Beam Deflection Method Research Articles

Dynamic force microscopy at high cantilever resonance frequencies using heterodyne optical beam deflection method

We have developed a dynamic force microscope (DFM) with a wideband cantilever deflection sensor using heterodyne optical beam deflection (HOBD) method. The bandwidth of HOBD method is limited only by the maximum frequency for laser power modulation, which can be as high as gigahertz order. This technique allows us to use high cantilever resonance frequencies for improving the sensitivity and time response of DFM. In this letter, basic principle and experimental setup of HOBD method are described. Deflection measurement of a cantilever vibration at about 7MHz is demonstrated. Using this cantilever, DFM imaging with a relatively fast scanning speed is performed.

Micron-scale apparatus for measurements of thermodiffusion in liquids

An ac beam deflection technique for measurements of thermodiffusion in liquid mixtures is described. In comparison to conventional beam deflection methods, the micron-scale geometry of our apparatus speeds up equilibration by a factor of ≈300. Our apparatus and analysis methods are validated with measurements on molecular polystyrene dissolved in toluene. Thermodiffusion experiments on 26 nm polystyrene colloids with carboxyl functionality (COOH) in water yield Soret coefficients of ST=−0.28±0.025 K−1.

An investigation of intercalation-induced stresses generated during lithium transport through Li 1 − δCoO 2 film electrode using a laser beam deflection method

The stress change, Δ σ, generated during lithium transport through the rf sputter-deposited Li 1 − δ CoO 2 film was exactly determined as a function of the lithium stoichiometry, (1 − δ), using a laser beam deflection method (LBDM) combined with cyclic voltammetry, galvanostatic intermittent titration technique and potentiostatic current transient technique. Tensile and compressive stresses were generated during the lithium intercalation and deintercalation, respectively. Δ σ varied remarkably with (1 − δ) in the single-α-phase region as well as in the two-phase region, but it remained almost constant in the single-β-phase region. Δ σ generated during a real potential step between an initial electrode potential and a final applied potential was uniquely specified by (1 − δ). The value of Δ σ coincided well with that value derived from the Δ σ versus (1 − δ) curve (stress transient) measured simultaneously along with the galvanostatic intermittent titration discharge curve. From the comparison between the values of Δ σ measured experimentally and calculated theoretically, it was suggested that Δ σ in the single-α-phase region and the two-phase region originate from the molar volume change of the α-phase and from the lattice parameter mismatch between the α-phase and β-phase, respectively.

Electric dipole polarizabilities of copper clusters.

The static electric dipole polarizabilities of Cu(9)-Cu(61) have been measured via a molecular beam deflection method. The clusters display per-atom polarizabilities that decrease monotonically with size, from approximately 16 A(3) per atom Cu(9-10) to approximately 5 A(3) (Cu(45-61)). Absent are any discernible discontinuities or odd-even alternations due to electronic shell filling or electron pairing effects. For the smallest clusters, the experimental polarizabilities are approximately 3 times larger than those predicted classically for conducting ellipsoids, and approach the classical values only for clusters containing more than approximately 45 atoms.

Effect of liquid film on near-threshold laser ablation of a solid surface

Enhancement of material ablation and photoacoustic excitation by an artificially deposited liquid film in the process of pulsed-laser ablation (PLA) is investigated in this paper. Ablation threshold, ablation rate, surface topography, and acoustic-transient emission are also measured for dry and liquid film-coated surfaces. The physical mechanisms of enhanced ablation in the liquid-assisted process are analyzed at relatively low laser fluences with negligible effect of laser-produced plasma. Particularly, correlation between material ablation and acoustic-transient generation is examined. In the experiment, aluminum thin-films and bulk foils are ablated by Q-switched Nd:YAG laser pulses. The dependence of ablation rate and laser-induced topography on liquid film thickness and chemical composition is also examined. Photoacoustic emission is measured by the probe beam deflection method utilizing a CW HeNe laser and a microphone. In comparison with a dry ablation process, the liquid-assisted ablation process results in substantially augmented ablation efficiency and reduced ablation threshold. The results indicate that both increased laser-energy coupling, i.e., lowered reflectance, and amplified photoacoustic excitation in explosive vaporization of liquid are responsible for the enhanced material ablation.

Tuning of a Ti3+:sapphire laser by an electro-optic beam deflection method.

A wavelength-switching method for tuning a self-injection-seeded Ti3+:sapphire laser that uses an electro-optic beam deflection technique is reported. A LiNbO3 prism was employed in a tuning arm of the dual-cavity Ti3+:sapphire laser, and wavelength tuning of approximately 94 pm was attained by altering the deflection angle with the application of an electric field of 10 kV/cm to the prism. The spectral characteristics of the output laser were mainly determined by the diffraction grating in the dual-cavity laser, and the electro-optic prism just behaved as a light-beam deflector for the wavelength tuning purpose. This configuration can allow a simple tuning approach where fast and stable electronic wavelength switching is required in a narrow tuning range, on an order between a few tens of picometers to nanometers, without involving any mechanical movement.

On calorimetry by optical beam deflection method

In this work, we analyze different factors that may affect heat measurements, in a device, based on the optical beam deflection method (OBD). We demonstrate that it is possible to improve the heat limit of detection (HLOD) of the device by increasing its sensitivity using a proper cell or a proper monitoring phase. On the other hand, we prove experimentally that the gradient of the refraction index is almost vertical, so it is possible to apply a theoretical model based on one-dimensional heat propagation to predict the temporal behavior and the magnitude of the deflection beam.

Volume and enthalpy profiles of CO rebinding to horse heart myoglobin.

Carbon monoxide binding to myoglobin was characterized using the photothermal beam deflection method. The volume and enthalpy changes coupled to CO dissociation were found to be 9.3+/-0.8 mL x mol(-1) and 7.4+/-2.8 kcal x mol(-1), respectively. The corresponding values observed for CO rebinding have the same magnitude but opposite sign: Delta V=-8.6+/-0.9 mL x mol(-1) and Delta H=-5.8+/-2.9 kcal x mol(-1). Ligand rebinding occurs as a single conformational step with a rate constant of 5 x 10(5) M(-1) s(-1) and with activation enthalpy of 7.1+/-0.8 kcal x mol(-1) and activation entropy of -22.4+/-2.8 cal x mol(-1) K(-1). Activation parameters for the ligand binding correspond to the activation parameters previously obtained using the transient absorption methods. Hence, at room temperature the CO binding to Mb can be described as a two-state model and the observed volume contraction occurs during CO-Fe bond formation. Comparing these results with CO dissociation reactions, for which two discrete intermediates were characterized, indicates differences in mechanism by which the protein modulates ligand association and dissociation.

Photothermal studies of pH induced unfolding of apomyoglobin.

Conformational dynamic and enthalpy changes associated with pH induced unfolding of apomyoglobin were studied using photoacoustic calorimetry and photothermal beam deflection methods. The transition between the native state and the I intermediate was induced by a nanosecond pH jump from o-nitrobenzaldehyde photolysis. Deconvolution of photoacoustic waves indicates two kinetic processes. The fast phase (T < 50 ns) is characterized by a volume expansion of 8.8 ml mol(-1). This process is followed by a volume contraction of about -22 ml mol(-1) (tau approximately 500 ns). Photothermal beam deflection measurements do not reveal any volume changes on the time scale between approximately 100 micros and 5 ms. We associate the volume contraction with structural changes occurring during the transition between the native state and the I intermediate. The lack of any processes on the ms time scale may indicate the absence of structural events involving larger conformational changes of apomyoglobin after the pH jump.

Electric dipole polarizabilities of Nb2–27

The static electric dipole polarizabilities of Nb2–Nb27 have been measured via a molecular beam deflection method. The clusters display per-atom polarizabilities that vary between 5.4±0.3 Å3 per atom (Nb10) to 37.7±0.3 Å3 (Nb13). The factor of ∼7 variation observed in the per-atom polarizabilities is the largest observed for any metal cluster system investigated thus far and implies large size-dependent variations in their electronic and/or geometric structures.

A low-temperature ultrahigh vacuum atomic force microscope for biological applications

We present an atomic force microscope (AFM) for operation at low temperatures under ultrahigh vacuum conditions. It uses the laser beam deflection method to measure the bending of the cantilever. The four quadrant photodiode allows the detection of vertical and lateral forces. The AFM has been developed for studying biological samples. Images of deoxyribonucleic acid plasmids have been obtained in contact mode.

Fabrication of micromechanical mass-sensitive resonators with increased mass resolution using SOI substrate

We have fabricated micromechanical single crystal silicon bridges for mass sensor application using silicon-on-insulator (SOI) substrate. Bridge structures, i.e. both-ends-supported beams, have a 6.3-times higher fundamental resonance frequency compared to one-end-supported cantilevers and, thus, have a higher mass sensitivity. The resonators are driven electrostatically and read out optically by means of the laser beam deflection method. Measurements of the resonator oscillation are in good agreement with the calculated fundamental resonance frequency of 262 kHz in the case shown; however, further improvements for a higher quality factor are required.

Nickel clusters: The influence of adsorbates on magnetic moments

Magnetic moments have been measured for bare, isolated nickel clusters Nin and their association complexes with carbon monoxide, oxygen, and hydrogen using a molecular beam deflection method. The moments measured for bare Nin are in general agreement with those previously reported by Apsel et al. [Phys. Rev. Lett. 76, 1441 (1996)], lying slightly lower overall. It is found that adsorbed carbon monoxide and hydrogen decrease magnetic moments of Nin. The reduction in moments can be substantial for smaller clusters: the moment of Ni8 is decreased by approximately 6 bohr magnetons by a single absorbed CO molecule. In general, the adsorbate-induced changes in magnetic moments diminish with increasing cluster size. The present results are in qualitative accord with previous measurements of the magnetization quenching effects of CO and H on nickel nanoparticles and thin nickel films. Atomic oxygen decreases cluster moments of some nickel clusters and increases those of others, an effect attributed to adsorbate-induced reconstruction. The experimental results are compared to detailed electronic structure calculations of nickel cluster–adsorbate complexes and to the predictions of the semiempirical bond order-rigid band model of Fourier and Salahub [Surf. Sci. 238, 330 (1990)].

Multi-degree-of-freedom displacement measurement system formilli-structures

A new multi-degree-of-freedom measurement system formilli-structures is presented. This methodology is based on optical beamdeflection method and triangulation. It employs a diffraction grating as areflective object, which reflects an incident laser beam into severaldirections. To obtain the pose information of a measured object, the detectingpositions of zeroth- and first-order diffracted rays are measured using threetwo-dimensional detectors. From these values, we can calculatesix-degree-of-freedom displacement through a kinematic analysis. Theperformance was evaluated with resolution, measurement errors and crosstalk.The results show that measurement errors and maximum crosstalk are within ±0.5 µm in translation and ±2''in rotation. As an application, we measuredthe multi-DOF motion of a bimorph type PZT actuator and obtained its frequencyresponse function.

Beam-deflection method of diagnosing impaired vision

We describe a simple method to assign a diagnosis of cataract to patients with obscurely impaired vision as well as to those with mild lens opacities. When the narrowest slit is used in a slitlamp examination, a small beam of light appears on the macula. Routine fundoscopy with the 78.0 diopter lens or a 3-mirror glass is appropriate. If a cataract is present, the beam of light is scattered into several straight lines, distorted lines, or both. This has proved a useful diagnostic tool when the lens appears clear but the patient’s vision is impaired, and extensive examinations such as computer tomography or nuclear magnetic resonance tomography for impaired vision may be avoided. The beam-deflection method uses devices that are generally available and can detect cataract in the early stages of development.

Enhancement of Pulsed-Laser Ablation by Phase Explosion of Liquid

Enhancement of pulsed-laser ablation by an artificially deposited liquid film is presented. Measurements of ablation rate, ablation threshold, and surface topography arc performed. Correlation between material ablation and photoacoustic effect is examined by the optical beam deflection method. The dependence of ablation rate on liquid-film thickness and chemical composition is also examined. The results indicate that photomechanical effect in the phase explosion of liquid is responsible for the enhanced ablation. The low critical temperature of liquid induces explosive vaporization with localized photoacoustic excitation in the superheat limit and increases the ablation efficiency. Experiments were carried out utilizing a Q-swiched Nd:YAG laser at near-threshold laser fluences with negligible plasma effect (up to ∼100 MW/cm).

One — dimensional laser beam steering using frequency detuning in two — wave mixing with a BaTiO 3 crystal

We demonstrate a method of one-dimensional laser beam deflection using frequency detuning in two-wave mixing. Energy exchange between the interfering beams in a photo-refractive BaTiO 3 crystal has been used for deflection of a pump beam into predetermined probe beam directions. A one-dimensional array of several beams is generated from a single probe beam, employing a piezo-mirror and beam splitter combination. Probe beams so produced are detuned by exciting the piezo-mirror with a periodic near-saw-tooth voltage so as to produce running fringes. However, stable holographic gratings are recorded by matching the frequency of the probe beam with that of a pump beam reflected from another vibrating piezo-mirror, thereby controlling the direction of beam deflection.

A CV/PBD coupled study of ionic exchanges at poly(pyrrole) films in phosphate buffered solutions

In order to propose new stable immunosensors with potential applications in the phosphate buffer saline solution (aqueous solution at pH 7.2 containing 0.13 M NaCl and 0.05 M potassium phosphate), poly(pyrrole) films with various counter-anions (chloride, benzene sulfonate, benzene disulfonate and dihydroxybenzene disulfonate) were prepared by electrooxidation of pyrrole in aqueous solutions. The aim of this work was to determine the ion exchange properties of these poly(pyrrole) films during redox transformations, these properties being intimately connected to the probing characteristics of the sensors. To investigate the system thoroughly, the behaviour of the films was studied successively in the three following aqueous media: firstly 0.13 M NaCl, then 0.05 M sodium phosphate at pH 7.2 and finally 0.13 M NaCl+0.05 M sodium phosphate at pH 7.2. This study was carried out by coupling a cyclic voltammetry technique to an optical method which allows the probing of the ionic fluxes in the diffusion layer of an electroactive material (probe beam deflection method). The results show that among all synthesized poly(pyrrole)s, only those with Cl − and dihydroxybenzene disulfonate as counter-anions have reversible redox changes in the phosphate buffer saline solution. In the poly(pyrrole) films with Cl − counter-anions, it is shown that the Cl − anion is the main ion exchanged during redox changes. On the other hand, mainly cationic motion has been found in the poly(pyrrole) films with dihydroxybenzene disulfonate anions.

Thermal and mass diffusion in a semidilute good solvent-polymer solution

The Soret coefficient ST and collective (mass) diffusion coefficient Dc of polystyrene dissolved in the good-solvent toluene has been measured over a range of concentrations and molecular masses with an optical beam-deflection method. Our measurements indicate that ST scales inversely with the polymer translational diffusion coefficient in dilute solutions, exhibits a power-law scaling with polymer concentration, and an independence of polymer molecular mass in semidilute solutions. These findings are consistent with the known scaling of 1/Dc in dilute and semidilute polymer solutions, the relative insensitivity of the thermal-diffusion coefficient Dth of polystyrene in toluene to polymer concentration, and the relation ST=Dth/Dc from irreversible thermodynamics. We are able to represent our ST and Dc data by theoretically motivated reduced-concentration master curves, but the concentration-molecular mass scaling variables are found to be different for each transport property, a result contrary to theoretical expectations. However, the asymptotic concentration scaling exponents deduced from these data fits are compatible with de Gennes’ scaling arguments for Dc and with modern estimates of the chain-size exponent ν for swollen polymers in good solvents.

Residual stress in sputtered gold films on quartz measured by the cantilever beam deflection technique

With resonator applications in mind, the residual stress in sputtered gold electrodes on quartz has been investigated with respect to various deposition rates (2, 10, and 50 A/s), pressures (1.0 and 3.0 10(-3) mbar), deposition temperatures (80 degrees C and room temperature (RT)), film thicknesses (approx. 400 to 800 A), and substrate smoothnesses (lapped and polished), using the cantilever beam deflection method. Samples were monitored for 4 weeks at room temperature followed by 13 weeks of annealing at 85 degrees C. The initial stress (ranging from -180 to -60 MPa) was compressive for all samples but turned tensile (a few megaPascals) in some of the samples after annealing. A significant decrease in initial compressive stress appeared with samples coated at an elevated temperature. From samples prepared at lower pressure and differing only in film thickness and substrate roughness, an increased compressive stress was found in thicker films and on rougher surfaces. The stress relaxation has been fitted to an exponential expression, and an attempt to relate the stress to a frequency shift (typically a few parts per million for ordinary, 100-mum thick AT blanks) has been made. With the help of transmission electron microscopy (TEM) the film morphology was investigated and related to the deposition parameters and aging. Judging from the increase in compressive stress and grain refinement with increased deposition rate and decreased pressure, the atomic peening mechanism is the most likely reason for the induced stress. Rutherford backscattering spectrometry (RBS) was employed to rule out the inclusion of argon (below or around 0.5%) as an explanation. From the vague, but clearly discernible, trend toward faster RT stress relaxation with higher initial stress, together with the finer film morphology, the relief mechanism is believed to be stress-promoted grain boundary diffusion.