Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 2Citation - Scopus: 2Tuning Thermal Transport in Graphene Via Combinations of Molecular Antiresonances(Elsevier Ltd., 2018) Sevim, Koray; Sevinçli, HaldunWe propose a method to engineer the phonon thermal transport properties of low dimensional systems. The method relies on introducing a predetermined combination of molecular adsorbates, which give rise to antiresonances at frequencies specific to the molecular species. Despite their dissimilar transmission spectra, thermal resistances due to individual molecules remain almost the same for all species. On the other hand, thermal resistance due to combinations of different species are not additive and show large differences depending on the species. Using a toy model, the physics underlying the violation of resistance summation rule is investigated. It is demonstrated that equivalent resistance of two scatterers having the same resistances can be close to the sum of the constituents or ∼ 70% of it depending on the relative positions of the antiresonances. The relative positions of the antiresonances determine the net change in transmission, therefore the equivalent resistance. Since the entire spectrum is involved in phonon spectrum changes in different parts of the spectrum become important. Performing extensive first-principles based computations, we show that these distinctive attributes of phonon transport can be useful to tailor the thermal transport through low dimensional materials, especially for thermoelectric and thermal management applications.Article Citation - WoS: 8Citation - Scopus: 10Experimental and Computational Investigation of Graphene/Sams Schottky Diodes(Elsevier Ltd., 2018) Aydın, Hasan; Bacaksız, Cihan; Yağmurcukardeş, Nesli; Karakaya, Caner; Mermer, Ömer; Can, Mustafa; Senger, Ramazan Tuğrul; Şahin, Hasan; Selamet, YusufWe have investigated the effect of two different self-assembled monolayers (SAMs) on electrical characteristics of bilayer graphene (BLG)/n-Si Schottky diodes. Novel 4″bis(diphenylamino)-1, 1′:3″-terphenyl-5′ carboxylic acids (TPA) and 4,4-di-9H-carbazol-9-yl-1,1′:3′1′-terphenyl-5′ carboxylic acid (CAR) aromatic SAMs have been used to modify n-Si surfaces. Cyclic voltammetry (CV) and Kelvin probe force microscopy (KPFM) results have been evaluated to verify the modification of n-Si surface. The current–voltage (I–V) characteristics of bare and SAMs modified devices show rectification behaviour verifying a Schottky junction at the interface. The ideality factors (n) from ln(I)–V dependences were determined as 2.13, 1.96 and 2.07 for BLG/n-Si, BLG/TPA/n-Si and BLG/CAR/n-Si Schottky diodes, respectively. In addition, Schottky barrier height (SBH) and series resistance (R s ) of SAMs modified diodes were decreased compared to bare diode due to the formation of a compatible interface between graphene and Si as well as π–π interaction between aromatic SAMs and graphene. The CAR-based device exhibits better diode characteristic compared to the TPA-based device. Computational simulations show that the BLG/CAR system exhibits smaller energy-level-differences than the BLG/TPA, which supports the experimental findings of a lower Schottky barrier and series resistance in BLG/CAR diode.Article Citation - WoS: 59Citation - Scopus: 64Interfacial Thermal Resistance Between the Graphene-Coated Copper and Liquid Water(Elsevier Ltd., 2016) Pham, An T.; Barışık, Murat; Kim, BohungThe thermal coupling at water-solid interfaces is a key factor in controlling thermal resistance and the performance of nanoscale devices. This is especially important across the recently engineered nano-composite structures composed of a graphene-coated-metal surface. In this paper, a series of molecular dynamics simulations were conducted to investigate Kapitza length at the interface of liquid water and nano-composite surfaces of graphene-coated-Cu(1 1 1). We found that Kapitza length gradually increased and converged to the value measured on pure graphite surface with the increase of the number of graphene layers inserted on the Cu surface. Different than the earlier hypothesis on the "transparency of graphene," the Kapitza length at the interface of mono-layer graphene coated Cu and water was found to be 2.5 times larger than the value of bare Cu surface. This drastic change of thermal resistance with the additional of a single graphene is validated by the surface energy calculations indicating that the mono-layer graphene allows only ∼18% van der Waals energy of underneath Cu to transmit. We introduced an "overall interaction strength" value for the nano-composites based the quantitative contribution of pair interaction potentials of each material with water into the total surface energy in each case. Similar to earlier studies, results revealed that Kapitza length shows exponentially variation as a function of the estimated interaction strength of the nano-composite surfaces. The effect of Cu/graphene coupling on thermal behavior between the nano-composite with water was characterized. The Kapitza length was found to decrease significantly with increased Cu/graphene strength in the case of weak coupling, while this behavior becomes negligible with strong coupling of Cu and graphene.