Ortak Dersler Bölümü

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Citation - WoS: 4
Citation - Scopus: 5
Calculation of the Raman Frequency, Damping Constant (Linewidth) and the Relaxation Time Near the Tetragonal-Cubic Transition in Pbtio3
(Elsevier Gmbh, 2017) Yurtseven, H.; Kiraci, A.; 42475; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
Frequencies, damping constants and the relaxation times of some Raman modes including the two soft modes are calculated as a function of pressure near the tetragonal-cubic transition in PbTiO3. Calculation of the Raman frequencies is performed using the observed volume data from the literature by means of the mode Gruneisen parameter at various pressures. Pressure dependence of the damping constant and the relaxation time is predicted using the pseudospin-phonon coupled model and the energy fluctuation model by considering that the Raman frequency can be taken as the order parameter (spontaneous polarization) for the tetragonal-cubic transition in PbTiO3. Expressions from both models for the damping constants are fitted to the observed Raman linewidths of the two soft modes and for the other Raman modes the damping constant and the relaxation time are predicted close to the transition. We find that damping constants diverge and the inverse relaxation time decreases for the soft modes with increasing pressure near the critical pressure (P-c similar to 11 GPa). The other Raman modes exhibit unusual critical behavior. Our results indicate that the observed behavior of the Raman frequencies can be predicted from the volume data through the mode Gruneisen parameter for the tetragonal-cubic transition in PbTiO3. The damping constant and the relaxation time for the Raman modes can also be predicted adequately using the pseudospin-phonon coupled model and the energy fluctuation model to explain the mechanism of the phase transition between the tetragonal and cubic phases in PbTiO3. (C) 2017 Elsevier GmbH. All rights reserved.
Citation - WoS: 9
Citation - Scopus: 14
Collaborations, Concepts, and Citations in Educational Technology: a Trend Study Via Bibliographic Mapping
(Springer, 2022) Soylu, Meryem Yilmaz; Akkoyunlu, Buket; Deryakulu, Deniz; Bardakci, Salih; 8539; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
Research trends studies have emerged in education technologies (ET) to determine research manner and changes. Although the precedent examples dated back to the 1950s, trend studies within ET have gradually been increasing since the 1970s. This study aimed to examine the ET publications and research trends in a 5-year time period from 2014 to 2018. With a bibliographic mapping tool, namely VOSviewer, three research questions were addressed relating to collaborations, concepts, and citations in educational technology studies. The data set was extracted from ISI Web of Science databases and included 1690 articles published in six educational technology journals between 2014 and 2018. We used co-authorship analysis to determine the collaborating researchers' institutions and their geographical locations (countries) when they published the articles. A co-occurrence analysis was used to investigate concepts. Finally, a co-citation analysis was employed to determine the most cited papers and journals. Co-authorship analyses revealed that the number of articles published by researchers affiliated with institutions in the USA was the highest in the data set. According to co-occurrence analysis, online learning, especially in open learning environments, was the most studied concept. Moreover, co-citation analysis showed that the most frequently cited articles were published in Computers & Education. Additional findings, discussion, and limitations of the study were explained in the full text.
Citation - WoS: 8
Citation - Scopus: 8
Damping Constant (Linewidth) and the Relaxation Time of the Brillouin La Mode for the Ferroelectric-Paraelectric Transition in Pbzr1-Xtixo3
(Ieee-inst Electrical Electronics Engineers inc, 2016) Kiraci, Ali; Yurtseven, Hamit; 42475; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
The damping constant (linewidth) of the longitudinal acoustic (LA) mode is calculated as a function of temperature using the observed Brillouin frequencies of this mode from the literature for the ferroelectric-paraelectric transition (T-C = 657 K) in PbZr1-xTixO3 (x = 0.45). For this calculation of the damping constant, the pseudospin-phonon coupled model and the energy fluctuation model are used by fitting to the observed data for the Brillouin frequencies of the LA mode in the ferroelectric (T < T-C) and paraelectric (T > T-C) phases of this compound (x = 0.45). Values of the activation energy are deduced for both ferroelectric and paraelectric phases. The relaxation time is also obtained by means of fitting to the observed data from the literature for the inverse relaxation time at various temperatures in the paraelectric phase of PbZr1-xTixO3. The temperature dependences of the damping constant and of the relaxation time with the values of the activation energy that we have calculated indicate that the pseudospin-phonon coupled model and the energy fluctuation model are capable of describing the ferroelectric-paraelectric transition (T-C = 657 K) in PbZr1-xTixO3 (x = 0.45) adequately.
Citation - WoS: 7
Citation - Scopus: 8
Damping Constant and the Relaxation Time Calculated for the Lowest-Frequency Soft Mode in the Ferroelectric Phase of Cd2nb2o7
(Elsevier Gmbh, Urban & Fischer verlag, 2016) Yurtseven, H.; Kiraci, A.; 42475; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
The temperature dependence of the phonon frequency omega(ph) and of the damping constant Gamma(sp) due to pseudospin-phonon coupling of the lowest-frequency soft mode is calculated in the ferroelectric phase near the transition temperature (T-C =196 K) in Cd2Nb2O7. Raman frequency of the soft mode is used as an order parameter which is calculated from the molecular field theory. On that basis, the damping constant is calculated by fitting the expressions from the pseudospin-phonon coupled model and the energy fluctuation model to the observed linewidth from the literature below T-C in Cd2Nb2O7. From our analysis, we find that the molecular field theory is adequate for the soft mode behaviour and that both models are also satisfactory for the divergence behaviour of the damping constant as T-C is approached from the ferroelectric phase in Cd2Nb2O7. Values of the activation energy U are extracted from the temperature dependence of the damping constant (HWHM) of the soft mode in the ferroelectric phase of this crystal. Also, the inverse relaxation time is predicted using the Raman frequency and damping constant close to the T-C in the ferroelectric phase of Cd2Nb2O7, which increases considerably as T-C is approached from the ferroelectric phase, as observed experimentally. (C) 2016 Elsevier GmbH. All rights reserved.
Citation - WoS: 2
Citation - Scopus: 3
Development of a Selective Wet-Chemical Etchant for Precise 3d Sculpting of Silicon Enabled by Infrared Non-Linear Laser Modification
(Elsevier Sci Ltd, 2024) Borra, Mona Zolfaghari; Radfar, Behrad; Nasser, Hisham; Colakoglu, Tahir; Tokel, Onur; Turnali, Ahmet; Bek, Alpan; 169107; 01. Çankaya Üniversitesi
Recently-demonstrated high-quality three-dimensional (3D) subsurface laser processing inside crystalline silicon (c-Si) wafers opens a door to a wide range of novel applications in multidisciplinary research areas. Using this technique, novel maskless micro-pillars with precise control on the surface reflection and coverage are successfully fabricated by etching the laser-processed region of the c-Si wafer. To achieve this, a particular selective wet chemical etching is developed to follow subsurface laser processing of c-Si to reveal the desired 3D structures with smooth surfaces. Here, we report the development of a novel chromium-free chemical etching recipe based on copper nitrate, which yields substantially smooth surfaces at a high etch rate and selectivity on the both laserprocessed Si surface and subsurface, i.e., without significant etching of the unmodified Si. Our results show that the etch rate and surface morphology are interrelated and strongly influenced by the composition of the adopted etching solution. After an extensive compositional study performed at room temperature, we identify an etchant with a selectivity of over 1600 times for laser-modified Si with respect to unmodified Si. We also support our findings using density functional theory calculations of HF and Cu adsorption energies, indicating significant diversity on the c-Si and laser-modified surfaces.
Citation - WoS: 34
Citation - Scopus: 46
Effectiveness of Gamification in Flipped Learning
(Sage Publications inc, 2020) Akkoyunlu, Buket; Gunduz, Abdullah Yasin; 8539; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
The success of the flipped learning approach is directly related to the preparation process through the online learning environment. It is clear that the desired level of academic achievement cannot be reached if the students come to class without completing their assignments. In this study, we investigated the effect of the use of gamification in the online environment of flipped learning to determine whether it will increase interaction data, participation, and achievement. We used a mixed-methods sequential explanatory design, which implies collecting and analyzing quantitative and then qualitative data. In the online learning environment of the experimental group, we used the gamification. However, participants in the control group could not access the game components. According to the findings, the experimental group had higher scores in terms of interaction data, participation, and achievement compared with the control group. Students with low participation can be encouraged to do online activities with gamification techniques.
Citation - WoS: 4
Citation - Scopus: 4
Growth and Characterization of Nabi(Mo0.5w0.5o4)2 Single Crystal: a Promising Material for Optoelectronic Applications
(Elsevier Sci Ltd, 2023) Isik, M.; Guler, I.; Gasanly, N. M.; 101531; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
The structural and optical characteristics of NaBi(Mo0.5W0.5O4)2 single crystals grown by Czochralski method were investigated. X-ray diffraction (XRD) pattern exhibited four well-defined peaks related to tetragonal crystalline structure with a space group I41/a. Raman and infrared transmittance spectra were recorded to investigate vibrational properties of the compound. Room temperature transmission spectrum was measured to reveal band gap energy of the crystal. The derivative spectral and absorption coefficient analyses resulted in direct band gap energy of 3.19 and 3.18 eV, respectively. Urbach energy of the crystal was also determined as 0.17 eV from photon energy dependency of absorption coefficient. The structural and optical parameters ob-tained for NaBi(Mo0.5W0.5O4)2 were compared with the parameters of the NaBi(XO4)2 (X: Mo,W) compounds to understand the effect of the composition on the studied properties. The reported characteristics of NaBi (Mo0.5W0.5O4)2 point out that the compound has significant potential to be used in optoelectronic devices.
Citation - WoS: 12
Citation - Scopus: 13
Implementing Bring Your Own Device (Byod) Model in Flipped Learning: Advantages and Challenges
(Springer, 2020) Gunduz, Abdullah Yasin; Akkoyunlu, Buket; Kibar, Pinar Nuhoglu; 8539; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
Flipped learning is a type of blended learning that reverses traditional conceptions about pre-class and in-class activities. This pedagogical approach offers students the opportunity to exert more control over their learning. However, teachers should monitor whether in-class activities deepen pre-learning. In this paper, we present students' experiences regarding the advantages, challenges and future preferences of using BYOD in flipped learning. According to students, being allowed to use their own devices in classroom activities provided them a more comfortable learning environment. The model increased their productivity because they were familiar with their personal devices. Students reported that the BYOD model made storing and retrieving files easier, which enabled them to continue studying without remembering settings. However, students identified challenges, such as being required to carry heavy devices and dealing with poor classroom infrastructure. A few students decided they would rather not bring their own devices again due to weight, but the others indicated that they would prefer to participate in BYOD-embedded flipped learning in the future.
Citation - WoS: 3
The Important Role of N(2) Ion in the Phase-Transition Mechanism of [N(ch3)4]2znbr4
(Ieee-inst Electrical Electronics Engineers inc, 2020) Kiraci, Ali; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
The chemical shift of the N(2)(CH3)(4) ion, which has been found to exhibit the similar anomalous behavior of the monoclinic angle $\Delta \beta $ , was related to the order parameter to evaluate the temperature dependence of the linewidth (damping constant) for N-14 nuclear magnetic resonance spectrum of this crystal in terms of the dynamic Ising models, namely the pseudospin-phonon-coupled (PS) and the energy fluctuation (EF) models. The results from both PS and EF models were successful to explain the abnormal behavior of the linewidth in the vicinity of the phase-transition temperature of ${T}_{C}= {287.6}$ K, when compared with the observed linewidth of the transverse acoustic soft mode in this crystal. As an extension of this work, the N-14 relaxation time and the values of the activation free energy were calculated as a function of temperature. The results indicate that the ferroelastic-paraelastic phase transition in this compound is of the order-disorder type.
Citation - WoS: 1
Citation - Scopus: 4
Integrating Scientific Communication Into Middle School Lessons: a Curriculum Design Research
(Springer, 2020) Akkoyunlu, Buket; Cetin, Nihal Menzi; 8539; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
In this study, a Scientific Communication Curriculum (SCC) was designed for middle school students and teachers to equip them with scientific communication (SC) skills, and the skills included in the SCC were integrated into the middle school lessons. Within the framework of the Curriculum Design Research (CDR), designing the Scientific Communication Curriculum (SCC) and integrating into the lessons were conducted by two cycles and each cycle consisted of four stages; analysis, design, implementation, and evaluation. In the first cycle, SCC was developed and implemented for the evaluating the effectiveness of the SCC in terms of teaching scientific communication skills to the students with the help of Information Technology (IT) course teacher. In the second cycle, the scientific communication skills were integrated into the lessons in collaboration with the teachers and the School Librarian (SL). As a part of the design process, the Teacher Training Program (TTP) was organized to equip all middle school teachers with scientific communication skills and to help them how to teach and how to integrate the SC skills. Furthermore the TTP served as a professional development component of the CDR framework. Based on the quasi-experimental study results and also opinions of the students and the IT teacher towards the first implementation stage, it was concluded that the SCC was effective in equipping students with scientific communication skills. Regarding the findings from the second cycle, the integration process was satisfying for the teachers and the SL. Teachers found the TTP helpful for their professional development. According to views of the teachers and the SL on the integration process was a positive and useful step for them. The results of this study were addressed and discussed under the headings of design principles, curriculum components, and professional development that are components of the CDR model.
Citation - WoS: 3
Citation - Scopus: 3
Optical and Photoelectrical Properties of Tlinsse Layered Single Crystals
(Elsevier Gmbh, 2018) Gasanly, N.; Guler, I.; 101531; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
Optical and electrical properties of TlInSSe layered single crystals have been studied by means of transmission, reflection and photoconductivity measurements. Transmission and reflection experiments have been carried out from 540 to 1000 nm at room temperature. Derivative analysis was applied to both transmission and reflection spectra and indirect band gap energy was found as 2.06 eV. Photoconductivity measurements have been performed in the temperature range from 245 to 300 K and in the voltage range from 10 to 80 V. From the temperature-dependent photoconductivity measurements, the observed single peak shifted to higher wavelengths with increase of temperature. The increase of photoconductivity with temperature is due to the increase in the mobility of photocarriers that can be explained by Bube model. From X112 method, room temperature indirect band gap of the crystal was also found as 2.06 eV. From voltage-dependent photoconductivity measurements, the peak maximum increased linearly with increase of voltage because of increase of the mobility of charge carriers. Dark current-voltage characteristic of TlInSSe crystal showed the ohmic behavior that means space charge limited current did not exist in the crystal. From the photocurrent with different illumination intensity analysis, the supralinear photoconductivity associated with the two center model was found. (C) 2017 Elsevier GmbH. All rights reserved.
Citation - WoS: 37
Citation - Scopus: 40
Peptide Nanoparticles (Pnps) Modified Disposable Platform for Sensitive Electrochemical Cytosensing of Dld-1 Cancer Cells
(Elsevier Advanced Technology, 2018) Akbal, Oznur; Bolat, Gulcin; Bozdogan, Betul; Denkbas, Emir Baki; Abaci, Serdar; Yaman, Yesim Tugce; 11534; 01. Çankaya Üniversitesi; 09. Rektörlük; 09.01. Ortak Dersler Bölümü
A novel diphenylalaninamid (FFA) based peptide nanoparticles (PNPs) modified pencil graphite electrodes (PGEs) for construction of electrochemical cytosensor was demonstrated for the first time in this study. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images revealed the spherical nanostructure of the synthesized FFA based PNPs while attenuated total reflectance-fourier transform infrared (ATR-FTIR) spectra provided information about the structure and conformation of proteins in their structure. Self assembly of PNPs on PGE surface and adhesion of DLD-1 cancer cells on this surface was also characterized by electrochemical measurements. PNP/PGE5 acted as a sensitive platform for simple and rapid quantification of low concentration of DLD-1 cancer cells in early diagnosis using the electrochemical impedance method (EIS). The offered cytosensor demonstrated outstanding performance for the detection of DLD-1 cells by the EIS method. The impedance of electronic transduction was associated with the amount of the immobilized cells ranging from 2 x 10(2) to 2.0 x 10(5) cells mL(-1) with a limit of detection of 100 cells mL(-1). The efficient performance of the cytosensor was attributed to the well-defined nanostructure and biocompability of PNPs on the substrate.
Citation - WoS: 3
Citation - Scopus: 3
A Phenomenological Study on Ferroelastic Kh3(Seo3)2 and Kd3(Seo3)2
(Pergamon-elsevier Science Ltd, 2021) Kiraci, A.; 42475; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
The anomalous behavior of the Brillouin frequency shift omega of the soft acoustic mode for KH3(SeO3)(2) and KD3(SeO3)(2), and also the volume thermal expansion proportional to(V) and the specific heat C of KH3(SeO3)(2) have been analyzed for various temperature intervals close to the phase transition temperatures TC at around 211 K and 302 K, respectively. Our extracted values of the critical exponent from C and proportional to(V) of KH3(SeO3)(2) within the temperature intervals of vertical bar T -T-C vertical bar < 7 K are nearly zero, while the critical exponent extracted from the Brillouin frequency shift data of both KH3(SeO3)(2) and KD3(SeO3)(2) within the same temperature interval of vertical bar T -T-C vertical bar < 7 K decrease very rapidly toward to zero as the phase transition temperatures are approached. Our results indicate that the critical behavior of omega, proportional to(V) and C of both KH3(SeO3)(2) and KD3(SeO3)(2) can be described with the same critical exponent within the temperature interval of vertical bar T -T-C vertical bar < 2 K.
Citation - WoS: 6
Citation - Scopus: 5
Pressure-Dependent Raman Modes Near the Cubic-Tetragonal Transition in Strontium Titanate
(Wiley, 2018) Yurtseven, Hamit; Kiraci, Ali; 42475; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
The pressure dependence of the Raman frequency shifts of various Raman modes is calculated at room temperature using the volume data from the literature for the cubic-tetragonal transition in SrTiO3. The isothermal mode Gruneisen parameters of those Raman modes are obtained, which decrease with increasing pressure for this molecular crystal. Calculated Raman frequencies are then used to predict the damping constant and the inverse relaxation time of those Raman modes as a function of pressure by means of the pseudospin-phonon (PS) coupled model and the energy fluctuation (EF) model to describe the cubic-tetragonal transition in SrTiO3. Also, the values of the activation energy are extracted for the Raman modes studied using both models (PS and EF). Our predicted damping constant and the inverse relaxation time for the Raman modes, can be compared with the experimental measurements close to the cubic-tetragonal transition in SrTiO3.
Citation - WoS: 1
Citation - Scopus: 2
Sample Design and Allocation for Random Digit Dialling
(Springer, 2005) Ayhan, HO; Islam, MQ; 01. Çankaya Üniversitesi
Sample design and sample allocation methods are developed for random digit dialling in household telephone surveys. The proposed method is based on a two-way stratification of telephone numbers. A weighted probability proportional to size sample allocation technique is used, with auxiliary variables about the telephone coverage rates, within local telephone exchanges of each substrata. This makes the sampling design nearly "self-weighting" in residential numbers when the prior information is well assigned. A computer program generates random numbers for the local areas within the existing phone capacities. A simulation study has shown greater sample allocation gain by the weighted probabilities proportional to size measures over other sample allocation methods. The amount of dialling required to obtain the sample is less than for proportional allocation. A decrease is also observed on the gain in sample allocation for some methods through the increasing sample sizes.
Citation - WoS: 20
Citation - Scopus: 33
Student Views on the Use of Flipped Learning in Higher Education: a Pilot Study
(Springer, 2019) Akkoyunlu, Buket; Gunduz, Abdullah Yasin; 8539; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
Flipped learning becomes increasingly popular in higher education with the widespread use of the Internet. The traditional methods are deeply teacher-centered and students usually listen to the teacher during the course. This is different in flipped learning and the time spent in the classroom involves rich learning activities. It allowed learners to take a more active role in the class than the traditional methods. However, flipped learning also has many challenges for students. The purpose of this study is to determine the benefits and challenges of flipped learning in higher education. Participants' views of flipped learning were collected through a questionnaire with open-ended questions. The results indicated that implementing flipped learning gave students a chance to experience greater instructional flexibility during both online and in-class sessions. The students said that they felt more responsible for their own learning. And some of them expressed disappointment with the lack of immediate feedback while watching videos and with their poor Internet accessibility outside of the classroom.
Citation - WoS: 10
Citation - Scopus: 11
Temperature Dependence of the Damping Constant and the Relaxation Time Close To the Tetragonal-Cubic Phase Transition in Srzro3
(Elsevier Science Bv, 2017) Kiraci, A.; Yurtseven, H.; 42475; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
The damping constant Gamma(sp) due to the pseudospin-phonon coupling is calculated as a function of temperature using the pseudospin-phonon coupled model and the energy fluctuation model close to the tetragonal-cubic transition (T-C = 1443 K) in SrZrO3. Using the observed Raman frequencies and the linewidth (FWHM) of the soft modes (E-g and A(1g)) from the literature, predictions of both models studied, are examined for the tetragonal-cubic transition in this crystalline system. Values of the activation energy U are extracted and also the inverse relaxation time is predicted as a function of temperature close to the phase transition studied in SrZrO3. Divergence behaviour of the damping constant (FWHM) of the soft modes is predicted from both models as also observed experimentally when T-C is approached from the tetragonal to the cubic phase in SrZrO3. The relaxation time also diverges close to the T-C in this crystal. It is indicated that the tetragonal cubic transition is of a second order as predicted from both models studied here, as also observed experimentally in SrZrO3. (C) 2016 Elsevier B.V. All rights reserved.
Citation - WoS: 5
Citation - Scopus: 5
Temperature Dependence of the Polarization, Dielectric Constant, Damping Constant and the Relaxation Time Close To the Ferroelectric-Paraelectric Phase Transition in Linbo3
(Elsevier Gmbh, Urban & Fischer verlag, 2017) Yurtseven, H.; Kiraci, A.; 42475; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
We calculate the order parameter (spontaneous polarization) and the inverse dielectric susceptibility at various temperatures in the ferroelectric phase of LiNbO3 for its ferroelectric-paraelectric phase transition (T-C =1260 K) using the Landau phenomenological model. For this calculation, the Raman frequencies of the soft optic mode (TO1) are used as the order parameter and the fitting procedure is employed for both the order parameter and the inverse dielectric susceptibility by means of the observed data from the literature. The temperature dependences of the damping constant and the inverse relaxation time are also computed using the pseudospin-phonon coupled model and the energy fluctuation model for the ferroelectric phase of LiNbO3. The activation energy is deduced from the damping constant for both models studied and compared with the k(B)T(C) value of LiNbO3. We find that the order parameter (Raman frequency of the TO1 mode) and the inverse dielectric susceptibility decrease with increasing temperature, as expected from the mean field model. We also find that the damping constant and the inverse relaxation time of this soft mode increases and decreases, respectively, with increasing temperature on the basis of the two models studied in the ferroelectric phase of LiNbO3. This indicates that our method of calculation is satisfactory to describe the observed behaviour of the ferroelectric-paraelectric phase transition in LiNbO3. (C) 2016 Elsevier GmbH. All rights reserved.
Citation - WoS: 4
Citation - Scopus: 4
Temperature-Dependent Absorption Edge and Photoconductivity of Tl2in2s3se Layered Single Crystals
(Elsevier Science Sa, 2013) Ambrico, M.; Ligonzo, T.; Gasanly, N. M.; Guler, I.; 101531; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
Temperature variation of indirect band gap of Tl2In2S3Se layered single crystals were obtained by means of absorption and photoconductivity measurements. The temperature coefficient of -7.1 x 10(-4) eV/K from absorption measurements in the temperature range of 10-300 K in the wavelength range of 520-1100 nm and -5.0 x 10(-4) eV/K from PC measurements in the temperature range of 132-291 K in the wavelength range of 443-620 nm upon supplying voltage V = 80 V were obtained. From the analysis of dark conductivity measurements in the temperature range of 150-300 K, conductivity activation energy was obtained as 0.51 eV above 242 K. The degree of the disorder, the density of localized states near Fermi level, the average hopping distance and average hopping energy of Tl2In2S3Se crystals were found as, 1.9 x 10(5) K, Nf = 4 x 10(20) cm(-3)eV(-1), 29.1 angstrom and 24.2 meV in the temperature range of 171-237 K, respectively. Activation energy of hopping conductivity at T = 171 K was obtained as 41.3 meV and the concentration of trapping states was found as 1.6 x 10(19) cm(-3). (C) 2012 Elsevier B.V. All rights reserved.
Citation - WoS: 2
Citation - Scopus: 2
Thermoluminescence Characterization of (Ga2se3)0.25 - (Ga2s3)0.75 Single Crystal Compounds
(Elsevier Sci Ltd, 2020) Guler, I; Gasanly, N. M.; Isik, M.; 101531; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
Ga2Se3 and Ga2S3 compounds take attention due to their potential applications in photovoltaics. Defects and impurities may affect the quality of optoelectronic devices. Therefore, it is worthwhile to determine the parameters (activation energy, order of kinetics, frequency factor) of traps associated with the defects and/or impurities. The aim of the present paper is to investigate the trapping parameters of (Ga2Se3)(0.25) - (Ga2S3)(0.75) single crystal which is one of the member of (Ga2Se3)(x) - (Ga2S3)(1-x) mixed crystals. For this purpose, thermoluminescence (TL) experiments were performed on (Ga2Se3)(0.25) - (Ga2S3)(0.75) single crystals in the 10-300 K region. TL spectra were also recorded using various heating rates in between 0.2 and 1.0 K/s and stopping temperatures from 30 to 60 K to get the detailed information about the characteristics of the trapping parameters. TL glow curves exhibited the overlapped peaks. The stopping temperature experimental data indicated that traps present quasi-continuous distribution within the band gap. Initial rise method analyses were applied to get the activation energies of quasi-continuously distributed revealed traps. Thermal activation energies of distributed traps were found as increasing from 108 to 246 meV as stopping temperature was increased from 30 to 60 K. The structural characteristics (lattice constants and atomic compositions of constituent elements) of used compound were also reported in the present study.

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