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Ion beam nanopatterning of binary alloy
- 1. Transitional morphology in binary mixtures via low energy ion beams By Basanta Kumar Parida Indian Institute of Technology Ropar, Punjab, India 4th International Conference on Nanostructuring by Ion Beam ICNIB-2017 October 11-13, 2017 DAVV, Indore
- 2. Outline β’ Introduction (Typical patterns formed) β’ Theoretical background for ion beam nanopatterns β’ Our region of interest β’ Our results β’ Summary 2
- 3. Ion induced patterns for elements and compounds Nanoripples Monoelemental Nanodots 3 https://www.hzdr.de/db/Cms?pOid=24344&pNid=2707 ArβGaSb 500 eV, 30 min, 0o ArβSi 500 eV, 30 min, 67o Binary compound Oblique Incidence Normal Incidence Oblique Incidence with rotation ArβInP 500 eV, 2 min, 10o Frost et.al. Phys. Rev. Lett(2000)
- 4. Theoretical background β’ Competition between two processes β Roughening due to sputtering β Smoothening due to diffusion 4 ππ ππ = βππ + πΈ(π½) ππ ππ + ππ ππ π πππ + ππ ππ π πππ β π²π΅π π Sputter roughening Diffusion smoothing Bradley-Harper Model Monoelemental Binary compound β’ Differential sputtering yield and Differential diffusivity β Results altered topography and composition A B Shenoy et.al., Phys. Rev. Lett., 98, 256101 (2007)
- 5. Binary alloy sputtering β’ Normal incidence over a binary compound leads arrays of nanodots β’ Coupling between topography and altered composition β’ For AB alloy sputtering yield and composition πΉπ΄ = πΉπ π΄ππ , πΉπ΅ = πΉππ΅(1 β ππ ) β’ For steady state bulk composition ππ¨ ππ© = ππ πβππ ππ= ππ©ππ ππ¨(π β ππ) + ππ©ππ 5 Shenoy et.al., Phys. Rev. Lett., 98, 256101 (2007) Shipman et.al., Phys. Rev. B, 84, 085420 (2011)
- 6. Ar+ο GaSb(001) Studies on binary materials (Low energy) 6 Plantevin et al. Appl. Phys. Lett.91, 113105 (2007) S.K. Tan et al. NIMB 248 ,83 (2006) 1 keV O2 +ο InP(100) Facsko et, al. Appl. Phys. Lett., 80,1 (2002) Ar+ο GaSb(100) Ar+ο GaSb(111) Ar+ο amorphous GaSb 100 eV Ar+ο GaSb El-Atwani et al. J. Appl. Phys.110, 074301 (2011)
- 7. Studies on surfactant sputtering - impurity addition β’ Impurity addition has a deterministic role in pattern formation β’ Co-deposition of small amounts of metallic atoms, e.g. Fe, Mo has tremendous impact on pattern 7 Without Mo seeding With Mo seeding Ar+(1 keV)ο Si Ozadyn et. al. Appl. Phys. Lett.87, 163104 (2005) Hofsass et. Al. Appl Phys A 111:653(2013)
- 8. Our domain of study β’ Mixtures containing initially well-mixed species (bulk composition) β’ Metal-semiconductor system β’ Widely different diffusivities - Deciding factor β’ Far from strongest coupling (50-50) composition β’ For impurity addition, surface or near-surface layer has a penetration depth of sub-nanometer β’ Sputtering can induce stoichiometric rearrangements in the bulk as well, which affect the surface concentration β’ Ion induced diffusivity is primarily confined to the surface 8 CoxSi1-x is chosen as the binary material
- 9. Experimental details β’ CoxSi1-x is chosen as binary material β’ Deposited over Si(100) with variable stoichiometries β’ Irradiated with different energies, fluence, stoichiometry and angles β’ Initial roughness β 5 nm 9 Si(100) CoxSi1-x After Ar ion irradiation at 1200 eV Unirradiated CoxSi1-x
- 10. Energy variation (Co27Si73) 10 500-1200 eV Morphology transitions from lower to higher value of energy Ar+ο Co27Si73
- 11. Fluence variation (Co16Si84) 11 Wavelength increment follows power law Ar+ο Co16Si84
- 12. Compositional variations and MFM study 12 Compositional variation Topographical changes Enrichment of cobalt at the peaks Hierarchical(bug-like) structures
- 13. -10 0 10 20 30 40 50 60 70 80 90 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Roughness (nm) Angle of incidence (degree) ion = Ar+ time =45 min energy =700eV Angle variation Ar ion on CoxSi1-x 13 ΞΈ=30o ΞΈ=80o ΞΈ=67o ΞΈ=0o z=4 nm z=4.4 nm z=74 nm z=23 nm Ar+ο Co53Si47 3D 10 -3 10 -2 10 -3 10 -2 10 -1 10 0 10 1 10 2 10 3 10 4 PSD (nm 4 ) Frequency(nm-1) 0 deg 30 deg 67 deg 80 deg Nanodot formation
- 14. Summary β’ Morphological transition at higher energies β nano to micro β’ Power law behavior for fluence variations β’ Heirarchical structures for higher Co concentrations β’ Enrichment of cobalt at crests β’ Formation of conical structures at higher angles. Lower angles give extremely smooth surfaces 14 Acknowledgement Supervisor - Dr. Subhendu Sarkar Dr. Mukesh Ranjan, FCIPT, IPR CRF, IIT Ropar MHRD, India
- 15. Thank you for your kind attention
- 16. Nanopatterning using ion beam 16 Advantages β’ Single step Faster and cheaper process for large area patterning β’ Nanoripples, dots, holes etc. β’ Easy to tune the parameters(ion energy, angle, flux,) Applications β’ Quantum dots in optoeletronic devices β’ Nanoripples for optical interference grating, plasmonic applications β’ Templates for functionalized surfaces S. Facsko et.al., Science, 285, 1551 (1999) CoSi 500 eV, 67o,45 min GaSb 500 eV, 0o,400Sec Ar ion flux IPR Our Work
- 17. Binary alloy sputtering(contdβ¦) β’ Power deposited per unit area π = π0 + πΌπ»2π’ + π½(π»π’)2 β’ Mass conservation πβ ππ‘ = βΞ©[ πΉπ΄ + π». π½π΄ + (πΉπ΅ + π». π½π΅)] β’ Rate of change of surface concentration β πππ ππ‘ = Ξ© ππ β 1 πΉπ΄ + π». π½π΄ + ππ πΉπ΅ + π». π½π΅ β’ Erosion rate π£0 = Ξ©(πΉπ΄ + πΉπ΅)π0 β’ Surface atomic current π±π = βπ«ππππ΅ππ π + π«πππ πππ΄πΈ ππ©π» π΅π΅π π‘ β πππ΅π , π’ = π, π β’ Instability πΌ πΉπ΄ + πΉπ΅ > ππ΄ + ππ΅ 17 Shipman ,Bradley Phys. Rev. B ,84,085420(2011)
- 18. Angle variation Xe ion on CoxSi1-x 18 Xe+ο Co64Si36 ΞΈ=30o z=11 nm ΞΈ=0o z=16 nm ΞΈ=50o z=28 nm ΞΈ=67o z=31 nm Irregular dot structures to triangular structures 10 -3 10 -2 10 -2 10 -1 10 0 10 1 10 2 10 3 PSD(nm 4 ) Frequency(nm -1 ) 0 deg 30 deg 50 deg 67 deg -10 0 10 20 30 40 50 60 70 1.0 1.5 2.0 2.5 3.0 3.5 Roughness (nm) Angle of incidence (degree) ion = Xe+ time = 45 min energy = 500 eV
- 19. I-V characteristic study 19 -20 -10 0 10 20 -0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 ion beam direction XX' pristine 60 min 45 min 30 min 15 min I (amp) V (volt) pristine 10 min 15 min 30 min 45 min 60 min 10 min X Y
Editor's Notes
- Typical patterns formed as I have explained earlier are nanoripples and dots. For monoelemental surfaces like Si, Ge and metals etc, IBS at oblique incidence create nanoripples, where as for binary compound cases like III-V semiconductors (GaSb, GaAs, InP etc) there is the formation of hexagonally ordered nanodots which are mostly crystalline nature for few minutes of sputtering. As referred in the fig. The two cases are normal incidence or oblique incidence ion beam with rotating substrate can create these nanodots. (1)ArβSi 500 eV, 67o (2)ArβGaSb 500 eV, 67o both for 30 min (3)ArβInP 500 eV, 2 min, 10o Representative patterns for different cases
- As energetic ion enters into the substance there forms a disturbed region inside the substance called Collison cascade. Few atoms get sufficient energy to come out of the surface due to these which can be explained by an instability theory of Bradley and Harper. The irregularities over the surface(like crests or trough) lead to instability due to which trough erodes faster than the crest. Hence the instability creates roughening of the surface which competes with the thermal surface diffusion where matters flow to the crests to the tough leads to the smoothening. Hence Formation of nanopattern are due to the competition between two processes. One is the roughening due to the surface curvature and other smoothening due to thermal diffusion. Both effect combinly result nanoripples. Our group basically works on binary compound which isβ¦.
- Height modulations lead to gradient in composition by colour composition Flux of surface eroded atoms due to ion beam Bulk composition surface composition phenomena
- Will you write the last line?
- These are AFM images for the Ar ion irradiated Co27Si73 surfaces with different energies. There is morphology change has been observed from 500 -1200 eV energy. Nanoscale ripples for 500 eV case. Peculiar semi-ellipsoidal structures have been observed for 1000 and 1200 eV cases. Variations like roughness, wavelength, amplitudes, aspect ratio are depicted in the diagrams.
- These are our results which confirms the compositional changes. Left side indicates the AFM images of various x values where we found linear dependence of roughness with cobalt /silicon composition. And pill bug like structures for higher cobalt stoichiometries. 2- Right side refers to the MFM images of the topographical images (left) and the cobalt enriched part in the MFM phase images which confirms the compositional change as in theory.
- Nanoscale surface ripples generated by oblique-incidence ion bombardment of a solid are generally full of defects, and this has prevented the widespread adoption of ion bombardment as a nanofabrication tool. We advance a theory that predicts that remarkably defect-free ripples can be produced by ion bombardment of a binary material if the ion species, energy and angle of incidence are appropriately chosen. This high degree of order results from the coupling between the surface height and composition, and cannot be achieved by bombarding an elemental material. surface ripples with an exceptionally low density of defects have already been generated by OIIB of silicon (ziberi jpcm 09)
- Over the past few decades, techniques to produce submicron and nanoscale features on surfaces have emerged. Recent innovations in the area of micro- and nanofabrication have created a unique opportunity for patterning surfaces with features with lateral dimensions over the nano- to millimeter range. The microelectronics industry and need for smaller and faster computing systems have pushed this development during the last two decades. Nanopatterns are nothing but patterns at nanoscale, which are used in various applications. The important part here is to discuss a cheaper way of creation of nanopattern, which is ion beam sputtering(IBS). Irradiating or bombarding the solid surface using the ion beam can create long range ordered nanopatterns(nanoripples, nanodots-few nanometer ) within a few second to few minute of irradiation. The main importance of this process is we can pattern upto few cm^2 area using this technique by suitably adjusting the ion beam parameters(like ion energy, incident angle, ion fluence means total ions/cm2). Easily tunable parameters are the main advantage of this method. Other importance of this method are any type of ion beam can be used for any type of material over (semiconductors, insulators, metals). Also space selectivity the main advantage-we can choose space where to be patterned according to our own way. It is a maskless process unlike the case of photolithography and other patterning techniques. Applications Quantum dots in optoeletronic devices, Nanoripples for optical interference grating, Templates for functionalized surfaces, also these surfaces can be used for plasmonics application which I will come later . In optical grating and other application these nm-scale patterns are useful.
- Diffusive surface current Ji u is a slowly varying function Alpha= is positive leading to surface instability beta term=slope dependence sputtering yield Del- is a characteristic length order of penetration depth