Handbook of Modern Coating Technologies

Registration of ion beam-induced luminescence

Registration of MeV ion beam-induced luminescence (IBIL) coupled with PIXE, RBS, or NRA makes it possible to derive information about the chemical nature of various materials. The physical principles behind IBIL are comprehensively described in monograph [9]. The most universal of them is energy transfer from beam ions to valence electrons of atomic structures in a sample, resulting in their excitation. The transition back to the ground state is accompa­nied by IR, visible, or UV radiation.

Ion beams with a current of ~100 pA are used to induce luminescence in SNMPs, bearing in mind the low efficiency of detectors accounting for the spatial resolution of the IBIL method on the order of 0.3 pm. In this context, Ref. [99] is worth mentioning, where the upgraded system for registration of radiation in a range of 300—1000 nm was used and the comparative analysis of photon- and proton-induced luminescence performed. The analysis showed that protons induce more intense luminescence and metastable states. These effects may constitute a basis for a new laser pumping setup. The scope of IBIL applications is rather wide; specifically, the method has been used in biological research at the cellular level [100] and studies of historical artifacts [101] and semiconducting materials [102].

• Single event effects

Methods based on the use of single ions are collectively called single event effects (SEEs). Although such events can be caused not only by ions but also by other types of single impacts on the object being studied (e.g., pulsed electromagnetic radiation or solitary uncharged parti­cles), we shall consider below only individual ions. The most interesting aspect of SEEs is related to the exploitation of civilian and military spacecraft. High-energy particles capable of penetrating deep into microelectronic devices are considered to be the most dangerous form of cosmic radiation. It produces a number of effects responsible for malperformance or com­plete failure of many devices. A classification scheme of such effects is proposed in Ref. [103].

Among the physical phenomena behind equipment failure is the mechanism of charged particle passage through semiconducting materials [104]. As shown earlier, the loss of energy by ions results in the formation of electron—hole pairs, which accounts for the malfunction­ing of a given device, while microstructural defects may cause its complete failure: hence, the importance of radiation resistance of microelectronic instruments and the particular interest in experimental simulation of the related processes.

Miniaturization of microchips and transition to the nanoscale level require the aiming hit of single ions with an energy of tens of microelectron-volts per nucleon exactly in the prede­termined region of the sample. The SNMP appears to be the MIF most suitable for such research. However, it should be borne in mind that the spatial resolution in a low-current mode (presently « 50 nm) is measured at the half-height of the total beam current distribu­tion over the target and that a large enough halo is present. This fact renders difficult direct application of an SNMP, which led some laboratories to modify microprobe facilities designed to study SEEs with single ions [105—107].

Studies of various microelectronic devices operated in a single-ion irradiation mode with the use of an SNMP were reviewed in Refs. [108,109]. The authors considered Si—Ge hetero­bipolar transistors (the cross section of one of them is depicted in Fig. 5—9A). The accumu­lated charge was measured by scanning with single ions along the horizontal direction. Fig. 5—9B shows the dependence of the accumulated charge on the beam coordinate during irradiation by single ions. Clearly the charge accumulated at the collector is significantly higher than at the base, and the physical area for the accumulated charge at the collector is much greater than the analogous base area.

Another field of research in the SEE mode currently underway is radiobiology. Unlike microelectronic devices, living cells must be studied under normal (nonvaccum) conditions, maintaining their vital activity. Moreover, the horizontal motion of ions imparts additional complexity to high-precision ion beam guidance. A traditional setup of cell irradiation with single ions is illustrated by Fig. 5—9C-E.

Of special interest among new, specialized MIFs designed for the study of single-ion irra­diation of living cells are those described in papers [111 —113]. A unique MIF with a vertically positioned PFS of an SNMP has been constructed in Surrey, UK [114]. This unique MIF is intended for the implementation of a cancer cell research project. It is based on a precision tandem electrostatic accelerator and permits in vitro irradiation of 100,000 cells per hour, aiming ions at each individual cell with an accuracy of 10 nm. To date, numerous data on the influence of single ions on living cells have been published (see, e.g., Refs. [115,116]).