Articles you may be interested inPhysical properties of epitaxial ZrN/MgO(001) layers grown by reactive magnetron sputtering J. Vac. Sci. Technol. A 31, 061516 (2013); 10.1116/1.4825349Effect of off stoichiometry on Raman scattering from epitaxial and polycrystalline HfN x ( 0.85 ≤ x ≤ 1.50 ) grown on MgO (001) While many transition metal ͑TM͒ nitrides-including TiN, ZrN, and TaN-have been widely studied and are currently used as hard wear-resistant coatings, diffusion barriers, and optical coatings, little is known about a related TM nitride, HfN. Here, we report the results of a systematic investigation of the growth and physical properties of HfN x layers, with 0.80ഛ x ഛ 1.50, deposited on MgO͑001͒ by ultrahigh vacuum reactive magnetron sputtering at 650°C in mixed N 2 /Ar discharges. HfN x layers with 0.80ഛ x ഛ 1.20 crystallize in the B1-NaCl structure with a cube-on-cube epitaxial relationship to the MgO͑001͒ substrate, while films with 1.24ഛ x ഛ 1.50 contain a N-rich second phase. The relaxed bulk lattice parameter of HfN x ͑001͒ decreases only slightly with increasing N / Hf ratio, ranging from 0.4543 nm with x = 0.80 to 0.4517 nm with x = 1.20. The room-temperature resistivity of stoichiometric HfN͑001͒ is 14.2 ⍀ cm and ͑x͒ increases with both increasing and decreasing x to 140 ⍀ cm with x = 0.80 and 26.4 ⍀ cm with x = 1.20. The hardness H and elastic modulus E of HfN͑001͒ are 25.2 and 450 GPa, respectively. H͑x͒ initially increases for both over-and understoichiometric layers due to defect-induced hardening, while E͑x͒ remains essentially constant. Single-phase HfN x ͑001͒ is metallic with a positive temperature coefficient of resistivity ͑TCR͒ between 50 and 300 K and a temperature-independent carrier density. It is also superconducting with the highest critical temperature, 9.18 K, obtained for layers with x = 1.00. In the two phase regime, ranges from 59.8 ⍀ cm with x = 1.24 to 2710 ⍀ cm with x = 1.50. TCR becomes positive with x ജ 1.38, no superconducting transition is observed, and both H and E decrease.

While NaCl-structure transition-metal nitrides have been widely studied over the past two decades, little is known about the corresponding NaCl-structure rare-earth nitrides. Polycrystalline CeN, for example, has been reported by different groups to be both a wide band-gap semiconductor and a metal. To address this controversy, we have grown epitaxial CeN layers on MgO͑001͒ and measured their physical properties. The films were grown at 700°C by ultrahigh vacuum reactive magnetron sputter deposition in mixed Ar/N 2 discharges maintained at 4 mTorr ͑0.53 Pa͒. X-ray diffraction and transmission electron microscopy results establish the film/substrate epitaxial relationship as cube-on-cube, (001) CeN ʈ(001) MgO with ͓100͔ CeN ʈ͓100͔ MgO , while Rutherford backscattering spectroscopy shows that the layers are stoichiometric with N/Ceϭ0.99Ϯ0.02. CeN is metallic with a positive temperature coefficient of resistivity and a temperature-independent carrier concentration, as determined by Hall effect measurements, of 2.8Ϯ0.2ϫ10 22 cm Ϫ3 with a room temperature mobility of 0.31 cm 2 V Ϫ1 s Ϫ1. At temperatures between 2 and 50 K, the resistivity is limited by defect scattering and remains constant at 29 ⍀ cm, while at higher temperatures it increases linearly, limited primarily by phonon scattering, to reach a room-temperature value of 68.5 ⍀ cm. The hardness and elastic modulus of CeN͑001͒ were determined from nanoindentation measurements to be 15.0Ϯ0.9 and 330Ϯ16 GPa.

Campylobacter is a food-borne zoonotic pathogen that causes human gastroenteritis worldwide. Campylobacter bacteria are commensal in the intestines of many food production animals, including ducks and chickens. The objective of the study was to determine the prevalence of Campylobacter species in domestic ducks, and the agar dilution method was used to determine resistance of the isolates to eight antibiotics. In addition, multilocus sequence typing (MLST) was performed to determine the sequence types (STs) of selected Campylobacter isolates. Between May and September 2012, 58 duck farms were analyzed, and 56 (96.6%) were positive for Campylobacter. Among the isolates, 82.1% were Campylobacter jejuni, 16.1% were C. coli, and one was unidentified by PCR. Of the 46 C. jejuni isolates, 87.0%, 10.9%, and 21.7% were resistant to ciprofloxacin, erythromycin, and azithromycin, respectively. Among the C. coli isolates, all 9 strains were resistant to ampicillin, and 77.8% and 33.3% were resistant to ciprofloxacin and azithromycin, respectively. The majority of the Campylobacter isolates were classified as multidrug resistant. Twenty-eight STs were identified, including 20 STs for C. jejuni and 8 STs for C. coli. The most common clonal complexes in C. jejuni were the ST-21 complex and the ST-45 complex, while the ST-828 complex predominated in C. coli. The majority of isolates were of STs noted in ducks and humans from earlier studies, along with seven STs previously associated only with human disease. These STs overlapped between duck and human isolates, indicating that Campylobacter isolates from ducks should be considered potential sources of human infection.

Fully strained single-crystal metastable Ge 1−x Sn x layers were grown on Ge͑001͒ in order to probe the role of Sn dopant and alloy concentrations ͑C Sn =1ϫ 10 18 cm −3 to 6.1 at. % ͒ on surface roughening pathways leading to epitaxial breakdown during low-temperature ͑155°C͒ molecular-beam epitaxy of compressively strained films. The addition of Sn was found to mediate Ge͑001͒ surface morphological evolution through two competing pathways. At very low Sn concentrations ͑x Շ 0.02͒, the dominant effect is a Sn-induced enhancement in both the Ge surface diffusivity and the probability of interlayer mass transport. This, in turn, results in more efficient filling of interisland trenches, and thus delays epitaxial breakdown. In fact, breakdown is not observed at all for Sn concentrations in the doping regime, 1 ϫ 10 18 ഛ C Sn Ͻ 4.4ϫ 10 20 cm −3 ͑2.3 ϫ 10 −5 ഛ x Ͻ 0.010͒! At higher concentrations, there is a change in Ge 1−x Sn x ͑001͒ growth kinetics due to a rapid increase in the amount of compressive strain. This leads to a gradual reduction in the film thickness h 1 ͑x͒ corresponding to the onset of breakdown as strain-induced roughening overcomes the surface smoothening effects, and results in an increase in the overall roughening rate. We show that by varying the Sn concentration through the dopant to dilute alloy concentration range during low-temperature Ge͑001͒ growth, we can controllably manipulate the surface roughening pathway, and hence the epitaxial thickness, over a very wide range.

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