Browsing by Author "Cambaz Buke, G."

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Open Access
Low-temperature synthesis and growth model of thin Mo2C crystals on indium
(Nature Publishing Group, 2021-04-15) Caylan, Ömer Refet; Cambaz Buke, G.
Chemical vapor deposition is a promising technique to produce Mo2C crystals with large area, controlled thickness, and reduced defect density. Typically, liquid Cu is used as a catalyst substrate; however, its high melting temperature (1085 °C) prompted research groups to search for alternatives. In this study, we report the synthesis of large-area thin Mo2C crystals at lower temperatures using liquid In, which is also advantageous with respect to the transfer process due to its facile etching. SEM, EDS, Raman spectroscopy, XPS, and XRD studies show that hexagonal Mo2C crystals, which are orthorhombic, grow along the [100] direction together with an amorphous carbon thin film on In. The growth mechanism is examined and discussed in detail, and a model is proposed. AFM studies agree well with the proposed model, showing that the vertical thickness of the Mo2C crystals decreases inversely with the thickness of In for a given reaction time.
Open Access
Synthesis and characterization of homogeneously dispersed graphene copper heterostructures with enhanced thermal properties
(Springer, 2023-12-15) Çakır, D.; Çaylan, Ömer R.; Cambaz Buke, G.; N. Ravishankar
Graphene-reinforced copper composites have gained significant attention due to their exceptional properties and potential applications across various industries. This study presents a novel approach to synthesize 3D graphene–copper heterostructures using a plasma-enhanced chemical vapor deposition (PECVD) technique. The method involves encapsulating Cu powders with graphitic layers through PECVD at a low temperature of 400 °C to prevent copper powder agglomeration during the process, ensuring uniform graphene coating across the entire copper surface. Microstructural characterization of the resulting 3D graphene–copper heterostructures confirms successful encapsulation, with graphitic coating thicknesses ranging from 5–15 nm. The unique graphene-encapsulated Cu powder structure facilitates pressureless sintering, yielding consolidated composites with exceptional structural integrity. Metallographic analysis of the consolidated samples revealed a uniformly distributed multilayer graphitic network within the graphene–copper (G/Cu) composite structure. The presence of graphene between copper grains is found to inhibit copper grain growth, leading to smaller copper grains compared to graphene-free copper monoliths. Furthermore, the G/Cu composite had significantly reduced pore size and ensuant higher density when compared to the sample prepared without graphene encapsulation. Graphene’s lubricating effect is presumed to enhance the freedom of rotation for copper grains during sintering and cause increased densification. The thermal diffusivity of the graphene–copper heterostructure is measured as 1.38 cm2/s using thermal flash technique, representing an approximate 40% improvement compared to graphene-free copper. This enhancement in thermal conductivity is attributed to the presence of strongly bonded graphene layers between copper grains and additional thermal transport originating from graphitic interface. Thermal diffusivity was decreased monotonically with increasing temperature at temperature range 20–200 °C indicating prevalent phonon contribution. In the context of technological implications, successful synthesis of 3D graphene–copper heterostructures using scalable plasma-enhanced chemical vapor deposition (PECVD) technique establishes a foundation for the development of advanced materials with tailored properties and multifunctional applications, particularly those requiring lightweight characteristics, high transport properties (thermal or electrical), and exceptional mechanical strength.