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25 Aug 2003

Volume 83, Issue 8, pp. 1497-1679

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 1671 (2003); http://dx.doi.org/10.1063/1.1604161 (3 pages)

Wenyi Cai, Christopher F. Powell, Yong Yue, Suresh Narayanan, Jin Wang, Mark W. Tate, Matthew J. Renzi, Alper Ercan, Ernest Fontes, and Sol M. Gruner
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Electron heating mode transition observed in a very high frequency capacitive discharge

E. Abdel-Fattah and H. Sugai

Appl. Phys. Lett. 83, 1533 (2003); http://dx.doi.org/10.1063/1.1604941 (3 pages) | Cited 36 times

Online Publication Date: 19 August 2003

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The effect of excitation frequency in the 13.56–60 MHz range on the electron energy distribution function (EDF) of capacitively coupled plasma is investigated. Under a fixed rf voltage (50–130 V peak-to-peak) and argon pressure (100 mTorr), a remarkable change in the EDF is observed: a Druyvesteyn type at low frequencies (≃13.56 MHz) evolves into a bi-Maxwellian type in a very high frequency (VHF) above 30 MHz. The transition frequency decreases with increasing the rf voltage. The observed frequency effect on the EDF is tentatively explained in terms of the transition of electron heating mode from the collisional ohmic heating at low frequencies into the plasma surface heating in the VHF range. © 2003 American Institute of Physics.
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52.80.Pi High-frequency and RF discharges
52.20.Fs Electron collisions
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons

Time-resolved electron shadowgraphy for 300 ps laser ablation of a copper film

Yasuaki Okano, Yoichiro Hironaka, Kazutaka G. Nakamura, and Ken-ichi Kondo

Appl. Phys. Lett. 83, 1536 (2003); http://dx.doi.org/10.1063/1.1604946 (3 pages) | Cited 12 times

Online Publication Date: 19 August 2003

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Time-resolved electron shadowgraphy measurement was performed in infrared 300 ps laser ablation of a copper film in order to investigate expanding plasma into vacuum with space-charge separation. The probe-electron pulse was generated by intense femtosecond laser irradiation on a tungsten bulk target. Time-resolved electron shadowgraphs showed evolving “bright” and “shadow” plumes with expanding speeds of 970 and 110 km/s, when the laser intensity was 980 G W/cm2. These are attributed to be space-charge separation field and ion plume, respectively. © 2003 American Institute of Physics.
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52.70.Nc Particle measurements
52.38.Mf Laser ablation
79.20.Ds Laser-beam impact phenomena
52.40.Mj Particle beam interactions in plasmas
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

Eliminating the transit-time instability in large-area electron-beam diodes

M. Friedman, Y. Chan, S. Obenschain, J. D. Sethian, and S. B. Swanekamp

Appl. Phys. Lett. 83, 1539 (2003); http://dx.doi.org/10.1063/1.1605244 (3 pages) | Cited 5 times

Online Publication Date: 19 August 2003

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The electron flow in large-area, space-charge-limited diodes is susceptible to transit time instability. The instability spatially and temporally modulates the electron beam and results in a wide, time-dependent, electron energy distribution and high-power rf emission. The electromagnetic waves that power the instability are guided and amplified in the anode–cathode (AK) region which acts as a parallel-plate transmission line with negative conductance. We investigated how to mitigate this instability in large-area rectangular electron diodes. We found that by slotting the rectangular cathode, along both its axes, with parallel grooves of predetermined depth and periodicity, the AK region was modified into a slow wave structure. The unstable electromagnetic waves are slowed down and attenuated to such an extent that the instability is eliminated and stable electron flow is achieved. © 2003 American Institute of Physics.
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84.47.+w Vacuum tubes

Ion energy and charge state distributions in zirconium nitride arc plasma

Manish Chhowalla

Appl. Phys. Lett. 83, 1542 (2003); http://dx.doi.org/10.1063/1.1606107 (3 pages) | Cited 10 times

Online Publication Date: 19 August 2003

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The charge states and ion energy distributions (IEDs) of cathodic arc zirconium (Zr) plasma in vacuum and in nitrogen are reported. The dominant charge states in vacuum and in nitrogen were found to be Zr4+ and Zr2+, respectively. In addition to Zrn+, N2+ and N+ species along with ionized zirconium nitride (ZrNn+) were also detected. The peak ion energies of all Zrn+ species in vacuum were found to be slightly higher (∼19 eV) than in nitrogen (∼15 eV). The IEDs of N2+ species exhibited two peaks, one at 2–4 eV and the other at ∼15 eV. The dual peaks in the N2+ IEDs indicate that some species are ionized in the plasma and others are emitted from, or near, the surface of the cathode. The peak energies of ZrN2+ and ZrN+ species were found to be ∼15 eV, indicating that they are emitted from the nitrided (“poisoned”) surface of the cathode or the from the dense plasma region above the arc spot. © 2003 American Institute of Physics.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Vp Discharge in vacuum
52.70.Ds Electric and magnetic measurements
52.77.Dq Plasma-based ion implantation and deposition
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