Nanomechanical probing of microbubbles using the atomic force microscope

Atomic force microscopy (AFM) is a versatile mechanical nanosensor that can be used to quantify the mechanical properties of microbubbles (MBs) and the adhesion mechanisms of targeted MBs.

Mechanical properties were investigated using AFM tipless cantilevers to microcompress the MBs. The range of compressive stiffness for biSphere^® was found to be between 1 and 10 N m⁻¹ using a cantilever with a spring constant of 0.6 N m⁻¹. This stiffness was shown to decrease with the MB size in a non-linear fashion. It is also possible to calculate a theoretical Young’s modulus of the shell.

The adhesion properties of targeted lipid based MBs that use avidin–biotin chemistry for the attachment of targeting ligands were also studied. The MBs were attached to poly-l-lysine treated tipless cantilevers with spring constants ranging from 0.03 to 0.1 N m⁻¹. This system interrogated individual cells with pulling cantilever distance of 15 μm, and scan rate at 0.2 Hz. The depth of contact was not larger than 0.4 μm. The targeted MBs provided a significantly larger adhesion to the cells compared to control ones. Average adhesion force was dependent on depth of contact. Analysis of the data demonstrated a single distribution of adhesion events with median at 89 pN, which is in agreement with the literature for such interactions.

The nanointerrogation of MBs using AFM provides new insight into their mechanical properties, and should be of assistance to MB design and manufacture.     

Dynamical friction coefficient maps using a scanning force and friction microscope

A novel method to analyze and to distinguish the non-dissipative component from the dissipative frictional component of the lateral force in a Scanning Force and Friction Microscope (SFFM) is worked out and applied to images acquired on various samples. We have determined the twisting spring constants of the cantilevers by computer statical analysis, since they are essential for the quantitative determination but are not provided by the manufacturer. Quantitative results for the _D dynamical friction coefficient images are reported. Comparison with the forward-backward lateral force image subtraction model is made.     

Scanned-cantilever atomic force microscope with large scanning range

A scanned-cantilever atomic force microscope (AFM) with large scanning range is proposed, which adopts a new design named laser spot tracking. The scanned-cantilever AFM uses the separate flexure x-y scanner and z scanner instead of the conventional piezoelectric tube scanner. The closed-loop control and integrated capacitive sensors of these scanners can insure that the images of samples have excellent linearity and stability. According to the experimental results, the scanned-cantilever AFM can realize maximal 100 × 100 (μm) scanning range, and 1-nm resolution in z direction, which can meet the requirements of large scale sample testing.     

Few-electron quantum dot fabricated with layered scanning force microscope lithography

Few-electron quantum dots with integrated charge read-out have been fabricated by layered local anodic oxidation of a Ga[Al]As heterostructure and a thin Titanium top gate. The additional set of gates provided by the metallic film is used to tune the quantum dots into the few-electron regime. Current through the quantum dots and the quantum dot charge have been simultaneously measured for electron numbers varying between zero and two. The singlet–triplet splitting varies in two different samples between 0.5 and 1.5 meV. The Zeeman splitting of the first conductance resonance is observed in parallel magnetic field. The high tunability and straightforward implementation of these structures are promising for future nanostructure design.     

Nanostructuring with laser radiation in the nearfield of a tip from a scanning force microscope

Platinum-carbon multilayer mirrors with a bilayer spacing of 50 Å were fabricated in an ultrahigh vacuum electron beam evaporator. The thermal stability of these multilayers was studied under vacuum annealing using X-ray reflectivity and X-ray diffraction. Up to 450°C, the bilayer spacing increases monotonically accompanied by a gradual increase in crystallite size and grain texture. At 500°C multilayer reflection vanishes, platinum crystallites grow abruptly, and there is a strong texture of platinum in the [220] -plane. Possible reasons for thermally induced structural modifications in these multilayers are discussed.     

Characterization of coating probe with Ti-DLC for electrical scanning probe microscope

In electrical scanning probe microscope (ESPM) applications, the wear and conductivity of the probe are undoubtedly serious concerns since they affect the integrity of the measurements. This study investigates the characterization of Ti doped diamond-like-carbon (DLC) as coating material on a silicon cantilever for ESPM. We deposited a layer of Ti-DLC thin film on the surface of Si cantilever by magnetron sputtering. The morphology and composition of the Ti-DLC films were characterized by scanning electron microscopy and Raman spectroscopy, respectively. We also compared the wear resistance, electric conductivity and scanning image quality of the Ti-DLC-coated probes with those of commercially available conductive probes. The results showed that the electric conductivity and the scanning image quality of the Ti-DLC-coated probes were the same as the commercial conductive probes, while the wear resistance and service life was significantly better.     

Optical fibre profiling using a scanning optical microscope

A scanning optical microscope is used to measure directly the refractive-index profile of an optical fibre. The effects of illuminating the fibre end with a highly convergent beam of light are considered.     

Semiconductor acousto-electric potential detection using a force microscope

Acousto-electric force microscopy (AEFM), developed as a technique for high-resolution mapping of carrier characteristics in solids is described. This technique is based on an acousto-electric voltage (AEV) detection scheme where AEV pulses are obtained from the cantilever deflection caused by the electrostatic force acting between the cantilever tip and the sample surface. AEFM appears to be feasible, but an improved AEV detection scheme is required.     

Determination of elastic constants using a scanning acoustic microscope

A cubic single crystal of GaAs with two polished (100)-surfaces was examined with a scanning acoustic microscope (SAM) in transmission mode. The images of the transmitted ultrasound amplitude measured at frequencies of 350–400 MHz contain sufficient information about the acoustic anisotropy of the crystal to determine the complete set of the three elastic constants C₁₁, C₁₂, C₄₄ numerically. This was done by an interactive fitting procedure correlating simulated images with the measured one. This technique seems to be universally applicable to virtually all sorts of single crystals. Compared to plane wave investigations it saves preparatory labour since one single crystal orientation suffices for a determination of all elastic constants.     

Force-feedback high-speed atomic force microscope for studying large biological systems

We designed and developed a high-speed atomic force microscope (HSAFM) utilizing a force-feedback scheme for imaging large biological samples. The system collects three simultaneous images: a deflection image, a topographic image, and a force image. We demonstrated that this force-feedback HSAFM is capable of acquiring large topographic images of Escherichia coli biofilms at approximately one frame per second in air. We discuss how the self-actuating cantilever and the piezo tube follow those larger biological topographic features during the HSAFM imaging process.     

Tapping mode atomic force microscope combined with reflection scanning near-field optical microscope (AF/RSNOM)

A new kind of scanning probe microscope is introduced in this paper, which is a combination of atomic force microscope and reflection scanning near field optical microscopy (AF/RSNOM) with equi-amplitude tapping mode. The principle and recent experiment result of AF/RSNOM are reported. Besides convenient operation, the bi-functional probe tip of AF/RSNOM brings an even illumination for every sampling position. Experiment result and analysis show that the signal to noise ratio (SNR) of AF/RSNOM optical image is much better than that of other RSNOM without tapping working mode.     

Lifetime measurements with a scanning positron microscope

First lifetime results obtained with a scanning positron microscope will be presented. A pulsed positron beam with a variable energy from 0.5 to 20 keV, with a spot diameter of 2 microm, can be electronically scanned over an area of 0.6x0.6 mm(2). This beam is formed after a double-stage stochastic cooling (moderation) of positrons emitted from a radioactive isotope. Included in the system is a conventional scanning electron microprobe for surface analysis. Three-dimensional positron lifetime spectra of a GaAs sample with a small surface scratch reveal the range due to the mechanical damage.     

On the operating stability of a scanning force microscope with a nanowhisker at the top of the probe

The functioning of the scanning probe microscope cantilever with a metal-carbon whisker at the top is studied. Metal-carbon whiskers grown by focused ion beam deposition in the presence of precursor gases have an aspect ratio in the range α = 10?200 and hold shape upon multiple scanning in the constant force mode. The advantage of probes with whiskers at the top in examining rough surfaces with vertical walls and narrow grooves is demonstrated experimentally. At high α, the scanning probe microscope is found to operate unstably, because the lateral surface of the whisker interacts with the specimen. It is shown that the axis of the whisker should be set normally to the specimen’s surface for the microscope to operate reliably at high aspect ratios.     

Simultaneous imaging of multiple focal planes using a two-photon scanning microscope

Despite all the advances in nonlinear microscopy, all existing instruments are constrained to obtain images of one focal plane at a time. In this Letter we demonstrate a two-photon absorption fluorescence scanning microscope capable of imaging two focal planes simultaneously. This is accomplished by temporally demultiplexing the signal coming from two focal volumes at different sample depths. The scheme can be extended to three or more focal planes.     

Calibration parameters for the probing tip of a magnetic force microscope in the field of a test current loop

The subject of discussion is calibration of the tip of a magnetic force microscope using the field of a ring-shaped current loop. To calculate the calibration parameters, the magnetic contribution from the extended tip of the probe in the field of the current loop to the rigidity of the cantilever is approximated by the contribution from a point magnetic dipole and magnetic “charge” in terms of the theoretical model adopted. Three simplified models of the conic tip (with a sharpened, blunted, and rounded top) are considered. The calculated dependences of the effective calibration parameters on the radius of the current loop are compared with experimental data. It is found that the model of a uniformly magnetized tip in the form of a blunted cone provides the best fit to the experiment. The calculation results may be helpful in simulating images obtained with a magnetic force microscope and numerically testing magnetic objects.     

Optical emission of CdSe nanocrystals induced by the electrical current of a scanning tunneling microscope

Electroluminescence from a single CdSe nanocrystal (NC) excited by the tunneling current of a scanning tunneling microscope (STM) is measured. Such samples produce no plasmon emissions. This allows us to measure pure signals from nanocrystals. The time dependence of electroluminescence differs from the photoluminescence of an identical nanocrystal because of different physical processes of excitation.     

Micromachining of diamond with a near-field scanning optical microscope

Direct-write laser micromachining of diamond on a submicrometer scale with a near-field scanning optical microscope with an uncoated tapered fiber tip has been demonstrated. Micromachined structures can be imaged in situ immediately after modification of the sample. An early stage of the ablation process, which is believed to be conversion of diamond into graphite, has been visualized.