82 research outputs found
Physics based modeling for 2D semiconductors as baseline materials for novel electron devices
No full textScaling CMOS technology has been the cornerstone of the continued progress in the silicon-based semiconductor industry. Nowadays, the FinFETs and nanosheet transistors are the most advanced device architectures respectively in production and under development in the industry. However, due to the many constraints posed by short-channel effects and to the limitations due to extrinsic resistive and capacitive components, the scaling of transistors has become an increasingly challenging task. Two-dimensional semiconductors are attractive materials for nanosheet transistors and for many other prospective applications, thanks to their very good intrinsic transport properties compared to 3D semiconductors at the same layer thickness. The discovery of graphene and then the development of transition metal dichalcogenides raised high expectations for a new and wide family of two-dimensional crystalline materials with remarkable electronic, mechanical, and optical properties. However, there are still many concerns about the limitations of 2D materials and several hurdles to reach the industrial maturity. In order to overcome such limitations, a physical understanding of novel electron devices based on 2D crystals is vital.
After an introduction about 2D materials presented in chapter 1 of this thesis, in the second chapter we report a simulations based study of metallic contacts to 2D materials. In fact, one of the key challenges preventing the harnessing of good intrinsic transport properties of 2D crystals is the poor quality of the contacts between metals and 2D materials. First, we show that Cu and Ni largely dope graphene at the minimum energy distance, whereas a long-range interaction is predicted for Au-graphene contact. Then we discuss by using ab-initio simulations the Fermi level pinning in defects free metals to MoS2 contacts. Then by using an ab-initio transport methodology, we investigate the contact resistance between several metals and MoS2. Our results examine quantitatively the trade-off between Schottky barrier height and tunneling barrier in contacts with a buffer layer and confirmed by simulations the superior performance of the bismuth-MoS2 n-type contact.
Chapter 3 is focused on sensors based on 2D materials. In this chapter, we first revisit the problem of the linearized Boltzmann transport equation for mobility calculations and the formulation of different scattering mechanisms. Then we use our mobility calculations to investigate piezo-resistance in MoS2, and in particular for the interpretation of a giant intrinsic Gauge factor experimentally observed in monolayer MoS2 This intrinsic piezoresistive can enable emerging applications in tactile sensing as well as improving the electronic transport in TMD electronics. The analysis in chapter 3 continues with the analysis and comparison with experiments for the temperature coefficient of resistance in MoS2, with fast temperature sensors as a prospective application. In the last part of chapter 3, we address some possible options for gas sensors based on the 2D materials. First we investigate the 2D Mxene as a potential ammonia sensor employing a first-principles study. Then we focus on fluorinated graphene as a potential material for humidity sensing applications.
Finally in chapter 4, by utilizing a multi-valley Monte Carlo transport simulator, uniform field transport in 2D MoS2 is analyzed. Our preliminary results for the high field uniform transport regime show that the electron’s saturation velocity in monolayer MoS2 is only slightly affected by scattering with Coulomb centers and neutral defects, while the effect of surface optical phonons is more subtle and it is, at the time of writing, still partly under investigation.Scaling CMOS technology has been the cornerstone of the continued progress in the silicon-based semiconductor industry. Nowadays, the FinFETs and nanosheet transistors are the most advanced device architectures respectively in production and under development in the industry. However, due to the many constraints posed by short-channel effects and to the limitations due to extrinsic resistive and capacitive components, the scaling of transistors has become an increasingly challenging task. Two-dimensional semiconductors are attractive materials for nanosheet transistors and for many other prospective applications, thanks to their very good intrinsic transport properties compared to 3D semiconductors at the same layer thickness. The discovery of graphene and then the development of transition metal dichalcogenides raised high expectations for a new and wide family of two-dimensional crystalline materials with remarkable electronic, mechanical, and optical properties. However, there are still many concerns about the limitations of 2D materials and several hurdles to reach the industrial maturity. In order to overcome such limitations, a physical understanding of novel electron devices based on 2D crystals is vital.
After an introduction about 2D materials presented in chapter 1 of this thesis, in the second chapter we report a simulations based study of metallic contacts to 2D materials. In fact, one of the key challenges preventing the harnessing of good intrinsic transport properties of 2D crystals is the poor quality of the contacts between metals and 2D materials. First, we show that Cu and Ni largely dope graphene at the minimum energy distance, whereas a long-range interaction is predicted for Au-graphene contact. Then we discuss by using ab-initio simulations the Fermi level pinning in defects free metals to MoS2 contacts. Then by using an ab-initio transport methodology, we investigate the contact resistance between several metals and MoS2. Our results examine quantitatively the trade-off between Schottky barrier height and tunneling barrier in contacts with a buffer layer and confirmed by simulations the superior performance of the bismuth-MoS2 n-type contact.
Chapter 3 is focused on sensors based on 2D materials. In this chapter, we first revisit the problem of the linearized Boltzmann transport equation for mobility calculations and the formulation of different scattering mechanisms. Then we use our mobility calculations to investigate piezo-resistance in MoS2, and in particular for the interpretation of a giant intrinsic Gauge factor experimentally observed in monolayer MoS2 This intrinsic piezoresistive can enable emerging applications in tactile sensing as well as improving the electronic transport in TMD electronics. The analysis in chapter 3 continues with the analysis and comparison with experiments for the temperature coefficient of resistance in MoS2, with fast temperature sensors as a prospective application. In the last part of chapter 3, we address some possible options for gas sensors based on the 2D materials. First we investigate the 2D Mxene as a potential ammonia sensor employing a first-principles study. Then we focus on fluorinated graphene as a potential material for humidity sensing applications.
Finally in chapter 4, by utilizing a multi-valley Monte Carlo transport simulator, uniform field transport in 2D MoS2 is analyzed. Our preliminary results for the high field uniform transport regime show that the electron’s saturation velocity in monolayer MoS2 is only slightly affected by scattering with Coulomb centers and neutral defects, while the effect of surface optical phonons is more subtle and it is, at the time of writing, still partly under investigation
Modeling Low and High Field Uniform Transport in Monolayer MoS2
No full textWe have developed a multi-valley Monte Carlo simulator to study uniform transport in MoS 2 monolayers. At low electric field, our solver is in excellent mutual agreement with a numerical solution of the linearized Boltzmann Transport Equation. We have then explored high field transport and analyzed the influence of different scattering mechanisms on the electron saturation velocity. Although scattering with neutral defects and Coulomb centers strongly affects the mobility, the effect on the saturation velocity is only modest. On the other hand, scattering with surface optical phonons has a significant influence on the saturation velocity, which we physically interpreted by inspecting the energy and momentum distributions of carriers
Large temperature coefficient of resistance in atomically thin two-dimensional semiconductors
No full textThe temperature coefficient of resistance (TCR) of thin metal lines is often used for applications in thermometry, bolometers, or thermal
accelerometers. However, metal TCR is much degraded in nanometer-thin films due to strong surface scattering, preventing their use as fast
thermal sensors, which simultaneously require low thermal mass and large TCR. In contrast, here we show that the TCR of doped two-
dimensional (2D) semiconductors is large ( 0.3% K 1 at 300 K in MoS2 and MoTe2) even at sub-nanometer thickness. This is larger than
that of any metals with thicknesses up to 35 nm and larger than that of 95 nm thick Cu lines (0.25% K 1) at 300 K. At 100 K, the TCR of
these 2D materials is doubled, 0.6% K 1. Comparison with detailed 2D transport models suggests that the TCR could be further enhanced
(up to 0.45% K 1 at 300 K and 2.5% K 1 at 100 K) by reducing the density of Coulomb impurities and scattering centers. Such high TCR
in atomically thin 2D semiconductors could lead to the design of fast thermal sensors
DFT study of graphene doping due to metal contacts
No full textThe experimental results of Metal–graphene (M–G) contact resistance (RC) have been investigated in–depth by means of Density Functional Theory (DFT). The simulations allowed us to build a consistent picture explaining the RC dependence on the metal contact materials employed in this work and on the applied back–gate voltage. In this respect, the M–G distance is paramount in determining the RC behavior
A study of metal-MoS2 contacts by using an in-house developed ab-initio transport simulator
No full textInternational audienc
An evaluation of the Massachusetts Department of Housing and Community Development's Moving to Work voucher program
No full textThesis (M.C.P.)--Massachusetts Institute of Technology, Dept. of Urban Studies and Planning, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 85-87).Since implementation nearly 10 years ago there has been limited research into the outcomes of the Massachusetts Department of Housing and Community Development's Moving to Work rental subsidy program. The Congressionally authorized Moving to Work Demonstration program (MtW) deregulated housing agencies in order to provide flexibility to design and test innovative approaches to administering housing assistance programs. In 1999, DHCD began planning and implementation for two MtW pilots, one in Boston, targeting the shelter population, and another in Southern Worcester County, targeting working or "work-ready" households. The current program design provides 183 clients with fixed shallow rental subsidy amounts, support budgets, time limits, and case management to encourage and facilitate self-sufficiency. Preparing to transition its full HCVP portfolio to MtW status, DHCD initiated a process of evaluation and learning focused on the pilots. These lessons, which involve data collection processes and program implementation as well as outcomes, will inform the future of the statewide MtW program. This research is a qualitative and quantitative assessment of both pilot programs. The research used available baseline and current client employment, income and locational data to determine how effective DHCD's MtW model was at facilitating self-sufficiency. Additionally, focus groups with MtW clients and interviews with administrators were conducted to understand the impact and effectiveness of the program from multiple perspectives.(cont.) Using various poverty and self-sufficiency, measures, the research finds that, in general, the program has successfully kept clients out of "deep poverty" but has not moved them out of poverty. Hence, the program has fallen short on facilitating economic self-sufficiency. The paper concludes with a set of recommendations for DHCD's future implementation and expansion efforts.by Pedram Mahdavi.M.C.P
PCB-Vision: A Multiscene RGB-Hyperspectral Benchmark Dataset of Printed Circuit Boards
No full textPCB-Vision Dataset
Description:
The PCB-Vision dataset is a multiscene RGB-Hyperspectral benchmark dataset comprising 53 Printed Circuit Boards (PCBs). The RGB images are collected using a Teledyne Dalsa C4020 camera on a conveyor belt, while hyperspectral images (HSI) are acquired with a Specim FX10 spectrometer. The HSI data contains 224 bands in the VNIR range [400 - 1000]nm.
Data Format
RGB Images: .png files
PCB Masks: .jpg files
HSI Data: Each hyperspectral data cube is accompanied by a data file and a .hdr file.
Folder Organization
PCBVision
HSI/
53 subfolders (one for each PCB)
'General_masks' folder for 'General' segmentation ground truth
'Monoseg_masks' folder for 'Monoseg' segmentation ground truth
'PCB_Masks' folder for masks of the 53 PCBs in the hyperspectral cube
RGB/
53 .jpg images
'General' folder for RGB images 'General' segmentation ground truth
'Monoseg_masks' folder for RGB images 'Monoseg' segmentation ground truth
Data Classes in Masks
Masks (both 'General' and 'Monoseg') contain 1 to 4 segmentation classes:
0: "Others"
1: "IC"
2: "Capacitors"
3: "Connectors"
Code Repository
To facilitate reading and working with the data, Python codes are available on the GitHub repository:
https://github.com/hifexplo/PCBVision
Citation
If you use this dataset, please cite the following article:
Word:
Arbash, Elias, Fuchs, Margret, Rasti, Behnood, Lorenz, Sandra, Ghamisi, Pedram, & Gloaguen, Richard. (2024). PCB-Vision: A Multiscene RGB-Hyperspectral Benchmark Dataset of Printed Circuit Boards (Version 1) [Data set]. Rodare. http://doi.org/10.14278/rodare.2704
Latex:
@article{arbash2024pcb, title={PCB-Vision: A Multiscene RGB-Hyperspectral Benchmark Dataset of Printed Circuit Boards}, author={Arbash, Elias and Fuchs, Margret and Rasti, Behnood and Lorenz, Sandra and Ghamisi, Pedram and Gloaguen, Richard}, journal={arXiv preprint arXiv:2401.06528}, year={2024} }
Contact
For further information or inquiries, please visit our website:
https://www.iexplo.space/
Contact Email: [email protected]
Recent advances in the synthesis and application of magnetic biochar for wastewater treatment
No full textMagnetic biochar (MBC) is a novel bio-carbon material with both desired properties as adsorbent and magnetic characteristics. This review provides an up-to-date summary and discussion on the latest development of MBC, which covers the progress on its synthesis, application, and techno-economic analysis. The review indicates that the direct hydrothermal synthesis has been catching more research attention to produce MBC due to its mild reaction conditions. Instead of the Fe-loaded MBC, there is a trend of using Mn for the magnetization. For the MBC application, how to improve its adsorption performance for water decontamination, ideally to match that of the biochar (BC) or activated carbon, is important. In addition, more studies on the environmental impacts of MBC and life-cycle assessment decoding the process optimization options are necessary. This review will provide valuable references for the development of MBC and MBC-based materials for wastewater treatment
Seismic vulnerability assessment of bridges for retrofitting and new design
No full textMany bridges in North Eastern region of U.S. were designed prior to the adoption of the AASHTO LRFD Guide Specifications for seismic design and may be vulnerable to damage during an earthquake event. This study evaluates the seismic vulnerabilities of those bridges and the structural factors that could affect their performance during a seismic event. The effects of load demands and age deteriorations were also studied. Aging of certain bridge components such as bearings, columns, and bent caps can affect the capacity and demands of these components and accordingly might affect the global behavior and capacity of a bridge during an earthquake event. The concept of fragility curves was studied as a potential tool for evaluating the seismic performance of new bridges, existing bridges and retrofitted bridges for various bridge types subjected to different peak ground acceleration levels. Fragility curves represent the probability of a structure to experience damage levels higher than specific damage state at different peak ground acceleration. Possible retrofit measures for various bridge components were reviewed, and analyzed for their effectiveness. These include superstructure restrainers, stoppers, shear keys, isolation bearings, bent cap strengthening and column jacketing. Existing research shows that the concept of fragility curves can be used to identify bridge vulnerability and level of damage. They can also be used to identify performance and level of damage of various retrofit measures. The effect of aging of certain components such as stiffening and locking of bearings and corrosion of confining steel in columns need to be included when evaluating bridge load demands and capacities. Different types of concrete bridges (typical in North Eastern United States) were analyzed using elastic response spectrum and nonlinear push-over analysis for low, medium-to-high, and high seismicity levels. The effects of pier configuration, continuity between the superstructure and the substructure, and the number of spans were investigated. Analysis results showed that in the longitudinal direction, the displacement demand increased for multi-column bents compared to single-column bents. However, the overall D/C ratio dropped in both transverse and longitudinal directions. The results also showed that in the longitudinal direction the benefit of having multi-column bent over single-column bents in integral bridges is dependent on the seismicity levels. The D/C (demand/capacity) ratio for single column bents in the longitudinal direction was much lower for integral (monolithic) bents compared to non-integral bents. In the transverse directions, the difference in the D/C ratio was not significant. For multi-column bents, the percent change by having integral bents over non-integral bents was dependent on the seismicity levels. For high seismicity zones, the benefits of having Integral bents becomes more significant. This investigation presents guidance on incorporating the effects of aging and retrofitting in the finite element modeling of bridges subjected to various levels of earthquake ground motions.M.S.Includes bibliographical referencesby Pedram Farok
Description of Ditylenchus azarbaijanensis n. sp. (Tylenchomorpha: Anguinidae) from West Azarbaijan province, northwest Iran
No full textDitylenchus azarbaijanensis n. sp. is described and illustrated based
upon morphological and morphometric characters. The new species is mainly
characterized by having six lines in the lateral field, rudimentary postuterine sac
(PUS) ca. 0.2 vulval body width long, anteriorly inclined vagina and conical
female tail with a pointed terminus, 48-70 μm long (c = 15-21, c = 2.4-3.7). It
is further characterized by having fine stylet 7.5-10.0 μm long with small knobs,
small pyriform pharyngeal bulb offset from the intestine, and males with 26.5-
31.0 μm long spicules
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