Workshop on characterization of semiconductor nanostructures; the

MP0901 Designing novel materials for nanodevices:

From Theory to Practice

Workshop on characterization of semiconductor nanostructures; the role of defects

2 - 4. 12. 2013 Rudjer Boskovic Institute

Zagreb, Croatia

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List of participants

Name Email 1 Carla Bittencourt [email protected] 2 Polona Umek [email protected] 3 Jose Coutinho [email protected] 4 Mustafa Culha [email protected] 5 Alberto Zobelli [email protected] 6 Alexandra Carvalho [email protected] 7 Katarzyna Grochowska [email protected] 8 Benjamin Hourahine [email protected] 9 Maria Gomes [email protected] 10 Mattia Scardamaglia [email protected] 11 Filiberto Ricciardella [email protected] 12 Carlos Silva [email protected] 13 Chris Ewels [email protected] 14 Jan Grym [email protected] 15 Peter Guttman [email protected] 16 Claudia Struzzi [email protected] 17 Ansgar Donner [email protected] 18 Hartmut Bracht [email protected] 19 Predrag Lazic [email protected] 20 Marko Karlusic [email protected] 21 Igor Djerdj [email protected] 22 Natasa Sijakovic Vujicic [email protected] 23 Robert Slunjski [email protected] 24 Zoran Eres [email protected] 25 Jordi Sancho Parramon [email protected] 26 Vesna Janicki [email protected] 27 Andreja Gajovic [email protected] 28 Ivana Capan [email protected] 29 Martin Loncaric [email protected] 30 Davor Gracin [email protected] 31 Branko Pivac [email protected] 32 Zoran Eres [email protected] 33 Jasna Dasovic [email protected] 34 Dijana Žilić [email protected] 35 Milivoj Plodinec [email protected] 36 Tihomir Knezevic [email protected]

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Timetable

02.12.2013 03.12.2013 04.12.2013 09:00-09.15 Opening 09:15-10:00 Jose Coutinho: Resonant

electrical levels from adsorbed molecules to improve the electron mobility of Si-nanocrystal thin films

Predrag Lazić: Adsorption and intercalation of Cs atoms on epitaxial graphene on Ir(111)

Benjamin Hourahine: Dislocated semiconductor nano-columns

Coffee 10:30-11:30 Peter Guttmann: X-ray

microscopy for in operando analysis of semiconductor defects

Alexandra Carvalho: Defects in WS2 and MoS2 monolayers

Ansgar Donner: Properties of Sol-Gel derived Ge nanocrystals in thin SiO2 layers

11:30-12:00 Polona Umek: Morphology and Oxidation States of Manganese in TiO2 Nanostructures Derived From Titanate Precursors Doped with Mn2+

Mattia Scardamaglia: Spectromicroscopy investigation of highly nitrogen-doped suspended graphene flakes: annealing effects and selectivity of sp2 nitrogen species

Davor Gracin: Estimation of defect concentration in a-nc-Si:H by photo deflection and photocurrent spectroscopy

12:00-12:30 Andreja Gajovic: Ag-functionalized titanate nanostructures for photo-catalytic application

Nataša Šijaković Vuji čić: Liquid Crystalline Supramolecular Gels: New Soft Nanomaterials

Lunch 13:30-14:30 Mustafa Culha:

Development of Boron Nitride Nanotube Synthesis Methods

Jordi Sancho Parramon: Ellipsometric characterization of thin films containing metal nanoparticles

14:30-15:00 Alberto Zobelli : Excitons and stacking order in h-BN

Jan Grym: Heteroepitaxial growth of lattice mismatched layers on porous substrates

15:00-15:30 Igor Djerdj : Electron microscopy study of one-dimensional functional materials synthesized by a nonaqueous route

Carlos Silva: Optical properties of organic-inorganic hybrid nanocomposites doped with CdS nanoparticles

Coffee 16:00-16:30 Marko Karlusic : Graphene

modifications using swift heavy ions

Maria Gomes: Surface Plasmon-Enhanced Optical Properties of SiC/Ag/SiC Nanostructures

16:30-17:00 Filiberto Ricciardella : The role of the edge defects in chemically exfoliated graphene for NO2 detection

Katarzyna Grochowska: Morphology and optical properties of defect-like quasi-regular Au nanoarrays

17:00-17:30 Zoran Ereš: Graphene based electromagnetic devices

Vesna Janicki: Optical coatings with metal island films

17:30-18:00 Robert Slunjski: Transport properties of Ge nano-crystals in SiO2 matrix

Dijana Žili ć: Magnetic properties of transition metal complexes as revealed by HF-ESR

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Resonant electrical levels from adsorbed molecules to improve the electron mobility of Si-nanocrystal thin films

J. Coutinho1, R. N. Pereira1,2, T. A. Oliveira1, M. J. Rayson3, P. R. Briddon4

1 Department of Physics and I3N, University of Aveiro, Campus Universitário de Santiago, 3810-193

Aveiro, Portugal 2 Walter Schottky Institut, Technische Universität München, Am Coulombwall 4, 85748 Garching,

Germany 3 Department of Engineering Sciences and Mathematics, Luleå University of Technology, Luleå S-

97187, Sweden 4 School of Electrical, Electronic and Computer Engineering, Newcastle University, Newcastle Upon

Tyne NE1 7RU, United Kingdom The future exploitation of the exceptional properties of nanocrystal (NC) thin films deposited from liquid dispersions relies upon our ability to produce films with improved electrical properties by simple and inexpensive means. At the physics level, when such thin films are made of NCs where the lowest unoccupied and highest occupied levels are localized at their core, they suffer from low inter-NC electronic coupling, and therefore show low electrical conductivity. We demonstrate that the electron conduction of solution-processed Si-NC films can be enhanced by up to two orders of magnitude, without the need of post-deposition treatments, via doping of film forming NC dispersions with a small amount of tetrafluoro- tetracyanoquinodimethane (F4-TCNQ). This effect is investigated by means of density functional theoretical calculations on infinite Si-NC/F4-TCNQ superlattices. We demonstrate that although the molecule produces an acceptor state edging the valence band top of the Si-NC superlattice, strong correlation interactions make its thermal ionization at room temperature unlikely. On the other hand, upon electron injection the molecule is able to accept up to two electrons. These acceptor states are suggested to act as additional channels by improving the inter-NP coupling, and therefore enhance the electrical performance of the films.

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X-ray microscopy for in operando analysis of semiconductor defects

P. Guttmann, S. Rehbein, S. Werner, G. Schneider

Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Institute Soft Matter and Functional

Materials, Albert-Einstein-Str. 15, 12489 Berlin, Germany Synchrotron based X-ray microscopy allows spectroscopic analysis of materials due to its energy tuneability and therefore, the determination of electronic energy states [1,2]. By this, lattice defects in small semiconductor structures can be localized with the high spatial resolution of the X-ray microscope. In addition, soft X-rays have a higher penetration depth than electrons enabling studies of buried interconnects. Therefore, X-ray microscopy is a complementary method to investigate defects in semiconductors. The benefits of an increased penetration depth by using soft X-ray microscopy were already demonstrated by in situ electromigration studies [3,4] as well as stress-migration analysis of advanced Back-end-of-Line (BeoL) integrated circuits. In the latter case 3-D localization of the generated voids was achieved due to the tomographic capabilities of the HZB X-ray microscope at the BESSY II electron storage ring [5]. In this talk results of these studies will be presented. Additionally, recent results of studies on small nanostructures for semiconductor devices are shown [6-8]. Future in-operando analysis of devices will be discussed. [1] P. Guttmann, C. Bittencourt, S. Rehbein, P. Umek, X. Ke, G. Van Tendeloo, C.P. Ewels, G. Schneider: Nanoscale spectroscopy with polarized X-rays by NEXAFS-TXM, Nature Photonics 6 (2012), 25-29, DOI:10.1038/nphoton.2011.268 [2] C. Bittencourt, P. Krüger, M.J. Lagos, X. Ke, G. Van Tendeloo, C. Ewels, P. Umek, P. Guttmann: Towards atomic resolution in sodium titanate nanotubes using near-edge X-ray absorption fine-structure spectromicroscopy combined with multichannel multiple-scattering calculations, Beilstein J. Nanotechnol. 3 (2012), 789-797, DOI: 10.3762/bjnano.3.88 [3] G. Schneider, S. Rudolph, A.M. Meyer, E. Zschech, P. Guttmann: X-ray microscopy: A powerful tool for electromigration studies in modern ICs, Future Fab International 19 (2005), 115-117 [4] G. Schneider, P. Guttmann, S. Rudolph, S. Heim, S. Rehbein, M.A. Meyer, E. Zschech: X-ray Microscopy Studies of Electromigration in Advanced Copper Interconnects, in: Stress-Induced Phenomena in Metallization: 8th International Workshop on Stress-Induced Phenomena in Metallization (Eds.: E. Zschech, K. Maex, P.S. Ho, H. Kawasaki, T. Nakamura), AIP Conference Proceedings 817 (2006), 217-222: Stress Workshop 2005, Dresden, September 12-14, 2005 [5] Ehrenfried Zschech, Rene Huebner, Dmytro Chumakov, Oliver Aubel, Daniel Friedrich, Peter Guttmann, Stefan Heim, Gerd Schneider:Stress-induced phenomena in nanosized copper interconnect structures studied by x-ray and electron microscopy, J. Appl. Phys. 106, 093711 (2009) [6] A.A. El Mel, M. Buffière, N. Bouts, E. Gautron, P.Y. Tessier, K. Henzler, P. Guttmann, S. Konstantinidis, C. Bittencourt, R. Snyders: Growth control, structure, chemical state, and photoresponse of CuO-CdS core-shell heterostructure nanowires, Nanotechnology 24 (2013), 265603 (11pp), DOI: 10.1088/0957-4484/24/26/265603 [7] T. Mönch, P. Guttmann, J. Murawski, C. Elschner, M. Riede, L. Müller-Meskamp, K. Leo: Investigating local (photo-)current and structure of ZnPC:C60 bulk-heterojunctions, Organic Electronics 14 (2013), 2777-2788, DOI: 10.1016/j.orgel.2013.07.031 [8] A. Koehl, H. Wasmund, A. Herpers, P. Guttmann, S. Werner, K. Henzler, H. Du, J. Mayer, R. Waser, R. Dittmann: Evidence for multifilamentary valence changes in resistive switching SrTiO3 devices detected by transmission X-ray microscopy, accepted for publication in APL Materials (2013)

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Morphology and Oxidation States of Manganese in TiO2 Nanostructures Derived From Titanate Precursors Doped

with Mn2+

Polona Umek1, Carla Bittencourt2, Alexandre Gloter3, Peter Guttmann4, Srečo D. Škapin1 and Denis Arčon1,5

1Jožef Stefan Institute, Jamova cesta 39, SI-1000 Ljubljana, Slovenia

2Chimie des Interactions Plasma Surface, CIRMAP, University of Mons, 23 Place du Parc, B-7000 Mons, Belgium

3Laboratoire de Physiques des Solides, Université Paris Sud, CNRS UMR 8502, F-91405 Orsay, France

4Helmholtz-Zentrum für Materialien und Energie GmbH, Institute for Soft Matter and Functional Materials, Albert-Einstein-Str. 15, 12489 Berlin, Germany

5Faculty of Mathematics and Physics, University of Ljubljana, Jadranska cesta 19, SI-1000 Ljubljana, Slovenia

Nanostructured alkali titanates are versatile materials that possess a variety of physical and chemical properties that can be tailored allowing their use in many application including catalysis and lithium ion batteries. Slight changes in their chemical composition, which can be achieved via ion-exchange process or in-situ doping, can lead to completely different physical and/or chemical properties. Of special interest is doping with transition metal ions and transformation of doped titanates to TiO2 nanostructures. In this presentation the results of in-situ doping of sodium titanate nanoribbons and nanotubes with Mn2+ ions will be presented. Under hydrothermal conditions was anatase TiO2 doped with Mn2+ in alkaline media transformed to Mn2+-doped sodium titanate nanostructures. By an ion-exchange process Na+ ions were exchanged with protons and by subsequent heat treatment between 400700 °C protonated titanates doped with Mn2+ were directly transformed into TiO2 nanostructures doped with manganese ions. In order to shed light on the basic mechanisms behind the doping of titanates, this work aims at determining the position of manganese ions in the titanate/TiO2 structures when the doping is performed via in-situ approach. More specifically we will try to address the following questions: • does the presence of Mn2+ ions in the reaction mixture has any impact on the formed morphologies? • in-situ doping: do the manganese ions accumulate between the titanate layers or do they exchange with the titanium atoms in the TiO6 octahedra? • what happens to the local environment and oxidation state of Mn2+ ions during calcination of protonated titanate nanostructures? The prepared sodium titanate nanostructures doped with Mn2+ ions and TiO2 nanostructures doped with manganese ions derived from protonated titanates were characterized with several characterization techniques: SEM, TEM, XRD, HAADF-STEM in combination with EELS, XPS, NEXAFS and EPR.

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Ag-functionalized titanate nanostructures for photo-

catalytic application

Milivoj Plodinec1, Andreja Gajovi ć1, Gregor Jakša2, Kristina Žagar2, Miran Čeh2 1 Ruñer Bošković Institute, Bijenička 54, HR-1002 Zagreb, Croatia

2 Institute Jožef Stefan, Jamova 39, 1000 Ljubljana, Slovenia

TiO2-based nanostructures have been extensively investigated materials over the past two decades, because of their promising physical and chemical properties, such as a high specific surface area, the low costs of synthesis, a high photo-activity and environmental stability. Because of these properties the titania nanostructures can be used for photocatalysis, in solar cells, sensors, and in the cosmetics industry. Since TiO2 has a relatively large bandgap of 3.2 eV for anatase and 3 eV for rutile, both crystal forms are photo active only under UV light irradiation. Thus, one of the key parameters essential to increase the photocatalytic activity in the visible and near-IR regions is to optimize the bandgap of TiO2-based materials. The aim of the work is to study how annealing in a reducing atmosphere of titanate nanotubes (TiNT) and Ag decorated titanate nanotubes (TiNT@Ag) influenced on their structure, morphology, phase transitions, UV-ViS-NIR absorbance and photocatalytic activity. Undoped titanate nanotubes (TiNT) and silver-doped titanate nanotubes (TiNT@Ag) were synthesized using the hydrothermal method. In the doped nanotubes the silver particles were obtained by the photoreduction of AgNO3 under UV light. For the structural characterization of the titanate nanotubes we used conventional and analytical transmission electron microscopy (TEM) techniques, X-ray diffraction (XRD) and Raman spectroscopy. The silver-doped titanate nanotubes were additionally studied by X-ray photo-electron spectroscopy (XPS) with the aim to investigate the surface chemistry. Using UV-ViS-NIR spectroscopy we studied the photocatalytic activity on caffeine for the TiNT and TiNT@Ag samples that were previously heat treated at high-temperature of 550°C in a hydrogen atmosphere. An increase of photocatalytic activity after a heat treatment in a reducing atmosphere was observed in the TiNT and TiNT@Ag (Fig 1). We found that the hydrogenated TiNT@Ag samples had a two-times higher photodegradation impact on the caffeine than the TiNT samples, which is a consequence of the increased absorption of visible light (Fig 2) and the synergetic effects between the silver and the TiO2 nanoparticles that increase the efficiency of the formation of electron-hole pairs and the charge transfer to the surface of the nanoparticles.

0 20 40 60 80 100 120

0.0

0.2

0.4

0.6

0.8

1.0

C/C

0

t(min)

TiNT@Ag - HA TiNT - HA TiNT@Ag

Figure 1: Time-dependent photo-degradation of caffeine stimulated by solar irradiation.

Figure 2: UV-ViS-NIR spectra of TiNT@Ag before and TiNT@Ag-HA after annealing. TEM images of nanostructures are shown as insets.

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Development of Boron Nitride Nanotube Synthesis

Methods

Şaban Kalay, Zehra Yilmaz and Mustafa Çulha*

*Department of Genetics and Bioengineering, Yeditepe University, Atasehir, 34755 Istanbul,

Turkey

Boron nitride nanotubes (BNNTs) known as the structural analogues of carbon nanotubes (CNTs) are more superior than CNTs due to their robust structure that resists to high temperature and harsh chemical conditions1, high hydrogen storage capacity2 and electronic properties. The BNNTs were first time synthesized in 1995 with arc-discharge method by Chopra et. al3. Recently several synthesis methods such as arc-discharge, chemical vapor deposition (CVD) or laser ablation using amorphous boron, boric acid, borazine or CNTs as starting materials have been reported. However, all these approaches are far from the desired outcomes such as uniformity, low cost and high yield. In this study, the BNNT were synthesized starting from commodity boron compounds in the presence of ammonium gas and iron (III) oxide catalyst at relatively low temperatures. The B-N and iron were the initial complex during the synthesis, then BNNTs were formed according to base growth mechanism4. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that BNNTs were at uniform structure at 10-30 nm outside diameter and 5 nm wall wideness (Figure 1). The high-resolution transmission electron microscopy (HRTEM) showed a 3.4 Å plane (002) inside of hexagonal boron nitride (h-BN), which proved the single crystalline structure of BNNTs5. A band-gap transition peak at 200 nm in UV/Vis spectrum and E2g band derived from atomic vibration between B and N bond at 1365 cm-1 in Raman spectrum were observed. FTIR spectrum showed in-plane bonding vibration peak of B-N-B at 1327 cm-1 and secondary absorption peak belonging to h-BN at 758 cm-1. In conclusion, a novel BNNT synthesis method has been developed to obtain high yield, economical and pure BNNT. The financial support from The Scientific and Technological Research Council of Turkey (TUBITAK) (Project no: 112M480) is gratefully acknowledged.

Figure1. A-SEM, and B-TEM, C-Electron diffraction images of synthesized BNNTs.

References

1- Golberg et. al. ACS Nano, 4, 2979-2993, 2010.

2-Yürüm et. al. Ind. Eng. Chem, Res. 51, 11341-11347, 2012.

3- Chopra et. al. Science, 269, 1995.

4- Chadderton et. al. Journal of Crystal Growth, 240, 164-169, 2002.

5- Tsai et. al. J. Phys. Chem. C, 113, 14732-14738, 2009.

A B

C

(002)

10 nm 2 µm

9

Excitons and stacking order in h-BN

Alberto Zobelli University Paris Sud, France

Hexagonal boron nitride (h-BN) is one of the most promising candidates for light emitting devices in the far UV region, presenting a single strong excitonic emission at 5.8 eV. However, a single line appears only in extremely pure monocrystals that can hardly be obtained only though complex synthesis processes. Common h-BN samples present more complex emission spectra that have been generally attributed to the presence of structural defects. Despite a large number of experimental studies up to now it was not possible to attribute specific emission features to well identify defective structures. Very recently, the Orsay team has developed a cathodoluminescence detection system integrated within a scanning transmission electron microscope. This unique experimental set up is now able to provide full emission spectra with a resolution as low as few tens of meV associated with an electron probe size of one nanometer. A cathodoluminescence spectrum-image can thus be recorded in parallel with an HAADF image. We present the first nanometric resolved cathodoluminescence on few-layer chemically exfoliated h-BN crystals. We show that emission spectra are strongly inhomogeneus within individual flakes. In particular light emission in the band gap energy region presents a high spatial localization, typically less than100 nm. However emission peaks close to the free exciton line appear in more extended regions. Complementary investigations through high resolution transmission electron microscopy allow to associate these latest additional emission lines with extended crystal deformation such as stacking faults and folds of the planes. Finally by means of ab-initio calculations in the framework of Many Body Perturbation Theory (GW approximation and Bethe-Salpeter equation) we provide an in-depth description of the electronic structure and spectroscopic response of bulk hexagonal boron nitride in the presence of extended morphological modifications. In particular we show that, in a good agreement with the experimental results, additional excitons can be lighten up by symmetry distortions induced by crystal stacking faults.

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Electron microscopy study of one-dimensional functional materials synthesized by a nonaqueous route

Igor Djerdj

Ruñer Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia

Anisotropic nanoparticles such as nanofibers, nanotubes, nanorods, and nanowires are of not only scientific but also technological interest. The anisotropy inherent in these nanomaterials provides unique properties which are expected to be critical to the function and integration of nanoscale devices. Among the different families of functional materials, metal oxides play an outstanding role due to their redox activity. The possibility to change the oxidation state and the stoichiometry provides unique opportunities to tailor the chemical and physical properties. The rapidly growing number of publications in the field of metal oxide synthesis by wet chemical routes suggests that the so-called nonaqueous (or nonhydrolytic) processes are particularly successful for the size- and shape-controlled preparation of colloidal inorganic nanoparticles [1,2]. In this talk, I will present two studied anisotropical low-dimensional systems synthesized by nonaqueous route, whose structural features were elucidated by the usage of electron microscopy. First presented study [3] involves the preparation of lanthanum hydroxide and manganese oxide nanoparticles, based on a nonaqueous sol–gel process involving the reaction of La(OiPr)3 and KMnO4 with organic solvents such as benzyl alcohol, 2-butanone and a 1:1 vol. mixture thereof. The lanthanum manganese oxide system is highly complex and surprising results with respect to product composition and morphology were obtained. In dependence of the reaction parameters, the La(OH)3 nanoparticles undergo a shape transformation from short nanorods with an average aspect ratio of 2.1(Figure 1) to micron-sized nanofibers (average aspect ratio is more than 59.5). Although not directly involved, KMnO4 plays a crucial role in determining the particle morphology of La(OH)3. The reason lies in the fact that KMnO4 is able to oxidize the benzyl alcohol to benzoic acid, which presumably induces the anisotropic particle growth in [0 0 1] direction upon preferential coordination to the ±(1 0 0), ± (0 1 0) and ± (−110) crystal facets. By adjusting the molar La(OiPr)3-to-KMnO4 ratio as well as by using the appropriate solvent mixture it is possible to tailor the morphology, phase purity and microstructure of the La(OH)3 nanoparticles. The second part of the presentation shows a nonaqueous liquid-phase route involving the reaction of vanadium oxychloride with benzyl alcohol leading to the formation of single-crystalline and semiconducting VO1.52(OH)0.77 nanorods with an ellipsoidal morphology, up to 500 nm in length and typically about 100 nm in diameter (Figure 2) [4]. Composition, structure, and morphology were thoroughly analyzed by neutron and synchrotron powder X-ray diffraction as well as by different electron microscopy techniques (SEM, (HR)TEM, EDX, and SAED). The data obtained point to a hollandite-type structure which, unlike other vanadates, contains oxide ions in the channels along the c-axis, with hydrogen atoms attached to the edge-sharing oxygen atoms, forming OH groups. According to structural probes and magnetic measurements (1.94 µB/V), the formal valence of vanadium is +3.81 (V4+/V3+ atomic ratio ≈ 4). The temperature-dependent DC electrical conductivity exhibits Arrhenius-type behavior with a band gap of 0.64 eV. The semiconducting behavior is interpreted in terms of electron hopping between vanadium cations of different valence states (small polaron model). Ab initio density-functional calculations with a local spin density approximation including orbital potential (LSDA + U with an effective U value of 4 eV) have been employed to extract the electronic structure. These calculations propose, on the one hand, that the electronic conductivity is based on electron hopping between neighboring V3+ and

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V4+ sites, and, on the other hand, that the oxide ions in the channels act as electron donors, increasing the fraction of V3+ cations, and thus leading to self-doping. Experimental and simulated electron energy-loss spectroscopy data confirm both the presence of V4+ and the validity of the density-of-states calculation. Temperature-dependent magnetic susceptibility measurements indicate strongly frustrated antiferromagnetic interactions between the vanadium ions. A model involving the charge order of the V3+ sites is proposed to account for the observed formation of the magnetic moment below 25 K.

1. I. Djerdj, D. Arčon, Z. Jagličić, and M. Niederberger, J. Solid State Chem. 181 (2008), 1571-1581. 2. I. Djerdj, G. Garnweitner, D. Arčon, M. Pregelj, Z. Jagličić, and M. Niederberger, J. Mater. Chem. 18 (2008), 5208-5217. 3. I. Djerdj, G. Garnweitner, D.S. Su, and M. Niederberger, J. Solid State Chem. 180 (2007), 2154-2165. 4. I. Djerdj, D. Sheptyakov, F. Gozzo, D. Arčon, R. Nesper, and M. Niederberger, J. Am. Chem. Soc. 130 (2008), 11364-11375.

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Graphene modifications using swift heavy ions

M. Karluši ć a,b), O. Ochedowski b), H. Bukowska b), K. Marinov b), M. Jakšić a), M. Schleberger b)

a) Ruñer Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia b) Fakultät für Physik and CeNIDE, Universität Duisburg-Essen, D-47048 Duisburg, Germany

Since its discovery in 2004, graphene research attracts great attention and its numerous applications are envisaged in the near future [1]. In this contribution, we show how swift heavy ions can be used as a tool for controled modification of graphene on the nanoscale. Very recently, it was demonstrated that passage of swift heavy ions delivered from cyclotron (GANIL, France) at grazing incidence with respect to the graphene results in unzipping and folding of exfoliated graphene [2]. These modifications can be produced in controlled manner since number of pores is determined by ion fluence. Here we show how less energetic swift heavy ions delivered from 6 MV Tandem Van de Graaff accelerator (Ruñer Bošković Institute, Zagreb) can be used for graphene modifications as well. In addition, we present first results on swift heavy ion induced modifications on other 2D materials. [1] K.S. Novoselov et al., A roadmap for graphene, Nature 490 (2012) 192 [2] S. Akcöltekin et al., Unzipping and folding of graphene by swift heavy ions, Appl. Phys. Lett. 98 (2011) 103103

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The role of the edge defects in chemically exfoliated graphene for NO2 detection

Filiberto Ricciardella 1,2, Tiziana Polichetti1, Maria Lucia Miglietta1, Filippo Fedi3, Ettore

Massera1, Nicola Lisi4, Theodoros Dikonimos Makris4 and Girolamo Di Francia1

1ENEA UTTP-MDB Laboratory, R.C. Portici, Piazzale E. Fermi 1, Portici (Naples), I-80055, Italy 2University of Naples ‘Federico II’, Department of Physics, Via Cinthia, I-80126, Naples, Italy 3CNR-Institute for Composite and Biomedical Materials, Piazzale E. Fermi 1, Portici (Naples),

I-80055, Italy 4ENEA UTTMT-SUP Laboratory, R.C. Casaccia, Via Anguillarese 301, I-00123 Rome, Italy

Graphene has been attracting enormous attention in physics and materials science research for both fundamental research and applications, due to its unique and amazing properties. The two-dimensionality and the absence of bulk make graphene particularly suitable to be adopted as sensitive layer for the detection of different gases. Thanks to the high sensitivity, flexibility and easy integrability of graphene with other material, the sensing field has been showing more and more interest. At the same time, the research is involved in pursuing the best trade-off between mass production and quality of the material aimed to match scalability as well as the best performances of the devices. Up to now, the two production methods that present the highest potentiality for scalability seem to be the liquid phase exfoliation (LPE) of graphite and the chemical vapor deposition (CVD) [1]. The main important differences are related to flakes lateral size: the former allows to obtain flakes in the range of few hundred nanometers with high yield in monolayer, the latter permits to grow sheets with surface up to few centimeters square. In the first case, however, so produced graphene film is formed by a huge amount of nanocrystals in which the role of the edges is quite relevant. Herein the role of the edge defects in the analytes detection is investigated through the study of the performances of the graphene-based chemiresistors realized by LPE. To this aim, we prepared colloidal suspensions of graphene by dispersing 2.5 mg/mL of graphite powder (Sigma-Aldrich) in different solvents, such as N-methyl-pyrrolidone (NMP) or 2-propanol (IPA), and sonicating in a low power bath (∼16 W) for different time. Unexfoliated graphite flakes were removed by centrifugation and the top half of the surnatants were collected and characterized by Dynamic Light Scattering technique with a Zetasizer Nano (Malvern Instruments), Raman spectroscopy (Renishaw InVia Reflex) and Transmission Electron Microscope (FEI TECNAI G12 Spirit-Twin). Chemiresistive devices were fabricated by drop-casting some microliters of suspensions onto Al2O3 transducers with interdigitated Au contacts. Devices were mounted in a Gas Sensor Characterization System (Kenosistec) and tested towards 350 ppb of NO2 for 10 min in wet nitrogen with a flow of 500sccm at T=250C and relative humidity of 50%. The normalized conductance reached remarkable values up to 27%, never seen up to now [2, 3]. In order to understand how much the size and the edges of the flakes could affect the interaction between the graphene layers and the gas molecules, the findings described before were compared to those obtained by chemiresistors based on CVD graphene. The devices were realized dipping the alumina substrates into acid solution on which graphene was floating, after the dissolution of the sacrificial copper layer. The chemiresistors were exposed towards the same analytes concentration showing a not appreciable conductance variation whilst the responses became to be significant (17%) when the NO2 concentration was increased to 1 ppm.

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Because of the CVD graphene flake sizes much larger than those of LPE graphene flakes, we inferred that not only the surface could be a crucial task in sensing field but also the edge defects could result to be fundamental to this purpose. References [1] K. S. Novoselov et al.: Nature, 490 (2012) 192-200. [2] G. Lu et al.: ACS Nano, 5 (2011) 1154-1164. [3] A. Serra et al.: Sensors and Actuators B, 161 (2012) 359-365.

15

Adsorption and intercalation of Cs atoms on epitaxial graphene on Ir(111)

Predrag Lazic

Rudjer Boskovic Institute, Croatia

From the experimental studies of surface adsorption of Cs atoms and their intercalation under epitaxial graphene on Ir(111) it is known that both - adsorbed and intercalated phase of Cs atoms coexist. However, adsorbed phase is realized as a diluted superlattice adlayer of Cs atom while intercalated phase is a dense Cs layer. The preference for intercalated phase at large Cs layer densities can not be obtained from the DFT calculations with semilocal (GGA) functionals. Only after the van der Waals interaction is taken into account the agreement with experiment is achieved. From the results of calculations it follows that the main energy contribution responsible for the switching of preference from adsorption to intercalation is the graphene delamination energy from the Ir(111) surface which is dominantly of the van der Waals nature.

16

Defects in WS2 and MoS2 monolayers

Alexandra Carvalho

NUS Graphene Research Centre, Singapore Transition metal dichalcogenide monolayers are promising materials for ultra-scaled electronic applications. Amongst them, MoS_2 and WS_2 have attracted most interest for their stability allied to the semiconductor properties and direct bandgaps of 1.8 and 2.1 eV, respectively. Like three dimensional semiconductors, the properties of MoS_2 and WS_2 are critically affected by the presence of electrically active defects. We used density functional theory calculations to investigate the stability and electronic levels of common defects and impurities, including vacancies, oxygen and silicon.

17

Spectromicroscopy investigation of highly nitrogen-doped suspended graphene flakes: annealing effects and

selectivity of sp2 nitrogen species

Mattia Scardamaglia, Carla Bittencourt

University of Mons, Belgium

Nitrogen doping of both chemical vapour deposition and exfoliated graphene flakes was performed by N+ ion bombardment in ultra high vacuum. A huge nitrogen content (up to 19%) can be reach through this very clean technique with absence of oxygen species in the final product. In particular, this work is the first reporting of nitrogen ion implantation on suspended graphene. The grafting was observed by scanning X-ray photoelectron microscopy which allows to follow the evolution of nitrogen species that are pyridinic, graphitic, and pyrrolic, at different doping stages and annealing temperatures. Variations in the ratio between sp2 nitrogen species (graphitic/pyridinic) was observed for increasing treatment time; annealing effects result in a total quenching of the sp3 component (pyrrolic) and in a decreasing of the pyridinic one, leaving the graphitic nitrogen as the most thermal stable component. The occurrence of graphitic species together with the absence of pyrrolic ones is a fingerprint of the hexagonal graphene lattice.

18

Liquid Crystalline Supramolecular Gels: New Soft Nanomaterials

Nataša Šijaković Vuji čić

Department of Organic Chemistry, Rudjer Boskovic Institute, Bijenicka 54, Zagreb 10000, Croatia

Liquid crystalline (LC) physical gels represent a new type of soft materials that possess induced or enhanced electro-optical, photochemical and electronic properties useful for the construction of supramolecular devices for advanced applications. It has been shown that in the case of liquid crystalline gels an LC phase was gelled playing a role of an ordinary solvent. The latter represent systems of phase segregated structures consisting of a mesogen as a solvent and gelator molecules, each capable of giving a different type of noncovalent supramolecular organization at a specific temperature. The influence of morphology of gel network on crystallization temperature and persistence of nematic phase of liquid crystalline molecules MBBA was investigated. Chiral bisoxalamide gelator 2c shows remarkable gelling capacity of the nematic and smectic B liquid-crystalline phases of trans-4-heptylcyclohexanecarboxylic acid (HCCA). Chiral nematic gel was formed if the gelator is present in amounts higher than 0.55 wt% containing left-handed helical fiber bundles. With lower amounts of 2c, no nematic gel forms, however, nematic to smectic B phase transition triggers instantenous self-assembly of gelator molecules into aligned fibers. The latter liquid crystalline gel system represents an example of controlled self-assembly induced by liquid crystalline phase transition. The ESR spectra revealed that the gelator network confines the HCCA into the domains within the bulk crystalline matrix where the local molecular dynamics is not frozen. It is proposed that nano scale inhomogeneity of molecular organization/packing in LC gels, evidenced by ESR spectroscopy, can be determinable for the physical properties of LC gel nanomaterials. References 1. Nataša Šijaković Vujičić, Zoran Glasovac, Niek Zweep, Jan H. van Esch, Marijana Vinković, Jasminka Popović, Mladen Žinić, Chemistry A European Journal, 2013, 19, 26, 8558-8572. 2. Mladen Andreis, Dejana Carić, Nataša Šijaković Vujičić, Milan Jokić, Mladen Žinić, Marina Kveder, Chemical Physics, 2012, 403, 81-88. 3. Šijaković Vujičić, N., Šepelj, M., Lesac, A., Žinić, M. Tetrahedron Letters 2009, 50, 31, 4430-4434.

19

Ellipsometric characterization of thin films containing metal nanoparticles

Jordi Sancho Parramon


Nanocomposite films consisting of a dielectric matrix with embedded metal nanoparticles show unique optical behavior due to the surface plasmon resonance of particles, with potential applications in solar cells, optical coatings or metamaterials. In order to exploit the use of these composites, it is essential to have an accurate characterization of their optical properties. When the size of particles is much smaller than the wavelength of light, the optical response of composites can be fully described through effective optical constants, that depend on the the optical constants of the mixing phases and their geometrical arrangement. Here we show the potential of spectroscopic ellipsometry as a useful tool for the determination of the optical constants of different kinds of thin films containing metal nanoparticles. It is demonstrated that standard effective medium theories are unable to accurately describe the optical behavior of the nanocomposites. Alternatively, a multiple oscillator model is a realizable alternative for characterization.

20

Heteroepitaxial growth of lattice mismatched layers on porous substrates

Jan Grym

Institute of Photonics and Electronics, Czech Republic

We report on the electrochemical preparation of porous GaAs substrates and discuss specific problems related to their application in epitaxial growth. We demonstrate that InGaAs lattice mismatched layers grown on porous substrates are capable of retaining a significantly larger amount of elastic strain than the layers grown on conventional substrates and that the porous substrates show a high degree of compliance. The pore etching was carried out in an electrochemical cell using a three-electrode configuration. Epitaxial layers of InGaAs with a different composition prepared by metal-organic vapor phase epitaxy were characterized by scanning electron microscopy (SEM), focused ion beam microscopy (FIBM), cross sectional transmission electron microscopy (XTEM), atomic force microscopy (AFM), x-ray diffraction (XRD), and low temperature photoluminescence spectroscopy (PL).

21

Optical properties of organic-inorganic hybrid nanocomposites doped with CdS nanoparticles

Luis F. F. F. Gonçalves(a,b), Carlos J. R. Silva(a), M.Jesus M. Gomes(b)

(a)Department of Chemistry, University of Minho, Braga 4710-057, Portugal

(b)Centre of Physics, University of Minho, Braga 4710-057, Portugal The sol-gel process has been recently used for the synthesis of nanocomposite materials consisting of a large diversity of NPs (semiconductors and metals) dispersed within a hybrid matrix . This process is based on the hydrolysis and condensation reactions of metal alkoxides that lead to the formation of an inorganic network . The fact that this process is carried out at room temperature allows the introduction of organic groups between the nodes of the inorganic network, giving rise to the formation of organic-inorganic hybrid (OIH) materials. In this paper will be presented two different synthesis approaches used for the preparation of OIH gel doped with CdS nanoparticles: single pot and by using previously synthesized CdS colloidal solutions. It was also studied the influence of stabilizing compounds on the optical properties (adsorption, photoluminescence and luminescence decay) of prepared nanocomposites. From the analysis of the optical properties it was observed that the CdS nanoparticles embedded within the prepared nanocomposites, using both methods, show photoluminescence from surface states. It was also confirmed that both synthesis routes allows the synthesis of stable embedded CdS NPs that exhibit quantum size effect.

22

Surface Plasmon-Enhanced Optical Properties of SiC/Ag/SiC Nanostructures

Koppole Kamakshi1 , K.C. Sekhar1, J. Agostinho Moreira2 , O. Conde3, A. Almeida2 and

M.J.M. Gomes1

1University of Minho, Centre of Physics, Braga, 4710-057, Portugal 2IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Departamento de Física e Astronomia,

Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal

3University of Lisbon, Science Fac., Physics Dept. and ICEMS, 1749-016 Lisboa, Portugal

In recent years silicon carbide (SiC) nanostructures have attracted great interest due to their potential applications in the stable emitting blue or ultraviolet light. Original optical properties of SiC nanostructures allowed their various promising applications as light-emitting agents. Unfortunately, despite their higher emission efficiency in comparison with bulk SiC materials, the photoluminescence (PL) intensity of SiC thin films and nanocrystals is very weak. To improve the luminescence intensity of the SiC nanostructures surface plasmon (SP) enhanced light emission has been proposed and become the ‘hot spot’ in the relevant research community. Herein, we report SP-enhanced PL in SiC/ Ag / SiC nanostructures.

Nanostructures of SiC/Ag/SiC with different Ag deposition times were grown using pulsed laser deposition and by the subsequent rapid thermal annealing (RTA) at 600 0C in argon atmosphere for 1 min. Atomic force microscope images show that Ag nanocrystals (NCs) are formed after RTA, and the size of NCs increases with increasing Ag deposition time. Sharp dip observed in the reflectance spectra confirmed the existence of Ag SPs. The infrared transmission spectra of SiC/Ag/SiC showed an intense and broad absorption band at 780 to 800 cm-1 that can be assigned to Si-C stretching vibration mode. Influence of Ag deposition time on the spectral characteristics of SP–enhanced photoluminescence (PL) in SiC films has been investigated. The photoluminescence (PL) enhancement depends on the size of Ag NCs and the maximum PL enhancement by 5.5 times for SiC nanostructures is achieved when the deposition time is 50 sec. Analyses show that the enhancement is due to the strong resonant coupling between SiC and the SP oscillations of the Ag NCs. These findings may widen the applications of the SiC nanostructures in photonics and life sciences.

23

Morphology and optical properties of defect-like quasi-regular Au nanoarrays

Katarzyna Grochowska

The Szewalski Institute of Fluid - Flow Machinery, Polish Academy of Sciences, Poland

Since nearly two decades the noble metal nanostructures evoke much interest due to their unique properties such as the oscillatory nature of the surface modes (plasmons) which enable the resonant enhancement of the incoming electromagnetic fields and its usage for Surface Enhanced Raman Spectroscopy (SERS) or in measurements based on the refractive index changes. Recently, growing interest is also observed in the damping phenomena of Surface Plasmon Resonance (SPR). It follows from literature that the decay mechanisms of the SPR are not sufficiently understood and their description seem not to be clear enough. Opinions on the origin and nature of the damping differ from each other, but it is believed that the main contributions are due to: radiative damping, surface scattering, Landau damping, chemical interface damping (CID) and direct emission of electrons. However, the identification and separation of the damping components represent an unsolved problem which becomes even more serious when the size and shape distributions of real nanoparticle arrays are taken into account. Contrary to the case of intensively investigated single particles and regular patterns of

particle arrays of strictly defined geometry, in this work the quasi-regular structures composed of particles of a shape close to spherical and characterized by inhomogeneous distributions of size and random interparticle distance prepared by Pulsed Laser Annealing (PLA) of thin Au films are studied. The structural and optical properties of those arrays are investigated in dependence on preparation conditions (film thickness, laser energy fluence, pulse number). Parameters of preparation are selected in dependence on initial thickness of the Au film. Moreover, the SPR dephasing time and damping components are derived from the absorbance spectra. The nonradiative damping is deduced to be approximately constant for all structures as the observed resonance energies lay below 2.3 eV. Therefore, the radiation damping is believed to be the most dominant damping mechanism. For the structures the enhancement factors of the optical far field are obtained from the micro-Raman spectra and it is confirmed that semi-regular structures can be successfully used as SERS-based sensors.

24

Optical coatings with metal island films

Vesna Janicki

Rudjer Boskovic Institute, Croatia Metal island films (MIF) can be produced using standard electron beam evaporation technique promoting island growth mode (or Volmer-Weber mode) on dielectric surfaces. MIF consist of a nearly two-dimensional random ensemble of nanometric metal clusters having size and shape distributions that depend on the deposition conditions (substrate temperature, deposition rate). MIF are interesting for their optical properties dominated by absorption due to surface plasmon resonance. Intensity and position of the resonance depends on the kind of metal, size, shape and density of the islands and dielectric constant of the environment. In this way, optical constants of MIF can be easily controlled. Combining absorption on surface plasmons and interferential properties in thin films, absorbing and bicolour coatings have been designed and successfully produced. The whole process, from relating deposition conditions with optical properties of MIFs to their incorporation into multilayer coatings, will be presented.

25

Magnetic properties of transition metal complexes as revealed by HF-ESR

Dijana Žili ć


Molecular magnets are being investigated as a part of our search for multifunctional materials as well as our need for the fundamental understanding of magnetism. Among a large number of new compounds, oxalate complexes of transition metals are interesting because of high efficiency of oxalate bridge (C2O42–) in transmission of exchange interaction between metal ions. One of the most important methods in solid state physics is electron spin resonance (ESR) which gives insight into local properties of paramagnetic centers and microscopic picture of interactions in the investigated systems. Commercial ESR spectrometers (X-band) which use microwaves of frequency ν = 9.5 GHz and magnetic field B up to 1 T, are not appropriate for investigation of the transition metal complexes with spin S > 1/2. In order to obtain the spin Hamiltonian parameters in these systems: g-tensor, D-tensor (zero-field splitting) and A-tensor (hyperfine splitting), it is necessary to have spectrometers that operate in high magnetic fields and at high frequencies (High Field-High Frequency ESR, HF-ESR).

26

Dislocated semiconductor nano-columns

Benjamin Hourahine

University of Strathclyde, Glasgow G4 0NG, U.K.

Nano-wires of semiconducting material often contain threading dislocations, which modify the structural and electronic properties. These are important, both because of their effects on the intrinsic properties, but also due to the use of patterned column growth and coalescence for example to produce nitride semiconductor films with low defect densities. While the atomistic and electronic structure of edge dislocations in these columns have been theoretically studied by several groups, investigations into screw dislocations are much rarer. This is largely due to to the additional complications of the helical geometry, since the translational repeat unit cell can contain millions of atoms. We recently developed a global optimisation approach to find several new core reconstructions for screw dislocations in bulk GaN, where both the composition and location of the core region lead to more stable dislocation structures. In order to investigate the properties of these dislocations within realistic sizes of nanocolumn, we also have developed a self-consistent density functional based tight bindin methodology using objective boundary conditions to study the energies and electronic structure of twisted [0001] GaN nanocolumns containing dislocations. As an aside, this methodology is also useful for investigation of other helical structures, such as chiral nanotubes.

27

Properties of Sol-Gel derived Ge nanocrystals in thin SiO2 layers

A. Donner, S. Knebel, H. Bracht, I. Capan, H. Rösner, and G. Wilde

Institute of Materials Physics, University of Münster, D-48149 Münster, Germany

Ge nanocrystals (NCs) are a promising alternative to poly-Si floating gates in nonvolatile memory such as Flash or EEPROM. In our group, a highly scalable wet-chemical sol-gel process for the synthesis of Germanium NCs embedded in thin SiO2 films has been developed. TEM investigations show that the structural properties of the Ge NCs can be varied over a wide range by different compositions of the precursor material and different annealing conditions. Electrical Capacitance-Voltage (C-V) measurements show a clear correlation of the density of the Ge NCs and the capability of the thin oxide film to store electrical charges. MOSFET structures utilizing Sol-Gel derived gate oxide layers were produced to enable more detailed studies of the charge retention mechanisms of these thin films.

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Estimation of defect concentration in a-nc-Si:H by photo deflection and photocurrent spectroscopy

Davor Gracin

Rudjer Boskovic Institute, Bijenicka 54, Zagreb, Croatia

The amorphous–nano-crystalline hydrogenated silicon (a-nc-Si:H) is composed of Si nano-crystals embedded in amorphous Si:H matrix. By variation of nano-crystal size distribution and volume contribution it is possible to vary optical gap in relatively wide range while maintaining high absorption. These makes a-nc-Si:H a promising material for thin film solar cells. However, the structural variations could influence the defect concentration which has to be controlled I order to ensure its applicability. Similar to pure amorphous material, absorption coefficient of a-nc-Si: H consists of three distinct energy regions: (i) one is the high-energy region (above E∼1.8 eV) which corresponds to a direct band-to-band transition with α above 104 cm-1. In this region, absorption coefficient is described by Tauc-type relation, (αE)1/2= B(E-EG) where B is a constant and EG defines the optical band gap. (ii) The second region is an exponential Urbach edge region ( E∼1.4-1.8 eV) where α can be expressed by the Urbach edge form, α(E,T) = αo exp ((E-Eoo)/Eo), where αo and Eoo are constants for whole class of material while Eo is different, from sample to sample. Eo is taken as measure of potential variation caused by structural, thermal and chemical disorder. This region corresponds to band-to-tail and tail-to-tail transitions. Typical values for α in this region are between 102 and 104 cm-1. (iii) The third energy region (below E∼1.4 eV) appears due to photon absorption b y gap states superimposed on the Urbach edge. The absorption in this energy region, α abs, is neither Tauc type nor does it has an exponential dependence. For this region, α is typically below 102 cm-1.From the sub gap tail and Urbach edge the excess absorption due to sub gap defect states, αex, is estimated as a difference between the observed value and the extrapolated value of the exponential tail: αex = α abs - α0 exp ((E-Eoo/Eo)). The sub-gap defect density (Nd) is calculated by the expression Nd = 7,9 1015 ∫ αex dE. The optical properties in the first region were estimated upon measured transmittance using point-wise unconstrained optimization approach (PUMA). The experimental error in transmittance measurements limits the determination of the absorption coefficient to values of 104 to 106 cm-1 for the thickness of actual layers. That is why for estimation of α in Urbach region and for band gap states, the photoconductivity and photo deflection spectroscopy were used. The last two methods do not give absolute values for α and need the normalization with values obtained with PUMA. The size distribution of nano-crystals in actual samples was broad and part of them has to be assumed as “macroscopic Si crystals” and contribution of theirs band-to-band transitions was included in estimation of defect density as well. Finally, the estimated values were used for calculation of solar cell efficiency and compared with experimental values.

29

Transport properties of Ge nano-crystals in SiO2 matrix

Robert Slunjski, Milivoj Plodinec, Andreja Gajović, Nikola Radić, Pavo Dubček, Branko Pivac

Rudjer Boskovic Institute, Bijenicka 54, Zagreb, Croatia

We produced MOS structures with nc-Ge embedded in SiO2 oxide. Nc-Ge condensate from a Ge-rich SiO2 oxide, made by the RF Magnetron sputtering technique, after thermal annealing. The existence of nc-Ge is confirmed by the use of PL, Raman and XRD measurements. With the use of electrical measurements techniques (current-voltage, capacitance-voltage) we confirmed the charge trapping in the nc-Ge and the character of the current transport phenomena through the MOS structure is found.

30

Fluorination of Vertically Aligned Carbon Nanotubes

Claudia Struzzi, Carla Bittencourt

University of Mons, Belgium

Carbon nanotubes provide benchmarks for new phenomena, based on the tuneability of their electronic states. The reproducibility of the strategies used to tune their electronic properties still a major concern of nanotechnology. These nanostructures are sensitive to local perturbations, such as surface charges and adsorbed gas molecules, the grafting of functional groups in a controllable way has been proposed as a feasible reproducible solution for band gap engineering and controllable doping. In this context, fluorination is a candidate to provide stable and tunable functionalization due to the different possible bonding between fluorine and carbon atoms. It is a promising method for expanding the use of graphene low dimensional structures to several areas where the tailoring of properties such as wettability, adhesion, chemical stability, permeation and electrical conductivity are important. The challenge is to carry out fluorination without deteriorating their intrinsic properties. Among the reported fluorination methods, plasma-based functionalization methods has the advantage to be solvent-free, be time efficient and be flexible as it provides a wide range of functional groups depending on the plasma parameters. In addition, fluorination via cold plasmas has the potential to limit fluorination to the surface of the nanostructure thus reducing degradation effects. In this work, we have performed the fluorination of vertically aligned carbon nanotubes (v-CNTs) carpets via exposure to CF4 or Ar:F2 RF plasmas. The fluorinated v-CNTs has been investigated by means of X-ray photoelectron spectroscopy (XPS) in order to carry out a detailed analysis of fluorine concentration, bonding type and patterning dependent on gas mixture and exposure time. Surface wettability studies demonstrate the changes on the surface properties of the nanotubes forests by the introduction of fluorine-containing groups, while scanning electron microscopy shows that overall nanotube alignment and separation is conserved. Finally, Scanning X-ray photoelectron spectromicroscopy (SPEM) shows the selectivity of the plasma functionalization, that takes place at the surface tips of the v-CNTs. This opens the way to nanotube carpet structures with activated surfaces, by maintaining the desirable conductive properties of the pristine nanotubes near to the substrate.

31

Understanding light scattering between plasmonic nano-particles

Ben Hourahine and Francesco Papoff

University of Strathclyde, Glasgow G4 0NG, U.K.

The strong enhancement of light intensity in regions close to metallic nano-particles underpins several applications and tools in nano-science. To further increase the strength of this field, placing another particle near by will add light to the region, not only through its scattering properties, but also via the optical interactions between particles. For example, this is of use for aperture-less NSOM/SNOM or to further increase signal in SERS. To understand the nature of these interactions, we have applied our theory, developed to study the optical modes of nano-particles, to investigate the plasmonic modes of pairs of gold particles as they are brought together to within a few Angstroms. The equatorial plasmonic resonance of this system is almost insensitive to the inter-particle separation, due to the nature of the modes being excited. This is in strong contrast to the red-shifting and broadening of the longitudinal plasmonic resonance that occurs as the particles approach each other. This behaviour can be understood as being due to the exclusion of the electromagnetic dipolar field from within the gap between particles, combined with a change towards the field being increasingly due to a combination of optical modes which are non-resonant for the individual spheres in the dimer.

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High-temperature hydrogenation of pure and silver-decorated titanate nanotubes to increase their solar

absorbance for photocatalytic applications

Milivoj Plodinec 1*, Andreja Gajović1, Gregor Jakša2, Kristina Žagar2, Miran Čeh2

1 Ruñer Bošković Institute, Zagreb, Bijenička 54, HR-10000 Zagreb, Croatia 2 Jozef Stefan Institute, Jamova 52, Si-1000 Ljubljana, Slovenia

Titanate (TiNT) and TiO2 nanotubes are a new mesoporous nanostructured materials

based on titanium dioxide attract huge interest in the last few years due to their attractive properties [1]. The properties include: the ease of synthesis with a relatively low cost (especially in comparison to the carbon nanotubes), a high specific surface area, ability to functionalize the surface via chemisorptions or the ion-exchange of species, and the possibility of reversible gas adsorption. Current application areas of titanium oxide nanostructures include: dye-sensitised solar cells; the photo-catalytic degradation of environmental contaminants; gas- and liquid-phase catalysis, function in solid-state lithium batteries, and biosensors [1].

We studied how the temperature treatment of H2Ti3O7 in reduce atmosphere influenced on morphology, phase transition and photo-catalytic properties of titania nanotubes. Titanate nanotubes (TiNT-H) were prepared by hydrothermal treatment of commercially P25 powder and then calcined on several temperature. Temperature treatment were performed in high temperature Astro furnace. Changes in morphology and properties were studied by TEM, HRTEM, Raman spectroscopy, XRD, UV/Vis/NIR spectroscopy, BET srfaces analysis.

Before thermal treatment TiNT – H show tubular morphology with high specific surface area of about 400 m2/g, inner diameter of 7-9 nm and outer diameter 9 – 12 nm, and average length from 300 nm up to 1 µm. After thermal treatment sample show a complete degradation of tubular structure to mostly elongated nanocrystals with well-defined crystal lattice and average size 10 – 20 nm. Raman spectra demonstrated that during thermal treatment occurred phase transition from trititanate H2Ti3O7 crystal structure to partly disordered tetragonal crystal structure of a TiO2 anatase. This study demonstrates that thermal treatment of TiNT–H nanotubes in reductive atmosphere significantly influenced on crystal structure and light absorption of TiO2 nanostructures in visible and IR region. High activity in visible and IR region obtained powder could increase photocatalytic properties of titania nanotubes.

Documents

Workshop on characterization of semiconductor nanostructures; the