News

11.11.2013. Publication in Nature Communications with results based on the Litographene project.
Related to the subject of graphene intercalation, coworkers on the UKF project have published the paper in the prestigious journal Nature Communications. In the paper "The mechanism of caesium intercalation of graphene", which in a large part contains results obtained through the UKF project "Photolithographic synthesis and electronic properties of graphene based devices and related structures", a detailed characterization of caesium intercalation of graphene on Ir(111) is presented. Information which clarify how and where does the penetration of caesium atoms through the graphene occur is obtained by utilizing several experimental techniques (LEEM, STM, ARPES, LEED) as well as by theoretical calculations (vdW-DFT). It is shown that in the process of intercalation the system exhibits phase separation of caesium atoms into a dilute adsorbed and a dense intercalated phase. Effects of such phase separation are also visible in the photoemission spectra in the form of the inhomogeneous electron doping of graphene. Results show that the van der Waals interaction plays a key role and, depending on the concentration of the caesium atoms, allows or blocks intercalation and also inhibits complete desorption of the intercalated caesium atoms. Microscopically, intercalation dynamics is governed by graphene wrinkles and substrate steps, structures which are intrinsic to epitaxial graphene systems. 

Litographene beyond UKF - follow up activities & actions.
  • UKF project enabled to establish a valuable facility, which will help to expand possibilities of scientific research at Institute of Physics and also at nearby research centers.
  • This new facility at Institute will help us in applying for new projects on national and international level.
  • In addition to data published during the project, the results which were obtained during the project will be subsequently published in scientific journals.
Summary of accomplished KPI's:




04.06.2011. Workshop no 2.
Workshop titled "Lithography and nanocharacterization in action" took place at the end of the official project time-frame. The focus of this workshop relied on younger project participants, PhD students, who gathered relevant experience through project activities. More details can be found on the Workshop page.

May 2012. Training.
Final 40-50 days of training is planned with our collaborator from the Max-Planck-Institut für Festkörperforschung. We will be working in the Technology Service Group headed by Dr. Gennady Logvenov and use their experimental facilities to gain additional practical experience in photolitography procedures.

21.-30.12.2011. Project coordinator in Zagreb. Official clean room opening.
Tonica Valla, the project coordinator, spends ten days in Zagreb where accomplished project activities and results are discussed and a final stage of project is planned. On December 22nd the Clean room and Photholitography lab is officially opened. Distinguished guest from UKF, Ruđer Bošković Institute, Physics Department of Zagreb University, Faculty of Electrical Engineering, and from the Institute of Physics have learned about new capabilities which are now available through realization of UKF project and which will serve the interested users well beyond a duration on the project.
Project coordinator, Tonica Valla, speaks to the audience during Photolitography lab opening. 

Photholitography lab at the Insitute of Physics.

13.-27.11.2011. Training no. 3.
Iva Šrut, 
Marin Petrović and Milorad Milun 
perform measurements at National Synchrotron Light Source (NSLS) and at Center for Functional Nanomaterials(CFN). Activities are now focused to LEEM/PEEM, AFM, and Raman spectroscopy techniques.

June 2011. Equipment.
All mayor equipment (Photolitography: spinner, mask aligner, wire bonder,... and STM sample storage and preparation) has been delivered during the month of June. At the same time, intensive operations to prepare more than 20 m2 of clean room space (see photo) are taking place.


06.06.2011. Workshop no 1.
Workshop titled "Novel materials for electronics: from production to devices" took place at the Institute of Physics. Six project participants presented their experience and expertise. More details can be found on the Workshop page.

20.05.-04.06.2011. Training no. 2.
Marin Petrović and Iva Šrut perform measurements at National Synchrotron Light Source (NSLS) and at Center for Functional Nanomaterials(CFN). Activities cover use of ARPES, LEEM/PEEM, AFM, and Raman spectroscopy techniques.


20.05.2011. Paper submitted, accepted, published.
Manuscript titled Graphene on Ir(111) characterized by ARPES by M. Kralj, I. Pletikosić, M. Petrović, P. Pervan, M. Milun, A. T. N'Diaye, C. Busse, T. Michely, J. Fujii, and I. Vobornik, has been submitted to Physical Review B.Paper addresses in detail the evolution of the electronic structure of grapheneupon epitaxial growth. Figure below shows a band structure of graphene on Ir imaged by ARPES. The work was reviewed and published in August: Physical Review B 84 (2011) 075427.


April 2011. Sample storage and preparation upgrade.
Our initial efforts ingrowing and characterizing graphene sample shall now be expanded to agreat extent. We have purchased sample storage and sample preparationstages that will be used at our STM setup to prepare and characterize upto five samples in UHV (without breaking the vacuum). This will speedup our capabilities and research.


April 2011. Buying basic components of photolitography setup.
After running public procurement procedure and after identified equipment has been inspected on April 1st at BidService by project leader Tonica Valla and photolitography expert colleague Tony Bollinger, a final decision to buy that particular equipment has been taken. It is expected that all shipping arrangements, contract and payment is done by the end of April. Below is a photo of mask aligner model (Karl Süss MJB-3) that we will soon have in Zagreb.


March-April 2011. Paper ready for submission.
Our understanding ofepitaxial graphene growth mainly concerns electronic quality of graphenethat can be achieved. In a detailed investigations of epitaxial growththat follow our initial success of understanding graphene on Ir(111)[Phys. Rev. Lett. 102 (2009) 056808], we studied graphene  growth onthat substrate in greater detail. Our combined STM-ARPES approach,addresses in detail evolution of the electronic structure of grapheneupon epitaxial growth. This work is ready to be submitted forpublication. ARPES spectra below focus on the K point of graphene andshow formation of the Dirac cone band.

24.02.2011. Clean room discussion.
Project members and experienced litography expert Milan Vukelić meet to discuss necessary conditions for the implementation of the photolitography setup and other necessary components, such as clean room, evaporation and sputtering etc, which are out of the scope of this project but are enabled through synergy of project participants.

16-17.02.2011.
We are ready for transport business.
Mario Basletić, Matija Čulo and Bojana Hamzić perform first Hall effect measurements in the magnetic fields up to 16 T in the temperature range 4.2-300 K. Mobility and Hall parameters agree well with other results previously published on exfoliated graphene on SiO2. Plans for more innovative measurements are discussed. We are in business! Optical microscopy image from below shows how a device looks after extensive measurements which included more than moderate range of back gate voltages.


January-February 2011.
Identifying photolitographic equipment.
Specific approach in this project is a purchase of used components to assemble microfabrication setup. This is the way how we can match available funds and our goal to have possibility of photolitography. After a long search we have identified several components (mask aligner, wire bonder, spin coater,...) and start purchase procedure from the supplier in the US. The procedure of purchase and delivery will take couple of  months and will include public procurement and other necessary steps.

09.02.2011. Discussing regional collaboration.
Petar Pervan and Marko Kralj visited the Instituteof Microelectronic Technologies and Single Crystals-IHTM in Belgrade and discussed practical solutions and photolitography concepts based both on mask aligner or on direct writing to Prof.dr. Zoran G. Djurić (from IHTM) and Dr. Radomir Žikić (from Institute of Physics, Belgrade). This visit opens various possibilities for future collaboration.

02.02.2011.
Raman identification of our devices.
Although not a part of this project, a major technique for the identification of carbon nanostructures is Raman spectroscopy. Project team member, Iva Šrut, in collaboration with members of the Molecular Physics Laboratory at Ruđer Bošković Institute, performed Raman measurements on graphene devices that were produced at BNL. Such collaboration with this nearby institute gives an added value and will be important in the future, once we begin to produce devices by photolitography in Zagreb.

Optical microscopy image (left) and Raman spectra (Right) of one of our devices. Preiliminary analysis indicates this is a monolayer device.

31.01.2011. Two proposals for the experiments at BNL submitted.
Part of the training activities shall be realized through competitive projects for the use of equipment at CFN and NSLS. Proposal titled Fabrication and characterization of single- and few-layer graphene devices: Systematic study of atomic scale defects and their relation to transport characteristics regard extensive use of nanofabrication tools at CFN. On the other hand, proposal Epitaxial graphene growth: Focus on a two dimensional wrinkles network tends to address important features in graphene layer which form during epitaxial growth and which shall be intensively studied by LEEM/PEEM instrumentation stationed at NSLS. Preliminary LEEM results have been obtained during first training activities. Results of proposals evaluation are to be known till mid March.
LEEM image of epitaxial graphene
LEEM image resolving wrinkles and other features (steps, defects, and small areas of uncovered iridium surface) of ex situ grown epitaxial graphene on Ir(111).

January- 2011. Topological insulators (TI).
Beginning of 2011 is also our beginning of STM studies on topological insulator samples provided by project leader. We hope that this initial research will help us to develop our own sample growth methods and help us understand how to optimize that process. We also hope to contribute to the understanding of the electronic properties of TI surfaces. Eventually, we intend to fabricate devices for transport characterizations based on TI materials.

Left image shows installed TI sample on STM sample holder before insertion into vacuum and cleave. Right images are STM topographs showing atomic resolution of TI surface and clearly imaging the presence of defects.

28.01.2011.
Discussing transport measurements in high magnetic fields.
Bojana Hamzić and Marko Kralj discussed transport measurements of Hall bar devices to be conducted in collaboration with Mario Basletić at Department of Physics of the University of Zagreb.

20.12.2010. Diploma work on graphene growth on stepped Ir(332).
Ida Delač defended her diploma thesis at University of Zagreb under mentorship of Marko Kralj. Thesis titled "Growth and properties of graphene on stepped surfaces" sets our efforts on the epitaxial growth of graphene on a right track.

19.11.-04.12.2010
. First training activities.
T. Valla, M. Petrović, M. Kralj
After a delay in planned training (due to changes in visa issuing policies), first training activities of Marin Petrović and Marko Kralj took place at BNL. Training components included use of the facilities at National Synchrotron Light Source (NSLS) and at Center for Functional Nanomaterials (CFN). It covered: studies of electronic structure of epitaxial graphene (by ARPES), studies of real space electronic modification of epitaxial graphene system (by LEEM/PEEM), mechanical exfoliation and identification of graphene, nanofabrication of graphene devices on SiO2 substrate (by lithography), etc. Pictured from left to right: Tonica Valla, Marin Petrović, Marko Kralj in front of U13UB@NSLS.

One of the first monolayer graphene Hall bar devices in this project. Optical microscopy image.

27.07.2010. Official UKF announcement.
UKF officially informed about new projects financed under the Scientific Cooperation Program. Litographene is one of nine awarded projects.

28.06.2010. Collaboration agreement. 
Collaboration agreement between the Leading organization (Institute of Physics, Zagreb) and the Partner organization (Brookhaven Lab) signed.

21.06.2010. Seminar.
Tonica Valla, project coordinator, gives a seminar at the Institute of Physics. In his talk "Modern photoemission - Ideal probe for new materials", Tonica also presented two materials of central physical interest in this project: graphene and topological insulators.

15.06.2010. Official starting date of the project. 
Project contract no. 66/10signed by the project coordinator Tonica Valla, the Institute of Physics represented by director, Petar Pervan, and the Minister of Science Education and Sports, Radovan Fuchs.

Joint project of


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