The field of implant systems is recently entering a new area of integrating drug delivery coating on the surface of the implant material to improve biocompatibility, treat possible inflammation, and resist bacterial infection.¹ These factors remain an intractable problem to a successful implant application. The conventional drug delivery route is inefficient in addressing these challenges due to its inherent limitation such as lack of selectivity, toxicity, short circulation time, and sometimes poor patient compliance.² The coating of nanoporous/nanotubular material on the implant is currently been investigated as a solution to achieving improved biocompatibility and the loading of drugs into these structures can serve to attain a localized and targeted delivery medium. Here, we present a strategy for improving the drug release characteristics in terms of limiting the undesireable initial burst release and extending the total release time via structral modification of zirconia nanotubes. Furthermore, efforts at improving the antibacterial properties of the coating by decorating with silver nanoparticles were also demonstrated. The modified zirconia nanotubes were characterized via SEM, XPS, and ToF - SIMS, while the drug release properties were monitored via UV - Vis spectroscopy. The depth profile image obtained by combining FIB and ToF - SIMS measuremnt confirms the loading of the drug along the length of the nanotube. These modifications illustrate a simplifiedand effective approach toward optimizing the interface between the host environment and the biomaterial surface to meet the very important criteria of biocompatibility and antibacterial properties.

References

(1) Pioletti, D.; Gauthier, O.; Stadelmann, V.; Bujoli, B.; Guicheux, J.; Zambelli, P.-Y.; Bouler, J.-M. Orthopedic Implant Used as Drug Delivery System: Clinical Situation and State of the Research. Curr. Drug Deliv. 2008, 5 (1), 59–63. https://doi.org/10.2174/156720108783331041.

(2) Losic, D.; Aw, M. S.; Santos, A.; Gulati, K.; Bariana, M. Titania Nanotube Arrays for Local Drug Delivery: Recent Advances and Perspectives. Expert Opin. Drug Deliv. 2015, 12 (1), 103–127. https://doi.org/10.1517/17425247.2014.945418.

Information on hydrogen, carbon and oxygen impurities (atmospheric gas species) introduced during processing and/or ageing is of major importance for a better understanding of semiconductor device lifetime and failure modes. Dynamic SIMS is often used in evaluating the concentration of impurities in solids because of its high sensitivity and depth profiling capabilities with good depth resolution and high throughput. Continuous ion beam sputtering with high density primary beam provides high sensitivity and reduced background contribution from residual gases within the analytical chamber. There is no difference between magnetic sector (MS) and Time of Flight (TOF) SIMS instruments performance as soon as a dynamic SIMS mode is used (continuous sputtering mode). Both the MS-SIMS and TOF-SIMS tools are supplied with UHV analysis chamber with optimized vacuum conditions, minimizing the background level created by residual gases sticking to the sample surface. High density Cs primary ion beam is often used because of high electronegativity of most of light element species, so, the Cs surface retention increases the negative secondary ions yield. Reducing the sputtering energy leads to increased Cs surface retention, thus, the ion yield. At the same time, it increases the surface accommodation of oxygen containing molecular species from the vacuum atmosphere (gettering effect). The variation of Cs retention can be also observed in multi-layered structures depth profiles (e.g. SiGe), when sputter yield is drastically changing from layer to layer. So, the oxygen background varies more than expected from ionization yield variation, observed during the calibration step. A modeling experiment can be performed, allowing us to estimate the background from the vacuum atmosphere. A comparison of continuous sputtering and using an interleaving sputtering mode (TOF or beam blanking) allows a direct measurement of background signal contribution from the vacuum. The difference in sputtering cycle between continuous sputtering mode and interleaving mode produces the time when molecular species were deposited from the vacuum. The difference in the background signal normalized to the sputtering cycle time can be safely subtracted from the depth profile and allows the improvement of the detection limit valid for both dynamic SIMS and TOF-SIMS instrumentation. The problem associated with SIMS data noise treatment is a subject of current study. The statistical analysis of oxygen (hydrogen) detection limits, observed with MS- and TOF-SIMS instruments will be presented.

ToF-SIMS is a very versatile and widely applicable method, but it also has its weaknesses with the most profound one being nonquantitative analysis caused by the matrix effect which also limits the capabilities of depth profiling. Namely, in SIMS depth profiling of thin films, chemically similar layers can be difficult to distinguish between each other and interfaces between them difficult to identify. The reason for this is changes in the ionization yield caused by the changes in the matrix as the chemical composition of the sample differs from layer to layer. This is the same effect that causes non-quantitative surface analysis and matrix-dependent detection limits of the same molecule or element. However, there are different ways of reducing the matrix effect. Most widely applied are laser or electron beam post ionization (SNMS), metal-assisted and matrix-enhanced SIMS, dynamic reactive ionization (DRI) and introduction of gases into the analysis chamber (gas flooding).

We applied the gas flooding approach to reduce the matrix effect and improve depth profiling results, testing different atmospheres such as H₂, C₂H₂, CO and O₂ during the analysis. Only O₂ was previously used, while the other three gases were introduced as a novelty by our group. We achieved the best results with the H₂ both in the field of depth profiling and the quantitative aspect of the results measured with the mass spectra. H₂ atmosphere enables easier and unambiguous differentiation of layers of metals and their oxides, different metals, and alloys with different compositions. Furthermore, the identification of interfaces becomes simpler. We also did not observe a change in the sputter rate during H₂ flooding. [1] Surface roughening caused by the ion bombardment taking place during depth profiling was reduced in the H₂ atmosphere as well. This effect is more evident after sputtering a greater amount of the material and also depends on the chemical composition of the layer of interest. We assume that the most probable reason for this observation is the level of amorphization that happens during the sputtering process. [2] Our last results also show a better correlation between ratios of the SIMS signals from metals in alloys when comparing alloys with different chemical compositions analyzed in the H₂ atmosphere. The O₂ atmosphere also gives better results than UHV conditions, but improvement is less pronounced than in the case of H₂ flooding. These findings bring ToF-SIMS one step closer to becoming at least a semiquantitative method.

[1] J. Ekar, P. Panjan, S. Drev, J. Kovač. ToF-SIMS Depth Profiling of Metal, Metal Oxide, and Alloy Multilayers in Atmospheres of H₂, C₂H₂, CO, and O₂. J. Am. Soc. Mass Spectrom. 2022, 33, 31– 44.

[2] J. Ekar, J. Kovač. AFM Study of Roughness Development during ToF-SIMS Depth Profiling of Multilayers with a Cs⁺ Ion Beam in a H₂ Atmosphere. Langmuir 2022, 38, 12871–12880.

The effects of light particle - electrons, protons, alfa particles - irradiation on silicon have been extensively studied for decades. Irradiation-induced lattice damage has been found to be responsible for N-type doping of silicon, and charge carrier lifetime shortening. The use of protons allows to create deep implanted regions, with lower beam energies and less implantation-induced damage compared to heavier species. Beneficial effects of low/medium dose proton irradiation have been observed for a variety of power devices, such as Fast Recovery Diodes (FRDs), Insulated Gate Bipolar Transistors (IGBTs), Gate Turn-Off (GTO) Thyristors, where improvements of switching properties have been attributed to charge carrier lifetime shortening resulting from irradiation. More recently, attention has been put on multiple proton implantation to achieve a more fine control on device electrical properties, and industrial scaling of the manufacturing process has been taken into consideration during the last years.

The realization of an efficient analysis protocol is of primary importance in this context, and the characterisation of such structures by depth profiling techniques is always required. Spreading Resistance Profiling (SRP) is commonly used to measure electrical depth profiles, and it finds application wherever the implanted species produce modifications of the substrate doping level. It has been found that electrical profiles of proton-implanted silicon resamble implantation-induced defect distribution, as suggested by TRIM numerical simulations. On the other hand, elemental depth profiling of implanted species is usually accomplished by means of Secondary Ion Mass Spectrometry (SIMS), but detection of hydrogen suffers of limitations due to the low secondary ion yield and high contamination levels, which make difficult the detection of the species below 10¹⁸ at/cm³. In addition, dynamic-SIMS analysis becomes challenging when probing deep implants because of instrumental artifacts, such as the so-called crater edge effect. For these reasons, SIMS depth profiling of low/medium dose proton implants is not always feasable and requires a careful optimization of instrumental parameters.

In this study, 8" P-type FZ silicon substrates are implanted with protons in the range 400-1200 KeV at various doses, and hydrogen concentration profiles - beyond 20 μm in-depth - are measured by SIMS with high sensitivity over a wide dynamic range. Successful determination of hydrogen with detection limits down to 10¹⁶ at/cm³ in optimized operating conditions is here demonstrated, and optimization procedure is described in detail. The results are compared with post-annealing SRP electrical profiles and TRIM simulations. A discriminating comparison between single and multiple implants is also discussed. Finally, a measurement strategy to standardize implant conditions and to define an in-line monitoring protocol - important to guarantee repeatability of electrical device performances - is proposed.