Seven Escherichia coli O157:H7 strains, three pathogenic (including epidemic EDL933 and Sakai) and four nonpathogenic (including mutants of EDL933 and Sakai), were compared to find a model strain to avoid the use of European third-class biological agents in biofilm studies. Comparison was performed on attached populations reached at the end of growth in eight environmental conditions defined as the combinations of three two-level factors: (i) culture medium composed of meat exudate and glucose-supplemented minimal salts medium (MSM), (ii) growth temperatures of 15 and 25 degrees C, and (iii) materials of stainless steel and polyurethane. The influence of each of these four factors (strain, medium, temperature, and material) often depended on the level of at least one of the others. Exudate produced attached populations that were larger than or similar to those obtained with MSM, except for EDL933 mutant at 15 degrees C. When exudate led to larger populations than did MSM, the highest differences of up to 1.8 log CFU/cm2 were observed with the nonepidemic strains grown at 25 degrees C. Populations of these strains were not significantly different in any of the conditions studied, but they were different from the epidemic strains in some conditions. No nonpathogenic mutant was representative of its parental strain. Furthermore, the Sakai mutant biofilm was significantly more reduced than its parental strain was after chemical shock. It is therefore not possible to find a surrogate of either EDL933 or Sakai, and it is advisable that main results be validated on a pathogenic strain whenever nonpathogenic strains are used.

In this paper, the sputtering-grown [Au 6nm/Co 0.5nm]×10 and [Pt 6nm/Co 0.5nm]×15 superlattices are irradiated using N+ 150keV ions with fluences ranging from 1012 up to 3×1016N+/cm2. The effect of this ion irradiation experiment on perpendicularly magnetized Co/Au and Co/Pt superlattices is presented. Combining structural and magneto-optical measurements, we reveal the differences in the ion induced mixing between miscible Co–Pt and immiscible Co–Au layered systems. For Co/Pt ones, the progressive ballistic intermixing between Co and Pt leads to a decrease of perpendicular anisotropy and to an in-plane reorientation of the easy axis of magnetization. Although, for Co/Au superlattices the mixing occurs but a thermodynamic phase separation is observed. The structural investigations show that for high fluences the Co layers are disrupted in islands with few nanometer size embedded in Au layers. The perpendicular magnetic anisotropy decreases with fluence but no anisotropy reorientation appears.

Some device design issues of the impact-ionization MOS (I-MOS)device are discussed in terms of the junction depth of the source extension region and the substrate doping concentration. It is found that the source extension region is needed to be as shallow as possible in order to minimize the avalanche breakdown voltage. Furthermore, it is observed that the dependence of the threshold voltage of the I-MOS device on the substrate doping concentration is contrary to that of the MOSFET, which is an interesting phenomenon. It is related to the junction abruptness between the channel and the i-region, which is explained by using the concept of maximum lateral electric field.

In silicon nanocrystal based metal-oxide-semiconductor memory structures, tuning of the electron tunneling distance between the Si substrate and Si nanocrystals located in the gate oxide is a crucial requirement for the pinpointing of optimal device architectures. In this work, we show how to manipulate and control the depth-position and the density of 2D arrays of Si ncs embedded in thin (< 10 nm) SiO2 layers, fabricated by ultra-low energy (typically 1 keV) ion implantation. It is demonstrated that the injection distance between the ncs band and the channel can be tuned from 10 to 2 nm by a judicious combination of ion beam energy and initial SiO2 thickness. Annealing under slightly oxidizing ambient has been found essential for the optimization of the memory properties of the devices. During such oxidations, the oxide integrity is restored, the ncs are passivated and a separation of connected ncs takes place, making possible a further increase of the ncs density and a decrease of their mean size.

In silicon nanocrystal based metal–oxide–semiconductor memory structures, tuning of the electron tunneling distance between the Si substrate and Si nanocrystals located in the gate oxide is a crucial requirement for the pinpointing of optimal device architectures. In this work it is demonstrated that this tuning of the “injection distance” can be achieved by varying the Si+ ion energy or the oxide thickness during the fabrication of Si nanocrystals by ultralow-energy silicon implantation. Using an accurate cross-section transmission electron microscopy (XTEM) method, it is demonstrated that two-dimensional arrays of Si nanocrystals cannot be positioned closer than 5 nm to the channel by increasing the implantation energy. It is shown that injection distances down to much smaller values (2 nm) can be achieved only by decreasing the nominal thickness of the gate oxide. Depth profiles of excess silicon measured by time-of-flight secondary ion mass spectroscopy and Si nanocrystal locations determined by XTEM are compared with Monte-Carlo simulations of the implanted Si profiles taking into account dynamic target changes due to ion implantation, ion erosion, and ion beam mixing. This combination of experimental and theoretical studies gives a safe explanation regarding the unique technological route of obtaining Si nanocrystals at distances smaller than 5 nm from the channel: the formation of nanocrystals requires that the interface mixing due to collisional damage does not overlap with the range profile to the extent that there is no more a local maximum of Si excess buried in the SiO2 layer.

The effect of N+ ion irradiation on the magnetic anisotropy of ultrathin Co films in the Pt/Co(1 nm)/Pt (111) system is investigated. The magneto-optical measurements indicate that the as-deposited trilayers display a perpendicular magnetic anisotropy whose properties drastically change with the fluence in the range of 1012 to 1016 ions/cm2. The coercive field progressively decreases as the fluence increases. The superconducting quantum interference device measurements evidence that, for the highest fluences, the paramagnetic limit is not reached moreover an in-plane switching of the anisotropy is observed. Simulations are performed to evaluate damage energy induced by N+ irradiation.

Effect of N+ ion irradiation on the magnetic anisotropy of Co ultrathin films in the Pt/Co/Pt systems has been investigated. The magneto-optical measurements indicate that the as-deposited trilayers display a perpendicular magnetic anisotropy whose properties drastically change with the fluence in the range of 1012–5×1015ions/cm2. The coercitive field progressively decreases as the fluence rises. However, even for the highest doses, the paramagnetic limit has not been reached while the perpendicular anisotropy was inhibited due to the intermixing produced by the ion irradiation.

Twenty nine bacterial strains were grown as binary culture biofilms with Listeria monocytogenes to assess their influence on the settlement of the latter on stainless steel coupons. Most of the strains had been isolated from food processing plants after cleaning and disinfection and were tentatively identified by the APILAB Plus 3.3.3 database (bioMérieux). Sixteen of them decreased L. monocytogenes biofilm colony forming units (CFU) counts. Three strains, Bacillus sp. CCL 9 an unidentified Gram-positive strain CCL 59 and Pseudomonas fluorescens E9. 1, led to a 3-log difference in CFU counts between the pure L. monocytogenes biofilms and the mixed biofilms. Eleven strains had no effect and only four, Kocuria varians CCL 73, Staphylococcus capitis CCL 54, Stenotrophomonas maltophilia CCL 47 and Comamonas testosteroni CCL 24, had a positive effect, with a 0.5- to 1.0-log increase in the L. monocytogenes biofilm CFU counts. On its own, L. monocytogenes settled as single cells, but in binary biofilms, different spatial arrangements were observed: (i) with K. varians CCL 73, K. varians CCL 56 and S. capitis CCL 54, L. monocytogenes cells gathered around the microcolonies of the partner strain; (ii) with the two Gram-negative strains, C. testosteroni CCL 24 and CCL 25, L. monocytogenes cells formed its own microcolonies. No link could be found between the exopolysaccharide production capacity of the bacterial strains in pure-culture biofilms and their effect on the L. monocytogenes population in mixed biofilms. With one strain, C. testosteroni CCL 24, adding filter-sterilized supernatant from a pure-culture biofilm to a pure culture of L. monocytogenes increased the number of L. monocytogenes cells adhering to the stainless steel coupons and forming microcolonies. This study suggests that the “house flora” can have a strong effect on the likelihood of finding L. monocytogenes on inert surfaces.

The electrical characteristics of thin silicon dioxide layers with embedded Si nanocrystals obtained by low-energy ion beam implantation and subsequent annealing have been investigated through capacitance and current–voltage measurements of MOS capacitors. The effects of the implantation energy (range: 0.65–2 keV), annealing temperature (950–1050°C) and injection oxide characteristics on charge injection and storage are reported. It is shown that the implantation energy allows for a fine control of the memory window characteristics, and various device options are possible including memory operation with charge injection at low gate voltages.

Silicon nanocrystals buried in a thin oxide can be used as charge storage elements and be integrated in standard CMOS technology to fabricate new non-volatile memory devices. The control of the distances between the nanocrystals layer and the two electrodes of the MOS determines the final characteristics of the device (write–erase and retention times). This 2D arrays of ncs can be elaborated by ion implantation. In this work, we study by TEM the effect of varying the beam energy and dose on the positioning of 2D-arrays of nanocrystals within 10nm thick oxide after annealing. Our results show that the “injection distance” can be precisely tuned in the 5–8nm range by varying the beam energy.

Metal-Oxide-Semiconductor structures exhibiting significant charge storage due to the presence of Si nanocrystals into the amorphous oxide matrix have been fabricated by 1keV Si ion implantation into 10nm SiO2 gate oxide layer. The effect of the implanted dose and annealing temperature on the memory window is reported. Large shifts of flat-band voltage are achieved at very low programming electric fields (4V at 2MV/cm).

Silicon nanocrystals buried in a thin oxide can be used as charge storage elements and be integrated in standard CMOS technology to fabricate new non-volatile memory devices. In this geometry, the control of the distances between the nanocrystals layer and the two electrodes, the channel and the gate, of the MOS determines the final characteristics of the device (write-erase and retention times). In this work, we report on a systematic study of the effect of varying the beam energy (0.65 - 2 keV) and the dose (10(15)-10(16) cm(-2)) on the positioning of 2D-arrays of nanocrystals within 10 urn thick oxide after annealing at 950 and 1050degreesC. For this, different Transmission Electron Microscopy (TEM) methods have been used including High Resolution Electron Microscopy (HREM) for imaging isolated nanocrystals and Fresnel contrast imaging of populations of nanocrystals. Our results show that the "injection distance" can be precisely tuned in the 5-8 nm range by varying the beam energy. Moreover, very large swelling of the SiO2 layer has been observed when increasing the implanted dose which could be the result of a partial oxidation of the Si ncs layer and/or of the SiO2/Si interface.

The survival of Listeria monocytogenes in a binary biofilm with a bacteriocin producer (Lactococcus lactis CNRZ 150) was investigated. Two situations were simulated: in the first, L. monocytogenes was deposited on a 1-day biofilm of Lactococcus lactis (deferred adhesion); in the second, L. monocytogenes was simultaneously mixed with Lact. lactis (simultaneous adhesion). Biofilms were cultivated in tryptic soy broth supplemented with 6 g l−1 of yeast extract (TSB-YE) and L. monocytogenes counts were followed for 48 h, both in co-culture with Lact. lactis and in pure culture. The influence of the mode of inoculation of L. monocytogenes (deferred or simultaneous adhesion) into the Lact. lactis biofilm, the size of the L. monocytogenes inoculum and the replacement of the culture medium at 20–24 h on the survival of L. monocytogenes was studied. Results showed that the antilisterial activity of the Lact. lactis started within the first 6 h of the deposition of L. monocytogenes. The log cycle reduction rate in number of L. monocytogenes in the mixed biofilm (compared to the pure biofilm) was greatly dependent on the inoculum size: when the smallest inoculum was used to colonise stainless steel coupons (106–107 CFU ml−1), the log cycle reduction was greater and L. monocytogenes was not detected after t=10 h (simultaneous adhesion) and t=24 h (deferred adhesion) in the adherent population as well as in the planktonic population. On the other hand, in the case of a greater supply of L. monocytogenes (108 CFU ml−1), the results showed that the early reduction of L. monocytogenes counts was relatively slow and was followed by a stabilisation of the population, leading to the establishment of a great number of resident cells in the biofilm (105 to 106 CFU cm−2). This population level was maintained during the 48 h of experimentation and replacement of the culture media with fresh medium at t=22 h (simultaneous adhesion) or t=24 h (deferred adhesion) did not modify the level of the population of L. monocytogenes within the biofilm.