MATERIALS FOR NANOTECHNOLOGIESCMAST (Computational MAterials Science & Technology) Virtual Lab

www.afs.enea.it/project/cmast

Computational Materials Science

Adhesion of organic molecules on inorganic surfaces

Projects:• META - Materials Enhancement for Technological

Applications (FP7-PEOPLE-2010-IRSES)

C.- Arcangeli (ENEA), F. Buonocore (ENEA), M. Celino (ENEA)

Results:• the aminoacids involved in the adhesion are identified. Arg seems to play the major role• the adhesion is mainly driven by the electrostatic interacions and by the interfacial water molecules which form a stable and oriented a hydrogenbonding network induced by the surface

Problem: It is known in nature that some animals , like gecko, can have an extraordinary adhesion on surfaces. This adhesion can be selective and very strong. This is due to surface proteins and their specific conformational properties.

Open questions:1) Why some proteins are so adhesive on inorganic surfaces ?2) Which is the recipe to engineer such proteins ? Which are the

critical aminoacids ?3) Organic-inorganic adhesion can be used to develop new

microelectronic devices ?

Method:Atomic scale molecular dynamics of proteins in contact with the (110) anatase TiO2 surfaces . Quantum approaches are used to study the adhesion fo singles aminoacids. Classical molecular dynamics is used to characterize the adhesion of the entire protein.

META project aims to develop a DNA nanogrid fixed via aptamer proteins to specific inorganic surfaces. This could be the first step of a new class of devices

Quantum total energy calculations select binding sites and charge transfer between aminoscides and surface

Classical molecular dynamics finds folding of an engineered protein in water

Classical molecular dynamics of the entire protein on the TiO2 surface

Pulling of the proteins to compute the adhesion force

Graphene production Projects:• European Future and Emerging Technology (FET) Iniziative on

GrapheneF. Buonocore (ENEA)

Problem: The production of graphene on large scale and high purity is still a challenging problem. Experiments indicate that CVD growth mechanism on copper could be a very promising process. However quality of the graphene should be improved.

Open questions:1) Which are the adhesion energies of graphene on liquid copper ?2) Which is the growth mechanism of graphene ?

Method:Quantum molecular dynamics simulations are used to model a graphene –liquid copper interface. Total energy calculations are used to compute electronic density of state and charge transfers. Quantum molecular dynamics is used to simulate the effect of temperature on the adhesion properties.

Chemical Vapour Deposition growth of graphene (ENEA, UTTMAT-SUP lab)

Model of graphene on crystalline copper

1 2 3 4 5 6 7-0.015

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esi

on E

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y (e

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^2)

graphene-surface (average) distance (Å)

LDA

Graphene-Copper Adhesion Energy

Graphene-Copper Band Structure

Charge density and interface dipole

0 10 20 300

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Vacuum Level

WF = 4.04 eV

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Fermi Energy

Work Function Calculation of Copper Functionalized with Graphene

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erg

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Graphene Band Structure

Dirac cone

Model of graphene on liquid copper

Results:• Electron transfer from copper substrate to

graphene was found and an interface dipole is generated

• In graphene Fermi level is shifted upwards due to the interface dipole so that graphene is electrostatically n-doped

C. Arcangeli et al. (2013) Nanosci. Nanotech. Lett 5(11):1147-1154

Adhesion of self-assembled alkylsilane coatings of a (111) silicon surface F. Gala (Univ. La Sapienza), G. Zollo (Univ. La Sapienza)

Open questions:1) Is the adhesion chemistry related to the uniformity of the SAM?2) What are the basic phenomena causing self-assembling?3) At which extent OTS SAM improves the isolation properties of Si (i.e. how the work function depend on the adhesion chemistry and SAM uniformity)? Method:OTS multiple adsorptions onto the (111) Si surface have beenvmodeled by ab initio density functional theory (DFT), with a generalized gradient approximation (GGA), using the Perdew−Burke−Ernzerhof formula19 (PBE) for the electron exchangeand correlation energy, together with norm-conserving pseudopotentials, constructed using the Troullier−Martins scheme,20 and a plane wave basis set expansion scheme. First-principles calculations have been performed using theQUANTUM-ESPRESSO package,

Results:• SAM are formed via hydrogen bonds formed between the silane adhesion groups only if OTS adhere with just one bond per molecule.•A simple model has been adopted to calculate the work function at full coverage involving partial dipoles.• structural information are provided to avoid a decrase in the device performance.

Fully relaxed configurations of the OTS adhesion on the hydrogenated (111) Si surface

Partial dipole as a function of z, for the H:Si slab (black line) and 1 × (1:1) structure (red line). The surface dipoles have been evaluated at zs, which is one of the special planes dividing the whole structure into two neutral subunits

Work function shifts ΔΦ with respect to the hydrogenated (111) Si surface as a function of Δds for the various configurations studied.

Problem Self-assembled monolayers (SAMs) octadecyltrichlorosilane films (CH3(CH2)17SiCl3, OTS) deposited on Si or SiO2 exhibit high insulating properties, provided that a good control of film quality is achieved, making this system highly appealing for the fabrication of efficient field emitting transistors (FETs) or organic thin film transistors (OTFTs) at the nanoscale, where silicon dioxide (SiO2) behaves as a poor insulator with high leakage currents. SAM coatings of semiconductor surfaces have been also employed in organic light-emitting diodes (OLED) as “adapting” dipolar thin films that may greatly improve the device performance by modifying the work function at the gate/substate interface.