Coaxial Tip Research Articles

Coaxial tips for a scanning microwave microscope and its calibration with dielectric references

Scanning microwave microscopy (SMM) is a combination of an atomic force microscope with a vector network analyzer (VNA) to measure locally resolved impedances. The technique finds application in the realms of semiconductor industries, material sciences, or biology. To determine quantitative material properties from the measured impedances, the system must be calibrated. Transferring the calibration from the calibration substrate onto the material under test is strongly limited when using unshielded probes, as the electromagnetic coupling to the surroundings can reach several centimeters. This work reports the fabrication of coaxially shielded probes for a scanning microwave microscope and their integration into such an instrument. We discuss a calibration method with dielectric references, using a simulation-assisted 1-port VNA calibration algorithm. Uncertainty considerations of the measurement process are included and propagation throughout the algorithm is performed. The calibration is verified with an additional dielectric reference. As an application example, the results for a static-random-access memory sample are presented. We identified system-related drift and trace noise as the dominant contributors to the uncertainties of the calibrated results. The here presented shielded tips can broaden the application scope of SMM, as they are door-openers for measurements in liquids.

Simultaneous scanning tunneling microscopy and synchrotron X-ray measurements in a gas environment

A combined X-ray and scanning tunneling microscopy (STM) instrument is presented that enables the local detection of X-ray absorption on surfaces in a gas environment. To suppress the collection of ion currents generated in the gas phase, coaxially shielded STM tips were used. The conductive outer shield of the coaxial tips can be biased to deflect ions away from the tip core. When tunneling, the X-ray-induced current is separated from the regular, ‘topographic’ tunneling current using a novel high-speed separation scheme. We demonstrate the capabilities of the instrument by measuring the local X-ray-induced current on Au(1 1 1) in 800 mbar Ar.

Inventing a co-axial atomic resolution patch clamp to study a single resonating protein complex and ultra-low power communication deep inside a living neuron cell.

To read the signals of single molecules in vitro on a surface, or inside a living cell or organ, we introduce a coaxial atom tip (coat) and a coaxial atomic patch clamp (COAPAP). The metal-insulator-metal cavity of these probes extends to the atomic scale (0.1[Formula: see text]nm), it eliminates the cellular or environmental noise with a S/N ratio 105. Five ac signals are simultaneously applied during a measurement by COAT and COAPAP to shield a true signal under environmental noise in five unique ways. The electromagnetic drive in the triaxial atomic tips is specifically designed to sense anharmonic vibrational and transmission signals for any system between 0.1[Formula: see text]nm and 50[Formula: see text]nm where the smallest nanopatch clamp cannot reach. COAT and COAPAP reliably pick up the atomic scale vibrations under the extreme noise of a living cell. Each protein's distinct electromagnetic, mechanical, electrical and ionic vibrational signature studied in vitro in a protected environment is found to match with the ones studied inside a live neuron. Thus, we could confirm that by using our probe blindly we could hold on to a single molecule or its complex in the invisible domain of a living cell. Our decade long investigations on perfecting the tools to measure bio-resonance of all forms and simultaneously in all frequency domains are summarized. It shows that the ratio of emission to absorption resonance frequencies of a biomaterial is around [Formula: see text], only a few in the entire em spectrum are active that regulates all other resonances, like mechanical, ionic, etc.

Self-sensing cantilevers with integrated conductive coaxial tips for high-resolution electrical scanning probe metrology

The lateral resolution of many electrical scanning probe techniques is limited by the spatial extent of the electrostatic potential profiles produced by their probes. Conventional unshielded conductive atomic force microscopy probes produce broad potential profiles. Shielded probes could offer higher resolution and easier data interpretation in the study of nanostructures. Electrical scanning probe techniques require a method of locating structures of interest, often by mapping surface topography. As the samples studied with these techniques are often photosensitive, the typical laser measurement of cantilever deflection can excite the sample, causing undesirable changes electrical properties. In this work, we present the design, fabrication, and characterization of probes that integrate coaxial tips for spatially sharp potential profiles with piezoresistors for self-contained, electrical displacement sensing. With the apex 100 nm above the sample surface, the electrostatic potential profile produced by our coaxial tips is more than 2 times narrower than that of unshielded tips with no long tails. In a scan bandwidth of 1 Hz–10 kHz, our probes have a displacement resolution of 2.9 Å at 293 K and 79 Å at 2 K, where the low-temperature performance is limited by amplifier noise. We show scanning gate microscopy images of a quantum point contact obtained with our probes, highlighting the improvement to lateral resolution resulting from the coaxial tip.

Visualization of a Coaxial Dielectric Barrier Discharge Driven by a Sub-ns Rising High-Voltage Pulse and Its Reflections

Dielectric barrier discharges generated in a coaxial tip to cylinder configuration at atmospheric pressure by a 5-ns high-voltage pulse with sub-ns rise time were investigated with a fast intensified CCD camera. Different discharge characteristics were found for the breakdown during the pulse itself and in the subsequent reflections of the pulse. There is a transition from a complete diffuse regime to a breakdown in constricted channels, which finally cross the whole gap.

Phacoemulsification Systems

Phacoemulsification Systems

Impact of low versus high fluidic settings on the efficacy and safety of phacoemulsification

To compare intraoperative efficiency and postoperative outcomes of cataract surgery with low and high fluidic settings. In this prospective, randomized, single-blinded study, 114 eyes of 57 patients were operated with low fluidic settings for one eye (group I) and high fluidic settings for the other eye (group II). Efficiency was judged as metred surgery time, effective phacoemulsification time (EPT) and the amount of balanced salt solution used. Visual outcome and endothelial cell count were determined 1 week and 18 months postoperatively. The overall effective phacoemulsification energy was statistically significantly lower (p = 0.003) in group II than in group I. Conquest of the nuclei was achieved with about two-thirds of the energy needed in group I, with 6.59 ± 4.79 effective ultrasound energy compared with 3.99 ± 3.18 (p = 0.001). Overall, about 12% more solution was used in group II than in group I. Median visual acuity was 1.0 for both groups 18 months after surgery. The mean endothelial cell loss was 5.0% in eyes in group I compared with 6.3% in eyes in group II (p > 0.5). Switching from low fluidic settings with a conventional coaxial 20G phacoemulsification tip to higher fluidic settings with a microcoaxial phaco tip statistically significantly decreases EPT. As only marginally more solution was used with the higher aspiration flow, occlusion must be accomplished more often with high than with low fluidics. Aspiration of the quadrants was therefore more efficient with high fluidic settings. The enhanced pump speed did not result in more tissue damage.

Online Coupling of Capillary Electrophoresis with Direct Analysis in Real Time Mass Spectrometry

The online coupling of capillary electrophoresis with ambient direct analysis in real time mass spectrometry (DART-MS) was realized by a coaxial tip interface. The analytes eluted from capillary electrophoresis (CE) were directly ionized by the metastable helium flux produced by DART and transferred into MS for the detection, with which the online separation and simultaneous detection were achieved. The CE-DART-MS can tolerate higher concentrations of detergents and salts than traditional CE-electrospray ionization (ESI)-MS and avoided the difficulties of collecting CE effluent and cleaning the interface, which simplified the experimental procedures and shortened the analysis time. The performance of the technique was successfully verified by capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) using a mixture of 4-aminoantipyrine, zolmitriptan, and quinine. This online technique showed good repeatability with the relative standard deviations (RSDs; n = 5) of 0.56-1.23% for the retention times and 2.01-7.41% for the peak areas. The quantitative analysis of 4-aminoantipyrine was accomplished in the range of 0.01-0.50 mg/mL with the linear correlation coefficient of 0.9995 and limit of detection of 14.7 fmol. Compared with CE-ESI-MS, the ion suppression effects of nonvolatile salts and detergents were efficiently minimized. The signal intensity remained constant when the concentrations reached 100 mM for sodium borate and 30 mM for SDS (in 30 mM sodium borate buffer). In addition, the proposed method was successfully applied to the detection of the endogenous caffeine in Chinese white tea.

Hyperspectral Nanoscale Imaging on Dielectric Substrates with Coaxial Optical Antenna Scan Probes.

We have demonstrated hyperspectral tip-enhanced Raman imaging on dielectric substrates using linearly polarized light and nanofabricated coaxial antenna tips. A full Raman spectrum was acquired at each pixel of a 256 by 256 pixel contact-mode atomic force microscope image of carbon nanotubes grown on a fused silica microscope coverslip, allowing D and G mode intensity and D-mode peak shifts to be measured with ∼20 nm spatial resolution. Tip enhancement was sufficient to acquire useful Raman spectra in 50-100 ms. Coaxial scan probes combine the efficiency and enhanced, ultralocalized optical fields of plasmonically coupled antennae with the superior topographical imaging properties of sharp metal tips. The yield of the coaxial tip fabrication process is close to 100%, and the tips are sufficiently durable to support hours of contact-mode force microscope imaging. Our coaxial probes avoid the limitations associated with the "gap-mode" imaging geometry used in most tip-enhanced Raman studies to date, where a sharp metal tip is held ∼1 nm above a metallic substrate with the sample located in the gap.

Scanning probe energy loss spectroscopy with microfabricated coaxial tips

We report scanning probe energy loss spectroscopy (SPELS) measurements of a graphite surface taken with microfabricated coaxial tips. The SPELS spectra of graphite obtained with a grounded coaxial tip show the $\ensuremath{\pi}$ and $\ensuremath{\sigma}$ plasmon peaks and intense secondary electron emission (SEE) peaks. In comparison, spectra taken with a simple Au cathode tip also showed the $\ensuremath{\pi}$ and $\ensuremath{\sigma}$ plasmon peaks but much weaker SEE peaks. The enhanced collection of secondary electrons enables the unoccupied band structure of the surface (i.e., above ${E}_{\text{vac}}$) to be explored.

Fabrication of co-axial field emitter tips for scanning probe energy loss spectroscopy

We report on the fabrication of a co-axial tip for application to scanningprobe energy loss spectroscopy (SPELS). The device consists of a 23.3 µm tall tip on a 76 µm tall mesa with amultilayer Si/Au/HfO2/Au structure;the outer Au and HfO2 layers are stripped from the apex of the tip. The inner Au layer is used as a field emittinglayer and the outer Au layer is grounded to screen the electric field between the tip and thesubstrate. The co-axial tip shows comparable field emission characteristics to electrochemicallyetched tungsten tips. The SPELS spectra of graphite obtained with the new tips showπ andσ plasmon peaks and intense secondary electron emission peaks. It is anticipated that suchco-axial tips will present a significant advantage for future angular resolved SPELSmeasurements.

Fabrication and characterization of coaxial scanning near-field optical microscopy cantilever sensors

A process scheme for the fabrication of scanning near-field optical and force microscopy cantilever sensors with coaxial tips is presented. A hollow fourfold pyramidal tip is used, coated from both sides by 100 nm aluminium. Focused Ion Beam milling is performed to structure the tips. First measurements on a model system demonstrate the performance of these sensors.

Mode Matching Analysis of a Tapered Coaxial Tip in a Parallel-Plate Waveguide

A tapered coaxial tip in a parallel plate waveguide is investigated. A boundary-value problem of electromagnetic scattering from a tapered coaxial monopole is solved rigorously based on the Fourier transform, eigenfunction expansion, and mode matching. Scattering parameters are represented in a series and computed to understand the behavior of the scattering in terms of the coaxial tip geometry.

Process for scanning near-field microwave microscope probes with integrated ultratall coaxial tips

The authors report a process for constructing a scanning near-field microwave microscope (SNMM) probe based on microelectromechanical systems technology. The SNMM probe is capable of performing as a multifunctional scanning probe microscope. Mechanically, it consists of a diving-board-like cantilever with an integrated, ultratall (>50μm) silicon tip and is interchangeable with typical commercial atomic force microscope probes. Electrically, it employs a coplanar waveguide running from the contact pads on a high-resistivity silicon chip body onto the cantilever and out to the ultratall coaxial tip at the free end of the cantilever. The ultratall coaxial tip functions as an electrically small antenna for scanning microwave microscopy applications, as well as simultaneously permitting atomic force microscopy to be carried out. The fabrication procedure and results are described, along with preliminary microwave measurements.

Measurements of air discharges from insulating, electrostatic dissipative and conductive materials with different ESD probes

In this work, we have compared the performance of three different kinds of passive resistor-transmission line ESD probes: an unshielded ball probe, a shielded ball probe with the ESD current collected on a coaxial wire tip, and a needle-like probe. We have measured discharges from ESD sources having different surface resistivities including charged insulator surfaces, electrostatic dissipative materials and metal plates. In compliance with the results, there is no single probe type that is ideal for all kinds of situations—there are significant differences between the probe responses comprising sensitivity, charge transferred and peak ESD current. As expected, the initiation of air discharges was suppressed in accordance with increasing surface resistivity of the ESD source.

Design and Fabrication of Scanning Near-Field Microwave Probes Compatible With Atomic Force Microscopy to Image Embedded Nanostructures

Design, fabrication, and characterization of near-field microwave scanning probes compatible with an atomic force microscope (AFM) for imaging of embedded nanostructures are discussed. The microwave probe discussed here bridges the frequency gap between the existing local probe microscopy systems, and enables localized microwave spectroscopy and imaging of molecules and nanostructures. The probe consists of a coaxially shielded heavily doped silicon tip, and an aluminum (Al) coplanar waveguide. The coaxial tip structure was formed by a thick photoresist and plasma etching process, enabling the silicon apex to protrude through a well-defined aperture in the Al layer. Using this technique, probes with 10-/spl mu/m-high coaxial tips of 5-nm apex radius and 500-nm aperture radius were realized. The aperture confines the electromagnetic fields in the exposed tip region, allowing microwave measurements with high spatial resolution. The mechanical and electrical characterizations of the microwave probes were performed to ensure their compliance with the requirement of an AFM, as well as that of the microwave measurements. Finally, simultaneous AFM and microwave imaging of standard AFM samples with grid structures was performed for the first time. The lateral spatial resolution of the microwave scans was approximately 50 nm at 2.8 GHz, compared to 100 nm for the AFM scans. The ability of the microwave signal to penetrate inside the sample opens new possibilities in hyperspectral and multimodal imaging of nanostructures. Correlations between AFM images and the microwave images enable proper registration and referencing of the microwave properties to landmarks in the topographic AFM images.

Microfabricated silicon coaxial field sensors for near-field scanning optical and microwave microscopy

We report a comprehensive process for fabricating silicon-based near-field electromagnetic antennas that are used with scanning force microscopy (SFM), and we also present initial results from measurements made with these tips. We present processes to make coaxial and diode tips. In both processes, anisotropic reactive ion etching (RIE) is used to define the tip and special resist spinning protocols are used to create sub-micrometer openings. One process results in a shielded coaxial tip structure used for electric field imaging in the microwave regime. By varying a few steps, Schottky diode junctions are formed at the tips and can act as optical sensors. The resulting tip opening is in the range of 100 nm for photodiode tips and 500 nm for open-ended coaxial tips. We have integrated such tips with the appropriate cantilevers, chip bodies, electrical interfaces and probe station necessary for routine experimental application. We show experimental data using both types of tips.

Coaxial probes for scanning near-field microscopy.

This paper deals with the development of coaxial aperture tips integrated in a cantilever probe for combined scanning near-field infrared microscopy and scanning force microscopy. A fabrication process is introduced that allows the batch fabrication of hollow metal aperture tips integrated on a silicon cantilever. To achieve the coaxial tip arrangement a metal rod is deposited inside the hollow tip using the focused ion beam technique. Theoretical calculations with a finite integration code were performed to study the transmission characteristics of coaxial tips in comparison with conventional aperture probes. In addition, the influence of the geometrical design parameters of the coaxial probe on its optical behaviour is investigated.

The coaxial tip as a nano-antenna for scanning near-field microwave transmission microscopy

A novel scanning-probe setup is reported that maps the complex transmission of microwaves. Response to topographic features as small as 15 nm was observed. The sharpened coaxial probe tip serves as a microwave antenna and, at the same time, as a tunnel tip to warrant precise distance control by STM (scanning tunneling microscope) feedback. The instrument can be applied to map the microwave conductivity of, e.g. thin films or low-dimensional semiconductors. Consequences for the development of an infrared microscope are outlined.

Extreme sub-wavelength resolution with a scanning radio-frequency transmission microscope

By scanning a metal grid sample between two coaxial transmission line tips, we resolve Δx ≈ 10 μm features using up to λ = 20 m wavelengths, achieving wavelength-relative resolution Δx λ < 5 × 10 −7 in both magnitude and phase. As an example of the technique's quite general application to conductivity-contrast microscopy, we measure the local transmittance of a GaAs AlGaAs heterostructure versus magnetic field. We view this work as a proof-of-principle experiment which justifies scaling down the coaxial tip geometry to the sub-micrometer regime.