Electronic structure of compounds at platinum - silicon (111) interface

The electronic structure of Platinum silicides produced by thin film reaction is studied using ultraviolet photoemission and Auger spectroscopy. Spectra have been taken during the various stages of Si-Pt intermixing, in order to monitor the changes in the valence band, which take place during the reaction. The experimental data are compared with semi-empirical LCAO calculations. The importance of the coupling between Silicon p and Platinum d-states in determining the basic features of the chemical bond is discussed.     

Embedded silicon nanocrystal interface structure and strain

The structure of nanocrystal-matrix interface and strain in embedded nanocrystals are studied using large-scale atomistic simulations, with the examples of Si nanocrystal embedded in amorphous matrix of SiO₂. Photoluminescence from silicon nanocrystals embedded in a dielectric matrix like SiO₂ and Si₃N₄ are promising for Si-based optical devices. The nanocrystal-matrix interface plays a crucial role in understanding its optical and electrical properties. Nanocrystals with diameters varying from 2.17 to 4.56 nm are studied. A detailed quantitative analysis of the variation of Si/SiO₂ interface structure and strain distribution with nanocrystal diameter is reported. A linear variation of the interface width with nanocrystal diameter is observed with thinner interfaces for larger nanocrystals. Local deformation analysis reveals that the smaller nanocrystals are highly strained, whereas the strain in the larger ones shifts to the interface. This is in accordance with observed increase in total percentage of defect states in the interface from 39 to 70% for diameter increasing from 2.17 to 4.56 nm. Moreover, based on the atomic arrangements at the interface, optically active defects like Pb centres, E centres and non-bridging oxygen centres are identified and a dominance of Pb centres is observed for all the nanocrystals. The detailed structural characterization-related investigations using the proposed simulation approach will find useful application in designing system-level response of embedded nanocrystals and also to correlate various experimental observations.     

Noncapillary-wave structure at the water-alkane interface

Synchrotron x-ray reflectivity is used to study the interface between bulk water and bulk n-alkanes with carbon numbers 6 through 10, 12, 16, and 22. For all interfaces, except the water-hexane interface, the interfacial width disagrees with the prediction from capillary-wave theory. The variation of interfacial width with carbon number can be described by combining the capillary-wave prediction for the width with a contribution from intrinsic structure. This intrinsic structure is determined by the gyration radius for the shorter alkanes and by the bulk correlation length for the longer alkanes.     

Formation of a ripple pattern at a water/silicon interface using an oscillating bubble

A single femtosecond laser pulse was irradiated at a water/silicon interface, and the processed surface was investigated. Rings surrounded by ripples were found within the irradiated spot. The diameter of the rings ranged from 500 nm to 10 μm. It is proposed that acoustic waves, caused by the oscillating motion of bubbles near the water/silicon interface, deformed the melting silicon surface. In the present work, a pulse (pulse width: 150 fs) was tightly focused in water to induce optical breakdown, and a bubble was generated at an arbitrary spot. When the power density was below the ablation threshold and above the melting threshold at the silicon surface and set above the breakdown threshold at the focus in water, a pattern was generated at a specific place and with a specific size. PACS 79.20.Ds; 42.62.Cf     

Electronic structure and spin polarization at the NiMnSb/GaAs(110) interface

Within the density functional theory, ab initio calculations of the electronic structure and magnetic properties of the (110) interface between the NiMnSb alloy and GaAs in dependence on configuration of contact atoms are carried out. It is found that two out of six possible atomic configurations of the interface exhibit a high degree of spin polarization, which attains 100% for one of the interfacial structures studied here. It is shown that contacts with a high degree of spin polarization are the most stable with an adhesion energy of about 1.3 J/m².     

Analysis of the current-transport mechanism across a CVD diamond/silicon interface

This work presents a study on the mechanism of injection and charge transport through a CVD diamond/n⁺-Si interface. The current-voltage-temperature characteristics of CVD diamond/silicon heterojunctions measured in the temperature range 119-400 K have been interpreted according to thermionic theory and thermionic field-emission theory. This junction shows deviations from the ideal thermionic theory current model, suggesting the presence of surface states, thin-layer depletion and/or non-homogeneity in the diamond/silicon interface. The T₀ anomaly has been used to explain the behaviour of the ideality factor with temperature. At very low temperatures tunnelling may occur because the E₀₀ values for these junctions are close to the value expected by thermionic field-emission theory. The usual activation-energy plot deviates from linearity at low temperatures. This deviation has been corrected supposing a ln(J_S/T²) versus 10³/nT plot. Under these conditions the Richardson constant is found to be 0.819 A cm⁻² K⁻², which is close to the theoretical value of 1.2 A cm⁻² K⁻². Field-emission device is a promising application for diamond/silicon structure.     

Space charge and surface state characteristics of the silicon/electrolyte interface

The essentially blocking nature of the silicon/electrolyte (S/E) interface enables charge to be induced electrostatically at the interface by an applied bias. The use of pulsed rather than DC biases provides a fairly detailed picture of the silicon interface. The results reported here concern the silicon space-charge layer, localized states at the S/E interface and charge leakage across the interface. As to the first, evidence is presented that strong, quantized accumulation layers of excess surface-electron densities as high as 10¹⁴ cm⁻² can be induced at the Si surface, an order of magnitude larger that can be attained in Si inversion layers in MOS structures. The localized states are of total density of about 10¹² cm⁻² and of capture cross sections around 5 × 10⁻¹⁸ cm². The nature of these states is not known; they are probably fast surface states at the silicon surface. The charge leakage occurs under strong accumulation conditions, very likely by electron tunneling from the silicon electrode into the electrolyte. It takes place practically instantaneously, but the leaked charge remains stored near the interface for a considerable time. Some suggestions concerning this unexpected behavior are put forward.     

Characterization of the low temperature dopant activation behavior at NiSi/silicon interface formed by implant into silicide method

Process temperature and thermal budget control are very important for high-k dielectric device manufacturing. This work focuses on the characteristics of low temperature activated nickel silicide/silicon (M/S) interface formed by implant into silicide (IIS) method. By combining SIMS, C-V, I-V, and AFM measurements in this work, it provides a clear picture that the high dopant activation ratio can be achieved at low temperature (below 600 °C) by IIS method. From SIMS and C-V measurements, high dopant activation behavior is exhibited, and from I-V measurement, the ohmic contact behavior at the M/S junction is showed. AFM inspection displays that under 2nd RTA 700 °C 30 s no agglomeration occurs. These results suggest that IIS method has the potential to integrate with high-k dielectric due to its low process temperature. It gives an alternate for future device integration.     

Atomic and electronic structure formation at the metal-Cd1−xMnxTe interface

Atomic and electronic structure modification of a metal-Cd_1−xMn_xTe interface is achieved using selective etching of the Cd_1−xMn_xTe surface (x=0, 0.34) and Cd adsorption. It is revealed that Te, TeO₂, Mn₃O₄, and CdTeO₃ are formed at the Cd_1−xMn_xTe surface etched in Br₂ solution. Te and Cd_1−xMn_xTe produce TeCd_1−xMn_xTe heterojunctions, the salient features of which are nearly symmetric nonlinear I-V characteristics. At the Cd_1−xMn_xTe surface with adsorbed Cd, CdTe might form, resulting in a CdTe-Cd_1−xMn_xTe heterojunction. The metal-CdTe-Cd_1−xMn_xTe microstructure is characterized by a nonlinear dependence of current on voltage and rectifying behaviour. The results obtained give deep insight into electronic processes in metal-Cd_1−xMn_xTe microstructures.     

Si/Cu interface structure and adhesion

An ab initio investigation of the Si(111)/Cu(111) interfacial atomic structure and adhesion is reported. Misfit dislocations appear naturally, as do hcp interfacial silicide phases that vary with temperature. The silicides form in the interface even at relatively low temperatures. These results are consistent with available experimental data.     

Ionic liquids at the air/water interface

We present molecular dynamics experiments of Langmuir monolayers of iodide and chloride salts of 1-octyl-3-methylimidazolium adsorbed at water/air interfaces, covering a concentration range that spans from a dilute regime up to the experimental surface saturation for both systems. For the chloride case we observed a propensity to form monolayers with nearly equal surface concentration of both cations and anions; whereas for the iodide system, the more marked propensity to surface solvation of the anionic species leads to the appearance of quasi-double-layered structures. At the surface, the imidazolium rings remain in contact with the aqueous substrate, with a wide variety of orientations with respect to the surface normal direction. The global tilt of the hydrophobic tail of the cations was found to be θ_tl ~ 40°and 50°, for the chloride and iodide salts, respectively. Polarization fluctuations of the interface are analyzed in terms of those describing charge distributions of the adsorbed species and the electrical response of the solvent as well. The characteristics of the local densities for the ionic species at the interface provide arguments for the microscopic interpretation of the differences observed in scattering experiments on the dependence of the surface tension with the surfactant concentration.     

Intercalation of metals and silicon at the interface of epitaxial graphene and its substrates

Intercalations of metals and silicon between epitaxial graphene and its substrates are reviewed. For metal intercala- tion, seven different metals have been successfully intercalated at the interface of graphene/Ru（O001） and form different intercalated structures. Meanwhile, graphene maintains its original high quality after the intercalation and shows features of weakened interaction with the substrate. For silicon intercalation, two systems, graphene on Ru（O001） and on Ir（l I 1）, have been investigated. In both cases, graphene preserves its high quality and regains its original superlative properties after the silicon intercalation. More importantly, we demonstrate that thicker silicon layers can be intercalated at the interface, which allows the atomic control of the distance between graphene and the metal substrates. These results show the great potential of the intercalation method as a non-damaging approach to decouple epitaxial graphene from its substrates and even form a dielectric layer for future electronic applications.     

Three-phase-boundary dynamics at the Ni/ScYSZ interface

Chronoamperometry using a three-electrode cell configuration was undertaken with a nickel point-electrode acting as the working electrode on a polished ScYSZ electrolyte in a hydrogen atmosphere at 750–850 °C. High anodic overpotentials resulted in the occurrence of distinct sawtooth oscillation patterns in the measured current signal. The current oscillations indicated that a dynamic electrode process was taking place. Decreasing the water content in the measurement atmosphere as well as lowering the applied anodic overpotential had the effect of lowering the frequency and the amplitude of the current oscillations. A mechanism accounting for the observed phenomena and possible implications for solid oxide fuel cell operation are presented.     

Surface chemistry at the liquid/solid interface

In this Prospective, a critical overview is provided on the status and future of the analytical techniques available for the study of chemistry at liquid/solid interfaces. A number of spectroscopies already available are identified, including infrared absorption, surface-enhanced Raman (SERS) and sum frequency generation (SFG) to obtain vibrational information, and second harmonic generation (SHG) and X-ray absorption (XAS) to provide electronic details of surfaces and adsorbates. X-ray scattering and X-ray diffraction techniques are also used for structural characterization, and surface plasmon resonance (SPR) and quartz crystal microbalance (QCM) to follow adsorption uptakes and kinetics. Finally, optical and scanning microscopies add a spatial dimension to these studies. Overall, a number of surface-sensitive techniques do already exist to address chemical issues at liquid/solid interfaces, but those are still limited, and have perhaps not been exploited to their fullest yet. There is also a need for more cross collaboration among different research communities, and for new and clever developments to augment the toolbox of liquid/solid interface characterization.     

Physical and mechanical properties of silicon near the SiO2/Si interface

The influence of an oxide coating on the strength characteristics of single-crystal silicon surface layers is investigated by the microindentation method. It is shown experimentally that a strengthened layer with a thickness of 0.2–0.4 μm and a microhardness of 20–35 GPa, which is two or three times as much as the microhardness of bulk single-crystal silicon, is present near the SiO₂/Si interface. The thickness and microhardness of this layer depends on the growth conditions of the oxide. The formation of this layer is most probably caused by interstitial silicon atoms formed near the SiO₂/Si interface during silicon oxidation.