Volume 80, Issue 6, June 2009
Index of content:
- CONDENSED MATTER; MATERIALS
80(2009); http://dx.doi.org/10.1063/1.3142463View Description Hide Description
A silicon nitride membrane-based nanocalorimeter is described for measuring the heat capacity of 30 nm films from 300 mK to 800 K and in high magnetic fields with absolute accuracy . The addenda heat capacity of the nanocalorimeter is less than at room temperature and at 2.3 K. This is more than ten times smaller than any existing calorimeter suitable for measuring thin films over this wide temperature range. The heat capacities of thin Cu and Aufilms are reported and agree with bulk values. The thermal conductivity of the thin low stress silicon nitride is substantially smaller than thicker membranes while the specific heat is enhanced below 20 K. Design of the nanocalorimeter will be discussed along with fabrication details and calibration results.
80(2009); http://dx.doi.org/10.1063/1.3145239View Description Hide Description
A miniature diagnostic apparatus, which consists of a target, a guiding tube, a nail-gun, and a simple base, has been developed in the proposed research to estimate batches of pinlike coaxial probes with selectable collision speeds, 198.3, 361.0, and 420.6 mps, corresponding to thrust capabilities of certain minibullets. This work aims at filling the gap between typical two stage light gas gun and pendulum machine with low cost and risk in realistic shock compressions. As a part of the experiment, the coefficient and the statistical agreement and reliability are all evaluated.
Cancellation of environmental effects in resonant mass sensors based on resonance mode and effective mass80(2009); http://dx.doi.org/10.1063/1.3143567View Description Hide Description
A novel technique is developed to cancel the effect of environmental parameters, e.g., temperature and humidity, in resonant mass sensing. Utilizing a single resonator, the environmental cancellation is achieved by monitoring a pair of resonant overtones and the effective sensed mass in those overtones. As an eminent advantage, especially compared to dual-mode temperature compensation techniques, the presented technique eliminates any need for previously measured look-up tables or fitting the measurement data. We show that a resonant cantilever beam is an appropriate platform for applying this technique, and derive an analytical expression to relate the actual and effective sensed masses on a cantilever beam. Thereby, it is shown that in applying the presented technique successfully, the effective sensed masses must not be the same in the investigated pair of resonance overtones. To prove the feasibility of the proposed technique, flexural resonance frequencies of a silicon cantilever are measured before and after loading with a strip of photoresist. Applying the presented technique shows significant reductions in influence of environmental parameters, with the temperature and humidity coefficients of frequency being improved from −19.5 to and from 0.7 to , respectively.
80(2009); http://dx.doi.org/10.1063/1.3155791View Description Hide Description
We present a state-of-the-art experimental apparatus and a proper setup to perform x-ray absorption spectroscopy(XAS) experiments in grazing incidence mode. This geometry is appropriate for doped thin films or interfaces buried at moderate depth in a thick matrix, whenever the scattering and/or fluorescence from the matrix has to be strongly attenuated. Both the calculation and the experimental data demonstrate that the specific setup that consists in a grazing incidence and grazing collection geometry is extremely advantageous. In fact, with respect to the standard geometry used to perform XAS experiments in fluorescence mode, the present setup allows an enhancement in the interesting fluorescence signal from the surface layer without a corresponding increase in the elasticscattering contribution from the matrix. The sample holder especially designed for this kind of experiment can work in vacuum and at low temperature. An easy and quick automatic sample alignment procedure is detailed.
80(2009); http://dx.doi.org/10.1063/1.3154386View Description Hide Description
We have expanded upon the “Magic Box” concept, a coil driven magnetic parallel plate capacitor constructed out of mu-metal, by introducing compensation sections at the ends of the box that are tuned to limit end-effects similar to those of short solenoids. This ability has reduced the length of the magic box design without sacrificing any loss in field homogeneity, making the device far more applicable to the often space limited neutron beam line. The appeal of the design beyond affording longer polarized lifetimes is that it provides a vertical guide field, which facilitates neutron spin transport for typical polarized beam experiments. We have constructed two end-compensated magic boxes of dimensions with measured, normalized volume-averaged transverse field gradients ranging from to for cell sizes ranging from to , respectively.