Silicon Tip Research Articles

Field emission from nanometer-scale tips of crystalline PbZrxTi1−xO3

The authors report field emission from nanometer-sharp tips of polarized PbZrxTi1−xO3 (PZT), silicon, and platinum. The PZT nanoemitters are fabricated in a batch fabrication process from single-crystal silicon tips that are coated with a 30 nm thick film of crystalline PZT. The nanoemitters start to emit electrons at fields as low as 2 V/μm and reach threshold emission, or turn-on, at fields as low as 3.9 V/μm. The turn-on field is 3.9 V/μm for PbZr0.2Ti0.8O3, 6.8 V/μm for PbZr0.52Ti0.48O3, and 10.75 V/μm for PbZr0.8Ti0.2O3. The silicon nanoemitters have an electron emission turn-on field of 7.2 V/μm, and the platinum nanoemitters have an electron emission turn-on field of 5.75 V/μm. Using a Fowler-Nordheim analysis, the calculated effective work function of the PbZr0.2Ti0.8O3 film is 1.00 eV, and the field amplification factor is ∼1526.

High sensitivity field emission based sensors using carbon nanotubes on silicon tip for high frequency vibration sensing

Field emission based cantilever sensor using carbon nanotubes on silicon tip was fabricated and electrical response of the device to the mechanical vibration was investigated. Plasma enhanced chemical vapor deposition was used to grow carbon nanotubes (CNTs). Field emission from nanotubes on silicon tip was realized for sensing the vibration. Exponential dependence of the field emission current to the distance between the anode and the emitter leads to a high sensitive device. The variation of the emission current during mechanical vibration of the cantilever was measured. We have obtained that frequency limit for field emission based sensors depends on the capacitance and equivalent resistance of the device. In this work we have introduced a CNT based sensor for sensing the mechanical vibration in nanometer ranges with capability of high frequency sensing. The fabricated device, due to a low distance between its electron emitters and the anode, works at low applied voltages with high emission current.

CHARACTERIZATION OF NANOMATERIAL-BASED CONTACT LENSES BY ATOMIC FORCE MICROSCOPY

In this paper the comparative studies were conducted of the surface areas of nanophotonic contact lens and contact lens made from base material, measured by Nanoprobe Atomic Force Microscope. Nanoprobe atomic force microscopy (AFM) provides information on the size structure on nano scale level, the form of recorded structures (cavities), their distribution of the surface, and the total roughness of the scanned area. The atomic force microscope used in this study is a SPM-5200 of JEOL, Japan. AFM consists of a cantilever with a sharp tip (probe) at its end that is used to scan the specimen surface. Images of the specimen surface are created by measuring the deflection of the cantilever. The cantilever used in this study is produced by MikroMasch (Estonia) by trade name NCS18/Co-Cr. This AFM probe is silicon etched probe tip that has conical shape. It is coated with Co and Cr layers. Images of surface topography were obtained for each type of contact lenses. The base material of contact lens was made from PMMA and the nanophotonic contact lens was made of fullerene doped PMMA. Fullerenes were used because of their good transitive characteristics in ultraviolet, visible and near infrared light spectrums. Measurements were done at room temperature. Results of topography for both materials are presented and compared.

CHARACTERIZATION OF NANOMATERIAL-BASED CONTACT LENSES BY ATOMIC FORCE MICROSCOPY

In this paper the comparative studies were conducted of the surface areas of nanophotonic contact lens and contact lens made from base material, measured by Nanoprobe Atomic Force Microscope. Nanoprobe atomic force microscopy (AFM) provides information on the size structure on nano scale level, the form of recorded structures (cavities), their distribution of the surface, and the total roughness of the scanned area. The atomic force microscope used in this study is a SPM-5200 of JEOL, Japan. AFM consists of a cantilever with a sharp tip (probe) at its end that is used to scan the specimen surface. Images of the specimen surface are created by measuring the deflection of the cantilever. The cantilever used in this study is produced by MikroMasch (Estonia) by trade name NCS18/Co-Cr. This AFM probe is silicon etched probe tip that has conical shape. It is coated with Co and Cr layers. Images of surface topography were obtained for each type of contact lenses. The base material of contact lens was made from PMMA and the nanophotonic contact lens was made of fullerene doped PMMA. Fullerenes were used because of their good transitive characteristics in ultraviolet, visible and near infrared light spectrums. Measurements were done at room temperature. Results of topography for both materials are presented and compared.

Light absorption in conical silicon particles

The problem of the absorption of light by a nanoscale dielectric cone is discussed. A simplified solution based on the analytical Mie theory of scattering and absorption by cylindrical objects is proposed and supported by the experimental observation of sharply localized holes in conical silicon tips after high-fluence irradiation. This study reveals that light couples with tapered objects dominantly at specific locations, where the local radius corresponds to one of the resonant radii of a cylindrical object, as predicted by Mie theory.

Semiconducted symphony: ultrafast field emitter array

Semiconducted symphony: ultrafast field emitter array

Ultrafast phenomena on the nanoscale

Ultrafast phenomena on the nanoscale

Tuning the Spring Constant of Cantilever-Free Tip Arrays

A method to measure and tune the spring constant of tips in a cantilever-free array by adjusting the mechanical properties of the elastomeric layer on which it is based is reported. Using this technique, large-area silicon tip arrays are fabricated with spring constants tuned ranging from 7 to 150 N/m. To illustrate the benefit of utilizing a lower spring constant array, the ability to pattern on a delicate 50 nm silicon nitride substrate is explored.

Friction and wear performance of the 0.5Ba(Ti0.8Zr0.2)O3-0.5(Ba0.7Ca0.3)TiO3 piezoelectric film

As a lead-free piezoelectric material with potential application, 0.5Ba(Ti0.8Zr0.2)O3-0.5(Ba0.7Ca0.3)TiO3 (BZT-0.5BCT) ceramics, which has a morphotropic phase boundary composition, deserves much attention due to its excellent ferroelectric and piezoelectric properties. BZT-0.5BCT lead-free piezoelectric film has been synthesized on a Si (100) substrate by Sol-Gel process. The topography of the film measured using an atomic force microscope and a scanning electron microscope shows that the surface of the prepared film is smooth, and the grain is in the shape of hemisphere with a diameter of 80-100 nm. The film is 1.7 μm in thickness, with pores inside. Friction experiments show that the friction between the tip and the piezoelectric film is much larger than that between the tip and the SiO2 substrate, because of the existence of electrostatic force between the film and the silicon tip. However, the friction coefficients obtained are approximately equal. Nano-scratch experiments show that the BZT-0.5BCT film has a high normal carrying capacity, but a poor tangential wear resistance. The average elastic modulus of the film is 23.64 GPa ± 5 GPa, and its hardness is 2.7-4 GPa, both being slightly lower than those of the bulk value in PZT ceramics.

Rugosidade e Microscopia de Força Atômica de Resinas Compostas Submetidas a Diferentes Métodos de Polimento

Este trabalho avaliou a rugosidade e a topografia de superfície de resinas compostas submetidas a diferentes métodos de polimento. Foram utilizadas 5 resinas (Filtek Z350, Master Fill, Vênus, Charisma e Durafill VS) e confeccionou-se 90 corpos de prova distribuídos em 6 grupos (n:15): SP: sem polimento; TB: ponta de borracha abrasiva; DL: disco de lixa em três granulações; FP: disco de feltro com pasta diamantada; ECS: escova de carbeto de silício; PS: ponta de silicone abrasiva. Após os polimentos, foram realizadas as análises da rugosidade com auxílio de um rugosímetro e da topografia de superfície com a microscopia de força atômica. Os valores foram tabulados e analisados estatisticamente pelos testes de Kruskal-Wallis, DUNN e ANOVA (α = 0,05). As médias variaram entre 0,01 μm (Filtek Z 350 - TB) e 0,27 μm (Charisma - ECS). Concluiu-se que para todas as resinas testadas o melhor método de polimento foi o feltro com pasta diamantada (FP).

Probing the thermal response of a silicon field emitter by ultra‐fast Laser Assisted Atom Probe Tomography

The interaction between an ultrashort laser pulse and a sub‐wavelength silicon tip under a high static electric field is investigated numerically and experimentally. Using an original autocorrelation setup of the laser‐assisted atom probe tomography, the temporal evolution of the lattice temperature at the tip apex is experimentally monitored. An ultrafast cooling process, related to a confinement of the heating at the surface, is reported. This confinement is well predicted by a new model taking into account the free charges generation by photon absorption, their drift‐diffusion motion under the electric field and their energy relaxation to the lattice.

Fabrication of bulk and epitaxial germanium field emitter arrays by dry etching techniques

We present the fabrication and characterization of novel high density field emitter arrays (FEAs) on CVD-grown epitaxial germanium on (001) silicon. In particular we propose a heterostructure made up of silicon as substrate and of germanium as active layer, exploiting the infrared transparency of Si and the infrared sensitivity of Ge to realize a semi-transparent photo-assisted electron beam source. We used a completely dry etching process in fluorinated gases (SF6) due to its significant under-etching for both silicon and germanium. High aspect ratio silicon and germanium FEAs, with minimum tip radii of 25nm and 40nm, respectively, and lower aspect ratio Ge/Si FEAs with minimum tip radii of 50nm were fabricated. The realized FEAs show good emission behavior with field emission characteristics straight related to tip geometry: low electric field threshold for silicon and germanium tips (<18V/@mm) and enhancement factor of more than 250 and 130, respectively; conversely for the epitaxial germanium we obtained 32V/@mm for electric field threshold and 70 for enhancement factor. Current emission time stability for silicon, for germanium and for Ge/Si field emitter arrays were demonstrated.

Correlation Between Mechanical Properties and Nanofriction of [Ti–Cr/Ti–Cr–N] n and [Ti–Al/Ti–Al–N] n Multilayers

In this work, thin films deposited by pulsed DC magnetron sputtering of [Ti–Al/Ti–Al–N] n and [Ti–Cr/Ti–Cr–N] n multilayers of nanometric periods were analyzed by AFM in contact mode to measure values of lateral and normal forces. From these measurements, the coefficient of friction (COF) of these materials in contact with the AFM tip was calculated. Measurements were made with three types of silicon tips, diamond-coated, Pt–Cr-coated, and bare silicon. Significant differences between the tip materials in contact with the samples, which affected the COF, were observed. The effect of the environmental layer of water covering the surface sample and the tip appears as the most important factor affecting the tribology behavior of the tip-sample contact. For diamond-coated and bare silicon tips there is an additional adherence force increasing the normal load. But for tips platinum–chromium-coated there is a repulsive force due to this water layer, which behaves as a lubricant layer before a threshold load.

Activation of metabotropic glutamate receptors improves the accuracy of coincidence detection by presynaptic mechanisms in the nucleus laminaris of the chick

Interaural time difference (ITD) is a major cue for localizing a sound source and is processed in the nucleus laminaris (NL) in birds. Coincidence detection (CD) is a crucial step for processing ITD and critically depends on the size and time course of excitatory postsynaptic potentials (EPSPs). Here, we investigated a role of metabotropic glutamate receptors (mGluRs) in the regulation of EPSP amplitude and CD in the NL of chicks. A non-specific agonist of mGluRs ((±)-1-aminocyclopentane-trans-1,3-dicarboxylic acid; t-ACPD) reduced the amplitude and extent of depression of excitatory postsynaptic currents (EPSCs) during a stimulus train, while the paired pulse ratio and coefficient of variation of EPSC amplitude were increased. In contrast, the amplitudes of spontaneous EPSCs were not affected, but the frequency was reduced. Thus, the effects of t-ACPD were presynaptic and reduced the release of neurotransmitter from terminals in the NL. Expression of group II mGluRs was graded along the tonotopic axis and was stronger towards the low frequency region in the NL. Both group II (DCG-IV) and group III (l-AP4) specific agonists reduced EPSC amplitude by presynaptic mechanisms, and the reduction was larger in the low frequency region; however, we could not find any effects of group I-specific agonists on EPSCs. The reduced EPSP amplitude in DCG-IV improved CD. A specific antagonist of group II mGluRs (LY341495) increased the amplitude of both EPSCs and EPSPs and enhanced the depression during a stimulus train, indicating constitutive activation of mGluRs in the NL. These observations indicate that mGluRs may work as autoreceptors and regulate EPSP size to improve CD in the NL.

Ultrananocrystalline diamond tip integrated onto a heated atomic force microscope cantilever

We report a wear-resistant ultrananocrystalline (UNCD) diamond tip integrated onto a heated atomic force microscope (AFM) cantilever and UNCD tips integrated into arrays of heated AFM cantilevers. The UNCD tips are batch-fabricated and have apex radii of approximately 10 nm and heights up to 7 μm. The solid-state heater can reach temperatures above 600 °C and is also a resistive temperature sensor. The tips were shown to be wear resistant throughout 1.2 m of scanning on a single-crystal silicon grating at a force of 200 nN and a speed of 10 μm s−1. Under the same conditions, a silicon tip was completely blunted. We demonstrate the use of these heated cantilevers for thermal imaging in both contact mode and intermittent contact mode, with a vertical imaging resolution of 1.9 nm. The potential application to nanolithography was also demonstrated, as the tip wrote hundreds of polyethylene nanostructures.

Stable field emission of single B-doped Si tips and linear current scaling of uniform tip arrays for integrated vacuum microelectronic devices

Advanced Si-based semiconductor technology is most suitable to fabricate uniform nanostructures as integrated field emitter arrays for novel vacuum electronic devices. In order to improve the field emission homogeneity and stability of p-type silicon tip arrays for pulsed sensor applications, the authors have systematically studied the influence of the fabrication parameters on the tip shape and on the specific operating conditions. Based on detailed design calculations of the field enhancement, they have fabricated two series of hexagonal arrays of B-doped Si-tips in a triangular arrangement. The first (second) type contains three (four) patches with different number of tips (1, 91, 547 and 1, 19, 1027, 4447 for the first and second type, respectively) of about 1 (2.5) μm height, ∼20 (20) nm apex radius, and 20 (10) μm pitch. The field emission properties of both individual tips and complete arrays were investigated with a field emission scanning microscope at a pressure of 10−9 mbar. The current plateau of these tips typically occurs at about 10 (3) nA and around 65 (25) V/μm field level. In this carrier saturation range, single tips provide the highest current stability (&amp;lt;5%) and optical current switching ratio (∼2.5). Fairly homogeneous emission of the tip arrays leads to an undershooting of the expected linear scaling of the mean plateau current as well as to a much improved current stability (&amp;lt;1%).

Nano-dot and nano-pit fabrication on a GaAs substrate by a pulse applied AFM

The nano-patterning characteristics of GaAs is investigated using a pulse applied atomic force microscope (AFM). Very short range voltage pulses of micro to nano-seconds’ duration are applied to a conductive diamond-coated silicon (Si) tip in contact mode, to regulate the created feature size. The effects of pulse conditions such as pulse voltage, duration, frequency, offset voltage, anodization time, and applied tip pressure on nano-dot generation are characterized, based on the experiments. An interesting phenomenon, nano-pit creation instead of nano-dot creation, is observed when the applied pulse duration is less than 100 μs. Pulse frequency and offset voltage are also involved in nano-pit generation. The electrical spark discharge between the tip and the GaAs's surface is the most probable cause of the nano-pit creation and its generation mechanism is explained by considering the relevant pulse parameters. Nano-pits over 15 nm in depth are acquired on the GaAs substrate by adjusting the pulse conditions. This research facilitates the fabrication of more complex nano-structures on semiconductor materials since nano-dots and nano-pits could be easily made without any additional post-processes.

Effects of Atomic Force Microscope Silicon Tip Geometry on Large-Scale Nanomechanical Modification of the Polymer Surface

The shape of an atomic force microscope (AFM) silicon tip has a significant effect on the mechanical modification of the polymer surface, especially for a longer sliding distance of from several to several hundreds of millimeters. In this work, a pyramidal silicon tip was used to cut into the polymethyl methacrylate (PMMA) surface, forming nanogrooves with a linear sliding distance of about 80 mm and wear box structures with a total tip sliding distance of 1,024 mm. The effects of the tip edges and the tip radius on the form of the wear debris chips, wear depth, and debris transferred to the tip were investigated. The experimental results showed that four sides of the tip influenced the morphology of the removed material. Adhesion appeared to play a role in the tip wear mechanism by successive removal of SiO2 layers during transfer of adhered PMMA from the tip to the surface. The tip radius generally increased with sliding distance. Simultaneously, adhesion of the removed materials to the tip induced a larger tip radius and a sharper tip was revealed as dropping off of the materials during the test from time to time. Thus, with the same normal load the worn tip may induce failure of the machining process. The results presented in this study provide insight into long-term nanoscratch/wear and nanomechanical machining of glassy polymer surfaces with a silicon AFM tip.

Ultrafast laser-triggered field ion emission from semiconductor tips

We study experimentally and theoretically the controlled field evaporation of single atoms from a semiconductor surface by ultrafast laser-assisted atom probe tomography. The conventional physical mechanisms of field evaporation cannot explain the experimental results recently reported for such materials. A new model is presented in which the positive dc field leads to band bending with a high density of laser-generated holes near the surface of the sample. The laser energy absorption by these holes and the subsequent energy transfer to the lattice considerably increase the tip temperature. We show that this heating plays an important role in the field ion emission process. In addition, experiments are carried out for germanium and silicon tips to check the role of the dc field in the absorption processes, as well as the heating of the tip and the following evaporation. Good agreement between the predictions of our model and the experimental data is found.

Numerical study of femtosecond laser-assisted atom probe tomography

We investigate the mechanisms of a laser-assisted atom probe tomography technique. In this method, a sub-wavelength tip is subjected both to a very strong static electric field and to a femtosecond laser pulse. As a result, ions are ejected from the tip one by one. By using femtosecond lasers, one can analyze not only metals but also semiconductors and dielectric materials. To better understand the ejection process, a numerical model is developed based on the drift-diffusion approach. The model accounts for such effects as field penetration, hole and electron movement, and laser absorption. For the given value of the dc field, a substantial band bending and an increase in hole density at the surface of the silicon tip are observed. This bending effect changes silicon absorption coefficient at the surface and significantly increases recombination time of laser-induced carriers.