Presentation is loading. Please wait.

Presentation is loading. Please wait.

Non-linear Effects in Diffusion on Nanoscale Department of Solid State Physics University of Debrecen D.L. Beke Z. Erdélyi, I.A. Szabó, Cs. Cserháti.

Similar presentations


Presentation on theme: "Non-linear Effects in Diffusion on Nanoscale Department of Solid State Physics University of Debrecen D.L. Beke Z. Erdélyi, I.A. Szabó, Cs. Cserháti."— Presentation transcript:

1 Non-linear Effects in Diffusion on Nanoscale Department of Solid State Physics University of Debrecen D.L. Beke Z. Erdélyi, I.A. Szabó, Cs. Cserháti

2 Diffusion in nanomaterials Two important features a) High numbers of grain- or phase boundaries (GB or PB) and dislocations - fast diffusion and solid st. reactions, segregation, etc. b) Principal problems (very short distances and preferably no structural defects)

3 Principal difficulties: -Short diffusion distances L  d (continuum description fails) - Gradient energy corrections - Stress effects

4 Discrete (Martin‘s) model dc i /dt = -z v [c i (1-c i-1 )  i,i-1 – (1-c i )c i-1  i-1,i + + c i (1-c i+1 )  i,i+1 – c i+1 (1-c i )  i+1,i ].  i,i+1 = exp(-E i,i+1 /kT) „Classical” Fick I.-II. „Classical” Fick I.-II. j i,i+1 = -D i (  c/  x)/   c i /  t =  [D i (  c/  x)/  ]/  x

5 E i,i +1 =E o -  i +  i and E i+1,i = E o -  i -  i, V=V AB -(V AA +V BB )/2  i = [z v (c i-1 +c i+1 +c i +c i+2 ) + z l (c i +c i+1 )](V AA -V BB )/2  i  V. Input parameters: z v, z l,V AA -V BB,V,T Input parameters: z v, z l,V AA -V BB,V,T(Z= 2z v +z l )

6 -validity limit -validity limit m= Z(V AA –V BB )/kT D i h =D(0)exp(mc)

7 Effect of the strong concentration dependence of D a-Si/Ge x Mo/V The interface reamins sharp and shifts! and shifts! T=1053 K 680K100h

8 Dissolution in ideal systems: Ni into Cu D(in Ni)<

9 Linear kinetics !!! Monte Carlo Ni side Interface Cu side

10 Experiment: AES from the top of Ni on Cu(111) T=679K

11 Sharpening of a wide interface (T=1000K, m’=9) Mo-VMo-V Ni-Cu

12 Growth of intermetallid layer:

13 i-1 ii+1 n nd             !3 2/ !2 2/ 2 x nd x nd x nd nn i d cc x c ii      1 d d cc d cc x c iiii        i-1 ii+1 n = =c/= =c/             !3 2/ !2 2/ 2 x nd x nd x nd nn i d cc x c ii      1 d d cc d cc x c iiii       

14 e.g.  i = (V AA -V BB ){cZ +(z v +Z/4)d 2  2 c/  x } = cZ(V AA -V BB )+  i ’ +... Introducing  i, = exp[-(E o -  i )/kT]=  i h exp[  i ’ /kT]. and if  i /kT«1 (i.e. exp[  i /kT]  1+  i /kT j i,i+1 = J i,i+1 /q= J i,i+1 d/  = -D i (  c/  x)/  + + D i [2  /f o ’’ - d 2 /24](  3 c/  x 3 )/  +... D i =z v d 2  i   ~V Fick I. Amorphous systems?, Stress effects…

15 X o =0 Constant concentration at the surface:

16 Conclusions (ideal systems): -At short distances the continuum descriptions fails and this strongly depends on the concentration dependence of D (non-linearity) - Non-linearity leads to shift of a sharp interface -The non-linearity leads to a linear shift of a sharp interface sharpening of an originally wide interface -Gradient energy corrections are important not only in the currents but also in the mobilities

17 Papers: CSIK, A., LANGER, G., BEKE, D.L., ERDÉLYI, Z., MENYHÁRD, M. SULYOK, A. Journal of Appl. Phys. 89/1, (2001) BEKE, D.L., LANGER. G.A., CSIK, A., ERDÉLYI, Z., KIS-VARGA, M.,SZABÓ, I.A., PAPP, Z. Defect and Diff. Forum , (2001) ERDÉLYI, Z., GIRARDEAUX., CH., BERNARDINI, J., BEKE, D.L, ROLLAND, A. Defect and Diff. Forum , (2001) ERDÉLYI, Z, GIRARDEAUX, CH. TŐKEI, ZS. BEKE, D.L. CSERHÁTI, C., ROLLAND, A. Surf. Sci., 496/1-2, 129 (2002) ERDÉLYI, Z, GIRARDEAUX, CH. TŐKEI, ZS. BEKE, D.L. CSERHÁTI, C., ROLLAND, A. Surf. Sci., 496/1-2, 129 (2002) ERDÉLYI, Z, SZABÓ I.A., BEKE, D.L. Phys. Lev. Letters, in print

18 Chapters: BERNARDINI, J, BEKE, D.L., „Diffusion in Nanomaterials” in „Nanocrystalline materials: Properties and Applications” (Eds. Knauth, P., Schoonman, J.) Kluwer Academic Publ., Boston, 2001 BEKE, D.L. CSERHÁTI, C., ERDÉLYI, Z., SZABÓ, I.A., “Segregation in Nanostructures” in „Advances in Nanophase materials and nanotechnology” Volume: „Nanoclusters” (ed. H.S. Nalwa) American Scientific Publ., 2002, in print SIDORENKO, S., BEKE. D.L., KIKINESHI, A., “Materials Science of Nanosctutures, Naukova Dumka, Kiyv, 2002


Download ppt "Non-linear Effects in Diffusion on Nanoscale Department of Solid State Physics University of Debrecen D.L. Beke Z. Erdélyi, I.A. Szabó, Cs. Cserháti."

Similar presentations


Ads by Google