Stress-induced Defects Research Articles

Combined Nanoscale and Device-Level Degradation Analysis of $\hbox{SiO}_{2}$ Layers of MOS Nonvolatile Memory Devices

In this paper, the impact of an electrical stress applied on MOS structures with a 9.8-nm-thick SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer has been investigated at the device level and at the nanoscale with conductive atomic force microscopy (AFM). The goal is to correlate both kinds of measurements when studying the degradation and breakdown (BD) of tunnel oxides of nonvolatile memory devices. In particular, the generation of defects and its impact on leakage current and charge trapping in the tunnel oxide have been analyzed through spectroscopic measurements and current images. The properties and energy of the stress-induced defects (before and after BD) have been roughly estimated by thermally stimulated luminescence and AFM measurements.

Diagnostic value of perfusion cardiovascular magnetic resonance in patients with angina pectoris but normal coronary angiograms assessed by intracoronary acetylcholine testing

BackgroundPerfusion cardiovascular magnetic resonance (CMR) has a high sensitivity for the detection of significant coronary artery disease (CAD). However, the specificity of this method is lower than its sensitivity. The...

Local charge transport in nanoscale amorphous and crystalline regions of high-k (Zr2)0.8(Al2O3)0.2 thin films

The charge transport in (Zr02)0.8(Al2O3)0.2 thin films consisting of nanoscale crystallites in an amorphous matrix were investigated by conductive atomic force microscopy. Local current-voltage curves were obtained either from multiple current images for different biases or by ramping the tip bias at a specific location. Comparison of both approaches for amorphous matrix sites implies that they are equivalent. Current-voltage curves for crystallite and amorphous sites are different, but repeated voltage ramps at amorphous sites yield curves as obtained at pristine crystallites. This suggests charge transport through leakage paths along defects at grain boundaries and along stress-induced defects at amorphous sites.

Time-dependent electroforming in NiO resistive switching devices

Time-dependent electroforming phenomena in NiO capacitors are investigated. Different current-voltage characteristics between dc sweep mode and pulse mode indicate that electroforming is time-dependent process. Statistical time-dependent dielectric breakdown (TDDB) measurements show the exponential dependence of electroforming time on applied voltage, confirming that forming process is not a spontaneous process at some critical voltage, but an upsurge process resulting from stress-induced defects. The statistical TDDB analysis explains not only the nature of electroforming process but also the anomalous forming and large variations in forming parameters.

Electron-Beam-Induced Current Study of Breakdown Behavior of High-K Gate MOSFETs

We report a dynamic and microscopic investigation of electrical stress induced defects in metal-oxide-semiconductor (MOS) devices with high-k gate dielectric by using electron-beam induced current (EBIC) technique. The correlation between time-dependent dielectric breakdown (TDDB) characteristics and EBIC imaging of breakdown sites are found. A systematic study was performed on pre-existing and electrical stress induced defects. Stress-induced defects are related to the formation of electron trapping defects. The origin of pre-existing defects is also discussed in terms of oxygen vacancy model with comparing different gate electrodes.

Adenosine-Induced Stress Myocardial Perfusion Imaging Using Dual-Source Cardiac Computed Tomography

This study sought to determine the feasibility of performing a comprehensive cardiac computed tomographic (CT) examination incorporating stress and rest myocardial perfusion imaging together with coronary computed tomography angiography (CTA). Although cardiac CT can identify coronary stenosis, very little data exist on the ability to detect stress-induced myocardial perfusion defects in humans. Thirty-four patients who had a nuclear stress test and invasive angiography were included in the study. Dual-source computed tomography (DSCT) was performed as follows: 1) stress CT: contrast-enhanced scan during adenosine infusion; 2) rest CT: contrast-enhanced scan using prospective triggering; and 3) delayed scan: acquired 7 min after rest CT. Images for CTA, computed tomography perfusion (CTP), and single-photon emission computed tomography (SPECT) were each read by 2 independent blinded readers. The DSCT protocol was successfully completed for 33 of 34 subjects (average age 61.4 +/- 10.7 years; 82% male; body mass index 30.4 +/- 5 kg/m(2)) with an average radiation dose of 12.7 mSv. On a per-vessel basis, CTP alone had a sensitivity of 79% and a specificity of 80% for the detection of stenosis > or =50%, whereas SPECT myocardial perfusion imaging had a sensitivity of 67% and a specificity of 83%. For the detection of vessels with > or =50% stenosis with a corresponding SPECT perfusion abnormality, CTP had a sensitivity of 93% and a specificity of 74%. The CTA during adenosine infusion had a per-vessel sensitivity of 96%, specificity of 73%, and negative predictive value of 98% for the detection of stenosis > or =70%. Adenosine stress CT can identify stress-induced myocardial perfusion defects with diagnostic accuracy comparable to SPECT, with similar radiation dose and with the advantage of providing information on coronary stenosis.

Analysis of photoluminescence spectra for detection of stress-induced defects in silicon substrates after the polycrystalline diamond film deposition

The low temperature (5 K) photoluminescence (PL) of silicon substrate in the range of 0.8–1.12 eV before and after microwave plasma assisted chemical vapor deposition of polycrystalline diamond films was studied. The diamond films were deposited onto the pure ( ρ ∼3 kOhm cm) dislocation-free silicon treated by mechanical polishing (MP) or by superior chemical–mechanical polishing (CMP). In the PL spectra of coated silicon substrates treated by CMP, the D 1 and D 2 lines related to the dislocation emission were registered. We suppose that the formation of dislocations in the substrate is caused by a strong adhesion of diamond film and as a consequence by the formation of inner tensions released as dislocations.

Curcumin reverses impaired cognition and neuronal plasticity induced by chronic stress

Chronic stress occurs in everyday life and induces impaired spatial cognition, neuroendocrine and plasticity abnormalities. A potential therapeutic for these stress related disturbances is curcumin, derived from the curry spice turmeric. Previously we demonstrated that curcumin reversed the chronic stress-induced behavioral deficits in escape from an aversive stimulus, however the mechanism behind its beneficial effects on stress-induced learning defects and associated pathologies are unknown. This study investigated the effects of curcumin on restraint stress-induced spatial learning and memory dysfunction in a water maze task and on measures related neuroendocrine and plasticity changes. The results showed that memory deficits were reversed with curcumin in a dose dependent manner, as were stress-induced increases in serum corticosterone levels. These effects were similar to positive antidepressant imipramine. Additionally, curcumin prevented adverse changes in the dendritic morphology of CA3 pyramidal neurons in the hippocampus, as assessed by the changes in branch points and dendritic length. In primary hippocampal neurons it was shown that curcumin or imipramine protected hippocampal neurons against corticosterone-induced toxicity. Furthermore, the portion of calcium/calmodulin kinase II (CaMKII) that is activated (phosphorylated CaMKII, pCaMKII), and the glutamate receptor sub-type (NMDA 2B) expressions were increased in the presence of corticosterone. These effects were also blocked by curcumin or imipramine treatment. Thus, curcumin may be an effective therapeutic for learning and memory disturbances as was seen within these stress models, and its neuroprotective effect was mediated in part by normalizing the corticosterone response, resulting in down-regulating of the pCaMKII and glutamate receptor levels.

Effects of Bushen Kangshuai Tang in retrieving oxidative stress-induced reproductive defects in Caenorhabditis elegans

To explore the function of Bushen Kangshuai Tang (BKT), a compound traditional Chinese herbal medicine, in alleviating oxidative stress-induced reproductive defects in organism nematode Caenorhabditis elegans. The L4-larvae were cultured with 25%, 50%, 75%, and 100% of BKT with the final concentration of 0.33 g/mL. Ultraviolet irradiation [20 J/(m(2) x min)], heat-shock (36 degrees centigrade, 2 h), and paraquat treatment (2 mmol/L, 2h) were exerted as the stresses. Reproduction was assayed by the egg number in uterus, brood size, and generation time. Ultraviolet irradiation, heat-shock, and paraquat treatment could significantly reduce egg number in uterus and brood size, increase generation time, and suppress activities of catalase and superoxide dismutase of the treated wild-type N2 nematodes. Administration of BKT did not cause toxic or altered effects on reproduction under wild-type background in C. elegans. However, BKT administration at higher concentrations could not only effectively alleviate the reproductive defects induced by ultraviolet irradiation, heat-shock, and paraquat treatment, but also increase the catalase and superoxide dismutase activities suppressed by ultraviolet irradiation, heat-shock, and paraquat treatment as compared with the control. Moreover, administration of BKT at higher concentrations could largely recover the reproductive defects formed in mev-1 mutant nematodes with elevated oxidative stress. Oxidative stress can negatively regulate the reproductive process, and the administration of high concentrations of BKT will largely retrieve the oxidative stress-induced reproductive defects in exposed nematodes.

Effect of 200 MeV Ag 15+ ion irradiation on structural and magnetic properties of Mg 0.95Mn 0.05Fe 2O 4 ferrite thin film

Nanocrystalline Mg 0.95Mn 0.05Fe 2O 4 ferrite thin films, prepared by pulsed laser deposition technique on a glass substrate coated with indium tin oxide, are irradiated with 200 MeV Ag 15+ ions at different fluence values in the range from 1 × 10 11 to 1 × 10 12 ions/cm 2. The as-deposited and irradiated thin films are investigated using X-ray diffraction, dc magnetization and atomic force microscopy techniques. X-ray diffraction analysis of the as-deposited as well as irradiated thin film indicates the single phase cubic structure as the main composition. The crystallite size evaluated from Scherrer's equation is found to be decreased from 26 nm for as-deposited thin films to 17 nm for irradiated at a fluence of 1 × 10 12 ions/cm 2. The decrease in crystallite size in all the thin film samples after irradiation indicates a distortion in the lattice structure caused by stress-induced defects. The zero-field-cooled (ZFC) and field-cooled (FC) magnetizations have been recorded in a low field of 100 Oe and they show a typical behavior of superparamagnetic particles. This is further supported by the magnetization hysteresis ( M– H) curve taken at 300 K, for the as-deposited thin film, which shows zero coercivity and remanence. The blocking temperatures calculated from the maxima of ZFC are found to decrease with the increase in irradiation fluence, which is consistent with XRD results.

Administration with Bushenkangshuai Tang alleviates UV irradiation- and oxidative stress-induced lifespan defects in nematode Caenorhabditis elegans

During normal metabolism, oxidative byproducts will inevitably generate and damage molecules thereby impairing their biological functions, including the aging process. Bushenkangshuai Tang (补肾抗衰方, BT) is a traditional Chinese medicine widely used for clinically treating premature ovarian failure. In the present study, BT administration at high concentrations significantly increased lifespan, slowed aging-related decline, and delayed accumulation of aging-related cellular damage in wild-type Caenorhabditis elegans. BT administration could further largely alleviate the aging defects induced by UV and oxidative stresses, and BT administration at different concentrations could largely rescue the aging defects in mev-1 mutant animals. The protective effects of BT administration on aging process were at least partially dependent on the Ins/IGF-like signaling pathway. Moreover, BT administration at different concentrations obviously altered the expression patterns of antioxidant genes and suppressed the severe stress responses induced by UV and oxidative stresses, suggesting that BT-induced tolerance to UV or oxidative stress might result from reactive oxygen species scavenging. BT administration during development was not necessarily a requirement for UV and oxidative stress resistance, and the concentrations of administrated BT examined were not toxic for nematodes. Therefore, BT administration could effectively retrieve the aging defects induced by UV irradiation and oxidative stress in Caenorhabditis elegans.

Myocardial Contrast Echocardiography in Assessment of Stable Coronary Artery Disease at Intermediate Dobutamine‐Induced Stress Level

Myocardial contrast stress echocardiography (stress MCE) is a novel method for diagnosing coronary artery disease (CAD). Few studies have compared the diagnosis of ischemia by stress MCE to angiographic CAD. Dobutamine stress MCE and SonoVue contrast infusion were performed before an elective percutaneous coronary intervention in 37 patients (8 women) aged 45-75 years with symptomatic CAD and at least one significant coronary artery stenosis measured by quantitative coronary angiography (QCA). The total and regional perfusion and wall motion (WM) were scored as normal or abnormal and attributed to the three main epicardial coronary arteries using a 17-segment left ventricular model. An intermediate stress level was obtained in 29 (78%) patients, and 2 (5%) patients obtained peak stress. A perfusion defect was detected in 92% and WM abnormality in 57% of the patients at peak stress (P < 0.01). By perfusion, 70% of stenoses were both detected and correctly anatomically located, compared to 42% by WM (P < 0.01). All 21 patients with multivessel disease and/or proximal left anterior descending (LAD) stenosis measured by QCA were identified by stress-induced perfusion defects, while only 11 of them were identified by WM abnormalities (P < 0.01). Perfusion scoring is superior to WM scoring during stress MCE for diagnosing significant CAD in patients obtaining intermediate stress level, in particular, when multivessel disease or proximal LAD stenosis is present.

Constant current stress of Ti-doped Ta2O5 on nitrided Si

The response of Ti-doped Ta2O5 stacked films (4–6 nm) to constant current stress (CCS) under gate injection has been investigated. Two doping methods (‘surface’ and ‘bulk’ doping of Ta2O5) as well as two Si-surface nitridation processes (rapid thermal annealing in N2O and NH3) have been used to prepare the stacks. The effect of doping approach, Si-surface nitridation and the metal electrode (Al and W) on the dielectric degradation has been discussed in terms of stress-induced leakage current (SILC), stress-induced flat band voltage shifts, charge trapping and defect generation. CCS generates charges in the bulk dielectric and in slow states, whose sign and amount depend on both the nitridation process and the doping approach. The method of doping has the strongest impact on the SILC whose behaviour is found to be substantially different from that in SiO2. The method of doping plays a crucial role in the CCS degradation and can be used as an enabling tool for control of this degradation. The gate-deposition-induced defects are another key factor which controls the stress degradation. These defects are very susceptible to electrical stress and could lead to serious reliability concerns.

Collateral Function in Patients with Coronary Occlusion Evaluated by 201Thallium Scintigraphy

The present study evaluated the impact of the angiographically documented collaterals on regional myocardial perfusion measured by 201thallium scintigraphy in patients with a chronic total occlusion. The study included 60 patients with chronic total occlusion who underwent rest-stress myocardial perfusion scintigraphy and coronary angiography. All patients had angiographic evidence of coronary collaterals. Patients were divided into two groups: group one had well-developed coronary collateral vessels (n=35) and group II had poor coronary collateral development (n=25). Patients with chronic total occlusion had severe and extensive stress-induced myocardial perfusion defects regardless of the grade of angiographic coronary collaterals. The perfusion defects in the group with good collaterals were predominantly reversible, suggesting that coronary collaterals preserved myocardial viability in the regions subtended by a total coronary occlusion. A significant correlation between good collaterals with complete protection and poor collaterals with no protection was noted. Our results demonstrate a protective effect of collaterals on myocardial perfusion during coronary occlusion. The effective angiographic collaterals may prevent resting regional wall motion abnormalities but do not appear to protect against stress-induced perfusion defect.

Drug enhancement of myocardial tracer uptake during myocardial perfusion imaging

Dear Sir, We read with great interest the article by Ergun et al., published in the August 2008 issue, concerning the use of metamizol during Tc-sestamibi myocardial perfusion scintigraphy (MPS), for the detection of perfusion reversibility [1]. The authors performed Tc-sestamibi MPS at stress, at rest and at rest after the oral administration of 1 g metamizol in 21 patients (14 males, 7 females; age range 46–74 years, mean age 57 years), who had partially reversible or irreversible perfusion defects on their stressrest sestamibi scintigram and no history of myocardial infarction. Metamizol-rest MPS displayed the defect reversibility better than rest MPS (defect reversibility was better delineated on metamizol-rest MPS in 33 segments, while 8 out of 14 fixed perfusion defects on stress-rest MPS were shown better on metamizol-rest MPS). Moreover, calculating sestamibi uptake ratios, metamizol-induced sestamibi uptake was significantly higher (p<0.001) than stress/baseline rest examinations. Hence, the authors concluded that “metamizol-enhanced rest MPS increases detectability of ischemic/viable myocardium during MPS” and they advocate obtaining “routine rest MPS with the induction of metamizol to increase the detection rate of the reversibility in the ischemic regions” [1]. It has been reported that technetium-labelled tracers (sestamibi, tetrofosmin) underestimate myocardial viability, mainly when blood flow is severely impaired and tracer delivery is reduced [2–4]. This observation has been supported by initial studies comparing rest-stress Tcsestamibi studies with exercise-redistribution-reinjection Tl-201 or FDG-PET imaging that have shown that Tcsestamibi underestimates viable myocardium [2–4]. However, many subsequent studies have provided convincing evidence of the potential use of Tc-sestamibi (and tetrofosmin) for viability assessment with one or a combination of these approaches: assessing the reversibility of stress-induced defects, determining the severity of resting defects (defect activity ≥60% of peak activity had high positive and negative predictive value of functional recovery after revascularization), assessing radiotracer uptake after nitroglycerin administration, and assessing regional myocardial function and thickening by performing gated-SPECT [5–7]. Nitrates (commonly 400–800 μg of sublingual nitroglycerin at least 5 min before tracer administration at rest, with the patient in the supine position to avoid symptomatic hypotension) can be administered to reduce myocardial resting hypoperfusion and to increase the correspondence of the rest imaging with myocardial viability [5–8]. This manoeuvre is indicated in patients referred for viability evaluation or with a severe defect of uptake in the stress images [8]. As nitrate administration has been used for more than 15 years to improve viability detection, a comparison of metamizol-enhanced MPS with nitrateenhanced MPS would be of significant interest. Although patients may exhibit hypotension due to nitrates, it is rarely of clinical importance when nitrates are given with the patient in the supine position [8]. Acquiring MPS data in a gated (ECG-triggered) mode and evaluating myocardial function and thickening and the related parameters (left ventricular global and regional Eur J Nucl Med Mol Imaging (2009) 36:160–161 DOI 10.1007/s00259-008-0974-z

Angina in Fabry Disease Reflects Coronary Small Vessel Disease

Chest pain is frequently reported in Fabry disease (FD). However, its mechanism and clinical relevance are unclear. Basal troponin I level, exercise stress test, single-photon emission computed tomography imaging with (99m)Tc sestamibi, coronary angiography with thrombolysis in myocardial infarction (TIMI) frame count and left ventricular angiography and endomyocardial biopsy were obtained in 13 patients with FD with angina. Ratio of external to lumen diameter of intramural arteries (E/L ratio), myocyte diameter, and extent of fibrosis were morphometrically evaluated by using tissue sections. Controls for coronary angiography and histology were 25 patients with FD without angina and 20 mitral stenosis patients with normal left ventricular function. Troponin I level was elevated in 6 of the 13 patients. Exercise stress test showed evidence of myocardial ischemia, and single-photon emission computed tomography was positive for stress-induced perfusion defects in all patients with FD with angina. Epicardial coronaries were structurally normal but showed slow flow in all and were associated with aneurisms of posterior left ventricular wall in 3 cases. Histology showed remarkable lumen narrowing of most intramural arteries (mean E/L ratio=3.5+/-1.2; P<0.001 versus both control groups), because of hypertrophy and proliferation of smooth muscle and endothelial cells, both engulfed by glycosphingolipids. Replacement fibrosis exceeded that of both controls (P<0.001). Small vessel disease correlated with coronary slow flow and extent of fibrosis, but did not with patients' age, sex, and degree of left ventricular hypertrophy. patients with FD with angina have perfusion defects, slow coronary flow, and luminal narrowing of intramural arteries. Small vessel disease may contribute to symptomatic limitation and progressive myocardial dysfunction.

Coronary Microvascular Dysfunction in Patients with Cardiomyopathies

Anginal symptoms and electrocardiographic changes suggestive of myocardial ischemia, despite angiographically normal coronary arteries, are common in patients with cardiomyopathies and those with left ventricular hypertrophy secondary to pressure overload. Studies using positron-emission tomography (PET) to measure regional myocardial blood flow have demonstrated that maximum myocardial blood flow and coronary flow reserve are severely blunted in patients with hypertrophic as well as dilated cardiomyopathy.1,2 In the absence of epicardial stenoses, blunted maximum myocardial blood flow and coronary flow reserve are suggestive of coronary microvascular dysfunction.3,4 Furthermore, it has been demonstrated that in both hypertrophic and dilated cardiomyopathy, the severity of coronary microvascular dysfunction, assessed by measuring myocardial blood flow with PET, is an independent predictor of prognosis.2,5 In patients with cardiomyopathies, coronary microvascular dysfunction can be sustained by a number of different pathogenetic mechanisms. These include structural and functional abnormalities of the intramural arterioles as well as extravascular mechanisms (eg, increased extramural compression).4 Article 161 Anderson-Fabry disease (AFD) is an X-linked deficiency of lysosomal α-galactosidase A.6 This deficiency results in multiorgan damage from glycosphingolipid deposition, leading to renal, cardiac, and cerebrovascular disease and premature death. Patients with AFD complain of angina despite angiographically normal coronary arteries. Recent studies have also shown that there is progressive deterioration in left ventricular systolic function and myocardial scarring in patients with AFD cardiomyopathy. A number of mechanisms may contribute to microvascular dysfunction in these patients. AFD cardiomyopathy is characterized by globotriaosyl-ceramide (Gb3) and related glycosphingolipid deposition in myocytes, conduction tissue, vascular endothelium, and valvular tissue. This is accompanied by secondary changes, such as myocyte hypertrophy and fibrosis, often mimicking hypertrophic cardiomyopathy.7 In the vasculature, Gb3 accumulates in endothelial and smooth muscle cells, possibly causing structural abnormalities that may be responsible for vascular dysfunction. In addition, it …

Insights on trap generation and breakdown in ultra thin SiO 2 and SiON dielectrics from low voltage stress-induced leakage current measurements

We review the advancements in the understanding of breakdown and trap generation that have been achieved using low voltage stress-induced leakage current as a probe of the interface states created during electrical stress of ultra thin SiO 2 and SiON gate dielectrics. The technique separates the effects of bulk and interface states on the post-stress I– V characteristics; senses interface traps at both contact interfaces, identifies the regime where interface rather than bulk state generation is the rate limiting step for breakdown, is useful for determining the operative trap creation processes, and reveals the role of trap generation mechanism in driving which stress-induced defect controls breakdown.

Chronic Psychoemotional Stress Impairs Cannabinoid-Receptor-Mediated Control of GABA Transmission in the Striatum

Exposure to stressful events has a myriad of consequences in animals and in humans, and triggers synaptic adaptations in many brain areas. Stress might also alter cannabinoid-receptor-mediated transmission in the brain, but no physiological study has addressed this issue so far. In the present study, we found that social defeat stress, induced in mice by exposure to aggression, altered cannabinoid CB(1)-receptor-mediated control of synaptic transmission in the striatum. In fact, the presynaptic inhibition of GABAergic IPSCs induced by the cannabinoid CB(1) receptor agonist HU210 [(6aR)-trans-3-(1,1-dimethylheptyl)-6a,7,10,10a-tetrahydro-1-hydroxy-6,6-dimethyl-6H-dibenzo[b,d]pyran-9-methanol] was reduced after a single stressful episode and fully abolished after 3 and 7 d of stress exposure. Repeated psychoemotional stress also impaired the sensitivity of GABA synapses to endocannabinoids mobilized by group I metabotropic glutamate receptor stimulation, whereas the cannabinoid CB(1)-mediated control of glutamate transmission was unaffected by repeated exposure to an aggressor. Corticosteroids released in response to the activation of the hypothalamic-pituitary-adrenal axis played a major role in the synaptic defects observed in stressed animals, because these alterations were fully prevented by pharmacological blockade of glucocorticoid receptors and were mimicked by corticosterone injections. The recovery of stress-induced synaptic defects was favored when stressed mice were given access to a running wheel or to sucrose consumption, which function as potent natural rewards. A similar rescuing effect was obtained by a single injection of cocaine, a psychostimulant with strong rewarding properties. Targeting cannabinoid CB(1) receptors or endocannabinoid metabolism might be a valuable option to treat stress-associated neuropsychiatric conditions.

Repeating of positive and negative high electric field stress and corresponding thermal post-stress annealing of the n-channel power VDMOSFETs

We have subjected n-channel power VDMOSFETs to a positive and negative high electric field stress (HEFS) followed by biased annealing at 150°C. Stress-induced defects have been monitored using midgap-subthreshold and charge-pumping techniques, the use of which in tandem has enabled an insight into behaviours of fixed and switching traps in the gate oxide and oxide/silicon interface. The repetition of the stress/annealing sequence has resulted in some quantitative but no qualitative differences in response compared to the original sequence. We have observed complex kinetics of different types the stress-induced defects during post-HEFS annealing, including an intriguing latent buildup of “true” interface traps. Comparison of post-HEFS and post-irradiation annealing data has indicated differences of the nature of defects induced by Fowler-Nordheim injection and irradiation in our samples.