits of (100÷106) cm-1 At the energies higher than 1,25 eV and 2,01 eV for InSe and GaSe respectively the light absorption are determined by the direct optical transitions in the centre of the Brillouin zone and at the energies higher than. At the absorption coefficients of (100÷102)cm-1 the indirect optic transitions are present. 3,0 eV also by the direct optical transitions in the points of the bands high symmetry. The resistive photosensitivity bands cover the spectral range Eg≤ hν ≤ 4,5 eV for lamellar photoresistors in which electric field EC6. The resistive photosensitivity band width could be controlled by the lamella thickness for d ≥1μm. The open circuit voltage spectral distribution is analysed from which results that at the oxidation temperature of 700°C in GaSe layer at the heterojunction interface the defects are formed on which the charge carriers, collected in the junction, are dissipated. The noneequilibrium charge carrier free path is of 0,8 μm.
OPTICAL AND PHOTOELECTRIC PROPERTIES OF NANOLAMELLAR STRUCTURES OBTAINED BY THERMAL ANNEALING OF InSe PLATES IN Zn VAPOURS
(John Wiley & Sons, 2018) Untila, Dumitru; Evtodiev, Igor; Caraman, Iuliana; Spalatu, Nicolae; Dmitroglo, Liliana; Caraman, Mihail
The structural, optical and photoelectric properties of InSe crystals grown by Bridgman–Stockbarger method and ZnSe/InSe structures obtained on InSe by thermal annealing in Zn vapours are studied in this paper. The study of structural properties confirms that ZnSe compound is formed. The analysis of photoelectric properties reveal that both the ZnSe‐InSe composite layer and the composite/InSe heterojunction are photosensitive in the VIS‐NIR spectral region. [ABSTRACT FROM AUTHOR]
OPTICAL AND PHOTOELECTRIC PROPERTIES OF NANOLAMELLAR STRUCTURES OBTAINED BY THERMAL ANNEALING OF INSE PLATES IN Zn VAPOURS
(2018) Untila, Dumitru; Evtodiev, Igor; Caraman, Iuliana; Spalatu, Nicolae; Dmitroglo, Liliana; Caraman, Mihail
The structural, optical and photoelectric properties of InSe crystals grown by Bridgman–Stockbarger method and ZnSe/InSe structures obtained on InSe by thermal annealing in Zn vapours are studied in this paper. The study of structural properties confirms that ZnSe compound is formed. The analysis of photoelectric properties reveal that both the ZnSe‐InSe composite layer and the composite/InSe heterojunction are photosensitive in the VIS‐NIR spectral region.