Growth Of Nanoislands Research Articles

Epitaxial growth of silver nanoislands on the surface of silicon nanowires in ambient air

We study the epitaxial growth of Ag nanoislands on the surface of silicon nanowires (SiNWs) in ambient air by annealing SiNWs fabricated by metal-assisted chemical etching using Ag particles as the catalysts. We demonstrate that the nucleation of Ag on the surface of SiNWs is realized either by the direct decomposition of AgmO or by the reaction between AgmO and Si depending on the annealing temperature; AgmO is an adspecies with a lower effective detachment barrier, commonly introduced in oxygen-induced Ag surface migration systems. Along with the formation of Ag nanoislands, a thin layer of SiOx is formed on the outside surface of Ag nanoislands. The ambient-air epitaxial growth of Ag islands on the surface of SiNWs offers great flexibility in designing ideal metal contacts and Schottky barrier formation, and studying the electronic, magnetic and optical properties of the Si/Ag system. We also believe that SiNWs decorated by Ag nanoislands have many potential applications in plasmonic photovoltaic cells, surface-enhanced Raman spectroscopy detection and electronic devices.

Improvement in the internal quantum efficiency of InN grown over nanoporous GaN by the reduction of Shockley-Read-Hall recombination centers

InN was grown over nanoporous GaN by metal-organic chemical vapor deposition. Additional free surfaces in the numerous GaN nanopores reduced the surface energy and encouraged extensive nucleation and uniform growth of InN nanoislands. Conversely, coarse and poorly distributed InN islands grew on planar GaN surfaces. Non-radiative Shockley-Read-Hall recombination rates were significantly lower in InN grown on nanoporous GaN than those on planar GaN, leading to the internal quantum efficiency increasing from 3% to 20%. This is attributed to the reorientation of InN during growth over the underlying nanoporous GaN, which relieved misfit stress and reduced defects associated with Shockley-Read-Hall recombination.

Growth and electronic properties of Ti nanoislands on Au(111)

The initial growth of titanium nanoislands on the reconstructed Au(111) surface was investigated by Scanning Tunneling Microscopy and Scanning Tunneling Spectroscopy (STM/STS). Ti atoms evaporated onto room temperature substrate start to nucleate preferentially at the elbows of the Au(111) herringbone reconstruction; however ordered nucleation is accompanied by an early occurrence of out-of-elbow islands. Titanium islands are irregularly shaped, composed of smaller sub-units as grains of about 1–2nm2 and their growth leads to a distortion of the underlying gold surface. We observe a retarded coalescence of titanium first layer islands with respect to other similar systems. Comparing the experimental data with a diffusive model, quantitative information about the interlayer diffusion of the first two layers is obtained. STS spectra and differential conductivity maps show peculiar electronic features outlining an important interaction between Ti atoms and the Au(111) surface.

Formation and structural features of silicon quantum dots in germanium

The formation of Si quantum dots on Ge is studied. Fundamental differences were found between the nucleation and growth of quantum dots on substrates with different orientations, related to both the formation of a SiGe solid solution layer and the shape of quantum dots. The temperature interval of formation of Si nanocrystals on Ge (111) is determined. It is shown that a change in the epitaxy temperature from 480 to 400 °C increases the silicon content in quantum dots from 58 to 75%. The effect of surfactants (in particular, hydrogen) on the nucleation and growth of silicon nanoislands is analyzed, showing that the use of hydrogen as a surfactant leads to a decrease in the size of quantum dots and a substantial increase in their density. The observed effects are attributed to the suppression of surface diffusion of atoms in the presence of hydrogen.

Nucleation and epitaxial growth of Ge nanoislands on Si surface prepatterned by ion irradiation

Experimental study of Ge nanoislands growth on groove-patterned Si(001) substrate formed by ion-beam-assisted nanoimprint lithography is carried out. Prepatterning procedure includes ion irradiation of Si substrate through imprinted resist mask and subsequent selective etching of irradiated Si domains. It is shown that temperature during ion irradiation affects the location of subsequently grown Ge nanoislands. The effect is interpreted in terms of additional surface tensile strain formed inside grooves by residual irradiation-induced defects. The effect is stronger for cold irradiated samples due to higher density of residual defects.

Growth and structure of CrN nanoislands on Cu(001) studied by scanning tunneling microscopy and X-ray photoemission spectroscopy

We report a method for the fabrication of high structural quality CrN nanoislands on Cu(001). The CrN nanoislands can be fabricated in ultrahigh vacuum conditions by means of Cr atoms deposition on saturated Cu(001)c(2×2)-N surface and subsequent annealing at 500°C. Existence of two types of nanoislands is shown by scanning tunneling microscopy investigations with atomic resolution for different CrN nanoislands formed on surface with 0.35 monolayer Cr coverage. The measured in-plane lattice constant (a=0.39±0.01nm) of the CrN nanoislands is 8% larger than the Cu substrate lattice. X-ray photoemission spectroscopy investigations reveal chromium nitride phase transition from CrN to Cr2N associated with changes of Cr concentration.

Nucleation of size calibrated three-dimensional nanodots in atomistic model of strained epitaxy: a Monte Carlo study

We introduce a simple model of strained epitaxy to study the growth of coherent several-monolayers-high nanoislands at low coverage. The size mismatch between the substrate (which is assumed to be rigid and passive) and the growing overlayer is modelled by the hard-sphere interaction between the adatoms. In the case of positive misfit the sphere diameter is larger than the substrate lattice parameter. Elastic interactions are described within the harmonic approximation to the substrate potential in the vicinity of the deposition sites. With additional attractive interaction between the nearest neighbour atoms the model exhibited the growth of miniature nanoislands of several morphologies with their kinetics similar to those found in real quantum dot (QD) systems. The 3D QDs exhibited narrow distributions of their heights, diameters and volumes in qualitative agreement with experimental observations.

Growth of GeSi nanoislands on nanotip-patterned Si (100) substrates with a stress-induced self-limiting interdiffusion

GeSi nanoislands grown on nanotip pre-patterned Si substrates at various temperatures are investigated. Nanoislands with a high density and narrow size distribution can be obtained within an intermediate temperature range, and the Ge atom diffusion length is comparable to half of the average distance of the Si nanotips. The Ge concentration distributions at the center and edge of the GeSi nanoislands are measured by scanning transmission electron microscopy. The results reveal that there is a Si core at the center of the GeSi nanoisland, but the Ge concentration presents a layered distribution above the Si nanotips. The radial component of the stress field in Ge layer near the Ge/Si interface on the planar, and the nanotip regions is qualitatively discussed. The difference of the stress field reveals that the experimentally observed concentration profile can be ascribed to the stress-induced interdiffusion self-limiting effect of the Si nanotips.

Influence of small miscuts on self-ordered growth of Ge nanoislands

Influence of small miscuts on self-ordered growth of Ge nanoislands

Growth of oriented Ag nanocrystals on air-oxidized Si surfaces: An in-situ reflection high energy electron diffraction study

Growth of Ag nanoislands on air-oxidized Si(001), (111) and (110) surfaces has been investigated by reflection high energy electron diffraction (RHEED), scanning tunneling microscopy (STM) and cross-sectional transmission electron microscopy. We have shown that the oriented nanocrystalline Ag, similar to the epitaxial growth of Ag on clean Si surfaces, can be grown on oxide-covered Si surfaces. A thin oxide layer (~ 2–3 nm thick) is formed on ultra-high vacuum (UHV)-cleaned Si surfaces via exposure of the clean reconstructed surface to air. Deposition of Ag was carried out under UHV at different substrate temperatures and monitored by RHEED. RHEED results reveal that Ag deposition at room temperature leads to the growth of randomly oriented Ag islands while, in spite of the presence of the oxide layer between Ag islands and Si, preferred orientations with an epitaxial relationship with the substrate evolve when Ag is deposited at higher substrate temperatures. STM images of the oxidized surfaces, prior to Ag deposition, apparently do not show any order. However, Fourier transforms of STM images show the presence of a short range order on the oxidized surface following the unit cells of the underlying reconstructed Si surface. It is intriguing that Ag nanoislands follow an epitaxial orientational relationship with the substrate in spite of the presence of a 2–3 nm thick oxide layer between Ag and Si. Apparently, the short range order existing on the oxide surface influences the orientation of the Ag nanoislands.

Simultaneous Growth of Nano and Submicrometer Sized ZnO Islands on Si and the Surface Electrical Properties

Simultaneous growth of two types of ZnO islands with different sizes has been observed on silicon substrate using radio frequency (rf) magnetron sputtering under an rf power of at substrate bias. Depositions were carried out using an (80:20) and gas mixture environment. The islands of the first type are well faceted, truncated pyramidal shaped ZnO islands on the Si surface with average base diameter and height . The other type is cone shaped ZnO islands with hemispherical base (upside down) which are embedded into the Si substrate. The size and height of the embedded ZnO cone shaped islands have been found to be in a range of and , respectively. These islands result from the bombardment of positive Ar ions into a negatively biased Si substrate. Morphology, shape, size, and microstructure have been investigated by transmission electron microscopy. Surface electrical properties of the bigger faceted ZnO islands have been measured by conductive atomic force microscopy. Enhanced current conduction has been found at the edges of the truncated pyramidal islands. This indicates that the nonpolar facets of and (10-11) are more electrically active than the polar facet of (0002).

Self-clustering phenomenon of epitaxial FeSi nanoislands on Si(001)

This study investigates the evolution in the growth of FeSi nanoislands on Si(001). Under proper growth conditions, nanoislands spontaneously cluster into groups on rectangular FeSi terraces depending on both substrate temperature and deposition coverage. This study discussed the self-clustering mechanism in the context of strain relaxation and mass transportation between nanoislands and terraces.

Direct transfer of gold nanoislands from a MoS2 stamp to a Si–H surface

A printing technique is proposed for the transfer of metallic nanoislands between two semiconductor surfaces in UHV. For the preparation of the stamp, a systematic study of the growth conditions of small, flat triangular shape Au nanoislands at the top surface of microfabricated MoS2 pillars is presented. Those pillars are organized in a stamping matrix to increase the transfer rate. Up to 10% of Au nanoislands can be transferred to a H-Si(100) surface. The atomic scale quality of the interface between the Au nanoislands and the semiconductor surface is characterized by transmission electron microscopy cross-sectional imaging. This MoS2 stamping technique is extended to other surfaces such as mica, SiO2, and graphite. It permits to handle well shaped Au nanoislands on surfaces where a direct growth of flat nanoislands is not possible. This printing of well defined triangular Au nanoislands offers the unique possibility to construct ultraclean interconnecting nanopad systems by scanning tunneling microscope on atomically clean and electronically suitable substrates, manipulating those nanopads one at a time. The apex of the triangular shaped island is suitable for nanocontact to a surface atomic scale conducting wire.

Stress-induced nanoislands nucleation during growth of Ge/Si heterostructures under low-energy ion irradiation

Stress-induced nucleation of nanoislands under pulsed low-energy ion-beam assisted growth of Si/Ge heterostructures is studied by molecular dynamics and Monte-Carlo calculations. It is shown that cluster of interstitials is produced in Si bulk by an ion impact. Stresses induced at the surface by clusters of interstitials affect migration ability, stimulating nucleation and growth of Ge nanoislands. The main effects of ion-beam action observed in experiments, e.g. increase in islands density, decrease in islands average size and nonmonotonous dependence of islands density upon degree of molecular beam ionization, are interpreted in terms of stress-induced mechanism.

Bilayer growth of nanoscale Co islands on Cu(111)

Combining kinetic Monte Carlo and molecular static simulations, we follow at the atomic scale the growth of Co nanoislands on Cu(111) surface over a wide range of surface temperatures $(130--300\phantom{\rule{0.3em}{0ex}}\mathrm{K})$. Atomistic processes responsible for the interlayer mass transport of Co atoms and the formation of 2 ML high nanoislands at temperatures $>200\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ are revealed. Transition from the two- to the three-dimensional growth mode with decreasing the temperature is demonstrated. Strain relaxations induced in the Cu substrate and in the Co nanoislands are found to have a strong impact on the formation of triangle Co islands at room temperatures. Results of our theoretical studies are supported by the scanning tunneling microscope measurements.

最近の研究から ＭＯＣＶＤ法によるＰｂＴｉＯ３ナノ島の作製とその強誘電性

PbTiO3 nanoislands were grown on Pt-covered SiO2/Si and SrTiO3 substrates by self assembly using metalorganic chemical vapor deposition (MOCVD) . Square-, triangular-prism- and pyramidal-shaped nanoislands with orderly in-plane direction were fabricated on Pt/SrTiO3 (001), (101) and (111) substrates, respectively, demonstrating structural control using epitaxial relationships. The size dependence of crystalline and domain structures was influenced by the experience of the phase transition from paraelectric to ferroelectric phase in the cooling process after MOCVD growth of nanoislands. Piezoresponse force microscopy revealed that the piezoelectric constant was dependent on not the width but the height in PbTiO3 (001) nanoislands with heights below 10 nm, suggesting intrinsic size effects. The minimum size of PbTiO3 (001) nanoislands showing ferroelectricity was 1.2 nm in height and 27 nm in width.

Growth of copper nanoislands on the Si(100)-c(4 × 12)-Al surface studied by scanning tunneling microscopy

The growth of copper island films on the Si(100)-c(4 × 12)-Al surface phase has been studied using scanning tunneling microscopy (STM). The dependence of the island concentration on their size and the substrate temperature is determined. The diffusion activation energy and the binding energy of copper dimers are determined from an analysis of the experimental STM data in terms of the kinetic theory of nucleation. The critical temperature corresponding to a change in the growth regime is evaluated from an Arrhenius plot. It is established that the c(4 × 12)-Al surface phase exhibits an orienting action on the crystalline structure of Cu nanoislands.

Cooperative growth of nano-islands on Si(1 0 0) surface

By setting up two low temperature regions on a terrace of a vicinal Si(1 0 0)-2 × 1 surface, we have studied growth of nano-islands in the two regions using a kinetic Monte Carlo simulation. At first two islands are formed and grow independently without any supply of atoms from the outside. As the growth proceeds further, two islands are connected with each other by forming a bridge region. After the connection, the growth changes dramatically showing a competitive mode in one stage and a cooperative mode in the other. Two islands grow cooperatively in a sense that a larger island ceases to grow and waits until the size of the other smaller island becomes similar to that of the larger one. When two islands become similar in size, one of the islands grows faster than the other competitively, by accumulating atoms from then smaller one. The origin of the growth mode is analyzed.

Effect of oblique-angle deposition on early stage of Fe–Si growth

We have investigated the initial stage of Fe growth on an Si substrate during reactive oblique-angle deposition (ROAD) at 470 °C by means of atomic force microscopy, reflection high-energy electron diffraction, and high-resolution Rutherford backscattering spectroscopy. During deposition along the normal direction, many Si atoms are displaced from their lattice positions because of reactions with the deposited Fe. However, for ROAD, the number of displaced Si atoms decreases significantly along with a selective growth of nanoislands with diameters of a few 10 nm. Evidently, the local nucleation processes required for iron silicide formation are modified by the geometrical deposition conditions.

Step edge growth of Co nanoislands on Cu(111) surface

Step edge growth of Co nanoislands on Cu(111) surface have been investigated by scanning tunneling microscopy (STM). The cobalt atoms cluster at the upper step edges and form bilayer islands of 2nm in diameter (about nine Co atoms in width) initially during the initial stage of Co deposition. This result is in accordance with the total energy calculations within density functional theory. Besides, the size and amount of nanoislands increase with increasing coverage. The average number of Co atoms contained in one island increases with a rate of 375 atoms per monolayer (ML). The statistics data on the STM images indicate that the cobalt nanoislands preferentially grow at the upper step edge during the first stage of Co deposition, then toward terrace, and finally, the growth rate of islands in edge is almost the same as that in terrace for Co thickness above 0.78–1.42 ML.