Ion Charge Compensation Research Articles

System for deposition of diamond like a-C:H films in Ar-C2H2 plasma with ion beam assistance

The paper presents a system which comprises a gas plasma source and an ion source and allows surface treatment of dielectrics due to ion charge compensation by plasma electrons. The ion energy corresponds to the discharge voltage of the ion source. The hardness of a-C:H coatings deposited by the method is up to 40–45 GPa.

Optimal acceleration of ions by laser pulses with a sharp leading edge**Reported at the Conference ‘Laser Optics’, Russia, St. Petersburg, June 2010.

We consider acceleration of ions through the interaction of a laser pulse with a sharp leading edge with nanofilms. At sufficiently large amplitude of the pulse, all the electrons can be expelled from the film, which provides an effective regime of ion acceleration. Limiting the maximum energy of ions can result from the longitudinal reverse motion of electrons to the initial position and by the transverse motion of electrons along the nanofilm surface, which causes the ion charge compensation. The characteristic parameters of the dynamics of ions and electrons in the system are analytically evaluated, which agree well with the results of twodimensional numerical simulations by the particle-in-cell method. Optimisation of the acceleration process by using the analytical estimates makes it possible to select the optimal parameters of the laser pulse and nanofilm. Numerical simulation of ion acceleration at these parameters shows that the maximum energy of ions can be substantially increased.

Electric-field-controlled conductance of “metallic” polymers in a transistor structure

It was recently reported that use of a doped ``metallic'' polymer as the active channel in a field effect transistor structure results in unexpected ``normally on'' transistorlike behavior. We report here the role of ion migration in transistors based on metallic polymer [poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonic acid) (PEDOT:PSS)]. The analysis of the ion flow into the active channel due to the gate voltage suggests that for the transistors studied compensating $\ensuremath{\sim}2$ counterions per 100 dopant molecules suppresses PEDOT conductance up to three orders of magnitude. We determine from the temperature dependence of the conductivity of the active channel that the change in conductance of the active channel is throughout the channel in contrast to confinement of gate field induced charge carriers to the channel/dielectric interface in conventional transistors. The decrease of channel conductance reflects an increase of activation energy of carriers. Therefore, we propose that removal of intermediate hopping sites in the disoriented PEDOT:PSS by a small fraction of ion charge compensation causes carriers to anisotropically hop over longer distance leading to a conductor-nonconductor transition.

Site-selective laser spectroscopy of deuterated SrF2:Er3+

Laser selective excitation and optical absorption of deuterated SrF2:0.05% Er3+ crystals have revealed eight Er3+ ion centers involving D− ion charge compensation, nine new Er3+–F− centers not associated with D− ions and several approximately cubic symmetry Er3+ centers. In contrast to the trigonal symmetry of the principal F− center, the dominant arrangements in the D− ion charge compensation case are derived from a tetragonal symmetry center. Detailed spectroscopic results for the new centers are presented. Fluorescence polarization ratios are listed for three centers ( J, B, and G1) present in either SrF2:Er3+ or CaF2:Er3+ and crystal-field analyses of these, based on assumed trigonal symmetry, are also reported.

Site-selective spectroscopy of hydrogenic sites in CaF2:Er3+ crystals

Laser selective excitation and optical absorption studies of hydrogenated CaF2:0.05% Er3+ crystals have revealed 16 Er3+ ion sites involving H− or D− ion charge compensation. The relative occurrence of these sites can be controlled over a wide range by varying the duration of the hydrogenation treatment. The hydrogenic nature of these sites is established by the observation of local mode absorption lines in the infrared, Er3+ ion electronic line isotope shifts and associated local mode vibronic lines involving the H− and D− ions. Local mode infrared absorption frequencies of four sites are reported for most rare-earth ions. Five new Er3+−F− sites were identified in the laser selective excitation study. For 〈100〉 and 〈111〉 oriented crystals the fluorescence spectra of several of the sites exhibit well-defined polarization which determines their Er3+ ion site symmetries. Symmetry confirmations are also established for the two previously reported single Er3+ ion sites involving fluoride ion compensation. Eleven of the hydrogenic sites reported here are classified into two families, each derived from a single Er3+ ion site of the parent crystal, while three others are attributed to sites of nearly cubic Er3+ ion symmetry. Detailed spectroscopic results for these sites are presented, together with a crystal-field analysis for the C4v symmetry sites and some model assignments.

Zeeman infrared spectra of calcium and strontium fluoride crystals containing cerium and neodymium

Infrared and Zeeman infrared measurements of the tetragonal symmetry cerium fluoride ion and neodymium fluoride ion charge compensation sites in calcium and strontium fluoride are reported. The neodymium results are supplemented by optical absorption and fluorescence measurements. Crystal field analyses successfully account for the observed2F72/(4f1) and4I92/,4I112/(4f3) multiplet crystal field splittings and for the measured Zeeman splitting values.

System for combined SIMS-AES-XPS studies of solids

We have have assembled a system for combined surface and thin film studies by SIMS, AES and XPS. The SIMS and AES investigations are performed in the same UHV chamber, while for XPS measurements the sample is transfered into the XPS system via an isolation valve. The SIMS-AES and XPS units can be operated independently, thus increasing the versatility of the entire instrumentation. The primary ion gun, used for sample erosion, supplies velocity-analyzed ions of either nonreactive or reactive gases at an acceleratiang potential of up to 15 kV. The ion source is differentially pumped. The base pressure in the target chamber after bakeout is in the mid 10−8 Pa. The unique feature of the primary ion column is a movable Einzel lens, which allows the width of the square shaped rastered area to be increased to about 5 mm at 12 keV. The large area scanning capability is required for XPS measurements. The SIMS instrumentation comprises a quadrupole mass spectrometer, a secondary ion energy filter and electronic gating in conjunction with rastering. By use of a capillary the sample can be exposed to a directed flow of oxygen gas (oxygen jet). AES studies are performed by use of a cylindrical mirror analyzer with a coaxial electron gun which is also employed for primary ion charge compensation in SIMS studies of insulators. Both the SIMS systems and the XPS unit can be operated under computer control. The performance characteristics of the complete SIMS-AES-XPS system are described in detail and are illustrated by several examples.