摘要:

The transient thermal response of a single spherical particle in a cold quiescent gas is considered when the particle is heated by a sequence of well‐characterized radiation pulses. The equations describing particle heating and cooling are formulated and a numerical solution is presented. The sensitivity of particle temperature as a function of heating pulse, particle, and gas properties is illustrated. Measured temperature histories of single particles suspended in an electrodynamic balance and pulse heated with a CO2laser are presented in support of the analysis. The combination of unique state of the art instrumentation with the heat transfer analysis described results in a powerful new method for characterizing thermophysical properties of materials such as heat capacity and absorptivity.

ISSN:0021-8979    

DOI:10.1063/1.351071

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A two‐dimensional axisymmetric model for materials removal during laser irradiation is presented by taking into account the reflections of the laser beam at the wall of the laser‐induced cavity. Also, the liquid metal flow due to the shear stress at the interface of the assist gas and the liquid metal is studied in this paper. The vaporization of the liquid metal and the melting of the solid substrate at the liquid‐vapor and the solid‐liquid interfaces, respectively, are modeled by applying the Stefan condition at various points on the interfaces. Maximum drilling rate is determined by considering that the laser energy is used only to melt and vaporize the material. The effects of various process parameters such as the laser power, laser beam radius, and the laser pulse‐on time on the cavity depth, the recast layer thickness, and the cavity tapering are examined in this study. It is found that the laser‐induced materials removal process can be described in terms of a single parameter called the ‘‘gross’’ laser intensity.

ISSN:0021-8979    

DOI:10.1063/1.351072

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Experimental results on the propagation and transport efficiency of a 1 MV, 5 kA, 50 ns annular proton beam through a two‐stage linear induction accelerator are presented. The beam is generated in a magnetically insulated diode and propagates with high‐efficiency along a 0.6 T axial magnetic field to a second accelerating gap located 30 cm downstream. The second accelerating gap increases the beam energy to 1.3 MeV. A full‐cusp geometry provides the magnetic insulation in both the diode and the second gap. We report in this paper an 86% (±5%) transport efficiency and an increase of 1.6° in the beam divergence for propagation through the post acceleration gap.

ISSN:0021-8979    

DOI:10.1063/1.351073

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

An analysis based on numerical solutions to the three moments of the Boltzmann equation is presented for magnetron discharges used in plasma processing of electronic materials. A chlorine discharge at 13.56 MHz is studied and the results are compared for discharges with and without the magnetic field. The charged particle densities increase by a factor of 5 and the ionization rate increases by an order of magnitude with the application of a 100 G magnetic field in a 50 mTorr discharge. The sheaths in the magnetron discharge are thin and the sheath electric field decreases with increasing magnetic field. The bulk ohmic heating is the dominant mechanism for power deposition under the conditions investigated here.

ISSN:0021-8979    

DOI:10.1063/1.351074

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A metal block, immersed in the electric field of an electrode, has been used to study the electrostatic discharge phenomenon. Using a high‐speed transient oscilloscope, current wave forms of air discharge across a small fixed gap between the metal block and a current probe have been measured. The combined bandwidth of the measurement setup, including the oscilloscope, cables, connectors, splitter, and the probe, is above 3.5 GHz. The setup is capable of measuring rise time as fast as 100 ps. Voltage change on the metal block was also measured by a low‐speed transient oscilloscope. For a gap of 0.01 cm and a voltage of 1086 V, the observed current wave form of the discharge exhibits a rise time of 300 ps, a peak current of 5.8 A, and a pulse width at half‐height of 770 ps, about 2.6 times the rise time. The existence of a residual voltage on the metal block after each discharge was also observed. Using the Townsend’s &agr; coefficient for the electron multiplication in air, an analytic model and a one‐dimensional numerical model have been developed to explain the wave‐form characteristics and the residual voltage observed.

ISSN:0021-8979    

DOI:10.1063/1.351075

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The enhanced plasma stopping of energetic (MeV/amu) multicharged ions is experimentally confirmed by inserting a fully ionized hydrogen column on a tandem accelerator ion beam line. Relevance to heavy ion driven inertial compression is emphasized. Measured energy losses are quantitatively matched by a theoretical extension of the cold matter stopping formula (Bethe).

ISSN:0021-8979    

DOI:10.1063/1.351076

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Raman scattering and ion channeling techniques were used to investigate the damage in GaAs implanted at room temperature with 100‐keV Si+ions. The ion‐induced damage was analyzed for different ion doses and dose rates (current densities). The development of different damage components was monitored by comparing a Raman signal which is specific to amorphization in GaAs to ion channeling results which are sensitive to small‐volume crystalline defects, as well as to amorphous regions. Raman analysis showed that the rate of growth of the amorphous fraction with implant dose was comparable to the growth rate of the total damage as determined by ion channeling. However, while Raman analysis indicated a weak dependence of damage on dose rate, the ion channeling results showed a substantially stronger dependence. These results demonstrate that the damage morphology in GaAs is dependent upon both dose and dose rate, and that the dose‐rate‐dependent component of the total damage consists primarily of crystalline defects.

ISSN:0021-8979    

DOI:10.1063/1.351077

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The structural and electrical properties of SiO2/Si structures irradiated by high‐energy (≳0.5 GeV) Xe and Ni ions have been investigated. Structural analysis of the irradiated SiO2films, performed with infrared spectroscopy, points to atomic displacements and broken and strained Si—O bonds induced by the irradiation. Using ir data, the damage cross section of the Xe and Ni ions has been deduced. The values are of about 8×10−13and 6×10−14cm2for, respectively, 762 MeV Xe and 551 MeV Ni ions. Electrical measurements of irradiated SiO2/Si structures show an increase of the interface‐state densityDitand of the oxide trapped‐charge densityN0twith the ion fluence. These results are compared with defects induced by heavy‐ion irradiation in bulk silica and by light particle radiation in silicon dioxide. Electrically active point defects have been detected in irradiated silicon and are associated with vacancy complexes.  

ISSN:0021-8979    

DOI:10.1063/1.351078

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Compositional disordering of III‐V compound superlattice structures has received considerable attention recently due to its potential application for photonic devices. The conventional method to induce compositional disorder in a layered structure is to implant a moderate dose of impurity ions (∼1015/cm2) into the structure at room temperature, followed by a high‐temperature annealing step (this process is referred to as IA here). Ion irradiation at room temperature alone does not cause any significant intermixing of layers. The subsequent high‐temperature annealing step tends to restrict device processing flexibility. Ion mixing (IM) is capable of enhancing compositional disordering of layers at a rate which increases exponentially with the ion irradiation temperature. As a processing technique to planarize devices, ion mixing appears to be an attractive technology. In this work, we investigate compositional disordering in the AlGaAs/GaAs and the InGaAs/InP systems using ion mixing. We found that the ion mixing behavior of these two systems shows a thermally activated regime as well as an athermal regime, similar to that observed for metal‐metal and metal‐semiconductor systems. Ion mixing is observed to induce compositional disordering at significantly lower temperatures than that for the IA process. We have compared the two processes in terms of five parameters: (1) irradiation temperature, (2) dose dependence, (3) dose rate dependence, (4) annealing, and (5) ion dependence (including electrical effects and mass dependence). We found that the IM process is more efficient in utilizing the defects generated by ion irradiation to cause disordering. Both the physical mechanism of ion mixing and possible device implications will be discussed.

ISSN:0021-8979    

DOI:10.1063/1.351079

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Under high‐dosage boron implant, the implant condition was found to be important for reducing the transient‐enhanced diffusion of boron in Si and forming shallowp+njunction with good rectifying characteristics as well as high dopant concentration in the diffused region. The BF2+‐implantation resulted in not only an excellent dopant activation but also a reduced anomalous diffusion due to the formation of amorphous layer and the scarce defects underneath the amorphous/crystalline (a/c) interface. The B+‐implanted crystalline samples manifested a poor activation efficiency, and a largely anomalous diffusion at the high temperature with prolonged‐time annealing ascribed to much damage induced by the high‐dose implant. The B+‐implanted pre‐Si+‐amorphized samples also displayed severely transient‐enhanced diffusion in spite of the good dopant activation.

ISSN:0021-8979    

DOI:10.1063/1.351082

出版商:AIP    

年代:1992

数据来源: AIP