WoS İndeksli Yayınlar Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/394

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3-Sulfopropyl methacrylate based cryogels as potential tissue engineering scaffolds
(TAYLOR & FRANCIS LTD, 2-4 PARK SQUARE, MILTON PARK, ABINGDON OR14 4RN, OXON, ENGLAND, 2019) Durukan, Adile Yuruk; Isoglu, Ismail Alper; 0000-0001-6428-4207; AGÜ, Yaşam ve Doğa Bilimleri Fakültesi, Biyomühendislik Bölümü
In this study, we developed cryogels containing 3-sulfopropyl methacrylate (SPMA) and 4-vinyl pyridine (4-VP) as a potential scaffold for tissue engineering applications. Cryogels with varying monomer ratios were synthesised by chemical cross-linking under cryogelation conditions. Effect of initiators and cross-linker amount (0.025-0.15 g MBA; 0.012-0.05 g APS; 2.5-12.5 mu l TEMED) and also freezing temperature (-20 and -80oC) were investigated, and the conditions were optimised according to the morphological structures examined by SEM. The functional groups of the materials were characterised by FT-IR. Compression test and swelling were applied to investigate mechanical properties and water absorption ability, respectively. As a preliminary study, selected materials were tested for cell cytotoxicity with MTT. According to our results, the ionic and biocompatible cryogels prepared in this study possessing a highly porous and interconnective structure with good mechanical characteristics and swelling properties can be suitable as tissue scaffolds for many applications.
Ab initio simulation of amorphous BC3
(Elsevier B.V., 2020) Durandurdu M.; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
We report the structural and electrical properties of an amorphous BC3 model based on ab initio molecular dynamics simulations. The amorphous network is achieved from the melt and has a layer-like structure consisting of mainly hexagonal (six membered) rings as in the crystal. However, the distribution of boron atoms in the noncrystalline configuration appears to differ significantly from that of boron atoms in the crystal. The network is a solid solution and has randomly distributed nanosized graphene-like domains at each layer. Boron atoms have a tendency to form more overcoordinated defects involving with boron-boron homopolar bond(s). The mean coordination of boron and carbon atoms is 3.2 and 3.0, respectively. Interestingly the amorphous configuration is found to have a slightly higher density and bulk modulus than the crystal, which are attributed to the existence of overcoordinated units in the amorphous state. Based on the localization of the band tail states, noncrystalline BC3 is speculated to be a semiconducting material.
Ab initio study of boron-rich amorphous boron carbides
(WILEY, 2023) Yıldız, Tevhide Ayça; Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Yıldız, Tevhide Ayça; Durandurdu, Murat
Amorphous boron carbide compositions having high B contents (BxC1−x, 0.50 ≤ x ≤ 0.95) are systematically created by way of ab initio molecular dynamics calculations, and their structural, electrical, and mechanical characteristics are inclusively investigated. The coordination number of both B and C atoms increases progressively with increasing B/C ratio and more close-packed materials having pentagonal pyramid motifs form. An amorphous diamond-like local arrangement is found to be dominant up to 65% B content, and beyond this content, a mixed state of amorphous diamond– and B-like structures is perceived in the models because sp3 hybridization around C atoms is still leading one for all compositions. The pentagonal pyramid motifs around C atoms are anticipated to appear beyond 65% content. The intericosahedral linear C–B–C chains do not form in any model. All amorphous boron carbides are semiconducting materials. The mechanical properties gradually increase with increasing B concentration, and some amorphous compositions are proposed to be hard materials on the basis of their Vickers hardness estimation.
Absorption enhancement by semi-cylindrical-shell-shaped structures for an organic solar cell application
(OPTICAL SOC AMER, 2010 MASSACHUSETTS AVE NW, WASHINGTON, DC 20036 USA, 2020) Hah, Dooyoung; 0000-0002-1290-0597; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü
Organic solar cells are attractive for various applications with their flexibility and low-cost manufacturability. In order to increase their attractiveness in practice, it is essential to improve their energy conversion efficiency. In this work, semi-cylindrical-shell-shaped structures are proposed as one of the approaches, aiming at absorption enhancement in an organic solar cell. Poly(3-hexylthiophene-2,5-diyl) blended with indene-C60 bisadduct (P3HT:ICBA) is considered as the active layer. Light coupling to the guided modes and a geometrical advantage are attributed to this absorption enhancement. Finite-difference time-domain methods and finite element analysis are used to examine the absorption spectra for two types of devices, i.e., a debossed type and an embossed type. It is shown that absorption enhancement increases as the radius of the cylinder increases, but reaches a saturation at about 4-mu m radius. The average absorption enhancement with an active layer thickness of 200 nm and radius of 4 mu m, and for incidence angles between 0 degrees and 70 degrees, is found as 51%-52% for TE-polarized input and as 30%-33% for TM-polarized input when compared to a flat structure. Another merit of the proposed structures is that the range of incidence angles where the integrated absorption is at the level of the normal incidence is significantly broadened, reaching 70 degrees-80 degrees. This feature can be highly useful especially when organic solar cells are to be placed around a round object. The study results also exhibit that the proposed devices bear broadband absorption characteristics. (C) 2020 Optical Society of America
Activation of methane by Os+: Guided-ion-beam and theoretical studies
(CHEMM, 2013) Armentrout P.B.; Parke, Laura; Hinton, Christopher; Citir, Murat; 0000-0002-7957-110X; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Citir, Murat
Activation of methane by the third-row transition-metal cation Os + is studied experimentally by examining the kinetic energy dependence of reactions of Os+ with CH4 and CD4 using guided-ion-beam tandem mass spectrometry. A flow tube ion source produces Os+ in its electronic ground state and primarily in the ground spin-orbit level. Dehydrogenation to form [Os,C,2 H]++H2 is exothermic, efficient, and the only process observed at low energies for reaction of Os+ with methane, whereas OsH+ dominates the product spectrum at higher energies. The kinetic energy dependences of the cross sections for several endothermic reactions are analyzed to give 0K bond dissociation energies (in eV) of D0(Os+-C)=6.20±0. 21, D0(Os+-CH)=6.77±0.15, and D0(Os +-CH3)=3.00±0.17. Because it is formed exothermically, D0(Os+-CH2) must be greater than 4.71eV, and a speculative interpretation suggests the exothermicity exceeds 0.6eV. Quantum chemical calculations at the B3LYP/def2-TZVPP level show reasonable agreement with the experimental bond energies and with previous theoretical values available. Theory also provides the electronic structures of the product species as well as intermediates and transition states along the reactive potential energy surfaces. Notably, the structure of the dehydrogenation product is predicted to be HOsCH+, rather than OsCH2+, in contrast to previous work.
Active Subnetwork GA: A Two Stage Genetic Algorithm Approach to Active Subnetwork Search
(BENTHAM SCIENCE PUBL LTDEXECUTIVE STE Y-2, PO BOX 7917, SAIF ZONE, 1200 BR SHARJAH, U ARAB EMIRATES, 2017) Ozisik, Ozan; Bakir-Gungor, Burcu; Diri, Banu; Sezerman, Osman Ugur; AGÜ, Mühendislik Fakültesi, Bilgisayar Mühendisliği Bölümü; Bakir-Gungor, Burcu
Background: A group of interconnected genes in a protein-protein interaction network that contains most of the disease associated genes is called an active subnetwork. Active subnetwork search is an NP-hard problem. In the last decade, simulated annealing, greedy search, color coding, genetic algorithm, and mathematical programming based methods are proposed for this problem. Method: In this study, we employed a novel genetic algorithm method for active subnetwork search problem. We used active node list chromosome representation, branch swapping crossover operator, multicombination of branches in crossover, mutation on duplicate individuals, pruning, and two stage genetic algorithm approach. The proposed method is tested on simulated datasets and Wellcome Trust Case Control Consortium rheumatoid arthritis genome-wide association study dataset. Our results are compared with the results of a simple genetic algorithm implementation and the results of the simulated annealing method that is proposed by Ideker et al. in their seminal paper. Results and Conclusion: The comparative study demonstrates that our genetic algorithm approach outperforms the simple genetic algorithm implementation in all datasets and simulated annealing in all but one datasets in terms of obtained scores, although our method is slower. Functional enrichment results show that the presented approach can successfully extract high scoring subnetworks in simulated datasets and identify significant rheumatoid arthritis associated subnetworks in the real dataset. This method can be easily used on the datasets of other complex diseases to detect disease-related active subnetworks. Our implementation is freely available at https://www.ce.yildiz.edu.tr/personal/ozanoz/file/6611/ActSubGA
Adaptive Re-use of Medieval Caravanserais in Central Anatolia
(GANGEMI EDITORE S P A, PIAZZA SAN PANTALEO 4, ROMA, 00186, ITALY, 2019) Yoney, Nilufer Baturayolu; Asiliskender, Burak; Urfalioglu, Nur; AGÜ, Mimarlık Fakültesi, Mimarlık Bölümü
Kayseri, located at the junction of two major trade routes from northeast to southwest and from southeast to northwest, has been a commercial center for at least 4,000 years. The 23,500 tablets found at the Assyrian trade colony in Kanesh-Karum dating around 2,000 BCE and located 20km from the modern city provide ample proof. The great number and relevant size of Medieval caravanserais around the city as well as commercial buildings at the center indicate that this importance continued. Some of these caravanserais are already in use, albeit with inadequate architectural preservation measures while others are abandoned and/or partially destroyed. Indeed, the preservation, restoration and adaptive re-use of Medieval buildings is a major problematic, bringing out issues and interventions related to lacunae and reintegration, liberation or clearance of additions, structural strengthening with traditional/contemporary technologies, partial reconstruction, consolidation, cleaning and conservation of original building materials, and preventive maintenance. This paper aims to consider the possible presentation and adaptive re-use of Seljukid caravanserais over and inventory of accessible and at least partially preserved examples, focusing on eight case studies from the late 12th and 13th centuries: Karatay Han (1240), Tuzhisar Sultan Han (1232-1236), Eshab-i Kehf Han (before 1235), Cirgalan Han, Saruhan, Agzikarahan (1231-1240), Alayhan and Oresin Han.
Advances in Micelle-based Drug Delivery: Cross-linked Systems
(BENTHAM SCIENCE PUBL LTDEXECUTIVE STE Y-2, PO BOX 7917, SAIF ZONE, 1200 BR SHARJAH, U ARAB EMIRATES, 2017) Isoglu, Ismail Alper; Ozsoy, Yildiz; Isoglu, Sevil Dincer; 0000-0002-6887-6549; AGÜ, Yaşam ve Doğa Bilimleri Fakültesi, Biyomühendislik Bölümü
There are several barriers that drug molecules encounter in body beginning from kidney filtration and reticulo-endothelial system (RES) clearance to cellular trafficking. Multifunctional nanocarriers have a great potential for the delivery of drugs by enhancing therapeutic activity of existing methodologies. A variety of nanocarriers are constructed by different material types, which have unique physicochemical properties for drug delivery applications. Micelles formed by amphiphilic polymers are one of the most important drug/nanocarrier formulation products, in which the core part is suitable for encapsulation of hydrophobic agent whereas the outer shell can be utilized for targeting the drug to the disease area. Micelles as self-assembled nanostructures may encounter difficulties in biodistribution of encapsulated drugs because they have a tendency to be dissociated in dilution or high ionic strength. Therefore, therapeutic efficiency is decreased and it requires high amount of drug to be administered to achieve more efficient result. To overcome this problem, covalently stabilized structures produced by cross-linking in core or shell part, which can prevent the micelle dissociation and regulate drug release, have been proposed. These systems can be designed as responsive systems in which cross-links are degradable or hydrolysable under specific conditions such as low pH or reductive environment. These are enhancing characteristics in drug delivery because their cleavage allows the release of bioactive agent encapsulated in the carrier at a certain site or time. This review describes the chemical methodologies for the preparation of cross-linked micelles, and reports an update of latest studies in literature.
Air-stable, nanostructured electronic and plasmonic materials from solution-processable, silver nanocrystal building blocks
(American Chemical Society, 2014) Fafarman, Aaron T.; Hong, Sung-Hoon; Oh, Soong Ju; Caglayan, Humeyra; Ye, Xingchen; Diroll, Benjamin T.; Engheta, Nader; Murray, Christopher B.; Kagan, Cherie R.; 0000-0002-0656-614X; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü; Caglayan, Humeyra
Herein we describe a room-temperature, chemical process to transform silver nanocrystal solids, deposited from colloidal solutions, into highly conductive, corrosion-resistant, optical and electronic materials with nanometer-scale architectures. After assembling the nanocrystal solids, we treated them with a set of simple, compact, organic and inorganic reagents: ammonium thiocyanate, ammonium chloride, potassium hydrogen sulfide, and ethanedithiol. We find that each reagent induces unique changes in the structure and composition of the resulting solid, giving rise to films that vary from insulating to, in the case of thiocyanate, conducting with a remarkably low resistivity of 8.8 × 10-6 ·cm, only 6 times that of bulk silver. We show that thiocyanate mediates the spontaneous sintering of nanocrystals into structures with a roughness of less than 1/10th of the wavelength of visible light. We demonstrate that these solution-processed, low-resistivity, optically smooth films can be patterned, using imprint lithography, into conductive electrodes and plasmonic mesostructures with programmable resonances. We observe that thiocyanate-treated solids exhibit significantly retarded atmospheric corrosion, a feature that dramatically increases the feasibility of employing silver for electrical and plasmonic applications.
Alkali activation of mortars containing different replacement levels of ground granulated blast furnace slag
(ELSEVIER SCI LTD, 2012) Bilim, Cahit; Atis, Cengiz Duran; 0000-0003-3459-329X; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü; Atis, Cengiz Duran
The aim of the present study is to investigate some properties of alkali-activated mortars containing slag at different replacement levels. Ground granulated blast furnace slag was used at 0%, 20%, 40%, 60%, 80% and 100% replacement by weight of cement, and liquid sodium silicate having three different Na dosages was chosen as the alkaline activator. In this research, carbonation resistance measurements and compressive and flexural strength tests were performed on the mortar specimens with size of 40 40 160 mm. The findings obtained from the tests showed that carbonation depth values of the mortars decreased with the increase of activator dosage. Additionally, compressive and flexural strength values increased with the increase in activator concentration and slag replacement level. Portland cement/slag mortars activated by liquid sodium silicate exhibited lower strength than the slag alone activated by the same activator.
Alliances to acquisitions: A road map to advance the field of strategic management
(Emerald Group Publishing Ltd., 2017) Zakaria, Rimi; Genc, Omer Faruk; AGÜ, Yönetim Bilimleri Fakültesi, İşletme Bölümü; Genc, Omer Faruk
Although primarily treated as two distinct research streams, strategic alliances and mergers and acquisitions together occupy much of the strategic management discourse. Alliances, in many cases, end in acquisitions as firms use alliances as intermediate strategic options to eventually acquire a partner. As the discipline of strategy matures and the frequency and the volume of inter-firm cooperation continue to rise, it is imperative to integrate these two research streams for a holistic understanding of the theory of the firm. The purpose of this conceptual piece is threefold. First, we review the extant studies that combine these two governance modes: alliance and acquisitions. Second, drawing on the dominant strategic management theories, we highlight how prior inter-firm alliances inform future acquisitions in terms of (a) pre-combination decisions, (b) post-deal integration processes, (c) alternatives and strategies, and (d) performance outcomes. Finally, in view of the emerging trends and evocative gaps, we offer a conceptual road map to encourage future theoretical development and empirical research. Copyright
AlN Piezoelectric Quad-Actuators for 2D Optical Micro Scanning
(TAYLOR & FRANCIS LTD, 2022) Hah, Dooyoung; 0000-0002-1290-0597; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü; Hah, Dooyoung
Piezoelectric actuation has been one of the frequent choices for optical micro scanning. In most of the cases, lead zirconate titanate (PZT) has been used as the piezoelectric material. However, PZT has a potential issue in biomedical applications due to the content of lead. For this, AlN can be used as an alternative. The main drawback of AlN is its low piezoelectric coefficients. In order to overcome such a drawback, this paper presents a novel actuator configuration, designed for a quasi-static operation mode. Quad-actuators and meander-shaped hinges are the essence of the proposed actuator configuration. Numerical simulation study is carried out to prove the concept of the device. The study also shows that the proposed scanner can have the optical scan angle of 9 degree at a quasi-static mode. Two different scan modes, a raster-like mode and a Lissajous mode are tested, demonstrating the two-dimensional scanning capability of the device.
Ambient Energy Harvesting for Low Powered Wireless Sensor Network based Smart Grid Applications
(IEEE, 345 E 47TH ST, NEW YORK, NY 10017 USA, 2019) Faheem, Muhammad; Ashraf, Muhammad Waqar; Butt, Rizwan Aslam; Raza, Basit; Ngadi, Md. Asri; Gungor, Vehbi Cagri; 0000-0003-4907-6359; AGÜ, Mühendislik Fakültesi, Bilgisayar Mühendisliği Bölümü
Limited battery lifetime is one of the most critical issues for wireless sensor networks (WSNs)-based smart grid (SG) applications. Recently, ambient energy harvesting (AEH) has been considered to significantly improve the network lifetime of the WSNs-based SG applications. However, extracting a significant amount of energy from the ambient energy resource due to time varying links quality affected by power grid environments is the main issue for WSNs-based applications in SG. In this paper, we propose a novel multi-source energy harvesting mechanisms for WSNs-based SG applications. The propose hybrid ambient energy harvesting framework through the designed circuitry successfully harvests massive power density by capturing the radial electric field (EF) and ambient radio frequency WiFi 2.4GHz band signals present in the vicinity of 500kV power grid station. The design energy harvesting schemes have been implemented on the recently developed routing protocol for SG applications. The experiments using EstiNet9.0, demonstrate that the designed framework is efficient in terms of energy harvesting capabilities to enable a long-lasting lifetime of the WSNs-based smart grid applications.
Amelioration potential of synthetic oxime chemical cores against multiple sclerosis and Alzheimer's diseases: Evaluation in aspects of in silico and in vitro experiments
(ELSEVIER, 2024) Yilmaz, Anil; Koca, Murat; Ercan, Selami; Acar, Ozden Ozgun; Boga, Mehmet; Sen, Alaattin; Kurt, Adnan; 0000-0002-8444-376X; AGÜ, Yaşam ve Doğa Bilimleri Fakültesi, Moleküler Biyoloji ve Genetik Bölümü; Sen, Alaattin
Alzheimer disease (AD) and multiple sclerosis (MS) are inflammatory neurological disorders. The main symptom of AD is dementia, and the main symptoms of MS are vertigo, sexual dysfunction, cognitive problems, and fatigue. Today, millions of people are affected by AD and MS, and the number is growing day by day. However, there are not any accurate remedies for both disorders. For this reason, discovering novel drug molecules against neurological disorders such as AD and MS is essential and precious. Oximes and benzofurans exhibit many pharmacological effects including anti-inflammatory and neurological activities. Thus, several novel compounds bearing oxime and benzofuran chemical cores were designed and synthesized, and their in vitro anticholinesterase activities were investigated in our previous study. A number of the synthesized molecules showed excellent anticholinesterase activity against both AChE and BChE enzymes. The mentioned study constituted a background for this study. In this study, we picked different chemical skeletons among all the synthesized molecules to conduct further in silico and in vitro experiments. In order to support our in vitro anticholinesterase findings, we also examined in silico anti-Alzheimer activity of the selected molecules. In addition, in silico and in vitro activities against MS disease of the synthesized molecules were investigated. Molecule 4 extraordinarily showed outstanding activity against AD disease both in silico and in vitro, as well as in silico activity against MS disease. This feature makes molecule 4 a possible drug lead molecule which is very limited in the market. On the other hand, molecule 1, a less substituted oxime skeleton, demonstrated the strongest in vitro activity against MS disease through in vitro anti-inflammatory effect. As an observation, molecule 4 was determined to be the most promising molecule to focus on in the further steps.
Amorphous BC5 from first principles calculations
(ELSEVIER, 2022) Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Durandurdu, Murat
A boron-substituted amorphous graphite (BC5) network is generated using a first principles molecular dynamics simulation and its atomic structure and electrical and mechanical properties are discussed in details. The network has a layered structure with primarily hexagonal (six membered) rings and its average coordination is about 3.0. The material is a solid solution having a minor amount of B-B homopolar bonds. It is structurally different from the BC5 crystal or monolayers proposed in the literature. The model is a semimetal material based on a generalized gradient approximation with the Hubbard correction (GGA+U) calculation. When its mechanical properties are concerned, they are comparable with those of graphite or amorphous graphite.
Amorphous boron arsenide
(ELSEVIER, RADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS, 2019) Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
The short-range order and electrical properties of amorphous boron arsenide (BAs) are evaluated by means of ab initio molecular dynamics simulations. The amorphous model is obtained from the fast solidification of the BAs melt and consists of B-rich and As-rich domains. The average coordination number of B- and As-atoms are found as 4.97 and 3.34, respectively. B-atoms have a tendency to form pentagonal pyramidal-like configurations as commonly seen in boron or boron rich materials. Yet B-12 molecules do not develop in the system but the formation of a B-10 cluster is perceived in the network. On the other hand, As-atoms have a trend to structure chain-like motifs and four-membered rings. Amorphization yield about 31% volume expansion in the amorphous network. All these findings reveal that the model shows strong chemical disorder and its short-range order is considerably different than that of the crystal. Amorphization-induced metallization is proposed for BAs.
Amorphous boron carbide from ab initio simulations
(ELSEVIER, RADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS, 2020) Yildiz, Tevhide Ayca; Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
An amorphous boron carbide (a-B4C) model is generated by means of ab-initio molecular dynamics calculations within a generalized gradient approximation and its structural, mechanical and electrical features are discussed in details. The mean coordination number of B and C atoms is estimated to be 5.29 and 4.17, respectively. The pentagonal pyramid-like motifs for B atoms, having sixfold coordination, are the main building units in a-B4C and some of which involve with the development of B-12 icosahedra. On the other hand, the fourfold-coordinated units are the leading configurations for C atoms. Surprisingly the formation of C-C bonds is found to be less favorable in the noncrystalline network, compared to the crystal. a-B4C is a semiconducting material having an energy band gap considerably less than that of the crystal. A noticeably decrease in the mechanical properties of B4C is observed by amorphization. Nonetheless a-B4C is categorized as a hard material due to its high Vickers hardness of about 24 GPa.
Amorphous boron carbonitride (BC4N) from ab initio simulations
(ELSEVIER, 2024) Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Durandurdu, Murat
This study utilizes ab initio molecular dynamics simulations to explore the structure and properties of amorphous boron carbonitride (a-BC4N). A 432-atom model, generated via a conventional melt-and-quench technique, exhibits a graphite-like structure with all elements possessing an average coordination number of about 3.0. C atoms dominate within individual layers, interspersed with distinct BN domains. This atomic arrangement deviates considerably from that proposed for crystalline BC4N structures. Despite this structural variation, the a-BC4N model is likely a narrow band gap semiconductor (0.15 eV), similar to its crystalline counterparts. In terms of mechanical properties, a-BC4N demonstrates similarities with various layered materials while exhibiting a notably larger bulk modulus.
Amorphous boron suboxide
(WILEY, 111 RIVER ST, HOBOKEN 07030-5774, NJ USA, 2019) Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
We study the atomic structure and the electronic and mechanical properties of amorphous boron suboxide (B6O) using an ab initio molecular dynamic technique. The amorphous network is attained from the rapid solidification of the melt and found to consist of boron and oxygen-rich regions. In the boron-rich regions, boron atoms form mostly perfect or imperfect pentagonal pyramid-like configurations that normally yield the construction of ideal and incomplete B-12 molecules in the model. In addition to the B-12 molecules, we also observe the development of a pentagonal bipyramid (B-7) molecule in the noncrystalline structure. In the oxygen-rich regions, on the other hand, boron and oxygen atoms form threefold and twofold coordinated motifs, respectively. The boron-rich and oxygen-rich regions indeed represent structurally the characteristic of amorphous boron and boron trioxide (B2O3). The amorphous phase possesses a small band gap energy with respect to the crystal. On the bases of the localization of the tail states, we suggest that the p-type doping might be more convenient than the n-type doping in amorphous B6O. Bulk modulus and Vickers hardness of the noncrystalline configuration is estimated are be 106 and 13-18 GPa, respectively, which are noticeably less than those of the crystalline structure. Such a noticeable decrease in the mechanical properties is attributed to the presence of open structured B2O3 glassy domains in the amorphous model.
Amorphous carbon nitride (C3N4)
(ELSEVIER, 2024) Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Durandurdu, Murat
This detailed investigation employs an ab initio approach to explore the atomic structure and electronic properties of an amorphous carbon nitride (C3N4) model. The model, designed with an exact 3:4 ratio, is based on an amorphous boron nitride configuration. The study reveals crucial insights into the mean coordination number for C and N atoms within the amorphous structure. With values of 2.95 for C atoms and 2.21 for N atoms, these coordination numbers closely resemble those observed in graphite-like crystals. The local structure of the amorphous network exhibits similarities to the triazine-based graphitic C3N4 crystal and is notably devoid of homopolar bonds. The estimated band gap for the amorphous C3N4 model is 1.2 eV, representing a significant reduction compared to the crystal structure, which exhibits a band gap of about 2.93 eV as determined through GGA+U calculations.

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