Tip Preparation Research Articles

Facile Preparation of a Platinum Silicide Nanoparticle-Modified Tip Apex for Scanning Kelvin Probe Microscopy.

In this study, we propose an ultra-facile approach to prepare a platinum silicide nanoparticle-modified tip apex (PSM tip) used for scanning Kelvin probe microscopy (SKPM). We combined a localized fluoride-assisted galvanic replacement reaction (LFAGRR) and atmospheric microwave annealing (AMA) to deposit a single platinum silicide nanoparticle with a diameter of 32 nm on the apex of a bare silicon tip of atomic force microscopy (AFM). The total process was completed in an ambient environment in less than 3 min. The improved potential resolution in the SKPM measurement was verified. Moreover, the resolution of the topography is comparable to that of a bare silicon tip. In addition, the negative charges found on the PSM tips suggest the possibility of exploring the use of current PSM tips to sense electric fields more precisely. The ultra-fast and cost-effective preparation of the PSM tips provides a new direction for the preparation of functional tips for scanning probe microscopy.

Characterization of ion-irradiation-induced nanodot structures on InP surfaces by atom probe tomography

Surfaces of InP were bombarded by 1.9keV Ar+ ions under normal incidence. The total accumulated ion fluence the samples were exposed to was varied from 1×1017cm−2 to 3×1018cm−2 and ion flux densities f of (0.4−2)×1014cm−2s−1 were used. Nanodot structures were found to evolve on the surface from these ion irradiations, their dimensions however, depend on the specific bombardment conditions. The resulting surface morphology was examined by atomic force microscopy (AFM). As a function of ion fluence, the mean radius, height, and spacing of the dots can be fitted by power-law dependences. In order to determine possible local compositional changes in these nanostructures induced by ion impact, selected samples were prepared for atom probe tomography (APT). The results indicate that by APT the composition of individual InP nanodots evolving under ion bombardment could be examined with atomic spatial resolution. At the InP surface, the values of the In/P concentration ratio are distinctly higher over a distance of ~1nm and amount to 1.3–1.8. However, several aspects critical for the analyses were identified: (i) because of the small dimensions of these nanostructures a successful tip preparation proved very challenging. (ii) The elemental compositions obtained from APT were found to be influenced pronouncedly by the laser pulse energy; typically, low energies result in the correct stoichiometry whereas high ones lead to an inhomogeneous evaporation from the tips and deviations from the nominal composition. (iii) Depending again on the laser energy, a prolific emission of Pn cluster ions was observed, with n≤11.

Preparation of magnetic tips for spin-polarized scanning tunneling microscopy onFe1+yTe

The interplay of electronic nematic modulations, magnetic order, superconductivity and structural distortions in strongly correlated electron materials calls for methods which allow characterizing them simultaneously - to allow establishing directly the relationship between these different phenomena. Spin-polarized STM enables studying both, electronic excitations as well as magnetic structure in the same measurement at the atomic scale. Here we demonstrate preparation of magnetic tips, both ferromagnetic and antiferromagnetic, on single crystals of FeTe. This opens up preparation of spin-polarized tips without the need for sophisticated ultra-high vacuum preparation.

Combining structural and chemical information at the nanometer scale by correlative transmission electron microscopy and atom probe tomography.

In many cases, the three-dimensional reconstructions from atom probe tomography (APT) are not sufficiently accurate to resolve crystallographic features such as lattice planes, shear bands, stacking faults, dislocations or grain boundaries. Hence, correlative crystallographic characterization is required in addition to APT at the exact same location of the specimen. Also, for the site-specific preparation of APT tips containing regions of interest (e.g. grain boundaries) correlative electron microscopy is often inevitable. Here we present a versatile experimental setup that enables performing correlative focused ion beam milling, transmission electron microscopy (TEM), and APT under optimized characterization conditions. The setup was designed for high throughput, robustness and practicability. We demonstrate that atom probe tips can be characterized by TEM in the same way as a standard TEM sample. In particular, the use of scanning nanobeam diffraction provides valuable complementary crystallographic information when being performed on atom probe tips. This technique enables the measurement of orientation and phase maps as known from electron backscattering diffraction with a spatial resolution down to one nanometer.

Note: Fabrication and characterization of molybdenum tips for scanning tunneling microscopy and spectroscopy.

We present a method for the preparation of bulk molybdenum tips for Scanning Tunneling Microscopy and Spectroscopy and we assess their potential in performing high resolution imaging and local spectroscopy by measurements on different single crystal surfaces in UHV, namely, Au(111), Si(111)-7 × 7, and titanium oxide 2D ordered nanostructures supported on Au(111). The fabrication method is versatile and can be extended to other metals, e.g., cobalt.

Determination of Root Canal Cleanliness by Different Irrigation Methods and Morphometric Analysis of Apical Third.

The aim of this study was to determine the root canal area before and after the instrumentation 1 mm short of the apical foramen by clinical and cone beam computed tomography (CBCT) methods, and to evaluate the cleanliness of the apical region in mesiodistal flattened teeth by using optical microscopy. Forty-two human single-canal mandibular incisors were instrumented using the Free Tip Preparation technique up to three, four or five instruments from the initial. Cone beam computed tomography scans were acquired of the samples before and after root canal preparation (RCP). Irrigation was performed by conventional or hydrodynamic means, using 2.5% sodium hypochlorite. The samples were prepared for observation under an optical microscope. Images were digitally obtained, analyzed and the results were submitted to statistical analysis (two-way ANOVA complemented by Bonferroni's post-test). There was no significant difference between the studied anatomical areas with both CBCT and clinical methods. There were no differences between irrigation methods. It was verified differences between instrumentation techniques. Instrumentation with four instruments from the initial instrument determined a significant increase in the contact area when compared to preparation with three instruments, but RCP with 5 instruments did not result in a better cleanliness. The analysis with CBCT was not capable to determine the precise shape of surgical apical area comparing to the clinical method. Both the conventional and hydrodynamic irrigation techniques were not able to promote root canals debris-free. The instruments action in root canal walls was proportional to the number of instruments used from the initial apical instrument.

Role of the resistivity of insulating field emitters on the energy of field-ionised and field-evaporated atoms

In order to improve the accuracy of laser atom probe analyses, it is important to understand all the physical processes induced by the combination of the high electrical field and the femtosecond laser beam during field evaporation.New information can be accessed from the energy of evaporated surface atoms or field-ionised atoms of an imaging gas. In order to study the ions energy, we combine La-APT and FIM analyses in a new experimental setup equipped with electrostatic lenses.We report measurements for semiconductors and oxides and we study the influence of the illumination conditions (laser power and wavelength), the evaporation rate, the sample geometry and the tip preparation processes. The results are discussed taking into account the resistive properties of non-metallic samples and the photo-stimulated conductivity.This work clarifies the role of the laser and DC field in the energy deficit of field evaporated ions.

Update on lasers in urology 2014: current assessment on holmium:yttrium–aluminum–garnet (Ho:YAG) laser lithotripter settings and laser fibers

The purpose of the study was to review the existing literature on holmium:yttrium-aluminum-garnet laser lithotripsy regarding lithotripter settings and laser fibers. An online search of current and past peer-reviewed literature on holmium laser lithotripsy was performed on several databases, including PubMed, SciElo, and Google Scholar. Relevant studies and original articles about lithotripter settings and laser fibers were examined, and the most important information is summarized and presented here. We examine how the choice of lithotripter settings and laser fibers influences the performance of holmium laser lithotripsy. Traditional laser lithotripter settings are analyzed, including pulse energy, pulse frequency, and power levels, as well as newly developed long-pulse modes. The impact of these settings on ablation volume, fragment size, and retropulsion is also examined. Advantages of small- and large-diameter laser fibers are discussed, and controversies are highlighted. Additionally, the influence of the laser fiber is examined, specifically the fiber tip preparation and the lithotripter settings' influence on tip degradation. Many technical factors influence the performance of holmium laser lithotripsy. Knowing and understanding these controllable parameters allows the urologist to perform a laser lithotripsy procedure safely, efficiently, and with few complications.

Sequential Phosphoproteomic Enrichment through Complementary Metal-Directed Immobilized Metal Ion Affinity Chromatography

Methodologies to enrich heterogeneous types of phosphopeptides are critical for comprehensive mapping of the under-explored phosphoproteome. Taking advantage of the distinct binding affinities of Ga(3+) and Fe(3+) for phosphopeptides, we designed a metal-directed immobilized metal ion affinity chromatography for the sequential enrichment of phosphopeptides. In Raji B cells, the sequential Ga(3+)-Fe(3+)-immobilized metal affinity chromatography (IMAC) strategy displayed a 1.5-3.5-fold superior phosphoproteomic coverage compared to single IMAC (Fe(3+), Ti(4+), Ga(3+), and Al(3+)). In addition, up to 92% of the 6283 phosphopeptides were uniquely enriched in either the first Ga(3+)-IMAC (41%) or second Fe(3+)-IMAC (51%). The complementary properties of Ga(3+) and Fe(3+) were further demonstrated through the exclusive enrichment of almost all of 1214 multiply phosphorylated peptides (99.4%) in the Ga(3+)-IMAC, whereas only 10% of 5069 monophosphorylated phosphopeptides were commonly enriched in both fractions. The application of sequential Ga(3+)-Fe(3+)-IMAC to human lung cancer tissue allowed the identification of 2560 unique phosphopeptides with only 8% overlap. In addition to the above-mentioned mono- and multiply phosphorylated peptides, this fractionation ability was also demonstrated on the basic and acidic phosphopeptides: acidophilic phosphorylation sites were predominately enriched in the first Ga(3+)-IMAC (72%), while Pro-directed (85%) and basophilic (79%) phosphorylation sites were enriched in the second Fe(3+)-IMAC. This strategy provided complementary mapping of different kinase substrates in multiple cellular pathways related to cancer invasion and metastasis of lung cancer. Given the fractionation ability and ease of tip preparation of this Ga(3+)-Fe(3+)-IMAC, we propose that this strategy allows more comprehensive characterization of the phosphoproteome both in vitro and in vivo.

Direct shoot regeneration from basal leaf segments of Lilium and assessment of genetic stability in regenerants by ISSR and AFLP markers

Here, we report a widely applicable procedure for direct shoot regeneration via basal leaf segments of Lilium. Leaf segments (0.8–1.0 cm long and 0.4 cm wide) were excised from leaves on shoot nodes 3 to 6 of 4-wk-old in vitro stock shoot cultures. The segments were wounded by three transverse cuts across the midvein on the abaxial side, with 1 mm between cuts, and cultured with the abaxial side in contact with a shoot regeneration medium composed of half-strength Murashige and Skoog medium supplemented with 1 mg/l naphthaleneacetic acid, 0.5 mg/l thidiazuron, 30 g/l sucrose, and 7 g/l agar (pH 5.8). The cultures were incubated for 4 wk under a 16-h photoperiod at 23 ± 2°C for adventitious shoot regeneration. With this procedure, a mean shoot regeneration frequency of 92–100% and mean number of shoots of 4.7–7.0 per segment were obtained in five Lilium species and hybrids, which represent diverse genotypes of Lilium and are commercially popular lilies. Histological studies with Lilium Oriental hybrid “Siberia” revealed that meristemoids initiated from subepidermal cells on the adaxial side of the explant and eventually developed into adventitious buds, without callus formation. In an assessment of genetic stability in the regenerants of “Siberia”, no polymorphic bands were detected by intersimple sequence repeat and only 0.73% polymorphic bands were detected by amplified fragment length polymorphism. The morphologies of the regenerants were identical to those of the control. These results demonstrated that the regenerants were genetically and morphological stable. Thus, this procedure has great potential application for micropropagation, genetic transformation, and preparation of shoot tips for cryopreservation and cryotherapy for virus eradication of Lilium.

Coupling atom probe tomography and photoluminescence spectroscopy: Exploratory results and perspectives

The development of laser-assisted atom probes makes it possible, in principle, to exploit the femtosecond laser pulse not only for triggering ion evaporation from a nanometric field emission tip, but also for generating photons via the radiative recombination of electron-hole pairs in tips made of dielectric materials. In this article we demonstrate a first step towards a correlation of micro-photoluminescence (μ-PL) and laser-assisted tomographic atom probe (LA-TAP) analysis applied separately on the same objects, namely on ZnO microwires. In particular, we assess that the use of the focused ion beam (FIB) tip preparation method significantly degrades the radiative recombination yield of the analyzed microwires. We discuss the strategies to avoid the FIB-induced damage on the optical properties of the sample and how to get beyond the correlated μ-PL and LA-TAP analysis with a coupled approach allowing to perform the two analyses within the same instrument.

Preparation of high-resolution magnetic force microscope tips coated with Co and FeCo films

Magnetic force microscope (MFM) tips are prepared by coating Si tips of 4 nm radius with Co and Fe65 Co35 (at. %) films by employing an ultra-high vacuum evaporation system. The effect of coating film thickness on MFM spatial resolution is investigated. With increasing the thickness from 10 to 20 nm, the resolutions of Co- and FeCo-coated tips improve from 8.4 to 6.9 nm and from 7.5 to 6.6 nm, respectively. Better resolutions are obtained for the FeCo-coated tips, which is due to enhanced sensitivities related with the higher magnetic moment of FeCo material. As the coating thickness further increases, the resolutions deteriorate due to increase of tip radius. The resolution is affected by the detection sensitivity and the tip radius. Magnetic bits of a perpendicular medium recorded at 1800 kFCI (bit length: 14.1 nm) and 1900 kFCI (13.4 nm) are respectively distinguishable in the MFM images observed by using tips coated with Co and FeCo films.

Tip preparation for near-field ablation at mid-infrared wavelengths

A fabrication method for high-throughput, fiber-based tips for near-field scanning microscopy (NSOM) in the mid-infrared (λ ~ 3 μm) has been developed. Several fiber materials have been investigated and recipes for wet-chemical etching have been varied to produce tips that are physically robust and are capable of low-loss transmission of high-power pulses of mid-infrared light. Ultimately, wet-chemical etching techniques are used on glass fibers to produce tips capable of focusing mid-infrared light to ablate material from sub-micron-sized regions of organic films. The power throughput of the tips is significantly increased by using a novel material, previously unreported for NSOM applications: germanate fibers. The tips produced are mechanically strong and capable of transmitting high light fluence without sustaining physical damage. Here, the development of these tips and their performance are described.

Highly reproducible low temperature scanning tunneling microscopy and spectroscopy with in situ prepared tips

An in situ tip preparation procedure compatible with ultra-low temperature and high magnetic field scanning tunneling microscopes is presented. This procedure does not require additional preparation techniques such as thermal annealing or ion milling. It relies on the local electric-field-induced deposition of material from the tip onto the studied surface. Subsequently, repeated indentations are performed onto the sputtered cluster to mechanically anneal the tip apex and thus to ensure the stability of the tip. The efficiency of this method is confirmed by comparing the topography and spectroscopy data acquired with either unprepared or in situ prepared tips on epitaxial graphene grown on Ru (0001). We demonstrate that the use of in situ prepared tips increases the stability of the scanning tunneling images and the reproducibility of the spectroscopic measurements.

Guide to video recording of structure dynamics and dynamic processes of proteins by high-speed atomic force microscopy

High-speed atomic force microscopy (HS-AFM) allows direct visualization of dynamic structural changes and processes of functioning biological molecules in physiological solutions, at subsecond to sub-100-ms temporal and submolecular spatial resolution. Unlike fluorescence microscopy, wherein the subset of molecular events that you see is dependent on the site where the probe is placed, dynamic molecular events unselectively appear in detail in an AFM movie, facilitating our understanding of how biological molecules function. Here we present protocols for HS-AFM imaging of proteins in action, including preparation of cantilever tips, step-by-step procedures for HS-AFM imaging, and recycling of cantilevers and sample stages, together with precautions and troubleshooting advice for successful imaging. The protocols are adaptable in general for imaging many proteins and protein-nucleic acid complexes, and examples are described for looking at walking myosin, ATP-hydrolyzing rotorless F(1)-ATPase and cellulose-hydrolyzing cellulase. The entire protocol takes 10-15 h, depending mainly on the substrate surface to be used.

Refined tip preparation by electrochemical etching and ultrahigh vacuum treatment to obtain atomically sharp tips for scanning tunneling microscope and atomic force microscope

A modification of the common electrochemical etching setup is presented. The described method reproducibly yields sharp tungsten tips for usage in the scanning tunneling microscope and tuning fork atomic force microscope. In situ treatment under ultrahigh vacuum (p ≤10(-10) mbar) conditions for cleaning and fine sharpening with minimal blunting is described. The structure of the microscopic apex of these tips is atomically resolved with field ion microscopy and cross checked with field emission.

Ultrafine Fiber Tip Etched in Hydrophobic Polymer Coated Tube for Near-Field Scanning Plasmonic Probe

We propose a novel one-step etching technique for the preparation of an optical fiber tip using a hydrophobic polymer coated tube (HP) containing 48% hydrofluoric acid (HF) to etch photosensitive single-mode fiber (PSMF). Dipping of PSMF in an HP tube suppresses the convex meniscus (CM) of the HF solution in the tube due to formation of a concave surface tension meniscus (SM) around the PSMF. The continuous etching reduces the diameter of PSMF and shortens the SM along PSMF resulting in elevation of CM around PSMF. The elevation of the CM and faster etching rate of the PSMF core digs a capillary ring along the fiber core-cladding boundary. Capillary action fills the ring with HF, which finally recedes and creates a tip at the apex of the fiber. We have fabricated a typical tip with typical features of tip height ~ 4 μm, base diameter ~ 3 μm , cone angle ~ 25°, and aperture ~ 30 nm. For the theoretical analysis, a tip similar to the fabricated one is modeled to estimate surface plasmon (SP) enhancement, ~ 200, at the end of the tip with a silver coating.

A compact sub-Kelvin ultrahigh vacuum scanning tunneling microscope with high energy resolution and high stability

We designed a scanning tunneling microscope working at sub-Kelvin temperatures in ultrahigh vacuum (UHV) in order to study the magnetic properties on the nanoscale. An entirely homebuilt three-stage cryostat is used to cool down the microscope head. The first stage is cooled with liquid nitrogen, the second stage with liquid (4)He. The third stage uses a closed-cycle Joule-Thomson refrigerator of a cooling power of 1 mW. A base temperature of 930 mK at the microscope head was achieved using expansion of (4)He, which can be reduced to ≈400 mK when using (3)He. The cryostat has a low liquid helium consumption of only 38 ml/h and standing times of up to 280 h. The fast cooling down of the samples (3 h) guarantees high sample throughput. Test experiments with a superconducting tip show a high energy resolution of 0.3 meV when performing scanning tunneling spectroscopy. The vertical stability of the tunnel junction is well below 1 pm (peak to peak) and the electric noise floor of tunneling current is about 6fA/√Hz. Atomic resolution with a tunneling current of 1 pA and 1 mV was achieved on Au(111). The lateral drift of the microscope at stable temperature is below 20 pm/h. A superconducting spilt-coil magnet allows to apply an out-of-plane magnetic field of up to 3 T at the sample surface. The flux vortices of a Nb(110) sample were clearly resolved in a map of differential conductance at 1.1 K and a magnetic field of 0.21 T. The setup is designed for in situ preparation of tip and samples under UHV condition.

A reproducible method for damage‐free site‐specific preparation of atom probe tips from interfaces

Atom probe tomography (APT) is a mass spectrometry method with atomic-scale spatial resolution that can be used for the investigation of a wide range of materials. The main limiting factor with respect to the type of problems that can be addressed is the small volume investigated and the randomness of common sample preparation methods. With existing site-specific specimen preparation methods it is still challenging to rapidly and reproducibly produce large numbers of successful samples from specifically selected grain boundaries or interfaces for systematic studies. A new method utilizing both focused ion beam (FIB) and transmission electron microscopy (TEM) is presented that can be used to reproducibly produce damage-free atom probe samples with features of interest at any desired orientation with an accuracy of better than 50 nm from samples that require very little prior preparation.

Preparation of tips coated with poly(dimethylsiloxane) for scanning tunneling microscopy in aqueous solutions

A simple and reliable method for preparing tips coated with poly(dimethylsiloxane) (PDMS) for scanning tunneling microscopy (STM) in aqueous solutions is reported. Au STM tips were dip-coated with PDMS and subsequently cured. The coated tips were characterized by scanning electron microscopy, energy dispersive x-ray spectroscopy, and voltammetry. We show that the PDMS layer smoothly covers the tip surface except for its very apex. These tips enable atomically resolved imaging of a sample surface and measurement of single-molecule conductance below 1.0 nS with STM in aqueous solutions. Because of the superior compatibility of PDMS with organic solvents, the PDMS-coated tips would be useful for preparing molecular tips via their chemical modification in such solvents, enabling chemically selective imaging of a single molecule in water.