Silicon Tip Research Articles

Comparison of Indentation and Scribing Behaviors of Crystalline and Initially Deformed Silicon Tips by Molecular Dynamics Simulation

Silicon probe tips are used widely in micro and nano-systems such as AFM, MEMS, and probe recording. The mechanical integrity of the tip is important to assure reliable performance of the tip during contact as well as sliding. Crystalline silicon normally forms a tetrahedral structure, however, under high pressure it is known that the structure transforms to a different phase. This can cause a change in the contact phenomena. In this work, the silicon probe tip deformation process during nano-indentation was investigated by using molecular dynamics simulation. In addition, scribing simulation was carried out to observe the frictional characteristics of crystalline and amorphous silicon structures. The simulation results showed that the structure of silicon near the surface was permanently deformed at a contact stress of approximately 17 GN/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and the deformation process could be monitored by observing the bond-angle distribution graph. It was also found that the atomic structure of the silicon tip in the contact region affected the frictional behavior of the tip with respect to fluctuation periodicity and magnitude.

W1552 Impairment By Allyl Isothiocyanate of Gastric Epithelial Wound Repair Through Inhibition of Ion Transporters

co- transporter (NBC). We examined the expression of TRPA1 and ion transporters in monolayers of the rat gastric epithelial cell line RGM1 and investigated the involvement of these factors in the inhibitory action of isothiocyanate on epithelial wound healing. After obtaining a confluent monolayer, a round artificial wound of constant size was induced in the center of the cell monolayer using a pencil-type mixer with a rotating silicon tip. Immediately after the wound induction, cells at the edge of the wound started to form lamellipodia, migrating towards the center of wound, and the cell-free area decreased with time. Addition of allyl isothiocyanate to standard buffer suppressed the recovery of the wound in a concentration- dependent manner without affecting the viability of the RGM1 cells. Icilin, another TRPA1 agonist, dose-dependently inhibited wound repair. Likewise, 4,4'-diisothio- cyanatostilbene-2,2'-disulfonic acid (DIDS), a stilbene compound containing an isothiocyanate group, also inhibited the recovery of epithelial wounds. In addition, the repair of epithelial wounds was suppressed when the cells were incubated in Na + , Cl- or HCO3 - free buffer. The RGM1 cells expressed the mRNAs of AE2a and NBC1 but not TRPA1. These results suggested that isothiocyanate impairs the repair of epithelial wounds in RGM1 cells, probably through the inhibition of ion transporters such as AE2a and NBC1 and not the activation of the TRPA1 channel. It is assumed that the process of epithelial repair is associated with the regulation of cell volume and intracellular pH (pHi) by these ion transporters.

Deep‐UV tip‐enhanced Raman scattering

AbstractWe report for the first time the tip‐enhancement of resonance Raman scattering using deep ultraviolet (DUV) excitation wavelength. The tip‐enhancement was successfully demonstrated with an aluminum‐coated silicon tip that acts as a plasmonic material in DUV wavelengths. Both the crystal violet and adenine molecules, which were used as test samples, show electronic resonance at the 266‐nm excitation used in the experiments. With results demonstrated here, molecular analysis and imaging with nanoscale spatial resolution in DUV resonance Raman spectroscopy can be realized using the tip‐enhancement effect. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Controlling the plasmon resonance wavelength in metal-coated probe using refractive index modification

We present a novel technique to tune the plasmon resonance of metal-coated silicon tips in the whole visible region without altering the tips original sharpness. The technique involves modification of the refractive index of silicon probe by thermal oxidization. Lowering the refractive index of silicon tip coated with metal shift the PRW of the metallic layer to shorter wavelength. Numerical simulation using FDTD agrees well with the empirical results. This novel technique is very useful in tip-enhanced Raman spectroscopy studies of various materials because plasmon resonance can tuned to a specific Raman excitation wavelength.

Fabrication of novel silicon dual atomic force microscope tip with narrow gap

We propose a novel fabrication process for twin probes of an atomic force microscope (AFM) that consist of a silicon dual tip with a narrow gap. The dual tip with a tetrahedral shape consists of an inclined silicon (111) plane and two vertical planes and was successfully fabricated by using the proposed fabrication process of combining deep reactive ion etching (D-RIE) for silicon trench formation along the silicon (001) direction, selective oxidation of the sidewalls of the trench, and crystalline anisotropic etching. The silicon tips could be sharpened by a low-temperature oxidation process, resulting in a tip radius of about 10 nm. In addition, the dual silicon tip formation, dual AFM probe with cantilever, and thermal actuator were also successfully fabricated from a silicon-on-insulator (SOI) water. The gap of the dual tip was about 2.9 µm, with trench etching 1 µm wide and sidewall oxidation 1 µm thick.

First principles studies of an Si tip on anSi(100)2 × 1 reconstructed surface

We present a systematic study of the interaction between a silicon tip and a reconstructedSi(100)2 × 1 surface by means of total energy calculations using density functional theory. We performgeometry optimization to obtain the reconstructed Si surface using the local densityapproximation and the generalized gradient approximation methods and compare ourresults with those obtained experimentally. We then study the effects of the tip of ascanning probe of an atomic force microscope (AFM) on the behaviour of atoms on thereconstructed surface when the tip translates at distances close to it. Our results show thatat certain positions of the tip relative to the surface and depending on the direction of thescan, the Si dimer on the surface flips, resulting in a local reconstruction of the surface intop(2 × 2) or c(4 × 2) configurations. These configurations exhibit energies lower by0.05 eV/dimer than theSi(100)2 × 1 structure.

Length Control and Sharpening of Carbon Nanotube Scanning Probe Microscope Tips Using Carbon Nanotube "Nanoknife"

Through nanomanipulation inside scanning electron microscope, a carbon nanotube scanning probe microscope tip was made by connecting a carbon nanotube with a silicon atomic force microscope tip. The carbon nanotube scanning probe microscope tip was then tailored to the desired length and end structure by a "nanoknife" which is a carbon nanotube adhered to a metal tip. Through mapping the same carbon nanotube on SiO2 substrate, it was found that the lateral resolution of the carbon nanotube tips can be improved significantly through sharpening the tip ends, and the sharpened carbon nanotube tips had better performance than commercial silicon tips.

Real-time transmission electron microscope observation of gold nanoclusters diffusing intosilicon at room temperature

Gold diffusion into silicon at room temperature was observed in real time with atomicresolution. Gold nanoclusters were formed on a silicon surface by an electricaldischarge between a silicon tip and a gold coated tip inside an ultrahigh-vacuumtransmission electron microscope (TEM) specimen chamber. At the moment of thegold nanocluster deposition, the gold nanoclusters had a crystalline structure.The crystalline structure gradually disappeared due to the interdiffusion betweensilicon and gold as observed after the deposition of gold nanoclusters. The shape ofthe nanocluster gradually changed due to the gold diffusion into the damagedsilicon. The diffusion front between silicon and gold moved toward the siliconside. From the observations of the diffusion front, the gold diffusivity at roomtemperature was extracted. The extracted activation energy, 0.21 eV, matchedthe activation energy in bulk diffusion between damaged silicon and gold. Thisinformation is useful for optimizing the hybridization between solid-state andbiological nanodevices in which gold is used as an adhesive layer between the twodevices.

Forced Air Plasma Treatment (FAPT) of Hybrid Wood Plastic Composite (WPC)–Fiber Reinforced Plastic (FRP) Surfaces

Forced atmospheric (air) plasma treatment (FAPT) was applied to wood plastic composite (WPC) and continuous glass fiber reinforced plastic (FRP) surfaces to improve their adhesive bonding properties. The FRP was composed of oriented continuous E-glass fibers in a polypropylene matrix, while the WPC was fabricated using wood flour, polypropylene and additives. The FAPT was applied using two levels of discharge length projected from the discharge head (2.5″ and 1″) to ionize the air, oxidize the surfaces and improve wettability. The treatment was performed by passing the electrode over either surface, five or ten times. Surface characterization consisted of thermodynamic (surface energy determination), chemical (X-ray photoelectron spectroscopy), mechanical (shear strength) and microscopic (atomic force microscopy (AFM)) analysis. The results indicate that the acid–base component of the surface energy for both WPC and FRP after FAPT correlates with an increase in wettability. X-ray photoelectron spectroscopy was performed on wood regions and non-wood regions of the WPC surfaces; the oxygen concentration increased to a larger extent in the non-wood regions. Bonding shear strength measurements indicated increases of 50% after FAPT on WPC surfaces (2.5″ discharge length, 1 pass) and up to 200% for the hybrid WPC–FRP. Atomic force microscopy measurements using a silicon tip probe showed increases in adhesive force interactions up to 56% on WPC surfaces post-FAPT.

Field emission properties of Si tip arrays coated with N-doped SrTiO3 thin films at different substrate temperature

The effect of substrate temperature (TS) on the behavior of field emission, microstructure, optical band gap, and the surface energy of N-doped SrTiO3 thin films coated on silicon tip arrays has been examined in detail. Results indicate that the TS dominates the chemical states of nitrogen added to the sputtered SrTiO3 films and hence the observations. At the critical temperature of 600 °C, nitrogen atoms incorporate into the oxide film with sp-hybridization features. The generation of the nonbonding lone pair states narrows the optical band gap and the lone pair induced antibonding dipoles lower the threshold field for electron emission substantially. At lowered TS, molecular adsorption of nitrogen dominates. Contact angle measurements further evidence for the presence of antibonding dipole states at the surfaces which is responsible for the adsorbate-induced surface stress.

The Effect of Temperature on Field Emission Current

In this paper, we present our recent works on the measurement of field emission performance of silicon tip arrays and investigate the thermal instability of emission current by measuring the emission current as the function of time under three different cooling conditions—natural free radiation，contact conduction and air forced convection respectively. Draw the conclusions that field emission performance of the silicon-based emitters is quite sensitive to the temperature change and resistive heating produced as emission current flowing through the apex of silicon emitters induces the instability of emission current.

Single asperity tribochemical wear of silicon by atomic force microscopy

Measurements of single asperity wear on oxidized silicon surface in aqueous potassium hydroxide (KOH) using atomic force microscopy (AFM), where the single crystal silicon tip was used both to tribologically load and image the surface, is presented. AFM was also operating in the lateral (frictional) force mode to investigate the pH dependence of kinetic friction between the tip and the SiO2 surface. It was shown that the Si tip wear amount strongly depended on the solution pH value and was at a maximum at around pH 10. It was also found that the Si removal volume in mol was approximately equal to that of SiO2 irrespective of the solution pH value. This equality implies that the formation of the Si–O–Si bridge between one Si atom of the tip and one SiO2 molecule of the specimen at the wear interface. The surface of the Si tip is then oxidized. Finally, the bond rupture by the tip movement will occur, the dimeric silica (OH)3Si–O–Si(OH)3, including the Si–O–Si bridge, is dissolved in the KOH solution. The frictional signal is also sensitive to the pH values of the solution and peaked at around pH 10. These results indicate that the removal behavior of the Si tip and SiO2 surface would be affected by the frictional force between the Si and the SiO2, because of an increased liquid temperature and a compressive stress in Si and SiO2 networks. Strong influence is observed by the pH of the ambient solution confirming the important role of the OH− in the wear mechanism. Pressure dependence of the microwear behavior under aqueous electrolyte solutions has also been investigated. A microscopic removal mechanism, which is determined by interplay of the diffusion of water in Si and SiO2, is presented.

Failure mechanisms of silicon-based atom-probe tips

Atom-probe (AP) analysis of silicon based samples frequently fail due to rupture of the tip. We have investigated the stability and failure mechanisms of silicon tips when prepared for AP analysis via Focused Ion Beam (FIB) milling. We observed four mechanisms that commonly lead to failure of the tips. These mechanisms are a deformation of the tips apex due to an interaction between the oxidized amorphous layer and induced mechanical vibrations, a rip off of an isolating oxide-layer, the rip off of a cap layer due to insufficient adhesion and a failure of the tip in the course of the analysis due to the rising voltage applied to the tip. In this paper we will discuss all four mechanisms show evidence of the causes of the breakdown and discuss options that allow avoiding tip failure.

NANOMETER-SCALE PATTERNING ON PMMA RESIST BY FORCE MICROSCOPY LITHOGRAPHY

Nanoscale science and technology has today mainly focused on the fabrication of nano devices. In this paper, we study the use of lithography process to build the desired nanostructures directly. Nanolithography on polymethylmethacrylate (PMMA) surface is carried out by using Atomic Force Microscope (AFM) equipped with silicon tip, in contact mode. The analysis of the results shows that the depth of scratches increases with the increase of applied normal force. The scanning velocity is also shown to influence the AFM patterning process. As the scanning velocity increases, the scratch depth decreases. The influence of time and number of scratching cycles is also investigated.

Development of a scanning surface probe for nanoscale tip-enhanced desorption/ablation

We report on the development of a versatile scanning apparatus for nanoscale surface sampling that utilizes the interaction of laser radiation at a sharp probe tip to effect desorption/ablation on opaque substrates. The process, which currently yields surface craters as small as approximately 50 nm diameterx5 nm deep, has been demonstrated with both metal-coated and bare silicon tips. Desorption/ablation under the tip occurs at illumination intensities below the corresponding optical far-field threshold, suggesting that the latter process should not degrade the spatial resolution attainable for proposed chemical imaging methods based on the scanning surface probe.

Effects of Self-Assembled Monolayer and PFPE Lubricant on Wear Characteristics of Flat Silicon Tips

The effects of self-assembled monolayer (SAM) and perfluoropolyether (PFPE) lubricant on the wear characteristics of flat silicon tips were investigated. The wear test consisted of sliding the silicon tips fabricated on a flat silicon specimen against SAM and PFPE (Z-tetraol) coated silicon (100) wafer. The tips were slid at a low speed for about 15 km under an applied load of 39.2 μN. The wear volume of the tip was obtained by measuring the tip profile using an Atomic Force Microscope (AFM). It was found that the coatings were effective in reducing the wear of the tips by an order of magnitude from 10−6 to 10−7.

Field emission properties of silicon field emitter arrays with volcano-shaped gate structure

Field emission properties of silicon field emitter arrays (Si-FEAs) with sputtered gate structures were described and analyzed about two different tip structures surrounded by volcano-shaped gates. The resulted field emission characteristics showed that some of the emitted electrons are diverted to the gate structure because of the asymmetrical geometry of fabricated Si-FEAs with volcano-shaped gate structures. However, although the gate structures of fabricated FEAs had fragile and non-uniform edged shapes as a result of the shadow effect during sputtering and lift-off process in ultrasonic bath, it was possible to obtain stable field emission properties as a result of electrical aging effects on the edge of the non-uniform gate electrode as well as the surface of silicon tip after repeated measurements. From the Fowler–Nordheim (F–N) plots and F–N equations, it was confirmed that the field enhancement factor was abruptly changed through the electrical aging and was more influenced in case of the volcano-shaped lateral tip structure.

Apertureless Near-Field Distance-Dependent Lifetime Imaging and Spectroscopy of Semiconductor Nanocrystals

Apertureless near-field scanning optical microscopy, along with time-resolving capabilities, is used to produce optical imaging and spectroscopy measurements of single-semiconductor nanocrystals, in correlation with the AFM topography scan. The strongly distance-dependent energy transfer between the excited particle and silicon or metallic-coated AFM tips provides a contrast mechanism for subdiffraction-limited optical imaging. Fluorescence lifetime optical images show excellent contrast, sharpness, sensitivity, and resolution equivalent to that of the AFM topography images (sub 20 nm) and significantly improved over fluorescence intensity images. The sharper resolution of lifetime images is consistent with model predictions of energy transfer between an emitting dipole and a dielectric surface. Lifetime images also enable resolving multiple emitters located in the excitation spot. The comprehensive time and distance dependent data is used to study the imaging mechanism and the properties of silicon tips and platinum-coated tips as energy acceptors and quenchers. The findings provide a basis for use of lifetime imaging, in conjunction with apertureless near field microscopy, for simultaneous high-resolution topography and optical imaging.

Atomistic Wear in a Single Asperity Sliding Contact

Abrasive wear of sharp silicon tips sliding distances of up to 750 m on a polymeric surface is studied using atomic force microscopy. The data cannot be explained by conventional macroscopic wear models. We present a new model in which the barrier for breaking an atomic bond is lowered by the frictional stress acting on the contact. Quantitative agreement is obtained between the model and wear data for all load forces and sliding distances studied.

Assessment of hydrous affinity of selected material

The deposition of films and coatings is well-known to be affected by the presence of physi-sorbed water, which can adversely influence the nucleation and growth processes. The importance of understanding the affinity of the substrate to water cannot be over-emphasized, especially in the case of semiconductors. Our technique centers on the use of atomic force microscopy (AFM) to measure the adhesion forces, which determine the degree of hydrophobicity or hydrophilicity. Previous results reported in recent literature give contradictory information. Our study shows that the choice of the AFM tip is critical in these measurements. This research conducted a systematic study of the influence of humidity on the adhesion forces between two different AFM tips (silicon and silicon nitride) and a cross-section of materials representing silicates, phylo-silicates, calcites, and carbon. Four sets of about ten each force–distance curves measured with the AFM (Park Scientific M5) have been gathered at a series of different humidity levels and different locations on the samples. From these curves the adhesion forces for hydrophobic and hydrophilic materials vs. humidity were obtained. Many of the previously reported measurements of adhesion force were obtained with silicon tips. This paper shows that silicon tips are not sensitive enough to measure the capillary and adhesion forces. On the other hand silicon nitride tips provide reliable results supported by theoretical calculation. The results also show that the adhesion force on graphite, which has hydrophobic character, is independent of humidity variation. Fused quartz, calcite, and mica were found to be hydrophilic and their adhesion forces and capillary forces showed drastic change with increasing humidity. Calcite shows a somewhat different behavior in that it is less hydrophilic than mica and fused quartz. In general the data are in good agreement with the theoretical calculations.