摘要:

A novel instrument has been developed for depositing Langmuir–Blodgett (LB) films composed of alternating molecular monolayers of amphiphilic molecules and adsorbed layers of soluble compounds. The main feature of the deposition method is the possibility to prevent the transfer of the monolayer onto the substrate when dipping up. This can be achieved by keeping the external boundary of the deposited monolayer in contact with the aqueous solution by means of a protecting hydrophilic plate which covers the substrate with the film while still immersed in water. After that, the plate is fixed to the substrate parallel to its surface and both can be transferred to other compartments of the instrument for adsorption of soluble compounds onto the active hydrophilic surface or for deposition of monolayers of other types. Principal design elements, electronics, and software of the LB instrument based on this principle are described. Results on the deposition of LB films composed of alternating monolayers of amphiphilic donor molecules of hexadecylbis(ethylenedithio)tetrathiafulvalene and adsorbed layers of the soluble protein cytochrome P 450sccare reported as an example of the device functioning. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147571

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A new technique of Brewster angle ellipsometry was developed for quantitative evaluation of the Langmuir films extended on water surface. A laser beam withPpolarization is focused onto the film with its main axis at the Brewster angle &thgr;B. The angular distribution of the reflected light is observed by spatial scan of a photodetector. The scan along the direction ofPpolarization for the reflected light gives the angular dependence of the reflectivity ofP‐polarized light, which has a minimum at &thgr;B. The presence of a Langmuir film causes an increase in the minimum reflectivity, from which the quantities such as thickness or density of the adsorbed molecules are obtained. A Langmuir film of stearic acid in its condensed phase was used as a test specimen. The result showed an increase of 2.0×10−6in the minimum reflectivity, determined accurately to 10−7. The curve of reflectivity was in very good agreement with a prediction by a theory of geometrical optics made with the assumption that the index of refraction of the film is equal to that of bulk liquid and that the film thickness is equal to the molecular length. The spatial resolution on the film is ∼100 &mgr;m determined by the focused spot of the laser. This technique has the potential for optical absorption measurement in monolayer film. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147572

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present the design and performance of a temperature‐ and pressure‐controlled sample cell for the small‐angle x‐ray diffraction analysis of lyotropic liquid crystalline materials. The particular requirements for such a system of high resolution, high intensity, and control on sample homogeneity can be particularly well fulfilled using line‐source diffraction. We thus designed a sample cell that will allow the use of a line source. Sample volume is kept small (20 &mgr;l) to keep the contained energy low. The hydrostatic system, based on beryllium x‐ray windows, Bridgman type seals with lead O rings and a stainless‐steel body is rated to achieve pressure control within ±3 bar between 0 and 3000 bar at ramping rates of 30–100 bar/s. Temperature control is achieved within ±0.03 K between room temperature and 180 °C. Maximum heating rates correspond to 0.8 K/s. Control algorithms are implemented on a Microrobotics K4 controller, using a modest amount of computing power. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147573

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In this article, for the necessity of measuring the damping of new materials, a detailed comparison was made between two important free vibration torsion pendulums, that is, the inverted torsion pendulum and the Collette pendulum. Special attention was paid to the strong effect of the torsionally weak suspension in both pendulums on the difference between measured damping of the overall system and the real damping exclusively contributed by the investigated specimen. This difference was successfully quantitatively characterized by a parameter: the sensitivity of the pendulum only via which the accurate damping for the specimen can be determined for each case. The comparison showed that the sensitivities of the two systems obviously behave differently. Although it produces smaller performing strain amplitude on the specimen and has a narrower preset vibration frequency range, the sensitivity of the Collette pendulum is always lower than that of the inverted torsion pendulum. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147574

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A mechanical resonance apparatus has been developed which allows automatic recording of internal frictionQ−1and dynamic Young’s modulusEas a function of temperature. The attainable accuracies &Dgr;Q−1/Q−1and &Dgr;E/Eare approximately equal to 3.5×10−2and 1×10−5, respectively. The vibrating sample is kept at resonance, during heating and cooling, by continuously readjusting the frequency of the driving signal supplied by a computer‐controlled frequency synthesizer. The frequency regulation is obtained by keeping either the amplitude of the response signal at its maximum level or the phase difference between the excitation and vibration signals at a fixed, selected value. In comparison with previous automatic control systems designed for similar applications, the one described here is more versatile, being able to measure internal friction from the width of the resonance curve as well as from the logarithmic decrement of freely decaying vibrations, and being able to regulate the vibration frequency by either the amplitude or the phase control method. The two automatically interchangeable measuring procedures allow recording over wide ranges of the dissipation coefficient (10−5≤Q−1≤10−2),while the two frequency regulation methods permit, according to the requirements, either higher data acquisition rates (phase control approach) or better accuracies (amplitude control approach). Tests carried out on a CuZnAl alloy show good performance of the apparatus during temperature‐induced martensitic transitions, which are associated with large relative changes of frequency and energy dissipation. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147575

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A micro‐thermocouple, made of tungsten versus gold‐0.07% Fe, is used in a scanning tunnel microscopelike setup to measure temperature profiles with submicrometer (100 nm) and submicrosecond (50 ns) resolution on centimeter (cm) area thin film surfaces. The installation is equipped with a new type of three‐directional piezoelectric inertia drive and enables measurements in the temperature range from 4 to 300 K. The thermal conductivity of a 10 &mgr;m gold foil and a silicon wafer (260 &mgr;m) has been measured from 8 to 300 K and the thermal boundary resistances of GE‐7031 varnish and In‐foil, used to mount the samples, were determined. The measured temperature profiles, as a function of time and tip location on the sample, were modeled and fitted by the finite element method. The installation has been designed for mesoscopic temperature profiling to investigate thermal conductivity and diffusivity of thin films, multilayers, and thermal boundary resistances. The results for gold films agree with data reported in the literature. The importance of the boundary resistance (and boundary conditions) in heat flow experiments is emphasized. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147576

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We propose a method to measure heat capacities at low temperature and in high magnetic field. The method is based on an improved version of the thermal relaxation technique and can also be used to measure the nuclear spin‐lattice relaxation timeT1and the nuclear heat capacity. As an example, we present the results of an experiment that measured the electronic heat capacity andT1of pure copper at temperatures below 1 K in a 10 T field. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147523

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A new method has been developed to measure the thermal diffusivity parallel to the surface of a platelike specimen using laser pulse heating. A pulsed laser beam which has a circular cross section is irradiated onto the front surface of the specimen. The time dependence of the temperature response of a circular area on the back surface at a certain distance from the irradiated area is determined using a radiation detector for which the spatial distribution of sensitivity is experimentally determined. The geometry of the apparatus is determined using standard specimens the thermal diffusivity of which is known. For isotropic samples, the values parallel to the surface obtained by the present method agree within 10% with those perpendicular to the surface obtained by the conventional pulse heating method. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147524

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We describe a novel thermal characterization technique based on a differential arrangement, which achieves spatially localized calorimetric analysis. It involves the use of an active probe which acts both as a highly localized heat source and a thermometer. This ability opens the way for the implementation of scanning calorimetric microscopy where image contrast will be created from thermal analysis data. For a number of polymers we have recorded events such as glass transitions, meltings, recrystallizations and thermal decomposition within volumes of material estimated at a few &mgr;m3. The data obtained are compared with those obtained from conventional calorimetry and the events registered in both cases are found to match. For a full quantitative analysis of the results obtained, mathematical modelling of the operation of the technique, taking account of physical and other changes in materials, is required. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147525

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We demonstrate the excitation of strong ruby fluorescence at multimegabar pressures by red incident radiation. We have studied the ruby R1and N2lines to 251 GPa and measured the R1line intensity as a function of pump wavelength. This new method of exciting ruby fluorescence enables easy pressure determination at pressures beyond the 250 GPa limit previously predicted by Ruoff. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147526

出版商:AIP    

年代:1996

数据来源: AIP