摘要:

General trends in integrated circuit technology toward smaller device dimensions, lower thermal budgets, and simplified processing steps present severe physical and engineering challenges to ion implantation. These challenges, together with the need for physically based models at exceedingly small dimensions, are leading to a new level of understanding of fundamental defect science in Si. In this article, we review the current status and future trends in ion implantation of Si at low and high energies with particular emphasis on areas where recent advances have been made and where further understanding is needed. Particularly interesting are the emerging approaches to defect and dopant distribution modeling, transient enhanced diffusion, high energy implantation and defect accumulation, and metal impurity gettering. Developments in the use of ion beams for analysis indicate much progress has been made in one-dimensional analysis, but that severe challenges for two-dimensional characterization remain. The breadth of ion beams in the semiconductor industry is illustrated by the successful use of focused beams for machining and repair, and the development of ion-based lithographic systems. This suite of ion beam processing, modeling, and analysis techniques will be explored both from the perspective of the emerging science issues and from the technological challenges. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365193

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present experimental and numerical results demonstrating the drastic influence of attractive forces on the behaviour of the atomic force microscope when operated in the resonant tapping tip mode in an ambient environment. It is often assumed that tapping is related to repulsive interaction. In contrast, we find that in general the attractive forces are the most dominant interaction in this mode of operation. We show that attractive forces in combination with the repulsive elastic type of forces cause points of instability in the parameter space constituted by: the cantilever swing amplitude, the frequency bias point, and the distance between the fixed end of the cantilever and the sample. These points of instability can result in disturbances during image acquisition on hard elastic surfaces. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365194

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new microwave generation mechanism involving a scalloping annular electron beam is discussed. The beam interacts with the axial electric field of aTM0nmode in a smooth circular waveguide through the axial free-electron laser interaction, in which the beam ripple period is synchronous with the phase slippage of the rf mode relative to the electron beam. In this paper, we analyze the ripple motion of the electron beam and derive the dispersion relation describing the exponential growth of the rf mode. We calculate the gain for a nominal design and as a function of beam current and ripple amplitude, and show that power gain on the order of 30 dB/m of interaction is achievable. We additionally demonstrate that, under the right conditions, the interaction is autoresonant. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365195

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

This work shows that the electric field enhancement of the plate edges in all-film capacitors has only a very small effect on the current value through the capacitor although this enhancement could lead to dielectric breakdown at low frequency for high voltage. On the other hand, the electric field along the plates depends on frequency and on the resistivity of the plates. Consequently, the surface admittanceYsof the capacitor will also vary with frequency. This latter parameter has been described by an equivalent circuit with lumped elements. Thanks to this equivalent circuit and to previous work, it will be possible to determine with good accuracy the current distribution in metallized capacitors. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365196

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Polarized fluorescence spectra produced by site-selective excitation, and conventional polarized absorption spectra were obtained forTm3+andEr3+ions individually incorporated into single crystals of strontium fluorapatite,Sr5(PO4)3F,also known as SFAP. Substitution of the trivalent rare earth ion for divalent strontium was achieved by passive charge compensation during Czochralski growth of the fluorapatite crystals. Spectra were obtained between 1780 and 345 nm at temperatures from 4 K to room temperature on crystals having the hexagonal structure[P63/m(C6h2)].The polarized fluorescence spectra due to transitions from multiplet manifolds ofTm3+(4f12),including1D2,1G4,and3H4to manifolds3H6(the ground-state manifold),3F4,3H5,3H4,and3F3were analyzed for the details of the crystal-field splitting of the manifolds. Fluorescence lifetimes were measured forTm3+transitions from1D2,1G4,and3H4at room temperature and from1G4at 16 K. Results of the analysis indicate that the majority ofTm3+ions occupy sites havingCssymmetry. A point-charge lattice-sum calculation was made in which the crystal-field components,Anm,were determined assuming that trivalent thulium replaces divalent strontium in the metal site havingCssymmetry. Results support the conclusion that the nearest-neighbor fluoride (F−) is replaced by divalent oxygen(O2−),thus preserving overall charge neutrality and local symmetry. Crystal-field splitting calculations predict energy levels in agreement with results obtained from an analysis of the experimental data. By varying the crystal-field parameters,Bnm,we obtained a rms difference of7 cm−1between 43 calculated and experimental Stark levels forTm3+(4f12)in Tm:SFAP. Absorption and fluorescence spectra are also reported forEr3+ions in Er:SFAP. Measurement of the temporal decay of the room temperature fluorescence from the4I11/2and4I13/2manifolds yielded fluorescence lifetimes of 230±20 &mgr;s and 8.9±0.1 ms, respectively. The experimental Stark levels obtained from an analysis of the spectroscopic data were compared with a crystal-field splitting calculation. The initial set ofBnmparameters forEr3+(4f11)was established from the three-parameter theory and the final set ofBnmparameters obtained forTm3+(4f12)in Tm:SFAP. The best overall agreement between calculated and experimental Stark levels is8 cm−1for 48 Stark levels, representing 12 observed multiplet manifolds ofEr3+(4f11)in Er:SFAP. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365197

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A spectroscopic study of a laser-induced plume created during the welding of stainless steel and other materials (iron and chromium) has been carried out. A pulsed Nd:YAG laser of 1000 W average power is used. The evolutions of the electron temperature and electron density have been studied for several welding parameters. We use working powers from 300 to 900 W and pulse durations between 1.5 and 5 ms. The influence of shielding gases like nitrogen and argon has been taken into account. Temperature and density calculations are based on the observation of the relative intensities and shapes of the emission peaks. We assume that the plasma is in local thermal equilibrium. The temperature is calculated with the Boltzmann plot method and the density with the Stark broadening of an iron line. The electron temperatures vary in the range of 4500–7100 K, electron density between 3×1022and 6.5×1022m−3.The absorption of the laser beam in the plasma is calculated using the Inverse Bremsstrahlung theory. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365198

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Tungsten was deposited on GaAs using a low-temperature laser-chemical vapor deposition process. A KrF excimer laser beam incident perpendicularly on a GaAs surface was found to induce metallic W formation from a gas mixture containingWF6andSiH4at laser energy densities as low as25 mJ/cm2.In-situx-ray photoelectron spectroscopy analysis shows thatSiH4plays an important role in the initiation of metallic W deposition at such low laser energy densities. Scanning electron microscopy of the W films shows a dense and regular columnar structure. Auger depth profiles show that the deposited W is pure. No impurities such as F, C, or O were observed, with a detection limit of 1 at. &percent;, and the interdiffusion between W and GaAs is minimal. X-ray diffraction shows that the W film is mostly in the stable, highly conductive &agr; phase, as confirmed by the low resistivity value of21 &mgr;&OHgr; cm.Metallic W features of 60 &mgr;m on GaAs were obtained by laser direct-projection patterning.I–Vmeasurements show that the W–GaAs structures formed provide good quality Schottky contacts, with an average barrier height of 0.71 eV and an average ideality factor of 1.2. To our knowledge, these are the first Schottky diodes obtained using a laser based resistless projection patterning process on GaAs. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365199

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present a mathematical model to describe the optical phase shift induced by polymer dispersed liquid crystals (PDLCs) on light impinging transversely on the sample. PDLCs are dispersions of liquid crystal microdroplets in a polymeric binder. Droplets appear as optically uniaxial spheres randomly oriented so that the material is optically isotropic. The application of an external electric field results in a reorientation of the liquid crystal and therefore in an electrically controllable optical uniaxicity of the material. The model is discussed by comparison with experimental data and with previous theory [F. Basile, F. Bloisi, L. Vicari, and F. Simoni, Phys. Rev. E48, 432 (1993)]. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365200

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Inversion layers of 2&mgr;m and 30&mgr;m thickness were formed at the negative dipole-end(−c)face of aZ-cut LiTaO3crystal plate by proton exchange followed by heat treatment. The phase velocities of leaky surface acoustic waves (LSAWs) on both the positive(+c)and negative(−c)faces of the plate were measured by line-focus acoustic microscopy versus the angle of propagation, at a frequency of 225 MHz, and the results were compared with theoretical predictions. It is shown that for an inversion layer of 30&mgr;m thickness the phase velocities of LSAWs on the+cand−cfaces are the same, and almost equal to the velocities of the virgin plate. This suggests that the material constants, which are decreased due to the proton exchange, are restored to the original values by the heat treatment. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365201

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report the results of two-dimensional particle simulations (computer experiments) of finite plasma expansion between biased plane parallel electrodes. We show that the simulation produces results consistent with the existing one-dimensional analytical model. While the plasma expansion on the low-potential side is space-charge limited, on the opposite side it is due to ambipolar diffusion. The time-dependent simulated ion current to the electrode exhibits a modulation which has not been experimentally observed. This is identified to be a consequence of the oscillation in sheath front ion density which occurs because of the ion acoustic waves generated during the expansion. This modulation, which is greater at lower ion temperatures and nonuniform with respect to the electrode surface, can be used to estimate the transient number density in the plasma. Modifications to conventional experimental detection circuits which could help in the detection of these waves are presented. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365202

出版商:AIP    

年代:1997

数据来源: AIP