• REFERENTS:
  PAOLA BASSANI
  CARLO FANCIULLI
  

• UNIT:
  LECCO
  

• REFERENTS:
  PAOLA BASSANI
  CARLO FANCIULLI
  

• UNIT:
  LECCO
  

Regarding CVD processes, Atomic Layer Deposition (ALD) technique stands out for producing high density nanostructured and nanosized layers with an optimal deposition control at atomic level. ALD allows the achievement of the cover layer by means of a cyclic process at reduced pressure. The overall layer material is indeed obtained by means of a chemical reaction between two reactants-precursors that are alternatively injected into the reactor. The reactor is purged between each reactant injection for removing the previous reactant excess. The technique allows the deposition of coatings with different chemical composition and morphology providing high chemical homogeneity, optimal conformal coverage and thickness control at atomic level. ALD is also scalable on high surface area samples, thus allowing its application at industrial level.
ALD can operate from low to intermediate temperature (from RT to 300°C), thus also allowing the coverage of thermally degradable substrates (i.e. hybrid organic-inorganic systems) and/or minimizing unwanted inter-diffusion film-substrate processes. Because of this reasons, ALD is suitable for the deposition of single- and multi-layers high functional material for different purposes, especially for oxide-based compounds.

Metal Organic Chemical Vapour Deposition (MOCVD) technique is a chemical process widely employed for the realization of single- and multi-component nanostructured materials by means of the chemical decomposition of one or more suitable precursors from vapour phase on a hot substrate.
The ICMATE-CNR reactors can operate at atmospheric or reduced pressure.
MOCVD versatility comes from the high number of adjustable chemical and physical parameters. The parameter set can be tuned for optimizing the deposition process, thus obtaining specific compositional, morphological and structural properties.
MOCVD allows the deposition of a wide range of materials as crystal or amorphous ones, for different types of advanced purposes such as in energetic, (photo)catalysis, sensor, biomedical, electronic, protective or decorative applications.
Three different reactors are available in the laboratory as a function of the specific experimental requirements (atmospheric or reduced pressure or suitable for wide samples, 10x40 cm).

The cold wall Metal Organic Chemical Vapour Deposition (MOCVD) reactor developed by ICMATE-CNR, operating at reduced pressure, allows the direct insertion into the reaction chamber of solid, low-volatile and air-sensitive chemical precursors, by means of specific evaporation cells. The precursor cell-holders are equipped with feedback controls for monitoring the precursor amount into the chamber and thus operating in strictly controlled and reproducible condition. The cold-wall reactor employment allows a high efficiency in the precursor utilization because chemical reactions occur only on the substrate surface (being the only heated element in the reactor). The reactor allows the obtainment on dense and solid inorganic oxide-based materials. The reactor can also be used as Plasma Enhanced Chemical Vapour Deposition (PECVD). In this configuration the precursors are activated by means of a cold RF plasma (13.56 MHz) obtained at low pressure. In such condition the deposition can occur at low temperature, thus avoiding the damage of thermal-sensitive substrates (i.e. plastic-based substrates). The deposition of different types of materials is possible with high deposition rate.

The Tencor Alpha-Step IQ stylus profiler is a simple instrument for the evaluation of the thickness of thin layers (obtained, as an example, by means of chemical deposition) and surface roughness of flat samples.
Thanks to the side and vertical motion of the electro-mechanical stylus on the sample surface, the vertical outline of the investigated line is identified. The outline is then collected and elaborated by means of a suitable software for the thickness and/or roughness calculation. Il profilometro Tencor Alpha-Step viene utilizzato per la determinazione dello spessore di un deposito (ottenuto mediante tecniche di deposizione chimica) e la rugosità superficiale dello stesso. Grazie alla presenza di uno stilo elettromeccanico che si muove lateralmente lungo la superficie del campione e verticalmente in contatto con esso, è possibile rilevare le variazioni del profilo verticale. La deviazione rilevata dalla punta viene amplificata, visualizzata su uno schermo e quindi misurata.

Hydrophilic/Hydrophobic properties of surfaces are very interesting in technology and contribute to the application field of the materials.
ICMATE-CNR has prepared an home-made apparatus for the wettability determination by means of the static contact angle measurement. The angle between the material surface and a liquid drop (typically water) is indeed determined. The employment of a dedicated video camera also allows the evaluation of the drop evolution as a function of time on the material surface, and thus studying the dynamic wettability.