Yuval E. Yaish

Kinetics of nickel silicide growth in silicon nanowires: From linear to square root growth

The common practice for nickel silicide formation in silicon nanowires (SiNWs) relies on axial growth of silicide along the wire that is initiated from nickel reservoirs at the source and drain contacts. In the present work the silicide intrusions were studied for various parameters including wire diameter (25–50 nm), annealing time (15–120 s), annealing temperature (300–440∘C), and the quality of the initial Ni/Si interface. The silicide formation was investigated by high-resolution scanning electron microscopy, high-resolution transmission electron microscopy (TEM), and atomic force microscopy. The main part of the intrusion formed at 420∘C consists of monosilicide NiSi, as was confirmed by energy dispersive spectroscopy STEM, selected area diffraction TEM, and electrical resistance measurements of fully silicided SiNWs. The kinetics of nickel silicide axial growth in the SiNWs was analyzed in the framework of a diffusion model through constrictions. The model calculates the time dependence of the intru...

Accurate carrier-type determination of nonhomogenously doped diamond

Electrical properties of B-doped homoepitaxialy grown diamond are characterized with and without mesa structures by Hall effect measurements as function of temperature in the as-grown state and following oxygen reactive ion etching (RIE). The extracted carrier type, concentration, and mobility are found to depend on the measurement contact configuration. For measurements performed without mesa major differences, even in carrier type, are found following the RIE treatment, however no changes what so ever are observed when measuring with a mesa structure. Finite element simulation confirms that carrier concentration or/and mobility inhomogeneities in the regions surrounding the contacts in Hall effect measurements using the Van der Pauw configuration can result in wrong assignments of carrier type, concentration and mobility.

Water assisted gate induced temporal surface charge distribution probed by electrostatic force microscopy

In this paper, we present a quantitative method to measure charge density on dielectric layers using electrostatic force microscopy. As opposed to previous reports, our method, which is based on force curve measurements, does not require preliminary knowledge of the tip-sample capacitance and its derivatives. Using this approach, we have been able to quantify lateral and temporal SiO2 surface charge distribution and have unveiled a gate-induced charge redistribution mechanism which takes place in the vicinity of grounded electrodes. We argue that this mechanism constitutes a dominant factor in the hysteresis phenomenon, which is frequently observed in the transfer characteristics of nano-scale devices.

Three-point bending analysis of doubly clamped silicon nanowire beams; Young's modulus, initial stress, and crystal orientation

A non-linear model is introduced describing the force-deflection relation of doubly clamped beams, including initial stress. Several approximations for the exact model are developed and compared, revealing the importance of considering the initial stress during 3-point bending measurements analysis. A novel approximation is found to be better than others, and both the exact model and this approximation are in perfect agreement with finite element simulations. A brief experimental example of silicon nanowires is presented in which the Youngs modulus, the initial stress, and the crystallographic growth orientation are extracted by 3-point bending analysis.

Visualization of electronic density

The spatial volume occupied by an atom depends on its electronic density. Although this density can only be evaluated exactly for hydrogen-like atoms, there are many excellent algorithms and packages to calculate it numerically for other materials. Three-dimensional visualization of charge density is challenging, especially when several molecular/atomic levels are intertwined in space. In this paper, we explore several approaches to this, including the extension of an anaglyphic stereo visualization application based on the AViz package for hydrogen atoms and simple molecules to larger structures such as nanotubes. We will describe motivations and potential applications of these tools for answering interesting physical questions about nanotube properties

Evolution of nickel silicide intrusions in silicon nanowires during thermal cycling

Thermally activated axial intrusion of nickel silicides into a silicon nanowire (NW) from pre-patterned Ni reservoirs is used in formation of nickel silicide/silicon contacts in SiNW field effect transistors. This intrusion consists usually of different nickel silicides which grow simultaneously during thermal annealing. Repeated annealing is often accompanied by local thickening and tapering of the NW, up to full disintegration of the silicide segment adjacent to Si. In the present work this process was investigated for SiNWs of various diameters in between 30 and 60 nm with pre-patterned Ni electrodes after a series of rapid thermal cycles including heating, holding at different temperatures of 400-440 °C for 5-15 s and cooling to room temperature. Kinetics of the nickel silicides axial growth was analyzed in the framework of diffusion model. This model is taking into account simultaneous formation of different nickel silicide phases and balance between transition of Ni atoms from the Ni reservoir to th...

From Contact to Diffusion Controlled Growth of Nickel Silicides in Silicon Nanowires

Semiconducting nanowires (NW) are implemented as the active channel of field effect transistor (FET) with linear and Schottky barrier source and drain contacts. Thermally activated axial intrusion of nickel silicides into the silicon NW from pre-patterned Ni reservoirs is used in the formation of nickel silicide/silicon contacts in SiNW FETs. In the present work, the kinetics of nickel silicide axial growth in SiNWs was analyzed in the framework of the model taking into account the balance between transition of Ni atoms from the Ni reservoir to the NW surface, diffusion transport of these Ni atoms from the contact area to the interfaces between different silicides and nickel silicide/Si interface, and corresponding reactions of Ni atoms with Si and the nickel silicides formed. Simultaneous growth of mono-and nickel rich silicide was described for different kinetic and geometrical parameters of the system. Critical parameters for transition from the linear to the parabolic dependences were introduced. The model was applied to the experimental results on nickel silicide growth in SiNWs of 25÷50 nm in diameters in a temperature range of 300÷440C°. The silicide intrusions were obtained by annealing of SiNWs with pre-patterned Ni electrodes in a rapid thermal annealing machine under nitrogen atmosphere for different temperatures and times up to 120 s. In most cases the intrusions consisted of two nickel silicides, Ni-rich and mono-silicide NiSi, as was confirmed by TEM and measuring the electrical resistance of the SiNW after full silicidation. The total intrusion length, L, and particular silicide lengths, showed various time dependences, from a linear (with low growth rates (1÷4nm/s)) to a square root, diffusion-type dependence (with higher rates (10÷15 nm/s)). This behavior is well described by the model developed.

Gate-Induced Modification of Water Adsorption on Dielectrics Probed by EFM and Carbon Nanotube FETs

Humidity plays an important role in molecular electronics. It facilitates charge movement on top of dielectric layers and modifies the device transfer characteristics. Using two different methods to probe temporal charge redistribution on the surface of dielectrics, we were able to extract the surface humidity for the first time. The first method is based on the relaxation time constants of the current through carbon nanotube field-effect transistors (CNTFETs), and the second is based on electric force microscopy (EFM) measurements. Moreover, we found that applying external gate biases modifies the surface humidity. A theoretical model based on dielectrophoretic attraction between the water molecules and the substrate is introduced to explain this observation, and the results support our hypothesis. Furthermore, it is found that upon the adsorption of two to three layers of water the surface conductivity saturates.

The effect of boundary conditions on the vibrations of armchair, zigzag, and chiral single-walled carbon nanotubes

Single-walled carbon nanotubes (SWCNTs) have three distinct structures: armchair, zigzag, and chiral. It is known that they have different electronic properties, but the situation regarding their vibrational behavior is less clear. Doubly clamped nanotubes of all three types exhibit the same vibrational modes, and their vibrations in the directions perpendicular to the nanotube axis are degenerate. In nanotube applications, such as sensors based on nano-electro-mechanical systems, their ends are not fully clamped, thus their vibrational behavior could differ. Careful molecular dynamics simulations of SWCNTs with boundary conditions, which imitate the partly clamped experimental conditions, show that armchair, zigzag, and chiral nanotubes indeed vibrate differently. The symmetry between the two perpendicular directions is broken, and SWCNT type does influence the vibrational modes.

Formation and Evolution of Nickel Silicide in Silicon Nanowires

Thermally activated axial intrusion of nickel silicides in silicon nanowires (SiNWs) is utilized to form nickel silicide/silicon contacts in SiNW field effect transistors. The growth of different nickel silicides is often accompanied by local thickening and tapering of the NW, up to its full disintegration. In this paper, this process was investigated in SiNWs of 30-60 nm in diameters with prepatterned Ni electrodes after annealing cycles at different temperatures of 300 °C-440 °C and times up to 120 s. From the temperature dependence of the intrusion lengths, activation energy of 1.45 eV for the surface diffusion of nickel was extracted. In several cases, periodic thickening of the nickel-rich part is accompanied by tapering of the monosilicide part up to its full dissolution. The kinetics of the nickel silicides growth was described by phenomenological model. For a certain set of parameters, tapering and dissolution of the monosilicide part of the intrusion were predicted, similar to the experimental results.