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Atomic defects in high-k materials affect the performance, reliability, variability, and scaling potential of electronic devices. Their characterization is thus of paramount importance, and methods exploiting electrical measurements are highly demanded. In this work we present a novel method for extracting the defect properties from I-V curve hysteresis measured at low electric field in thick metal-insulator-metal (MIM) stacks. The I-V curve hysteresis allows detecting the defects located near the electrode-insulator interfaces and aligned with the stack Fermi level, and extracting their properties. The defects are profiled cross-correlating the information provided by the low-field current hysteresis and the high-field steady-state current. This technique can be applied to MIM stacks fabricated in Back-End-of-Line for capacitors, embedded memories and thin film transistors.

Originally introduced in electronic manufacturing to replace the SiO2 insulating layer, metal oxides are now extensively used in a multitude of electronic devices. Understanding charge transport mechanisms in metal oxides is of paramount importance for device optimization; however, a detailed and self-consistent discussion of electron conduction at all applied electric fields is lacking in the literature. In this work, we investigated the conduction mechanisms in three model systems, Al2O3, HfO2, and Al-doped HfO2 metal-insulator-metal capacitors, determining the path that the electrons travel within the metal oxide. Traps properties are extracted from experimental current-voltage characteristics using the Ginestra® simulation software. Furthermore, the analysis allowed to visualize the location of traps most involved in the conduction and the dominant transport mechanisms at each applied electric field. Despite the different oxide properties, a similar trend was recognized at low electric fields, the electron transport through the oxide is negligible, and the dominant contribution to the measured current is ascribed to the charge/discharge of traps located near the metal/oxide interfaces, leading to displacement currents. At high electric fields, the transport of electrons occurs through the defect rich oxides in the two following ways: if a large density of traps is energetically located near the electrodes Fermi level (as in HfO2), the electrons tunnel from trap to trap until they reach the anode; otherwise, when traps are closer to the conduction band (as in Al2O3 and AlHfO), the electrons tunnel from the cathode into one trap and then into the oxide conduction band, interacting only with traps near the cathode.

In this chapter we present results on system-level integration of memristive devices with neuromorphic circuits and systems. Specifically we present an overview of the current state-of-the-art hybrid memristive-complementary metal–oxide–semiconductor (CMOS) mixed-signal neuromorphic circuits for learning and plasticity and present perspectives toward integration of memristive devices in neuromorphic spiking neural network architectures. We focus on neuromorphic circuits and architectures that allow for a relatively natural integration of memristive devices, irrespective of the specific characteristics of the specific memristive device technology adopted. We address the cointegration of memristive devices with on-chip learning mechanisms, using both analog and digital CMOS circuits, to build a solid background of the functionality of neuromorphic circuits explaining how memristive devices can be implemented on them. Furthermore we also address the system-level integration of such architectures in multicore and multichip systems, for connecting them to input and output devices, such as sensors, actuators, and conventional CMOS processing devices.

Objectives—The aim of this study was to evaluate the application of shear waveelastography (SWE) in the routine management of thyroid nodules, as a possibleadditional tool to the standard sonographic triage.Methods—A total of 248 consecutive patients scheduled for ultrasound-guidedthyroidfine-needle aspiration were included in the study. The presence of a purecolloid lesion was an exclusion criterion. Absolute and relative SWE stiffnessmeasurements on color-coded elastograms, expressed in kilopascals and metersper second, were correlated with radiologic and pathologic features.Results—SWE values in thyroid nodules were significantly higher than normalthyroid tissue (P= .0001), proving the different elastic properties of the patho-logic tissues. Regarding the radiologic characteristics of the nodules, SWE high-est values were associated with the largest lesions (P= .0105) but independentfrom sonographic and Dopplerfindings. The SWE elasticity was not influencedby the characteristics of the biopsy smears. Thefinal correlation between theSWE results and the pathologic diagnoses showed a trend in stiffness fromtender tumors (follicular adenoma) to papillary thyroid carcinoma (P= .016).Conclusions—SWE allows the identification of nodules within normal paren-chyma; however, the present study does not confirm the potential role in differ-entiating between benign and malignant thyroid nodules.

A 107Gb/s net-rate DMT optical signal was generated using a single-mode long-wavelength VCSEL with a modulation bandwidth of 23 GHz. We experimentally demonstrated a total net-rate up to 726.7Gb/s at 1.5μm over 2.5km 7-core dispersion-uncompensated MCF. © 2018 OSA., QC 20181122

We experimentally demonstrate a net-rate 503.61-Gbit/s discrete multitone (DMT) transmission over 10-km 7-core fiber with 1.5μm single mode VCSEL, where low-complexity kernel-recursive-least-squares algorithm is employed for nonlinear channel equalization., QC20190816

A 107Gb/s net-rate DMT optical signal was generated using a single-mode long-wavelength VCSEL with a modulation bandwidth of 23GHz. We experimentally demonstrated a total net-rate up to 726.7Gb/s at 1.5 mu m over 2.5km 7-core dispersion-uncompensated MCF., QC 20180802

100 Gbps/λ/core PAM-4 transmission is successfully demonstrated over 1-km and 10-km single mode 7-core fiber links, enabled by directly modulated 1.5-μm single mode VCSEL of 23 GHz modulation bandwidth with pre- and post-digital equalizations. © 2018 OSA., QC 20181128

We report on our recent work in supporting up to 100 Gbps/λ/core transmissions with a directly modulated 1.5-μm single mode VCSEL and multicore fiber, enabled by low-compleixty pre- and post- digital equalizations., QC 20181022

Spiking neural networks (SNNs) employing memristive synapses are capable of life-long online learning. Because of their ability to process and classify large amounts of data in real-time using compact and low-power electronic systems, they promise a substantial technology breakthrough. However, the critical issue that memristor-based SNNs have to face is the fundamental limitation in their memory capacity due to finite resolution of the synaptic elements, which leads to the replacement of old memories with new ones and to a finite memory lifetime. In this study we demonstrate that the nonlinear conductance dynamics of memristive devices can be exploited to improve the memory lifetime of a network. The network is simulated on the basis of a spiking neuron model of mixed-signal digital-analogue sub-threshold neuromorphic CMOS circuits, and on memristive synapse models derived from the experimental nonlinear conductance dynamics of resistive memory devices when stimulated by trains of identical pulses. The network learning circuits implement a spike-based plasticity rule compatible with both spike-timing and rate-based learning rules. In order to get an insight on the memory lifetime of the network, we analyse the learning dynamics in the context of a classical benchmark of neural network learning, that is hand-written digit classification. In the proposed architecture, the memory lifetime and the performance of the network are improved for memristive synapses with nonlinear dynamics with respect to linear synapses with similar resolution. These results demonstrate the importance of following holistic approaches that combine the study of theoretical learning models with the development of neuromorphic CMOS SNNs with memristive devices used to implement life-long on-chip learning.

Recent advances in integrated opto-electronic devices and front end circuits have made it possible to efficiently transmit very high data rates over optical links for HPC/datacenter applications. This paper reviews our current progress towards serial 100-Gb/s optical interconnects, with emphasis on electrical duobinary (EDB) modulation., QC 20170830

This study compared the diagnostic value of Whole-Body Ultra Low-Dose computed tomography (WBULDCT) with that of Spinal Magnetic Resonance Imaging (SMRI) in identification of spinal bone marrow involvement in patients with Multiple Myeloma (MM). Thirty-five patients with histologically proven MM underwent WBULDCT and dedicated SMRI. Unenhanced WBULDCT was performed on a 256-slice scanner, with 120 kV and 40 mAs. SMRI was performed on a 1·5T magnet, with T1-turbo spin echo and T2-short tau inversion recovery sequences on sagittal plane. WBULDCT was compared with SMRI in terms of lesion detection, pattern and bone marrow involvement. The overall concordance between WBULDCT and SMRI in lesion detection was 76·7%, detecting (25/35) or excluding (8/35) involvement of the axial skeleton, while in 2/35 patients WBULDCT and SMRI were discordant in terms of axial skeleton involvement. The concordance in spinal distribution of lesions was 61·6% on cervical, 71·5% on dorsal, 86·4% on lumbar and 94·4% on sacral, while for the pattern of disease, it was 56·1% for the focal and 88·7% for the combined pattern. Cohen's kappa index was 0·85 (P < 0·001) assessing an excellent agreement. WBULDCT represents a useful diagnostic tool in the detection of spinal involvement of MM patients, offering detailed information about extra-axial involvement, which could be potentially missed with dedicated SMRI.

Al:HfO2 is grown on III-V compound substrates by atomic layer deposition after an in situ trimethylaluminum-based preconditioning treatment of the III-V surface. After post-deposition rapid thermal annealing at 700 degrees C, the cubic/tetragonal crystalline phase is stabilized and the chemical composition of the stack is preserved. The observed structural evolution of Al:HfO2 on preconditioned III-V substrates shows that the in-diffusion of semiconductor species from the substrate through the oxide is inhibited. Al-induced stabilization of the Al:HfO2 crystal polymorphs up to 700 degrees C can be used as a permittivity booster methodology with possibly important implications in the stack scaling issues of high-mobility III-V based logic applications.

For the fabrication of n-type metal-oxide-semiconductor field-effect transistor based on high mobility III-V compound semiconductors as channel materials, a major requirement is the integration of high quality gate oxides on top of the III-V substrates. A detailed knowledge of the interface between the oxide layer and the substrate is mandatory to assess the relevance of interdiffusion and related defects, which are detrimental. Here we grow high dielectric constant (k) Al:MO2 (M = Hf, Zr) gate materials on In0.53Ga0.47As substrates by atomic layer deposition, after an Al2O3 pre-treatment based on trimethylaluminum is performed to properly passivate the substrate surface. Time of flight secondary ion mass spectrometry depth profiles reveal not only the film integrity and the chemical composition of the high-k oxide but also well elucidate the effect of the Al2O3 pre-treatment on Al:MO2/In0.53Ga0.47As interface. Even though the chemical profile is well defined in both cases, a broader interface is detected for Al:ZrO2. X-ray photoemission spectroscopy evidenced the presence of As3+ states in Al:ZrO2 only. Accordingly, preliminary capacitance-voltage measurements point out to a better field effect modulation in the capacitor incorporating Al:HfO2. Based on the above considerations Al:HfO2 looks as a preferred candidate with respect to Al:ZrO2 for the integration on top of In0.53Ga0.47As substrates.

The role played by electric dipoles at the interface Al2O3/In0.53Ga0.47As(001) has been investigated in a whole in situ approach by means of scanning tunneling microscopy/spectroscopy and X-ray photoelectron spectroscopy (XPS) in order to study local and macroscopic features, respectively. The initial pinned Fermi level (FL) shifts toward midgap after oxide deposition in both (2 x 4) and (4 x 2) reconstructions, while a reconstruction-dependent FL restoring is observed after annealing at 200 degrees C. This behavior is rationalized in terms of formation and suppression of positive charge in the as-grown oxide resulting from in situ XPS of the interface band line up.

We have investigated the atomic layer deposition (ALD) on SiO2 and III-V (i.e., In0.53Ga0.47As) substrates of Al-doped ZrO2 (Al-ZrO2) films. The aim is to benefit from trimethylaluminum-based chemistry as adopted in the ALD of Al2O3 while concomitantly obtaining an improvement in the value of the dielectric constant of the gate stack. An in situ monitoring of the process with spectroscopic ellipsometry was carried out in order to address the formation of the first few monolayers of the films. The correlation with the structural and chemical characterization provides insights about the interface composition upon ALD. A k value of 19 +/- 2 is demonstrated for Al-ZrO2 films deposited on SiO2. The electrical performances of capacitors fabricated on In0.53Ga0.47As including Al-ZrO2 as gate dielectric exhibit encouraging properties compared to those acquired for Al2O3. However, a further optimization of the interface reactivity in order to prevent the formation of undesired In, Ga and As oxidized species appears still needed for the combination of the Al2O3 and ZrO2 ALD processes. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.034203jes] All rights reserved.

Al-doped ZrO2 (Al-ZrO2) films deposited by atomic layer deposition onto silicon substrates and the interface with the TaN metal gate are investigated. In particular, structural properties of as-grown and annealed films in the 6-26 nm thickness range, as well as leakage and capacitive behavior of metal-oxide-semiconductor stacks are characterized. As-deposited Al-ZrO2 films in the mentioned thickness range are amorphous and crystallize in the ZrO2 cubic phase after thermal treatment at 900 degrees C. Correspondingly, the dielectric constant (k) value increases from 20+/-1 to 27+/-2. The Al-ZrO2 layers exhibit uniform composition through the film thickness and are thermally stable on Si, whereas chemical reactions take place at the TaN/Al-ZrO2 interface. A transient capacitance technique is adopted for monitoring charge trapping and flat band instability at short and long time scales. The role of traps nearby the TaN/Al-ZrO2 interface is discussed and compared with other metal/high-k oxide films. Further, analytical modeling of the flat band voltage shift with a power-law dependence on time allows extracting features of bulk traps close to the silicon/oxide interface, which exhibit energy levels in the 1.4-1.9 eV range above the valence band of the Al-ZrO2. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4731746]

In this work we investigate the effect of different III-V surface passivation strategies during atomic layer deposition of Al2O 3. X-ray photoelectron spectroscopy indicates that bare As-decapped and sulfur passivated In0.53Ga0.47As present residual oxides on the surface just before the beginning of the Al2O 3 deposition while the insertion of a Ge interface passivation layer results in an almost oxide free Ge/III-V interface. The study of the initial growth regimes, by means of in situ spectroscopic ellipsometry, shows that the growth of Al2O3 on Ge leads to an enhanced initial growth accompanied by the formation of Ge-O-Al species thus affecting the final electrical properties of the stack. Alternatively, deposition on decapped and S-passivated In0.53Ga0.47As results in a more controlled growth process. The sulfur passivation leads to a better electrical response of the capacitor that can be associated to a lower oxide/semiconductor interface trap density

In this work we present an in situ investigation of the interface composition between an In0.53Ga0.47As substrate and an Al2O3 oxide grown by molecular beam deposition in ultra high vacuum conditions. In the effort to improve the chemical quality of the interface, reduction of semiconductor-oxygen bonding at the interface can be obtained by growing a few thick pure Al layer before starting exposure of the surface to the atomic oxygen flux. Conversely, when a Ge interface passivation layer is intercalated between the semiconductor and the oxide stack, the interface chemistry is governed by Ge reaction with other species (Al, O), leading only to a partial suppression of the interface oxides. © 2010 Elsevier B.V. All rights reserved.

Resistive switching memory (RRAM) based on the redox-induced conductivity change in some metal oxides attracts considerable interest as a new technology for next-generation nonvolatile electronic storage. Although resistance-switching phenomena in several transition metal oxides have been known from decades, the details of the switching mechanisms and the nature of the different resistive states are still largely debated. For nonvolatile memory applications, the scaling potential of RRAMs is the most relevant issue, and understanding the scaling capability of RRAM devices requires a sound interpretation of resistance-switching operation and reliability aspects. This work addresses the scaling dependence of RRAM switching parameters. The dependence on the electrode area and on the size of the conductive filament (CF) responsible for low-resistance memory state is investigated. The RRAM conduction modes depending on CF size are discussed based on temperature dependent resistance analysis. Reset characteristics in different resistance states are explained by a Joule heating model for CF oxidation. (C) 2011 American Institute of Physics. {[doi:10.1063/1.3544499]}

This paper reports a direct observation of resistive switching occurring on the nanoscale within NiO layers deposited on top of a tungsten pillar bottom electrode. Filamentary conduction was evidenced by atomic force microscopy using a conductive tip that enabled performing electroforming and reset operations at nanoscale. In the low resistive state, it is shown that the current is driven by multiple conductive nanometric regions in agreement with the filamentary conduction models. In the high resistive state, conduction originates from weak residual conductive regions remaining after reset operation. Finally, retention measurements performed at the nanoscale demonstrated the persistence of localized conductive regions after more than 30 days.

Atomic layer deposition of Al:ZrO(2) films on In(0.53)Ga(0.47)As substrates is shown to be a promising route to boost the oxide permittivity with respect to Al(2)O(3) gate dielectrics and concomitantly take benefit from the reducing effect of the trimethylaluminum precursor on the In(0.53)Ga(0.47)As surface. We demonstrates that increasing the number of initial Al(2)O(3) cycles in the growth sequence can improve the physical quality and the electrical response of the Al:ZrO(2)/In(0.53)Ga(0.47)As interface while preserving the overall composition of the oxide. (C) 2011 The Japan Society of Applied Physics

In the effort to ultimately shrink the size of logic devices towards a post-Si era, the integration of Ge as alternative channel material for high-speed p-MOSFET devices and the concomitant coupling with high permittivity dielectrics (high-k) as gate oxides is currently a key-challenge in microelectronics. However, the Ge option still suffers from a number of unresolved drawbacks and open issues mainly related to the thermodynamic and electrical compatibility of Ge substrates with high-k gate stack. Strictly speaking, two main concerns can be emphasized. On one side is the dilemma on which chemical/physical passivation is more suitable to minimize the unavoidable presence of electrically active defects at the oxide/semiconductor interface. On the other side, overcoming the SiO2 gate stack opens the route to a number of potentially outperforming high-k oxides. Two deposition approaches were here separately adopted to investigate the high-k oxide growth on Ge substrates, the molecular beam deposition (MBD) of Gd2O3 and the atomic layer deposition (ALD) of HfO2. In the MBD framework epitaxial and amorphous Gd2O3 films were grown onto GeO2-passivated Ge substrates. In this case, Ge passivation was achieved by exploiting the Ge4+ bonding state in GeO2 ultra-thin interface layers intentionally deposited in between Ge and the high-k oxide by means of atomic oxygen exposure to Ge. The composition of the interface layer has been characterized as a function of the oxidation temperature and evidence of Ge dangling bonds at the GeO2/Ge interface has been reported. Finally, the electrical response of MOS capacitors incorporating Gd2O3 and GeO2-passivated Ge substrates has been checked by capacitance–voltage measurements. On the other hand, the structural and electrical properties of HfO2 films grown by ALD on Ge by using different oxygen precursors, i.e. H2O, Hf(OtBu)2(mmp)2, and O3, were compared. Exploiting O3 as oxidizing precursor in the ALD of HfO2 is shown to play a benefi

The composition of GeO2 films grown on Ge has been studied for different molecular deposition processes and after exposure to ambient air. The stoichiometry, the interaction with moisture, and the interfacial details of the films are shown to be dramatically process dependent.

NiO films were grown on Si(100) by atomic layer deposition using Ni(Cp)(2) (Cp=cyclopentadienyl, C5H5) or Ni(EtCp)(2) [EtCp=ethylcyclopentadienyl, (C2H5)C5H4)] and ozone in the 150-300 degrees C temperature range. The growth temperature dependence of structure, electronic density, and impurity levels for the prepared NiO films was studied using X-ray reflectivity, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, time of flight-secondary ion mass spectroscopy (ToF-SIMS), and transmission electron microscopy. The behavior of films deposited using Ni(Cp)(2) and Ni(EtCp)(2) is compared and discussed. NiO films with good stoichiometry and low amounts of contaminants are obtained at a growth temperature (T-g) of 250 degrees C or above. At a fixed T-g, the growth rate for NiO films deposited using Ni(Cp)(2) is higher than the one of films deposited using Ni(EtCp)(2). Furthermore, the growth rate for NiO deposited using Ni(Cp)(2) at T-g = 150 degrees C is 0.32 nm/cycle and decreases substantially in films deposited at higher temperatures. The electronic density of NiO films deposited at 300 degrees C is close to the one of bulk NiO (1.83 e(-)/A(3)). According to XRD and FTIR results, films deposited at T-g >= 200 degrees C have a simple cubic polycrystalline structure. Impurities in NiO films decrease with increasing T-g, as detected by ToF-SIMS

In the perspective of exploring alternative gate dielectrics for the future generation of microelectronic devices, we investigated experimentally and theoretically the interface energy barriers induced on (001) silicon by La2 Hf2 O7, whose growth has been recently attained by molecular-beam epitaxy. Experimental results show that the 5.6±0.1 eV band gap of La2 Hf2 O7 is aligned to the band gap of silicon with a valence band offset of 2.4±0.1 eV and a conduction band offset of 2.1±0.1 eV. Density functional theory calculations yield valence band offset values ranging between 1.8 and 2.4 eV. © 2006 American Institute of Physics.

Internal photoemission spectroscopy has been used to determine the band alignment in Lu2O3 based metal-oxide-semiconductor structures. The Si/Lu2O3 interface conduction- and valence-band offsets were determined to be 2.1±0.1 and 2.6±0.1 eV, respectively. The energy barrier for electrons at the Al/Lu2O 3 interface is 2.4±0.1 eV. The value of the Lu 2O3 transport band gap, obtained by photoconductivity measurements, was found to be 5.8±0.1 eV. Optical absorption spectroscopy gave a value of 4.89±0.02 eV for the Lu2O3 optical band gap. © 2004 American Institute of Physics.

Rare earth oxides could represent a valuable alternative to SiO2 in complementary metal-oxide-semiconductor devices. Lu2O3 is proposed because of its predicted thermodynamical stability on silicon and large conduction band offset. We report on the growth by atomic-layer deposition of lutetium oxide films using the dimeric {[C5H4(SiMe3)](2)LuCl}(2) complex, which has been synthesized for this purpose, and H2O. The films were found to be stoichiometric, with Lu2O3 composition, and amorphous. Annealing in nitrogen at 950degreesC leads to crystallization in the cubic bixbyite structure. The dielectric constant of the as-grown Lu2O3 layers is 12+/-1.

The formation and the structural properties of Sn nanocrystals produced by ion implantation in thin SiO2 films was investigated by 119Sn conversion electron Moessbauer spectroscopy (CEMS), x-ray absorption spectroscopy (XAS), and transmission electron microscopy (TEM). Sn ion implantation was performed at 80 keV with a fluence of 1x1016 cm2, positioning the peak of the implantation profile in the middle of the SiO2. The annealing treatments were performed in the temperature range 800–1100 °C by rapid thermal processing. CEMS and XAS provided unique information on the local atomic and electronic environment of Sn in SiO2 allowing a detailed investigation of the effect of different annealing conditions. In the as-implanted state all Sn ions are oxidized (with both Sn2+ and Sn4+ oxidation states present), while annealing induces the formation of beta-Sn nanoclusters. TEM showed that cluster sizes are in the range 7–17 nm. For clusters with average diameter ,10 nm, XAS detected a reduction in coordination number and interatomic distances. Both XAS and CEMS indicate an increase in the static disorder in the metallic clusters. The investigated annealing treatments do not lead to a complete precipitation of Sn atoms in the metallic phase, leaving a fraction of them oxidized.

The preparation and the properties of the silicon nanoclusters embedded in thin silicon oxide layers were studied. All the annealed samples of the nanoclusters had shown a broad photoluminescence spectrum with increasing intensity as a function of annealing time. The use of a dual beam time of flight secondary ion mass spectrometry had allowed to observe variations in Si- signal due to excess of silicon atoms introduced by implantation.

The ion beam synthesis (IBS) of nanoparticles in amorphous matrix has received great attention in the last years as a promising technique for nanocrystal formation in insulating layers. Metallic and semiconducting nanoclusters embedded in SiO2 have been recognized as potential materials for the production of memory devices and optoelectronic components. Sn nanoclusters has been proposed, together with Si and Ge nanoclusters, as potential candidates for charge storage. One of the critical point for the technological application of nanocrystals is that they must be isolated and similar in size. In addition, their position and spacing, their structure and stability after formation should be controllable. In this work we address the formation of Sn nanoclusters by ion implantation and thermal treatments in thin SiO2 films (< 100 nm), where the cluster formation mechanism is not well understood yet. The local structure of Sn in SiO2 has been addressed by 119 Sn CEMS and EXAFS. EXAFS and CEMS analyses provided unique information on the local atomic and electronic environment of Sn in SiO2. Sn 2+ and Sn 4+ oxidized phases or the Sn 0 metallic phase have been found under different annealing conditions. By comparing these data with TEM and RBS analyses we concluded that metallic beta-Sn phase is related to big Sn crystalline clusters formed after annealing, while the oxidized Sn is due to atoms dissolved in the matrix or in small precipitates of SnO2 or SnOx. In addition, the formation mechanism of Sn nanoclusters may be influenced by H2O absorption in the highly damaged SiO2 film after ion implantation, and by in-diffusion of moisture during the annealing. Low energy ion implantation (10–15 keV) showed the possibility for a better control of the cluster size distribution and positioning inside the SiO2 films. This may be relevant for the application of this kind of nanoclusters for charge storage applications in memory devices. Preliminary electrical characterization confir

The increasing interest in low-dimensional materials is based on both fundamental and technological issues. Recently, Sn nanoclusters have been proposed as potential candidates for charge storage. However, a better understanding of formation and properties of nanocrystals is required for their technological applications. Sn nanoclusters have been formed in thin SiO2 films by ion implantation (80 KeV, 1x1016 cm-2) and annealing at different temperatures. The high brilliance of third generation sources at high energies makes it feasible to perform Sn K edge spectroscopy on these systems in which the Sn concentration is at the detection limit for XAS. In particular, we have used fluorescence - detected XAS at the GILDA beamline of the ESRF to probe the local structure of the implanted Sn atoms. Complementary structural information have been obtained by 119Sn Conversion Electron Mössbauer Spectroscopy (CEMS) and Transmission Electron Microscopy (TEM). XAS has provided unique information on the local environment of Sn nanoclusters in the SiO2 with respect to different annealing conditions. Sn ions are fully oxidized in the as-implanted state, while after annealing also the ß-Sn phase is found. By comparing XAS data with CEMS and TEM we concluded that the metallic ß-Sn phase is related to the bigger crystalline nanoclusters formed after annealing, while the oxidized Sn is present in the matrix as dissolved SnO or as small oxide precipitates.

In this work we investigate the ion beam synthesis of Sn and Sb clusters in thin oxides. 80 keV (doses of 0.1-1 x 1016 cm-2) Sn implanation in 85 nm thick SiO2 followed by RTP annealing (800-1000°C for 30-300 under Ar or N2 dry ambient) leads to the formation of two cluster bands, near the SiO2 surface and the Si/SiO2 interface. In addition, big isolated clusters are randomly distributed in the middle of the oxide. Cluster-size distribution and cluster-crystallinty are related to implantation dose and annealing time. Low energy (10-12 kev) Sb and Sn implantation (doses 2-5 x 1015 cm-2) leads to the formation of very uniform cluster-size distribution. Under specific process conditions, only an interface cluster band is observed.