Nanoparticle bombardment -deposition-

1. Meeting report 11.1.2007 Nanoparticle bombardment-deposition- Inkyu Eu Univ.of Michigan Ann Arbor Mechanical Engineering

2. Overview 1.Second application of NanoFET 2.What is the CBD? 3.How can nanoparticles be deposited on a substrate? 4. Cluster sources 5.How to get nanoparticles’ formation? 6.Future work

3. 1.Second application of NanoFET NanoFET deposit can be called the CBD. NanoFET as a way of deposit Both NanoFET and CBD are applied nanoparticles Fig1.Scanning electron micrograph of A thick film formed by carbon nanoparticles deposition using CBD.

4. 2.What is the CBD? • Cluster Beam Deposition • Method that deposits nanoparticles as a type of cluster on substrate • High degree of purity and exact nanoparticle size control Figure 2. Schematic showing the deposition of patterned films(SEM)

5. 3.How can nanoparticles be deposited on a substrate? Gas phase nanoparticle formation and growth Formation and growth processes of objects relevant for CBD follow the same physical and chemical echanisms as any gas-phase particle synthesis process. Hence, the process from NanoFET deposit is as same as CBD’s. 1. Particle formation 2. Particle growth

6. 3.How can nanoparticles be deposited on a substrate? 1. Particle formation The starting material can be vaporized from a hot source into a low density inert gas employing Joule heating, thermal plasma or laser ablation. (1)Homogeneous nucleation: Cooling of the vapor rapidly leads to super-saturation followed by homogeneous nucleation and the formation of first product clusters.[1] A criterion to determine the formation path of a cluster is its thermodynamically critical diameter, the Kelvin diameter d1,C : : Surface tension : Molecular volume of the cluster : Boltzmann constant. : Dimensionless saturation ratio at temperature T 1.Granqvist C G and Buhrman R A (1976)

7. 3.How can nanoparticles be deposited on a substrate? • Critical diameter of cluster << Diameter of a single molecule of the product species • -A nucleus is stable and there will be no growth or shrinkage by condensation or evaporation and the particle will form by coagulation • Critical diameter of cluster >> Diameter of a single molecule of the product species • A nucleus is unstable and particles are formed by homogeneous nucleation: • balanced condensation and evaporation of molecules to and from clusters of the • product species. (2)Coagulation (collision): It is applied to particle growth in combination with coalescence. 2.K Wegner and P Piseri (2006)

8. 3.How can nanoparticles be deposited on a substrate? 2. Particle growth The newly formed particles continue to grow either by surface growth (addition of atoms or molecules to the particle) or by coagulation (inelastic particle–particle collisions) which is usually followed by coalescence. Coagulation describes particle–particle collisions due to Brownian motion or other mechanisms such as shear or electrostatic forces. Particle growth by coagulation has to be distinguished between collisions in the free molecular regime (particle diameter dp smaller than the mean free path of the gas λ) and in the continuum regime (dP>>λ). (1).Coagulation (collision) 2.K Wegner and P Piseri (2006)

9. 3.How can nanoparticles be deposited on a substrate? The classical theory for Brownian coagulation of monodisperse spheres in the continuum regime at temperature T is used to calculate dp [3] (Neglecting the particle morphology and the spread of the particle size distribution): : Initial particle diameter : Initial particle concentration : Dynamic viscosity of the gas : Residence time If the particle diameter is much smaller than the mean free path of the gas, as is usually the case with clusters, the coagulation theory in the free molecular regime has to be applied. (Neglecting the spread of the particle distribution and the morphology): : Total volume of particles per unit volume of gas : Density of the particles 3.Friedlander S K (2000)

10. 3.How can nanoparticles be deposited on a substrate? Self-preserving size distributions [3] :Particles that grow by Brownian coagulation typically reach asymptotic distributions tSPSD: Time to reach the self-preserving size distribution in the free molecular regime.[4] 3.Friedlander S K (2000) 4.Wegner K and Walker B(2002)

11. 3.How can nanoparticles be deposited on a substrate? 2.Surface growth Surface growth consists of a first step of molecule or atom transport to the surface of an already-formed particle and a second step involving a chemical reaction or a phase change at the particle surface. Especially during the first stages of particle formation from supersaturated vapour, surface growth can be significant as the initially formed clusters act as condensation seeds for the remaining vapour. By controlling the supersatura- tion at a low level, particle nucleation can be slowed down while the rate of surface growth by vapour deposition can be increased 2.K Wegner and P Piseri (2006)

12. 3.How can nanoparticles be deposited on a substrate? The rate of change of the particle diameter dp at temperature T by vapor deposition in the free molecular regime is given by [3]: : Volume of the transported molecule in the particle phase :Partial pressure of the gas or vapor topical far from the particle : Partial pressure at the particle surface obtained from the equilibrium vapor pressure : Fuchs–Sutugin factor for bridging the free molecular with the continuum regime [41] 3.Friedlander S K (2000)

13. 3.How can nanoparticles be deposited on a substrate? In the continuum regime, the rate of change of the particle diameter is [3]: : Diffusion coefficient of the gas or vapor : Fuchs–Sutugin factor for bridging the continuum with the free molecular regime 3.Friedlander S K (2000)

14. 4. Cluster sources 4.1. Joule heating 4.2. Sputtering 4.3. Laser vaporization 4.4. Arc discharge 4.5. Pulsed microplasma cluster source (PMCS)

15. 5.How to get nanoparticles’ formation (method)- (1)Supersonic beam cluster 1.Nanostructured TiO2 films were grown by depositing clusters produced by a pulsed microplasma cluster source (PMCS), in high vacuum conditions. 2.Particles with different masses have different inertia so that a spatial separation takes place and the particles are deposited in different regions of the collecting surface, called impactor. 3.Oxidation of titanium clusters constituting the films takes place immediately after exposition to the air,due to the high reactivity of titanium and to the high porosity of the cluster-assembled films. Ref. E.Barborini,I.N.Kholmanov(2002) Fig.2.TEM image showing the nanostructure of the film:Grains with size below 10 nm are randomly assembled to constitute a porous structure such as those typical of the ballistic aggregation regime.

16. 1.XPS, Auger, and EELS spectroscopies confirm that the LECBD technique in UHV allows us to produce nanostructured silicon films with a rather low oxygen contamination. In the deposited size range under consideration in our experiments (below 300 atoms) the general behavior of the film is comparable to amorphous silicon 2.The silicon nanograins are partially connected by their dangling bonds leading to a minimization of their total numbers. In addition, cluster surface reconstructions involving the formation of oddmembered rings is at the origin of dangling bond minimization. Ref.P.Melinon P.Keghelian (1997) The x-ray photoelectron spectroscopy technique (XPS), associated with the Auger electron spectroscopy (AES), and the electron energy loss spectroscopy (EELS) techniques are applied on samples in ultrahigh vacuum conditions (UHV) for the investigation of the electronic structure. 2.How to get nanoparticles’ formation- (2)Low energy cluster beam deposition Specific electronic properties

17. 5.How to get nanoparticles’ formation (method)- (2)Low energy cluster beam deposition A slight increase of the magnetic anisotropy in the mixed SmCo5 cluster films compared to the pure Co-cluster ones. Ref. M. Negrier, J.Tuaillon-Combes (1999) Magnetic properties The structural properties and the magnetic behavior of pure SmCo5 cluster assembled lms prepared by the LECBD technique, and SmCo5 clusters embedded in a silver matrix

18. 2.How to get nanoparticles’ formation (method)- (3)Different examples • The electron dynamics is studied in silver nanoparticles of different sizes embedded either in asilicate glass or in a porous alumina matrix, using time-resolved optical spectroscopy. Ref. V.halte,J.Y.Bigot(1999) • Nanodispersed gold targets (2–100 nm grains) were bombarded for the first time in the nuclear stopping region by 1 MeV Au5 cluster ions (P(dE/dx)n = 45 keV/nm and (P(dE/dx)e = 4.5 keV/nm in gold). Ref.Baranov.S, Della-Negra (2006)

19. 6.Future work 1.Cluster Source 2.Etching investigation both ion and nano- particles bombardment 3.More detailed and wide investigation of nanoparticles bombardment 4.Parallel to ion bombardment

20. The End