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International audience; The nitrogen-vacancy (NV) center in 3C-SiC, the analog of the NV center in diamond, has recently emerged as a solid-state qubit with competitive properties and significant technological advantages. Combining first-principles calculations and magnetic resonance spectroscopy we provide thorough insight in its magneto-optical properties. By applying resonantly excited electron paramagnetic resonance spectroscopy, we identified the zero-phonon absorption line of the 3 A 2 → 3 E transition at 1289 nm (within the telecom Oband) and measured its phonon sideband, the analysis of which reveals a Huang-Rhys factor of S = 2.85 and a Debye-Waller factor of 5.8 %. The low temperature spin-lattice relaxation time was found to be exceptionally long (T 1 = 17 s at 4 K). All these properties make NV in 3C-SiC a strong competitor for qubit application. In addition, the strong variation of the zero-field splitting in the range of 4K to 380K allows its application for nanoscale thermal sensing.

Ferromagnetic resonance (FMR) uses the same equipment as EPR to study strong interactions between spins characterising crystallised ferromagnetic materials. The parameters describing these very anisotropic interactions are deduced from the variation in the position of the resonance line as a function of the direction of the applied magnetic field. This technique is illustrated by experiments performed on several types of nano structured materials: Fe films deposited by epitaxy on GaAs, thin layers of semiconductors doped with Mn2+ and ferrofluids. Its applications relate to magnetic recording, spintronics, and biomedical fields.

International audience; An alternative strategy for the synthesis of terpyridine based switchable molecular tweezers has been developed to incorporate anisotropic Mn(iii)-salphen complexes. The free ligand was synthesized using a building block strategy based on Sonogashira coupling reactions and was then selectively metalated with manganese in a last step. The conformation of the tweezers was switched from an open 'W' shaped form to a closed 'U' form by Zn(ii) coordination to the terpyridine unit bringing the two Mn-salphen moieties in close spatial proximity as confirmed by X-ray crystallography. An alternate switching mechanism was observed by the intercalation of a bridging cyanide ligand between the two Mn-salphen moieties that resulted in the closing of the tweezers. These dual stimuli are attractive for achieving multiple controls of the mechanical motion of the tweezers. A crystallographic structure of unexpected partially oxidized closed tweezers was also obtained. One of the two Mn-salphen moieties underwent a ligand-centered oxidation of an imino to an amido group allowing an intramolecular Mn-Oamide-Mn linkage. The magnetic properties of the manganese(iii) dimers were investigated to evaluate the magnetic exchange interaction and analyze the single molecule magnet behavior.

International audience; For the first time, direct evidence of a photoinduced intramolecular electron transfer has been found in the “molybdenum-copper“ family of cyanide complexes that corresponds to a [MoIV–CuII]→[MoV–CuI] transition. The design and synthesis of a diluted molecular system, [Mo(Zn(1–x)Cux)2-tren] (x = 0, ε, 1, 5 and 10 %, , with ε corresponding to ppm ratio), viewed as new model compounds, have allowed good characterization of the metastable states involved in the process and provided evidence for two different mechanisms. By using squid magnetometry, EPR spectroscopy and X-ray diffraction, the results of this study have confirmed not only the photoinduced electron transfer, but also supports the light-induced excited spin state trapping effect centred on the molybdenum, thought to be due to the presence of a high-spin state (S = 1). This article provides a better understanding of the photomagnetic behaviour in Mo-Cu complexes and reveals the importance of orbital overlap to differentiate the two effects.

NV centers in silicon carbide have been identified in the three main polytypes 3C, 4H, 6H by magnetic resonance and photoluminescence experiments and related ab initio calculations. Their properties show them to be promising centers for applications in quantum technology, similar to the case of NV in diamond. However, their spectral range is in the near-infrared, which should allow their integration in telecommunication systems.

Whereas intrinsic defects in silicon carbide (SiC) have been widely considered for qubit applications, transition metals in this material have not yet been recognized as alternative systems. We have investigated the magneto-optical properties of the ${\mathrm{V}}^{3+}$ center in $4H\text{-SiC}$ by electron paramagnetic resonance (EPR) and photo-EPR spectroscopy in view of their possible application in quantum technology. We show that they fulfill all the requirements for such applications: a high-spin $S=1$ ground state, optically induced ground-state spin polarization of more than 70%, long spin-lattice relaxation times of the order of a second, as well as associated zero-phonon photoluminescence emission lines in the range of 1.8 \ensuremath{\mu}m. Further, the zero-field splitting parameter $D$ is temperature dependent and increases between $T=4\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and $T=292\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ linearly with a rate of 440 kHz/K, allowing potential nanoscale temperature sensing. These properties make the vanadium acceptor an extremely promising candidate for qubit applications with optical properties in the telecommunication optical range.

Atomlike defect levels in silicon carbide (SiC) polytypes have been proposed and proven to be an excellent platform for various quantum technology applications. Single-photon emitters, coherent control at room temperature, and temperature and magnetic field sensing at the nanoscale have already been demonstrated for the case of vacancy and divacancy defects in SiC and more recently proposed for negatively charged NV centers. NV centers, which allow a better control of their generation, offer in addition a further shift of the spectral range in the near infrared, i.e., in the $O$- and $S$-band telecom range. We demonstrate here that the association of high resolution optical spectroscopy and electron paramagnetic resonance spectroscopy combined with first-principles calculations allow the identification of the microscopic structure of the six distinct NV centers in $6H\ensuremath{-}\mathrm{SiC}$ and the assignment of their associated zero-phonon photoluminescence lines. Time resolved photo-EPR measurements at $T=4\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ show that NV centers in $6H\ensuremath{-}\mathrm{SiC}$ present spin lattice relaxation times of several seconds. These excellent qubit properties should enable their application and implementation in quantum information devices.

In this chapter, we will focus on the study by EPR of point defects in semiconductor materials. Indeed, impurities, vacancies, anti -sites and complexes of them, in a diamagnetic material, may exhibit a local electronic reconstruction favoring unpaired electrons, and consequently, such defects have a nonzero electon spin. Of course, point defects may exist in an S = 0 state and then be EPR silent. Nevertheless, in semiconductors, most of the point defects have several charge states in the gap, and generally, each of them corresponds to a different spin state. Changing the defect charge state by electrical polarization or by light irradiation is then an efficient mean to reveal and detect the defects by EPR.

The defects in Si-doped \ensuremath{\epsilon}-${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ epitaxial layers have been investigated by electron paramagnetic resonance (EPR) spectroscopy. The results show that Si doping introduces a single, paramagnetic defect, attributed to Si incorporation on the tetrahedral gallium lattice site. It is a spin $S=1/2$ center with an axial $g$ tensor with principal values of $g//c=1.9573$ and $g\ensuremath{\perp}c=1.9591$. The temperature dependence of the EPR parameter demonstrates that it is a shallow effective mass donor, which is at the origin of the $n$-type conductivity. The EPR spectrum is modified by motional narrowing effects, the analysis of which allows one to reveal different transport regimes, including localization, hopping conductivity, and ionization in the conduction band when the temperature is raised from $T=4\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ to room temperature. Partial electrical compensation and donor clustering are equally evidenced by the EPR results, which are confirmed by correlated electrical transport measurements. Silicon is thus a promising dopant for the formation of highly conductive $n$-type \ensuremath{\epsilon}-${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$.

International audience; A high-nuclearity metal-cyanide cluster [Mo 6 Cu 14 ] has been prepared and its photomagnetic properties investigated. The photoswitchable magnetic phenomenon observed is thermally reversible (T 230 K). In the field of photomagnetism, [Mo 6 Cu 14 ] represents a unique example of nanocage and the highest nuclearity observed so far.

We have investigated the conduction mechanism in n-type, Si doped β-Ga2O3 bulk samples and evidenced carrier dynamics in the GHz frequency range at room temperature by electron paramagnetic resonance (EPR) spectroscopy. The Si shallow donor EPR and conduction electron spin resonance (CESR) spectra show an unusual temperature dependence of the linewidth and line shape, which reveals a variable range hopping conduction and donor clustering. The temperature dependence of the EPR signal intensity can be fitted with two thermally activated processes with energies of 4 meV and 40 meV in the below and above 40 K temperature range. The value of 40 meV is attributed to the ionization energy of the Si shallow donor, indicating that hopping proceeds via the conduction band. Above T = 130 K and up to room temperature, the conduction electron spin resonance (CESR) can be observed with a decreasing linewidth of ΔB

We have investigated the optical properties of the ${(\mathrm{NV})}^{\ensuremath{-}}$ center in 3C-SiC to determine the photoluminscence zero phonon line (ZPL) associated with the $^{3}\mathrm{E}\ensuremath{\rightarrow}^{3}\mathrm{A}_{2}$ intracenter transition. Combining electron paramagnetic resonance and photoluminescence spectroscopy, we show that the ${\mathrm{NV}}^{\ensuremath{-}}\phantom{\rule{0.28em}{0ex}}\mathrm{center}$ in 3C-SiC has a ZPL line at 1.468 $\ensuremath{\mu}\mathrm{m}$ in excellent agreement with theoretical predictions. The ZPL line can be observed up to $T=100$ K. The negatively charged NV center in 3C-SiC is the structural isomorphe of the NV center in diamond and has equally a spin $S=1$ ground state and a spin $S=1$ excited state, long spin lattice relaxation times and presents optically induced groudstate spin polarization. These properties make it already a strong competitor to the NV center in diamond, but as its optical domain is shifted in the near infrared at $1.5\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{m}$, the NV center in 3C-SiC is compatible with quantum photonic networks and silicon based microelectronics.

We show that electron paramagnetic resonance (EPR) tagged high resolution photoexcitation spectroscopy is a powerful method for the correlation of zero phonon photoluminescence spectra with atomic point defects. Applied to the case of NV centers in $4H$-SiC it allows to associate the photoluminescence zero phonon lines (ZPL) at 1243, 1223, 1180, and 1176 nm with the (hk, kk, hh, kh) configurations of the ${\mathrm{NV}}^{\ensuremath{-}}$centers in this material. These results lead to a revision of a previous tentative assignment. Contrary to theoretical predictions, we find that the NV centers in $4H$-SiC show a negligible Franck-Condon shift as their ZPL absorption lines are resonant with the ZPL emission lines. The high subnanometer energy resolution of this technique allows us further to resolve additional fine-structure of the ZPL lines of the axial NV centers which show a doublet structure with a splitting of 0.8 nm. Our results confirm that NV centers in $4H$-SiC provide strong competitors for sensing and qubit application due to the shift of their optical transitions into the technology compatible near-infrared region and the superior material properties of SiC. Given that single center spin readout will be realized, they are suitable for scalable nanophotonic devices compatible with optical communication network.

High-purity illite specimens from the Mesoproterozoic unconformity-related uranium deposits of Kiggavik, Thelon basin, Nunavut (Canada), and Shea Creek (Athabasca basin, Saskatchewan, Canada) have been studied using electron paramagnetic resonance spectroscopy to determine the thermal stability of the main radiation-induced defects and question the potential of using illite as a natural dosimeter. The observed spectra are complex as they can show in the same region several contributions: (1) an unstable native defect, (2) the main stable defect named Ai by reference to a previous study (Morichon et al. in Phys Chem Minerals 35:339–346, 2008), (3) a signal at g = 2.063 assigned to a new defect, not yet fully characterized, named Ai2 center and (4) impurities such as vanadyl complex or divalent manganese. Isochronal heating shows that the new signal corresponds to a stable species. Isothermal heating experiments at 400 and 450 °C provide values of half-life extrapolated at room temperature and activation energy of 1.9–29,109 years and 1.3–1.4 eV, respectively, corresponding to the Ai center. These parameters allow the use of stable radiation-induced defects as a record of radioactivity down to the Paleoproterozoic period.

Fluorescent paramagnetic defects in solids have become attractive systems for quantum information processing in recent years. One of the leading contenders is the negatively charged nitrogen-vacancy (NV) defect in diamond with visible emission, but an alternative solution in a technologically mature host is an immediate quest for many applications in this field. It has been recently found that various polytypes of silicon carbide (SiC), that are standard semiconductors with wafer scale technology, can host a NV defect that could be an alternative qubit candidate with emission in the near infrared region. However, there is much less known about this defect than its counterpart in diamond. The inequivalent sites within a polytype and the polytype variations offer a family of NV defects. However, there is an insufficient knowledge on the magneto-optical properties of these configurations. Here we carry out density functional theory calculations, in order to characterize the numerous forms of NV defects in the most common polytypes of SiC including $3C, 4H$, and $6H$, and we also provide new experimental data in $4H$ SiC. Our calculations mediate the identification of individual NV qubits in SiC polytypes. In addition, we discuss the formation of NV defects in SiC, providing detailed ionization energies of NV defects in SiC, which reveals the critical optical excitation energies for ionizing these qubits in SiC. Our calculations unravel the challenges to produce NV defects in SiC with a desirable spin bath.

Nitrogen-martensite thin films are known to present a perpendicular magnetic anisotropy (PMA) depending on the nitrogen content. Additionally, weak magnetic stripe domains have been studied in Fe-N samples made by ion implantation. In this work, ion implantation proves to be a good technique to make nitrogen-martensite thin films presenting both tunable PMA and stripe domains. We report on the changes in magnetic and structural properties of nitrogen-implanted iron thin films, resulting from various implantation conditions. Fluences from 1.8 × 1016 N2+/cm2 to 3.5 × 1016 N2+/cm2 at 26 keV and 5.3 × 1016 N2+/cm2 at 40 keV were used to implant iron thin films epitaxially grown on ZnSe/GaAs(001). X-ray diffraction measurements disclosed the presence of body-centered tetragonal nitrogen-martensite whose c-axis is perpendicular to the thin film plane and the c-parameter increases with fluence. Vibrating sample magnetometer measurements revealed that nitrogen implantation induced strong changes in magnetic prope...

International audience; A six level molecular switch based on terpyridine(Ni-salphen) 2 tweezers and addressable by three orthogonal stimuli (metal coordination, redox reaction and guest binding) is reported. By a metal coordination stimulus, the tweezers can be mechanically switched from an open " W "-shaped conformation to a closed " U "-shaped form. Theses two states can each be reversibly oxidized by the redox stimulus and bind to a pyrazine guest resulting in four additional states. All six states are stable and accessible by the right combination of stimuli and were studied by NMR, XRD, EPR spectroscopy and DFT calculations. The combination of the supramolecular concepts of mechanical motion and guest binding with the redox non-innocent and valence tautomerism properties of Ni-salphen complexes added two new dimensions to a mechanical switch.

The outstanding magneto-optical properties of the nitrogen-vacancy (NV) center in diamond have stimulated the search for similar systems. We show here that NV triplet centers can also be generated in all the main SiC polytypes. We have identified by electron paramagnetic resonance spectroscopy and first-principles calculations the axial ${\mathrm{NV}}^{\ensuremath{-}}$ pairs in $3C,4H$, and $6H$ SiC, showing polytype and lattice site-specific magnetic and optical properties. We demonstrate very efficient room-temperature spin polarization of the ground state upon near infrared optical excitation for the NV center in $3C$ SiC and axial NV centers in the hexagonal $(4H,6H)$ polytypes; the signals of basal pairs are much lower in intensity. Axial NV centers in hexagonal SiC polytypes and thus constitute unidirectional ensembles which may be useful in nanosensing applications.

International audience

International audience; We present evidence of near-infrared photoluminescence (PL) signature of nitrogen vacancy centers (NCVSi)− in silicon carbide (SiC). This center exhibits an S=1 ground state spin similar to the NV− center in diamond. We have performed photoluminescence excitation measurements at cryogenic temperature and demonstrated efficient photoexcitation of distinct photoluminescence from (NCVSi)− in 4H-SiC. Furthermore, by correlating the energies of measured zero phonon lines (ZPLs) with theoretical values derived from hybrid density functional theory each of the ZPLs has been associated to the respective occupation of hexagonal (h) and quasicubic (k) lattice sites in close analogy to neutral divacancy centers (VCVSi)0 in the same material. Finally, with the appropriate choice of excitation energy we demonstrated the selective excitation of (NCVSi)− PL with no contamination by (VCVSi)0 PL, thereby opening the way towards the optical detection of (NCVSi)− electron spin resonance.

International audience; A control of the interaction between two spin centers was achieved by using a mechanical motion in a terpy(Cu–salphen)2 complex. Upon coordination a conformation change and switching from a paramagnetic to an antiferromagnetically coupled system was observed by EPR and SQUID measurements.

Two types of cyanide bridged molybdenum–copper photomagnetic films have been obtained: the first one is based on a molecular [MoCu6] complex, the other being a two-dimensional [MoCu2] coordination network. Both systems employ surfactant functionalized ligands and films were deposited on Melinex substrates using the Langmuir–Blodgett technique. All systems, including monolayer films, showed full retention of the intrinsic photomagnetic properties known for analogous solids as demonstrated by EPR spectroscopy.

Photo-induced spin transition in a molybdenum–zinc complex has been evidenced and fully characterized by Squid magnetometry and several spectroscopies performed under irradiation (IR, EPR, etc.). The phenomenon has been confirmed by X-ray diffraction and DFT calculations yielding a Light-Induced Excited Spin State Trapping Effect (LIESST) on a 4d transition metal ion.

Previous Electron Paramagnetic Resonance (EPR) studies identified the carbon dangling bond center as the main paramagnetic interface defect in 3C, 4H, 6H-SiC/SiO2, We demonstrate that this defect, called P-bC center, can be passivated by forming gas annealing at 400 degrees C. We have measured the PbC density at annealed 4H- and 3C-SiC/SiO2 interfaces and attributed its reduction to the transformation of the dangling bonds into EPR inactive C-H bonds. We have also studied the reverse phenomenon occurring during vacuum annealing at temperatures ranging from 600 degrees C up to 1000 degrees C and have determined a dissociation energy of approximate to 4.3 eV for the 3C and 4H polytypes.

6H-SiC single crystalline substrates were implanted at room temperature with 2 MeV Al2+ ions to fluences from 2x10(14) Al-2, cm(-2) to 7x10(14) Al2+ cm(-2) and with different current densities (from 6.6 to 33x10(10) Al2+ cm(-2) s(-1)). The depth profile of the damage induced by the Al2+ ions was determined by Backscattering Spectrometry in channeling geometry (BS/C) with a 3.5 MeV He2+ beam. The BS/C spectra were evaluated using the RBX. code. The samples were subsequently annealed at 1100D C in N-2 for one hour, in order to analyze their structural recovery by BS/C and the amount of the remaining defects by means of Electron Paramagnetic Resonance (EPR). The results from the BS/C spectra corresponding to the as-implanted samples indicate that the damage depends strongly on the total fluence but also, although to a lesser extent, on the beam current density. The BS/C measurements reveal that all the samples, except the one implanted with the highest fluence, recover completely their original crystalline structure after the annealing. Furthermore the angular anisotropy of the EPR spectra indicates that the implanted region recovered a good crystallinity, although some residual defects were observed.

The defects at the 3C-SiC/SiO2 interface have been studied by X-band EPR spectroscopy in oxidized porous 3C-SiC. One interface defect is detected; its spin Hamiltonian parameters, spin S=1/2, C3V symmetry, g//=2.00238 and g⊥=2.00317, central hyperfine interaction (CHF) with one carbon atom and AB//[001]=48G and superhyperfine (SHF) interaction with three equivalent Si neighbour atoms and TB//[001]=12.4G, allow us to attribute the center to a sp3 coordinated carbon dangling bond center, PbC.

Variable frequency EPR measurements between 9 and 285 GHz show that a-C layers with the exception of strongly polymer-like layers present even at the highest frequency a simple, single line EPR spectrum for which exchange interactions are still dominating. The high frequency EPR spectra are characterized by temperature dependent g -factor anisotropies, the numerical value of which varies with the particular samples. From the angular variation, temperature and microwave frequency dependence this g -factor anisotropy is attributed to the influence of demagnetizing fields which at 285 GHz and 4 K are of the order of 100 G for the diamond like layers.

Gallium nitride (GaN) light emitting diodes (LEDs) were irradiated at room temperature with electrons in the range 300-1400 keV. A threshold energy of 440 keV was observed, corresponding to a gallium atom displacement energy of 19/spl plusmn/2 eV. This value of the displacement energy compares with that of silicon carbide but is smaller than that of diamond and larger than that of gallium arsenide (GaAs). No threshold energy for the nitrogen atom was observed. It is concluded that the nitrogen sublattice repairs itself through annealing. The measured displacement energy is used to determine the Rutherford cross section, which permits a theoretical comparison of electron and proton irradiation damage in GaN. The effects of 2.5 MeV electrons on gallium nitride films have been studied by photoluminescence (PL), and according to the literature, they introduce transitions in the near infrared part of the spectrum. Experiments on gallium nitride films using 2 MeV protons are reported in this work. The same transitions in the near infrared part of the spectrum are observed by PL. It is deduced that 2 MeV protons are about 1000 times more damaging than 2.5 MeV electrons. The Rutherford cross section predicts a value of 214. The difference is attributed to the defect recombination rate which depends on the particle type. The nature of the transitions in the near infrared part of the spectrum is reviewed. The GaN films were annealed at 400/spl deg/C for 30 min. As a result of annealing, another transition appears in the green part of the spectrum. Transitions involving the gallium vacancy in irradiated GaN are discussed.

The defects at abrupt and ultrathin thermal silicon dioxide mediated Si( 100)/a-Al 2 O 3 interfaces have been studied by X-band electron paramagnetic resonance spectroscopy. Amorphous Al 2 O 3 films of 40 A thickness were deposited by atomic layer deposition at 300 °C. Different deposition conditions and post deposition annealing have been investigated. In all cases the main interface defects are found to be the two Pb centers (P b0 , P b1 ) known from previous Si/SiO 2 interface studies. The P b0 center is dominating in concentration with P b0 /P b1 ratios higher than 5. The concentrations are in the 10 12 -10 13 cm -3 range. Forming gas annealing at 450 °C did reduce the Pb center concentrations only by 50%.

Ion implantation is frequently employed in SiC for doping, electrical isolation or in the SiC on isolator technology. The ion implantation process is accompanied by the formation of intrinsic defects, which introduce deep electron and hole traps. They are believed to be mainly multivacancy complexes but the exact microscopic nature of these defects and their distribution versus the ion penetration depth is not well established. We have analyzed by electron paramagnetic resonance spectroscopy the defects introduced by high energy (MeV) proton implantation. In this study we extend the previous investigations on n-type SiC to the case of p-type Al doped bulk samples. Both silicon monovacancy and carbon vacancy related defects are observed. Their nature and introduction rate have been determined. The results obtained will be compared to the published electrical studies in order to correlate the vacancy defects with the known electron and hole traps.

The defects introduced in n-type, intrinsic and p-type doped SiC by low energy (300 keV) room temperature electron irradiation near the silicon atom displacement threshold have been analyzed by electron paramagnetic resonance. We observed the predominant formation of defects currently assigned to carbon vacancy–hydrogen complexes in the Al doped and the high purity intrinsic material and no isolated carbon vacancies. If the models are correct, our results imply the presence of highly mobile H and their interaction with V C defects even at 300 K. In the n-type SiC two V Si related centers are observed tentatively attributed to 2−/3− charge states.

In this work, we investigate by nuclear reaction analysis (NRA), electron paramagnetic resonance (EPR) spectroscopy and atomic force microscopy (AFM) the NO-induced modifications of the physical properties of oxide layers of thickness 20 nm), and typical concentration of 2×10 15 cm −2 can be achieved. The N profiles varies with oxide type. In both cases, the interface defect concentration is reduced after furnace NO treatments by up to a factor of six. Our study reveals that this reduction is not only the consequence of the N incorporation but that the thermal relaxation of the nitrided layer also plays a major role. To investigate this effect, we performed He annealings which change the thermal budget of the dielectric layer. We show that the He annealings of the NO treated layers delays the re-oxidation process further and changes the chemical composition of the nitrided oxide layer. By AFM, we show that the NO treatment does not form a continuous nitrided layer but forms islands at the interface.

The microscopic structure and introduction rate of point defects in n-type 6H- and 4H-SiC generated by room-temperature proton implantation have been studied by the electron paramagnetic resonance technique. In order to selectively study the effects of defect introduction in the trace region, 12-MeV implantation in 300-\ensuremath{\mu}m-thick samples was employed, for which the protons completely cross the sample. In both polytypes we observe three dominant paramagnetic defects attributed to the Si monovacancy in the negative charge state and the neutral Si monovacancy in the hexagonal and quasicubic lattice sites, respectively. The concentration of all three defects increases linearly with proton dose. Their total introduction rate is \ensuremath{\sim}19 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, which amounts only to 4% of the concentration expected from SRIM simulations. No carbon-vacancy-related defect is observed. Thermal annealing at 1100 \ifmmode^\circ\else\textdegree\fi{}C is sufficient to anneal out the ${V}_{\mathrm{Si}}$ defects and to restore n-type conductivity. The observation of the neutral Si vacancy at hexagonal and quasicubic sites under thermal equilibrium conditions at 4 K does not support their previous assignment to an excited state.

The intrinsic defects in p-type $6H\ensuremath{-}\mathrm{S}\mathrm{i}\mathrm{C}:\mathrm{A}\mathrm{l}$ generated by electron irradiation at 300 keV, which is close to the threshold of the silicon atom displacement, have been studied by electron paramagnetic resonance spectroscopy. We observed two dominant irradiation-induced paramagnetic defects: (i) a silicon-vacancy-related spin $S=3/2$ defect with a zero-field splitting of $D=68.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1},$ which is tentatively attributed to a Si Frenkel pair aligned parallel to the c axis and (ii) a carbon-vacancy-related spin $S=1/2$ defect already previously attributed to ${V}_{\mathrm{C}}^{+}.$ A slight increase of the electron energy to 350 keV creates in addition a lower-symmetry $S=3/2$ spectrum equally attributed to Si Frenkel pairs with the interstitial being located at six equivalent off-axis sites. High-energy irradiation (2 MeV) creates only isolated Si vacancies with no zero-field splitting.

A comparative study is presented on the pore propagation directions of porous silicon layers (PSL) formed on p+-type substrates of different orientations. PSLs were formed on plain (0 0 1) and (1 1 1) silicon wafers as well as on structured (0 0 1) wafers containing facets of various orientations. During anodization, regular pores follow the 〈0 0 1〉 direction on the (0 0 1) planes. While on the (1 1 1) planes fewer regular pores develop and seemingly propagate closely to the 〈1 1 1〉 direction. These results indicate that the pores propagate perpendicular to the surface i.e. along the field lines when the surface orientation is either (0 0 1) or (1 1 1).

Nitrogen doped N-type 6HSiCOI structures have been obtained by the Smart Cut® technique. The process induced defects and their electrical activity have been analysed by electron paramagnetic resonance (EPR) spectroscopy, photoluminescence and Hall measurements. The influence of thermal annealing at temperatures between 800 and 1300°C has been studied. The 1300°C annealing step is required to recover the N-type conductivity, even though compensating defects at concentrations of 1×10 18 cm −3 are still present.

The $(100){\mathrm{S}\mathrm{i}/\mathrm{S}\mathrm{i}}_{3}{\mathrm{N}\mathrm{}}_{4}$ interface, formed by the deposition of ${\mathrm{Si}}_{3}{\mathrm{N}}_{4}$ layers on bulk (100) Si by distributed electron-cyclotron-resonance plasma-enhanced chemical vapor deposition, has been studied by electron-paramagnetic-resonance spectroscopy. Only one interface defect, the ${P}_{b0}$ center, characterized by trigonal point symmetry and principal values of the g tensor, ${g}_{\ensuremath{\parallel}}=2.0018\ifmmode\pm\else\textpm\fi{}0.0002$ and ${g}_{\ensuremath{\perp}}=2.0089\ifmmode\pm\else\textpm\fi{}0.0002$, has been detected. Its area concentration is of the order of $(2--5)\ifmmode\times\else\texttimes\fi{}{10}^{11} {\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}.$ The characteristic defect of the $(100){\mathrm{S}\mathrm{i}/\mathrm{S}\mathrm{i}\mathrm{O}}_{2}$ interface, the ${P}_{b1}$ center, is not observed. The ${\mathrm{Si}}_{3}{\mathrm{N}}_{4}$ layers contain one main native bulk defect, the K center, at concentrations of $5\ifmmode\times\else\texttimes\fi{}{10}^{17} {\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}.$

The modification by postoxidation NO treatments of the Si/SiO2 interface in thermally grown Si(100)/SiO2 layers has been studied by nuclear reaction analysis and electron paramagnetic resonance spectroscopy. Our results demonstrate a selective incorporation of NO molecules at the Si/SiO2 interface and a drastic reduction in the interface defect density. In this new configuration, the Pb center density, which is typically 2×1012 cm−2 in the as oxidized samples, is reduced to below 1011 cm−2 without any hydrogen passivation. The thermal treatment in NO atmospheres opens the perspective for the formation of hydrogen free low defect Si(100)/SiOxNy interfaces conserving the qualities of the SiO2 dielectric.

The total dose response of Si/SiO/sub 2/ structures with ultrathin (20-40 /spl Aring/) thermal oxide layers grown on porous silicon substrates has been studied by Electron Paramagnetic Resonance (EPR) spectroscopy. The modification of the interface defect passivation and the generation of oxide defects have been analysed as a function of dose for three series of samples with different initial hydrogen passivation states.

A structural study of p- and p+-type porous Si1−xGex materials and a comparison with non-porous epitaxial Si1−xGex layers is reported. The pore morphology is studied by electron microscopy and compared to that of porous silicon. It is shown that the shape of the porous structure is similar to that of porous silicon but with preferential etching near the threading dislocations. In order to investigate the influence of the porosity on the crystalline structure, high-resolution X-ray diffraction is used to determine the strains in the layer. Moreover asymmetric Bragg reflection gives the value of the lattice parameter of the layer, parallel to the sample surface. It appears that the porosification has only a weak influence on the crystalline structure of the Si1−xGex layers. © 1997 Elsevier Science S.A.

Si 0.8 Ge 0.2 /Si 0.8 Ge 0.2 O 2 interface defects were studied by the electron paramagnetic resonance (EPR) technique in 1 μm thick epitaxial porous SiGe layers. Two different intrinsic interface defects, the silicon and germanium P b centers, have been identified. These defects are respectively Si and Ge dangling bond centers with trigonal point symmetry. The EPR parameters such as g -values, linewidths and spin concentrations have been determined for different oxidation conditions: native oxide formation at room temperature and 300 °C low-pressure oxidation. The spin concentrations of the two defects strongly depend on the oxidation conditions. The spin concentration ratio differs from the [Si]/[Ge] atomic concentration ratio of the porous layer.

The magnetism in \ensuremath{\sim}1 at$%$ Mn-doped nanometric Bi${}_{2}$Se${}_{3}$ epitaxial layers has been studied by ferromagnetic resonance (FMR), magnetometry, and polarized neutron reflectivity (PNR) measurements. The FMR results reveal the formation of an intrinsic homogeneous FM bulk phase, as confirmed by the PNR measurements. Its critical temperature is low: ${T}_{c}$ \ensuremath{\approx} 6 K; no surface magnetic phase is detected above this temperature. The FMR measurements at $T$ $=$ 4.2 K show a single uniform mode spectrum with a strong uniaxial in-plane/out-of-plane symmetry. The uniaxial anisotropy field at $T$ $=$ 4 K is ${H}_{a}$ \ensuremath{\sim} \ensuremath{-}2500 Oe, corresponding to a uniaxial anisotropy constant of \ensuremath{-}9 \ifmmode\times\else\texttimes\fi{} 10${}^{3}$ erg/cm${}^{3}$. The easy axis of magnetization is oriented in the film plane for temperatures between 4 K and ${T}_{c}$. Conduction electron-mediated FM in this (very) diluted magnetic semiconductor is considered as the most probable origin of the FM phase formation.

Point defects in bulk Si have been studied for over thirty years and a very detailed understanding of their microscopic structure and electronic properties has been achieved. The recent development of porous Si has allowed a further advancement in Si related defect studies, which will be reviewed here. Two aspects of porous Si have turned out to be of particular importance for defect studies by the magnetic resonance techniques: the larger number of nanocrystals contained in a cubic millimeter sized sample and the high internal surface area with values up to 1000 m2 cm−3. The first allows classical EPR studies of defects in nanocrystals and the second the observation of interfacial defects under highly improved conditions. We present recent results on donor defects in nanocrystalline Si, detailed EPR and ENDOR measurements of the Pb center in Si SiO 2 prepared by native, thermal and anodic oxidation, the study of the 17O superhyperfine interaction of the Pb center in isotopically enriched samples, the study of the Pb1 center, the dominant interface defect at (100) Si SiO 2 interfaces, as well as of the native defect structure in very thin ( ≈ 20 A ) thermal oxides and nitrides. First results on interfacial defects in oxidized SiGe epitaxial layers will also be reported.