Investigations of local electrical properties using tunneling/atomic force microscope with a quartz tuning fork nearfield sensor

Ability to determine local electric surface properties with a high resolution is a key issue in many modern industrial applications. In this article, authors will describe low-cost and reliable methods for investigations of electrical surface properties with a nanoscale resolution using a homebuilt modular tunneling/atomic force microscope with a quartz tuning fork as a probe. We will present the architecture of the designed system and the calibration method of the applied sensor. In our work, the usage of the tunneling atomic force microscope in the high-resolution investigations of the surface topography and identification of local spots where the tunneling current is observed will be demonstrated. We will also present current-voltage (I-V) spectroscopy performed on a gold thin film sputtered on silicon substrate and a highly oriented pyrolitic graphite (HOPG) surface, which we obtained in air ambient and at room temperature.     

Shear-mode magnetic force microscopy with a quartz tuning fork in ambient conditions

We have demonstrated high-resolution shear-mode magnetic force microscopy (MFM) using a quartz tuning fork in ambient conditions. A commercial magnetic cantilever tip was attached to one prong of the tuning fork to realize shear-mode MFM operation. We have obtained MFM images with a spatial resolution of less than 100?nm and demonstrated a frequency resolution of ～1?mHz, values which are achieved by phase shift detection methods.     

Two-section InGaAsP/InP Fabry-Perot laser with a 12 nm tuning range

Wavelength tuning over a 12 nm range is obtained for a two-section InGaAsP/InP Fabry-Perot laser (λ=1.55 μm). The method used to vary the gain profile of the laser allows one to predict the range of possible wavelength tuning. Pis’ma Zh. Tekh. Fiz. 23, 10–15 (March 26, 1997)     

Measuring the interaction force between a tip and a substrate using a quartz tuning fork under ambient conditions

Tuning forks mounted with sharp tips provide an alternate method to silicon microcantilevers for probing the tip-substrate interaction in scanning probe microscopy. The high quality factor and stable resonant frequency of the tuning fork allow accurate measurements of small shifts in the resonant frequency as the tip approaches the substrate. To permit an accurate measure of surface interaction forces, the electrical and piezomechanical properties of a tuning fork has been characterized using techniques derived from scanning probe microscopy. After proper calibration, representative interaction force data for a conventional Si tip and an HOPG substrate are obtained under ambient conditions.     

High-efficiency generation of a continuous-wave single-frequency 780 nm laser by external-cavity frequency doubling

We demonstrated a 670 mW continuous-wave single-frequency laser source at 780 nm by using external-cavity-enhanced second-harmonic generation of a seeded fiber amplifier in periodically poled lithium niobate. A maximum second-harmonic conversion efficiency of 58% was achieved. The source can work stably over 1 h by locking the frequency-doubling cavity, while the power stability is less than 2%.     

Probing near-surface nanoscale mechanical properties of low modulus materials using a quartz crystal resonator atomic force microscope

We describe the development of a technique for making indentations on the top 5-20 nm of the surfaces of relatively low modulus materials using a high spatial and force sensitivity atomic force microscope (AFM) whose optical cantilever has been replaced by a quartz crystal resonator (QCR). Unlike conventional optical-cantilever-based AFMs, the accuracy of this technique is not compromised by the compliance of the loading system due to the high stiffness of the QCR. To obtain material modulus values from the indentation results, we find the commonly used Oliver-Pharr model to be unsuitable because of our use of a sharp tip and relatively deep indentation. Instead, we develop a new analysis that may be more appropriate for the geometry we use as well as the non-linear constitutive behavior exhibited by the materials we examined. We calculated values for the moduli of several different materials, which we find to be consistent with the range of published data.     

Silicon nanowire transistors with a channel width of 4 nm fabricated by atomic force microscope nanolithography

The emergence of an ultrasensitive sensor technology based on silicon nanowires requires both the fabrication of nanoscale diameter wires and the integration with microelectronic processes. Here we demonstrate an atomic force microscopy lithography that enables the reproducible fabrication of complex single-crystalline silicon nanowire field-effect transistors with a high electrical performance. The nanowires have been carved from a silicon-on-insulator wafer by a combination of local oxidation processes with a force microscope and etching steps. We have fabricated and measured the electrical properties of a silicon nanowire transistor with a channel width of 4 nm. The flexibility of the nanofabrication process is illustrated by showing the electrical performance of two nanowire circuits with different geometries. The fabrication method is compatible with standard Si CMOS processing technologies and, therefore, can be used to develop a wide range of architectures and new microelectronic devices.     

Nanoscale operation of a living cell using an atomic force microscope with a nanoneedle

We have developed a tool for performing surgical operations on living cells at nanoscale resolution using atomic force microscopy (AFM) and a modified AFM tip. The AFM tips are sharpened to ultrathin needles of 200-300 nm in diameter using focused ion beam etching. Force-distance curves obtained by AFM using the needles indicated that the needles penetrated the cell membrane following indentation to a depth of 1-2 microm. The force increase during the indentation process was found to be consistent with application of the Hertz model. A three-dimensional image generated by laser scanning confocal microscopy directly revealed that the needle penetrated both the cellular and nuclear membranes to reach the nucleus. This technique enables the extended application of AFM to analyses and surgery of living cells.     

Atomic force microscope cantilever calibration using a focused ion beam

A calibration method is presented for determining the spring constant of atomic force microscope (AFM) cantilevers, which is a modification of the established Cleveland added mass technique. A focused ion beam (FIB) is used to remove a well-defined volume from a cantilever with known density, substantially reducing the uncertainty usually present in the added mass method. The technique can be applied to any type of AFM cantilever; but for the lowest uncertainty it is best applied to silicon cantilevers with spring constants above 0.7?N?m(-1), where uncertainty is demonstrated to be typically between 7 and 10%. Despite the removal of mass from the cantilever, the calibration method presented does not impair the probes' ability to acquire data. The technique has been extensively tested in order to verify the underlying assumptions in the method. This method was compared to a number of other calibration methods and practical improvements to some of these techniques were developed, as well as important insights into the behavior of FIB modified cantilevers. These results will prove useful to research groups concerned with the application of microcantilevers to nanoscience, in particular for cases where maintaining pristine AFM tip condition is critical.     

Thin-film characterization using a scanning laser acoustic microscope with surface acoustic waves

The use of surface acoustic waves in a scanning laser acoustic microscope for the characterization of the mechanical or acoustic properties of thin films deposited on piezoelectric substrates is demonstrated. Quantitative measurements of mass loading effects of 5000-A-thick tungsten films deposited on lithium niobate substrates were obtained using 100-MHz surface acoustic waves. No information about the tungsten film could be obtained using 100-MHz compressional waves. Methods of generating surface waves on nonpiezoelectric materials so that this technique could be used on arbitrary substrates are discussed.     

Fabrication of nanostructure on a polymer film using atomic force microscope

SPM based lithographic techniques have been developed to pattern various substrates such as metals, semiconductors, and organic/polymer films due to its simplicity and high spatial precision nanostructure. Fabrication of nanostructure using polymeric materials is a key technique for the development of nanodevices. Here, we report the fabrication of nanostructures from polyacrylicacid (PAA) and polymethacrylicacid (PMAA) film on a silicon substrate using atomic force microscope (AFM). The formation of the nanopattern from the polymer film was studied using electrostatic nanolithography and the optimization of the conditions for nanopatterning of the polymer film was investigated with respect to the applied potential and translational speed of the AFM tip. The nanostructure of size 28 nm was created using the biased AFM tip on the PMAA film coated on Si(100) substrate and found that this method is a direct and reliable method to produce uniform nanostructures on a polymer film.     

Innovative design of a tunable laser using liquid crystal tuning elements

An innovative non-mechanical and low power consumption tunable external cavity laser (ECL) using liquid crystal tuning elements is proposed. This contains a gain chip, a collimating lens, tuning elements and a partial-reflection mirror. The proposed tunable ECL can achieve both coarse tuning and fine tuning, and it is designed to lase at wavelength matching the International Telecommunication Union (ITU) channels, which is one of the important requirements in optical communication. The tuning elements include an ITU etalon, a liquid crystal Fabry–Pérot interferometer (LC-FPI) and a fine tuner. Only two parameters are required to tune the wavelength over the whole C-band, namely the voltage over the LC-FPI and the fine tuner. This high reliability cost-effective design proposes a theoretical tuning range of about 80?nm. The LC tuning elements including LC-FPI and fine tuner has been fabricated and tested.     

Mechanical characterization of nickel nanowires by using a customized atomic force microscope

A new experimental method to characterize the mechanical properties of metallic nanowires is introduced. An accurate and fast mechanical characterization of nanowires requires simultaneous imaging and testing of the nanowires. However, existing mechanical characterization techniques fail to accomplish this goal due either to the lack of imaging capability of the mechanical test setup or the difficulty of individual alignment and manipulation of single nanowires for each test. In this study, nanowire specimens prepared by an electroplating technique are located on a silicon substrate with trenches. A customized atomic force microscope is located inside a scanning electron microscope (SEM) in order to establish the visibility of the nanowires, and the tip of the atomic force microscope cantilever is utilized to bend and break the nanowires. The ability to visualize the nanowires in an SEM improves the speed and accuracy of the tests. Experimentally obtained force versus bending displacement curves are fitted into existing analytical formulations to extract the mechanical properties. Experimental results reveal that nickel nanowires have significantly higher strengths than their bulk counterparts, although their elastic modulus values are comparable to bulk nickel modulus values.     

Long-path monitoring of NO2 with a 635 nm diode laser using frequency-modulation spectroscopy

In situ monitoring of traffic-generated nitrogen dioxide (NO2) emissions using long-path absorption spectroscopy is reported. High-sensitivity detection of NO2 is achieved by employing two-tone frequency-modulation spectroscopy at a visible absorption band using a tunable high-power diode laser operated around 635 nm. A real-time absorption spectrometer is accomplished by repetitively applying a rectangular current pulse to the diode-laser operating current, allowing detection of isolated NO2 absorption lines. A detection limit of 10 microg/m3 for NO2 at atmospheric pressure using a 160 m absorption path is demonstrated. Continuous monitoring of NO2 over a road intersection at peak traffic is performed.     

Atomic force microscope study of crater formation in ion bombarded polymer

Polyimide Kapton films with a thickness of 62 m were bombarded by Ar+, N+, He+ and D+ ions at energies from 10–50 keV. After bombardment at room temperature, the surface topographic changes of the polymer were investigated using an atomic force microscope (AFM). The most common feature of the ion-bombarded Kapton surface is the formation of craters which often have circular shape and rims. The crater sizes suggest they are unlikely to have been caused by a single ion but by the collective effects including diffusion and trapping of gas atoms and gas molecules in ion-bombarded polymer. A model for the formation of these craters is proposed.     

Lorentz force actuation of a heated atomic force microscope cantilever

We report Lorentz force-induced actuation of a silicon microcantilever having an integrated resistive heater. Oscillating current through the cantilever interacts with the magnetic field around a NdFeB permanent magnet and induces a Lorentz force that deflects the cantilever. The same current induces cantilever heating. With AC currents as low as 0.2 mA, the cantilever can be oscillated as much as 80 nm at resonance with a DC temperature rise of less than 5 °C. By comparison, the AC temperature variation leads to a thermomechanical oscillation that is about 1000 times smaller than the Lorentz deflection at the cantilever resonance. The cantilever position in the nonuniform magnetic field affects the Lorentz force-induced deflection, with the magnetic field parallel to the cantilever having the largest effect on cantilever actuation. We demonstrate how the cantilever actuation can be used for imaging, and for measuring the local material softening temperature by sensing the contact resonance shift.     

Two-colour strong-field ionization and dissociation of H2 using 780 and 390 nm femtosecond pulses

Abstract

We report the observation of a substantial enhancement in H₂ ⁺ and H⁺ ion production when the two-colour (780 and 390 nm) pulses are superposed. A strong dependence of ion yield on the relative directions of the polarization of the two fields is observed. The experimental results are discussed and compared with existing theoretical calculations.     

Direct visualization and identification of biofunctionalized nanoparticles using a magnetic atomic force microscope

Because of its outstanding ability to image and manipulate single molecules, atomic force microscopy (AFM) established itself as a fundamental technique in nanobiotechnology. (1) We present a new modality that distinguishes single nanoparticles by the surrounding magnetic field gradient. Diamagnetic gold and superparamagnetic iron oxide nanoparticles become discernible under ambient conditions. Images of proteins, magnetolabeled with nanoparticles, demonstrate the first steps toward a magnetic analogue to fluorescence microscopy, which combines nanoscale lateral resolution of AFM with unambiguous detection of magnetic markers.