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Context Sound reproductive efficiency is a key determinant for the overall productivity and profitability of a beef breeding business. Failure of a cow to conceive results in either culling or the cost of carrying non-pregnant animals. Aims This study aimed to determine and quantify the major factors associated with non-pregnancy in commercial beef breeding herds of northern Australia. Methods A prospective population-based epidemiological study of the likelihood of non-pregnancy in cows after an annual mating in northern Australian beef breeding cows used data from 73 herds from four broad country types and 62 323 animal years; approximately 80 property-, management-group- and cow-level risk factors were considered. A multivariable model building process was employed to scrutinise the resulting dataset, so as to identify what herd management practices, nutritional, environmental, and individual cow factors were associated with non-pregnancy and estimate their magnitude of effect. Key results Non-pregnancy was disproportionately high in the Northern Forest (32.1%), compared with the Northern Downs, Central Forest and Southern Forest where it was 17.1%, 16.0% and 13.2% respectively. Time of expected calving had the largest impact on occurrence of non-pregnancy. Parity also had a significant influence, with first-lactation cows typically having 5–12% higher non-pregnancy than did mature cows. Non-pregnancy decreased with an increasing body condition score at the branding/weaning muster for lactating cows. The difference in non-pregnancy when comparing availability of wet-season pasture phosphorus content and digestibility of pasture during the dry season was 13.2 and 10.2 percentage points respectively. Conclusions This study demonstrated the substantial impact environment, herd management practices, nutrition and disease factors can have on the reproductive performance of females. Implications To optimise the efficiency of females (through reducing the occurrence of non-pregnancy) under commercial conditions in northern Australia, production systems should support beef herds calving early in the production year, being in at least moderate body condition and having access to more digestible pastures that address the nutritional requirements for both protein and phosphorus. This indicates focus for management, especially in the Northern Forest where the likelihood of non-pregnancy was highest.

Context Sound reproductive efficiency is a key determinant for the overall productivity of a beef breeding business. For beef breeding herds to obtain high levels of reproductive productivity, breeding females need to efficiently become pregnant while lactating. Aims This study aimed to determine and quantify the major factors associated with lactating cows becoming pregnant within 4 months of calving (P4M) in commercial beef breeding herds of northern Australia. Methods A prospective epidemiological study was conducted using 78 commercial northern Australian beef breeding herds and involved 78 000 cattle that were monitored for 3–4 years. A multivariable model-building process was employed to scrutinise the resulting dataset to identify what herd-management practices, and nutritional, environmental and individual cow factors were major determinants of lactating cows becoming pregnant within 4 months of calving (P4M) and to estimate their magnitudes of effect. Key results Overall, 41.6% of cows per production year were successful for P4M. Country type was strongly associated with 65.4%, 57.5%, 61.8% and 16.4% P4M for the Southern Forest, Central Forest, Northern Downs, and Northern Forest respectively. Between-year variability ranged between 3.3 and 11.7 percentage points. Cows calving in December–January (61%) had a substantially higher occurrence of P4M than did cows calving between July and September (15%). The difference in P4M when comparing availability of wet-season pasture protein and phosphorus was 12.7 and 20.3 percentage points respectively. Modelling of the impact of group seroprevalence and management group prevalence of recent infection with several infectious diseases was estimated, with a large negative association between group bovine viral diarrhoea seroprevalence and P4M suggested. Conclusions This study further demonstrated the substantial impact that environment, herd management practices, nutrition and disease factors can have on the reproductive performance of females. Implications To optimise the performance of females (through increasing the occurrence of cows contributing calves in consecutive years) under commercial conditions in northern Australia, herd managers should focus on maximising the proportion of cows within a herd calving at the desired time of the year, ensuring that any nutritional deficiencies and herd health issues are managed, and that cows are managed such that they are of good body condition score at the time of calving.

Context There are multiple reports of high annual cow mortality rates in northern Australia, but no reports clearly indicating the overall rates and the impact of primary risk factors. Aims The research aimed to determine which measured region-, property-, management group- and animal-level risk factors are associated with missing pregnant females. Methods Risk factors for the annual rate of pregnant-cow mortality were investigated in an epidemiological study using outcomes for 21 554 cows from 52 beef herds in 2009 and 2010 in four primary country types within the mostly-dry tropical north Australian environment. Modelling of 2001–2011 Australian beef-herd statistics was used to corroborate and further quantify findings. Key results In the epidemiological study, the overall predicted annual mean incidence of missing pregnant cows, a surrogate for mortality, was 10.9%, including lost tags and unrecorded cow movement that were estimated to constitute up to 9% missing cows. Risk factors associated with higher pregnant-cow mortality were as follows: not having follow-up rainfall more than 30 days after the first wet-season storms (4 percentage point increase)

Context Sound reproductive efficiency is a key determinant for the overall productivity of a beef breeding business. For beef breeding herds to obtain high levels of reproductive productivity, breeding females need to efficiently become pregnant while lactating. Aims This study aimed to determine and quantify the major factors associated with lactating cows becoming pregnant within 4months of calving (P4M) in commercial beef breeding herds of northern Australia. Methods A prospective epidemiological study was conducted using 78 commercial northern Australian beef breeding herds and involved 78 000 cattle that were monitored for 3–4years. A multivariable model-building process was employed to scrutinise the resulting dataset to identify what herd-management practices, and nutritional, environmental and individual cow factors were major determinants of lactating cows becoming pregnant within 4months of calving (P4M) and to estimate their magnitudes of effect. Key results Overall, 41.6% of cows per production year were successful for P4M. Country type was strongly associated with 65.4%, 57.5%, 61.8% and 16.4% P4M for the Southern Forest, Central Forest, Northern Downs, and Northern Forest respectively. Between-year variability ranged between 3.3 and 11.7 percentage points. Cows calving in December–January (61%) had a substantially higher occurrence of P4M than did cows calving between July and September (15%). The difference in P4M when comparing availability of wet-season pasture protein and phosphorus was 12.7 and 20.3 percentage points respectively. Modelling of the impact of group seroprevalence and management group prevalence of recent infection with several infectious diseases was estimated, with a large negative association between group bovine viral diarrhoea seroprevalence and P4M suggested. Conclusions This study further demonstrated the substantial impact that environment, herd management practices, nutrition and disease factors can have on the reproductive performance of females. Implications To optimise the performance of females (through increasing the occurrence of cows contributing calves in consecutive years) under commercial conditions in northern Australia, herd managers should focus on maximising the proportion of cows within a herd calving at the desired time of the year, ensuring that any nutritional deficiencies and herd health issues are managed, and that cows are managed such that they are of good body condition score at the time of calving.

Objective To evaluate the effect of collecting serial tracheal aspirate (TA) and bronchoalveolar lavage (BAL) samples on the cytological findings of subsequent fluid samples obtained from horses without clinical signs of respiratory disease. Study design Experimental. Study population Six healthy Standardbred horses. Methods Endoscopically-guided TA samples, and BAL samples collected using the blind field technique were obtained from the six horses on days 1, 2, 3, 4, 5, 12, and 17. On day 17, horses were sampled three times: at baseline and at 2.5 h and 4 h apart. The differential cytology of the fluid samples collected at each time point was expressed as percentages and compared statistically. Results There was a significant increase in neutrophil percentage in the TA samples taken at day 17 (at 2.5 h but not at 4 h apart). There was no significant change in the neutrophil percentages in the TA samples when repeated samples were taken ≥24 h apart. There was no significant change in the neutrophil percentages in the BAL fluid at any collection point. There were inconsistent changes in the percentages of lymphocytes and macrophages in the BAL fluid over time, but these remained within normal reference ranges and were considered clinically insignificant. Conclusions Serial TA and BAL samples can be taken at 24 h intervals without affecting the cytological findings of subsequent fluid samples collected using the techniques described.

The bag-shelter moth, Ochrogaster lunifer Herrich-Schaffer (Lepidoptera: Notodontidae), is associated with a condition called equine amnionitis and fetal loss (EAFL) on horse farms in Australia. Setal fragments from O. lunifer larvae have been identified in the placentas of experimentally aborted fetuses and their dams, and in clinical abortions. The gregarious larvae build silken nests in which large numbers cohabit over spring, summer and autumn. The final instars disperse to pupation sites in the ground where they overwinter. Field-collected O. lunifer larvae, their nests and nearby soil were examined using light and electron microscopy to identify setae likely to cause EAFL and to determine where and how many were present. Microtrichia, barbed hairs and true setae were found on the exoskeletons of the larvae. True setae matching the majority of setal fragments described from equine tissue were found on third to eighth instar larvae or exuviae. The number of true setae increased with the age of the larva; eighth instars carried around 2.0-2.5 million true setae. The exuvia of the pre-pupal instar was incorporated into the pupal chamber. The major sources of setae are likely to be nests, dispersing pre-pupal larvae and their exuviae, and pupal chambers.

Retail live poultry markets (LPMs) may act as a reservoir of avian influenza viruses (AIV). In this study we test the hypothesis that a rest day in the LPMs where the stalls are completely emptied of poultry, cleansed, and restocked will reduce the isolation rates of avian influenza viruses. The isolation rate of H9N2 subtype viruses from chicken was significantly lower after the rest day than prior to it, indicating its impact in reducing transmission. In contrast, Newcastle disease virus (NDV) isolation rates appear unaffected by this intervention, possibly reflecting differences in herd immunity or virus transmission dynamics.

We have observed significant dark-field diffraction contrast from adjacent terraces of the GaN (0001) surface in low-energy electron microscopy, an unexpected result, as the surface is not reconstructed and thus has no superlattice reflections. Calculations show that the contrast originates from a 60° rotation of the hexagonal unit cell across odd-multiple bilayer-high steps. The result is general: the terrace morphology from any {0001} surface of wurtzite structures can be simply imaged even if the surface is not reconstructed.

The surface morphology and structure of AlN deposited by metal organic vapor phase epitaxy (MOVPE) on Si (111) at growth temperatures ranging from 825 to 1175°C was investigated. Transmission electron microscopy (TEM), reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), and secondary ion mass spectrometry (SIMS) techniques were used to study the resulting film structure. Growth at high temperatures but less than ∼1100°C, resulted in a wire texture with some degree of in-plane alignment with (0001)AlN/ /(111)Si, < 10 0>AlN//< 11>Si, and 110>AlN//<10>Si. Deposition at temperatures greater than 1100°C results in single crystal films consisting of domains 60 nm across with an aspect ratio near unity. Growth below1100°C leads to degraded crystal quality with the grains developing random rotational misalignments around the AlN [0001] axis. Growth at lower temperatures produces islands elongated along the [110] direction. At the growth temperature of 825°C, the aspect ratio of the islands increased to 3 and a width of 25 nm. Cross-sectional TEM reveals that these islands are faceted due to slow growth on the {1 01}planes.

We report spectroscopic ellipsometry (SE) and low-temperature reflectance data on epitaxial GaN thin-film samples covering the widest range of tensile and compressive stress (−3.8 to 3.5 kbar) thus far. SE allows us to assess the preparation of smooth and abrupt GaN surfaces by chemical treatments in real time, and, coupled with the reflectance data, the E d n /d E contribution to dispersion, which is important for laser action. The reflectance data explicitly show the non-linear behavior of the B-A and C-A splittings vs. the energy of the A exciton. Lineshape ambiguities that hindered previous interpretations have been resolved with reciprocal space analysis, allowing us to obtain band parameters such as Δ SO =17.0±1 meV and Δ CF =9.8±1 meV with increased confidence.

We report spectroscopic ellipsometry (SE) and low-temperature reflectance data on epitaxial GaN thin film samples covering the widest range of tensile and compressive stress (−3.8–3.5 kbar) thus far. SE allows us to assess the preparation of smooth and abrupt GaN surfaces by chemical treatments in real time, and, coupled with the reflectance data, the E dn/dE contribution to dispersion, which is important for laser action. The reflectance data explicitly show the nonlinear behavior of the B–A and C–A splittings versus the energy of the A exciton. Lineshape ambiguities that hindered previous interpretations have been resolved with reciprocal space analysis, allowing us to obtain band parameters such as ΔSO=17.0±1 meV and ΔCF=9.8±1 meV with increased confidence.

The effects of flow rate variation and geometry on the growth rate, growth uniformity and crystal quality were investigated in a horizontal gallium nitride vapor-phase epitaxy reactor. The effects of these parameters, were studied through the comparison of numerical model predictions to experimentally observed values. Gas-phase reactions between Groups III and V sources and deposition of material on the wall are shown to lead to reduced overall growth rates and may be responsible for inferior crystal quality. A low ammonia concentration is correlated with the deposition of polycrystalline films. A low V III ratio and ammonia concentration lead to inferior crystalline quality and increased yellow luminescence. An optimum HVPE growth process requires selection of reactor geometry and operating conditions to minimize gas-phase reactions and wall deposition while providing a uniform reactant distribution across the substrate.

The metalorganic vapor phase epitaxial (MOVPE) growth of II–VI compounds for visible light-emitting structures is complicated by a variety of growth chemistry, defect, and doping issues. While MOVPE has been successful in the growth of individual layers required in such structures, MOVPE has lagged behind molecular beam epitaxy (MBE) in the formation of working devices. The choice of the specific heterojunction systems utilized in the device structure can have a strong impact on the utility of MOVPE in the eventual formation of II–VI visible light emitters. The current stage of development of MOVPE for these applications is reviewed in the paper, with emphasis on the development of suitable growth and doping technologies.

Cesarean section has become a common surgical procedure and there is a tendency for both veterinarians and their clients to regard it as routine. It is important to remember, however, that a cesarean section entails major abdominal surgery, with inherent risks, irrespective of the prevailing conditions or personnel involved.

Equine amnionitis and fetal loss (EAFL) is an unusual form of abortion in mid- to late-gestation mares, first identified in Australia in 2004. It has been shown that both whole processionary caterpillars (Ochrogaster lunifer) and their shed exoskeletons can induce abortion in mares during midgestation. These abortions exhibited gross pathology and bacteriology results consistent with field cases of EAFL.To determine whether exposure of mares to the shed exoskeletons of processionary caterpillars can induce abortion in the preplacentation (35 days' gestation) and early placentation (45-60 days) stages of pregnancy.In vivo experimental study.Mares less than 35 days' gestation and between 45 and 60 days' gestation were exposed to a slurry of shed processionary caterpillar exoskeletons by nasogastric intubation. Mares were monitored by clinical examination daily. Transrectal ultrasonography was performed daily (control and treated preplacentation mares, treated early placentation mares) or every second day (control early placentation mares). Uterine swabs were collected from mares that aborted. All live foals underwent a clinical examination. Placentas were examined, with sampling for bacteriology and histopathology if appropriate.Abortions occurred in treated mares in both experiments without signs of impending abortion. One mare aborted in the embryonic stage experiment and 2 in the early placentation experiment. Embryonic and fetal death was detected on transrectal ultrasonography prior to abortion. In the early placentation experiment, one foal was born 5 weeks preterm and was very small, with laxity of the tendons in all limbs. Enteric or environmental bacteria, consistent with EAFL, were isolated from the mares that aborted. Focal mucoid placentitis lesions were present on the placentas of 2 treated mares, one from each experiment.Processionary caterpillar exposure may be associated with EAFL-related embryonic and early fetal loss in mares. Processionary caterpillars may also play a role in the occurrence of focal mucoid placentitis.

To assess the clinical suitability of alfaxalone as an anaesthetic induction and maintenance agent for kittens aged less than 12 weeks.The study group comprised 34 kittens aged less than 12 weeks that were presented for surgical desexing. They were aged by dentition, examined and weighed prior to premedication with acepromazine, atropine and morphine. At 20-30 min after premedication, animals were anaesthetised with intravenous alfaxalone administered to effect, using a target maximum expected dose of 5 mg/kg. All cats were intubated: 25 were maintained with isoflurane in oxygen administered with a non-rebreathing circuit and 8 were maintained by supplemental intravenous administration of alfaxalone. Subjective measures of anaesthetic quality and vital signs were recorded from enrolment to recovery. Cats receiving supplemental alfaxalone for maintenance were evaluated for time to first supplemental dose and the total dose of supplemental alfaxalone (mg/kg/h). Descriptive and comparative statistics were used to analyse and present collected data.The mean (± SD) dose of alfaxalone for induction was 4.7 ± 0.5 mg/kg body weight. Subjective measures of anaesthetic quality indicated acceptable induction, maintenance and recovery standards. Measured cardiovascular and respiratory parameters were well maintained.Alfaxalone in 2-hydroxypropyl-beta-cyclodextrin (Alfaxan®) is a suitable injectable anaesthetic induction agent for juvenile cats aged less than 12 weeks requiring anaesthesia. Maintenance of anaesthesia with supplemental doses of alfaxalone may be a suitable alternative in kittens when the use of inhalant anaesthetic maintenance is not feasible.

In Australia, there have been recent reports of unusual abortions in mid- to late-gestation mares. These were clinically distinct from other recognised causes of pregnancy loss and the term 'equine amnionitis and fetal loss' (EAFL) was adopted to describe this syndrome. Initial investigations concluded that possible causal factors included the presence on affected stud farms of Processionary caterpillars (Ochrogaster lunifer).To determine if exposure of pregnant mares to Processionary caterpillars or their shed exoskeletons can induce EAFL.Processionary caterpillars and their shed exoskeletons were collected and stored frozen. Mid-gestation mares were dosed with a slurry of caterpillars or shed exoskeleton by nasogastric intubation. Their clinical responses and times to abortion were recorded. All aborted fetuses were autopsied and samples taken for bacteriological and virological culture and histopathology.Intubating mares in mid-pregnancy with preparations of either whole Processionary caterpillars or shed caterpillar exoskeletons induced abortion with few impending clinical signs. The gross pathological and bacteriological findings of the aborted fetuses were similar to those observed in field cases of EAFL.Possible exposure to Processionary caterpillars should be considered when examining cases of fetal loss in the mare. The present results provide a starting point to further explore the aetiology and pathogenesis of EAFL.

At the time of the initial notification of the occurrence of equine influenza (EI) in Australia in August 2007, vaccination was restricted to horses for which it was an import requirement and only with the approval of the state or territory Chief Veterinary Officer. This paper describes the complexities involved in the selection of a vaccine and its distribution. A combination of ring, predictive and blanket vaccination was implemented during the response. The specific vaccination programs, including its use in buffer zones and for movement of horses, the performance of the vaccine, any adverse reactions and the effect on exposure of vaccinated horses to circulating virus, are also described. Vaccination is considered to have made a valuable contribution to the containment and subsequent eradication of EI from Australia and to risk management in the resumption of horse activities in affected areas from December 2007. Movement restrictions and other biosecurity measures were critically important in controlling the spread of EI and contributing to its eventual eradication, and vaccination was an aid to these measures.

An outbreak of equine influenza (EI) caused by influenza A H3N8 subtype virus occurred in the Australian states of Queensland and New South Wales in August 2007. Infection in the Australian horse population was associated with the introduction of infection by horses from overseas. The first case of EI in Queensland was detected on 25 August 2007 at an equestrian sporting event. Infection subsequently spread locally and to other clusters through horse movements prior to the implementation of an official standstill. There were five main clusters of infected properties during this outbreak and several outliers, which were investigated to find the potential mechanism of disease spread. To contain the outbreak, Queensland was divided into infection status zones, with different movement controls applied to each zone. Vaccination was implemented strategically in infected areas and within horse subpopulations. Control and eventual eradication of EI from Queensland was achieved through a combination of quarantine, biosecurity measures, movement control, rapid diagnostic testing and vaccination.

During the 2007 equine influenza (EI) outbreak, infected horses were quarantined at Morgan Park Recreational Grounds (MPRG) near Warwick, Queensland. Some individuals caring for horses were reported to have made return journeys between MPRG and home properties containing other horses during the time there was active infection at MPRG.A retrospective cohort study to assess the biosecurity and hygiene measures undertaken and their outcomes.All individuals recorded as being responsible for caring for one or more horses at MPRG, and who were also recorded on entry and exit logs at the gate to MPRG during the period of interest, and kept horses at their home property were contacted for a telephone questionnaire.Of the 31 individuals identified, valid responses were obtained from 27 (87% response rate). Respondents had 2-25 horses at their home property, and 1-10 return trips were reported; 11 respondents reported contact with horses at home and provided information on biosecurity practices.Although horses at some home properties became infected with EI, it appears unlikely that this was the result of spread from MPRG via horse handlers. Simple preventive measures based on personal decontamination and other biosecurity measures are considered likely to have prevented spread of infection from MPRG to other properties.

Objective Determine the prevalence of the major enteric pathogens in dairy and dairy beef calves with diarrhoea in Australia. Design Cross‐sectional study. Methods Faecal samples from 84 Australian dairy and dairy beef properties (597 samples) were screened for rotavirus and coronavirus using real‐time reverse transcription polymerase chain reaction, for Salmonella spp. using selective enrichment faecal culture, and for enterotoxigenic Escherichia coli (K99) and Cryptosporidium parvum using a commercial enzyme‐linked immunosorbent assay. A logistic regression with random effects model was used to compare prevalence of pathogens in dairy and dairy beef operations. Results Enteric pathogens were isolated from 97.6% of outbreaks and 95.0% of samples. Rotavirus was the most common pathogen identified (477/597, 79.9%) followed by C. parvum (349/597, 58.5%), Salmonella spp. (142/597, 23.8%), coronavirus (129/597, 21.6%) and E. coli K99 (104/597, 17.4%). Multiple pathogens were identified on 96.4% of farms and from 71.0% of samples. Samples from dairy beef properties were more likely to have multiple pathogens than dairy properties (P < 0.05), whereas rotavirus and Salmonella spp. were more likely to be identified in samples collected from dairy beef than dairy properties (P < 0.05). Conclusion Most outbreaks of calf diarrhoea in dairy and dairy beef operations involve multiple pathogens. Rotavirus and C. parvum were the most frequently identified pathogens across production systems. Salmonella spp. and rotavirus were more frequently identified in dairy beef operations.

A report on two cases of pregnancy losses in mares which were associated to exposure with caterpillars in Kentucky, USA and the other one in Australia was presented. Highlight of the report focused on the clinical aspects and on the aetiology of two reproductive disorders namely: mare reproductive loss syndrome (MRLS) and equine amnionitis and fetal loss (EAFL).

The photoluminescence of in situ-doped GaN:Er during hydride vapor phase epitaxy was compared to an Er-implanted GaN sample. At 11 K, the main emission wavelength of the in situ-doped sample is shifted to shorter wavelengths by 2.5 nm and the lifetime is 2.1±0.1 ms as compared to 2.9±0.1 ms obtained for the implanted sample. The 295 K band edge luminescence of the in situ-doped sample was free of the broad band luminescence centered at 500 nm which dominated the spectrum of the implanted sample. Reversible changes in the emission intensity of the in situ-doped sample upon annealing in a N 2 versus a NH 3 / H 2 ambient indicate the probable role of hydrogen in determining the luminescence efficiency of these samples.

Low-temperature reflectance data on epitaxial GaN thin-film samples covering the widest range of tensile and compressive stress (−3.8–3.5 kbar) thus far explicitly show the nonlinear behavior of the B–A and C–A splittings versus the energy of the A exciton. Lineshape ambiguities that hindered previous interpretations have been resolved with reciprocal-space analysis, allowing us to obtain band parameters such as ΔSO=17.0±1meV with increased confidence.

Platinum silicide (PtSi) and Pt Schottky contacts on n-GaN have been investigated and compared. The PtSi contacts were formed on n-GaN by annealing a multilayer structure of Pt/Si with the appropriate thickness ratio at 400 °C for 1 h in forming gas. The barrier height of the as-formed PtSi contacts was found to be 0.87 eV capacitance–voltage (C–V), and remained unchanged after further annealing at 400 and 500 °C. Upon annealing at 600 °C for 1 h, the barrier height decreased to 0.74 eV (C–V), but the diodes remained well-behaved. The as-deposited Pt yielded a barrier height of 1.0 eV (C–V). Upon annealing at 400 °C for 1 h, the Pt diodes degraded and most of the diodes did not survive additional annealing at 400 °C for longer times. The electrical measurements and the Rutherford backscattering spectrometry results indicated that PtSi contacts are thermally much more stable than Pt contacts on GaN.

Epitaxy of Al films deposited on GaN has been studied using reflection high-energy electron diffraction (RHEED), atomic force microscopy (AFM), x-ray diffraction, and ion channeling techniques. Al (111) films have been found to grow epitaxially on GaN (0001) surfaces with Al 〈211〉‖GaN〈2110〉. For growth at 15 and 150 °C with a deposition rate of 0.26 A/s, the epitaxial quality of the film was poor initially, as evidenced by the observation of diffuse RHEED patterns. After a few monolayers, a sharp and streaky RHEED pattern develops and is maintained during subsequent deposition, indicating an improvement in epitaxial quality with a two-dimensional growth mode. AFM studies indicate that the initial GaN surface quality is a significant factor in achieving epitaxial growth, and that the size of Al epitaxial islands increases substantially for higher growth temperatures. X-ray diffraction and ion channeling results confirm the epitaxial nature of the Al films in spite of a significant lattice mismatch of 1...

A new metallization scheme has been developed to form Ohmic contacts to n-GaN. Contacts were fabricated by sputtering the intermetallic compound, PtIn2 on metal–organic vapor phase epitaxy grown n-GaN (n∼5×1017 cm−3) with some of the contacts subjected to rapid thermal annealing. Contacts in the as-deposited state exhibited nearly Ohmic behavior with a specific contact resistance of 1.2×10−2 Ω cm2. Contacts subjected to rapid thermal annealing at 800 °C for 1 min exhibited linear current–voltage characteristics and had specific contact resistances less than 1×10−3 Ω cm2. Auger depth profiling and glancing angle x-ray diffraction were used to examine the interfacial reactions of the PtIn2/n-GaN contacts. Consistent with estimated phase diagram information, the results from Auger depth profiling and glancing angle x-ray diffraction indicated the formation of (InxGa1−x)N at the contact interface, which could be responsible for the Ohmic behavior of PtIn2 contacts.

We have achieved spatially resolved photoluminescence from GaN films using a near‐field scanning optical microscope (NSOM). GaN films grown by hydride vapor phase epitaxy (HVPE) and metal‐organic vapor phase epitaxy (MOVPE) on sapphire substrates have been studied. We have performed spatial scans of topography, band edge, and yellow luminescence signals. Atomic force microscopy measurements were also made and compared with the NSOM topography. We have found spatial variations in photoluminescence characteristics at the submicron scale for both HVPE and MOVPE GaN. The observed enhancement of yellow luminescence at multiatomic step edges on the HVPE GaN surface suggests that the yellow luminescence is associated with chemical impurities incorporated during the growth of GaN films.

Surfaces of GaN films have been investigated with photoemission spectroscopy. The measured valence band is in good agreement with band structure calculations and correlates well with tunneling luminescence measurements performed on the same samples. The effect of N depletion on band structure is explored, clarifying disagreements in previous photoemission measurements.

Pd films deposited at room temperature have been found to grow epitaxially on GaN grown by metalorganic vapor phase epitaxy (MOVPE). The Pd films were deposited on GaN substrates cleaned by chemicals only, and in a conventional e‐beam evaporation system with a vacuum of ∼1×10−7 Torr. MeV 4He backscattering spectrometry and the Read x‐ray camera were used to evaluate the Pd films. The effects of various chemical etchants—such as aqua regia, HCl:H2O, and HF:H2O—on the epitaxial quality of the Pd films have also been investigated. Ni and Pt films deposited on GaN in a similar manner were also found to be epitaxial.

Free available chlorine (FAC) concentrations in drinking water supplied to broiler chickens grown commercially in New Zealand were monitored for 11 farms in two companies. Different sites within a growout house were examined at different times of the day to determine spatial and temporal differences in FAC concentrations. Taps provided water with significantly higher FAC concentrations than did drinkers. There were no significant differences between the concentrations of FAC taken from various drinkers around the growout house. There were differences in the variations of measurements taken from the same drinker within a growout house at different times of the day, with variations increasing in the afternoon. No growout houses provided an average FAC content of 2 ppm, the suggested standard in one company. Three growout houses consistently met the chlorine concentration of 0.2 ppm suggested by the New Zealand Drinking Water Standards.

The surface morphology and structure of AIN deposited by metal organic vapor phase epitaxy (MOVPE) on Si (111) at growth temperatures ranging from 825 to 1175°C was investigated. Transmission electron microscopy (TEM), reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), and secondary ion mass spectrometry (SIMS) techniques were used to study the resulting film structure. Growth at high temperatures but less than ∼1100°C, resulted in a wire texture with some degree of in-plane alignment with (0001)AIN //(111)si, 10>AIN //<211>si, and 20>AIN. // <110>si. Deposition at temperatures greater than 1100°C results in single crystal films consisting of domains 60 nm across with an aspect ratio near unity. Growth below 1100°C leads to degraded crystal quality with the grains developing random rotational misalignments around the AIN [0001] axis. Growth at lower temperatures produces islands elongated along the [1120] direction. At the growth temperature of 825°C, the aspect ratio of the islands increased to 3 and a width of 25 nm. Cross -sectional TEM reveals that these islands are faceted due to slow growth on the {1101} planes.

Influence of C, N and O ion-implantation on the yellow luminescence (YL) of halide vapor phase epitaxy (HVPE) and metal-organic vapor phase epitaxy (MOVPE) grown GaN has been studied by photoluminescence (PL) spectroscopy. For the HVPE-grown samples, only C implantation produces a significant enhancement of YL while its corresponding overall PL integrated intensity is only ˜72% of its original value. Implantation of O or N do not appreciably change the YL but decrease the BE integrated intensities by a factor of ten. The full-width-halfmaximum (FWHM) of the BE band expanded to about 1.4 × of the original value in all three cases. These results indicate that one source of the YL is strongly correlated to incorporation of C into the GaN film. The C-induced defect complexes in GaN are optically active while O or N does not lead to any new luminescence features. The variable-temperature PL measurements on the C-implanted HVPE-grown GaN reveal that the FWHM of the YL band increases linearly and the peak energy of the YL changes very little with the increasing measurement temperature, while the integrated intensity of the YL band decreases monotonically. This trend of the YL FWHM and peak energy with the measurement temperature can be explained by a two-channel transition model. For MOVPE-grown GaN films., all ion-implanted samples exhibit a significant loss of both the YL and overall integrated PL intensity. Residual C contamination in the MOVPE samples could be large compared to the additional ion-implanted carbon leading to a reduced impact of the ion-implanted carbon.

The epitaxy, defect structure, and heterointerface microstructure of MOVPE-grown A1N on oriented Si were studied by transmission electron microscopy (TEM) in an investigation of the affects of the growth temperature (925°C–1175°C) on the microstructure of low thickness (~0.2 urn) films. A film grown at 1175°C was single crystalline with the following orientation relationship: (0001)AIN||(111)si. % MathType!MTEF!2!1!+- % feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB % PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY-Hhbbf9v8qqaqFr0x % c9pk0xbba9q8WqFfea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8fr % Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaacqGH8a % apcaaIXaGaaGymamaanaaabaGaaGOmaaaacaaIWaGaeyOpa4ZaaSba % aSqaaiaabgeacaqGSbGaaeOtaaqabaGccaGG8bGaaiiFaiabgYda8i % aaigdacaaIXaGaaGimaiabg6da+maaBaaaleaacaqGtbGaaeyAaaqa % baaaaa!4798! $$ _{{\text{AlN}}}}|| _{{\text{Si}}}}$$ and AIN|| si. All A1N films grown at temperatures below 1100°C were wire-textured polycrystals with (0001)AIN largely par-allel to (lll)si and some in-plane preferred orientation similar to that of 1175°C A1N epifilms. Columnar grains/domains with faceted top surfaces were observed for the entire growth tem-perature range. The mean column diameters decreased from 50 nm to 35 nm as the growth tem-perature decreased. The columnar grain/domain structure and the faceted tops resulted in peak-to-valley surface roughness on the order of 20 nm. Sharp interfaces of AIN/Si were generally ob-served in all A1N films studied by HREM except for the 1075°C film where a transitional layer of approximately 15A thick was observed at some interface regions. Defects typically encoun-tered in large lattice mismatched heteroepitaxial systems were observed.

A new metallization scheme has been developed to form ohmic contacts to n-GaN. Contacts were fabricated by sputtering the intermetallic compound, PtIn2 on n-GaN (n ∼ 5 ×l017 cm−3) grown by metalorganic vapor phase epitaxy (MOVPE) with some of the contacts subjected to rapid thermal annealing. Contacts in the as-deposited state exhibited nearly ohmic behavior with a specific contact resistance of 1.2 × 10−2 Ω cm2. Contacts subjected to rapid thermal annealing at 800 °C for 1 minute exhibited linear current-voltage characteristics and a decrease in contact resistance. To rationalize the reaction at the contact interface the phase diagram of the PtIn2-PtGa2-InN-GaN reciprocal system at 800 °C was calculated based on known and estimated thermodynamic values. This phase diagram suggests that there will be a solid state exchange of In and Ga atoms at the Ptln2/GaN contact interface producing (InxGa1-x)N and Pt(In,Ga)2. Results from Auger depth profiling used to examine the Ptln2/n-GaN contacts are consistent with this estimated phase diagram information. It is proposed that the formation of (InxGa1-x)N at the contact interface is responsible for the ohmic behavior of Ptln2 contacts.

The effects of flowrate variation and geometry on the growth rate, growth uniformity and crystal quality were investigated in a horizontal Gallium Nitride vapor phase epitaxy reactor. To better understand the effects of these parameters, numerical model predictions are compared to experimentally observed values. Parasitic gas phase reactions between group III and group V sources and deposition of material on the wall are shown to lead to reduced overall growth rates and may be responsible for inferior crystal quality. A low ammonia concentration is correlated with the deposition of polycrystalline films. A low V/III ratio and an ammonia concentration lead to poor crystalline quality and increased yellow luminescence. An optimum HVPE growth process requires selection of reactor geometry and operating conditions to minimize these parasitic reactions and wall deposition while providing a uniform reactant distribution across the substrate.

We report a structural analysis of GaN layers with thicknesses ranging from 10 μm to 250 μm which have been grown on sapphire substrates by halide vapor phase epitaxy (HVPE). The effect of growth rate during HVPE growth has also been examined. The growth was performed using GaCl and ammonia as reactants; growth rates in excess of 90 μm/hr have been achieved. The structural characteristics of these layers have been performed wit'i high resolution x-ray diffractometry. Longitudinal scans parallel to the GaN [0002] direction, transverse scans perpendicular to the [0002], and reciprocal space maps of the total diffracted intensity have been obtained from a variety of GaN layers. The transverse scans typically show broad rocking curves with peak breadths of several hundreds of arcseconds. In contrast, the longitudinal scans (or “θ/2θ scans”) which are sensitive only to strains in the GaN layers (and not their mosaic distributions) showed peak widths that were at least an order of magnitude smaller and in some cases were as narrow as 16 arcseconds. These results suggest that the defect structure of the GaN layers grown by HVPE is dominated by a dislocation-induced mosaic distribution, with the effects of strain in these materials being negligible in comparison.

We have investigated the nucleation and growth of gallium nitride (GaN) films on silicon and sapphire substrates using halide vapor phase epitaxy (HVPE). GaN growth was carried out on bare Si and sapphire surfaces, as well as on MOVPE-grown GaN buffer layers. HVPE growth on MOVPE GaN/AlN buffer layers results in lower defect densities as determined by x-ray than growth directly on sapphire. HVPE GaN films grown directly on sapphire exhibit strong near-edge photoluminescence, a pronounced lack of deep level-based luminescence, and x-ray FWHM values of 16 arcsec by an x-ray θ-2θ scan. The crystallinity of GaN films on sapphire is dominated by the presence of rotational misorientation domains, as measured by xray ω-scan diffractometry, which tend to decrease with increasing thickness or with the use of a homoepitaxial MOVPE buffer layer. The effect of increasing film thickness on the defect density of the epilayer was studied. In contrast, the HVPE growth of nitride films directly on silicon is complicated by mechanisms involving the formation of silicon nitrides and oxides at the initial growth front.

We provide the widest estimate thus far of the range of tensile and compressive stress (−3.8 to 3.5 kbar) that GaN epitaxial material can withstand before relaxation occurs, and an unambiguous determination of the spin-orbit splitting Δso = 17.0 ± 1 meV for the material. These are achieved by analyzing 10K reflectance data for the energy separation of transitions between the uppermost valence bands and the lowest conduction band of wurtzitic GaN as a function of biaxial stress for a series of GaN films grown on both Al2O3 and 6H-SiC substrates. Our data explicitly show the nonlinear behavior of the excitonic energy splittings B-A and C-A vs. the energy position of the A exciton, which stands in contrast to the linear approximations used by previous workers analyzing material grown only on Al2O3 substrates. Further, the lineshape ambiguities present in GaN reflectance spectra that hindered the accurate determination of such excitonic energies have also been resolved by analyzing these data in reciprocal space, where critical point energies are determined by phase effects to an accuracy of ±0.5 meV.

A variety of metal films deposited at room temperature have been found to grow epitaxially under conventional vacuum conditions on GaN grown by metalorganic vapor phase epitaxy on sapphire substrates. The metal films have been characterized by X-ray diffraction using a thin-film Read camera and by MeV ion channeling measurements. Lattice mismatch between the epitaxial metals and the GaN basal planes ranges from ∼ 0.2% to ∼ 22%, and does not appear to be the determining factor in the epitaxy reported here. Surface structure of the epitaxial metal films has been studied by atomic force microscopy and found to differ considerably from that of nonepitaxial metal films grown on similar GaN substrates.

A numerical model of an experimental gallium nitride horizontal vapor phase epitaxy reactor is presented. The model predicts the flow, concentration profiles, and growth rates. The effects of flowrate variation and geometry on the growth rate, growth uniformity and crystal quality were investigated. Numerical model predictions are compared to experimentally observed values. Parasitic gas phase reactions between group III and group V sources and deposition of material on the wall are shown to lead to reduced overall growth rates and inferior crystal quality. A low ammonia concentration is correlated to deposition of polycrystalline films. An optimum HVPE growth process requires selection of reactor geometry and operating conditions to minimize parasitic reactions and wall deposition while providing a uniform reactant distribution across the substrate.

We report scanning tunneling microscopy (STM) images of surfaces of GaN films and the observation of luminescence from those films induced by highly spatially localized injection of electrons or holes using STM. This combination of scanning tunneling luminescence (STL) with STM for GaN surfaces and the ability to observe both morphology and luminescence in GaN is the first step to investigate possible correlations between surface morphology and optical properties., Comment: 12 pages, Revtex 3.0, submitted to Appl. Phys. Lett., three figures available from Jian Ma at JMA@mrgcvd.engr.wisc.edu

A major limitation of the current technology for GaN epitaxy is the availability of suitable substrates matched in both lattice constant and thermal expansion coefficient. One alternative for the development of GaN substrates rests in the application of halide vapor phase epitaxy (HVPE) to produce GaN films at high growth rates. In this paper, we describe the growth of thick GaN films via the HVPE technique on (0001) sapphire and (111) Si substrates. At a temperature of 1030°C, films are grown at rates between 70 and 90 μm/hr, yielding total thicknesses exceeding 200 μm on sapphire. DCXRD measurements of GaN/sapphire indicate FWHM values less than 220 arcsec on 180 μm thick films. Room temperature PL measurements of GaN/sapphire indicate strong emission at 3.41 eV, with a FWHM value of 65 meV. Moreover, no detectable deep level emission was found in room temperature PL measurement. Under optimized conditions, films are morphologically smooth and optically clear. The GaN morphology appears to be a strong function of the initial nucleation conditions, which in turn are strongly affected by the partial pressure of GaCl. HVPE growth on (111) Si substrates is accomplished using an AlN MOVPE buffer layer.

ZnTe has gained attention as a promising material for short wavelength optoelectronic applications. Unlike ZnSe, ZnTe can be doped p-type but not n-type. There are few reports detailing the growth and doping of ZnTe films through the MOVPE technique. We present growth and doping studies for ZnTe formed through low pressure MOVPE. Dimethylzinctriethylamine and diisopropyltelluride were chosen as the metalorganic precursors. Growth studies were carried out on both GaAs (100) and GaSb (100) substrates. Growth morphology was very sensitive to both the lattice mismatch and the initial surface preparation. This is particularly evident on the GaSb substrates. ZnTe growth temperatures ranged from 340 to 420°C, and growth rates of up to 1 μm/hour were achieved. ZnTe was found to be readily doped using tertiarybutylphosphine, with p-type concentrations ranging from 4×1016 cm−3 to 2x1019 cm−3, and corresponding room temperature hole mobilities between 55 and 12 cm2/V-sec. Tertiarybutylphosphine was also observed to significantly improve the surface morphology for growths on GaSb substrates.

Existence of ultradian variation in serum progesterone concentration and the relation between progesterone and luteinizing hormone (LH) secretory patterns were investigated in nonpregnant and pregnant mares. Blood samples were taken every 15 minutes for a 24-hour period on day 8 of the estrous cycle and day 18 of pregnancy, respectively. Progesterone and LH concentrations were determined by radioimmunoassay. Progesterone was secreted in pulsatile manner in nonpregnant and pregnant mares. Luteinizing hormone also was secreted in a pulsatile manner in both groups of mares. There was little temporal relation between LH and progesterone pulses in either pregnant or nonpregnant mares.

A 15-year-old Standard-bred mare was examined because of signs of abdominal discomfort in late gestation. Palpation per rectum revealed tight broad ligaments above and below the uterus, with the right broad ligament running across the top of the uterine body down toward the left, ventral side of the abdomen. A diagnosis of counterclockwise uterine torsion was made and surgical correction was approached via a left, flank laparotomy with the horse standing. The uterus was repositioned and a uterine tear encompassing 180 degrees of the uterine surface was found in the lateral, uterine body just cranial to the cervix. A live colt was delivered vaginally after uterine repositioning and the laparotomy incision was closed. The uterine tear was then repaired via a blind, vaginal approach. The mare was discharged 10 days after surgery. Repair per vaginum of a uterine tear is presented as an alternative treatment in cases for which the tear is recent, abdominal contamination is minimal, and the tear is easily accessible from the vaginal approach.

Pathways of peripheral lymph flow from the legs in horses were studied with casts, and with light and electron microscopic techniques. Although lymph nodes in horses occur in large groups, each lymph vessel draining from the periphery appeared to terminate on a single node within a group. The larger branches of each vessel divided either on the node surface or after penetrating into the node, and 25 to 60 terminal afferent vessels entered either the subcapsular, medullary or trabecular sinuses. Numerous initial efferent lymphatics arose either within the medulla, or at its surface, and they often coalesced to form an anastomosing network on the node surface. Almost all of the one to four efferent lymphatics that left the vicinity of the node terminated on other nodes, usually within more centrally placed groups. This arrangement may aid in the amplification and propagation of immune responses initiated in primary nodes.