Session B46: Instumentation I: Detectors,Sensors, Signal Processing & Analysis

Contemporary Issues in Ultra-Low Alpha Particle Counting

Single-Event Upsets (SEU) in CMOS devices are caused by the passage of ionizing radiation either from terrestrial neutrons or from the natural alpha particle radiation within the materials surrounding the transistors. Interactions of the neutrons with the silicon cause spallation reactions which emit energetic highly ionizing elements. Alpha particles, on the other hand, can upset the devices through direct ionization rather than through a nuclear reaction as in the case of the neutrons. In order to minimize the alpha-particle component of SEU, the radiation from the materials within a distance 100 $\mu $m of the transistors, currently needs to have an alpha particle emissivity of less than 2 alpha particles per khr per square centimeter. Many alpha particle detectors have background levels that are larger than this, which can make these measurements inaccurate and time consuming. This talk will discuss what is involved in making alpha particle emissivity measurements of materials used in the semiconductor industry using an ultra-low background commercially-available ionization detector. Detector calibration and efficiency, radon adsorption on the samples, and the effect of surface charge on electrically insulating samples will be discussed.   

TRIASSIC: the Time-Resolved Industrial Alpha-Source Scanning Induced Current microscope

Time-resolved ion beam induced current (TRIBIC) microscopy yields useful information such as carrier mobility and lifetimes in semiconductors and defect locations in devices; however, traditional TRIBIC uses large, expensive particle accelerators that require specialized training to operate and maintain. The time-resolved industrial alpha-source scanning induced current (TRIASSIC) microscope transforms TRIBIC by replacing the particle accelerator facility with an affordable, tabletop instrument suitable for use in research and education at smaller colleges and universities. I will discuss the development of, successes with, setbacks to and future directions for TRIASSIC.   

Superconducting Nuclear Recoil Sensor for Directional Dark Matter Detection

The Universe consists of 72{\%} dark energy, 23{\%} dark matter and only 5{\%} of ordinary matter. One of the greatest challenges of the scientific community is to understand the nature of dark matter. Current models suggest that dark matter is made up of slowly moving, weakly interacting massive particles (WIMPs). But detecting WIMPs is challenging, as their expected signals are small and rare compared to the large background that can mimic the signal. The largest and most robust unique signature that sets them apart from other particles is the day-night variation of the directionality of dark matter on Earth. This modulation could be observed with a direction-sensitive detector and hence, would provide an unambiguous signature for the galactic origin of WIMPs. There are many studies underway to attempt to detect WIMPs both directly and indirectly, but solid-state WIMP detectors are widely unexplored although they would present many advantages to prevalent detectors that use large volumes of low pressure gas. We present first results of a novel multi-layered architecture, in which WIMPs would interact primarily with solid layers to produce nuclear recoils that then induce measureable voltage pulses in adjacent superconductor layers.   

It may be possible to use Speech Recognition Algorithms to sort through Particle Detection

There are some similarities between recognizing speech and written language and in recognizing Particle interaction and decays. In the Viterbi Algorithm or speech recognition, a target word is recursively compared with the unknown utterance. Say one remembered the word Motion in a song and wanted to find that song. First the letter M is typed in and the most common words with M show up say it is the word "Menards", then an "O" is typed in and statistically the most common word is now "Movies", now the "t" is typed in and the most common word is "Motley Crue" finally all the letters are typed in and the song that matches is "Motion Lyrics". We all recognize the Algorithm and perhaps a few have realized that this Algorithm could also be applied to Decay Chains in Particle Scattering and Detection. Also there may come a day when perhaps Neutrinos where transmitted with the purpose of Communication, one system would be to use a type of "Morse Code", but another could be to use Decay Chains themselves. Perhaps the sender could tune the Energy such that the information received would rely on the Energy being transmitted, since it may be that only a few of the particles are received, too few for "Morse Code" to work.   

Bayesian 2D Current Reconstruction from Magnetic Images

We employ a Bayesian image reconstruction scheme to recover 2D currents from magnetic flux imaged with scanning SQUIDs (Superconducting Quantum Interferometric Devices). Magnetic flux imaging is a versatile tool to locally probe currents and magnetic moments, however present reconstruction methods sacrifice resolution due to numerical instability. Using state-of-the-art blind deconvolution techniques we recover the currents, point-spread function and height of the SQUID loop by optimizing the probability of measuring an image. We obtain uncertainties on these quantities by sampling reconstructions. This generative modeling technique could be used to develop calibration protocols for scanning SQUIDs, to diagnose systematic noise in the imaging process, and can be applied to many tools beyond scanning SQUIDs.   

Detection of zeptojoule microwave pulses using an electrothermal bifurcation

We utilize electrothermal feedback for the threshold detection of weak 8.4 GHz microwave pulses containing approximately $200 \times h \times (8.4\textnormal{ GHz}) \approx 1.1 \times 10^{-21} \textnormal{ J}$ of energy. The feedback couples the electrical and thermal degrees of freedom in the central component of our detector, a metallic nanowire that absorbs the incoming microwave radiation and transduces the temperature change into a radio-frequency electrical signal. We can tune the feedback in situ, which provides access to both positive and negative feedback regimes with rich nonlinear dynamics. In particular, strong positive feedback leads to the emergence of two metastable electron temperature states in the millikelvin range. We use these states in the threshold detection protocol.   

Micro-Hall devices for magnetic, electric and photo-detection

Multifunctional mesoscopic sensors capable of detecting local magnetic ($B)$, electric ($E)$, and optical fields can greatly facilitate image capture in nano-arrays that address a multitude of disciplines. The use of micro-Hall devices as $B$-field sensors [1] and, more recently as $E$-field sensors [2] is well established. Here we report the real-space voltage response of InSb/AlInSb micro-Hall devices to not only local $E$-, and $B$-fields but also to photo-excitation using scanning probe microscopy. We show that the ultrafast generation of localised photocarriers results in conductance perturbations analogous to those produced by local $E$-fields. Our experimental results are in good agreement with tight-binding transport calculations in the diffusive regime. At room temperature, samples exhibit a magnetic sensitivity of \textgreater 500 nT/$\surd $Hz, an optical noise equivalent power of \textgreater 20 pW/$\surd $Hz ($\lambda \quad =$ 635 nm) comparable to commercial photoconductive detectors, and charge sensitivity of \textgreater 0.04 $e$/$\surd $Hz comparable to that of single electron transistors. [1] Boero, G.; Demierre, M.; Besse, P. A.; Popovic, R. S. \textit{Sensors and Actuators A-Physical} \textbf{2003,} \textit{106} (1-3), 314-320. [2] Barbolina, I. I. et al. \textit{Applied Physics Letters} \textbf{2006,} \textit{88} (1), 013901.   

Understanding the TERS Effect with On-line Tunneling and Force Feedback Using Multiprobe AFM/NSOM with Raman Integration

Tip enhanced Raman scattering (TERS) has evolved in several directions over the past years. The data from this variety of methodologies has now accumulated to the point that there is a reasonable possibility of evolving an understanding of the underlying cause of the resulting effects that could be the origin of the various TERS enhancement processes. The objective of this presentation is to use the results thus far with atomic force microscopy (AFM) probes with noble metal coating, etching, transparent gold nanoparticles with and without a second nanoparticle [Wang and Schultz, ANALYST 138, 3150 (2013)] and tunneling feedback probes [R. Zhang et. al., NATURE 4 9 8, 8 2 (2013)]. We attempt at understanding this complex of results with AFM/NSOM multiprobe techniques. Results indicate that TERS is dominated by complex quantum interactions. This produces a highly confined and broadband plasmon field with all k vectors for effective excitation. Normal force tuning fork feedback with exposed tip probes provides an excellent means to investigate these effects with TERS probes that we have shown can circumvent the vexing problem of jump to contact prevalent in conventional AFM methodology and permit on-line switching between tunneling and AFM feedback modes of operation.   

A Cantilever Torque Magnetometer for Measuring Hall Conductivity

We propose a cantilever-based torque magnetometer of Corbino-disc patterned samples in magnetic field. Applying a voltage difference across the disc, a magnetic dipole moment is created which will interact with the magnetic field, exerting a torque on the cantilever. A circulating current will flow in the presence of potential difference between the two edges of the disc which is placed at the end of a vibrating cantilever. The induced magnetic dipole moment will interact with the magnetic field, creating a torque. The measured torque yields information about the transverse conductance of the ring - hence $\sigma_{xy}$.   

Carbon Nanotube Bolometer for Absolute FTIR Spectroscopy

We have developed and calibrated planar electrical-substitution bolometers which employ absorbers made from vertically-aligned carbon nanotube arrays. The nearly complete absorption of light by the carbon nanotubes from the visible range to the far-infrared can be exploited to enable a device with read-out in native units equivalent to optical power. Operated at cryogenic temperatures near 4 K, these infrared detectors are designed to have time constant near 10 ms and a noise floor of about 10 pW. Built upon a micro-machined silicon platform, each device has an integrated heater and thermometer, either a carbon nanotube thermistor or superconducting transition edge sensor, for temperature control. We are optimizing temperature-controlled measurement techniques to enable high resolution spectral calibrations using these devices with a Fourier-transform spectrometer.   

Optical design of a compact near-infrared multispecies gas sensor

In this work we present the design of a compact and cost effective near infrared (NIR) gas sensor system that can detect nitrous oxide (NO$_{\mathrm{x}})$, ammonia (NH$_{\mathrm{3}})$, and methane (CH$_{\mathrm{4}})$ simultaneously. These three gases were chosen as they are environmental pollutants and their monitoring is especially important in agricultural states like Iowa. As a first step in our design process, we have developed a Matlab model based on Beer-Lambert's law to generate sample sensor data for each of the gases at different concentrations. The data measured from the sensor system will be as a function of time instead of wavelength, so we performed Fourier Transform analysis on the sensor data to convert it to voltage versus time. The simulated sensor data will enable to design software algorithms to separate the absorption signals for each of the three gases. As a second step, we have developed a lab-based sensor system comprising of three components: (i) a NIR lead sulfide (PbS) photodiode, (ii) an LED that emits 1900 nm to 2600 nm, and (iii) an optical cavity where the gases are introduced. We are designing the optical cavity using ray optics COMSOL finite element method simulator using the principles of a compact chaotic cavity that will allow the LED light to have a path length of greater than 100 m within the cavity, enabling high sensitivity gas detection. Our end goal is to have an autonomous drone mounted device that is simple and inexpensive to use. We plan to license this technology to agricultural equipment manufacturers.   

Enthalpy of sublimation as measured using a silicon oscillator.

In this study, we report the enthalpy of sublimation of common gases (nitrogen, oxygen, argon, carbon dioxide, neon, krypton, xenon, and water vapor) using a large area silicon oscillator with a sub-ng ($\approx $0.027 ng/cm$^{2})$ mass sensitivity. The double paddle oscillator design enables high frequency stability (17 ppb) at cryogenic temperatures and provides a consistent technique for enthalpy measurements. The enthalpies of sublimation are derived from the rate of mass loss during programmed thermal desorption and are detected as a change in the resonance frequency of the self-tracking oscillator. These measured enthalpy values show excellent agreement with the accepted literature values.   

Conversion of far ultraviolet to visible radiation: absolute measurements of the conversion efficiency of tetraphenyl butadiene

Far ultraviolet (FUV) scintillation of noble gases is used in dark matter and neutrino research\footnote{``Liquid noble gas detectors for low energy particle physics,'' V. Chepel and H. Ara\'ujo, {\em JINST} {\bf 8}, R04001 (2013)} and in neutron detection.\footnote{``Noble gas excimer scintillation following neutron capture in boron thin films,'' J. C. McComb,{\em et al., J. Appl. Phys.} {\bf 115}, 144504 (2014)} Upon collisional excitation, noble gas atoms recombine into excimer molecules that decay by FUV emission. Direct detection of FUV is difficult. Another approach is to convert it to visible light using a wavelength-shifting medium. One such medium, tetraphenyl butadiene (TPB) can be vapor-deposited on substrates. Thus the quality of thin TPB films can be tightly controlled. We have measured the absolute efficiency of FUV-to-visible conversion by 1 $\mu$m-thick TPB films vs. FUV wavelengths between 130 and 300 nm, with 1 nm resolution. The energy efficiency of FUV to visible conversion varies between 1\% and 5\%. We make comparisons with other recent results.\footnote{``Fluorescence efficiency and visible re-emission spectrum of tetraphenyl butadiene films at extreme ultraviolet wavelengths,'' V. M. Gehman, {\em et al., Nuc. Inst. Meth. }{\bf A654}, 116 (2011)}