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Citation - WoS: 3
Citation - Scopus: 2
Characterization of Linear and Nonlinear Optical Properties of Nabi(Wo4)2 Crystal by Spectroscopic Ellipsometry
(Elsevier, 2024) Guler, I.; Gasanly, N. M.; Isik, M.
NaBi(WO4)2 compound has been a material of considerable attention in optoelectronic applications. The present research, in which we examined the linear and nonlinear optical properties of NaBi(WO4)2 crystal using the spectroscopic ellipsometry method, elucidates the optical behavior of the crystal in detail. Our work provides a sensitive approach to determine the spectral characteristic of the crystal. The spectral dependence of various optical parameters such as refractive index, extinction coefficient, dielectric function and absorption coefficient was reported in the range of 1.2-5.0 eV. Optical values such as bandgap energy, critical point energy, single oscillator parameters were obtained as a result of the analyses. In addition to linear optical properties, we also investigated the nonlinear optical behavior of NaBi(WO4)2 and shed new light on the potential applications of the crystal. Absorbance and photoluminescence spectra of the crystal were also reported to characterize optical, electronic and emission behavior of the compound. Our findings may form the basis for a number of technological applications such as optoelectronic devices, frequency conversion, and optical sensors. This research contributes to a better understanding of the optical properties of NaBi(WO4)2 crystal, highlighting the material's role in future optical and electronic technologies.
Citation - WoS: 10
Citation - Scopus: 15
Collaborations, Concepts, and Citations in Educational Technology: a Trend Study Via Bibliographic Mapping
(Springer, 2022) Soylu, Meryem Yilmaz; Akkoyunlu, Buket; Deryakulu, Deniz; Bardakci, Salih
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: 9
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
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: 3
Citation - Scopus: 4
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
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: 48
Effectiveness of Gamification in Flipped Learning
(Sage Publications inc, 2020) Akkoyunlu, Buket; Gunduz, Abdullah Yasin
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: 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
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
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
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: 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
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: 6
Citation - Scopus: 5
Pressure-Dependent Raman Modes Near the Cubic-Tetragonal Transition in Strontium Titanate
(Wiley, 2018) Yurtseven, Hamit; Kiraci, Ali
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: 21
Citation - Scopus: 35
Student Views on the Use of Flipped Learning in Higher Education: a Pilot Study
(Springer, 2019) Akkoyunlu, Buket; Gunduz, Abdullah Yasin
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: 8
Citation - Scopus: 8
Study of Vibrational Modes in (Ga2s3)x - (ga2se3)1-X Mixed Crystals by Raman and Infrared Reflection Measurements
(Elsevier, 2019) Guler, I.; Gasanly, N. M.; Isik, M.
Raman and infrared (IR) reflection characteristics were investigated in the frequency region of 100-450 cm(-1) for (Ga2S3)(x) - (Ga2Se3)(1-x) mixed crystals for compositions of x increasing from 0.0 to 1.0 by intervals of 0.25 obtained by Bridgman crystal growth technique. In the Raman spectra of these crystals four dominant peak features were observed while two bands were detected in the IR spectra of interest samples. Kramers-Kronig dispersion relations applied to IR spectra presented the frequencies of transverse optical modes. The compositional dependencies of revealed Raman- and IR-active mode frequencies on (Ga2S3)(x) - (Ga2Se3)(1-x) crystals were established. One-mode behavior was displayed from indicated dependencies.
Citation - WoS: 3
Citation - Scopus: 3
Temperature and Excitation Intensity Tuned Photoluminescence in Ga0.75in0.25se Crystals
(Elsevier Science Bv, 2013) Isik, M.; Guler, I.; Gasanly, N. M.
Photoluminescence (PL) spectra of Ga0.75In0.25Se layered single crystals have been studied in the wavelength range of 580-670 nm and temperature range of 7-59 K. Two PL emission bands centered at 613 nm (2.02 eV, A-band) and 623 nm (1.99 eV, B-band) were revealed at T = 7K. The excitation laser intensity dependence of the emission bands have been studied in the 0.06-1.40 W cm(-2) range. Radiative transitions from shallow donor levels located at E-A = 0.11 and E-B = 0.15 eV below the bottom of conduction band to single shallow acceptor level located at 0.01 eV above the valence band are suggested to be responsible for the observed A- and B-bands. A simple model was proposed to interpret the recombination processes in Ga0.75In0.25Se single crystals. (c) 2012 Elsevier B.V. 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.
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.

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