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Dejan Stekovic

Bio: Dejan Stekovic is an academic researcher from University of California, Riverside. The author has contributed to research in topics: Ferromagnetism & Graphene. The author has an hindex of 7, co-authored 11 publications receiving 115 citations.

Papers
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Journal ArticleDOI
01 Dec 2016-Carbon
TL;DR: In this article, the authors report a novel graphene transfer technique which provides a route to high-throughput, reliable and economical transfer of graphene without introducing large cracks and residue contamination from polymers, such as PMMA or magnetic impurities.

36 citations

Journal ArticleDOI
TL;DR: A naphthalene-assisted graphene transfer technique is reported which provides a reliable route to residue-free transfer of graphene to both hard and flexible substrates and has the potential to broaden the applications of CVD graphene in fields where ultraclean graphene and mild graphene transfer conditions are required.
Abstract: Advances in the chemical vapor deposition (CVD) growth of graphene have made this material a very attractive candidate for a number of applications including transparent conductors, electronics, optoeletronics, biomedical devices and energy storage. The CVD method requires transfer of graphene on a desired substrate and this is most commonly accomplished with polymers. The removal of polymer carriers is achieved with organic solvents or thermal treatment which makes this approach inappropriate for application to plastic thin films such as polyethylene terephthalate substrates. An ultraclean graphene transfer method under mild conditions is highly desired. In this article, we report a naphthalene-assisted graphene transfer technique which provides a reliable route to residue-free transfer of graphene to both hard and flexible substrates. The quality of the transferred graphene was characterized with atomic force microscopy, scanning electron microscopy, and Raman spectroscopy. Field effect transistors, based on the naphthalene-transfered graphene, were fabricated and characterized. This work has the potential to broaden the applications of CVD graphene in fields where ultraclean graphene and mild graphene transfer conditions are required.

26 citations

Journal ArticleDOI
TL;DR: The substitutional doping of solid-state spiro-bis(5-methyl-1,9-oxido-phenalenyl)boron radical ([2]2B) is reported by co-crystallization of this radical with the corresponding spiro/sub 2Be compound, and at certain compositions the results provide a graphic picture of the structural transformations undergone by the lattice.
Abstract: We report the substitutional doping of solid-state spiro-bis(5-methyl-1,9-oxido-phenalenyl)boron radical ([2]2B) by co-crystallization of this radical with the corresponding spiro-bis(5-methyl-1,9-oxido-phenalenyl)beryllium compound ([2]2Be). The pure compounds crystallize in different space groups ([2]2B, P1, Z = 2; [2]2Be, P21/c, Z = 4) with distinct packing arrangements, yet we are able to isolate crystals of composition [2]2B(1–x)Bex, where x = 0–0.59. The phase transition from the P1 to the P21/c space group occurs at x = 0.1, but the conductivities of the solid solutions are enhanced and the activation energies reduced for values of x = 0–0.25. The molecular packing is driven by the relative concentration of the spin-bearing ([2]2B) and spin-free ([2]2Be) molecules in the crystals, and the extended Huckel theory band structures show that the progressive incorporation of spin-free [2]2Be in the lattice of the [2]2B radical (overall bandwidth, W = 1.4 eV, in the pure compound) leads to very strong n...

17 citations

Journal ArticleDOI
TL;DR: In this paper, a new metallic vdW ferromagnets, Fe5-xGe2Te2 or FG2T, was successfully synthesized and fully characterized, which is a metal that orders ferromagnetically with a very sharp transition at 250 K (bulk and single crystal thin flakes) and shows large PMA, as found by both experimental and computational studies.
Abstract: Layered van der Waals (vdW) crystals with intrinsic magnetic properties such as high Curie temperature (TC) and large perpendicular magnetic anisotropy (PMA) are key to the development and application of spintronic devices. The ferromagnetic vdW metal Fe3-xGeTe2 (FGT) has gained prominence recently due to its high TC (220 K) and strong PMA. Here, we introduce a new metallic vdW ferromagnets, Fe5-xGe2Te2 or FG2T, which was successfully synthesized and fully characterized. FG2T is a metal that orders ferromagnetically with a very sharp transition at 250 K (bulk and single crystal thin flakes) and shows large PMA, as found by both experimental and computational studies. This work enables novel heterostructure devices with near room temperature capabilities by using FG2T as spin injector.

12 citations


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TL;DR: In this paper, it was shown that the itinerant ferromagnetic order persists in Fe3GeTe2 down to the monolayer with an out-of-plane magnetocrystalline anisotropy.
Abstract: Materials research has driven the development of modern nano-electronic devices. In particular, research in magnetic thin films has revolutionized the development of spintronic devices1,2 because identifying new magnetic materials is key to better device performance and design. Van der Waals crystals retain their chemical stability and structural integrity down to the monolayer and, being atomically thin, are readily tuned by various kinds of gate modulation3,4. Recent experiments have demonstrated that it is possible to obtain two-dimensional ferromagnetic order in insulating Cr2Ge2Te6 (ref. 5) and CrI3 (ref. 6) at low temperatures. Here we develop a device fabrication technique and isolate monolayers from the layered metallic magnet Fe3GeTe2 to study magnetotransport. We find that the itinerant ferromagnetism persists in Fe3GeTe2 down to the monolayer with an out-of-plane magnetocrystalline anisotropy. The ferromagnetic transition temperature, Tc, is suppressed relative to the bulk Tc of 205 kelvin in pristine Fe3GeTe2 thin flakes. An ionic gate, however, raises Tc to room temperature, much higher than the bulk Tc. The gate-tunable room-temperature ferromagnetism in two-dimensional Fe3GeTe2 opens up opportunities for potential voltage-controlled magnetoelectronics7-11 based on atomically thin van der Waals crystals.

1,017 citations

Journal ArticleDOI
TL;DR: In this article, an ultrathin epitaxial graphite graphite (NPEG) was grown by thermal decomposition on the (0001) surface of 6H-SiC and characterized by surface-science techniques.
Abstract: We have produced ultrathin epitaxial graphite films which show remarkable 2D electron gas (2DEG) behavior. The films, composed of typically 3 graphene sheets, were grown by thermal decomposition on the (0001) surface of 6H-SiC, and characterized by surface-science techniques. The low-temperature conductance spans a range of localization regimes according to the structural state (square resistance 1.5 kOhm to 225 kOhm at 4 K, with positive magnetoconductance). Low resistance samples show characteristics of weak-localization in two dimensions, from which we estimate elastic and inelastic mean free paths. At low field, the Hall resistance is linear up to 4.5 T, which is well-explained by n-type carriers of density 10^{12} cm^{-2} per graphene sheet. The most highly-ordered sample exhibits Shubnikov - de Haas oscillations which correspond to nonlinearities observed in the Hall resistance, indicating a potential new quantum Hall system. We show that the high-mobility films can be patterned via conventional lithographic techniques, and we demonstrate modulation of the film conductance using a top-gate electrode. These key elements suggest electronic device applications based on nano-patterned epitaxial graphene (NPEG), with the potential for large-scale integration.

290 citations

Journal ArticleDOI
Guojian Yang1, Yu-Mo Zhang1, Yiru Cai1, Baige Yang1, Chang Gu1, Sean Xiao-An Zhang1 
TL;DR: This review highlights the latest exciting results regarding the design and application of new and unique nanomaterials for each layer of ECDs and the remaining challenges and corresponding strategies of this field are proposed.
Abstract: Electrochromic devices (ECDs) have been regarded as promising candidates for energy-saving smart windows, next-generation displays and wearable electronics due to their significant benefits of simple and adjustable structures, low power consumption, flexible and stretchable features, and eye-friendly modes for displays. However, there are many existing issues waiting to be solved such as durability, reversibility and inadequate switching performances. These insurmountable technical bottlenecks significantly slow down the commercialization of next-generation ECDs. Nanomaterials with superior active reaction surface area have played indispensable roles in optimizing heterogeneous electron transfer and homogeneous ion transfer for ECDs and other optoelectronic devices. In recent years, with the joint efforts of various outstanding research teams, new kinds and methods for nanomaterials to fabricate ECDs with excellent performances have been rapidly developing. This review highlights the latest exciting results regarding the design and application of new and unique nanomaterials for each layer of ECDs. Meanwhile, the structures, mechanisms, features and preparation of the reported nanomaterials to improve the electrochromic properties have been discussed in detail. In addition, the remaining challenges and corresponding strategies of this field are also proposed. Hopefully, this review can inspire more and more researchers to enrich the nanomaterials for ECDs and other related fields to overcome faced technical barriers by innovative means and promote industrialization of ECDs and other optoelectronic technologies.

140 citations

Journal ArticleDOI
TL;DR: In this article, the authors discuss recent advances in the transfer of as-grown CVD graphene to target substrates, including transfer with a support layer, transfer without support layer and direct growth on target substrate.
Abstract: The unique two-dimensional structure and outstanding electronic, thermal, and mechanical properties of graphene have attracted the interest of scientists and engineers from various fields. The first step in translating the excellent properties of graphene into practical applications is the preparation of large area, continuous graphene films. Chemical vapour deposition (CVD) graphene has received increasing attention because it provides access to large-area, uniform, and continuous films of high quality. However, current CVD synthetic techniques utilize metal substrates (Cu or Ni) to catalyse the growth of graphene and post-growth transfer of the graphene film to a substrate of interest is critical for most applications such as electronics, photonics, and spintronics. Here we discuss recent advances in the transfer of as-grown CVD graphene to target substrates. The methods that afford CVD graphene on a target substrate are summarized under three categories: transfer with a support layer, transfer without a support layer, and direct growth on target substrates. At present the first two groups dominate the field and research efforts are directed towards refining the choice of the support layer. The support layer plays a vital role in the transfer process because it has direct contact with the atomically thin graphene surface, affecting its properties and determining the quality of the transferred graphene.

110 citations