Area Si Research Articles

Selective Functionalization with PNA of Silicon Nanowires on Silicon Oxide Substrates.

Silicon nanowire chips can function as sensors for cancer DNA detection, whereby selective functionalization of the Si sensing areas over the surrounding silicon oxide would prevent loss of analyte and thus increase the sensitivity. The thermal hydrosilylation of unsaturated carbon–carbon bonds onto H-terminated Si has been studied here to selectively functionalize the Si nanowires with a monolayer of 1,8-nonadiyne. The silicon oxide areas, however, appeared to be functionalized as well. The selectivity toward the Si–H regions was increased by introducing an extra HF treatment after the 1,8-nonadiyne monolayer formation. This step (partly) removed the monolayer from the silicon oxide regions, whereas the Si–C bonds at the Si areas remained intact. The alkyne headgroups of immobilized 1,8-nonadiyne were functionalized with PNA probes by coupling azido-PNA and thiol-PNA by click chemistry and thiol–yne chemistry, respectively. Although both functionalization routes were successful, hybridization could only be detected on the samples with thiol-PNA. No fluorescence was observed when introducing dye-labeled noncomplementary DNA, which indicates specific DNA hybridization. These results open up the possibilities for creating Si nanowire-based DNA sensors with improved selectivity and sensitivity.

Si doped GaN films grown by reactive co-sputtering of GaAs and Si

Si doped GaN films were grown on sapphire by RF reactive co-sputtering of GaAs and Si in argon–nitrogen atmosphere at 700 °C. The incorporation of Si in the films was controlled by varying Si area coverage on GaAs target and argon to nitrogen ratio in sputtering atmosphere. X-ray diffraction shows significant stress relaxation and improvement in structural quality with the incorporation of Si in films deposited with 2%–12% Si area coverage and 10%–20% nitrogen in sputtering atmosphere. Resistivity and Hall measurements show that the films deposited with 5%–12% Si area coverage and 20% nitrogen in sputtering atmosphere exhibit resistivity of ∼1.5 × 10−2 Ω cm, along with carrier concentration of ∼2 × 1019 cm−3 and mobility in the range of 20–22 cm2/V-s. The film deposited with 10% nitrogen in sputtering atmosphere and 8% Si area coverage, exhibits high carrier concentration of 1.5 × 1020 cm−3 along with mobility of 7.1 cm2/V-s, resulting in the lowest resistivity of ∼6 × 10−3 Ω cm. The behavior of electrical parameters is explained by invoking carrier trapping and scattering at the grain boundaries, in conjunction with the observed changes in their structural quality. The film with high carrier concentration ∼1020 cm−3, exhibits strong free carrier effects, such as, plasma resonance in NIR, high reflectivity in IR and significantly larger optical gap of 3.60 eV, due to the combined effect of Burstein-Moss shift and band gap narrowing.

Raman investigation of air-stable silicene nanosheets on an inert graphite surface

The fascinating properties of two dimensional (2D) crystals have gained increasing interest for many applications. The synthesis of a 2D silicon structure, namely silicene, is attracting great interest for possible development of next generation electronic devices. The main difficulty in working with silicene remains its strong tendency to oxidation when exposed to air as a consequence of its relatively highly buckled structure. In this work, we univocally identify the Raman mode of air-stable low-buckled silicene nanosheets synthesized on highly oriented pyrolytic graphite (HOPG) located at 542.5 cm−1. The main focus of this work is Raman spectroscopy and mapping analyses in combination with ab initio calculations. Scanning tunneling microscopy images reveal the presence of a patchwork of Si three-dimensional (3D) clusters and contiguous Si areas presenting a honeycomb atomic arrangement, rotated by 30° with respect to the HOPG substrate underneath, with a lattice parameter of 0.41 ± 0.02 nm and a buckling of the Si atoms of 0.05 nm. Raman analysis supports the co-existence of 3D silicon clusters and 2D silicene. The Raman shift of low-buckled silicene on an inert substrate has not been reported so far and it is completely different from the one calculated for free-standing silicene and the ones measured for silicene grown on Ag(111) surfaces. Our experimental results are perfectly reproduced by our ab initio calculations of deposited silicene nanosheets. This leads us to conclude that the precise value of the observed Raman shift crucially depends on the strain between the silicene and the HOPG substrate.

Effect of MACE parameters on length of porous silicon nanowires (PSiNWs)

Silicon nanowire-based devices have properties such as optical, electronic, and physical that can outperform their traditional counterparts in various ways because the silicon nanowires (SiNWs) have a high surface Si area to volume ratio and unique quasi-one-dimensional (1D) electronic structure. A variety of approaches are being classified into top-down and bottom-up methods to fabricate SiNWs. The present work demonstrates the synthesis of porous SiNWs (PSiNWs) through the metal-assisted chemical etching (MACE). The MACE produces PSiNWs using an aqueous solution composed of hydrofluoric acid (HF) and hydrogen peroxide (H2O2). Effect of MACE parameters such as H2O2 concentration, etching time, and Si wafer resistivity variation on the morphological characteristics (especially length) of PSiNWs are compared and thoroughly discussed. The structure and morphology of PSiNWs are characterized by transmission electron microscopy (TEM), environmental scanning electron microscopy (ESEM), and X-ray diffraction (XRD). The XRD data show the PSiNWs crystal growth direction.

Differentiating benign and malignant inflammatory breast lesions: Value of T2 weighted and diffusion weighted MR images

ObjectivesBenign and malignant inflammatory breast lesions demonstrate similar findings on both T2 weighted imaging (T2WI) and dynamic contrast enhanced (DCE) images. We hypothesized that benign inflammatory lesions might be differentiated form malignancies using a combination of apparent diffusion coefficient (ADC) values derived from diffusion weighted images (DWI) and T2WI. Materials and methodsWe retrospectively reviewed 162 patients undergoing breast MRI (T2WI, DWI and DCE images) between 2008 and 2015 who had breast lesions with high T2WI signal intensity (High T2 SI) including 14 benign inflammatory lesions, 69 benign non-inflammatory lesions, 16 malignant inflammatory lesions and 63 malignant non-inflammatory lesions. On the High T2 SI and low T2WI signal intensity (Low T2 SI) areas in these breast lesions, we calculated ADC values from b values of 0 and 1000 s/mm2. ResultsThe mean ADC values ± standard deviation (10−3 mm2/s) of the High T2 SI areas in benign inflammatory, benign non-inflammatory, malignant inflammatory and malignant non-inflammatory breast lesions were 0.75 ± 0.18, 1.77 ± 0.33, 2.06 ± 0.32 and 1.88 ± 0.41, respectively. Those of the Low T2 SI areas in benign inflammatory, benign non-inflammatory, malignant inflammatory and malignant non-inflammatory lesions were 0.89 ± 0.15, 1.31 ± 0.28, 0.87 ± 0.20 and 0.94 ± 0.27 respectively. ADC values of High T2 SI areas of the benign inflammatory lesions were significantly lower than those of benign non-inflammatory, malignant inflammatory, and malignant non-inflammatory lesions (p < 0.001). ADC values of Low T2 SI areas in benign inflammatory lesions were not significantly different from those of malignant inflammatory (p = 0.99) or malignant non-inflammatory lesions (p = 0.72). ConclusionFor breast lesions with High T2 SI, segmenting the High T2 SI for ADC mapping distinguishes benign from malignant inflammatory conditions. Using ADC mapping of the Low T2 SI areas will not result in this distinction.

Determination of etching parameters for pulsed XeF2 etching of silicon using chamber pressure data

A technique is presented for determination of the depletion of the etchant, etched depth, and instantaneous etch rate for Si etching with XeF2 in a pulsed etching system in real time. The only experimental data required is the pressure data collected temporally. Coupling the pressure data with the knowledge of the chemical reactions allows for the determination of the etching parameters of interest. Using this technique, it is revealed that pulsed etching processes are nonlinear, with the initial etch rate being the highest and monotonically decreasing as the etchant is depleted. With the pulsed etching system introduced in this paper, the highest instantaneous etch rate of silicon was recorded to be 19.5 µm min−1 for an initial pressure of 1.2 Torr for XeF2. Additionally, the same data is used to determine the rate constant for the reaction of XeF2 with Si; the reaction is determined to be second order in nature. The effect of varying the exposed surface area of Si as well as the effect that pressure has on the instantaneous etch rate as a function of time is shown applying the same technique. As a proof of concept, an AlN resonator is released using XeF2 pulses to remove a sacrificial poly-Si layer.

Multipulse nanosecond laser irradiation of silicon for the investigation of surface morphology and photoelectric properties

We irradiate the single crystal boron-doped silicon (Si) with different number of laser pulses at constant fluence (7.5 J cm−2) in ambient air using Nd:YAG laser and examine its surface morphology and photoelectric properties in details. The results obtained from optical micrographs reveal the increase in heat affected zone (HAZ) and melted area of laser irradiated Si with increasing number of laser pulses. The SEM micrographs evidence the formation of various surface morphologies like laser induced periodic surface structures, crater, microcracks, clusters, cavities, pores, trapped bubbles, nucleation sites, micro-bumps, redeposited material and micro- and nano-particles on the surface of irradiated Si. The surface profilometry analysis informs that the depth of crater is increased with increase in number of incident laser pulses. The spectroscopic ellipsometry reveals that the multipulse irradiation of Si changes its optical properties (refractive index and extinction coefficient). The current–voltage (I–V) characteristic curves of laser irradiated Si show that although the multipulse laser irradiation produces considerable number of surface defects and damages, the electrical properties of Si are well sustained after the multipulse irradiation. The current findings suggest that the multipulse irradiation can be an effective way to tune the optical properties of Si for the fabrication of wide range of optoelectronic devices.

Graphene as plasma-compatible blocking layer material for area-selective atomic layer deposition: A feasibility study for III-nitrides

Plasma-assisted atomic layer deposition (PA-ALD) is a promising method for low-temperature growth of III-nitride materials. However, selective film deposition using PA-ALD is challenging mainly due to the plasma-incompatibility of conventional deactivation/blocking layers including self-assembled monolayers and polymers. The main motivation behind this work is to explore alternative plasma-resistant blocking layer materials. Toward this goal, single/multilayered graphene (SLG/MLG) sheets were investigated as potential growth-blocking layers for III-nitride grown via PA-ALD. Prior to PA-ALD growth experiments, partially graphene-covered Si(100) samples were exposed to N2/H2 and N2-only plasma cycles to evaluate the plasma resistance of SLG and MLG. While SLG degraded fairly quickly showing signs of completely etched areas and rough surface morphology, MLG surface displayed certain degree of plasma-resistance. Based on this result, III-nitride PA-ALD experiments were carried out on MLG-patterned Si(100) samples. Crystalline III-nitride film deposition was observed on both Si(100) and graphene surfaces, confirming the rather ineffective nucleation blocking property of graphene surface against PA-ALD process. However, as graphene layers feature relatively weak van der Waals bonds at the substrate/graphene interface as well as between the multilayer graphene interfaces, conventional lift-off process was sufficient to remove the deposited excessive nitride films. InN and AlN-coated samples were ultrasonicated, and blocked/unblocked surfaces were characterized using scanning electron microscopy, x-ray photoelectron spectroscopy, and spectroscopic ellipsometer. While ∼50 nm thick films were measured in the open Si(100) areas, graphene-coated sample portions exhibited limited material growth in the range of 5–15 nm. Although not completely, the MLG surface has considerably blocked the PA-ALD growth process resulting in a usable thickness difference, enabling growth selectivity with postgrowth etch process. An Ar-based physical dry etching recipe was utilized to completely etch the unwanted nitride films from graphene coated area, while about 30 and 40 nm thick InN and AlN films remained on the nonblocked parts of the samples, respectively. As a result, selective deposition of PA-ALD grown AlN and InN has been achieved via graphene-assisted lift-off technique along with subsequent dry-etch process, achieving a maximum growth selectivity of ∼40 nm. With further process recipe optimization and integrating with a suitable patterning technique, the demonstrated graphene-assisted lift-off technique might offer an alternative feasible pathway toward area-selective deposition of III-nitrides and other plasma-necessitating materials.

Specific properties of the SI and SII somatosensory areas and their effects on motor control: a system neurophysiological study.

Sensorimotor integration is essential for successful motor control and the somatosensory modality has been shown to have strong effects on the execution of motor plans. The primary (SI) and the secondary somatosensory (SII) cortices are known to differ in their neuroanatomical connections to prefrontal areas, as well as in their involvement to encode cognitive aspects of tactile processing. Here, we ask whether the area-specific processing architecture or the structural neuroanatomical connections with prefrontal areas determine the efficacy of sensorimotor integration processes for motor control. In a system neurophysiological study including EEG signal decomposition (i.e., residue iteration decomposition, RIDE) and source localization, we investigated this question using vibrotactile stimuli optimized for SI or SII processing. The behavioral data show that when being triggered via the SI area, inhibitory control of motor processes is stronger as when being triggered via the SII area. On a neurophysiological level, these effects were reflected in the C-cluster as a result of a temporal decomposition of EEG data, indicating that the sensory processes affecting motor inhibition modulate the response selection level. These modulations were associated with a stronger activation of the right inferior frontal gyrus extending to the right middle frontal gyrus as parts of a network known to be involved in inhibitory motor control when response inhibition is triggered over SI. In addition, areas important for sensorimotor integration like the postcentral gyrus and superior parietal cortex showed activation differences. The data suggest that connection patterns are more important for sensorimotor integration and control than the more restricted area-specific processing architecture.

High Photocurrent in Gated Graphene-Silicon Hybrid Photodiodes.

Graphene/silicon (G/Si) heterojunction based devices have been demonstrated as high responsivity photodetectors that are potentially compatible with semiconductor technology. Such G/Si Schottky junction diodes are typically in parallel with gated G/silicon dioxide (SiO2)/Si areas, where the graphene is contacted. Here, we utilize scanning photocurrent measurements to investigate the spatial distribution and explain the physical origin of photocurrent generation in these devices. We observe distinctly higher photocurrents underneath the isolating region of graphene on SiO2 adjacent to the Schottky junction of G/Si. A certain threshold voltage (VT) is required before this can be observed, and its origins are similar to that of the threshold voltage in metal oxide semiconductor field effect transistors. A physical model serves to explain the large photocurrents underneath SiO2 by the formation of an inversion layer in Si. Our findings contribute to a basic understanding of graphene/semiconductor hybrid devices which, in turn, can help in designing efficient optoelectronic devices and systems based on such 2D/3D heterojunctions.

A low-power low-jitter DLL with a differential closed-loop duty cycle corrector

A low-power low-jitter delay locked loop (DLL) with a first order differential closed-loop duty cycle corrector (DCC) is presented in this paper. The proposed DCC has a differential closed-loop structure that corrects the input clock duty cycle from 10 to 90%. To have a wide range DLL, a low-power voltage control delay line using wide bandwidth and large tuning range delay cells is employed. The proposed DLL has been fabricated in a 0.13 μm CMOS process technology with an active Si area of 0.11 mm2. The measured results show the DLL exhibits a lock range of 0.1–1.2 GHz while the peak-to peak jitter and rms jitter are 7.3 and 1.2 ps at 1.2 GHz, respectively. The total power dissipated by the DLL is 4.8 mW with 1.2 V supply voltage at 1.2 GHz.

Effect of Heat Treatment on Microstructure and Thermal Fatigue Properties of Al-Si-Cu-Mg Alloys

AbstractThe effect of heat treatment on the microstructure and thermal fatigue properties were studied by means of optical microscope (OM) and scanning electron microscope (SEM). Energy dispersive X-ray detector (EDX) was used to analyze the role of phase composition in fatigue crack propagation. The results show that after heat treatment, the ultimate tensile strength increased from 285 MPa to 368 MPa and the elongation increased from 5.8 % to 6.5 %. During the initiation of fatigue crack, the crack was mainly propagated through eutectic Si area. With the long needles of eutectic Si particles spherodized after heat treatment, the split action from brittle Si particles to α-Al matrix was reduced and prolonged the fatigue crack initiation period. After aging for 6 h, the dispersed precipitation of secondary phases (Al2Cu, Mg2Si) elevated the driving force of crack propagation, blocked the spread of crack in the grain boundary, decreased the rate of fatigue crack growth and improved the fatigue resistance of alloy at the same time. In the process of crack initiation, the surplus-phase around the grain boundary fell off from α-Al matrix under thermal cycling stresses. The combination of interfaces was weaken by cycling stress and the fatigue crack was finally grown up in the weakness area between matrix and secondary phase.

Pattern-dependent anisotropic stress evaluation in SiGe epitaxially grown on a Si substrate with selective Ar+ ion implantation using oil-immersion Raman spectroscopy

Biaxial stress states in SiGe stripes on Si substrates fabricated by a novel selective Ar+ ion implantation technique were evaluated by oil-immersion Raman spectroscopy. The oil-immersion technique is appropriate for the measurement of strain induced in nanostructure devices, because it has a higher spatial resolution than conventional Raman spectroscopy and can evaluate anisotropic stress states owing to the excitation of multiple optical phonon modes. Results indicate that quasi-uniaxial stress states exist in SiGe layers in unimplanted Si areas, which depends on the stripe-width ratio of implanted and unimplanted areas, and that quasi-uniaxial stress states are successfully induced in SiGe by the present technique, which can be considered as the channel materials of high-performance transistors.

Noise figure improvement by controlling wiring effects in RF low noise amplifiers

In this letter, we evaluate the noise figure (NF) improvement that results from controlling the parasitic gate resistance of a radio-frequency (RF) low noise amplifier (LNA). By optimizing the number of gate contacts and wiring modifications in our fabricated device, the customized layout exhibited an approximately 25% reduction in the gate electrode resistance (Relect) when compared to a reference device provided by the foundry. The fabricated LNA, which used a customized layout in a 0.18 μm standard CMOS process, improved the NF by almost 6% without affecting the Si area and DC power consumption, and exhibited a NF of 2.57 dB, gain of 11.6 dB, DC power dissipation of 4.0 mW, and return loss at both the input and output of more than 10 dB. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1405–1407, 2017

Simultaneous acoustic stimulation of human primary and secondary somatosensory cortices using transcranial focused ultrasound.

BackgroundTranscranial focused ultrasound (FUS) is gaining momentum as a novel non-invasive brain stimulation method, with promising potential for superior spatial resolution and depth penetration compared to transcranial magnetic stimulation or transcranial direct current stimulation. We examined the presence of tactile sensations elicited by FUS stimulation of two separate brain regions in humans—the primary (SI) and secondary (SII) somatosensory areas of the hand, as guided by individual-specific functional magnetic resonance imaging data.ResultsUnder image-guidance, acoustic stimulations were delivered to the SI and SII areas either separately or simultaneously. The SII areas were divided into sub-regions that are activated by four types of external tactile sensations to the palmar side of the right hand—vibrotactile, pressure, warmth, and coolness. Across the stimulation conditions (SI only, SII only, SI and SII simultaneously), participants reported various types of tactile sensations that arose from the hand contralateral to the stimulation, such as the palm/back of the hand or as single/neighboring fingers. The type of tactile sensations did not match the sensations that are associated with specific sub-regions in the SII. The neuro-stimulatory effects of FUS were transient and reversible, and the procedure did not cause any adverse changes or discomforts in the subject’s mental/physical status.ConclusionsThe use of multiple FUS transducers allowed for simultaneous stimulation of the SI/SII in the same hemisphere and elicited various tactile sensations in the absence of any external sensory stimuli. Stimulation of the SII area alone could also induce perception of tactile sensations. The ability to stimulate multiple brain areas in a spatially restricted fashion can be used to study causal relationships between regional brain activities and their cognitive/behavioral outcomes.Electronic supplementary materialThe online version of this article (doi:10.1186/s12868-016-0303-6) contains supplementary material, which is available to authorized users.

Fully Monolithically Fabricated Si One-Chip Miniature Fuel Cell -Electrolyte Polymerization in Porous Si Layer

A novel electrolyte layer formation for miniature fuel cells was proposed. Polymerization of electrolyte monomer was attempted in a porous Si layer. We have been developing a miniature fuel cell with MEMS techniques, and our prototype fuel cells with monolithically fabricated Si electrodes showed relatively good performance among miniature fuel cells[1]. However, adhesion between the Si electrodes and electrolyte membranes (PEM) was problematic, and poor adhesion causes lower performance. Besides, adhesion process of the electrodes and PEM is not suitable to MEMS process. Therefore, more monolithic structure is desired. Then, we have proposed a one-chip miniature fuel cell as shown in figure 1[2]. The one-chip fuel cell has a through porous Si layer, which is formed by anodization in HF solution, and the porous Si area is expected to work as a electrolyte layer. On both side of the through chip porous Si layer, catalyst layer is formed by wet plating technique. Some reports said porous Si showed ion conductivity, but the conductivity was too small for the fuel cell electrolyte layer, and electrolyte filling into the porous Si layer is needed. In some studies, polymer solution was immersed into the porous Si layer, but the performance of the obtained layer seems limited due to shrinkage of the electrolyte polymer. In this study, we attempted to fill electrolyte into the porous Si layer by electrolyte monomer polymerization in the porous Si. Viscosity of monomer solution was low, and easy penetration of the solution into the porous Si layer was expected. Then, the electrolyte monomer is polymerized and the packed polymer electrolyte layer is formed in the porous Si area. Experimental The through chip porous Si layer, which was formed by anodization in HF solution, showed independent straight pores with no connection to neighbor pores. The diameter of the pore was 40-70nm. After the porous layer formation, to raise hydrophilicity of porous Si surface for the easier penetration of the monomer solution, slight thermal oxidation (673 K for 10 min) was performed. 2-Acrylamido-2-methylpropane sulfonic acid (AMPS), which is a typical monomer containing sulfonic acid group, was chosen as the monomer. The AMPS solution was filled into the porous Si, and polymerization was performed by heating the chip. The monomer filling process was performed in nitrogen atmosphere at 275 K to prevent irregular polymerization. After 6 h immersion of the chip into the monomer solution, the chip was heated to 333 K in an oven for 6 h. Results After the polymerization, the chip was cleaved and the cross-section was analyzed as shown in figure 3. Uniform sulfur distribution, which is the component of the electrolyte, was observed in the porous Si region. A high magnification SEM image with low acceleration voltage in figure 4 showed that polymer was successfully formed in the pores. Crossover of hydrogen gas was also reduced to 1/600 by the electrolyte filling. But the crossover is still large, and further optimization will be performed.

Study of Annealing Temperature for Ni/Cu/Ag Plated Front Contact Single Crystalline Solar Cells

Ni/Cu/Ag contact formed by plating has continuously been studied as a future metallization technique of solar cells due to the lower cost of material and better electrical performance compared with the screen-printed Ag contact. For the metallization of samples, native oxide on a laser-patterned Si area was etched with a buffered oxide etch solution for uniform plating. A Ni seed layer for Cu plating was deposited by using alkaline electroless plating. Afterward, a Cu–Ag metal stack was plated by light-induced plating followed by annealing in a tube furnace with an ${{\rm{N}}_2}$ gas atmosphere. This annealing process forms NiSix, which enhances contact resistance and adhesion. However, Ni penetration through the emitter layer can produce shunting paths, which decrease cell performance. In this experiment, 2.6 N/mm was obtained as the highest adhesion result. In addition, voids that can degrade adhesion were observed at the interface of Cu–Ag due to the Kirkendall effect. According to the experiment's results, the suggestion of annealing condition was discussed to have good electrical and physical properties of plated Ni/Cu/Ag front contact.

On the use of a localized STRASS technique to obtain highly tensile strained Si regions in advanced FDSOI CMOS devices

AbstractStrain boosters are an effective way to improve performances in advanced CMOS FDSOI devices. Hole mobility is higher in pFETs with compressive channels. Meanwhile, electron mobility is higher for nFETs with tensile channels. We present an alternative technique to blanket sSOI substrates. The efficiency of the “Strained Silicon by Top Recrystallization of Amorphized SiGe on SOI” technique has been previously successfully demonstrated on blanket SOI (+ 1.6 GPa tensile strain achieved). Here we demonstrate a simple and efficient STRASS module integration in an advanced FDSOI route (14 nm design rules) which allows to cointegrate tensile Si for nFETs and unchanged pFETs.After pFETs have been protected (SiN), the STRASS technique has been used in the SOI nFET patterns. This process requires SiGe selective epitaxy, buried amorphization by ion implantation, recrystallization and SiGe removal. Raman spectroscopy is used to characterize the stress in Si areas with respect to process conditions (implantation, active area dimensions). Moreover, the mechanisms of SiGe relaxation will be discussed as function of device dimensions and SiGe layer properties (thickness, Ge content). We demonstrate the successful integration of localized STRASS module: tensile Si patterns (for nFETs) with a level of stress of + 1.6 GPa, cointegrated with unmodified pFETs. (© 2016 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Speech intelligibility assessment of protective facemasks and air-purifying respirators

ABSTRACTSpeech Intelligibility (SI) is the perceived quality of sound transmission. In healthcare settings, the ability to communicate clearly with coworkers, patients, etc., is crucial to quality patient care and safety. The objectives of this study were to: (1) assess the suitability of the Speech Transmission Index (STI) methods for testing reusable and disposable facial and respiratory personal protective equipment (protective facemasks [PF], N95 filtering facepiece respirators [N95 FFR], and elastomeric half-mask air-purifying respirators [EAPR]) commonly worn by healthcare workers; (2) quantify STI levels of these devices; and (3) contribute to the scientific body of knowledge in the area of SI. SI was assessed using the STI under two experimental conditions: (1) a modified version of the National Fire Protection Association 1981 Supplementary Voice Communications System Performance Test at a Signal to Noise Ratio (SNR) of −15 (66 dBA) and (2) STI measurements utilizing a range of modified pink noise levels (52.5 dBA (−2 SNR) – 72.5 dBA (+7 SNR)) in 5.0 dBA increments. The PF models (Kimberly Clark 49214 and 3 M 1818) had the least effect on SI interference, typically deviating from the STI baseline (no-mask condition) by 3% and 4% STI, respectively. The N95FFR (3 M 1870, 3 M 1860) had more effect on SI interference, typically differing from baseline by 13% and 17%, respectively, for models tested. The EAPR models (Scott Xcel and North 5500) had the most significant impact on SI, differing from baseline by 42% for models tested. This data offers insight into the performance of these apparatus with respect to STI and may serve as a reference point for future respirator design considerations, standards development, testing and certification activities.

Inter-hemispheric plasticity in patients with median nerve injury

Peripheral nerve injuries result in reorganization within the contralateral hemisphere. Furthermore, recent animal and human studies have suggested that the plastic changes in response to peripheral nerve injury also include several areas of the ipsilateral hemisphere. The objective of this study was to map the inter-hemispheric plasticity in response to median nerve injury, to investigate normal differences in contra- and ipsilateral activation, and to study the impact of event-related or blocked functional magnetic resonance imaging (fMRI) design on ipsilateral activation. Four patients with median nerve injury at the wrist (injured and epineurally sutured >2 years earlier) and ten healthy volunteers were included. 3T fMRI was used to map the hemodynamic response to brain activity during tactile stimulation of the fingers, and a laterality index (LI) was calculated. Stimulation of Digits II–III of the injured hand resulted in a reduction in contralateral activation in the somatosensory area SI. Patients had a lower LI (0.21±0.15) compared to healthy controls (0.60±0.26) indicating greater ipsilateral activation of the primary somatosensory cortex. The spatial dispersion of the coordinates for areas SI and SII was larger in the ipsilateral than in the contralateral hemisphere in the healthy controls, and was increased in the contralateral hemisphere of the patients compared to the healthy controls. There was no difference in LI between the event-related and blocked paradigms. In conclusion, patients with median nerve injury have increased ipsilateral SI area activation, and spatially more dispersed contralateral SI activation during tactile stimulation of their injured hand. In normal subjects ipsilateral activation has larger spatial distribution than the contralateral. Previous findings in patients performed with the blocked fMRI paradigm were confirmed. The increase in ipsilateral SI activation may be due to an interhemispheric disinhibition associated with changes in the afferent signal inflow to the contralateral primary somatosensory cortex.