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Notes: The photon-driven (2.5 to 6.4 eV) desorption of SO2 (coverages up to 2.7 monolayers) on Ag(111) has been studied by time-of-flight mass spectrometry in combination with temperature programmed desorption and Auger electron spectroscopy. The photodesorption yields per incident photon increase with photon energy. Consistent with substrate-mediated excitation, the mean translational energy 〈Etrans/2k〉 is constant (650 K) for photon energies between 3.5 and 6.4 eV, but decreases at longer wavelengths (480 K at 2.5 eV). The decrease is attributed to changes in the energy distribution of the hot substrate carriers responsible for desorption. The photodesorption yields vary with the initial coverage, the method of preparing the initial coverage, and the extent of photolysis. These variations are attributed, in part, to changes in the SO2 orientation on the surface. Even at 6.4 eV, where unimolecular photodissociation occurs in the gas phase and multilayer, there is no photodissociation in monolayers. This effect is attributed to strong substrate quenching.

Notes: We suggest a new design of rapid single flux quantum (RSFQ) logic circuits which is based on a single superconducting layer and does not require a superconducting ground plane. Small inductances of about 10 pH, obligatory for RSFQ circuits, are formed as narrow slits of widths comparable to the London penetration depth ((approximately-equal-to)0.15 μm). The design allows us to decrease the geometric size of the RSFQ cell. Test circuits with YBaCuO grain boundary junctions on asymmetric 32° Y– ZrO2 bicrystals were used to measure the slit inductance per unit length and the mutual inductance of neighboring slits. A typical inductance of a 0.4 μm slit was found to be 0.7–0.8 pH/μm. © 1995 American Institute of Physics.

Notes: We have fabricated and tested integrated magnetometers based on the superconducting quantum interference device (SQUID). The magnetometer consists of two patterned films of YBa2Cu3O7, separated by an insulating layer of SrTiO3. A multiturn input coil was integrated on top of the SQUID, where the misorientation angle in a SrTiO3 bicrystal substrate was used to form the grain boundary junctions. The noise spectrum was characterized at 77 K and showed that above 10 Hz the magnetometer sensitivity is limited by a white noise level of around 4×10−5 Φ0/Hz1/2. In the 4 mm × 4 mm detection area of the input coil, this translates into a magnetic field sensitivity of 320 fT/ Hz1/2 at 100 Hz. Compared to the theoretical value of an optimized SQUID the white noise level of the magnetometer is two times higher. Below 10 Hz the noise is dominated by 1/f noise mainly due to the critical current fluctuations. © 1995 American Institute of Physics.

Notes: The surface photochemistry of submonolayer to multilayer amounts of CF3I, adsorbed on Ag(111) at 95 K, has been studied using 248 and 193 nm pulsed laser excitation. For low doses, there is some thermally activated dissociation, limited to 30% of the first monolayer, to form adsorbed CF3 and I. The remaining CF3I adsorbs molecularly. Neither CF3 nor I is photoactive, but adsorbed CF3I is photodissociated, by C–I bond cleavage, at both 248 and 193 nm. A fraction of the resulting CF3 and I desorbs during photolysis; the remainder is retained as chemisorbed CF3 and I. The former processes were probed using time-of-flight and Fourier transform mass spectrometry. The retained products were detected by post-irradiation temperature programmed desorption and Auger electron spectroscopy. The photochemistry varied with wavelength and coverage. Regarding the mechanism, for both 193 and 248 nm, there is good evidence that both submonolayer and multilayer CF3I molecules absorb photons and dissociate into CF3 and I, i.e., direct photodissociation. There is evidence, based on time-of-flight distributions of CF3 photofragments, that I(2p1/2), electronically excited I, is produced at both wavelengths, while ground state atomic iodine is produced only at 248 nm. At both 193 and 248 nm, and for coverages up to three monolayers, there is also evidence for a charge transfer process involving hot electrons produced by photon absorption in Ag(111), i.e., substrate mediated photodissociation. These hot carriers attach to CF3I, and the resulting anion dissociates into CF3 and I−. The latter is detected by Fourier transform mass spectrometry and the former as a low-velocity component in time-of-flight mass spectrometry. At 193, but not 248 nm, there is evidence for a second, substrate independent, charge transfer process also leading to CF3 and I−. For coverages exceeding ten monolayers, approximately 80% of the reaction was through this channel, the remaining 20% occurring through the direct photodissociation channel. To account for this second charge transfer channel, photoinduced intermolecular charge transfer is proposed. © 1995 American Institute of Physics.

Notes: The low temperature thermal chemistry of CF3I on Ag (111) presents an example of competing reaction pathways; molecular desorption vs desorption of radical CF3. Temperature programmed desorption and angle resolved temperature programmed desorption, complemented with Auger electron spectroscopy and low energy electron diffraction, were used to discern the mechanism of the CF3 radical desorption channel. CF3 desorption is limited to the first monolayer of CF3I; 0.75 ML CF3I is the coverage used for angular dependence measurements. At 90 K most of the CF3I adsorbs molecularly to the metal, but also present under these conditions are dissociative adsorption and thermal decomposition channels limited to C–I bond cleavage. The decomposition product, CF3, desorbs as a radical at high temperatures (∼320 K) with the I remaining on the surface until 850 K. At submonolayer CF3I coverages, thermal activation produces a low temperature (100–150 K) radical desorption channel. Results indicate that low temperature CF3 thermal desorption occurs via dissociative electron attachment to molecular CF3I, yielding radical CF3 and adsorbed iodine. © 1996 American Institute of Physics.

Notes: 
 A, assimilation rate
a, fractionation against 13C for CO2 diffusion through air
b, net fractionation against 13C during CO2 fixation
Ca, ambient CO2 concentration
Cc, CO2 concentration at the chloroplast
Ci, intercellular CO2 concentration
D, vapour pressure deficit
En, needle transpiration rate
Ep, whole plant water use
gw, leaf internal transfer conductance to CO2
gs, stomatal conductance to water vapour
L, projected leaf area
NUE, nitrogen use efficiency
PEP, phosphoenolpyruvate
Rubisco, ribulose-1,5-biphosphate carboxylase
TDR, time domain reflectometry
WUE, water use efficiency
Δ, carbon isotope discrimination
δ13C, carbon isotope abundance parameter
δ13Ca, carbon isotopic composition of atmospheric CO2
θ, volumetric soil water content

The effect of nitrogen stress on needle δ13C, water-use efficiency (WUE) and biomass production in irrigated and dry land white spruce (Picea glauca (Moench) Voss) seedlings was investigated. Sixteen hundred seedlings, representing 10 controlled crosses, were planted in the field in individual buried sand-filled cylinders. Two nitrogen treatments were imposed, nitrogen stressed and fertilized. The ranking of δ13C of the crosses was maintained across all combinations of water and nitrogen treatments and there was not a significant genetic versus environmental interaction. The positive relationships between needle δ13C, WUE and dry matter production demonstrate that it should be possible to use δ13C as a surrogate for WUE, and to select for increased WUE without compromising yield, even in nitrogen deficient environments. Nitrogen stressed seedlings had the lowest needle δ13C in both irrigated and dry land conditions. There was a positive correlation between needle nitrogen content and δ13C that was likely associated with increased photosynthetic capacity. There was some indication that decreased nitrogen supply led to increased stomatal conductance and hence lower WUE. There was a negative correlation between intrinsic water use efficiency and photosynthetic nitrogen use efficiency (NUE). This suggests that white spruce seedlings have the ability to maximize NUE when water becomes limited. There was significant genetic variation in NUE that was maintained across treatments. Our results suggest that in white spruce, there is no detectable effect of anaplerotic carbon fixation and that it is more appropriate to use a value of 29‰ (‘Rubisco only’) for the net discrimination against 13C during CO2 fixation. This leads to excellent correspondence between values of Ci/Ca derived from gas exchange measurements or from δ13C.

Notes: The relationship among water use efficiency (WUE), productivity and carbon isotopic composition (δ13C) in white spruce (Picea glauca (Moench) Voss) seedlings was investigated. Sixteen hundred seedlings representing 10 controlled crosses were planted in the field in individual buried sand-filled cylinders. The soil water content in the cylinders was measured using time domain reflectometry over two growing seasons and seedling water use determined by water balance. Two watering treatments were imposed: irrigation and dry land. There was significant (1.6–2.0%c) genetic variation in needle δ13C. Ranking of crosses in terms of δ13C was generally maintained over watering treatments and there was not a significant genetic versus environmental interaction. There was a positive correlation between δ13C and both intrinsic and long-term WUE (more positive δ13C with increased WUE) and between δ13C and productivity, suggesting a correlation due to variation in photosynthetic capacity. Root to shoot ratios did not increase in water-stressed plants, indicating that responses to drought were primarily at the level of gas exchange, rather than through morphological changes. Our results indicate that it should be possible to use δ13C as a surrogate for WUE and to select white spruce genotypes for high WUE without compromising yield.