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Light-induced plating (LIP) of solar-cell metal contacts is a scalable alternative to silver paste. However, LIP requires an additional patterning step to create openings in the silicon nitride (SiNx) antireflection coating (ARC) layer prior to metallization. One approach to pattern the SiNx is masking and wet chemical etching. In-situ real-time photoluminescence imaging (PLI) is demonstrated as a process-monitoring method to determine when SiNx has been fully removed during etching. We demonstrate that the change in PLI signal intensity during etching is caused by a combination of (1) decreasing light absorption from the reduction in SiNx ARC layer thickness and (2) decreasing surface lifetime as the SiNx/Si interface transitions to an etch-solution/Si. Using in-situ PLI to guide the etching process, we demonstrate a full-area plated single-crystalline silicon device. In-situ PLI has the potential to be integrated into a commercial processing line to improve process control and reliability.

In utero exposure to antiepileptic drugs carries teratogenic risks, but little is known about the potential effects of such agents on neurocognitive development. The results from a large prospective study that set out to address this issue add to the mounting evidence against the use of valproate in women with epilepsy during childbearing years.

Silicon supersaturated with sulfur by ion implantation and pulsed laser melting exhibits broadband optical absorption of photons with energies less than silicon's band gap. However, this metastable, hyperdoped material loses its ability to absorb sub-band gap light after subsequent thermal treatment. We explore this deactivation process through optical absorption and electronic transport measurements of sulfur-hyperdoped silicon subject to anneals at a range of durations and temperatures. The deactivation process is well described by the Johnson-Mehl-Avrami-Kolmogorov framework for the diffusion-mediated transformation of a metastable supersaturated solid solution, and we find that this transformation is characterized by an apparent activation energy of EA=1.7 ± 0.1 eV. Using this activation energy, the evolution of the optical and electronic properties for all anneal duration-temperature combinations collapse onto distinct curves as a function of the extent of reaction. We provide a mechanistic interpret...

Silicon doped with an atomic percent of chalcogens exhibits strong, uniform sub-bandgap optical absorptance and is of interest for photovoltaic and infrared detector applications. This sub-bandgap absorptance is reduced with subsequent thermal annealing indicative of a diffusion mediated chemical change. However, the precise atomistic origin of absorptance and its deactivation is unclear. Herein, we apply Se K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy to probe the chemical states of selenium dopants in selenium-hyperdoped silicon annealed to varying degrees. We observe a smooth and continuous selenium chemical state change with increased annealing temperature, highly correlated to the decrease in sub-bandgap optical absorptance. In samples exhibiting strong sub-bandgap absorptance, EXAFS analysis reveals that the atoms nearest to the Se atom are Si at distances consistent with length scales in energetically favorable Se substitutional-type point defect complexes as calculated by density functional theory. As the sub-bandgap absorptance increases, EXAFS data indicate an increase in the Se-Si bond distance. In specimens annealed at 1225 K exhibiting minimal sub-bandgap absorptance, fitting of the EXAFS spectra indicates that Se is predominantly in a silicon diselenide (SiSe2) precipitate state. The EXAFS study supports a model of highly optically absorbing point defects that precipitate during annealing into structures with no sub-bandgap absorptance.

Research at Harvard was supported by The U.S. Army Research Office under contracts W911NF-12-1-0196 and W911NF-09-1-0118. M.T.W. and T.B.’s work was supported by the U.S. Army Research Laboratory and the U.S. Army Research Office under Grant No. W911NF-10-1-0442, and the National Science Foundation (NSF) Faculty Early Career Development Program ECCS-1150878 (to T.B.). M.J.S., J.T.S., M.T.W., T.B., and S.G. acknowledge a generous gift from the Chesonis Family Foundation and support in part by the National Science Foundation (NSF) and the Department of Energy (DOE) under NSF CA No. EEC- 1041895. S.C. and J.S.W.’s work was supported by The Australian Research Council. J.M. was supported by a National Research Council Research Associateship.

We present a methodology for estimating the efficiency potential for candidate impurity-band photovoltaic materials from empirical measurements. This methodology employs both Fourier transform infrared spectroscopy and low-temperature photoconductivity to calculate a “performance figure of merit” and to determine both the position and bandwidth of the impurity band. We evaluate a candidate impurity-band material, silicon hyperdoped with sulfur; we find that the figure of merit is more than one order of magnitude too low for photovoltaic devices that exceed the thermodynamic efficiency limit for single band gap materials.

We describe a method to control the sub-surface dopant profile in “hyperdoped” silicon fabricated by ion implantation and pulsed laser melting. Dipping silicon ion implanted with sulfur into hydrofluoric acid prior to nanosecond pulsed laser melting leads to a tenfold increase in the rate of sulfur evaporation from the surface of the melt. This results in an 80% reduction of the near-surface dopant concentration, effectively embedding the hyperdoped region in a layer up to 180 nm beneath the surface. This method should facilitate the development of blocked impurity band devices.

Objective To describe the association between electrographically detected seizures and brain injury evaluated by magnetic resonance imaging in newborns treated with hypothermia. Study design A total of 56 newborns treated with hypothermia were monitored using video electroencephalography through cooling and rewarming, and then imaged at a median of 5 days. The electroencephalograms were reviewed for indications of seizure and status epilepticus. Moderate-severe injury detected on magnetic resonance imaging was measured using a classification scheme similar to one predicting abnormal outcome in an analogous population. Results Seizures were recorded in 17 newborns (30%), 5 with status epilepticus. Moderate-severe injury was more common in newborns with seizures (relative risk, 2.9; 95% CI, 1.2-4.5; P =.02), and was present in all 5 newborns with status epilepticus. Newborns with moderate-severe injury had seizures that were multifocal and of later onset, and they were more likely to experience recurrent seizures after treatment with 20 mg/kg phenobarbital. Newborns with only subclinical seizures were as likely to have injury as those with seizures with a clinical correlate (57% vs 60%). Conclusion Seizures represent a risk factor for brain injury in the setting of therapeutic hypothermia, especially in neonates with status epilepticus, multifocal-onset seizures, and a need for multiple medications. However, 40% of our neonates were spared from brain injury, suggesting that the outcome after seizures is not uniformly poor in children treated with therapeutic hypothermia.

We apply soft x-ray emission spectroscopy (XES) to measure the electronic structure of crystalline silicon supersaturated with sulfur (up to 0.7 at. %), a candidate intermediate-band solar cell material. Si L2,3 emission features are observed above the conventional Si valence band maximum, with intensity scaling linearly with S concentration. The lineshape of the S-induced features change across the insulator-to-metal transition, indicating a significant modification of the local electronic structure concurrent with the change in macroscopic electronic behavior. The relationship between the Si L2,3XESspectral features and the anomalously high sub-band gap infrared absorption is discussed.

Highly supersaturated solid solutions of selenium or sulfur in silicon were formed by ion implantation followed by nanosecond pulsed laser melting. n+p photodiodes fabricated from these materials exhibit gain (external quantum efficiency >3000%) at 12 V of reverse bias and substantial optoelectronic response to light of wavelengths as long as 1250 nm. The amount of gain and the strength of the extended response both decrease with decreasing magnitude of bias voltage, but >100% external quantum efficiency is observed even at 2 V of reverse bias. The behavior is inconsistent with our expectations for avalanche gain or photoconductive gain.

It is well known that in low-frequency hyperbolic navigational systems the phase differences measured by the receiver do not correspond precisely to the hyperbolas on the plotting chart. This is largely because of variations in the terrain over which the waves are propagated. The system service area may be sampled so that the curve distortions can be ascertained at selected points. This article discusses how the whole service area can be calibrated, given a knowledge of the grid distortions at a sample of points. The mathematical treatment takes into account the correlation between the grid distortions at adjacent sampling points by using autocorrelation theory.The degree to which fixing accuracy is improved by the proposed method of calibration is assessed against the background of an actual set of field measurements.Mr. Sullivan is Head of the Applied Research Group of the Navigation and Guidance Laboratory at the Institute of Science and Technology. Dr. Porter is Assistant Professor of Electrical Engineering at The University of Michigan, and Head, Analytical Research Group of Navigation and Guidance Laboratory at the Institute of Science and Technology.In low-frequency ground-wave navigation systems such as Loran-C and Decca, position information is determined from measurements of time and/or phase differences in signals received from several separately located transmitter stations. A pair of stations generates a family of hyperbolic lines which are the loci of points of constant time/phase difference. Two station pairs provide a grid of hyperbolas. By measurement of the time/phase difference between the signals from two transmitters, the receiver is located on a hyperbolic line. The same receiver is located on a second line by similar measurement which uses another pair of stations; the receiver is thus fixed specifically at the intersection of the two lines.

I was fascinated by the report by Glass et al.1 on EEG seizures in almost 50% of newborns monitored during therapeutic hypothermia. The findings indicate that the antiepileptic effects of hypothermia may be less effective than anticipated—at least using standard cooling protocols. The lack of correlation between clinical risk factors and seizures was also surprising. However, there are 2 important issues regarding continuous neonatal EEG monitoring that were not addressed in the article or accompanying editorial. First, how frequently do the recordings need …

IN THIS STUDY, we derive alternative linear decision rules for the Federal Reserve and obtain estimates of the parameters of these rules. The basic assumptions are: (1) that the Federal Reserve acts as if it minimizes a quadratic loss function in certain variables and (2) that the Federal Reserve possesses a model of the economy. To obtain the alternative decision rules, we can either (a) hold (1) constant and vary (2), or (b) hold (2) constant and vary (1). For example, given a quadratic loss function, we derive decision rules conditional on differing views of the economic structure. To accomplish this we use the concept of an intermediate financial variable (e.g., free reserves or total reserves). It is assumed that the Federal Reserve acts through this intermediate variable to affect the variables in its loss function. By assuming different intermediate financial variables and different lag structures we obtain alternative models of the economic structure. The assumed loss function is minimized with respect to a policy instrument subject to the alternative models. The resulting functions are linear decision rules-each conditional on an assumed model. The results suggest that, in each model, operations to stabilize financial markets (defensive operations) were dominant. Evidence is offered that the Federal Reserve has, since 1959, responded to the balance-of-payments problem while providing for growth in real income (dynamic operations). A clear choice of "the" intermediate financial variable used by the Federal Reserve in the 1952-65 period cannot be made; several are equally plausible.