Ion beam characterization of advanced luminescent materials for application in radiation effects microscopy

The ion photon emission microscope (IPEM) is a technique developed at Sandia National Laboratories (SNL) to study radiation effects in integrated circuits with high energy, heavy ions, such as those produced by the 88” cyclotron at Lawrence Berkeley National Laboratory (LBNL). In this method, an ion-luminescent film is used to produce photons from the point of ion impact. The photons emitted due to an ion impact are imaged on a position-sensitive detector to determine the location of a single event effect (SEE). Due to stringent resolution, intensity, wavelength, decay time, and radiation tolerance demands, an engineered material with very specific properties is required to act as the luminescent film. The requirements for this material are extensive. It must produce a high enough induced luminescent intensity so at least one photon is detected per ion hit. The emission wavelength must match the sensitivity of the detector used, and the luminescent decay time must be short enough to limit accidental coincidences. In addition, the material must be easy to handle and its luminescent properties must be tolerant to radiation damage. Materials studied for this application include plastic scintillators, GaN and GaN/InGaN quantum well structures, and lanthanide-activated ceramic phosphors. Results from characterization studies on these materials will be presented; including photoluminescence, cathodoluminescence, ion beam induced luminescence, luminescent decay times, and radiation damage. Results indicate that the ceramic phosphors are currently proving to be the ideal material for IPEM investigations.     

Radiation hardness of polysiloxane scintillators analyzed by ion beam induced luminescence

The radiation hardness of polysiloxane based scintillators has been measured by ion beam induced luminescence (IBIL). The light intensity as a function of the irradiation fluence with an He⁺ beam at 1.8 MeV (1.0 μA/cm²) has been measured on undoped polymers synthesized with different amounts of phenyl units and on polysiloxanes doped with two different dye molecules (BBOT and Lumogen Violet) sensitizing the scintillation yield.     

In situ luminescence qualification of radiation damage in aluminas: F-aggregation and Al colloids

Recent work for in situ sequential measurement of ion beam induced luminescence and surface electrical conductivity has identified a correlation between surface electrical degradation and the luminescence for aluminas and sapphire during 45 keV He ion bombardment. Detailed measurements for the initial stages of degradation where rapid changes in the luminescence emission bands occur, have now identified processes related to oxygen vacancy (F centre) aggregation and aluminium colloid production as precursors to measurable surface electrical degradation in the irradiated region. This understanding enhances the possibility of using ion beam induced luminescence as a potential monitoring tool for material evolution and insulator surface degradation during irradiation, not only in ITER and future fusion devices, but also in present experimental reactor materials test programmes.     

Charge sharing in multi-electrode devices for deterministic doping studied by IBIC

Following a single ion strike in a semiconductor device the induced charge distribution changes rapidly with time and space. This phenomenon has important applications to the sensing of ionizing radiation with applications as diverse as deterministic doping in semiconductor devices to radiation dosimetry. We have developed a new method for the investigation of this phenomenon by using a nuclear microprobe and the technique of Ion Beam Induced Charge (IBIC) applied to a specially configured sub-100 μm scale silicon device fitted with two independent surface electrodes coupled to independent data acquisition systems. The separation between the electrodes is comparable to the range of the 2 MeV He ions used in our experiments. This system allows us to integrate the total charge induced in the device by summing the signals from the independent electrodes and to measure the sharing of charge between the electrodes as a function of the ion strike location as a nuclear microprobe beam is scanned over the sensitive region of the device. It was found that for a given ion strike location the charge sharing between the electrodes allowed the beam-strike location to be determined to higher precision than the probe resolution. This result has potential application to the development of a deterministic doping technique where counted ion implantation is used to fabricate devices that exploit the quantum mechanical attributes of the implanted ions.     

Ion beam induced luminescence of polyethylene terephthalate foils under MeV H and He ion bombardment

The evolution of the ion beam induced luminescence (IBIL) of the polyethylene terephthalate (PET) foils was studied under the irradiation of H and He ions of MeV energy. The optical and chemical changes of the samples were also examined by photo-stimulated luminescence and optical absorption measurements after the irradiation. A prominent broad emission peak of IBIL appeared at around 380 nm, and its intensity monotonically decreased during the ion irradiation. The decay curves of the emission intensity were quantitatively explained as a function of the electronic energy deposition of the incident H and He ions. On the contrary, to the decrease of the main emission peak, a growth of new peaks was observed in the wavelengths between 500 and 600 nm.     

Phosphors’ lifetime measurement employing the Time Between Photons method

The Time Between Photons theory (hereafter TBP) is applied to the evaluation of the lifetime of phosphors employed in the Ion Photon Emission Microscope (IPEM). IPEM allows Radiation Effects Microscopy (REM) without focused ion beams and appears to be the best tool for the radiation hardness assessment of modern integrated circuit at cyclotron energies. IPEM determines the impact point of a single ion onto the sample by measuring the light spot produced on a thin phosphor layer placed on the sample surface. The spot is imaged by an optical microscope and projected at high magnification onto a Position Sensitive Detector (PSD). Phosphors, when excited by an ion, emit photons with a particular lifetime, which is important to evaluate. We measured the statistical distribution of the Time Between consecutive detected Photons (TBP) for several phosphors and have been able to link it to their lifetime employing a theory that is derived in this paper. The single-photon signals are provided by the IPEM-PSD, or faster photomultipliers when high-speed materials had to be assessed.     

IBIL在氚增殖材料研究中的应用

在氚增殖材料辐照效应的研究中,离子激发发光(ion beam induced luminescence,IBIL)是一种高效实用的实时分析技术。本文介绍了国外MeV离子束对多种氚增殖材料的IBIL研究。研究表征了样品中的辐照缺陷特征及其演变情况,对辐照缺陷的产生机制进行了讨论,并提出辐照过程中的相关动力学模型。最后,介绍了北京师范大学串列加速器上IBIL装置应用现状,并对IBIL应用在氚增殖材料研究中的前景进行了讨论。     

组合离子技术在硅基材料芯片中的应用

将组合技术和离子束技术结合起来。用于硅基发光材料的研究。用组合离子束技术在硅基材料上制备了６４个直径为２ｍｍ的单元－材料芯片,并对硅基材料芯片各进行了卢瑟辐背散射,质子弹性散射和扫描阴极射一发光特性分析。     

Preliminary Research Results for the Generation and Diagnostics of High Power Ion Beams on FLASH II Accelerator

The preliminary experimental results of the generation and diagnostics of highpower ion beams on FLASH II accelerator are reported, The high-power ion beams presently are being produced in a pinched diode, The method for enhancing the ratio of ion to electron current is to increase the electron residing time by pinching the electron flow, Furthermore, electron beam pinching can be combined with electron reflexing to achieve ion beams with even higher efficiency and intensity. The anode plasma is generated by anode foil bombarded with electron and anode foil surface flashover. In recent experiments on FLASH II accelerator, ion beams have been produced with a current of 160 kA and an energy of 500 keV corresponding to an ion beam peak power of about 80 GW. The ion number and current of high power ion beams were determined by monitoring delayed radioactivity from nuclear reactions induced in a ^12C target by the proton beams, The prompt γ-rays and diode bremsstrahlung X-rays were measured with a PIN semi-conductor detector and a plastic scintillator detector, The current density distribution of ion beam were measured with a biased ion collector array. The ion beams were also recorded with a CR-39 detector.     

Ion bombardment induced surface electrical degradation monitoring by means of luminescence in aluminas

Oxide ceramics for use as electrical insulators in future fusion devices, will be exposed to ionization and displacement damage (neutrons, gammas, ion bombardment). Enhanced oxygen loss due to ion bombardment increases surface electrical conductivity, and at the same time the surface emits light due to ion beam induced luminescence (IBIL). Results for 3 types of α-alumina and sapphire measuring electrical surface conductivity and IBIL as a function of dose at different temperatures between 20 and 200 °C, show a clear correlation between luminescence and surface electrical degradation. This indicates the potential to remotely monitor insulating material degradation not only in ITER and beyond, but also in the more immediate in-reactor experiments required for materials testing. Partial reduction of degradation by heating in air suggests the possibility for in situ recovery of the insulating properties.     

The ion photon emission microscope on SNL’s nuclear microprobe and in LBNL’s cyclotron facility

Radiation effects microscopy (REM) has evolved into an essential tool for the study, diagnostics and remedy of single event effects (SEE) in microelectronics devices, However, we are entering an era where the ion energies of the current systems are becoming inadequate for diagnosing SEE problems in modern ICs due to the great thickness of interlevel dielectric, metallization and passivation layers found on top of the active radiation-sensitive Si. Our solution is the ion photon emission microscope (IPEM), which eliminates the need to focus several GeV heavy ions. A tabletop IPEM is currently in use at Sandia National Laboratories (SNL), operating with alpha particles, and showing 4 μm resolution. We have recently developed a second system, and installed it on one of the SNL nuclear microprobe lines to demonstrate the principle and prove its potential as a portable radiation effects microscope that can be installed at the LBNL GeV cyclotron facility. The microprobe system is currently operating with ～2 μm resolution. The determined advantages of installing a similar system at the LBNL cyclotron facility will be discussed, in addition to recently measured optical characteristics of the various phosphor materials being investigated.     

Axial ion–electron emission microscopy of IC radiation hardness

A new system for performing radiation effects microscopy (REM) has been developed at Sandia National Laboratory in Albuquerque. This system combines two entirely new concepts in accelerator physics and nuclear microscopy. A radio frequency quadrupole (RFQ) linac is used to boost the energy of ions accelerated by a conventional Tandem Van de Graaff–Pelletron to velocities of 1.9 MeV/amu. The electronic stopping power for heavy ions is near a maximum at this velocity, and their range is 20 μm in Si. These ions therefore represent the most ionizing form of radiation in nature, and are nearly ideal for performing single event effects testing of integrated circuits. Unfortunately, the energy definition of the RFQ-boosted ions is rather poor ( a few %), which makes problematic the focussing of such ions to the submicron spots required for REM. To circumvent this problem, we have invented ion electron emission microscopy (IEEM). One can perform REM with the IEEM system without focussing or scanning the ion beam. This is because the position on the sample where each ion strikes is determined by projecting ion-induced secondary electrons at high magnification onto a single electron position sensitive detector. This position signal is then correlated with each REM event. The IEEM system is now mounted along the beam line in an axial geometry so that the ions pass right through the electron detector (which is annular), and all of the electrostatic lenses used for projection. The beam then strikes the sample at normal incidence which results in maximum ion penetration and removes a parallax problem experienced in an earlier system. Details of both the RFQ-booster and the new axial IEEM system are given together with some of the initial results of performing REM on Sandia-manufactured radiation hardened integrated circuits.     

Mapping ion beam induced current changes in a commercial MOSFET

We demonstrate a novel nuclear microprobe imaging and analysis modality for micrometre-scale field effect transistor devices probed with focused beams of MeV ions. By recording the drain current as a function of time during ion irradiation it is possible to identify current transients induced by the passage of single ions through the sensitive structures of the device. This modality takes advantage of the fact that the ionization produced by the passage of a single ion acts in an equivalent way to a transient change in the gate bias which therefore modulates the drain current as a function of time. This differs from the traditional ion beam induced charge technique where the ionization drifts in an internal electric field and induces a single charge pulse in an electrode applied to the device. Instead a richer variety of phenomena are observed, with different time constants which depend on the proximity of the ion strike to the channel of the device. The signals may be used to examine device function, radiation sensitivity or to count ion impacts within the channel.     

First results obtained using the CENBG nanobeam line: Performances and applications

A high resolution focused beam line has been recently installed on the AIFIRA (“Applications Interdisciplinaires des Faisceaux d’Ions en Région Aquitaine”) facility at CENBG. This nanobeam line, based on a doublet-triplet configuration of Oxford Microbeam Ltd. OM-50™ quadrupoles, offers the opportunity to focus protons, deuterons and alpha particles in the MeV energy range to a sub-micrometer beam spot. The beam optics design has been studied in detail and optimized using detailed ray-tracing simulations and the full mechanical design of the beam line was reported in the Debrecen ICNMTA conference in 2008. During the last two years, the lenses have been carefully aligned and the target chamber has been fully equipped with particle and X-ray detectors, microscopes and precise positioning stages. The beam line is now operational and has been used for its first applications to ion beam analysis. Interestingly, this set-up turned out to be a very versatile tool for a wide range of applications. Indeed, even if it was not intended during the design phase, the ion optics configuration offers the opportunity to work either with a high current microbeam (using the triplet only) or with a lower current beam presenting a sub-micrometer resolution (using the doublet-triplet configuration).The performances of the CENBG nanobeam line are presented for both configurations. Quantitative data concerning the beam lateral resolutions at different beam currents are provided. Finally, the first results obtained for different types of application are shown, including nuclear reaction analysis at the micrometer scale and the first results on biological samples.     

离子束诱导电荷显微术的现状与发展趋势

离子束诱导电荷显微术（IBIC）是核子微探针显微成像技术的又一新发展，它具有低束流（fA量级），高效率的特点，已被广泛应用于半导体材料和微电子材料研究中。本文简述了离子束诱导电荷显微术（IBIC）的原理和实验方法，综述了IBIC 研究的现状和进展。     

Ion-luminescence properties of GaN films being developed for IPEM

Radiation effects microscopy (REM) for the next generation integrated circuits (ICs) will require GeV ions both to provide high ionization and to penetrate the thick overlayers in present day ICs. These ion beams can be provided by only a few cyclotrons in the world. Since it is extremely hard to focus these higher-energy ions, we have proposed the ion photon emission microscope (IPEM) that allows the determination of the ion hits by focusing the emitted photons to a position sensitive detector. The IPEM needs a thin luminescent foil that has high brightness, good spatial resolution and does not change the incident ion’s energy and direction significantly. Available organic-phosphor foils require a large thickness to produce enough photons, which results in poor spatial resolution. To solve this problem, we have developed thin, lightly doped n-type GaN films that are extremely bright. We have grown high quality GaN films on sapphire using metal organic chemical vapor deposition (MOCVD), detached the films from the substrate using laser ablation, and made them self-supporting. The smallest foils have 1 mm² area and 1 μm thickness. The optical properties, such as light yield, spectrum and decay times were measured and compared to those of conventional phosphors, by using both alpha particles from a radioactive source and 250 keV ions from an implanter. We found that the GaN performance strongly depends on composition and doping levels. The conclusion is that 1-2 μm GaN film of a 1 mm² area may become an ideal ion position detector.     

Ion beam induced luminescence on white inorganic pigments for paintings

Ion beam induced luminescence (IBIL) has been used for studying the emission features and the radiation hardness of white pigments. In particular, ZnO, gypsum and basic lead sulphate pigments have been analyzed with a 3.0 MeV H⁺ beam at the AGLAE Louvre laboratory. The same pigments mixed with different binders have been also analyzed on a canvas, in order to evaluate the contribution of the binders both to the IBIL spectra and to the radiation hardness. It turns out that the binder affects both the IBIL spectra and the radiation hardness of pigments when the emission bands are related to point defects, as occurs for ZnO.     

The performance of the Ljubljana ion microprobe

In August 2000 the setup of the Ljubljana ion microprobe, based on OM 150 triplet, has been completed. The beam line is installed at the 10° exit port of the 2 MeV Tandetron accelerator. It is equipped with motor driven slits, a precise five-axis goniometer and a spherically shaped measuring chamber with detectors for PIXE, PIGE, PESA, SE and RBS. In order to understand the beam optics along the complete system, consisting of the tandem accelerator and the beam line optical elements, an interactive computer code, based on a linear approximation, has been developed. The program is used both to determine the optimal parameters of the tandem focusing system in its daily use and to develop new beam line configurations. Test measurements performed on a copper grid yielded a spatial resolution of 1.0×1.5 μm² in the high current mode (30–100 pA) and 0.5×0.9 μm² in low current mode (10⁴ counts/s). First analytical results confirmed excellent performance of the new Ljubljana ion microprobe.     

脉冲离子束流聚焦装置的研制

用小型化的质量分析系统进行脉冲离子束流实验研究时,从真空弧离子源中引出的束流脉冲幅度大、能量低,由于空间电荷效应使脉冲束流发散度很大,使得离子束流成分分析的不确定度增大。为克服在有限的空间范围内脉冲离子束流聚焦的困难,研制了一种新的双限束光阑三膜片透镜离子束流聚焦装置。双限束光阑着重减少束流发射度,三膜片透镜则适合小尺度空间的脉冲束流聚焦。计算机模拟的结果符合这种大脉冲离子束流聚焦的设计思想。磁质谱仪应用该聚焦装置后,发散到质量分析器分析盒上的脉冲离子束流幅值从未加聚焦前的115 mA减少至0.06 mA,脉冲离子束流质量分析的不确定度降低。     

释光探源

释光技术用于年龄测定的依据是磷光体能够储存辐射的能量,但磷光体对不同辐射种类的能量吸收效率和释光响应各不相同,因此释光测定年龄这一技术本身要求各种学科知识的支撑,有些知识甚至是本学科都尚未深入研究的。作者简述了释光测年技术的历史,并以自身的实践阐述在对释光的认识过程中所必须具备的知识。还以长石为例,叙述了在自行开发的BG2003释光谱仪上新进行的研究工作。