Direct Experimental Evidence of Metal-Mediated Etching of Suspended Graphene

Atomic resolution high angle annular dark field imaging of suspended, single-layer graphene, onto which the metals Cr, Ti, Pd, Ni, Al and Au atoms had been deposited was carried out in an aberration corrected scanning transmission electron microscope. In combination with electron energy loss spectroscopy, employed to identify individual impurity atoms, it was shown that nano-scale holes were etched into graphene, initiated at sites where single atoms of all the metal species except for gold come into close contact with the graphene. The e-beam scanning process is instrumental in promoting metal atoms from clusters formed during the original metal deposition process onto the clean graphene surface, where they initiate the hole-forming process. Our observations are discussed in the light of calculations in the literature, predicting a much lowered vacancy formation in graphene when metal ad-atoms are present. The requirement and importance of oxygen atoms in this process, although not predicted by such previous calculations, is also discussed, following our observations of hole formation in pristine graphene in the presence of Si-impurity atoms, supported by new calculations which predict a dramatic decrease of the vacancy formation energy, when SiOx molecules are present.Comment: final version accepted in ACS Nano + supplementary info. 22+6 pages, 4+5 figure

KİMYASAL BUHAR BİRİKTİRME YÖNTEMİ İLE GRAFEN SENTEZİNE TAVLAMA VE BÜYÜTME SÜRELERİNİN ETKİSİ

ÖZET: Son yılların en ilgi çekici malzemelerinden biri olan grafen yüksek iletkenlik, yüksek dayanım ve saydamlık gibi birçok üstün özelliğe sahiptir. Grafenin kimyasal buhar depolama tekniği kullanılarak sentezlenmesinde, büyütme sıcaklığı, büyütme süresi, tavlama süresi, basınç, kullanılan alt-taş, kullanılan gazların saflıkları ve akış miktarları gibi birçok parametre etkilidir. Bu parametrelerden büyütme ve tavlama süreleri grafen sentezinde en önemli parametrelerdendir, bu nedenle bu çalışmada büyütme ve tavlama sürelerinin tek katmanlı homojen grafen sentezine olan etkisi araştırılmıştır. Farklı büyütme ve tavlama süreleri kullanılarak üretilen grafen filmler Raman Spektrokopisi tekniği kullanılarak karakterize edilmiş olup tek tabakalı homojen grafen sentezi için üretim süreci optimize edilmiştir

Atomically Resolved Imaging of Highly Ordered Alternating Fluorinated Graphene

One of the most desirable goals of graphene research is to produce ordered 2D chemical derivatives of suitable quality for monolayer device fabrication. Here we reveal, by focal series exit wave reconstruction, that C2F chair is a stable graphene derivative and demonstrates pristine long-range order limited only by the size of a functionalized domain. Focal series of images of graphene and C2F chair formed by reaction with XeF2 were obtained at 80 kV in an aberration-corrected transmission electron microscope. EWR images reveal that single carbon atoms and carbon-fluorine pairs in C2F chair alternate strictly over domain sizes of at least 150 nm^2 with electron diffraction indicating ordered domains >/= 0.16 square micrometer. Our results also indicate that, within an ordered domain, functionalization occurs on one side only as theory predicts. Additionally we show that electron diffraction provides a quick and easy method for distinguishing between graphene, C2F chair and fully fluorinated stoichiometric CF 2D phases

Graphene re-knits its holes

Nano-holes, etched under an electron beam at room temperature in singlelayer graphene sheets as a result of their interaction with metalimpurities, are shown to heal spontaneously by filling up with either non-hexagon, graphene-like, or perfect hexagon 2D structures. Scanning transmission electron microscopy was employed to capture the healing process and study atom-by-atom the re-grown structure. A combination of these nano-scale etching and re-knitting processes could lead to new graphene tailoring approaches.Comment: 11 pages, 4 figure

Bi2-xTbxPbxSr2Ca3Cu4Oy süperiletken malzemesine Tb katkısının etkileri

TEZ6038Tez (Yüksek Lisans) -- Çukurova Üniversitesi, Adana, 2006.Kaynakça (s.7-79) var.ix, 80 s. ; 29 cm.The purpose of this work, investigation Tb of doping effects on structural properties in BSCCO superconductors which produced melt quenched method. For this, structure and physicial properties of Bi1.7Pb0.3-xTbxSr2Ca3Cu4Oy superconductors are investigated. In addition Superconductivity changing occured during heat treatment have been analysed by using XRD, R-T and SEM. In this results, it can be say Tb doping is decreased superconductivity.Bu çalışmanın amacı, eritme-döküm yöntemiyle üretilen BSCCO süperiletken sistemine yapılan Tb katkısının, sistemin yapısal özelliklerine etkisini incelemektir. Bu amaçla çalışmada Bi1.7Pb0.3-xTbxSr2Ca3Cu4Oy yüksek sıcaklık süperiletkenlerinin mikro yapısı ve fiziksel özellikleri incelendi. Ayrıca BSCCO süperiletkenlerinin XRD, SEM, ve R-T sonuçlarından faydalanılarak ısıl işlemler sırasında oluşan mikro yapısal, fiziksel ve süperiletkenlik özelliklerdeki değişiklikler analiz edildi. Sonuçlar BSCCO sistemine Tb katkılanmasının süperiletkenlik özellikleri olumsuz etkilediğini gösterdi.Bu çalışma Ç.Ü. Bilimsel Araştırma Projeleri Birimi Tarafından Desteklenmiştir. Proje No:FEF2004YL3