Molecular Beam Epitaxy “MBE”

Molecular Beam Epitaxy - MBE
 

Carlo Ottaviani  - carlo.ottaviani@ism.cnr.it

Laboratory IC11

 
In an epitaxy (from ancient Greek έπί, epì, "Top" e τάξίξ, tàxis, ”order-arrangement trough ordering”) process, atoms or molecules are deposited on a substrate and some structures evolve as a result of a multitude of processes. This is a non-equilibrium phenomenon and any synthesized growth is governed by the competition between kinetics and thermodynamics. Self-assembly and self-organization are modes through which nanometer-size structures, called here nanostructures, grow on a surface. In the simplest case, the growth proceeds in a 2D fashion, one atomic layer after the next, up to some required film thickness. This is called layer-by layer Frank-Van der Merwe (FV) growth. Very often the deposited material coagulates into islands/clusters, which at a first stage may form a polycrystalline layer. This is the Volmer-Weber (VW) type growth: 3D crystallites form upon deposition and some surface areas remain uncovered since the initial stages of deposition. The Stranski-Krastanov (SK) growth is in-between: a few layers may grow in FV mode before 3D clusters begin to form.
 

TECHNICAL SPECIFICATIONS

  • Working pressure ~10-11mbar
  • Si(C-BN-1400 °C), Ge(BN-1200 °C, Mn(BN-1200 °C) K-cells from RIBER; Si (flux=0.04 Å/min); Ge (flux=0.16 Å/min);
  • Sb, As, Bi- Surfactants effusion cells;
  • Ag, Au- Capping Layer effusion cells;
  • DC direct sample heating (RT-1200 °C) and Indirect heating (RT-450 °C ) systems;
  • Air-vacuum Fast Load-lock Sample Transfer System;

AVAILABLE TECHNIQUES

  • STAIB EK-3315-R RHEED Ultra-High Vacuum (UHV) System for Surface Science Investigations;  

  • Cleaning Semiconductor (SC), Metal (M)-Surfaces reconstruction;  

  • Epitaxial growth SC/SC, SC/Metal/SC;

  • Homo- and Hetero-structures growth: 1D, 2D and 3D Materials.

 

SAMPLES

  • Sample lateral dimensions: 10 x 5 mm (ideal), 3 x 3 mm (minimal), 10 x 10 mm (maximal);

  • Sample thickness: ideally up to 2 mm (thicker and/or smaller samples also feasible).

 

USED FOR

  • Fundamental Surface Science study;

  • Artificial Atomic Epitaxial Growth;

  • Discovery of new 1D, 2D and 3D epitaxial  SC/SC; M/SC for micro-nanoelectronics and solar cells purposes;

  • Semiconductors for Microelectronics;

  • Microcircuits;

  • Ultra-thin Films;

  • Samples Cleaning;

  • Thin-film Stability;

  • Barrier Layers;

  • Lubrication;

  • Chemical Industry;

  • Coatings/Catalysis.

 

CASE STUDIES

Cross-sectional HRTEM Mn0.06Ge0.94on Ge(001)2x1

The structural, electronic, and magnetic properties of the Mn0.06Ge0.94 diluted magnetic semiconductor, grown at 520 K by molecular-beam epitaxy on Ge(001)2✕1, have been investigated. Diluted and highly ordered alloys, containing Mn5Ge3nanocrystals, were grown. The valence band photoelectron spectrum of Mn0.06Ge0.94 shows a feature located at −4.2 eV below the Fermi level, which is the fingerprint of substitutional Mn atoms in the Ge matrix. Magnetization measurements show the presence of a paramagnetic component due to substitutional Mn atoms and of a ferromagnetic like component due to Mn5Ge3nanocrystallites. The Mn L2,3 x-ray absorption spectrum of this polyphase film shows no marked multiplet structure, but a bandlike character.

See: P. De Padova, et al., Phys. Rev. B 77,  045203 (2008).

 
Cross-sectional high-resolution transmission electron microscopy (HRTEM) image of a Mn0.06Ge0.94 film grown on a Ge(001)2x1 substrate held at 520 K.
 
 
 
HRTEM cross-sectional image of a Mn5Ge3 film grown on Ge(1 1 1), taken along the [-1- 1 2] zone axis of the Ge(1 1 1) substrate. (b) Ball and stick side-view of a coherent epitaxy between Mn5Ge3 film and Ge substrate.

Mn5Ge3 film on Ge(111)

An investigation of the structural, magnetic and electronic properties of≈3 nm thick Mn5Ge3 films epitaxially grown on a Ge(111)-c(2✕8) reconstructed surface is reported. High resolution transmission electron microscopy and selected area electron diffraction give evidence of 2.2% in-plane compressive strain between the Mn5Ge3 film and the Ge substrate. Magneto optical Kerr effect measurements show that the films are ferromagnetic with a Curie temperature of ≈325 K. The analysis of Ge 3d core level photoelectron spectra of the Mn5Ge3 films allows determining an upper limit of 76 meV for the Ge 3d5/2 core-hole lifetime broadening. The Ge 3d3/2 core-hole lifetime broadening is found to be 15 meV larger than that of the Ge 3d5/2 core hole, because of the existence of a Coster–Kronig decay channel due to the metallic character of Mn5Ge3.

See: P. De Padova, et al., Phys. Rev. B 77,  045203 (2008).

 
 

Nanoparticles, nanocomposites and nanoarchitectures

The ISM has a consolidated experience for the design and synthesis through chemical and physical methods of multifunctional materials engineered at the nanometer scale with controllable chemical-physical and functional properties (e.g. electronic, magnetic, optical and optoelectronic) of great interest for fundamental studies and applications such as energy, biomedicine, catalysis and photonics.
Processes and approaches followed in synthesis are characterized by techniques such as: i) solid state, hydrothermal, sol-gel and sono-chemical ones which allow the production of nanocomposites and nanohybrids for energy storage and biomedicine; ii) nanochemical and mechanical grinding synthesis for the preparation of metal nanoparticles, magnetic alloys and multifunctional nanocomposites combining nanoparticles and carbon-based materials (CNTs and graphene) which are of interest in different fields such as energy and catalysis; iii) soft chemical synthesis (e.g. co-precipitation and thermal decomposition) for the preparation of magnetic nano-architectures that are formed by magnetic nanoparticles having controlled morphology and core-shell/multi-shell bi-magnetic structures representing elements for superstructures 2D and 3D magnetic and liquid systems (ferrofluids); iv) laser ablation in liquid regarding the chemical free synthesis of colloidal solutions of nanoparticles, which can even be in the form of core-shells structures, of any material (e.g. metals, alloys, oxides and carbides). This green synthesis approach does not need the use of surfactants or specific chemical reagents aiming the application of laser ablation in liquid in catalysts and/or for providing highly pure reagents for being used in chemical and biochemical synthetic routes.

 

 

Nanocomposites and nanohybrids synthesis Magnetic Nano-Architecture

Nanochemistry for the synthesis of nanoparticles and nanocomposites Nanoparticles synthesis by Laser Ablation in Liquid

Molecules and hybrid materials

ISM has been working since many years in the design and development of organic, hybrid and (bio)ceramic materials regarding cutting-edge highly sustainable technologies, such as the latest generation of photovoltaic and flexible electronics and applications of the circular economy paradigm through the development of innovative decarbonization catalytic processes.
In this context are included the synthesis of: i) variously functionalized organic and metalorganic molecular semiconductors with extended conjugation (e.g. phthalocyanines, porphyrins, perylenes and thiophenic derivatives) obtained through scalable and sustainable chemical processes that minimize the use of toxic solvents and the production of waste materials; ii) hybrid and inorganic perovskites of various compositions; iii) zeolitic, ceramic and bio-glasses bulk materials by hydrothermal, sol-gel and batch processes.
The know-how and facilities currently available at the ISM Montelibretti branch, allow:  i) the design and synthesis of either well established or original target materials, as well as their purification by extractive, chromatographic and thermal techniques; ii) depositions on substrates of various kind of molecules and hybrid solutions through spin-coating and Langmuir-Blodgett techniques, with regard to their characterization the optical and charge transport properties of the resulting films can even be performed; iii) the preparation of catalysts for energy conversion applications such as from waste (e.g. biomass) such as HDO of lignin, environmental decarbonization by direct capture of atmospheric CO2 or thermochemical H2O/CO2 splitting.

Organic and metallorganic synthesis Inorganic synthesis of porous materials by catalysis