Clean Si Research Articles

Precise chemical state analyses of ultrathin hafnium films deposited on clean Si(111)-7 × 7 surface using high-resolution core-level photoelectron spectroscopy

Herein, well-defined ultrathin hafnium films on Si(111) -7 × 7 [Hf/Si(111)] were prepared by using electron beam heating in an ultrahigh vacuum (UHV) chamber at a pressure below 1.1 × 10−8 Pa. High-resolution core-level photoelectron spectroscopy of the Si 2p1/2, 3/2 and Hf 4f5/2, 7/2 levels combined with a synchrotron radiation X-ray light source was employed to reveal the chemical states at the interface and surface of ultrathin Hf/Si(111) films. Ultrathin Hf layers grow on clean Si(111)-7 × 7 surfaces by a lever rule that the first phase is not consumed when subsequent phases form. Therefore, it was found that the surface and interface of Hf/Si(111) certainly contains three components, which can be ascribed as metallic Hf layers, Hf monosilicide (HfSi), and Si-rich Hf silicide just above the Si substrate (HfSi4). The metallic Hf layers were observed to comprise some diffused Si atoms. According to the results obtained from photoelectron spectroscopy and scanning electron microscopy, ultrathin Hf layers change into HfSi2 islands on a bare Si(111)-7 × 7 surface after annealing at 1073 K. Small dot-shaped islands of HfSi2 appeared after annealing a two-monolayer thick Hf sample; whereas, rectangular HfSi2 islands including metallic Hf species randomly appeared after annealing a six-monolayer thick Hf sample. The long axes of the rectangle islands expanded in a direction that connected the corner holes in a model with dimers, adatoms, and stacking-faults (DAS model) of a clean Si(111)-7 × 7 surface. Our precise chemical analyses will be very useful for preparing well-defined interfaces and surface structures for obtaining next generation 3D metal-oxide-semiconductor field effect transistors and ferroelectric devices.

Thermal dissociation of CO molecules and carbon incorporation on the Si(111)-(7 × 7) surface

Incorporation of carbon (C) atoms in the Si(111)-(7 × 7) surface is investigated by using scanning tunneling microscopy and density-functional theory calculations. C atoms are supplied through thermal dissociation of CO molecules adsorbed on the Si(111)-(7 × 7) surface. One C atom can be incorporated substitutionally below the Si adatoms of the (7 × 7) structure. However, the stable (7 × 7) surface can accommodate only a very small amount of C atoms and the surplus C atoms are swept away to the step edges in the form of silicon-carbon clusters, restoring the clean Si(111)-(7 × 7) structure on the flat terrace. In contrast to the B-induced 3×3 reconstruction, high density C atoms do not induce a single crystalline 3×3 reconstruction over a wide area of Si(111).

Mechanism study of SiO2 layer formation and separation at the Si die sidewall during nanosecond laser dicing of ultrathin Si wafers with Cu backside layer

Laser dicing of ultrathin dies is promising and is gaining importance because of its cost and quality advantages over mechanical and plasma dicing. However, the effects of laser dicing on the mechanical strength and microstructure of ultrathin Si dies need to be further understood, especially when dicing through Si wafers with backside Cu layer. A critical phenomenon effecting the Si die sidewall strength after nanosecond laser dicing of Si wafers with backside Cu is the formation and separation of a SiO2 layer at the sidewall. The mechanisms behind the SiO2 layer formation and separation were studied in this work. Si wafer samples without and with backside Cu layer were prepared by dicing with nanosecond laser using standard production parameters. The microstructure and phases formed were investigated by energy dispersive spectroscopy and nanobeam diffraction in a transmission electron microscope. In die samples without backside Cu, the sidewall consists of a thin surface layer of amorphous Si, followed by a polycrystalline Si layer, and finally an epitaxial Si layer. In die samples with backside Cu, the sidewall microstructure was observed to be vastly different. At the upper region of the sidewall, a surface layer of polycrystalline Cu was found, followed by a polycrystalline Cu3Si layer, a SiO2 layer mixed with Cu3Si, and finally a thick SiO2 layer. The Cu3Si catalyzes the growth of the SiO2 through an oxidation step of the Cu3Si on the sidewall surface as well as at the SiO2/Si interface. In the lower region of the sidewall, the microstructure is similar to the upper region, but there is a separation of the SiO2 layer from the crystalline Si. The SiO2 undergoes a decomposition reaction at the SiO2/Si interface, releasing volatile SiO which causes microvoids to form and grow laterally at the interface. The growth and coalescence of the microvoids eventually lead to the separation of the SiO2 layer from the crystalline Si, leaving behind a clean and rough crystalline Si surface with a peak-to-peak roughness of 100–200 nm. In the areas where the SiO2 layer has separated from the Si die sidewall, the fracture strength of the sidewall is dependent on the material property and surface roughness of the crystalline Si, and not on the SiO2 layer. In the sidewall region near the die frontside, the SiO2 thickness is more than regions near the die backside, and no microvoiding and separation at the SiO2/Si interface were detected. This is hypothesized to be due to a higher O2 pressure at the upper region of the narrow dicing trench which is open to the atmosphere compared to the lower regions where there could be O2 deprivation and lower O2 pressure.

Improved figures of merit of nano-Schottky diode by embedding and characterizing individual gold nanoparticles on n-Si substrates

Improving Schottky diode characteristics in semiconducting devices is essential for better functionality in electronic and optoelectronic devices at nanoscale. In this paper, we investigate the electric transport characteristics of a gold (Au)-tip/n-Si-based nano-Schottky diode by using a conductive-mode atomic force microscope (CAFM). First, 10 nm average diameter Au nanoparticles (NPs) are monodispersed on the highly cleaned n-type Si substrate using an optimized spin-coating technique. The controlled and well dispersed NPs are confirmed by using the AC imaging mode of the AFM. The electrical characteristics are established by using an Au-coated AFM tip, by either soft engaging at the surface of the n-Si substrate or at the top of an individual Au NP. Landing of the AFM tip on the NP or n-Si substrate is validated by the force curves of the AFM. From the localized CAFM electrical characteristics, we observed the improvement in the figures of merit (FOM) that characterize the rectification performance including the (1-V) asymmetry (fASYM), and the turn-on voltage due to placing the Au NP between the AFM tip and n-Si substrate. These improved FOM of the nanoscale diodes are explained based on the increase in the tunneling current at the nanoscale Au-NP/n-Si interface. Moreover, the nanoscale control of interface structure is extremely important to improve the characteristics of nano-Schottky diodes.

Surface-Enhanced IR-Absorption Microscopy of Staphylococcus aureus Bacteria on Bactericidal Nanostructured Si Surfaces.

Surface-enhanced IR absorption (SEIRA) microscopy was used to reveal main chemical and physical interactions between Staphylococcus aureus bacteria and different laser-nanostructured bactericidal Si surfaces via simultaneous chemical enhancement of the corresponding IR-absorption in the intact functional chemical groups. A cleaner, less passivated surface of Si nanoripples, laser-patterned in water, exhibits much stronger enhancement of SEIRA signals compared to the bare Si wafer, the surface coating of oxidized Si nanoparticles and oxidized/carbonized Si (nano) ripples, laser-patterned in air and water. Additional very strong bands emerge in the SEIRA spectra on the clean Si nanoripples, indicating the potential chemical modifications in the bacterial membrane and nucleic acids during the bactericidal effect.

Initial oxidation processes of ultrathin hafnium film and hafnium disilicide islands on Si(100)-2 × 1 surfaces studied using core-level X-ray photoelectron spectroscopy

We investigated the initial oxidation of ultrathin hafnium (Hf) film on Si(100)-2 × 1 [Hf/Si(100)] using high resolution Hf 4f5/2, 7/2, Si 2p1/2, 3/2, and O 1s core-level photoelectron spectroscopy. Ultrathin Hf/Si(100) film was prepared using electron-beam evaporation in an ultrahigh vacuum chamber below 1.5 × 10−8 Pa. Our results revealed the formation of metallic Hf layers containing a few Si atoms on the Si(100)-2 × 1 substrate. A Hf monosilicide (HfSi) component was also formed in the vicinity of the interface region. Metallic Hf rapidly oxidized, transforming into hafnium dioxide (HfO2) and its suboxides, after exposure to O2 molecules at <4.1 Langmuir. In accordance with the oxidation of metallic Hf, Si atoms in metallic Hf layers were also oxidized into typical Si (sub)oxides and Hf silicate. The other HfSi component at the interface was nearly unreactive with O2 molecules. These facts suggest that the metallic Hf component plays a vital role in the initial oxidation of the ultrathin Hf/Si(100) film. After annealing from 873 K to 973 K, the Hf suboxides in low ionic valences progressed into fully oxidized HfO2. Once the annealing temperature reached ~1073 K, oxygen atoms were entirely removed from the ultrathin HfO2/Si(100) film containing SiO2 at the interface. Simultaneously, ultrathin HfO2 layers changed into islands of Hf disilicide (i-HfSi2) on a bare Si(100)-2 × 1 surface. The i-HfSi2 component showed slight reactivity with O2 molecules at 298 K. In contrast to the initial oxidation of clean Si(100)-2 × 1 surface, the dangling bonds on bare Si(100)-2 × 1 surface among i-HfSi2 oxidized preferentially. This was due to some back-bonds of the Si dimers on bare Si(100)-2 × 1 that were occupied by Hf atoms in the form of HfSi2.

Dimer-vacancy defects on Si(1 0 0): The role of nickel impurity

Using scanning tunneling microscopy, x-ray photoelectron spectroscopy, and low-energy electron diffraction, we have studied clean and Ni-containing Si(1 0 0) surfaces and shown that the Ni contamination can easily appear at the Si(1 0 0) during its annealing at high temperature (1230 °C) because of migration of this impurity from heated parts of the sample holder, even though they are nominally Ni-free. The difference of dimer-vacancy (DV) defects, which are common features of Si(1 0 0), and their patterns on both surfaces is examined. It is also found that the density of DV defects on the Ni-contaminated surface is proportional to the number of Ni atoms. The analysis indicates that the fully saturated DV structure, i.e., Ni-induced Si(1 0 0)(2 × n) phase contains one metal atom per defect. The findings are valuable for constructing atomic models of defects on the Si(1 0 0) as well as preparation of clean Si(1 0 0) substrate and monitoring the Ni segregation on its surface. In addition, the results can be useful for Ni silicide metal-contact formation in metal-oxide-semiconductor field-effect transistor technology.”

Dissociation of CH3–O as a Driving Force for Methoxyacetophenone Adsorption on Si(001)

The coverage-dependent behavior of p-methoxyacetophenone on the clean Si(001) surface was followed using X-ray photoelectron spectroscopy and supporting density functional theory calculations. Unlike other multifunctional organic molecules, this compound exhibits a high selectivity of adsorbate species formation by forming only two distinct adsorbate structures at low coverage, with a third configuration forming at high coverages. At low coverage, surface chemisorption is driven by methoxy group dissociation. However, at high coverage, the surface footprint required for this process is no longer available, leading to the formation of less thermodynamically stable adsorbates that are datively bonded to the surface with a smaller footprint. This coverage-dependent but well-defined behavior is promising in designing functional organic–inorganic interfaces on silicon.

Surface multiferroics in silicon enabled by hole-carrier doping

We predict a coexistence of magnetic and electric orders on clean Si(0 0 1) surfaces by first-principles calculations. Upon hole-carrier doping, the Si surfaces can be ferromagnetic, with polarized spins concentrated in an atom-thick space near the surface, due to an exchange splitting of localized s-like surface states on surface Si dimers. The surface magnetization can be controlled by reorienting the electric polarization of Si dimers, manifested as a transition from the magnetic antiferroelectric ground state to ferroelectric p(2 × 1) reconstruction that can be driven by an in-plane external electric field. The coupling between magnetic and electric orders can be further enhanced by strain silicon technology, rendering the Si surfaces as the first metal-free material displaying a multiferroic behavior.

Initial Growth of Pentacene Thin Film on Si(001) Substrate

Initial growth process of pentacene molecules on clean Si(001)-2 × 1 substrate was investigated by scanning tunneling microscopy. It is found that the wetting layer, which is not crystalline but disordered, forms before the growth of a first crystalline layer. The wetting layer consists of double layer of the flatly adsorbed pentacene molecules. The formation of the wetting double layer is discussed. The first crystalline layer that is grown on the disordered wetting layer with standing-up pentacene molecules consists of some domains that differ in their crystal structures. Among them, a new pentacene crystal structure is found that can form only on the first layer. In contrast, the second crystalline layer has only single domain. Moreover, we investigated the electronic properties of the pentacene layers by the current–voltage measurements. The pentacene layers are semiconducting with a band gap of about 4 eV.

First-principles study on the diffusion dynamics of Al atoms on Si surface

&lt;sec&gt;Density functional theory is used to calculate the adsorption and diffusion behavior of Al atoms on clean, H-terminate, Cl-terminate Si(100) and Si(111) surfaces. The most stable position of Al atom adsorption and the diffusion path are different on Si(100) surface terminated by different methods. On the surface of clean Si(100), the &lt;i&gt;Tr&lt;/i&gt; site is the most stable site for Al atom with an adsorption energy of 4.01 eV, and the &lt;i&gt;H&lt;/i&gt; and &lt;i&gt;M&lt;/i&gt; sites are the sub-stable stable sites with the adsorption energies of 3.51 eV, and 3.63 eV, respectively. When the Al atom is adsorbed at the &lt;i&gt;Tr&lt;/i&gt; site on the clean Si(100) surface, it bonds with the Si atom to destroy the Si—Si bond in the dimer. Therefore Al is easily adsorbed at the &lt;i&gt;Tr&lt;/i&gt; site of the trench and diffuses in a zigzag pattern along the trench. On the H-terminate and Cl-terminate Si(100) surface, Si—Si bonds in the dimer column are changed from cross to parallel. Al is easily adsorbed at the &lt;i&gt;H&lt;/i&gt; position at the top of the dimer column, and diffuses along the line at the top of the dimer. The differential charge density shows that the Al atom transfers electrons to the Si atoms on the surface, and the surface H-terminate and Cl-terminate weaken the interaction between Al atoms and Si, and reduces the diffusion energy barrier of Al atoms. &lt;/sec&gt;&lt;sec&gt;The Si(111) surface terminated by different methods has the same stable position (&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;4&lt;/sub&gt; site) for the adsorption of Al atoms. When Al atom adsorbs at the &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;4&lt;/sub&gt; site on the clean Si(100) surface, it bonds to Si atom, which located at the three &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;1&lt;/sub&gt; site, then Al atom is firmly fixed by the three Al—Si bonds with a bond length of 2.55 Å. Thus Al atom can has the largest adsorption energy and form the most stable state at the &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;1&lt;/sub&gt; site. With the diffusion and migration of Al atom, the bond between Al atom and the &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;1&lt;/sub&gt; site in the opposite direction appears to be broken. When Al atom migrating to the saddle point position is the most unstable. Here Al atom bonds to the Si atoms of the two adjacent &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;1&lt;/sub&gt; sites to form a bond with a length of 2.49 Å, which is 0.06 Å shorter than the initial Al—Si bond (2.55 Å). What’s more, the diffusion energy barrier of Al atom at this position is 0.65 eV, which impede Al atom to diffuse and migrate. When Al atom migrates to the &lt;i&gt;H&lt;/i&gt; site, it rebonds to the three Si atoms on the adjacent surface and forms a bond with a length of 2.52 Å, which is 0.03 Å shorter than the Al—Si bond (2.55 Å) at the initial position. On the H-terminate and Cl-terminate Si(111) surface, Al atom doesn’t bond with Si atom for the H or Cl saturates the dangling bonds on the Si surface. The Si(111) surface terminated by different methods has the same stable position for adsorption of Al atoms. The diffusion paths of Al atoms are similar, and they are easy to be adsorbed to the top position (&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;4&lt;/sub&gt; site) of the second Si atom, and the path along &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;4&lt;/sub&gt; to &lt;i&gt;H&lt;/i&gt;&lt;sub&gt;3&lt;/sub&gt; is diffused. Similarly, the H-terminate or Cl-terminate of Si(111) surface weakens the electron transfer between Al and Si atoms and reduces the diffusion energy barrier of Al atoms. Regardless of the Si(100) or Si(111) surface, the H-terminate and Cl-terminate Si surfaces are effective in reducing the diffusion barrier of Al atoms.&lt;/sec&gt;

Growth of Ag(1 1 1) on Si(1 1 1) with nearly flat band and abrupt interface

Growth of Ag films of up to 30 nm thickness on Si(1 1 1) 7 × 7 at room temperature is investigated by low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). LEED revealed the coexistence of Ag and Si spots starting with 1 monolayer (ML) of Ag deposited. The Ag lattice constant, starting with 25 ML, is slightly higher than for bulk Ag and increase linearly with Ag thickness, reaching about 4.2 nm for the thickest films. The average terrace widths detected from LEED spot profile analysis are about 30 nm for clean Si(1 1 1) 7 × 7 and about 5.5 nm for the thickest Ag(1 1 1) film, in agreement with STM observations. The intensity variation of core levels analyzed by XPS is taken into account by a model assuming the initial formation of Ag islands with linear variation of coverage vs. the amount of Ag deposited, followed by growth in a quasi layer-by-layer mode. The interface barrier is in the range of 0.4 eV, lower than all values reported previously. Ag deposited on Si(1 1 1) 7 × 7 at room temperature provides flat Ag(1 1 1) for synthesis of 2D materials, and may be used for low barrier Schottky diodes.

Atomic and electronic structure of the Si(331)-(12 1) surface.

We report on the investigation of the atomic and electronic structures of a clean Si(331)-(12 × 1) surface using a first-principles approach with both plane wave and strictly localized basis sets. Starting from the surface structure proposed by Zhachuk and Teys [Phys. Rev. B 95, 041412(R) (2017)], we develop significant improvements to the atomic model and localized basis set which are critical for the correct description of the observed bias dependence of scanning tunneling microscopy (STM) images. The size mismatch between the Si pentamers from the surface model and those seen by STM is explained within the context of the Tersoff-Hamann model. The energy barriers that separate different Si(331) buckled configurations were estimated, showing that the surface structure is prone to dynamic buckling at room temperature. It is found that empty electronic states on Si(331) are essentially localized on the pentamers with interstitials and under-coordinated Si sp 2-like atoms between them, while filled electronic states are localized on under-coordinated Si sp 3-like atoms and dimers on trenches. The calculated electronic density of states exhibits two broad peaks in the fundamental bandgap of Si: one near the valence band top and the other near the conduction band bottom. The resulting surface bandgap of 0.58 eV is in an excellent agreement with spectroscopy studies.

Atomic-layer doping of SiGe heterostructures for atomic-precision donor devices

As a first step to porting scanning tunneling microscopy methods of atomic-precision fabrication to a strained-Si/SiGe platform, we demonstrate post-growth P atomic-layer doping of SiGe heterostructures. To preserve the substrate structure and elastic state, we use a T $\leq 800^\circ$C process to prepare clean Si$_{0.86}$Ge$_{0.14}$ surfaces suitable for atomic-precision fabrication. P-saturated atomic-layer doping is incorporated and capped with epitaxial Si under a thermal budget compatible with atomic-precision fabrication. Hall measurements at T$=0.3$ K show that the doped heterostructure has R$_{\square}=570\pm30$ $\Omega$, yielding an electron density $n_{e}=2.1\pm0.1\times10^{14}$cm$^{-2}$ and mobility $\mu_e=52\pm3$ cm$^{2}$ V$^{-1}$ s$^{-1}$, similar to saturated atomic-layer doping in pure Si and Ge. The magnitude of $\mu_e$ and the complete absence of Shubnikov-de Haas oscillations in magnetotransport measurements indicate that electrons are overwhelmingly localized in the donor layer, and not within a nearby buried Si well. This conclusion is supported by self-consistent Schr\"odinger-Poisson calculations that predict electron occupation primarily in the donor layer.

Influence of temperature and Al/N ratio on structural, chemical & electronic properties of epitaxial AlN films grown via PAMBE

The present article investigates structural, chemical and electronic properties of epitaxial AlN films grown via plasma assisted molecular beam epitaxy on atomically clean Si (1 1 1) substrates. An inclusive optimization process of growth parameters by varying the substrate temperature (790–825 °C) and Al/N (III/V) ratio is demonstrated. The AlN film grown with optimized parameters yielded an FWHM of 24.6 arcmin, crystallite size of 11.6 nm, screw dislocation density of 4.43 × 109/cm2 and a surface roughness of 3.11 nm. Besides, the chemical states and electronic structure analysis displayed absence of remnant metallic aluminium and native surface oxide (∼2%) with Fermi level (3.0 eV) pinned near its intrinsic value. A growth mechanism has been proposed for the optimized growth of AlN. Further, the high quality AlN film can potentially be used for the fabrication of smart optoelectronics for deep UV application and field emission devices.

The RBS analysis for a thin amorphous Si layer formed on clean and H-terminated Si(0 0 1) surfaces followed by medium-energy IBIEC treatments

We have investigated the crystallization process of an amorphous Si layer grown on a clean and hydrogen-terminated Si(0 0 1) surfaces by ion beam induced epitaxial crystallization (IBIEC). It is widely known that the amorphous/crystalline (a/c) interface should be atomically controlled to achieve the high-quality Si epitaxy. In this study, we quantitatively clarify the influence of interfacial H amount to the IBIEC rate of the deposited amorphous Si layer. We initially prepared a typical H-free pristine Si(0 0 1)-(2 × 1) surface and two kinds of chemically H-terminated surfaces of as-treated and sequentially annealed at 350 °C in ultrahigh vacuum, corresponding to high (dihydride) and low (monohydride) hydrogen coverage, respectively. An amorphous Si layer was then in-situ deposited on these three types of surfaces by an electron bombardment evaporator at room temperature. The samples were irradiated by 180-keV Ar+ ions with an ion fluence of 5 × 1015 ions cm−2 at 300–500 °C. The Rutherford backscattering (RBS) analysis showed that the deposited Si on the dihydride surface is not crystallized at these temperatures; whereas, that on the monohydride surface is crystallized by Ar+ irradiation at 500 °C. The crystallization on the MH surface was found at significantly higher temperature than that on the H-free clean surface. The behavior of the interfacial H atoms during IBIEC process is discussed by means of RBS analysis.

Influence of ionic interfacial layers on electronic properties of Alq3/Si(100) interface

The electronic structures of Alq3/Si(100), Alq3/LiBr/Si(100), and Alq3/KCl/Si(100) systems are presented in this report. Their energy level diagrams were prepared and discussed. The formation of the LiBr and KCl interfacial layers between an Alq3 film and a Si(100) substrate results in a decrease of the energy barrier at the interface. The studies were carried out in situ in ultrahigh vacuum by ultraviolet photoelectron spectroscopy. Alq3 as well as LiBr and KCl layers were vapour evaporated onto n‐type Si(100) crystal. The electron affinity of clean Si(100) surface was 4.0 eV, and the position of the valence band maximum was 0.7 eV below EF. The energetic distance between the valence band maximum of Si(100) and the highest occupied molecular orbital level were 1.5, 2.6, and 2.2 eV, for the Alq3/Si(100), Alq3/LiBr/Si(100), and Alq3/KCl/Si(100) systems, respectively.

The effect of Ga pre-deposition on Si (111) surface for InAs nanowire selective area hetero-epitaxy

Vertical InAs nanowires (NWs) grown on a Si substrate are promising building-blocks for next generation vertical gate-all-around transistor fabrication. We investigate the initial stage of InAs NW selective area epitaxy (SAE) on a patterned Si (111) substrate with a focus on the interfacial structures. The direct epitaxy of InAs NWs on a clean Si (111) surface is found to be challenging. The yield of vertical InAs NWs is low, as the SAE is accompanied by high proportions of empty holes, inclined NWs, and irregular blocks. In contrast, it is improved when the NW contains gallium, and the yield of vertical InxGa1-xAs NWs increased with higher Ga content. Meanwhile, unintentional Ga surface contamination on a patterned Si substrate induces high yield vertical InAs NW SAE, which is attributed to a GaAs-like seeding layer formed at the InAs/Si interface. The role of Ga played in the III-V NW nucleation on Si is further discussed. It stabilizes the B-polarity on a non-polar Si (111) surface and enhances the nucleation. Therefore, gallium incorporation on a Si surface is identified as an important enabler for vertical InAs NW growth. A new method for high yield (&amp;gt;99%) vertical InAs NW SAE on Si using an InGaAs nucleation layer is proposed based on this study.

Selective adsorption of toluene-3,4-dithiol on Si(553)-Au surfaces

The adsorption of small organic molecules onto vicinal Au-stabilized Si(111) surfaces is shown to be a versatile route towards controlled growth of ordered organic-metal hybrid one-dimensional nanostructures. Density functional theory is used to investigate the site-specific adsorption of toluene-3,4-dithiol (TDT) molecules onto the clean Si(553)-Au surface and onto a co-doped surface whose steps are passivated by hydrogen. We find that the most reactive sites involve bonding to silicon at the step edge or on the terraces, while gold sites are relatively unfavored. H passivation and TDT adsorption both induce a controlled charge redistribution within the surface layer, causing the surface metallicity, electronic structure, and chemical reactivity of individual adsorption sites to be substantially altered.

Mixed-dimensional 2D/3D heterojunctions between MoS2 and Si(100).

For utilization of two-dimensional (2D) materials as electronic devices, their mixed-dimensional heterostructures with three-dimensional (3D) materials are receiving much attention. In this study, we have investigated the atomic and electronic structures of the 2D/3D heterojunction between MoS2 and Si(100) using density functional theory calculations; especially, we focus on the contact behavior dependence on the interfacial structures of heterojunctions by considering two types of surface termination of Si(100) surfaces. Calculations show that MoS2 and clean Si(100) form an almost n-type ohmic contact with a very small Schottky barrier height (SBH) due to strong covalent bonds between them, and that the contact between MoS2 and H-covered Si(100) makes a p-n heterojunction with weak van der Waals interactions. Such a difference in contact behaviors can be explained by different electric dipole formation at the heterojunction interfaces. Overall, it is concluded that contact properties can be varied depending on the interfacial structures of 2D(MoS2)/3D(Si) semiconductor heterojunctions.