Dr. Andreea Costas - project leader

Dr. Ionut Enculescu

Dr. Nicoleta Preda

Dr. Monica Enculescu

Dr. Corina Ciobotaru

Dr. Mihaela Beregoi

Dr. Andrei Kuncser

Dr. Mihaela Bunea

Drd. Melania Onea

Nowadays flexible optoelectronic devices have a significant impact in many areas of research. Particularly, in the last years, flexible light emitting diodes (LEDs) focused the attention of the researchers, representing an energy efficient lighting technology due to their substantial role in reducing the global energy consumption, making them the perfect candidates for street lighting in Smart Cities. Compared to the conventional light sources, flexible LEDs present a series of advantages, like flexibility, lumen efficiency, low power consumption, long life time, controllable emission properties and the possibility to use wavelengths from ultraviolet to infrared. Such features recommend LED’s for applications in rollable displays, wearable intelligent electronics, light sources, sensors, optical fibers, digital displays, traffic lights, communications, medical treatments, etc. Thus, LED devices have become very important from scientific and socio-economic point of view. In this context, the scope of the project is the development proof-of-concept energy efficient flexible light emitting diodes with low power consumption and improved light extraction efficiency, the LEDs being based on vertically aligned coaxial ZnO-ZnSe heterojunction nanowires arrays and on single coaxial ZnO-ZnSe heterojunction nanowires. The coaxial ZnO-ZnSe heterojunction nanowire arrays will be prepared using Zn foils and Si/SiO2 wafers patterned with specific geometries as substrates, combining thermal oxidation in air with RF magnetron sputtering, two simple and low cost techniques. Fabricating flexible and nanoscale LEDs based on coaxial ZnO-ZnSe nanowires, will provide new insights in the field of light emitting diodes, expanding the possibilities for their implementation in applications such as rollable displays, street lighting and wearable intelligent electronics, energy efficient devices.

The objective of the second stage of the project - Optimization of the processes regarding the preparation of the vertically aligned coaxial ZnO-ZnSe heterojunction nanowire arrays: Activity 2.1 Preparation of the vertically aligned nanowire arrays containing ZnO nanowire segments at the base and coaxial ZnO-ZnSe nanowire segments in the upper part using RF magnetron sputtering and thermal treatment. Optimizing the shell thickness by controlling the RF magnetron sputtering parameters; Activity 2.2 Complex characterization of the vertically aligned coaxial ZnO-ZnSe heterojunction nanowire arrays obtained on Zn foils and lithographically patterned substrates; Activity 2.3 Fabrication of flexible LEDs based on arrays of ZnO-ZnSe heterojunction nanowires by incorporating the ZnO-ZnSe nanowires arrays into a PDMS film, dry etching both ends of the polymer and depositing Ohmic ultra-thin transparent (bellow 20 nm in thickness) upper metallic contacts; Activity 2.4 Investigating the optoelectronic properties of the LED’s based on coaxial ZnO-ZnSe heterojunction nanowire arrays and put in evidence the influence of the substrate used in the preparation of the ZnO nanowire arrays and of the ZnSe shell thickness on the LED’s performances; Activity 2.5 Obtaining metallic interdigitated electrodes by combining photolithography with magnetron sputtering and thermal vacuum evaporation; Activity 2.6 Transferring the coaxial ZnO-ZnSe heterojunction nanowire arrays onto the metallic interdigitated electrodes; Activity 2.7 Dissemination of results by presentation of the scientific results to general public including possible investors, at 2 international conferences, at 2 national innovation events, by publishing 2 article in ISI indexed journals with a high impact factor (impact factor > 4) and by making 1 patent application at the state office for inventions and trademarks (OSIM). In this context, the preparation of the vertically aligned coaxial (core-shell) ZnO-ZnSe nanowire arrays were fabricated by coating the surface of the ZnO nanowire arrays obtained by thermal oxidation in air with ZnSe shells (with different thicknesses) employing RF magnetron sputtering. Moreover, LEDs based on arrays of ZnO-ZnSe core-shell nanowires were developed on glass substrates patterned with Ti/Pt metallic electrodes. Furthermore, the scientific results were disseminated by publishing 1 article in an ISI indexed journal, writing another article and presenting the results at 3 national and international conferences.

Scientific papers published:

1. “Silver nanoparticles decorated ZnO–CuO core–shell nanowire arrays with low water adhesion and high antibacterial activity”, Andreea Costas, Nicoleta Preda, Irina Zgura, Andrei Kuncser, Nicoleta Apostol, Carmen Curutiu, Ionut Enculescu, Scientific Reports, 13, 10698-15, 2023.

Scientific papers presented at international conferences:

1. “Patterned interdigitated electrodes covered with ZnO nanowire arrays: preparation, characterization and optoelectronic applications”, Andreea Costas, Melania Onea, Nicoleta Preda, Corina Ciobotaru, Victor Diculescu, Ionut Enculescu, poster presentation at the 2023 13^th International Advances in Applied Physics & Materials Science Congress & Exhibition (APMAS) Oludeniz, Turkey, October 11-17 2023.
2. “ZnO-ZnSe core-shell nanowires based devices for sensing applications”, Andreea Costas, Nicoleta Preda, Andrei Kuncser, Mihaela Bunea, Victor Diculescu, Ionut Enculescu, poster presentation at the 74^th Annual Meeting of the International Society of Electrochemistry (ISE) Lyon, France, September 3-8 2023.
3. “Materiale nanostructurate integrate in dispozitive optoelectronice cu potentiale aplicatii in (bio)sensing”, Andreea Costas, Nicoleta Preda, Camelia Florica, Andrei Kuncser, Adrian Enache, Victor Diculescu, Ionut Enculescu, oral presentation at the 2023 SMART DIASPORA, Noi frontiere și provocări ale abordărilor transdisciplinare – Analiza și Controlul Dinamicii Sistemelor Celulare, April 10-13 2023.
4. “Semiconductor core-shell nanowires: synthesis, characterization and photodetecting applications”, Andreea Costas, Nicoleta Preda, Monica Enculescu, Andrei Kuncser, Ionut Enculescu, poster presentation at the 2022 12^th International Advances in Applied Physics & Materials Science Congress & Exhibition (APMAS).

Dr. Andreea Costas

andreea.costas@infim.ro

National Institute of Materials Physics