Insights into the Early Growth of Homogeneous Single-Layer Graphene over Ni–Mo Binary Substrates

Rü,mmeli, Mark H.,Zeng, Mengqi,Melkhanova, Svetlana,Gorantla, Sandeep,Bachmatiuk, Alicja,Fu, Lei,Yan, Chenglin,Oswald, Steffen,Mendes, Rafael G.,Makarov, Denys,Schmidt, Oliver,Eckert, Ju&#x308,r American Chemical Society 2013 Chemistry of materials Vol.25 No.19

<P>The employment of Ni–Mo films has recently been shown to yield strictly homogeneous single-layer graphene. In this study, we systematically investigate the different stages of nucleation and growth of graphene over Ni–Mo layers. The studies reveal that the Ni film breaks up and diffuses into the underlying Mo foil, forming a Ni–Mo intermetallic. Nucleation only occurs from Ni sites, and thus, the nucleation density can be controlled by the Ni film thickness. Both nucleation and growth of the graphene are shown to be susceptible to very efficient self-termination processes to the formation of molybdenum carbide, and this guarantees the formation of large area graphene that consists <I>entirely</I> of monolayer graphene.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2013/cmatex.2013.25.issue-19/cm4020783/production/images/medium/cm-2013-020783_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm4020783'>ACS Electronic Supporting Info</A></P>

On the Role of Vapor Trapping for Chemical Vapor Deposition (CVD) Grown Graphene over Copper

Rü,mmeli, Mark H.,Gorantla, Sandeep,Bachmatiuk, Alicja,Phieler, Johannes,Geißler, Nicole,Ibrahim, Imad,Pang, Jinbo,Eckert, Ju&#x308,rgen American Chemical Society 2013 Chemistry of materials Vol.25 No.24

<P>The role of sample chamber configuration for the chemical vapor deposition of graphene over copper was investigated in detail. A configuration in which the gas flow is unrestricted was shown to lead to graphene with an inhomogeneous number of layers (between 1 and 3). An alternative configuration in which one end of the inner tube (in which the sample is placed) is closed so as to restrict the gas flow leads a homogeneous graphene layer number. Depending on the sample placement, either homogeneous monolayer or bilayer graphene is obtained. Under our growth conditions, the data show local conditions play a role on layer homogeneity such that under quasi-static equilibrium gas conditions not only is the layer number stabilized, but the quality of the graphene improves. In short, our data suggests vapor trapping can trap Cu species leading to higher carbon concentrations, which determines layer number and improved decomposition of the carbon feedstock (CH<SUB>4</SUB>), which leads to higher quality graphene.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2013/cmatex.2013.25.issue-24/cm401669k/production/images/medium/cm-2013-01669k_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm401669k'>ACS Electronic Supporting Info</A></P>

Room Temperature in Situ Growth of B/BO_<i>x</i> Nanowires and BO_<i>x</i> Nanotubes

Gonzalez-Martinez, Ignacio G.,Gorantla, Sandeep M.,Bachmatiuk, Alicja,Bezugly, Viktor,Zhao, Jiong,Gemming, Thomas,Kunstmann, Jens,Eckert, Ju&#x308,rgen,Cuniberti, Gianaurelio,Rü,mmeli, Mark H. American Chemical Society 2014 NANO LETTERS Vol.14 No.2

<P>Despite significant advances in the synthesis of nanostructures, our understanding of the growth mechanisms of nanowires and nanotubes grown from catalyst particles remains limited. In this study we demonstrate a straightforward route to grow coaxial amorphous B/BO<SUB><I>x</I></SUB> nanowires and BO<SUB><I>x</I></SUB> nanotubes using gold catalyst particles inside a transmission electron microscope at room temperature without the need of any specialized or expensive accessories. Exceedingly high growth rates (over 7 μm/min) are found for the coaxial nanowires, and this is attributed to the highly efficient diffusion of B species along the surface of a nanowire by electrostatic repulsion. On the other hand the O species are shown to be relevant to activate the gold catalysts, and this can occur through volatile O species. The technique could be further developed to study the growth of other nanostructures and holds promise for the room temperature growth of nanostructures as a whole.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2014/nalefd.2014.14.issue-2/nl404147r/production/images/medium/nl-2013-04147r_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl404147r'>ACS Electronic Supporting Info</A></P>

Few-Layer Graphene Shells and Nonmagnetic Encapsulates: A Versatile and Nontoxic Carbon Nanomaterial

Bachmatiuk, Alicja,Mendes, Rafael G.,Hirsch, Cordula,Ja&#x308,hne, Carsten,Lohe, Martin R.,Grothe, Julia,Kaskel, Stefan,Fu, Lei,Klingeler, Rü,diger,Eckert, Ju&#x308,rgen,Wick, Peter,Rü,mme American Chemical Society 2013 ACS NANO Vol.7 No.12

<P>In this work a simple and scalable approach to coat nonmagnetic nanoparticles with few-layer graphene is presented. In addition, the easy processing of such nanoparticles to remove their core, leaving only the 3D graphene nanoshell, is demonstrated. The samples are comprehensively characterized, as are their versatility in terms of functionalization and as a material for electrochemical storage. Indeed, these 3D graphene nanostructures are easily functionalized much as is found with carbon nanotubes and planar graphene. Electrochemical investigations indicate these nanostructures are promising for stable long-life battery applications. Finally, initial toxicological investigations suggest no acute health risk from these 3D graphene nanostructures.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2013/ancac3.2013.7.issue-12/nn4051562/production/images/medium/nn-2013-051562_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn4051562'>ACS Electronic Supporting Info</A></P>

Optical-Power Dependence of Gain, Noise, and Bandwidth Characteristics for 850-nm CMOS Silicon Avalanche Photodetectors

Myung-Jae Lee,Rü,cker, Holger,Woo-Young Choi IEEE 2014 IEEE journal of selected topics in quantum electro Vol.20 No.6

<P>We investigate the effects of incident optical powers on the performance of 850-nm silicon avalanche photodetectors (APDs) realized with P<SUP>+</SUP>/N-well junctions in standard CMOS technology. The current-voltage characteristics, responsivities, avalanche gains, noise power spectral densities, excess noise factors, electrical reflection coefficients, and photodetection frequency responses of the fabricated CMOS-APD are measured for different incident optical powers. In addition, the photodetection frequency responses at different incident optical powers are modeled with equivalent circuits and the influence of the optical power on photodetection bandwidth is analyzed. From these, we show that, near the avalanche breakdown voltage, the CMOS-APD avalanche gain and excess noise factor increase and photodetection bandwidth decreases with decreasing incident optical power. These results should be very useful for realizing high-performance CMOS integrated optical receivers for various optical-interconnect applications.</P>

Template-Based Preparation of Free-Standing Semiconducting Polymeric Nanorod Arrays on Conductive Substrates

Haberkorn, Niko,Weber, Stefan A. L.,Berger, Rü,diger,Theato, Patrick American Chemical Society 2010 ACS APPLIED MATERIALS & INTERFACES Vol.2 No.6

<P>We describe the synthesis and characterization of a cross-linkable siloxane-derivatized tetraphenylbenzidine (DTMS-TPD), which was used for the fabrication of semiconducting highly ordered nanorod arrays on conductive indium tin oxide or Pt-coated substrates. The stepwise process allow fabricating of macroscopic areas of well-ordered free-standing nanorod arrays, which feature a high resistance against organic solvents, semiconducting properties and a good adhesion to the substrate. Thin films of the TPD derivate with good hole-conducting properties could be prepared by cross-linking and covalently attaching to hydroxylated substrates utilizing an initiator-free thermal curing at 160 °C. The nanorod arrays composed of cross-linked DTMS-TPD were fabricated by an anodic aluminum oxide (AAO) template approach. Furthermore, the nanorod arrays were investigated by a recently introduced method allowing to probe local conductivity on fragile structures. It revealed that more than 98% of the nanorods exhibit electrical conductance and consequently feature a good electrical contact to the substrate. The prepared nanorod arrays have the potential to find application in the fabrication of multilayered device architectures for building well-ordered bulk-heterojunction solar cells.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2010/aamick.2010.2.issue-6/am100085t/production/images/medium/am-2010-00085t_0002.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am100085t'>ACS Electronic Supporting Info</A></P>

A Growth Mechanism for Free-Standing Vertical Graphene

Zhao, Jiong,Shaygan, Mehrdad,Eckert, Ju&#x308,rgen,Meyyappan, M.,Rü,mmeli, Mark H. American Chemical Society 2014 NANO LETTERS Vol.14 No.6

<P>We propose a detailed mechanism for the growth of vertical graphene by plasma-enhanced vapor deposition. Different steps during growth including nucleation, growth, and completion of the free-standing two-dimensional structures are characterized and analyzed by transmission electron microscopy. The nucleation of vertical graphene growth is either from the buffer layer or from the surface of carbon onions. A continuum model based on the surface diffusion and moving boundary (mass flow) is developed to describe the intermediate states of the steps and the edges of graphene. The experimentally observed convergence tendency of the steps near the top edge can be explained by this model. We also observed the closure of the top edges that can possibly stop the growth. This two-dimensional vertical growth follows a self-nucleated, step-flow mode, explained for the first time.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2014/nalefd.2014.14.issue-6/nl501039c/production/images/medium/nl-2014-01039c_0007.gif'></P>

Nanosized Carbon Black Combined with Ni₂O₃ as “Universal” Catalysts for Synergistically Catalyzing Carbonization of Polyolefin Wastes to Synthesize Carbon Nanotubes and Application for Supercapacitors

Wen, Xin,Chen, Xuecheng,Tian, Nana,Gong, Jiang,Liu, Jie,Rü,mmeli, Mark H.,Chu, Paul K.,Mijiwska, Ewa,Tang, Tao American Chemical Society 2014 Environmental science & technology Vol.48 No.7

<P>The catalytic carbonization of polyolefin materials to synthesize carbon nanotubes (CNTs) is a promising strategy for the processing and recycling of plastic wastes, but this approach is generally limited due to the selectivity of catalysts and the difficulties in separating the polyolefin mixture. In this study, the influence of nanosized carbon black (CB) and Ni<SUB>2</SUB>O<SUB>3</SUB> as a novel combined catalyst system on catalyzing carbonization of polypropylene (PP), polyethylene (PE), polystyrene (PS) and their blends was investigated. We showed that this combination was efficient to promote the carbonization of these polymers to produce CNTs with high yields and of good quality. Catalytic pyrolysis and model carbonization experiments indicated that the carbonization mechanism was attributed to the synergistic effect of the combined catalysts rendered by CB and Ni<SUB>2</SUB>O<SUB>3</SUB>: CB catalyzed the degradation of PP, PE, and PS to selectively produce more aromatic compounds, which were subsequently dehydrogenated and reassembled into CNTs via the catalytic action of CB together with Ni particles. Moreover, the performance of the synthesized CNTs as the electrode of supercapacitor was investigated. The supercapacitor displayed a high specific capacitance as compared to supercapacitors using commercial CNTs and CB. This difference was attributed to the relatively larger specific surface areas of our synthetic CNTs and their more oxygen-containing groups.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/esthag/2014/esthag.2014.48.issue-7/es404646e/production/images/medium/es-2013-04646e_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/es404646e'>ACS Electronic Supporting Info</A></P>

Mapping of Local Conductivity Variations on Fragile Nanopillar Arrays by Scanning Conductive Torsion Mode Microscopy

Weber, Stefan A. L.,Haberkorn, Niko,Theato, Patrick,Berger, Rü,diger American Chemical Society 2010 NANO LETTERS Vol.10 No.4

<P>A gentle method that combines torsion mode topography imaging with conductive scanning force microscopy is presented. By applying an electrical bias voltage between tip and sample surface, changes in the local sample conductivity can be mapped. The topography and local conductivity variations on fragile free-standing nanopillar arrays were investigated. These samples were fabricated by an anodized aluminum oxide template process using a thermally cross-linked triphenylamine-derivate semicondcutor. The nanoscale characterization method is shown to be nondestructive. Individual nanopillars were clearly resolved in topography and current images that were recorded simultaneously. Local current−voltage characteristics suggest a space-charge limited conduction in the semiconducting nanopillars.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2010/nalefd.2010.10.issue-4/nl9035274/production/images/medium/nl-2009-035274_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl9035274'>ACS Electronic Supporting Info</A></P>

Quantum Confinement Induced Excitonic Mechanism in Zinc-Oxide-Nanowalled Microrod Arrays for UV-Vis Surface-Enhanced Raman Scattering

Kim, Jayeong,Glier, Tomke E.,Grimm-Lebsanft, Benjamin,Buchenau, So&#x308,ren,Teubner, Melissa,Biebl, Florian,Kim, Nam-Jung,Kim, Heehun,Yi, Gyu-Chul,Rü,bhausen, Michael,Yoon, Seokhyun American Chemical Society 2019 The Journal of Physical Chemistry Part C Vol.123 No.40

<P>We studied surface-enhanced Raman spectroscopy (SERS) in 4-mercaptopyridine (4-Mpy) deposited on zinc oxide (ZnO) nanostructures, by using resonance Raman scattering covering a range of incident photon energies from 1.7 to 5.7 eV. We investigated all primary routes of the energy-specific resonances that are associated with the electronic transitions between the ZnO valence band (VB) to the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) to the ZnO conduction band (CB), respectively. Two resonances at 5.55 and 5.15 eV in the ultraviolet (UV) spectral range can be associated with transitions into the CB and most importantly into an excitonic-related state below the ZnO CB, respectively. The energy difference between the UV resonances is 0.4 eV corresponding to the excitonic binding energy as a result of excitonic quantum confinement in the 10-20 nm thick ZnO nanowalls. The observed excitonic SERS resonance enhancement of the ring-breathing mode of 4-Mpy is about 15 times stronger than for the VB resonance observed at 2.43 eV and free of luminescence background. Hence, we outline new pathways of improving the detectability of molecules by chemical SERS due to tuning of the quantum confinement in the excitonic resonance enhancement.</P> [FIG OMISSION]</BR>