摘要:

The analysis of the static deflection of cantilever plates is of fundamental importance in application to the atomic force microscope (AFM). In this paper we present a detailed theoretical study of the deflection of such cantilevers. This shall incorporate the presentation of approximate analytical methods applicable in the analysis of arbitrary cantilevers, and a discussion of their limitations and accuracies. Furthermore, we present results of a detailed finite element analysis for a current AFM cantilever, which will be of value to the users of the AFM.

ISSN:0021-8979    

DOI:10.1063/1.354137

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Bubble dosimeters measure a neutron flux by its effect upon microscopic droplets of superheated liquid encased in a polymer gel. It has been observed that a microwave field can also induce bubble formation in some of the droplets. This article considers the theory of this phenomenon as an effect of a microwave‐induced temperature increase. Although the droplets are superheated, their confinement by a smooth gel surface and lack of impurities such as dust particles allow only homogeneous nucleation to occur. At room temperature the thermal fluctuations that give rise to critical size bubbles are very rare; the dosimeter thus has a long shelf life and a low spontaneous noise level. In the presence of a microwave field, the gel and droplets absorb energy and can be heated by 1–2 K for moderate powers; a high‐power microwave field is needed to produce an observable nucleation rate. The electromagnetic properties of the dosimeter determine the internal field and the microwave absorption. Then the microwave heating and thermal properties of the dosimeter lead to an elevated steady‐state temperature for the droplets. Finally, the nucleation rate is obtained from classical homogeneous nucleation theory, while the number of bubbles formed in an ensemble of droplets is found by a simple statistical argument. Although a special case is considered and several approximations are invoked, the qualitative results show this effect could lead to spurious neutron readings only for intense microwave fields or for an ambient temperature close to the nucleation temperature. For microwave bubble dosimetry, some nonthermal mechanism would be much more useful.

ISSN:0021-8979    

DOI:10.1063/1.354141

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Photopumped laser action in a HgCdTe double‐heterostructure grown by metalorganic chemical vapor deposition on a CdTe substrate containing (311)‐ and (211)‐oriented grains was studied. The (311)‐oriented device exhibited laser action around &lgr;=4 &mgr;m with a threshold power increasing exponentially from 56 mW atT=12 K to 2.8 W at the highest lasing temperature of 90 K. The (211)‐oriented laser device emitted around 2.5 &mgr;m. The threshold power of the (211) device was much higher than that of the (311) one (1.5 W at 12 K) and increased with temperature at a lower rate to 4.8 W at the highest lasing temperature of 110 K. Front illumination photoluminescence from both active and cladding layers of the (311)‐oriented heterostructure was studied as a function of temperature.

ISSN:0021-8979    

DOI:10.1063/1.354133

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Waveguides of high refractive index aluminum garnets have been epitaxially grown on ⟨111⟩‐oriented crystal wafers of yttrium aluminum garnet (Y3Al5O12, YAG) and clad with epitaxial YAG. Epitaxy was by the liquid phase solution growth technique from supercooled mixtures of lead oxide and boron oxide, as is common for the epitaxy of iron garnets. One composition which is particularly suited for waveguides is Tb1.78Lu1.22Al5O12, which has a refractive index at 632.8 nm of about 1.854, as compared with 1.828 for YAG, and has no absorption bands in the visible and near IR spectra. Since aluminum garnets have melting points above 1900 °C, such waveguides should find application in high temperature optical sensors.

ISSN:0021-8979    

DOI:10.1063/1.354147

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

It is shown that the multipulse free‐running ruby laser irradiation ofz‐cut LiNbO3single‐crystalline samples with 400 A˚‐thick Ti deposits results, under certain conditions, in an efficient Ti indiffusion with minimum perturbation. Implanted zones exhibit optical characteristics appropriate for the preparation of optical devices.

ISSN:0021-8979    

DOI:10.1063/1.354154

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Ballistic and diffusive phonon transport under small time and spatial scales are important in fast‐switching electronic devices and pulsed‐laser processing of materials. The Fourier law represents only diffusive transport and yields an infinite speed for heat waves. Although the hyperbolic heat equation involves a finite heat wave speed, it cannot model ballistic phonon transport in short spatial scales, which under steady state follows the Casimir limit of phonon radiation. An equation of phonon radiative transfer (EPRT) is developed which shows the correct limiting behavior for both purely ballistic and diffusive transport. The solution of the EPRT for diamond thin films not only produces wall temperature jumps under ballistic transport but shows markedly different transient response from that of the Fourier law and the hyperbolic heat equation even for predominantly diffusive transport. For sudden temperature rise at one film boundary, the results show that the Fourier law and the hyperbolic heat equation can significantly over‐ or underpredict the boundary heat flux at time scales smaller than the phonon relaxation times.

ISSN:0021-8979    

DOI:10.1063/1.354111

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The unsteady flow of a thin layer of a Maxwell fluid is being considered. The radial speed and the thickness of the film are obtained analytically and numerically. The results obtained by both methods are in agreement.

ISSN:0021-8979    

DOI:10.1063/1.354125

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The cloud of products formed following the detonation of lead azide (LA) contains solid particles. Utilizing a pulsed beam of a neodymium: yttrium aluminum garnet (Nd:YAG) laser, the particles are evaporated and hole burning through the opaque cloud is demonstrated. The characteristics of the hole and of the expanding cloud are monitored in real time by a HeNe beam, high‐speed framing photography and emission of excited Pb atoms. The hole is carried with the cloud and propagates at a constant velocity of 0.5–2.8 km/s, depending on the time and location of burning and given byd(h)/t(h), whered(h) is the distance from the LA sample to the center of the Nd:YAG beam andt(h) is the time from detonation to hole burning. The reduction in the number and size of the particles is monitored by scanning electron microscopy of the deposits formed on a substrate following the detonation. The propagation of the Nd:YAG laser pulse through the cloud is numerically modeled and provides an estimate of the increase in the temperature and the decrease of the size of the particles as a result of the interaction with the laser beam.  

ISSN:0021-8979    

DOI:10.1063/1.355253

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The dispersed emission in the vacuum ultraviolet (VUV) (1200–3000 A˚) from the plasma generated by the interaction of a KrF excimer laser with an Al and a YBa2Cu3O7target has been measured. Emission spectra were collected as a function of distance above the target surface and as a function of laser fluence. The qualitative features of the plasmas from the two different targets were similar. The character of the emission spectra changed from a pseudocontinuous emission at the target surface to discrete emission from singly, doubly ionized species as well as neutrals at distances greater than ∼1.5 mm. The spatial variation indicated two regions: a high‐density sheath along the target where the core emission is close to blackbody; and beyond, a plasma with large opacity emitting a UV spectrum of intensity decreasing fast with distance. Estimates of the plasma temperature and density were between 2 and 4 eV and ∼1018/cm3, respectively.

ISSN:0021-8979    

DOI:10.1063/1.355267

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Neutral molecules and positive ions, extracted directly from the reaction zone during reactive ion etching of silicon in NF3plasma, have been identified by quadrupole mass spectrometry. The main etching end products are SiF4molecules and SiF+3ions. Reactive species that contribute to the etching are atomicFradicals and F+2molecular ions. Most of the positive ions in the plasma hold NF+2ions and this facilitates etching of negatively biased Si by bombardment. Likewise, the kinetic energy of ions that impinge on an electrically grounded surface can be measured by using a cylindrical mirror analyzer. Within a certain range of plasma parameters there are no obvious differences in kinetic energies among the observed ions in the plasma. Under a constant NF3pressure of 6.7 Pa, the characteristic mean ion energy of 4 eV at an rf power of 10 W increases to 20 eV by increasing the rf power to 90 W.

ISSN:0021-8979    

DOI:10.1063/1.355250

出版商:AIP    

年代:1993

数据来源: AIP