Session J21: Focus Session: Measurement Techniques for In Operando and Extreme Conditions

Multi-faceted characterization of battery reactions: the case of spinel hosts for Mg-ion batteries

Electrochemical energy storage was an important enabler of the wireless revolution and it is touted as a key component of a society that shifts away from its dependence on fossil fuels. Batteries are the primary technology when high energy devices are required. They are complex reactors in which multiple physico-chemical phenomena are concurrent in time and space. As a result, it is increasingly clear that holistic approaches to define such phenomena require a breadth of characterization tools. I will exemplify this need in the context of our quest for hosts that are able to reversibly intercalate Mg$^{2+}$ ions. Systems based on the intercalation of multivalent ions are pushed as next generation devices because, while they can resemble systems using Li$^{+}$ ions, they can store more charge per mol of intercalated species, and adopt metals as the anode. Using a combination of characterization tools, including X-ray diffraction, spectroscopy and scattering, electron microscopy and nuclear magnetic resonance, we ascertained that spinel oxides are able to reversibly and extensively accommodate Mg$^{2+}$. The mechanisms of this reaction were also elucidated. The rationale for the choice of techniques and the key pieces they provided to complete the picture will be discussed.   

Atomic-scale roughness of Li metal surface evident in soft X-ray absorption spectroscopy

Realizing Li metal electrodes depends on fundamental understanding and efficient control of surface properties, which requires reliable characterization of the Li metal surface. Controlled experiments of Li $K$-edge soft X-ray absorption spectroscopy (XAS) reveal evidence of steady oxidation of the Li metal surface even under ultrahigh vacuum (UHV) conditions. The XAS of the short-lived Li metal surface, prepared by \textit{in-situ} scratching, exhibits a prominent peak at 55.6~eV, more intense and at a slightly higher energy than the first peak expected for bulk Li metal at 55~eV. First-principles XAS calculations explain the origin of both the increased intensity and energy shift. This required the use of surface structural models with under-coordinated Li atoms and an estimated 4~\AA~inelastic mean-free-path for Auger electrons, implying extreme surface sensitivity of the measurements to the first 2-3 atomic layers. This work provides a benchmark on both experiment and theory for further studies of Li and other reactive metal surfaces, which are currently under scrutiny for next-generation energy storage devices.   

Neutron Imaging of Rapid Water Imbibition in Fractured Sedimentary Rock Cores

Advances in nondestructive testing methods, such as neutron, nuclear magnetic resonance, and x-ray imaging, have significantly improved experimental capabilities to visualize fracture flow in various important fossil energy contexts, e.g. enhanced oil recovery and shale gas. We present a theoretical framework for predicting the rapid movement of water into air-filled fractures within a porous medium based on early-time capillary dynamics and spreading over rough fracture surfaces. The theory permits estimation of sorptivity values for the matrix and fracture zone, as well as a dispersion parameter which quantifies the extent of spreading of the wetting front. Dynamic neutron imaging of water imbibition in unsaturated fractured Berea sandstone cores was employed to evaluate the proposed model. The experiments were conducted at the Neutron Imaging Prototype Facility at Oak Ridge National Laboratory. Water uptake into both the matrix and fracture zone exhibited square-root-of-time behavior. Both theory and neutron imaging data indicated that fractures significantly increase imbibition in unsaturated sedimentary rock by capillary action and surface spreading on rough fracture faces. Fractures also increased the dispersion of the wetting front.   

Tuning Fork Oscillators as Downhole Viscometers in Oilfield Applications

The commerciality of oil wells is greatly influenced by the physical properties of the fluids being produced. A key parameter in determining how producible the hydrocarbons are is their viscosity. Pressure and temperature changes in recovering a downhole sample to the surface can alter viscosity while accurate downhole measurement of this critical property remains a rudimentary effort in the industry. In this presentation we describe the challenges of measuring and quantifying the viscosity of reservoir fluids in situ at downhole conditions, as well as present an overview of some of the different measurement techniques currently used. Additionally, we show our characterization of a piezoelectric tuning fork oscillator used as a viscosity sensor. In an attempt to recreate the environment found in oil wells, its mechanical and electrical properties were studied while the device was immersed in different fluids and, separately, under different conditions of pressure and temperature. This device is a first step toward the development of an inexpensive, integrated, and miniaturized sensing platform for the in situ characterization of reservoir fluids.   

Detecting the topographic, chemical and magnetic contrast at surfaces with nanometer spatial resolution

Since the mid of the 1980s and over the past few decades various conventional electron spectroscopies were combined with electron spin sensitivity to investigate the magnetic properties of surfaces and thin films, evolving into the Scanning-Electron-Microscopy with Polarization Analysis (SEMPA) technique, which made it possible to directly observe the re-entrant transitions of magnetic-domain patterns in thin films of Fe on Cu(001) with several tens of nm resolution. The possibility of resolving magnetic-textures in direct space at atomic scale may trigger both fundamental perspectives and novel applications. Inspired by the Russell Young topografiner we redesigned the SEMPA setup by replacing the primary electron beam source and the probing method. We dubbed this new technique Near Field-Emission Scanning Electron Microscopy (NFESEM). Recently, we have used NFESEM to map the surface of some metals and semiconductors with nanometer lateral resolution. We report here on the latest results showing energy-resolved surface images and the first attempt to endowing this technique with the polarisation analysis of the detected secondary electrons by using of a Mott-detector, emphasizing the true potential of this new technique.   

Multifarious apparatus for dynamic measurements in intense magnetic fields

We describe a versatile apparatus which implements multiple types of measurement techniques suitable for intense magnetic field environment. Our approach capitalizes on recent advances in hardware/software co-design solutions to realize dynamic mapping and tracking of field-dependent phenomena in typically short time frame of pulsed measurements. The apparatus is capable of carrying out simultaneous dissimilar measurements such as resistivity, current-voltage characteristics, magnetic torque etc., both in pulse and continuous mode. The control logic can track and respond to changes in sample properties, such as onset of dissipation or changes in high-frequency oscillatory response, in sub- microsecond timescale.   

Two-axis piezo rotator for orienting samples in magnetic fields at millikelvin temperatures

The ability to apply large magnetic fields in any arbitrarily-chosen direction with angular precision at the millikelvin temperature scale enables a range of condensed matter experiments. Here we report on the integration of a custom attocube 2-axis rotary stepper positioner, with the ability to rotate a sample over the full 3D sphere with milli-degree precision, into a cryogen-free, top-loading dilution refrigerator with a single-axis 14 T magnet. We discuss technical details of the rotator unit, refrigerator probe wiring and construction, and proof-of-principle measurements demonstrating precise closed loop control of magnetic field orientation.   

Low Energy Electron Potentiometry

Charge transport measurements form an essential tool in condensed matter physics. The usual approach is to contact a sample by two or four probes, measure the resistance and derive the resistivity, assuming homogeneity within the sample. A more thorough understanding, however, requires knowledge of local resistivity variations. Here, we present a new way to determine spatial potential maps of a current-carrying sample, based on low-energy electron microscopy (LEEM). In this surface imaging technique the image intensity depends sensitively on the local electron landing energy. Specifically, we probe the in-plane potential distribution between laterally spaced electrical contacts on a layered quasi-two-dimensional (2D) sample (single to triple layer graphene). We make use of the property that incoming electrons are resonant with interlayer graphene states for well-defined (local) landing energies. Our method is straightforwardly extendable to other quasi-2D systems, most prominently to the upcoming class of layered van der Waals materials.   

Development of a Nonlinear Acoustic Phased Array and its Interaction with Thin Plates

Numerous technologies are based on the principle of focusing acoustic energy. We propose a new device to focus sound waves which exploits highly nonlinear dynamics. The advantages of this device are the capability of generating very highly powerful acoustic pulses and potential operation in high-temperature environments where traditional piezoelectrics may fail. This device is composed of rows of ball bearings placed in contact with a medium of interest and with an actuator on the top. Elastic spherical particles have a contact force that grows with their relative displacement to the three-halves power (Hertzian contact). When several spheres are placed in a row, the particles support the propagation of ``solitary waves''---strong, compact stress-wave pulses whose tendency to disperse is counteracted by the nonlinearity of the sphere's contact force. We present results regarding the experimental operation of the device and its comparison to theory and numerical simulations. We will show how well this system is capable of focusing energy at various locations in the medium, and the limits imposed by pre-compression. Finally, the effects of timing error on energy focusing will be demonstrated.   

Investigation of acoustically dead materials for resonant ultrasound spectroscopy

Resonant Ultrasound Spectroscopy is used to excite mechanical resonances in solid samples. By precisely knowing the resonant frequency the complete elastic tensor of the sample can be calculated. In practice unwanted resonances are also created in the sample holder structure, these resonances are not related to the sample and can often confuse the measurement. To reduce this problem we have investigated the use of acoustically ``dead'' materials. We present data from various natural and synthetic materials. We also present RUS sample holder designs that can be used from \textless 4K up to 700K and in magnet fields up to 45T. The elastic tensor of poly-crystal beryllium will be presented as a demonstration of the system performance.   

Closed cycle refrigeration for routine magnetotransport measurements

Condensed matter physics is often interested in the behavior of materials at very low temperatures. Low temperatures have traditionally been realized using liquid helium. However, the recent scarcity of liquid helium and the rapid rise in its cost has encouraged the development of alternative approaches, based on closed cycle refrigerators, for realizing low temperatures. Here, we convey our experiences in developing a home-made, low cost, variable temperature closed cycle refrigeration system for routine magnetotransport measurements down to 10K, and present measurements obtained with this system relating to the electronic properties of the high mobility GaAs/AlGaAs 2D semiconductors system. The setup was constructed to examine 0.5cm $\times$ 0.5cm semiconductor chips including up to 49 leads and reach $\sim$ 10K within 3 hours. A computer controlled data acquisition system was assembled to collect resistivity and Hall effect data, and extract the carrier Hall mobility and density as a function of the temperature.