Novel functional nano-composite nanowires

• Research unit: COST
• Project number: C11.0138

Key words (English)

Focused electron beam induced deposition; nanocomposite nanowires; nanosensors; superparamagnetism; Hall sensors

Research programs (English)

COST-Action MP0901 - Designing novel materials for nanodevices: From Theory to Practise (NanoTP)

Short description (English)

The primary objective of this project is the synthesis of nano-composite nanowires (nc-NW) enabling the fabrication of novel nanodevices. We want to employ focused beams of scanning electron and ion microscopes in conjunction with injected, surface adsorbed gas molecules for synthesis[1]. The locally synthesized material obtained from the interaction of electrons (ions) with surface adsorbed organo-metallic molecules is typically of nano-composite type: it contains metal nanocrystals embedded in a carbonaceous matrix [2]. It was recently shown that the metal-to-matrix ratio can be tuned by smart irradiation schemes, and, that nanocomposite compositions can be tailored such that the properties of the nanocomposite nanostructures exceed those of the pure metal structures[3]. The tasks of this project are a) to develop novel metal-carbon model nanocomposite nanowires b) to characterize their electronic, magnetic and mechanical properties, and c) to link these properties to their internal nanocomposite structure (metal-matrix) as well as their low-dimensional shape. The project will establish design and synthesis rules which permit to engineer such novel nano-materials as well as to demonstrate the material's functionality in devices such as mechanical strain gauges and magnetic sensors[4].

Further information (English)

Full name of research-institution/enterprise: Eidg. Materialprüfungs- und Forschungsanstalt EMPA

Partners and International Organizations (English)

BE; BG; HR; CY; CZ; DK; FI; FR; DE; EL; HU; IE; IT; NL; PL; PT; RO; SI; ES; SE; TR; UK; AM; RU; MX; AU

Abstract (English)

We studied gas assisted focused electron beam induced deposition (FEBID) as a direct write method with nanometer scale resolution to deposit novel nanocomposite nanowire materials: 1) We established FEBID models which account for one precursor molecule species injected as well as two molecule species injected. We were able i) to extract analytical scaling laws for the lateral deposit size with respect to electron beam exposure period and surface diffusion, ii) to develop a methodology for determining the surface diffusion coefficient and average residence time of organometallic adsorbates, iii) to apply this model to different scanning strategies when 3D structures are grown from the Me3-Pt-CpMe precursor, and iv) to predict surface composition gradients in alloy deposits obtained from FEBID. 2) We have integrated pulsed infrared laser heating into the SEM which can be synchronised with the electron beam exposure cycles or it can be used for post-deposition annealing of the FEBID deposits. Depending on the laser pulse duration and power, the nanocomposite wire material could be tuned in composition and nanostructure. Most importantly, pure copper nanocrystals could be obtained by post-deposition annealing from Cu-carbon FEBID deposits obtained from Cu(hfac)2. A model was established to determine the temperature pulse from calibration experiments. 3) Co-injection of two precursor molecules was performed. Binary metal nanocomposite materials were obtained with Au, Co, Ge, W and Cu as nanocrystals embedded in a carbonaceous matrix. However, the carbon content of these materials was relatively high. Post-deposition annealing treatments should allow increasing the metal content in future. 4) Another add-on was integrated into the SEM; an oxygen and hydrogen microplasma. We could show that the plasma can be used for post-write treatments to reduce the carbon content. 5) The magnetic and electric characterization of nanowires has been performed in the temperature range (4K-293K) and for high external magnetic fields up to 9Tesla. The samples showed metallic conductivity and weak anisotropic magnetoresistance signal with a ratio below 0.1%. 6) A platform for 4-probe electrical resistance measurements has been integrated to the FEBID setup for novel in-situ measurements and end-point detection of the FEBID process and post growth treatments: irradiation with electrons, annealing with laser. This setup was also used for calibrating the laser heating pulse. 7) A SEM-integrated setup for the detection of the movement of micron-sized superparamagnetic beads above FEBID magnetic Hall sensors of Co-C material with a sensing area of around 100x100 nm2 was developed and successfully tested on our own FEBID nanodevice sensors. It was shown that the FEBID material has a very high potential to monitor very small and localized magnetic fluxes due to its sub-100nm downscalability (outperforming semiconductor materials).

References in databases (English)

Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. [phone] Swiss Project-Number: C11.0138