Pyramidal Tip Research Articles

Dip Pen Nanolithography: A Desktop Nanofabrication Approach Using High-Throughput Flexible Nanopatterning

Abstract Dip Pen Nanolithography (DPN) is a scanning probe lithography technique where an atomic force microscope tip is used to transfer molecules to a surface via a solvent meniscus. This technique allows surface patterning on scales of under 100 nanometres. DPN is the nanotechnology analog of the dip pen (also called the quill pen), where the tip of an atomic force microscope cantilever acts as a “pen,” which is coated with a chemical compound or mixture acting as an “ink,” and put in contact with a substrate, the “paper.” DPN enables direct deposition of nanoscale materials onto a substrate in a flexible manner. The vehicle for deposition can include pyramidal scanning probe microscope tips, hollow tips, and even tips on thermally actuated cantilevers. Recent advances have demonstrated massively parallel patterning using two-dimensional arrays of 55,000 tips, depicted below. Applications of this technology currently range through chemistry, materials science, and the life sciences, and include such work as ultra high density biological nanoarrays, additive photomask repair, and brand protection for pharmaceuticals.

Effect of Tip Geometry on Photo-Electron-Emission from Nanostructures

We show in this paper the strong effect of tip geometry on the photo-electron-emission behavior of nanostructured surfaces. To study the effect of tip geometry we compared the photo-emissivity of Ru and Pt nanorods with pyramidal shaped tips to that of carbon nanorods that display flat top (planar) tips. Flat top architectures gave no significant increase in the emission current, while nanostructures with pyramidal shaped tips showed 3-4 fold increase in photo-emission compared to a thin film of the same material. Pyramidal tip geometries increase the effective surface area that is exposed to the incident photon-flux thereby enhancing the photon-collection probability of the system. Such nano-structured surfaces show promise in a variety of device applications such as photo-detectors, photon counters and photo-multiplier tubes.

Correlating Nanoparticle Dispersion to Surface Mechanical Properties of TiO2/Polymer Composites

AbstractThe objective of this study is to characterize the nanoparticle dispersion and to investigate its effect on the surface mechanical properties of nanoparticle-polymer systems. Two types of TiO2 nanoparticles were chosen to mix in two polymeric matrices: solvent-borne acrylic urethane (AU) and water-borne butyl-acrylic styrene latex (latex) coatings. Nanoparticle dispersion was characterized using laser scanning confocal microscopy. Overall, Particle A (PA, without surface treatment) dispersed better than Particle B (PB, organic treatment) in both systems. The AU-PA system exhibited the best dispersion of the four systems, however PB forms big clusters in both of the matrices. Surface mechanical properties, such as surface modulus at micron and sub-micron length scales were determined from depth sensing indentation equipped with a pyramidal tip or a conical tip. The surface mechanical properties were strongly affected by the dispersion of nanoparticle clusters, and a good correlation was found between dispersion of nanoparticle clusters near surface and the modulus-depth mapping using a pyramid tip.

Theoretical and Experimental Study of Tip Electronic Structure in Scanning Tunneling Microscope

AbstractThe atomic and electronic structures of pyramidal model STM tips of transition metals (W, Rh, Pd, Ir and Pt) were investigated using density functional theory (DFT) method. The calculated density of states show that d electrons of the apex atoms in the M4 (M = W, Rh, Pd, Ir, Pt) model tips behave differently near the Fermi level, with the dz2 state being dominant only for W tip. The electronic structures of pyramid structures of W and Pd single-atom tips with larger sizes are studied and compared. The density of states of Pd apex atom and W apex atom show different occupation of d-bands leading to asymmetric density of states for Pd tip. The asymmetric tunneling currents measured by W and Pt-Ir STM tips are explained by the calculated electronic structures of W and Pd model tips.

Novel nanocarbons with a mushroom shape found in glassy carbon powder

Two types of novel nanocarbons with a mushroom shape were found in commercial glassy carbon powder. Both types of nanocarbons have ca. 2 μm length and ca. 0.5 μm diameter. One has a conical tip, and the other a pyramidal tip. Electron diffraction studies revealed that the former is made from helically stacked graphitic cones, and the latter from graphitic cups stacking to each other. These nanocarbons showed diamagnetic behavior strongly depending on both the temperature and the magnetic field.

Sulfated Polysaccharides Promote the Assembly of Amyloid β1–42 Peptide into Stable Fibrils of Reduced Cytotoxicity

The histopathological hallmarks of Alzheimer disease are the self-aggregation of the amyloid beta peptide (Abeta) in extracellular amyloid fibrils and the formation of intraneuronal Tau filaments, but a convincing mechanism connecting both processes has yet to be provided. Here we show that the endogenous polysaccharide chondroitin sulfate B (CSB) promotes the formation of fibrillar structures of the 42-residue fragment, Abeta(1-42). Atomic force microscopy visualization, thioflavin T fluorescence, CD measurements, and cell viability assays indicate that CSB-induced fibrils are highly stable entities with abundant beta-sheet structure that have little toxicity for neuroblastoma cells. We propose a wedged cylinder model for Abeta(1-42) fibrils that is consistent with the majority of available data, it is an energetically favorable assembly that minimizes the exposure of hydrophobic areas, and it explains why fibrils do not grow in thickness. Fluorescence measurements of the effect of different Abeta(1-42) species on Ca(2+) homeostasis show that weakly structured nodular fibrils, but not CSB-induced smooth fibrils, trigger a rise in cytosolic Ca(2+) that depends on the presence of both extracellular and intracellular stocks. In vitro assays indicate that such transient, local Ca(2+) increases can have a direct effect in promoting the formation of Tau filaments similar to those isolated from Alzheimer disease brains.

Effect of Cavities on the Optical Properties of Bullet Rosettes: Implications for Active and Passive Remote Sensing of Ice Cloud Properties

AbstractBullet rosette particles are common in ice clouds, and the bullets may often be hollow. Here the single-scattering properties of randomly oriented hollow bullet rosette ice particles are investigated. A bullet, which is an individual branch of a rosette, is defined as a hexagonal column attached to a hexagonal pyramidal tip. For this study, a hollow structure is included at the end of the columnar part of each bullet branch and the shape of the hollow structure is defined as a hexagonal pyramid. A hollow bullet rosette may have between 2 and 12 branches. An improved geometric optics method is used to solve for the scattering of light in the particle. The primary optical effect of incorporating a hollow end in each of the bullets is to decrease the magnitude of backscattering. In terms of the angular distribution of scattered energy, the hollow bullets increase the scattering phase function values within the forward scattering angle region from 1° to 20° but decrease the phase function values at side- and backscattering angles of 60°–180°. As a result, the presence of hollow bullets tends to increase the asymmetry factor. In addition to the scattering phase function, the other elements of the phase matrix are also discussed. The backscattering depolarization ratios for hollow and solid bullet rosettes are found to be very different. This may have an implication for active remote sensing of ice clouds, such as from polarimetric lidar measurements. In a comparison of solid and hollow bullet rosettes, the effect of the differences on the retrieval of both the ice cloud effective particle size and optical thickness is also discussed. It is found that the presence of hollow bullet rosettes acts to decrease the inferred effective particle size and to increase the optical thickness in comparison with the use of solid bullet rosettes.

3D finite element analysis of electrostatic deflection and shielding of commercial andFIB-modified cantilevers for electric and Kelvin force microscopy: II. Rectangular shapedcantilevers with asymmetric pyramidal tips

This paper deals with an application of 3D finite element analysis to the electrostaticinteraction between (i) a commercial rectangular shaped cantilever (with an integratedanisotropic pyramidal tip) and a conductive sample, when a voltage difference is appliedbetween them, and (ii) a focused ion beam (FIB) modified cantilever in order to realize aprobe with reduced parasitic electrostatic force. The 3D modelling of their electrostaticdeflection was realized by using multiphysics finite element analysis software and applied tothe real geometry of the cantilevers and probes as used in conventional electric and Kelvinforce microscopy to evaluate the contribution of the various part of a cantilever to the totalforce, and derive practical criteria to optimize the probe performances. We report alsoon the simulation of electrostatic shielding of nanometric features, in order toquantitatively evaluate an alternative way of reducing the systematic error caused by thecantilever-to-sample capacitive coupling. Finally, a quantitative comparison between theperformances of rectangular and triangular cantilevers (part I of this work) is reported.

3D finite element analysis of electrostatic deflection of commercial and FIB-modifiedcantilevers for electric and Kelvin force microscopy: I. Triangular shaped cantilevers withsymmetric pyramidal tips

The investigation of the nanoscale distribution of electrostatic forces on materialsurfaces is of paramount importance for the development of nanotechnology, sincethese confined forces govern many physical processes on which a large number oftechnological applications are based. For instance, electric force microscopy (EFM) andmicro-electro-mechanical-systems (MEMS) are technologies based on an electrostaticinteraction between a cantilever and a specimen.In the present work we report on a 3D finite element analysis of the electrostatic deflectionof cantilevers for electric and Kelvin force microscopy. A commercial triangular shapedcantilever with a symmetric pyramidal tip was modelled. In addition, the cantilever wasmodified by a focused ion beam (FIB) in order to reduce its parasitic electrostatic force,and its behaviour was studied by computation analysis. 3D modelling of the electrostaticdeflection was realized by using a multiphysics finite element analysis software and it wasapplied to the real geometry of the cantilevers and probes obtained by using basic CADtools. The results of the modelling are in good agreement with experimental data.

Novel Method of Growing Ultrananocrystalline Diamond Tips and Their Field Emission Property Study

Different forms of diamond have been shown to have qualities as field emission sources. As a consequence, much effort has been focused on both the synthesis of diamond nanostructures to increase the field enhancement factor and understanding the emission mechanism in these nominally insulating materials. In our recent study, we have grown ultrananocrystalline diamond (UNCD) coated nanocrystalline diamond (NCD) tips on NCD films for field emitters. The films were characterized using field emission scanning electron microscopy and Raman spectroscopy to identify the quality of the films. The fabricated different sizes of pyramid tips and their field emission properties are reported. It has been observed that with increase in tip size, the turn on voltage also increases.

Micromechanics of pyramidal indentation in fcc metals: Single crystal plasticity finite element analysis

This work concerns analysis of Vickers and Berkovich indentation experiments through extensive crystal plasticity finite element simulations. The simulations are performed by recourse to the Bassani and Wu hardening model for pure fcc crystals undergoing both easy-glide stage I and stage II deformations, as well as with the model proposed by Pierce, Asaro and Needleman for precipitation hardened fcc crystals, deforming initially under stage II which also undergo strong hardening saturation in stage III. Simulations are also conducted with a model based on the hardening description by Bassani and Wu, whose physical basis and predictive capability have been enhanced for pure copper crystals. Based upon the activity of the slip systems and the strength of dislocation interactions, this work provides a fundamental insight into the influence of prior work hardening in single crystal indentation. Discussions are given on the role of the latent hardening description upon the development of material pileup and sinking-in at the contact boundary as well as on the correlation between the single crystal and polycrystalline contact responses. The present investigation further illustrates on the influence of the orientation of the slip systems with respect to the pyramidal tip upon the formation of irregular imprint morphologies. Extraction of the single crystal hardening parameters from instrumented indentation P– h s curves is also briefly addressed. Finally, the contact deformation regimes ruling the response of isotropic strain hardening media are examined in light of the simulations for single crystal indentation.

Effects of scratching directions on AFM-based abrasive abrasion process

AFM-based single abrasive abrasion process is widely employed in the surface micro/nanomachining for fabrication of structures at the nanometer scale. The wear depth and roughness are significantly important in the application of these structures. To study effects of scratching directions on the wear depth and roughness within the wear mark, single groove scratching test and wear test on the surface of polished single crystal silicon were carried out using AFM with a pyramidal diamond tip. Single groove scratching tests indicated that tip geometry leads to different removal states such as cutting and plowing. At the same load, deeper wear depth and rougher surface were produced by using the scratching direction perpendicular to the long axis of the cantilever rather than parallel to the long axis of the cantilever. Surface roughness decreases with respect to the feed scratching perpendicular to the long axis of the cantilever, whereas while scratching along the long axis of the cantilever, the surface roughness is rougher at the small feed. This is attributed to the different stiffness of the cantilever along different scratching directions and different removal states between the tip and sample.

Estimation of Three-Dimensional Atomic Force Microscope Tip Shape from Atomic Force Microscope Image for Accurate Measurement

We studied methods of estimating three-dimensional (3-D) tip structure using impulse response technique. We have proposed a 3-D tip estimation method using an infinite small diameter standard column as the impulse response technique. The standard column has been made by image processing of a finite-small-diameter-column standard sample by a software elimination technique. We demonstrated how to obtain the 3-D atomic force microscope (AFM) pyramidal tip shape using a commercial pyramidal tip and a 665-nm-diameter-column sample. The estimated tip radii are 10–15 nm in various profiles of the top. The results indicate that the method is effective to estimate a 3-D AFM tip structure in order to obtain an accurate AFM image.

13.4: Copper Nanowires with Five‐Twinned Structure Grown by Chemical Vapor Deposition and their Application to Field Emission Displays

AbstractA prototype field emission display device was fabricated using copper nanowires as emitters. The copper nanowires were grown by chemical vapor deposition without any catalyst or template, which were analyzed by electron microscopy to show a five‐fold twinned structure with a pentagonal pyramid tip. The electron diffraction pattern disclosed that the twin boundaries were mismatched irregularly. The anisotropic growth of the copper nanowires in gas phase could be attributed to the passivation of the {100} side planes by the phosphite molecules dissociated from the precursor. Field emission characteristics of the nanowires were measured.

Probing elasticity and adhesion of live cells by atomic force microscopy indentation

Atomic force microscopy (AFM) indentation has become an important technique for quantifying the mechanical properties of live cells at nanoscale. However, determination of cell elasticity modulus from the force-displacement curves measured in the AFM indentations is not a trivial task. The present work shows that these force-displacement curves are affected by indenter-cell adhesion force, while the use of an appropriate indentation model may provide information on the cell elasticity and the work of adhesion of the cell membrane to the surface of the AFM probes. A recently proposed indentation model (Sirghi, Rossi in Appl Phys Lett 89:243118, 2006), which accounts for the effect of the adhesion force in nanoscale indentation, is applied to the AFM indentation experiments performed on live cells with pyramidal indenters. The model considers that the indentation force equilibrates the elastic force of the cell cytoskeleton and the adhesion force of the cell membrane. It is assumed that the indenter-cell contact area and the adhesion force decrease continuously during the unloading part of the indentation (peeling model). Force-displacement curves measured in indentation experiments performed with silicon nitride AFM probes with pyramidal tips on live cells (mouse fibroblast Balb/c3T3 clone A31-1-1) in physiological medium at 37 degrees C agree well with the theoretical prediction and are used to determine the cell elasticity modulus and indenter-cell work of adhesion.

Dynamic strain measurements in a sliding microstructured contact

A novel experiment is described which measures the tangential strain developmentacross the contact between a PDMS (polydimethylsiloxane) block and a glasssurface during the initial stages of sliding. The surface of the PDMS block hasbeen microfabricated to take the form of a regular array of pyramidal tips at20 µm separation. Tangential strain is measured by means of light scattering from the interfacebetween the block and surface. Three phases are observed in all experiments: initial sheardeformation of the whole PDMS block, a pre-sliding tangential compression of the tip arraywith stepwise increase of the compressive strain, and sliding in stick–slip movements asrevealed by periodic variation of the strain. The stick–slip sliding between the regular tiparray and the randomly rough counter surface always takes on the periodicity of the tiparray. The fast slip can cause either a sudden increase or a sudden decrease in compressivestrain.

A micromachined elastomeric tip array for contact printing with variable dot size and density

We report a flexible and versatile microcontact printing process using a micromachined elastomeric PDMS (poly-dimethylsiloxane) stamp with two-dimensional arrays of pyramidal tips. The PDMS stamp was molded from a bulk-etched single-crystalline silicon master. By changing the contact pressure, arrayed dot patterns with different dot sizes (from submicron to a few microns) were obtained controllably with one single PDMS stamp. Variable density of dot patterns was also achieved in a ‘step-print’ manner by conducting multiple printing on a transitional stage. This technique is expected to be useful in many nano- and biotechnology applications, including single cell and neuron studies.

Localized Current Injection and Submicron Organic Light-Emitting Device on a Pyramidal Atomic Force Microscopy Tip

An organic light-emitting device was fabricated on a commercial atomic force microscopy (AFM) probe having a pyramidal tip by a lithography-free vacuum thermal evaporation (VTE) process. The line-of-sight molecular transport characteristic of VTE results in controlled thickness variation across the nonplanar substrate, such that localized current injection occurs at the tip region. Furthermore, the high curvature of the AFM tip vertex concentrates the electric field, causing highly localized bipolar charge injection, accompanied by photon emission from a region less than a micrometer across. This light source exhibits a range of features potentially attractive for applications such as probe-based optical microscopy, nanoscale light sensing, and chemical detection.

High-aspect ratio metal tips attached to atomic force microscopy cantilevers with controlled angle, length, and radius for electrostatic force microscopy

We demonstrate a method to fabricate a high-aspect ratio metal tip attached to microfabricated cantilevers with controlled angle, length, and radius, for use in electrostatic force microscopy. A metal wire, after gluing it into a guiding slot that is cut into the cantilever, is shaped into a long, thin tip using a focused ion beam. The high-aspect ratio results in considerable reduction of the capacitive force between tip body and sample when compared to a metal coated pyramidal tip.

Synthesis of Silicon Nanoneedles

Nanoneedles are novel silicon nanostructures. With the use of silicon monoxide as the starting material, a small quantity of deionized water as the reaction medium, and argon as the protection gas, silicon nanoneedles were successfully synthesized. The growth conditions were controlled at 490°C with a pressure of 3.2–3.5 MPa. High-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED) and electron energy-dispersive spectroscopy (EDS) revealed that the as-grown nanoneedles had pyramidal tips with the diamond structure. The chemical composition at the pyramidal tip was silicon with a small amount of oxygen. Compared with single-crystal silicon, the Raman spectra of silicon nanoneedles were found to be downshifted because of their small size.