Surface Evolution During Mbe Growth of Eute Studied by Uhv-Stm and Rheed Investigations

1993 ◽  
Vol 317 ◽  
Author(s):  
N. Frank ◽  
G. Springholz ◽  
G. Bauer
Keyword(s):  
Layer Thickness ◽  
Growth Conditions ◽  
High Energy ◽  
Layer Growth ◽  
Scanning Tunneling ◽  
Root Mean Square Roughness ◽  
Layer By Layer ◽  
Tunneling Microscopy ◽  
Surface Evolution ◽  
Mbe Growth

ABSTRACTMBE growth of 2% lattice-Mismatched EuTe on PbTe (111) is studied combining in-situ reflection high-energy electron diffraction (RHEED) with UHV scanning tunneling Microscopy (STM) to investigate the evolution of the EuTe surface Morphology. Using RHEED we have found that 2D nucleation and layer-by-layer growth occurs only in a very narrow range of growth conditions as a result of a strain induced coherent islanding of the surface[l], which leads to a roughening transition at the critical layer thickness hc of 45 Monolayers (ML). Starting with a very smooth initial (111) PbTe surface with terrace widths of 50 to 200 nm, islands of monolayer height are formed due to 2D nucleation of EuTe. For EuTe layer thicknesses below hc, the root mean square roughness (RMS) is essentially constant and equal to about one ML. Beyond hc, the surface roughness increases strongly and islands of about 20 ML height are observed for an EuTe layer thickness of 66 ML.

Structural Evolution During the Initial Epitaxial Growth of Moon on Sapphire

1999 ◽  
Vol 584 ◽  
Author(s):  
P. A. Ryan ◽  
F. Tsui
Keyword(s):  
Epitaxial Growth ◽  
Structural Evolution ◽  
Lattice Relaxation ◽  
High Energy ◽  
Layer Growth ◽  
Scanning Tunneling ◽  
Layer By Layer ◽  
Initial Growth ◽  
Tunneling Microscopy ◽  
Length Scales

AbstractStructural evolution during initial epitaxial growth of Mo (111) and (110) on Al2O3 substrates has been studied using real-time reflection high energy electron diffraction and in-situ scanning tunneling microscopy. The Mo (111) growth on sapphire (0001) is initiated by the formation of small mound-like 3-dimensional (3D) islands that are correlated with unique length scales. The observed surface length scales depend on growth temperature and rate, and they coarsen as the thickness increases. The initial growth of Mo (110) on sapphire (1120) begins with layer-by-layer growth for the first monolayer, and subsequently the growth is 3D with mound-like features that are larger than those corresponding (111) counterparts. In both orientations lattice relaxation occurs within the first 2 – 3 monolayers.

Influence of Surface Structure on Epitaxial Growth of Si on Si(111)-(7 × 7) Substrate

1998 ◽  
Vol 05 (03n04) ◽  
pp. 865-872 ◽  
Author(s):  
Yukichi Shigeta
Keyword(s):  
Surface Structure ◽  
Epitaxial Growth ◽  
High Energy ◽  
Layer Growth ◽  
Scanning Tunneling ◽  
Layer By Layer ◽  
Initial Growth ◽  
Lateral Growth ◽  
Tunneling Microscopy ◽  
Starting Point

To make clear the influence of surface structure on epitaxial growth, we have studied the growth of Si on a Si(111)-(7 × 7) superlattice surface by using scanning tunneling microscopy and reflection high energy electron diffraction. In the initial growth stage on the 7 × 7 superlattice, multilayer islands are formed because lateral growth of the first layer is prevented by the stable 7 × 7 structure and some migrating atoms climb up the first layer and nucleate on it. However, lateral growth of the second layer on the first one is not prevented and the layer-by-layer growth starts, because the structure of the first layer is composed of small domains with some metastable surface structures, which is rather easier to rearrange than the 7 × 7 structure. The starting point of the layer-by-layer growth depends on the substrate temperature, because the surface structure formed on a growing layer is influenced by the temperature. We obtained the result that the nucleation of a two-dimensional island on the 7 × 7 superlattice is also influenced by the surface structure. The island, whose size is less than the half-unit of the 7 × 7 structure, is unstable. The result suggests that, for the nucleation on the stable surface structure, the activation energy of rearrangement of the surfue structure should be taken into the consideration of the formation energy of the nucleus.

Direct Observations of the Strain-Limited Island Growth of Sn-Doped GaAs(100)

1998 ◽  
Vol 05 (03n04) ◽  
pp. 783-795 ◽  
Author(s):  
A. M. Dabiran ◽  
S. M. Seutter ◽  
P. I. Cohen
Keyword(s):  
Native Species ◽  
Surface Segregation ◽  
High Surface ◽  
Three Dimensional ◽  
High Energy ◽  
Layer Growth ◽  
Scanning Tunneling ◽  
Layer By Layer ◽  
Island Growth ◽  
Tunneling Microscopy

We have used scanning tunneling microscopy (STM) in ultrahigh vacuum and atomic force microscopy (AFM) in air to investigate the microscopic mechanisms of Sn surface segregation during the molecular beam epitaxial growth of GaAs and AlAs(100). Submonolayer amounts of Sn segregate to the surface during growth and strongly modify the growth kinetics. This is indicated by both extra-ordinary reflection high energy electron diffraction (RHEED) measurements, and the STM and AFM images of rapidly quenched growth fronts. At the high surface coverages of 0.1–0.6 monolayers of Sn, studied in this work, neither step bunching nor three-dimensional (3D) growth of GaAs(100), was observed. Instead, STM and RHEED measurements indicated a significantly enhanced layer-by-layer growth of GaAs with increasing surface coverage of Sn. STM snapshots of the initial stages of GaAs growth revealed 2D islands which contained a higher-than-equilibrium bulk concentration of Sn, in Ga-substitutional sites, of up to 50%. Other directly observed Sn effects which are presented in this work include the removal of GaAs(100) island growth anisotropy and the formation of 2D islands with a relatively narrow distribution of size and separation. The completion of the top layers is shown to proceed by the coalescence of these islands before any significant nucleation of the next layer islands. This effect is used to explain the Sn enhancement of the layer-by-layer growth which was indicated in our RHEED and scanning probe observations. A model is presented for Sn segregation which explains these results based on an island-size-dependent, strain-driven, oscillatory Sn occupation of Ga-substitutional sites and surface interstitial sites on top GaAs(100) layers during growth. This model, which introduces a strain-limiting mechanism for the size and shape of the 2D islands, can also explain the observed enhancement of postgrowth surface recovery, as well as a delayed onset in increasing adatom surface diffusion length with increasing Sn coverage. The main conclusion is that, if impurity incorporation results in significant strain, then in addition to step climbing by surface impurities, the exchange of incorporated impurities with native species in top layers can be an important path for impurity segregation during expitaxial growth.

Defect-Mediated Growth of YBa2Cu3O7-δ Films

1992 ◽  
Vol 280 ◽  
Author(s):  
D. G. Schlom ◽  
D. Anselmetti ◽  
J. G. Bednorz ◽  
Ch. Gerber ◽  
J. Mannhar
Keyword(s):  
Growth Conditions ◽  
Substrate Material ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Surface Evolution ◽  
Screw Dislocations ◽  
Surface Steps ◽  
Defect Sites ◽  
Wide Range ◽  
Intrinsic Feature

ABSTRACTThe evolution of the surface microstructure of sputtered c-axis oriented epitaxial YBa2Cu3O7-δ films has been monitored by scanning tunneling microscopy (STM). The results indicate that growth is dominated by the incorporation of depositing species at defect sites. These defect sites, which provide energetically favorable positions for accommodating the arriving species, are at ledges—either along growth spirals emanating from screw dislocations, or due to the closely spaced surface steps arising from the macroscopic tilt of the substrate. If the substrate is misoriented sufficiently, the depositing species may diffuse to and be accommodated by these surface steps, without the supersaturation on the terraces attaining a high enough level for two-dimensional nucleation to occur. Under these conditions, growth occurs by step propagation. Otherwise, a high density of screw dislocations (≈109 cm-2) is nucleated during the initial stages of growth, which provides a continual supply of ledge incorporation sites in the vicinity of the depositing species. The surface evolution reported appears to be an intrinsic feature of c-axis oriented YBa2Cu3O7-δ films for a wide range of growth conditions, irrespective of the substrate material or vapor phase deposition method.

Reflection High Energy Electron Diffraction Studies of the Growth of DyBa2Cu3O7−x Films and Structures Grown on SrTiO3 Substrates

1992 ◽  
Vol 275 ◽  
Author(s):  
V. S. Achutharaman ◽  
N. Chandrasekhar ◽  
A. M. Goldman
Keyword(s):  
Electron Diffraction ◽  
Specular Reflection ◽  
Growth Conditions ◽  
High Energy ◽  
Layer Growth ◽  
Energy Electron ◽  
Layer By Layer ◽  
High Energy Electron ◽  
Epitaxial Relationship ◽  
Superlattice Structures

ABSTRACTIntensity oscillations of the specular reflection high energy electron diffraction (RHEED) beam contain useful information on the mode of growth and the evolving structure of thin films. We present RHEED studies of the growth of DyBa2Cu3O7−x films and DyBa2Cu3O7−x/DY2O3/DyBa2Cu3O7−x structures on SrTiO3; substrates deposited by ozone-assisted molecular beam epitaxy. The effect of substrate temperature, ozone flux and surface step densities on the epitaxial relationship and evolving microstructure will be discussed. The strong damping of the oscillations and identical time periods under different nuoleation and growth conditions suggest that the intensity oscillations are a consequence of to diffuse scattering from step edges rather than a layer-by-layer growth mode. It was also found that Dy2O3 can be used to fabricatee tri-layer type structures but not superlattice structures.

Investigation of growth rates and morphology for diamond growth by chemical vapor deposition

1992 ◽  
Vol 7 (6) ◽  
pp. 1438-1444 ◽  
Author(s):  
M.P. Everson ◽  
M.A. Tamor
Keyword(s):  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Layer Growth ◽  
Diamond Growth ◽  
Scanning Tunneling ◽  
Layer By Layer ◽  
Tunneling Microscopy ◽  
Limited Growth ◽  
Diffusion Limited

We describe two complementary studies of diamond growth by chemical vapor deposition. In the first, the early stages of growth of randomly distributed nuclei on silicon are studied by scanning tunneling microscopy. For growth times from 1 to 30 min nearly all crystallites are three dimensional, and increase in volume as t1.5. Although this result could be interpreted in terms of diffusion limited growth, the conditions for diamond CVD are more consistent with rate limited growth where the crystals are expected to gain volume as t3. This anomaly can be explained in terms of a two-species growth mechanism in which the rate constant for carbon addition is proportional to the diffusion limited flux of atomic hydrogen. Other mechanisms giving rise to the observed t1.5 dependence are also considered. The second study uses both scanning electron and tunneling microscopies to examine the morphology of a boron-doped film homoepitaxial to the {100} surface of natural type 2a diamond. In regions distant from gross defects, this film is very smooth. However, gross defects appear to initiate growth of new epitaxial layers at a rate much higher than in defect-free regions. This observation suggests that diamond growth is promoted by “enabling defects” and that without such defects nucleation of new layers is a slow process and permits layer-by-layer growth at a much lower rate.

Initial Growth and morphology of Ultrathin Magnetic Films Studied Using Scanning Tunneling Microscopy.

1993 ◽  
Vol 313 ◽  
Author(s):  
David D. Chambliss ◽  
K.E. Johnson ◽  
K. Kalki ◽  
S. Chiang ◽  
R.J. Wilson
Keyword(s):  
Magnetic Films ◽  
Layer Growth ◽  
Scanning Tunneling ◽  
Layer By Layer ◽  
Initial Growth ◽  
Island Growth ◽  
Tunneling Microscopy ◽  
High Coverage ◽  
Local Structures ◽  
Low Coverage

ABSTRACTThe room-temperature growth of Fe on Cu(100) has been studied using the scanning tunneling Microscope (STM) to determine low-coverage growth mode and local structures related to the FCC-BCC structural transformation. Results for submonolayer deposition demonstrate an initial interchange of deposited Fe atoms with substrate Cu. This leads to a highly rough Fe-Cu interface and growth characteristics that for different experimental techniques can resemble 3-D island growth or layer-by-layer growth. For a thickness ∼14 Monolayers, the FCC-BCC transition is observed to occur via the formation of fairly large martensitic grains, rather than by a change in atomic aggregation. The implications of the instability of FCC-Fe, as evident in both low- and high-coverage data, are considered.

NANOWIRES ON STEPPED METAL SURFACES

1997 ◽  
Vol 04 (02) ◽  
pp. 371-380 ◽  
Author(s):  
F. J. HIMPSEL ◽  
T. JUNG ◽  
J. E. ORTEGA
Keyword(s):  
Metal Surfaces ◽  
Electronic States ◽  
Surface States ◽  
Energy Shift ◽  
Layer Growth ◽  
Scanning Tunneling ◽  
Layer By Layer ◽  
Tunneling Microscopy ◽  
One Dimensional ◽  
Inverse Photoemission

The electronic properties of solids can be tailored by structuring them on the nanometer scale. Such a program is becoming reality as surface analysis techniques and sophisticated growth methods are merging. Here, we present results of a venture into one-dimensional nanostructures, grown by decoration of steps at metal surfaces. The growth modes and electronic states are studied using scanning tunneling microscopy (STM) and inverse photoemission. Two-dimensional analogs of Stranski–Krastanov and layer-by-layer growth are found for Cu on stepped Mo(110) and W(110), respectively. Contrast between different metals is achieved in STM pictures by resonant tunneling via surface states and image states, with the latter providing a map of the work function. The limit of single atomic rows decorating step edges is studied by inverse photoemission, and an energy shift of 0.4 eV is found for electronic states of step atoms. Stripe structures are attractive for the study of two- versus one-dimensional magnetism, for magnetoresistive sensors, and in the design of anisotropic materials.

Nano-Size Surface Materials Stabilized by Weak Interaction

2009 ◽  
Vol 614 ◽  
pp. 21-26
Author(s):  
Kenichi Tanaka ◽  
Xiao Hong Jiang
Keyword(s):  
Scanning Tunneling Microscopy ◽  
Band Gap ◽  
Cell Layer ◽  
Layer Growth ◽  
Unit Cell ◽  
Solid Surfaces ◽  
Scanning Tunneling ◽  
Layer By Layer ◽  
Tunneling Microscopy ◽  
Nano Size

Scanning tunneling microscopy (STM) proved the existence of quasi-compounds on solid surfaces. A typical example is (-Ag-O-) or (-Cu-O-) chains grown on Ag(110) or Cu(110) surface by exposing to O2. The (-Ag-O-) chains on a Ag(110) reacts with Cu atoms to form a new quasi-compound of (-Cu-O-) chains on the Ag(110) surface. The (-Cu-O-) on the Ag(110) readily decomposes at ca. 570ºK to form Cu6 dots, and a reversible reaction of (Cu2)3 + O2. ↔ (-Cu-O-) takes place by exposing to O2. Deposited Zn, Sn and Ag atoms on a Si(111)-7x7 surface stabilize by forming Zn3, Sn2 and Sn, and Ag in a half unit cell. Layer-by-layer growth of Zn3 clusters occurs in a half unit cell, which results in the growth of a semi-conductive honeycomb layer of Zn3 clusters on the Si(111)-7x7 surface. By prohibiting hopping migration of Ag atoms on the Si(111)-7x7 surface by the adsorption of C2H5OH, nano-size Ag dots grow layer-by-layer in a limited mold spacing. The band gap of Ag-dots becomes narrower and narrower and becomes metallic at higher than 6 layers.

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