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This work outlines conditions suitable for the heteroepitaxial growth of Cr2O3(0001) films (1.5-20 nm thick) on a Ru(0001)-terminated substrate. Optimized growth is achieved by sputter deposition of Cr within a 4 mTorr Ar/O2 20% ambient at Ru temperatures ranging from 450 to 600 °C. The Cr2O3 film adopts a 30° rotated honeycomb configuration with respect to the underlying Ru(0001) substrate and exhibits a hexagonal lattice parameter consistent with that for bulk Cr2O3(0001). Heating to 700 °C within the same environment during film preparation leads to Ru oxidation. Exposure to temperatures at or above 400 °C in a vacuum, Ar, or Ar/H2 3% leads to chromia film degradation characterized by increased Ru 3d XPS intensity coupled with concomitant Cr 2p and O 1s peak attenuations when compared to data collected from unannealed films. An ill-defined but hexagonally well-ordered RuxCryOz surface structure is noted after heating the film in this manner. Heating within a wet Ar/H2 3% environment preserves the Cr2O3(0001)/Ru(0001) heterolayer structure to temperatures of at least 950 °C. Heating an Ru-Cr2O3-Ru heterostacked film to 950 °C within this environment is shown by cross-sectional scanning/transmission electron microscopy (S/TEM) to provide clear evidence of retained epitaxial bicrystalline oxide interlayer structure, interlayer immiscibility, and epitaxial registry between the top and bottom Ru layers. Subtle effects marked by O enrichment and O 1s and Cr 2p shifts to increased binding energies are noted by XPS in the near-Ru regions of Cr2O3(0001)/Ru(0001) and Ru(0001)/Cr2O3(0001)/Ru(0001) films after annealing to different temperatures in different sets of environmental conditions., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

Opioid use disorder has become an epidemic in the United States, fuelled by the widespread availability of fentanyl, which produces rapid and intense euphoria followed by severe withdrawal and emotional distress. We developed a new preclinical model of fentanyl seeking in outbred male and female rats using volitional oral self-administration (SA) that can be readily applied in labs without intravascular access. Using a traditional two-lever operant procedure, rats learned to take oral fentanyl vigorously, escalated intake across sessions, and readily reinstated responding to conditioned cues after extinction. Oral SA also revealed individual and sex differences that are essential to studying substance use risk propensity. During a behavioural economics task, rats displayed inelastic demand curves and maintained stable intake across a wide range of fentanyl concentrations. Oral SA was also neatly patterned, with distinct 'loading' and 'maintenance' phases of responding within each session. Using our software DeepSqueak, we analysed ultrasonic vocalizations (USVs), which are innate expressions of current emotional state in rats. Rats produced 50 kHz USVs during loading then shifted quickly to 22 kHz calls despite ongoing maintenance of oral fentanyl taking, reflecting a transition to negative reinforcement. Using fibre photometry, we found that the lateral habenula differentially processed drug cues and drug consumption depending on affective state, with potentiated modulation by drug cues and consumption during the negative affective maintenance phase. Together, these results indicate a rapid progression from positive to negative reinforcement occurs even within an active drug taking session, revealing a within-session opponent process., (© 2023 The Authors. Addiction Biology published by John Wiley & Sons Ltd on behalf of Society for the Study of Addiction.)

The striatum, both dorsal and ventral, is strongly implicated in substance use disorder. Chronic consumption of abused substances, such as cocaine, can cause an oversaturation of mesostriatal dopamine, which results in alterations in the firing of striatal neurons. While most preclinical studies of drug self-administration (S-A) are focused on these alterations, individual differences in a subject's early responses to drugs can also account for substantial differences in addiction susceptibility. In this study, we modeled longitudinal pharmacokinetics using data from a previous longitudinal study (Coffey et al., 2015) and aimed to determine if firing in specific dorsal and ventral striatal subregions was subject to changes across chronic cocaine S-A, and if individual animal differences in striatal firing in response to early drug exposure correlated with increases in drug intake. We observed that the firing patterns of nucleus accumbens (NAc) core and shell neurons exhibited increasing sensitivity to cocaine over the first 6 S-A sessions and maintained a strong negative correlation between drug intake and neuronal firing rates across chronic S-A. Moreover, we observed that the early sensitivity of NAc shell neurons to cocaine correlated with future increases in drug intake. Specifically, rats whose NAc shell neurons were most inhibited by increasing levels of cocaine upon first exposure exhibited the strongest increases in cocaine intake over time. If this difference can be linked to a genetic difference, or druggable targets, it may be possible to screen for similar addiction susceptibility in humans or develop novel preemptive pharmacotherapies., Competing Interests: Declaration of Competing Interest The authors declare that they do not have any conflicts of interest (financial or otherwise) related to the data presented in this manuscript.

Single-crystal nanowires are of broad interest for applications in nanotechnology. However, such wires are subject to both the Rayleigh-Plateau instability and an ovulation process that are expected to lead to their break up into particle arrays. Single crystal Ru nanowires were fabricated with axes lying along different crystallographic orientations. Wires bound by equilibrium facets along their length did not break up through either a Rayleigh-Plateau or ovulation process, while wires with other orientations broke up through a combination of both. Mechanistic insight is provided using a level-set simulation that accounts for strongly anisotropic surface energies, providing a framework for design of morphologically stable nanostructures.

Background: Microglia have recently been implicated in opioid dependence and withdrawal. Mu Opioid (MOR) receptors are expressed in microglia, and microglia form intimate connections with nearby neurons. Accordingly, opioids have both direct (MOR mediated) and indirect (neuron-interaction mediated) effects on microglia function., Methods: To investigate this directly, we used RNA sequencing of ribosome-associated RNAs from striatal microglia (RiboTag-Seq) after the induction of morphine tolerance and followed by naloxone precipitated withdrawal (n=16). We validated the RNA-Seq data by combining fluorescent in-situ hybridization with immunohistochemistry for microglia (n=18). Finally, we expressed and activated the Gi/o-coupled hM 4 Di DREADD receptor in CX3CR1-expressing cells during morphine withdrawal (n=18)., Results: We detected large, inverse changes in RNA translation following opioid tolerance and withdrawal. WGCNA analysis revealed an intriguing network of cAMP-associated genes that are known to be involved in microglial motility, morphology, and interactions with neurons that were downregulated with morphine tolerance and upregulated rapidly by withdrawal. Three-dimensional histological reconstruction of microglia allowed for volumetric, visual colocalization of mRNA within individual microglia that validated our bioinformatics results. Direct activation of Gi/o-coupled DREADD receptors in CX3CR1-expressing cells exacerbated signs of opioid withdrawal rather than mimicking the effects of morphine., Conclusions: These results indicate that Gi-signaling and cAMP-associated gene networks are inversely engaged during opioid tolerance and early withdrawal, perhaps revealing a role of microglia in mitigating the consequences of opioids., Competing Interests: Competing Interests Kevin R. Coffey has no conflicts of interest to disclose. Atom J. Lesiak has no conflicts of interest to disclose. Russell G. Marx has no conflicts of interest to disclose. Emily K. Vo has no conflicts of interest to disclose. Gwenn A. Garden has no conflicts of interest to disclose. John F. Neumaier has no conflicts of interest to disclose.

The lateral preoptic area is implicated in numerous aspects of substance use disorder. In particular, the lateral preoptic area is highly sensitive to the pharmacological properties of psychomotor stimulants, and its activity promotes drug-seeking in the face of punishment and reinstatement during abstinence. Despite the lateral preoptic area's complicity in substance use disorder, how precisely lateral preoptic area neurons signal the individual components of drug self-administration has not been ascertained. To bridge this gap, we examined how the firing of single lateral preoptic area neurons correlates with three discrete elements of cocaine self-administration: (1) drug-seeking (pre-response), (2) drug-taking (response) and (3) receipt of the cocaine infusion. A significant subset of lateral preoptic area neurons responded to each component with a mix of increases and decreases in firing-rate. A majority of these neurons signal the operant response with increases in spiking, though responses during the drug-seeking, taking and reciept windows were highly correlated., (© 2021 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

The lateral habenula (LHb) integrates critical information regarding aversive stimuli that shapes decision making and behavioral responses. The three major LHb outputs innervate dorsal raphe nucleus (DRN), ventral tegmental area (VTA), and the rostromedial tegmental nucleus (RMTg). LHb neurons that project to these targets are segregated and nonoverlapping, and this led us to consider whether they have distinct molecular phenotypes and adaptations to stress exposure. In order to capture a time-locked profile of gene expression after repeated forced swim stress, we used intersectional expression of RiboTag in rat LHb neurons and next-gen RNA sequencing to interrogate the RNAs actively undergoing translation from each of these pathways. The "translatome" in the neurons comprising these pathways was similar at baseline, but diverged after stress, especially in the neurons projecting to the RMTg. Using weighted gene co-expression network analysis, we found one module, which had an overrepresentation of genes associated with phosphoinositide 3 kinase (PI3K) signaling, comprising genes downregulated after stress in the RMTg-projecting LHb neurons. Reduced PI3K signaling in RMTg-projecting LHb neurons may be a compensatory adaptation that alters the functional balance of LHb outputs to GABAergic vs. monoaminergic neurons following repeated stress exposure., (© 2020 The Authors.)

The lateral habenula (LHb) processes information about aversive experiences that contributes to the symptoms of stress disorders. Previously, we found that chemogenetic inhibition of rat LHb neurons reduced immobility in the forced swim test, but the downstream target of these neurons was not known. Using an intersectional viral vector strategy, we selectively transduced three different output pathways from the LHb by injecting AAV8-DIO-hM 4 Di into the LHb and CAV2-CRE (a retrograde viral vector) into one of the three target areas as follows: dorsal raphe nucleus (DRN), ventral tegmental area (VTA), or rostromedial tegmentum (RMTg). Using the forced swim test, we found that chemogenetic inhibition of DRN-projecting LHb neurons reduced passive coping (immobility), whereas inhibition of the other pathways did not. Chemogenetic activation of DRN-projecting neurons using hM3Dq in another cohort did not further exacerbate immobility. We next examined the impact of inhibiting DRN-projecting LHb neurons on reward sensitivity, perseverative behavior, and anxiety-like behavior using saccharin preference testing, reward-omission testing, and open-field testing, respectively. There was no effect of inhibiting any of these pathways on reward sensitivity, locomotion, or anxiety-like behavior, but inhibiting DRN-projecting LHb neurons reduced perseverative licking during reward-omission testing, whereas activating these neurons increased perseverative licking. These results support the idea that inhibiting LHb projections to the DRN provides animals with resilience during highly stressful or frustrating conditions but not under low-stress circumstances, and that inhibiting these neurons may promote persistence in active coping strategies.

Rodents engage in social communication through a rich repertoire of ultrasonic vocalizations (USVs). Recording and analysis of USVs has broad utility during diverse behavioral tests and can be performed noninvasively in almost any rodent behavioral model to provide rich insights into the emotional state and motor function of the test animal. Despite strong evidence that USVs serve an array of communicative functions, technical and financial limitations have been barriers for most laboratories to adopt vocalization analysis. Recently, deep learning has revolutionized the field of machine hearing and vision, by allowing computers to perform human-like activities including seeing, listening, and speaking. Such systems are constructed from biomimetic, "deep", artificial neural networks. Here, we present DeepSqueak, a USV detection and analysis software suite that can perform human quality USV detection and classification automatically, rapidly, and reliably using cutting-edge regional convolutional neural network architecture (Faster-RCNN). DeepSqueak was engineered to allow non-experts easy entry into USV detection and analysis yet is flexible and adaptable with a graphical user interface and offers access to numerous input and analysis features. Compared to other modern programs and manual analysis, DeepSqueak was able to reduce false positives, increase detection recall, dramatically reduce analysis time, optimize automatic syllable classification, and perform automatic syntax analysis on arbitrarily large numbers of syllables, all while maintaining manual selection review and supervised classification. DeepSqueak allows USV recording and analysis to be added easily to existing rodent behavioral procedures, hopefully revealing a wide range of innate responses to provide another dimension of insights into behavior when combined with conventional outcome measures.

Striatal medium spiny projection neurons (MSNs) output through two diverging circuits, the 'direct and indirect pathways' which originate from minimally overlapping populations of MSNs expressing either the dopamine receptor D1 or the dopamine receptor D2. One modern theory of direct and indirect pathway function proposes that activation of direct pathway MSNs facilitates output of desired motor programs, while activation of indirect pathway MSNs inhibits competing motor programs. A separate theory suggests that coordinated timing or synchrony of the direct and indirect pathways is critical for the execution of refined movements. These hypotheses are made testable by a common type of striatal neuron known as type IIb MSNs. Clusters of these MSNs exhibit phasic increases in firing rate related to sensorimotor activity of single body parts. If these MSNs were to reside in only the direct pathway, evidence would be provided that D1 MSNs are 'motor program' specific, which would lend credence to the 'competing motor programs' hypothesis. However, if type IIb MSNs reside in both pathways, evidence would be provided for the 'coordinated timing or synchrony' hypothesis. Our results show that type IIb neurons may express either D1 or D2. This evidence supports the theory that the coordinated timing or synchrony of the direct and indirect pathways is critical for refined movements. We also propose a model in which the direct and indirect pathways act as a differentiator circuit, providing a possible mechanism by which coordinated activity of D1 and D2 neurons may output meaningful somatosensorimotor information to downstream structures., (© 2017 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Periodically patterned Au nanorods in TiO 2 nanocavities (Au NRs@TiO 2 ) were fabricated via magnetron sputtering followed by a thermal dewetting process. This innovative Au NRs@TiO 2 heterostructure was used as a plasmonic sensing platform for photoelectrochemical detection of glucose and lactose. This Au NRs@TiO 2 patterned heterostructure possesses superior sensing properties to other Au nanoparticle-based sensors because (i) localized surface plasmon resonance (LSPR) generated at Au/TiO 2 interfaces enhanced sensitivity of glucose (lactose) amperometric detection; (ii) periodic Au nanocrystals in TiO 2 nanocavities accelerated charge separation and transfer rate, especially under monochromatic blue light irradiation; (iii) discrete planar architectures comprising Au NRs immobilized on TiO 2 substrates significantly improved stability and reusability of the sensors. A low detection limit of 1 μM (10 μM) and a high sensitivity of 812 μA mM -1 cm -2 (270 μA mM -1 cm -2 ) were achieved on the Au NRs@TiO 2 heterostructures for glucose (lactose) detection without the addition of enzymes. Good selectivity and superb stability over more than 8 weeks was also demonstrated using these Au NRs@TiO 2 heterostructures for glucose (lactose) detection. Additionally, this cost-efficient technique can be easily extended to other photoelectrochemical sensing systems when considering the combination of sensing and visible or infrared light source enhancement.

Numerous studies have shown that certain types of striatal interneurons play a crucial role in selection and regulation of striatal output. Striatal Fast-Spiking Interneurons (FSIs) are parvalbumin positive, GABAergic interneurons that constitute less than 1% of the total striatal population. It is becoming increasingly evident that these sparsely distributed neurons exert a strong inhibitory effect on Medium Spiny projection Neurons (MSNs). MSNs in lateral striatum receive direct synaptic input from regions of cortex representing discrete body parts, and show phasic increases in activity during touch or movement of specific body parts. In the present study, we sought to determine whether lateral striatal FSIs identified by their electrophysiological properties, i.e., short-duration spike and fast firing rate (FR), display body part sensitivity similar to that exhibited by MSNs. During video recorded somatosensorimotor exams, each individual body part was stimulated and responses of single neurons were observed and quantified. Individual FSIs displayed patterns of activity related selectively to stimulation of a discrete body part. Most patterns of activity were similar to those exhibited by typical MSNs, but some phasic decreases were observed. These results serve as evidence that some striatal FSIs process information related to discrete body parts and participate in sensorimotor processing by striatal networks that contribute to motor output., Statement of Significance: Parvalbumin positive, striatal FSIs are hypothesized to play an important role in behavior by inhibiting MSNs. We asked a fundamental question regarding information processed during behavior by FSIs: whether FSIs, which preferentially occupy the sensorimotor portion of the striatum, process activity of discrete body parts. Our finding that they do, in a selective manner similar to MSNs, begins to reveal the types of phasic signals that FSI feed forward to projection neurons during striatal processing of cortical input regarding a specific sensorimotor event. These findings suggest new avenues for testing feed-forward inhibition theory as applied to striatum in naturalistic conditions, such as whether FSI decreases facilitate excitation of MSNs related to the current movement while FSI increases silence MSNs unrelated to the current movement., Competing Interests: The authors declare no competing financial interests., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Novel Au@TiO 2 plasmonic films were fabricated by individually placing Au nanoparticles into TiO 2 nanocavity arrays through a sputtering and dewetting process. These discrete Au nanoparticles in TiO 2 nanocavities showed strong visible-light absorption due to the plasmonic resonance. Photoelectrochemical studies demonstrated that the developed Au@TiO 2 plasmonic films exhibited significantly enhanced catalytic activities toward oxygen reduction reactions with an onset potential of 0.92 V (vs reversible hydrogen electrode), electron transfer number of 3.94, and limiting current density of 5.2 mA cm -2 . A superior ORR activity of 310 mA mg -1 is achieved using low Au loading mass. The isolated Au nanoparticle size remarkably affected the catalytic activities of Au@TiO 2 , and TiO 2 coated with 5 nm Au (Au 5 @TiO 2 ) exhibited the best catalytic function to reduce oxygen. The plasmon-enhanced reductive activity is attributed to the surface plasmonic resonance of isolated Au nanoparticles in TiO 2 nanocavities and suppressed electron recombination. This work provides comprehensive understanding of a novel plasmonic system using isolated noble metals into nanostructured semiconductor films as a potential alternative catalyst for oxygen reduction reaction.

Interest in the dorsolateral striatum (DLS) has generated numerous scientific studies of its neuropathologies, as well as its roles in normal sensorimotor integration and learning. Studies are informed by knowledge of DLS functional organization, the guiding principle being its somatotopic afferent projections from primary somatosensory (S1) and motor (M1) cortices. The potential to connect behaviorally relevant function to detailed structure is elevated by mouse models, which have access to extensive genetic neuroscience tool kits. Remaining to be demonstrated, however, is whether the correspondence between S1/M1 corticostriatal terminal distributions and the physiological properties of DLS neurons demonstrated in rats and non-human primates exists in mice. Given that the terminal distribution of S1/M1 projections to the DLS in mice is similar to that in rats, we studied whether firing rates (FRs) of DLS neurons in awake, behaving mice are related to activity of individual body parts. MSNs exhibited robust, selective increases in FR during movement or somatosensory stimulation of single body parts. Properties of MSNs, including baseline FRs, locations, responsiveness to stimulation, and proportions of responsive neurons were similar to properties observed in rats. Future studies can be informed by the present demonstration that the mouse lateral striatum functions as a somatic sensorimotor sector of the striatum and appears to be a homolog of the primate putamen, as demonstrated in rats (Carelli and West, 1991)., (Copyright © 2016 Elsevier B.V. All rights reserved.)

As drug use becomes chronic, aberrant striatal processing contributes to the development of perseverative drug-taking behaviors. Two particular portions of the striatum, the nucleus accumbens (NAc) and the dorsolateral striatum (DLS), are known to undergo neurobiological changes from acute to chronic drug use. However, little is known about the exact progression of changes in functional striatal processing as drug intake persists. We sampled single-unit activity in the NAc and DLS throughout 24 daily sessions of chronic long-access cocaine self-administration, and longitudinally tracked firing rates (FR) specifically during the operant response, an upward vertical head movement. A total of 103 neurons were held longitudinally and immunohistochemically localised to either NAc Medial Shell (n = 29), NAc Core (n = 30), or DLS (n = 54). We modeled changes representative of each category as a whole. Results demonstrated that FRs of DLS Head Movement neurons were significantly increased relative to baseline during all sessions, while FRs of DLS Uncategorised neurons were significantly reduced relative to baseline during all sessions. NAc Shell neurons' FRs were also significantly decreased relative to baseline during all sessions while FRs of NAc Core neurons were reduced relative to baseline only during training days 1-18 but were not significantly reduced on the remaining sessions (19-24). The data suggest that all striatal subregions show changes in FR during the operant response relative to baseline, but longitudinal changes in response firing patterns were observed only in the NAc Core, suggesting that this region is particularly susceptible to plastic changes induced by abused drugs., (© 2015 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

In vivo electrophysiological recordings in the awake, behaving animal provide a powerful method for understanding neural signaling at the single-cell level. The technique allows experimenters to examine temporally and regionally specific firing patterns in order to correlate recorded action potentials with ongoing behavior. Moreover, single-unit recordings can be combined with a plethora of other techniques in order to produce comprehensive explanations of neural function. In this article, we describe the anesthesia and preparation for microwire implantation. Subsequently, we enumerate the necessary equipment and surgical steps to accurately insert a microwire array into a target structure. Lastly, we briefly describe the equipment used to record from each individual electrode in the array. The fixed microwire arrays described are well-suited for chronic implantation and allow for longitudinal recordings of neural data in almost any behavioral preparation. We discuss tracing electrode tracks to triangulate microwire positions as well as ways to combine microwire implantation with immunohistochemical techniques in order to increase the anatomical specificity of recorded results.

This protocol includes the designs and software necessary to upgrade an existing stereotaxic instrument to a robotic (CNC) stereotaxic instrument for around $1,000 (excluding a drill), using industry standard stepper motors and CNC controlling software. Each axis has variable speed control and may be operated simultaneously or independently. The robot's flexibility and open coding system (g-code) make it capable of performing custom tasks that are not supported by commercial systems. Its applications include, but are not limited to, drilling holes, sharp edge craniotomies, skull thinning, and lowering electrodes or cannula. In order to expedite the writing of g-coding for simple surgeries, we have developed custom scripts that allow individuals to design a surgery with no knowledge of programming. However, for users to get the most out of the motorized stereotax, it would be beneficial to be knowledgeable in mathematical programming and G-Coding (simple programming for CNC machining). The recommended drill speed is greater than 40,000 rpm. The stepper motor resolution is 1.8°/Step, geared to 0.346°/Step. A standard stereotax has a resolution of 2.88 μm/step. The maximum recommended cutting speed is 500 μm/sec. The maximum recommended jogging speed is 3,500 μm/sec. The maximum recommended drill bit size is HP 2.

Stereological analysis has been coupled with transmission electron microscope (TEM) orientation mapping to investigate the grain boundary character distribution in nanocrystalline copper thin films. The use of the nanosized (<5 nm) beam in the TEM for collecting spot diffraction patterns renders an order of magnitude improvement in spatial resolution compared to the analysis of electron backscatter diffraction patterns in the scanning electron microscope. Electron beam precession is used to reduce dynamical effects and increase the reliability of orientation solutions. The misorientation distribution function shows a strong misorientation texture with a peak at 60°/[111], corresponding to the Σ3 misorientation. The grain boundary plane distribution shows {111} as the most frequently occurring plane, indicating a significant population of coherent twin boundaries. This study demonstrates the use of nanoscale orientation mapping in the TEM to quantify the five-parameter grain boundary distribution in nanocrystalline materials.

Long Evans rats (n=32) were trained for 2 weeks to respond to an auditory conditioned stimulus (CS) which signaled the delivery of a 20% sucrose unconditioned stimulus (US) with varying probabilities. Animals were randomly assigned to 1 of 4 groups. In the control groups, the CS signaled sucrose delivery with equal probabilities across two weeks, at 100% (Group 100-100) and 25% (Group 25-25) respectively. In the experimental groups (Group 100-25) and (Group 25-100), sucrose probabilities were switched between weeks 1 and 2. Three behavioral measures were recorded: latency to enter the sucrose port upon CS presentation, head entries throughout the session and ultrasonic vocalizations. The results suggest that all groups formed associations between the CS and US, as evidenced by a decrease in latency to respond to the CS across days. The experimental groups were also able to detect when sucrose probability changed, as evidenced by Group 25-100's increase in head entries, to the level of Group 100-100 in week 2, and Group 100-25's decrease in head entries, to the level of Group 25-25 in week 2. Group 100-25 also produced an increase in "22 kHz" ultrasonic vocalizations following the downshift on the first day of week 2. The increase in this ultrasonic frequency range, which is associated with negative affect in rats, preceded both the decrease in head entries and the increase in missed trials, consistent with a multistage model of behaviors resulting from US probability reduction., (Copyright © 2012 Elsevier B.V. All rights reserved.)

This work demonstrates an anisotropic increase in resistivity with decreasing width in single crystal tungsten (W) nanowires having a height of 21 nm. Nanowire-widths were in the range of 15-451 nm, with the anisotropy observed for widths below 50 nm. The longitudinal directions of the nanowires coincided with the <100>, <110> and <111> orientations of the body centered cubic phase of W. The resistivity increase was observed to be minimized for the <111>-oriented single crystal nanowires, exhibiting a factor of two lower increase in resistivity at a width of ~15 nm, relative to the thin film resistivity (i.e., an infinitely wide wire). The observed anisotropy is attributed to crystallographic anisotropy of the Fermi velocity and the resultant anisotropy of the electron mean free path in W, and underscores the critical role of crystallographic orientation in nanoscale metallic conduction.

Rationale: It has been proposed that cocaine abuse results in skilled or "automatic" drug-taking behaviors. Brain regions important for skill learning are implicated in cocaine self-administration. However, the development of skill during self-administration has not been investigated., Objectives: The present experiment investigated the development of skilled self-administration over extended drug use by employing a novel operant vertical head movement under discriminative stimulus (S(D)) control. In addition, the capacity of the head movement to serve as an operant was tested by manipulating drug levels above or below satiety drug levels via frequent noncontingent microinfusions (0.2 s) of cocaine., Results: Animals acquired the vertical head movement operant, which increased in number over days. Task learning was demonstrated by reduced reaction time in response to the S(D), increased propensity to self-administer upon S(D) presentation, and escalated drug consumption over days. Skill learning was demonstrated by (1) an increase over days in the velocity of operant movements, as a function of shorter duration but not altered distance, and (2) an increase over days in the probability of initiating the operant at the optimal starting position. Evidence that responding was specific to self-administration was revealed during periods of experimenter-manipulated drug level: maintaining drug levels above satiety decreased responding while maintaining drug levels below satiety increased responding., Conclusions: Under the specific set of circumstances tested herein, cocaine self-administration became skilled over extended drug use. The vertical head movement can be used as an operant comparable to lever pressing with the additional benefit of quantifying skill learning.

We use split ring resonators (SRRs) at optical frequencies to study strong coupling between planar metamaterials and phonon vibrations in nanometer-scale dielectric layers. A series of SRR metamaterials were fabricated on a semiconductor wafer with a thin intervening SiO(2) dielectric layer. The dimensions of the SRRs were varied to tune the fundamental metamaterial resonance across the infrared (IR) active phonon band of SiO(2) at 130 meV (31 THz). Strong anticrossing of these resonances was observed, indicative of strong coupling between metamaterial and phonon excitations. This coupling is very general and can occur with any electrically polarizable resonance including phonon vibrations in other thin film materials and semiconductor band-to-band transitions in the near to far IR. These effects may be exploited to reduce loss and to create unique spectral features that are not possible with metamaterials alone.

In this paper, we describe hollow-cone dark field (HCDF) transmission electron microscopy (TEM) imaging, with a slightly convergent beam, as an improved technique that is suitable to form high contrast micrographs for nanocrystalline grain size quantification. We also examine the various factors that influence the HCDF TEM image quality, including the conditions of microscopy (alignment, focus and objective aperture size), the properties of the materials imaged (e.g., atomic number, strain, defects), and the characteristics of the TEM sample itself (e.g., thickness, ion milling artifacts). Sample preparation was found to be critical and an initial thinning by wet etching of the substrate (for thin film samples) or tripod polishing (for bulk samples), followed by low-angle ion milling was found to be the preferred approach for preparing high-quality electron transparent samples for HCDF imaging., (Copyright 2009 Elsevier Ltd. All rights reserved.)

For the first time, a tunable reflected phase reflectarray is demonstrated in the thermal infrared. This is done using thermochromic VO(2) square-patch elements in a reflectarray metamaterial configuration. A sixty degree change in reflected phase is measured using a Twyman-Green interferometer, and FTIR measurements show that the resonance reflection minima shifts from 9.2 to 11.2 mum as the sample is heated from 45 through 65 degrees C. These results are in agreement with finite-element method simulations using the optical properties of VO(2) which are measured by infrared ellipsometry.

Infrared metamaterials fabricated on semiconductor substrates exhibit a high degree of sensitivity to very thin (as small as 2 nm) layers of low permittivity materials between the metallic elements and the underlying substrate. We have measured the resonant frequencies of split ring resonators and square loops fabricated on Si wafers with silicon dioxide thicknesses ranging from 0 to 10 nm. Resonance features blue shift with increasing silicon dioxide thickness. These effects are explained by the silicon dioxide layer forming a series capacitance to the fringing field across the elements. Resonance coupling to the Si-O vibrational absorption has been observed. Native oxide layers which are normally ignored in numerical simulations of metamaterials must be accounted for to produce accurate predictions.

Cross-sectional transmission electron microscopy (XTEM) is a very useful technique to study the interfacial diffusion and reactions and the grain growth of thin films. However, the preparation of XTEM samples of thin films is tedious and challenging. Difficulties may include the delamination of films from the substrate, fracture of brittle substrates and differential milling rates of the substrate and the film. This paper describes an improved technique using a combination of tripod polishing and focused ion beam milling to prepare XTEM samples of thin films. The technique can be widely used for high-throughput production of samples having varying film and substrate properties. Two different geometries are introduced. The first one is suitable for XTEM sample preparation of most films at a high yield rate, but with a limited view area. The other geometry is able to give a larger view area and is more suitable for thicker films. The technique is illustrated by an example of the sample preparation of Fe/Pt multilayer films on SiO2/Si substrates.

Back-etch methods have been widely used to prepare plan view transmission electron microscopy (TEM) samples of thin films on membranes by removal of the Si substrate below the membrane by backside etching. The conventional means to determine when to stop the etch process is to observe the color of the light transmitted through the sample, which is sensitive to the remaining Si thickness. However, most metallic films thicker than 75 nm are opaque, and there is no detectable color change prior to film perforation. In this paper, a back-etch method based on the observation of an abrupt change of optical reflection contrast is introduced as a means to determine the etch endpoint to prepare TEM samples for these films. As the acid etchant removes the Si substrate material a rough interface is generated. This interface becomes a relatively smooth and featureless region when the etchant reaches the membrane (film/SiO2). This featureless region is caused by the mirror reflection of the film plane (film/SiO2 interface) through the optically transparent SiO2 layer. The lower etch rate of SiO2 (compared with Si) gives the operator enough time to stop the etching without perforating the film. A clear view of the morphology and control of Si roughness during etching are critical to this method, which are discussed in detail. The procedures of mounting wax removal and sample rinsing are also described in detail, as during these steps damage to the membrane may easily occur without appropriate consideration. As examples, the preparation of 100-nm-thick Fe-based amorphous alloy thin film and 160-nm-thick Cu-thin film samples for TEM imaging is described.

A modified back-etch method is described that has been successfully used to prepare samples of thin films and nanoparticles on Si wafer substrates for examination by high-resolution transmission electron microscopy (HRTEM). This process includes ultrasonic cutting, abrasive pre-thinning and a two-stage etching procedure. Unlike previous reports of back-etching methods, tetramethyl ammonium hydroxide, which has a very high-etching selectivity of Si to SiO(2), is used for the final etching to allow removal of the Si without degradation of the SiO(2) membrane. An innovative wrapping method is also described. This novel approach reduces the preparation time for HRTEM samples to <1 h per sample for groups of 10 or more samples. As an example, the preparation of FePt nanoparticle samples for HRTEM imaging is described.

A series of sputtered multilayers of Ni(80)Fe(20)-Ag was prepared to examine the giant magnetoresistance effect before and after annealing. For a wide range of NiFe and Ag thicknesses, no giant magnetoresistance was observed in the unannealed films. After annealing, a large, negative magnetoresistance was observed of order 4 to 6% in applied fields of order 5 to 10 oersteds at room temperature. The appearance of giant managetoresistance is concurrent with the breakup of the NiFe layers, which is attributable to a magnetostatic interaction that favors local antiparallel alignment of the moments in adjacent layers. These structures may be of significant practical importance as sensors that require large changes in resistance at low fields, such as magnetoresistive heads used in magnetic recording systems.