Resonance Frequency Detection Research Articles

Vacuum compatible high-sensitive Kelvin probe force microscopy

A vacuum compatible Kelvin probe force microscopy (KPFM) is presented. Difficulties in operating KPFM in a vacuum were overcome by utilizing the direct cantilever resonance frequency detection in the tip height control whereas the indirect resonance frequency detection scheme was used in primordial KPFM. The potential measurement sensitivity was improved by 14 dB compared to that in air. It is due to the increased cantilever Q value and the reduction in the interference from the tip height detection signal because potential measurement is conducted using the cantilever’s second resonance while tip height control was conducted using the first resonance. A silicon wafer whose surface is partially doped with arsenic by ion implantation was observed, and surface potential difference at the junctions were clearly imaged.

Silicon pn junction imaging and characterizations using sensitivity enhanced Kelvin probe force microscopy

We observed the surface potential of silicon pn junctions using a Kelvin probe force microscope whose sensitivity was about five times better than that of a conventional one. It was achieved by three major improvements: electrostatic force detection using the second cantilever resonance, cantilever Q-value enhancement by operating in a vacuum, and direct cantilever resonance frequency detection using the frequency modulation technique. It was demonstrated that the surface potential of the pn junctions made by thermal diffusion varies gradually compared to those made by ion implantation, possibly reflecting their gradual dopant concentration profile.

Three Dimensional Simulation of the Acoustic Response of Fruit for Firmness Sorting

A theoretical analysis based on numerical simulation of elastic and viscoelastic fruit subjected to dynamic boundary conditions is presented. The fruit is represented as a three-dimensional continuum of an arbitrary shape satisfying the elastodynamic wave equation and the boundary conditions. The fruit response is obtained by solving these equations using the Boundary Element Method (BEM). The simulation provides a solution to the displacement and traction fields over the surface of the fruit in both time or frequency domains. The analog viscoelastic model is established by applying the correspondence principle. Results obtained from frequency response agree qualitatively with previously published experimental data and corroborate the fact that it is possible to sort fruit for firmness according to their resonance frequencies. It was found that measuring the phase-lag between response and excitation signals, or measuring the traction at the excitation point, allowed the detection of the fruits resonance frequencies. A main advantage of the simulation presented is its realistic description of the non-destructive testing of fruit. It also enables the evaluation of the response at different points on the surface of the fruit. The simulation may be used instead of real fruit in further investigation of the dynamic behavior of fruit for the purpose of firmness sorting.

CW and Pulse Response of a Mechanical Resonator: Numerical Evaluation and Experimental Observations

The response of a finite size mechanical resonator under acoustic excitation has been studied in the “propagating wave” model. The results give a good understanding of the experimental patterns observed in standard `pulse echo' and CW experiments. The formation of modulated pulse echo pattern, observed in coherent pulse/CW technique, has also been analysed in detail and the analysis supports the method of detection of the mechanical resonance frequencies by vanishing the modulation pattern. Moreover, the analysis suggests a method of measuring ultrasonic attenuation constant from the modulated pulse echo pattern. The acoustic velocity and attenuation constants have been measured experimentally using the above technique for Al and Cu single crystal and also for polycrystalline Cu. The measured values of acoustic velocities have been compared with other measurements where available.

High-resolution calcium-43 NMR in solids

The resolution afforded by alkaline earth ion NMR in solution is often insufficient to obtain individual lines for chemically distinct sites, particularly in macromolecular environments (Z-4). The problem inherent in a small chemical shift range of about 70 ppm is aggravated further by broadening associated with the often complex spin relaxation driven by the nuclear electric quadrupole interactions with fluctuating electric field gradients (5). The dynamical part of the broadening may be defeated if the nucleus to be observed is immobilized. The solid-state experiment has been successful on a number of nonintegral spin quadrupole nuclei where the central (+f c-) -1) transition is exploited and the residual second-order quadrupole broadenings are minimized by rapid sample rotation at the magic angle (6-9). However, the possible gain in resolution is made at the cost of decreased sensitivity because only the central transition in a ; or $ manifold is observed (IO). In principle, the loss may be regained using magnetization-transfer methods such as those exploited by Pines, Gibby, and Waugh (II). Double-resonance approaches have been discussed for calcium fluoride (12,13), and a direct detection of calcium-43 reported using adiabatic demagnetization methods at low temperature (14). We report here observation of the high-resolution calcium-43 NMR spectrum using CP-MASS methods which demonstrates the feasibility of the more routine experiment in a noncubic environment and defines several of the critical experimental parameters. Figure 1 shows the CP-MASS calcium-43 NMR spectrum of calcium acetate obtained at 4.7 T using a spectrometer constructed in this laboratory. The relevant experimental parameters are summarized in the caption. The proton-calcium doubleresonance probe employed a Doty Scientific stator and rotor coupled to the proton tuning elements using a half wavelength coaxial line tapped at the proton null point for injection and detection of the calcium-43 resonance frequency. The spectrometer used Amplifier Research (AR-200L) and Henry Radio power amplifiers, Nicolet-GE 1280 data system, and a quadrature receiver built in the laboratory. The phase-shifting circuitry was designed after a very similar version by Robert MacKay, Monsanto Chemical Company. The match for the magnetization transfer was found by changing the power level on the calcium side while keeping the proton field fixed at 46 kHz; the optimum cross-polarization rate was found when the strength of the calcium rf field was approximately the same as that which gave w1 for calcium of 45 kHz in a saturated aqueous solution of calcium chloride. For calcium acetate, optimum contact times were long, in the tens of milliseconds range as shown in Fig. 2.

Pure Quadrupole Resonances in Multibromobenzenes

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Pure Quadrupole Resonances in Multichlorobenzenes

The location and measurement of the nuclear quadrupole resonances of Cl35 in all multichlorobenzenes has been completed with the detection of resonance frequencies in five such compounds. A summary of the data on all the multichlorobenzenes is presented, including these reported for the first time: 1,2,3-trichlorobenzene; 1,3,5-trichlorobenzene; 1,2,3,4-tetrachlorobenzene; 1,2,3,5-tetrachlorobenzene; and pentachlorobenzene. These data indicate that the chlorine resonance frequency acquires frequency increments approximately proportional to the number of ortho chlorine neighbors. This effect may be interpreted primarily in terms of electron induction away from the resonant chlorine, although out of plane bending and double bond character also affect the resonance frequency. A correlation of the chlorine quadrupole frequencies with the Hammett sigma parameter is also given.