Nanoscale mechanics of focused ion beam processing

Focused ion beam (FIB) processing is a widely used microscopic material removal method with precise dimensional control, for applications ranging from electron microscope sample preparation to DNA sequencing nanopore processing. Despite the widespread use of FIB, the basic material removal mechanisms are not well understood. In this study we present the first complete atomistic computational studies of high-flux FIB. We use large-scale parallel molecular dynamics simulations to study nanopore fabrication in freestanding thin film targets. Our simulations consider up to 5.1 million atoms, for durations of up to millions of time steps. We focus on understanding two key nanoscale mechanics phenomena that emerge from the large scale MD simulations of FIB: the role of explosive boiling as a material removal mechanism, and the role of Marangoni effects in the mixing and transport that occur at the atomic scale. Nanopore fabrication using FIB is typically understood to occur via sputter erosion. It is thought that, on average, each ion impact sputters two or three target atoms from a typical freestanding silicon specimen, thinning the target, and eventually forming a through-thickness nanopore. Although this theory may work for low-flux systems, where individual ion impacts are sufficiently separated in time that it is possible to consider them as independent events, it cannot explain the thermal events observed during high flux simulations. Our detailed molecular dynamics simulations suggest that for ion beam fluxes above a threshold level, the dominant mechanism of material removal changes to a significantly accelerated, thermally dominated process. During this time, the target is heated faster than it cools via thermal conduction, leading to melting, with local temperatures approaching the critical temperature. This leads to explosive boiling of the target material, as identified by the violent phase change occurring in the rapidly heated liquid. Spontaneous bubble formation occurs because of large fluctuations of density in a very small volume. Atomic mass is rapidly rearranged via bubble growth and coalescence, leading to a material removal process order of magnitude faster than would occur by sputter erosion. When a high flux FIB process is tightly focused on a silicon target, as in the case of nanopore formation, a large temperature gradient gives rise to a circulating flow of liquid silicon because of steep surface tension gradients – or a Marangoni flow. This drives mass transfer inside the target and along the newly created nanopore surfaces, from regions of high temperature to regions of low temperature. For films of a particular thickness, two counter-circulating atomic scale flow regions form in the target. Thus, the Marangoni flow phenomenon drives mass transfer and material rearrangement at the top and bottom free surfaces

Mechanisms of focused ion beam (FIB) material removal and rearrangement at high beam flux

Focused ion beam (FIB) is widely used as a material removal tool for applications ranging from electron microscope sample preparation to nanopore processing for DNA sequencing. Despite the wide spread use of FIB, the basic material removal mechanisms are not well understood and may depend upon FIB operations. We present the first complete atomistic simulation of high-flux FIB using large-scale parallel molecular dynamics (MD) simulations of nanopore fabrication in freestanding thin films. We focus on the root mechanisms as described by large-scale MD simulations of FIB and describe the role of explosive boiling and Marangoni effect as a material removal and rearrangement mechanism and the mixing and transport that occur at the atomic scale. Nanopore fabrication using FIB is typically understood to occur via sputter erosion. While this theory may describe low-flux systems, where individual ion impacts are sufficiently separated in time to consider them as independent events, it cannot explain the thermal events observed during high flux simulations. A dimensionless number is introduced, which is constructed from the key variables including material properties and FIB parameters. This number suggests strong thermal effects when it is greater than unity. Similarly, our detailed MD simulations suggest that for ion beam fluxes above a threshold level, the dominant mechanism of material removal changes to a significantly accelerated, thermally dominated process, consistent with our dimensional analysis. During this time, the target is heated faster than it cools, leading to melting, with local temperatures approaching the critical temperature. This leads to an explosive boiling of the target material with spontaneous bubble formation. Atomic mass is rapidly rearranged via bubble growth and coalescence and material removal is orders of magnitude faster than would occur by simple sputtering. For a range of ion intensities in a realistic configuration, a recirculating melt region develops, which is seen to flow at high speed though symmetrically rather than driven by the ion momentum flux. Relevant length and time scales and estimated physical properties of silicon under these extreme conditions suggest that thermocapillary effects are important. A flow model with a Marangoni forcing term, based upon the temperature gradient from the atomistic simulation, confirms the presence of thermocapillary effect by reproducing the flow

Strengthening primary health care in rural western India-team based approach

Background: Non-communicable diseases (NCDs), such as cardiovascular diseases (CVDs), diabetes, have taken an epidemic form. With a huge population and existing sedentary lifestyle, in developing countries like India, there exists a struggle to deliver quality chronic care. A reorganization of systems in healthcare service delivery is crucial to improve primary healthcare. We have reported our model to address primary healthcare service delivery in rural settings. The SPARSH team-based care approach is designed with the objective of improving adherence to anti-hypertensive and anti-diabetic medications to improve blood pressure (BP) and blood sugar (BS) control among hypertension (HTN) and diabetes mellitus (DM) patients. Methods: This is a descriptive study describing a model and array on interventions delivered through a team-based care approach from 2016 till 2020 by Shree Krishna Hospital, Karamsad across three districts in Gujarat. Data was collected on case record forms and later was analysed using Microsoft excel. Results: From the financial year of 2016 till 2020 patients enrolled in SPARSH increased from 932 till 1920 for availing treatment and ongoing care. A total of 108 training sessions were conducted and facilitated by a senior member of SPARSH. Average monthly cost of treatment for hypertensive, diabetic and patients with both conditions was Rs. 38, 78 and 130 respectively. Conclusions: Our model described here can be tested for effectiveness through a rigorous community trial focusing on objective outcome measures such as BP control and glycemic control

The Impact of Information and Communication Technologies on Informal Economy Growth: A National-Level Study

Informal economy (IE) is second only to the US economy in size; however, the role of ICT in IE remains largely unexplored. In this study, we conduct an empirical analysis of the role of ICT in IE growth. With PLS analysis involving more than 100 nations, we show that ICT products and software piracy may play important roles in IE growth, that impact of ICT and other determinants on IE growth remains largely unchanged over years; however the impact of ICT- and other determinants on IE growth for developing and developed nations may not be the same

Evaluation of DECT for low latency real-time industrial control networks

c. 1905. Pale yellow rayon faille Princess line dress with a bobbinet overlay appliquéd with cream wool Art Nouveau lilies and finished with machine-made Chantilly lace flounces, closing in back, with short sleeves and a floor-length skirt. The dress is made from long fitted panels without a waist seam. Eight shaped pieces extend from the bodice to the skirt hem: two narrow front panels with a center seam, two side-front panels, two side-back panels, and two back panels with a center-back opening with twenty hooks. The panels narrow at the waist, curve over the hips and flare to the hem. The bodice portion of the dress is lined with white cotton just past the waist, made with one front panel shaped with two darts, and two back panels with one dart each. The dress has a scooped neckline in front and back, and has close-fitting sleeves ending above the elbow, made with one seam. The overlay is a two-twist bobbinet appliquéd before construction. Tightly woven cream wool was machine-sewn to the bobbinet with continuous lengths of pale yellow braided cord outlining columns of large stylized Art Nouveau lilies, stems, and leaves. The wool ground was then carefully cut away from the bobbinet, leaving the floral elements behind, as evidenced in part by a lily at the left front skirt hem missing its interior detail cut on one petal. There are two panels in the overlay, sewn to each other with a free-floating center-front seam and sewn to the dress at the neckline (dipping about 10.2 cm / 4 in. down from the edge at center-front), shoulders, and scyes. The overlay’s center-front seam runs precisely down the middle of a column of lilies, matching flower halves from left and right, and the join is reinforced by retaining the full, continuous length of the wool seam allowance and by leaving the interior details of flowers straddling the seam uncut. The bobbinet is, by its nature, stretchy and so drapes closely to the contours of the dress beneath; the panels wrap diagonally around the sides to the back, pulled up from their straight grain center-front seam into a bias angle in back where the columns of lilies form chevrons where they meet at center. The ends of the panels fold over the edges of the center-back opening of the underlying fabric. This draping results in the overlay skirt coming to a point just above the hem in front and rising almost to waist level in back. A machine-made Chantilly lace flounce, shorter in front and lengthening to the back, is added to the bottom edge of the bobbinet, so that the complete overlay skirt is 99.1 cm / 39 in. long in front as measured from the waistline, and 35.6 cm / 14 in. long in back. In the bodice, the flowers and leaves are applied individually to create a horizontal trim across the neckline, reaching slightly past its edge. At the front, an asymmetrical Chantilly flounce is sewn beneath the appliqué, shorter and fuller on the left side than on the right, hanging to the waist in front and ending in back at the shoulders. A lily is centered at the top of the bodice opening, sewn down on the right side and overlapping the opening to hook closed on the left. The sleeves are covered with the same bobbinet and appliqué, and are finished with a gathered, knotted band of the Chantilly lace. Machine-sewn and hand-sewn.https://scholars.unh.edu/bowen_collection/2008/thumbnail.jp

A Distributed Management Scheme for supporting energy-harvested I/O devices

Current wireless technologies for industrial application, such as WirelessHART and ISA100.11a, are not designed to support harvester-powered input/output (I/O) devices, where energy availability varies in a non-deterministic manner. The centralized management approach of these standards makes it difficult and costly for harvester-powered I/O devices (sensor/actuators) to re-join in the network in case of power failure. The communication overhead and delay to cope with the dynamic environment of a large-scale industrial network are also very high for an I/O device. In this paper, we therefore propose a Distributed Management scheme for Hybrid networks to provide Real-time communication (D-MHR) based on the IEEE 802.15.4e and Routing Protocol for Low power and Lossy Networks (RPL) standards, which can address the requirements of energy constrained I/O devices. In D-MHR, the routers can dynamically reserve communication resources and manage the I/O devices in the local star sub-networks. We demonstrate that D-MHR achieves higher network management efficiency compared to IS100.11a standard, without compromising the latency and reliability requirements of industrial wireless networks