University of Bucharest – Faculty of Physics MDEO Research Center RESEARCH AND DEVELOPMENT CENTRE FOR MATERIALS AND ELECTRONIC&OPTOELECTRONIC DEVICES (MDEO)

University of Bucharest – Faculty of PhysicsMDEO Research Center

RESEARCH AND DEVELOPMENT CENTRE FOR MATERIALS AND ELECTRONIC&OPTOELECTRONIC DEVICES (MDEO) Director Prof. univ.

Dr. Stefan ANTOHE

Telefon: +40214574418/4574419, fax: +40214574418/4574521

Director of MDEO Research Centre

UNIVERSITY OF BUCHAREST,

FACULTY OF PHYSICS,RESEARCH AND DEVELOPMENT CENTRE FOR MATERIALS

AND ELECTRONIC&OPTOELECTRONIC DEVICES (MDEO)

Ştefan ANTOHE Ph.D

University of Bucharest, Faculty of Physics, P.O.Box:MG-11, Bucharest-Magurele, 077125 ROMANIA, E-mail:

[email protected]



Dr. Stefan ANTOHE

The Research Development Centre for Materials and Electronic and Optoelectronic Devices (MDEO) was established in 2006 at the Faculty of Physics of the University of Bucharest, centred on the first Laboratory of Organic Materials and Electronic and Optoelectronic Devices, from our country. Today the Centre, with modern experimental facilities and a good expertise of the research team, develops research activities in the fields of: Physics of Semiconductors; Electrical and photoelectric properties of the organic semiconductor thin films; Organic Photovoltaic Cells; Organic Field-Effect Transistors; Organic-on-inorganic semiconductor diodes; Theory of carrier transport mechanism and semiconductors wafers diagnostic techniques; Polycrystalline semiconductors thin films from AII-BVI compounds; Effect of ionizing radiations on the structural, electrical and optical properties of the semiconducting thin films; Semiconducting oxides; Nanostructured materials; Simulation and Modeling of different kind of semiconducting materials and electronic and optoelectronic devices.Applied research is focused on the assessment of possible applications of new generation of hybrid organic/inorganic photovoltaic cells as low power energy sources and to increase the performances and life time of solar cells based on AII-BVI thin films for space applications.



Dr. Stefan ANTOHE

RESEARCH AREA at the

Research Development Centre for ,,Materials and Electronics &Optoelectronics Devices”

A2B6 thin films – production and characterization Structural properties Morphological properties Electrical properties Optical properties

Photovoltaic Cells Based on Organic Thin Films & Hybrid Inorganic/Organic Structures

Defects in semiconductors Nanowires based on A2B6 semiconductors Electronic devices based on A2B6 nanowires Numerical simulations in solid state physics

Numerical modeling at nano-scale Electrical transport



Dr. Stefan ANTOHE

For the preparation of the thin films there are three equipments each dedicate to deposition of Metallic thin films, Organic thin films and AII-BVI semiconducting compounds thin layers, respectively, all running in high dry vacuum conditions, assured by the turbo molecular pumps.

The thickness of the grown thin films is done in-situ with a Quartz resonator based system.



Dr. Stefan ANTOHE

Facilities for producing thin films by:

thermal evaporation

electrochemical methods

THIN FILMS PRODUCTIONS

Equipments for thermal vacuum evaporation operating

in 10-6 – 10-5 Torr range



Dr. Stefan ANTOHE

Deposition of the Organic Thin Films on Flexible and Transparent Substrates



Dr. Stefan ANTOHE

The preparation of different kind of nanostructures (nanowires and nanotubes) take place in a Clean Room – ISO 6 class, using an electrochemical deposition system, based on template approaches.



Dr. Stefan ANTOHE

APPLICATIONS BASED ON NANOWIRES

Facilities for producing metallic and semiconductor nanowires: Clean room – ISO 6 class Electrochemical deposition based

on template approaches



Dr. Stefan ANTOHE

Electrochemical deposition based on template approaches



Dr. Stefan ANTOHE

Preparation and characterization of CdTe nanowiresPhysical properties of CdTe determining the increased

scientific interest in the last decades Band gap of 1.4 eV properly for the base absorber

layer in a solar cell; Large optical absorption coefficient; Good chemical stability; Potential candidates for CdS/CdTe and hybrid

organic/inorganic solar cells.



Dr. Stefan ANTOHE

Preparation of CdTe nanowires Acidic deposition bath:Acidic deposition bath: 1 M CdSO1 M CdSO44,, 0.3 mM TeO0.3 mM TeO22 at a pH of 1.6 adjusted with at a pH of 1.6 adjusted with

HH22SOSO44)) HTeOHTeO22

++ + 3H + 3H+++ 4e+ 4e-- Te +2H Te +2H22OO CdCd2+2+ + Te + 2e + Te + 2e-- CdTe CdTe• 101088 pores/cm pores/cm22 • 80 nm pore diameter80 nm pore diameter • deposition at 74deposition at 74CC

-700 -600 -500 -400 -300 -200 -100 0 100-0.30

-0.25

-0.20

-0.15

-0.10

-0.05

0.00

0.05

0.10

sweep1 sweep2 sweep3

Cu

rren

t (m

A)

Potential (mV)

Polarisation curves for CdTe nanowires deposition. Sweep rate was 5 mV/s. The peak at 500 mV corresponds to the potential where CdTe is deposited. The shift towards more positive potential at the second and third sweep, is most probably due to the fact that the deposition is further favorised by the presence in the substrate of Te atoms.



Dr. Stefan ANTOHE

The structural characterization of the prepared thin films and structures is done with a XRD - High Resolution X-ray Diffractometer Bruker D8 Discover for thin film application, equipped with four motorized axes stage, having as typical applications: XR Reflectometry, Rocking measurements, /2 measurements and structural phase identification



Dr. Stefan ANTOHE

STRUCTURAL CHARACTERIZATION

Typical applications:

XRD - High Resolution X-ray Diffractometer Bruker D8 Discover for

thin film application, equipped with four motorized axes stage

XR Reflectometry

Rocking measurements

/2 measurements

structural phase identification



Dr. Stefan ANTOHE

Morphology of prepared organic and inorganic thin films or nanostructured layers is assessed ex-situ using our AFM - Atomic Force Microscope able to operates in the following modes: STM, C-AFM, M-AFM, and the SEM - Scanning Electron Microscope TESCAN VEGA XM having the following characteristics: Dual mode operation, High and medium vacuum, equipped with 5 axes stage fully monitorized , 3 nm imaging resolution, conductive and dielectric sample can be analyzed, respectively, both equipped with modules for nanolithography.



Dr. Stefan ANTOHE

SEM - Scanning Electron Microscope TESCAN VEGA XM characteristics:

Dual mode operationHigh and medium vacuumequipped with 5 axes stage

fully monitorized3 nm imaging resolutionequipped with a module for

nanolithographyboth conductive and dielectric

sample can be analyzed

TOOLS FOR LITHOGRAPHY AND MORPHOLOGICAL INVESTIGATIONS



Dr. Stefan ANTOHE

MORPHOLOGICAL INVESTIGATIONS of CdTe Nanowires Arrays



Dr. Stefan ANTOHE

• CdTe nw array

• 108 wires/cm2

• 300 nm diameter

• Voltage: -500 mV;

• Composition:49% Cd; 51%Te

SEM micrographs of an array of CdTe wires (108 wires/cm2, 300 nm diameter) deposited at -500 mV vs. SCE and the result of Energy Dispersive X-ray (EDX) analysis.



Dr. Stefan ANTOHE

TOOLS FOR LITHOGRAPHY AND MORPHOLOGICAL INVESTIGATIONS

AFM - Atomic Force Microscope operates in the following modes:

STM C-AFM M-AFM Capable of lithography



Dr. Stefan ANTOHE

Morphological investigations S of P3HT:PCBM (1:1) thin films



Dr. Stefan ANTOHE

As concerning the electrical characterization the Centre has extensive expertise in Space Charge Limited Currents (SCLC) and Thermo Stimulated Currents (TSC) measurements as well as in Semiconducting Organic Inorganic Surface Analysis Spectroscopy (SOISAS) for determining of the surface state density in equilibrium with any inorganic wafer or epitaxial film. The experimental setups contain two Helium closed cycle cryostats with the samples in vacuum and with 10 pin electrical feed through for sample contacting, one in the 8 – 325 K range, and with optical access to the samples through 4 quartz windows, used for electrical and optical material characterization, and the other one in the range of 2,6-325 K for galvanomagnetic applications used especially for Hall effect and magneto resistance measurements. Both cryostats are use frequently to process Resistivity and Hall Effect measurements as function on temperature, for different samples.



Dr. Stefan ANTOHE

ELECTRICAL CHARACTERIZATIONS

Determination:Resistivity and Hall Effect measurements as function on temperatureThermostimulated Current (TSC)Space Charge Limited Current (SCLC)

Thermoelectrical effect

Solar Simulator - Equipped with an Hg-Xe high pressure lamp with highly stabilized output and AM 1.5 filters



Dr. Stefan ANTOHE

Helium closed cycle cryostat sample in vacuum 8 – 325 K range optical access to the samples through 4 quartz windows 10 pin electrical feedthrough for sample contacting electrical and optical material characterization

Helium closed cycle cryostat for galvanomagnetic applications

Hall effect and magnetoresistance

2.6 – 325 K range

sample in vacuum

ELECTRICAL CHARACTERIZATIONS



Dr. Stefan ANTOHE

-20 -15 -10 -5 0 5 10 15 20

-1.2x10-6

-8.0x10-7

-4.0x10-7

0.0

4.0x10-7

8.0x10-7

-1.0 -0.5 0.0 0.5 1.0

-1.0x10-8

0.0

1.0x10-8

300 K 270 K 250 K 240 K 200 K 100 K 130 K 100 K 80 K 50 K

I (A

)

U (V)

300 K

100 120 140 160 180 200 220 240 260 280

2.0x107

4.0x107

6.0x107

8.0x107

1.0x108

1.2x108

1.4x108

3 4 5 6 7

2x107

3x107

4x107

5x107

6x107

7x107

8x107

9x107

R ()

T (K)

a) I-V characteristics recorded for a CdTe multisegment wire array (300 nm diameter, 106 wires/cm2). The sequence of the segments is specified in Table I (CT8 sample). b) Temperature dependence of the electrical resistance of the sample, measured at applied voltages in the range where I-V curves were linear.

Multisegment wires (300 nm diameter, 106 pores/cm2):- CdTe, deposited at -680 mV, 700 nm long;- CdTe stoichiometric, deposited at -510 mV;- Cd, deposited at -680 mV, 700 nm long.

Tk

ERR

B

acexp0

The resistance is thermally activated, with an activation energy of 0.03 eV in the high temperature range



Dr. Stefan ANTOHE

Characterization of the photo-active layer of different structures of photovoltaic cells, is performed one a hand through optical measurements, (absorption, reflection, transmission and photoluminescence spectra), using our UV-VIS Spectrophotometer Perkin Elmer Lambda 35 with the characteristics: 190 – 1100 nm wavelength, equipped with integrating sphere, specular reflectance accessories, operating in Transmission, Reflection and Absorption modes, and on the other hand the action spectra are performed using a on-line experimental setup containing a monochromator step by step monitorized, and adequate light sources.

The current voltage characteristics of the photovoltaic cells in forth quadrant, and the determination of typical parameters in regime of photoelement: Open-Circuit Photovoltage (Voc), Short-Circuit Photocurrent (Isc), Fill Factor (FF) and Power Conversion Efficiency (η) are performed using a special setup containing as light source a Solar Simulator - Equipped with an Hg-Xe high pressure lamp with highly stabilized output and AM 1.5 filters and a load resistor in the range of 10 Ω - 2 TΩ.



Dr. Stefan ANTOHE

OPTICAL CHARACTERIZATIONS

UV-VIS Spectrophotometer Perkin Elmer Lambda 35 190 – 1100 nm wavelength

equipped with integrating sphere, specular reflectance accesories

operating in Transmission, Reflection and Absorption modes



Dr. Stefan ANTOHE

Referring to the research in the field of organic photovoltaic cells, in the last 15-20 years our team of research was involved in the study of the electrical and photoelectrical properties of the single, double and three-layered photovoltaic cells based on the organic thin layers. Using new materials and new design of the structures, the power conversion efficiency was permanently increased. As concerning the modeling and simulation of organic photovoltaics, for each type of prepared and characterized PV structure the dark Current-Voltage Characteristics were measured in a wide range of temperatures. In this way the transport parameters of the charge carriers were determined and different models to explain the involved charge carrier transport mechanisms were developed. A special model to extract, with accuracy, the quality factor and saturation current, removing the effect of series and shunt resistance was developed. Also for each type of cell the complete characterization in fourth quadrant (PV mode) has been done explaining the PV mechanism involved. An extended review of the expertise of our group in the field of organic electronics and optoelectronics, is given in the reference [2], in the next section.

The research team of the centre has participated in several national and international projects in the field of organic electronics, including, EU Framework projects and bilateral projects. The staff members have extensive publications in area of organic electronics and optoelectronic devices acquiring a big number of citations in ISI journals.



Dr. Stefan ANTOHE

I International Research Projects: [1] Stefan ANTOHE Director of the Romania-Slovenia Bilateral Project, Nr 5CB/30.05.2008 ,,Electrical and Optical Properties of ,, BULK HETEROJUNCTION”, Organic Solar Cells(2008-2009) ~ 25 000 Euro

II National Research Projects: 1) Director of Project: CEEX05 Nr. D11_43/06.10.2005 ,Hibride Structures from AIIBVI Nanowires

Arrays/Organic thin films for Optoelectronic Devices” (MATNANORG) 2) Director of Project: CEEX05 Nr. D11_63/03.10.2005 "Electronical and Optical Phenomena in Organic materials with Conjugated Bonds for Photonics " (ORGFOTON) 3) Scientific Director of the Project: CEEX05 Nr.4./05.10.2005: " Amorphous and nanostructured Chalcogenics materials for Sensors and Optoelectronics " (CANSO) 4) Scientific Director of the Project: CEEX05 Nr.21/05.10.2005: "Multilayered nanowires for Giant magneto resistance”(NANOSPINVALVE) 5) Scientific Director of the Project: CEEX05 Nr. 105/03.10.2005: "New Flexible Photovoltaic Systems based on Polymeric materials" (SOLAR) 6) Scientific Director of the Project: CEEX05 Nr.46./05.10.2005: "Optical and Electronic Transport Properties of Transition Metals Doped ZnO Nanowires" (NANOXID) 7) Scientific Director of the Project: CEEX05 Nr.4/03.10.2005: "Multifunctional materials with applications in micro- and milimetric- waves" (MATMIUM) 8) Scientific Director of the Project: CEEX06 Nr.53 /2006: " Optical nanostructured Sensors for advanced gases detection" (SONDAG) 9) Scientific Director of the Project: CEEX06 Nr. 33 /2006: „Investigation of bor Nitride as semiconductor for extreme conditions”(SEMNITBOR),

II. 2008-2009 Scientific Research Report of (MEOD) Centre



Dr. Stefan ANTOHE

10) Scientific Director of the Project: CEEX06 Nr. 24/25.07.2006:„Fundamental Research on InN multifunctional materials for flexible optoelectronic Devicesl”(INDIN), 11) Scientific Director of the Project: CEEX06 Nr. 29 /2006: "The Orientation of the semiconducting and magnetic properties of nanostructured ZnO thin Films for Optoelectronics and Spintronics"(DISEMAZON) 12) Member in the research team of the project: CEEX06 Nr. 2/2006: “Active laser Mediums for IR range” (MALIR) 13) Member in the research team of the project: CEEX06 Nr. 1/2006: “nanowires from metalic Oxides with semiconducting and magnetic propertiesi” (NANOSEMIMAGNET) 14) Director of Project: PN II PVCELLSA, D8- 81-030/2007, ,, Photovoltaic Cells for Space Applications15) Scientific Director of the Project: PN II Nr. 71-134 /2007 ELECTROCISCELL: " New type of flexible solar cells based on electrodeposited CIGS compounds, 16) Scientific Director of the Project: PN II Nr. 81-053 /2007 TERASCAN: " Research on emission, modulation, scaning and detaction of the electromagnetic waves in the field of THZ. 17) Scientific Director of the Project: PN II nr.: 72-162 “New materials with variable gap based on InN, for Optoelectronic Devices – MinNA” 18) Scientific Director of the Project: PN II nr.: 71-149 ,,Materials for oxidic heterostructures for Optoelectronic Devices”-HETOX 19) Scientific Director of the Project: PN II nr.22-132: Photovoltaic Cells based on thin films prepared by alternative technologies for clean energy production.(VOLTERA), 20) Scientific Director of the Project: PN II nr.72-162 “Non linear functionalities in nanostructured photonic materials for IT applications” (FUNFOTON)



Dr. Stefan ANTOHE

III. Articles published in ISI journals 2008-2009:

[1] Synthesis and properties of Ba(Zn1/3Ta2/3)O3 for microwave and millimeter wave applications, A Ioachim, M.I. Toacsan, M. G. Banciu, L. Nedelcu, C. A. Dutu, H. V. Alexandru, S. Antohe, E. Andronescu, S. Jinga, P. Nita, Thin Solid Films 516 (2008) 1558-1562[2] G. Socol, I. N. Mihailescu, A.-M. Albu, S. Antohe, F. Stanculescu, A. Stanculescu, L. Mihut, N. Preda, O. Rasoga, M. Socol (2008): “MAPLE Prepared Polymeric Thin Films for Non-linear Optics Applications”, Applied Surface Science, (doi: 10. 1016/j.apsusc.2008.07.206)[3] Electrical and optical properties of nanostructured ZnO thin films for optoelectronic applications, L. Ion, M. I. Rusu, G. Socol, I. N. Mihailescu, C. Tazlaoanu, S. Antohe, Journal of Optoelectronics and Advanced Materials, Vol. 10 , No. 10, October 2008, 2599-2602[4] Effects of proton irradiation on CdTe thin films used in photovoltaic applications, R. Bazavan, O. Ghenescu, M. Ghenescu, D. Crisan, A. Radu, L. Ion, S. Antohe, Journal of Optoelectronics and Advanced Materials, Vol. 10 , No. 11, November 2008, 3048-3051[5] Structural and morphological properties of NiCu magnetic thin films, D. Bazavan, R. Bazavan, I. Enculescu, E. Matei, L. Ion, S. Antohe, Journal of Optoelectronics and Advanced Materials, Vol. 10 , No. 11, November 2008, 3054-3058[6] Physical properties of CdTe nanowires electrodeposited by a template method, for photovoltaic applications, Lucian ION, Ionut ENCULESCU, Stefan ANTOHE, Journal of Optoelectronics and Advanced Materials, Vol. 10 , No. 12, December 2008,[7] Organic Photovoltaic Cells Based on ZnO Thin Film Electrodes, C.Ghica, L. Ion, G. Epurescu, L. Nistor, S. Antohe, M. Dinescu, submitted to Nanostructured Materials 03.11.2008[8] A versatile method to grow localized arrays of nanowires for highly sensitive capacitive devices, V. A. ANTOHE*, A. RADUa, S. YUNUS, A. ATTOUT, P. BERTRAND, M. MÁTÉFI-TEMPFLI, L. PIRAUX, S. MÁTÉFI-TEMPFLI*JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS Vol. 10, No. 11, November 2008, p. 2936 – 2941[9] Spin-box algorithm for low temperature dynamics of short range disordered Ising spin systems, G.A. Nemnes a, , K.H. Hoffmannb ∗ Computer Physics Communications doi:10.1016/j.cpc.2008.12.038



Dr. Stefan ANTOHE

[10] Nanowire-templated microelectrodes for high-sensitivity pH detection, Vlad Andrei Antohe,1,a_ Adrian Radu,2 Mária Mátéfi-Tempfli,1 Anne Attout,1 Sami Yunus,1Patrick Bertrand,1 Constantin Augustin Duţu,3 Alexandru Vlad,3 Sorin Melinte,3, Stefan Mátéfi-Tempfli,1 and Luc Piraux1 APPLIED PHYSICS LETTERS 94, 073118 _2009_

[11] G. Socol, I. N. Mihailescu, A.-M. Albu, S. Antohe, F. Stanculescu, A. Stanculescu, L. Mihut, N. Preda, O. Rasoga, M. Socol (2008): “MAPLE Prepared Polymeric Thin Films for Non-linear Optics Applications”, accepted for publication in Applied Surface Science, Volume:255 Issue:10,Pages 5611-5614, published: 2009[12] Optical Properties of Pulsed-laser Deposited ZnO Thin Films, R. Bazavan, L. Ion, G. Socol, I. Enculescu, D. Bazavan, C. Tazlaoanu, A. Lorinczi, I. N. Mihailescu, M. Popescu, S. Antohe, Journal of Optoelectronics and Advanced Materials, Vol. 11 , No. 4, April 2009, p. 425-428[13] D. Băzăvan, Rosemary Băzăvan, I. Enculescu, Elena Matei, C. Necula, L. Ion, Ş. Antohe - Magnetic properties of NiCu thin films obtained by electrodeposition, Optoelectronics and Advanced Materials-Rapid Communications (OAM-RC), Volume 3, No. 5, May 2009, p. 484 – 488; [14] Submicron wires with nanosized grain structure M. Sima, L. Ion , S. Antohe, E. Vasile Superlattices and Microstructures 46 (6) (2009) 833_839[15] Self-consistent potentials and linear regime conductance of cylindrical nanowire transistors in the R-matrix formalism, G. A. Nemnes, L. Ion, S. Antohe, Journal of Applied Physics, 106, 113714-113720, (2009)[16] Effects of proton irradiation on structural and optical properties of CdS thin films used in photovoltaic applications Veta GHENESCU2, L. ION1, M. GHENESCU2, M. RUSU3, M. GUGIU4, G. VELISA1,4, Oana PPORUMB1, S. ANTOHE1 OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS Volume: 3 Issue: 10 Pages: 1023-1026 Published: 2009 [17] Thermo-electrical properties of nano-structured ballistic nanowires in the R-matrix formalism using the Implicity Restarted Arnoldi Method, G. A. Nemnes, L. Ion, S. Antohe, PHYSE_D-09-00422, accepted to be published in Physica E: Low-dimensional systems and Nanostructures, Vol ..pp (2010)

Documents

University of Bucharest – Faculty of Physics MDEO Research Center RESEARCH AND DEVELOPMENT CENTRE FOR MATERIALS AND ELECTRONIC&OPTOELECTRONIC DEVICES (MDEO)