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Notes: We report characterization of Si p-n junction arrays using simultaneous conductance imaging and constant current mode (topographical) scanning tunneling microscopy imaging over a range of reverse bias conditions. Both constant current and conductance imaging of the electrically different regions (n, p, and inverted region) show a pronounced dependence on applied p-n junction bias. Tunneling spectra measured across the p-n junction show that the conductance contrast agrees well with the expected variation due to tip-induced band bending. Taken in combination with the topographical image, conductance images can be used to characterize spatial variations of carrier densities across the device. © 2002 American Institute of Physics.

Notes: The utility of vertical propagation by the Green's function to test response linearity has been explored for magnetic force microscopy (MFM) data from current-carrying wires, by comparing the measured signal at various tip heights to the corresponding propagated MFM signals. Application of a one-dimensional Green's function was found to be sufficient to predict signal height variation for sample regions of high to moderate field symmetry. For regions of high field asymmetry, the two-dimensional Green's function was required to obtain good prediction of the height variation. Agreement between the measured and propagated signals was generally within 5%, except at the tails where the signal is not well behaved. The quality of agreement deteriorates gradually with the size of the height propagation. The good agreement spanning a decade of tip and sample separation suggests that the MFM signal is not significantly affected by nonlinearities and can thus be interpreted in terms of classical electromagnetic relations governing current flow. © 2002 American Institute of Physics.

Notes: Voltage-modulated scanning force microscopy (Piezoresponse microscopy) is applied to investigate the domain structure in epitaxial PbZr0.2Ti0.8O3 ferroelectric thin films grown on (001) SrTiO3. By monitoring the vertical and lateral differential signals from the photodetector of the atomic force microscope it is possible to separate out and observe the out-of-plane and in-plane polarization vectors in the thin film individually. The relative orientation of the polarization vectors across a 90° domain wall is observed. Nucleation of new reversed 180° domains at the 90° domain wall is studied and its impact on the rotation of polarization within the a domain is analyzed as a function of reversal time. © 2002 American Institute of Physics.

Notes: We present a model that describes doping-induced contrast in photoelectron emission microscopy by including the effect of surface state distributions and doping-induced band gap reduction. To quantify the contrast, the photoyield from the valence band for near-threshold photoemission is calculated as a function of p-type doping concentration in Si(001). Various surface state distributions appropriate for a native-oxide covered Si device are investigated in order to determine the effect on doping-induced contrast. The lower limit on the number of surface states necessary for doping-induced contrast to occur is approximately 5×1013 cm−3. An interesting result is that neither the position nor the energy distribution of the surface donor states affects the contrast, which corresponds to approximately a factor of 2 change in intensity for each decade change in doping density. However, the overall intensity increases with any one of: increased surface state density, narrowing of surface state distribution, or increased energy of surface states with respect to the valence band. The band bending profile generated by the model predicts that doping-induced contrast will be affected by varying the incident photon energy. Experimentally, we verify this prediction by imaging with photon energies between 4.5 and 5.2 eV. © 2002 American Institute of Physics.

Notes: The spatial variation of current density in lines with model void defects fabricated using focused-ion beam milling has been imaged using magnetic force microscopy (MFM). At current densities of 3–4×106 A/cm2, an asymmetry in the MFM signal is clearly visible at (1×1) μm2 and (0.5×0.5) μm2 notches at the edge of a 10 μm wide line. Comparison to a simple model calculation suggests that the asymmetry is due to current crowding, with the displaced current 70% localized to within 1μm of the notch. © 2001 American Institute of Physics.

Notes: The time-dependent relaxation of the remanent polarization in epitaxial lead zirconate titanate (PbZr0.2Ti0.8O3) ferroelectric thin films, containing a uniform two-dimensional grid of 90° domains (c axis in the plane of the film), is examined using piezoresponse microscopy. The 90° domain walls preferentially nucleate the 180° reverse domains during relaxation, with a significant directional anisotropy. Relaxation occurs through the nucleation and growth of reverse domains, which subsequently coalesce and consume the entire region as a function of time. © 2000 American Institute of Physics.

Notes: We investigate the variation in doping-induced contrast with photon energy in photoelectron emission microscopy images of Si pn devices using a free-electron laser as a tunable monochromatic light source. Photoyield is observed from p-doped regions of the devices for photon energies as low as 4.5 eV. Band tailing is the dominant effect contributing to the low energy photoyield from the heavily doped p regions. The low intensity tail from the n regions, however, may be from surface states. © 2001 American Institute of Physics.

Notes: Experiments were undertaken to define the conditions under which seeds and seedlings of Agropyron repens and Agrostis gigantea may start infestations in cereal crops.When seedlings were planted early or late in spring wheat and spring barley, most growth of shoots and rhizomes was produced by Agropyron planted early in wheat. Late planting halved the amount of shoot growth and severely inhibited rhizome formation. In winter wheat given a moderate or zero amount of nitrogen fertilizer in spring, growth of the weed seedlings was slow. Rhizomes were not produced during the time the crop was growing but only after harvest. Agrostis made more growth than Agropyron in most treatments throughout most of the experiment. Late planting decreased growth more than in the spring cereals. Nitrogen fertilizer, although it had little effect on the amount of growth made by winter wheat, increased the growth of the early-planted seedlings but decreased that of the late-planted ones of both weed species. When planted into plots given nitrogen, more seedlings of both species died after late than after early planting.Clearly, the amount of growth and rhizome produced by seedlings of these two species will depend on the type of cereal, the time of emergence of the seedlings in relation to the cereal, and on other factors affecting the relative vigour of cereal and weed. Evidently, where the weed seedlings emerge early in weakly or moderately competitive cereal crops or when growth is unchecked in the cereal stubble, seedlings could give rise to infestations.

Notes: Results arc reported of two experiments done during 1971–76. which investiga ted the germination and longevity in soil of seeds of Agropyron repens L. Beauv. and Agrostis gigantea Roth. The effects of different cultivation regimes and paraquat were investigated in a field experiment and the effects of different frequencies of cultivation in a sandy loam and silty loam soil were studied in the glasshouse.Seeds of neither species were innately dormant and most germination occurred during the first autumn. Agrostis seeds germinated most readily on the soil surface and persisted longest where the seeds were incorporated in soil al the outset and not cultivated in the spring. In contrast. Agropyron seeds germinated most readily when incorporated in soil at the cutset and their depletion was largely independent of cultivations in the spring; they persisted longest where they remained on the soil surface dtiring the firstautumn. Paraquat, sprayed on to dry seeds, greatly decreased the number of Agropyron seeds, giving emerged seedlings early during the first autumn but did not afTect the number emerging after this. Agrostis was aflected little by paraquat. Agrostis seeds were more persistent than Agropyron in most treatments of both experiments; in the field, on average, only abotit 0.3% of Agropyrim seeds gave emerged seedlings during the fourth year whereas about three times as many Agrostvis seedlings would be expected to emerge during the fifth year. The number of seedlings, particularly of Agrostis. emerging in consecutive years did not decrease continuously from year to year. There was some indication that longevity of Agrostis seeds might be greater in a sandy loam than in a silly loam soil.The much smaller percentage of seeds accounted for in the field than in the glasshouse is emphasised and the implications of the findings to practical control measures, particularly that depletion of seed reserves is dependent on initial cultivations, are briefly discussed. Germination et longévité des sentences d' Agropyron repens L. Beauv. et d'Agrostis gigantea Roth, dans le sol, en relation avec different régimes de culture.Les auteurs rapportent les résultats de deux expériénces effectuées de 1971 à 1976, destinées àétudier la germination et la longevité dans le sol des seremencesd d' Agropyron repens(L.) Beauv. et d'Agrostis gigantea Roth. Les effets de différents régimes de culture et du paraquat ont étéétudiés dans une expérience au champ et les effets de différentes fréquences de culture, dans un sol de limon sableux et dans un limon fm ont étéétudies en serre.Les semenees des deux espéces ne se sont pas révélées naturellement dormantes et la plus grande partie de la germination s'est produite durant le premier automne, Les semenees d'Agrostis ont germé plus aisément à la surface du sol et ont persisté plus longtemps là oü les semenees ont été incorporées dans le sol dés le début el non irultivées au printemps. En revanche, tes sentences d’ Agropyron ont germé plus aisément lcirsqu'elles ont été incorporées dans les sol dés le debut et leur épuisement a été en grande partie indépendant des facons culturales effectuées au printemps; elles ont persisté plus longtemps lä oü elles sont restées à la surface du sol durant le premier automne. Le paraquat, pulvérisé sur les semenees séches, a diminué de facon importante le nombre de semenees d'Agropyron donnant des levées précoces de plantules durant le premier automne; par la suite, le paraquat n'a pas eu d'effet sur le nombre des levées. L'Agrostis a été peu aftecté par le paraquat.Les semenees d’ Agrostis se sont montrées plus persistantes que celles ti’ Agropyron dans la plupart des conditions des deux expériences; au champ environ 0,03% seulement en moyennede semenees d'Agropyron ont levé au cours de la quatriéme année alors que trois fois autani de levées d'Agrostisétaient attendues au cours de la cinquiéme année. Le nombre de plantules d’Agrosits en particulier. levant au cours des annees consecutives n'a pas continuellement diminué d'année en année, ll y a quelques raisons de penser que la longévité des semenees d'Agrostis pourrait étre plus grande dans un limon sableux que dans un limon fin.Les auteurs insistent sur le fait que le pourcentage de semenees enregistré au champ a été beaucoup plus faible qu'en serre. Les implications des constatations faites dans les mesures pratiques de lutte sont briévement discutées, en particulier le fait que la diminution des reserves des semenees dépend des facons culturales initiates. Keimung und Lebensdauer der Samen von Agropyron repens L. Beauv. und Agrostis gigantea Roth, im Boden in Be:iehung zu unterschiedlicher BodenhearbeitungEs wird üher Versuche berichiet, die in der Zeit von 1971–1976 durchgeführt wurden. und in denen die Keimung und die Lebensdauer der Samen von Agropyron repens (L.) Beauv. und Agrostis gigantea Roth, im Boden untersucht wurden. In einem Feldversuch wurde die Wirkung verschiedener Bodenbearbeitungen und von Paraquat untersucht. und in einem Gewâhshausversuch die Wirkung unterschiedlichcr Abstände in der Bodenbearbeitung bei cinem saodigen Lehmboden und einem Schluff-Lenmbodcn.Bei keiner der beiden Arten waren die Samen endogen dormant, und die mcisten keimten im ersten Herbst. Die Samen von Agrostis keimten am schnellsten auf der Bodenoberfläche und überlebten am längsten, wenn sie am Anfang eingearbeitet wurden. der Boden im Frühjahr aber niirht bearbeitet wurde. In Gegensatz dazu keimten die Samen von Agropyron am schnelllsten, wenn sie am Anfang eingearbeitel wurden, und die Erschöpfung des Samenvorrats war unabhängig von Bodenbearbeirtungen im Frühjahr; sie überlebten am längsten, wenn sie im ersten Herbsi auf der Bodenoherflächc verblieben. Wurde Paraquat auf trockene Samen gespritzl. dann nahmen die Agropyron-Sdmen stark ab, da im Frühberbst des ersten Jahres Pflanzen aufliefen, was aber keine Auswirkung auf die Anzahl der auflaufenden Pflanzen in der Folgezeit hatte. Bei Agrostis wirkte Paraquat nur schwach.In den meisten Varianien der beiden Versuche überlebten mehr Samen von Agrostis ah von .Agropyron. Im vicrten Jahr des Feldvcrsuchs liefen durchschnittlich etwa 0,03% der Agropvron-Samcn auf, während bei .Agrostis im fünften jahr etwa dreimal soviel erwartet werden können. Die Zahl der in den Folgejahren a ufgelaufenen Keimpflanzen nahm bcsounders bei Agrostis nicht kontinuierlich von Jahr zu Jahr ab. Es gab einige Hinweise dafür. dass die Lebensdauer von .Agrostiis-Samen im sandigen Lehmboden grösser sein könnte als im Schluff-Lehm- boden.Es wird auf den wesentlich geringeren Prozentsatz an Samen unter Feld- als unter Gewächshausbedingungen hingewiesen. Die Folgen diescr BEfunde für die praktische Bekämplung, insbesondere, dass dcr SamenvorraT im Boden von der ersten Bodenbearbeitung abhängig ist, werden kurzdiskutiert.

Notes: Synopsis A tetrazolium technique has been developed for the demonstration of rat brain monoamine oxidase (MAO). This method, which allows the use of a variety of phenyl and indolealkylamine substrates, depends on exposing unfixed cryostat sections to high concentrations of aqueous buffered sodium sulphate solution prior to incubation in amine-Nitro Blue tetrazolium medium. Sites of MAO activity are visualized by formazan deposition. The specificity and mechanism of formazan production has been studied. Reduction of the tetrazolium salt by aldehyde formed by oxidative deamination of the monoamine substrate is the most likely basis of the reaction. It is suggested that exposure to sulphate may modify the inhibitory effect of the tetrazolium salt on MAO, resulting in improved demonstration of enzyme activity. The ability to use 5-hydroxytryptamine and tyramine as substrates in this method, in conjunction with the use of the specific inhibitor clorgyline, permits the histological demonstration of multiple forms of the enzyme (A- and B-MAO). This technique may, therefore, be of value in the study of the physiological role of MAO and monoamines in rat brain.