Browsing by Author "Karatutlu, A."

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Open Access
Liquid-phase synthesis of nanoparticles and nanostructured materials
(Elsevier, 2018) Karatutlu, A.; Barhoum, A.; Sapelkin, A.
Nanoparticles less than 100nm in size have attracted significant interest over the past 20 years due to their unique properties led by quantum size effect. This chapter evaluates the synthesis methods in liquid phase conducted under operation in high/room temperature and at vacuum/atmospheric environment for nanoparticles and nanostructured materials. We draw attention to the fact that various synthesis methods for formation of colloidally stable matrix-free nanoparticles are available. These methods including chemical stain etching, electrodeposition methods, direct-precipitation methods, sol-gel methods, colloidal synthesis methods, hot-injection synthesis methods, hydrothermal and solvothermal methods, microwave-assisted synthesis methods, ultrasonic synthesis methods, and laser ablation in liquid-phase.
Open Access
Preferential MBE growth and characterization of SiGe nanoislands on depth-selective Si Pits Etched by Ar+ Plasma
(Wiley-VCH Verlag, 2018) Şeker, İ.; Karatutlu, A.; İstengir, S.
In this study, the size selective deposition of SiGe nanoislands is demonstrated to be possible only in Si nanopits using a molecular beam epitaxy (MBE) system. The depth of the etched Si substrate prepared by Ar+ plasma etching just before the deposition seems to be playing a role in the selectivity of keeping the SiGe nanoislands only inside the nanopits. We observed that, when the thickness of the deposited SiGe layer is around the mean pit depth, which is 4 nm in this case, Ge nucleation takes place selectively on the pre-etched pits. Relatively larger deposition thickness (e.g., 40 nm) is demonstrated to suppress the preferential growth of the Ge nanocrystals (NCs)/Si NCs which are in return observed all along the surface of the Si substrate. On the other hand, surface migration is considered to play a role in very small depth (relatively more shallow pits) and yielding the unfilled Si nanopits (ca. 1.5 nm) whereas Ge NCs selectively nucleate only within those having larger depths (ca. 3 nm). Such site-specific 3D controlled growth of nanoislands is shown for the deposition of different semiconductor nanocrystals on top of another for formation of nanodevices fabricated in a single nanopit.
Open Access
Structural and electrical investigations of MBE-grown SiGe nanoislands
(Springer Verlag, 2018) Şeker, İ.; Karatutlu, A.; Gürbüz, O.; Yanık, S.; Bakış, Y.; Karakız, M.
SiGe nanoislands were grown by Molecular Beam Epitaxy (MBE) method on Si (100) substrates with comparative growth parameters such as annealing temperature, top Ge content and layer-by-layer annealing (LBLA). XRD and Raman data suggest that annealing temperature, top Ge content and layer-by-layer annealing (LBLA) can overall give a control not only over the amorphous content but also over yielding the strained Ge layer formation in addition to mostly Ge crystallites. Depending on the layer design and growth conditions, size of the crystallites was observed to be changed. Four Point Probe (FPP) Method via Semiconductor Analyzer shows that 100 °C rise in annealing temperature of the samples with Si0.25Ge0.75 top layers caused rougher islands with vacancies which further resulted in the formation of laterally higher resistive thin film sheets. However, vertically performed I-AFM analysis produced higher I-V values which suggest that the vertical and horizantal conductance mechanisms appear to be different. Ge top-layered samples gained greater crystalline structure and better surface conductivity where LBLA resulted in the formation of Ge nucleation and tight 2D stacking resulting in enhanced current values.
Open Access
Theories of nanoparticle and nanostructure formation in liquid phase
(Elsevier, 2018) Karatutlu, A.; Barhoum, A.; Sapelkin, A.
Nanoparticles (NPs) and nanostructured materials exhibit shape- and size-dependent properties that are desired for a wide variety of applications, such as catalysis, sensing, drug delivery, energy production, and storage. In view of this, it is essential to produce well-defined NPs and nanostructures with desired characteristics, to understand their formation and growth mechanisms, and to define the critical size below which they act differently from bulk materials in order to develop synthetic strategies. For example, quantum dots (below 20nm) are mainly single nanocrystals characterized by a single-domain crystalline lattice without grain boundaries. These tiny individual crystals differ drastically from bulk polycrystalline materials. In fact, existing investigations indicated that ordered polycrystalline particles are preferably formed at high supersaturations, where rapid nucleation generates many NPs, which subsequently tend to aggregate randomly at high NP concentrations. Single crystals, such as quantum dots, form at low supersaturations. The reduction of the supersaturation to a level at which primary NPs are still formed in solution yields mesocrystals. This chapter discusses the advanced nucleation and growth theories that are used to explain the growth of the obtained nanoparticles and nanostructures to the desired structures.