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Title: Growth and structural evolution of Sn on Ag(001): Epitaxial monolayer to thick alloy film

Abstract

The growth and structure of Sn on Ag(001), from submonolayer to thick film coverages at room temperature, are studied using low energy electron diffraction, x-ray photoemission spectroscopy and angle-resolved photoemission spectroscopy (ARPES) techniques. The authors observe different growth modes for submonolayer Sn coverages and for higher Sn coverages. Systematic surface structural evolution, consistent with the substitution of surface Ag atoms by Sn atoms, is observed for submonolayer Sn coverages while an ordered Ag-Sn bulk alloy film is formed for higher Sn coverages with an Ag overlayer. For monolayer coverage of Sn, a pseudomorphic growth of a Sn layer without alloying is determined. ARPES results also confirm the presence of an ordered Ag overlayer on the bulk Ag-Sn alloy film, suggesting the formation of an Ag/Ag{sub 3}Sn/Ag(001) sandwich structure at the surface for higher Sn coverages. The present results illustrate the complex interplay of atomic mobilities, surface free-energies, and alloy formation energies in determining the growth and structural properties of the system.

Authors:
 [1];  [2]
  1. Surface Physics and Material Science Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064, India and Department of Applied Sciences, Haldia Institute of Technology, Haldia, 721657 Purba Medinipur, West Bengal (India)
  2. Surface Physics and Material Science Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064 (India)
Publication Date:
OSTI Identifier:
22592879
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Vacuum Science and Technology. A, Vacuum, Surfaces and Films; Journal Volume: 34; Journal Issue: 4; Other Information: (c) 2016 American Vacuum Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ELECTRON DIFFRACTION; EPITAXY; FILMS; FORMATION HEAT; FREE ENERGY; LAYERS; PHOTOELECTRON SPECTROSCOPY; PHOTOEMISSION; SILVER ALLOYS; SURFACES; TEMPERATURE RANGE 0273-0400 K; TIN ALLOYS; X-RAY DIFFRACTION

Citation Formats

Chakraborty, Suvankar, and Menon, Krishnakumar S. R., E-mail: krishna.menon@saha.ac.in. Growth and structural evolution of Sn on Ag(001): Epitaxial monolayer to thick alloy film. United States: N. p., 2016. Web. doi:10.1116/1.4953543.
Chakraborty, Suvankar, & Menon, Krishnakumar S. R., E-mail: krishna.menon@saha.ac.in. Growth and structural evolution of Sn on Ag(001): Epitaxial monolayer to thick alloy film. United States. doi:10.1116/1.4953543.
Chakraborty, Suvankar, and Menon, Krishnakumar S. R., E-mail: krishna.menon@saha.ac.in. Fri . "Growth and structural evolution of Sn on Ag(001): Epitaxial monolayer to thick alloy film". United States. doi:10.1116/1.4953543.
@article{osti_22592879,
title = {Growth and structural evolution of Sn on Ag(001): Epitaxial monolayer to thick alloy film},
author = {Chakraborty, Suvankar and Menon, Krishnakumar S. R., E-mail: krishna.menon@saha.ac.in},
abstractNote = {The growth and structure of Sn on Ag(001), from submonolayer to thick film coverages at room temperature, are studied using low energy electron diffraction, x-ray photoemission spectroscopy and angle-resolved photoemission spectroscopy (ARPES) techniques. The authors observe different growth modes for submonolayer Sn coverages and for higher Sn coverages. Systematic surface structural evolution, consistent with the substitution of surface Ag atoms by Sn atoms, is observed for submonolayer Sn coverages while an ordered Ag-Sn bulk alloy film is formed for higher Sn coverages with an Ag overlayer. For monolayer coverage of Sn, a pseudomorphic growth of a Sn layer without alloying is determined. ARPES results also confirm the presence of an ordered Ag overlayer on the bulk Ag-Sn alloy film, suggesting the formation of an Ag/Ag{sub 3}Sn/Ag(001) sandwich structure at the surface for higher Sn coverages. The present results illustrate the complex interplay of atomic mobilities, surface free-energies, and alloy formation energies in determining the growth and structural properties of the system.},
doi = {10.1116/1.4953543},
journal = {Journal of Vacuum Science and Technology. A, Vacuum, Surfaces and Films},
number = 4,
volume = 34,
place = {United States},
year = {Fri Jul 15 00:00:00 EDT 2016},
month = {Fri Jul 15 00:00:00 EDT 2016}
}
  • Evolution of surface roughness in epitaxial Si{sub 0.7}Ge{sub 0.3} alloys grown on Si(001) as a function of temperature (200-600 C), thickness ({ital t}=7.5-100 nm), and substrate miscut were investigated by atomic force microscopy and quantified in terms of the height-difference correlation function {ital G}({rho}), in which {rho} is lateral distance and [{ital G}({rho}{r_arrow}{infinity})]{sup 1/2} is proportional to the surface width. The films were deposited by ultrahigh vacuum ion-beam sputter deposition at 0.1 nms{sup {minus}1}. Strain-induced surface roughening was found to dominate in alloys grown on singular Si(001) substrates at {ital T}{sub {ital s}}{approx_gt}450{degree}C where [{ital G}({rho}{r_arrow}{infinity})]{sup 1/2} initially increases withmore » increasing {ital t} through the formation of coherent islanding. The islands are preferentially bounded along {l_angle}100{r_angle} directions and exhibit 105 faceting. This tendency is enhanced, with much better developed {l_angle}100{r_angle} islands separated by deep trenches{emdash}of interest for growth of self-assembled nanostructures{emdash}in films grown on Si(001)-4{degree}[100]. Increasing the film thickness above critical values for strain relaxation leads to island coalescence and surface smoothening. At very low growth temperatures ({ital T}{sub {ital s}}{le}250{degree}C), film surfaces roughen kinetically, due to limited adatom diffusivity, but at far lower rates than in the higher-temperature strain-induced regime. Si{sub 0.7}Ge{sub 0.3} alloy surfaces are smoother, while the films exhibit larger critical epitaxial thicknesses, than those of pure Si films grown in this temperature regime. There is an intermediate growth temperature range, however, over which the alloy film surfaces remain extremely smooth even at thicknesses near critical values for strain relaxation. This latter result is of potential importance for device fabrication. {copyright} {ital 1996 American Institute of Physics.}« less
  • The structure and element-specific local magnetic moments in Fe{sub 100{minus}x}Co{sub x}/Ag(001) (16{lt}x{lt}70) epitaxial ultrathin alloy films have been determined by photoelectron diffraction (PED) and related magnetic linear dichroism in angle-resolved core-level photoemission, using a laboratory x-ray source. The PED peaks of the Fe and Co 2p core levels for any of the alloy compositions are at emission angles as expected for a bcc lattice. The dichroism increases for the Fe 2p{sub 3/2} core level with increasing x, whereas that of the Co 2p{sub 3/2} dichroism is virtually independent on the alloy composition. The dichroism of both the Fe and themore » Co core levels scales well with the calculated dependence of the local magnetic moment on the alloy composition rather than with the average saturation magnetization. {copyright} {ital 1998 American Institute of Physics.}« less
  • Epitaxial metastable Ge{sub 1{minus}x}Sn{sub x} alloys with x up to 0.26 (the equilibrium solid solubility of Sn in Ge is {lt}0.01) were grown on Ge(001)2{times}1 by low-temperature molecular beam epitaxy. Film growth temperatures T{sub s} in these experiments were limited to a relatively narrow range around 100{degree}C by the combination of increased kinetic surface roughening at low temperatures and Sn surface segregation at high temperatures. All Ge{sub 1{minus}x}Sn{sub x} films consisted of three distinct sublayers: the first is a highly perfect epitaxial region followed by a sublayer, with an increasingly rough surface, containing 111 stacking faults and microtwins, while themore » terminal sublayer is amorphous. Based upon reflection high energy electron diffraction and cross-sectional transmission electron microscopy (XTEM) analyses, critical epitaxial thicknesses t{sub epi}, defined as the onset of amorphous growth, were found to decrease from 1080 {Angstrom} for pure Ge to {approx_equal}35{Angstrom} for alloys with x=0.26. TEM and XTEM analyses revealed no indication of misfit dislocations (except in Ge{sub 0.74}Sn{sub 0.26} samples) and high-resolution x-ray reciprocal lattice mapping showed that epitaxial Ge{sub 1{minus}x}Sn{sub x} layers were essentially fully strained. From an analysis of t{sub epi}(x) results, surface morphological evolution leading to epitaxial breakdown is controlled by kinetic roughening for alloys with x{approx_lt}0.09 and by strain-induced roughening at higher Sn concentrations. We propose that the thermal activation required for the cross-over, reported here for the first time, from kinetic to strain-induced roughening is partially overcome by the fact that kinetic roughening provides local surface chemical potential gradients over lateral length scales which are sufficiently small to initiate strain-induced roughening even at these low temperatures. {copyright} {ital 1998 American Institute of Physics.}« less
  • Fully strained single-crystal metastable Ge{sub 1-x}Sn{sub x} layers were grown on Ge(001) in order to probe the role of Sn dopant and alloy concentrations (C{sub Sn}=1x10{sup 18} cm{sup -3} to 6.1 at. %) on surface roughening pathways leading to epitaxial breakdown during low-temperature (155 deg. C) molecular-beam epitaxy of compressively strained films. The addition of Sn was found to mediate Ge(001) surface morphological evolution through two competing pathways. At very low Sn concentrations (x < or approx. 0.02), the dominant effect is a Sn-induced enhancement in both the Ge surface diffusivity and the probability of interlayer mass transport. This, inmore » turn, results in more efficient filling of interisland trenches, and thus delays epitaxial breakdown. In fact, breakdown is not observed at all for Sn concentrations in the doping regime, 1x10{sup 18}{<=}C{sub Sn}<4.4x10{sup 20} cm{sup -3} (2.3x10{sup -5}{<=}x<0.010){exclamation_point} At higher concentrations, there is a change in Ge{sub 1-x}Sn{sub x}(001) growth kinetics due to a rapid increase in the amount of compressive strain. This leads to a gradual reduction in the film thickness h{sub 1}(x) corresponding to the onset of breakdown as strain-induced roughening overcomes the surface smoothening effects, and results in an increase in the overall roughening rate. We show that by varying the Sn concentration through the dopant to dilute alloy concentration range during low-temperature Ge(001) growth, we can controllably manipulate the surface roughening pathway, and hence the epitaxial thickness, over a very wide range.« less
  • Epitaxial MgO thin films were grown on Si(001) by pulsed laser deposition. In spite of a large ({minus}22.5%) lattice mismatch, epitaxy occurs with alignment of all crystallographic axes. Epitaxial quality and deposition rate are both sensitive to temperature and oxygen pressure. We believe this is the first demonstration of epitaxial MgO on Si. We employ MgO intermediate layers for superconducting epitaxial YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}/BaTiO{sub 3} thin films on Si with a critical current density of 6.7{times}10{sup 5} A/cm{sup 2} at 77 K.