Lab 1 Realization of nanostructured transition metal oxides photo-anodes for photovoltaics

The syntesis of nanostructured metal oxide photoanodes and TCO (e.g. TiO2, AZO) and of semiconductor QD (e.g. Si) will be carried out by means of Physical Vapor Deposition Techniques, and mainly by Pulsed Laser Deposition. In this technique, a high energy UV laser pulse (duration of the order of ns) is focused onto a target material which is ablated in vacuum or in an inert or reactive atmosphere. The ablated plasma is then deposited on the substrate.

This well established technique is well known for its versatility to grow a wide variety of materials. Recently, it has been demonstrated that it is possible to grow complex, high surface area films of different oxides via a fine control of the growth parameters (e.g. background gas pressure, laser fluency, deposition temperature or time); in particular, the variation of the plasma expansion dynamics by means of a reactive atmosphere during the ablation process allows a fine tuning of morphology and crystalline structure of different metal oxides at the nano- and mesoscale.

The lab will be equipped with a deposition apparatus for Pulsed Laser Deposition and a UV excimer laser allowing use of different wavelengths (typically KrF, 248 nm). The deposition chamber will also be equipped with a system for magnetron sputtering deposition for increasing the synthesi capabilities.  Post-deposition treatments (annealing in controlled atmosphere) will be possible using different furnaces.

Lab 2 Ink-Jet printing and wet lab

Inkjet Printing
Ink-jet printing, which is a direct-write, solution-based printing technique, has been historically extremely successful for graphical arts.  Recently there has been a growing interest for several other applications in fields as diverse as electronics and biology. These novel applications are based on the idea of using this technology to position a controlled volume of functional inks on a substrate. In the field of electronics, additive printing offers advantages in terms of process simplification, layer-to-layer alignment, compatibility with large-area processing, and potential cost reduction compared to subtractive lithographic patterning.
CNST-IIT@PoliMi is developing an internal facility and expertise on inkjet printing techniques of functional materials, especially solution processable organic semiconductors and highly conducting metallic inks.  This research activity addresses the design, fabrication and characterization of inkjet printed opto-electronic devices, paying attention to the detailed understanding of the basic physical mechanisms affecting their performances. The investigations mainly focus on organic semiconductor based photo-detectors and field-effect transistors, whose integration is believed to provide great advantage for detecting and imaging applications. A strong effort is delivered to the development of stable printing processes, as a pre-requisite for the fabrication of reliable devices with acceptable yield and uniformity.
The lab is equipped with high-precision, drop-on-demand piezoelectric systems. The first system (installation: November 2010) is Microfab’s jetlab 4xl-A, supplied by Altatech Semiconductor S.A. The nozzle design enables picoliter droplets of conductive ink to be deposited with a positioning accuracy of 25 microns. In addition, the jetlab platform can achieve placement repeatability within 5 microns across a printable area of 210 mm by 260 mm. Using this highly precise deposition technology and a recently developed self-aligned printing technique [Caironi et al. ACS Nano, 2010, 4 (3), pp 1451–1456], electrode gaps of 100 nm to 500 nm can be defined with high yield and uniformity while tightly controlling the volume of material deposited per droplet and the spread of material on the substrate.

Control of substrates surface energy and wettability is a prerequisite to achieve an optimal ink spreading and uniform printed patterns. The lab is equipped with an expanded version of the Dataphysics OCA15-EC tool to perform static and dynamic contact angle measurements and drop shape analysis. The system has an electronic syringe which allows the comfortable and reproducible handling and dosing of liquids. Camera frame rate can be as high as 311 fps to capture fast dynamics, also of small droplets. With this instrument it is also possible to calculate surface free energies on solids and dispersive and polar contributions of liquids based on measured surface and interfacial tensions as well.

WetLab  and Lithography suite
This laboratory is aimed to provide the instruments for materials processing, patterning and coating in a controlled environment, fundamental aspect in many of the CNST-IIT@PoliMi research activities. Specific fumehoods allow the safe manipulation of chemicals and solutions. Spin-coaters are installed for the deposition of thin films. Thermal evaporators enable metallization of samples and deposition of organic small molecules. Oxygen plasma ashers and sonicators allow the cleaning and the conditioning of surfaces and samples. Furnaces and hot plates are present for thermal annealing processes. Two nitrogen glove boxes complement the ambient equipment for processing of oxygen/moisture sensitive samples. An optical microscope and a profilometer are installed for thin films and samples analysis. The WetLab environment is humidity and temperature controlled, with HEPA filters and air recirculation.
A lithography suite for lithographic patterning of samples is also present. This area is kept under clean-room conditions. This is composed by a photoresists deposition bench and a refurbished Suss-Microtec MJB3-UV400 mask-aligner, supplied by Electron mec., capable of ~ 1 μm lateral patterning resolution.

Lab 3 Laser assisted fabrication and structuring

Micro-fabrication technologies have miniaturised many fields from micro-electronics to optofluidics. Various micro structures like microfluidic-channels and patterns can be fashioned by conventional lithographic techniques, but these approaches are primarily limited to the fabrication of two-dimensional patterns on the surface.

In order to create a true 3-D structure several layers of substrates need to be patterned, etched and fused together. A relatively new technique of Femtosecond laser based modification and structuring of materials, can add nuance to these fabrication approaches. Femtosecond lasers in recent years have emerged as a powerful micro-fabrication tool due to their unique characteristics.

Femtosecond micro-fabrication, compared with traditional techniques, offers several striking advantages:

• it is a direct fabrication technique that does not require any photolithographic process;
• compared to conventional laser micromachining, which uses linear light absorption, it offers superior performance in terms of both spatial resolution and fabrication quality;
• it is an intrinsically three-dimensional technique;
• since with a single laser can be used both for fabrication (surface and subsurface micro-structures) and their integration with optical waveguides, these femtosecond laser based fabrication technologies are fast becoming a one-stop solution for fabrication novel devices in dielectric transparent media.

The Femtosecond laser based fabrication technology will be exploited for structuring and modification of materials for light harvesting and for production of novel optofluidic devices.