Engineering Science and Materials Commons^™

Enhancing Stability And Efficiency Of Perovskite Solar Cells With Crosslinkable Silane-Functionalized And Doped Fullerene, Yang Bai, Qingfeng Dong, Yuchuan Shao, Yehao Deng, Qi Wang, Liang Shen, Dong Wang, Wei Wei, Jinsong Huang

Department of Mechanical and Materials Engineering: Faculty Publications

The instability of hybrid perovskite materials due to water and moisture arises as one major challenge to be addressed before any practical application of the demonstrated high efficiency perovskite solar cells. Here we report a facile strategy that can simultaneously enhance the stability and efficiency of p–i–n planar heterojunction-structure perovskite devices. Crosslinkable silane molecules with hydrophobic functional groups are bonded onto fullerene to make the fullerene layer highly water-resistant. Methylammonium iodide is introduced in the fullerene layer for n-doping via anion-induced electron transfer, resulting in dramatically increased conductivity over 100-fold. With crosslinkable silane-functionalized and doped fullerene electron transport layer, the …

Stabilized Wide Bandgap MapbbrXI3– X Perovskite By Enhanced Grain Size And Improved Crystallinity, Miao Hu, Cheng Bi, Yongbo Yuan, Yang Bai, Jinsong Huang

Department of Mechanical and Materials Engineering: Faculty Publications

Methylammonium lead trihalide perovskite (MAPbX₃, where MA is methylammonium, and X is a halide)-based solar cells have been intensively investigated recently, with the demonstrated certified solar power conversion efficiency (PCE) exceeding 20%. To further boost the PCE to beyond the Schockley–Queisser limit, tandem structured solar cells have been investigated based on integrating MAPbX₃ and low bandgap solar cells. However, the efficiency of the two-terminal integrated perovskite-silicon tandem cells is still low. The best reported efficiency of 13.7% for this type of tandem cells is far smaller than the individual cells yet, partially due to the limited performance …

Ultrahigh Sensitivity Of Methylammonium Lead Tribromide Perovskite Single Crystals To Environmental Gases, Hong-Hua Fang, Sampson Adjokatse, Haotong Wei, Jie Yang, Graeme R. Blake, Jinsong Huang, Jacky Even, Maria Antonietta Loi

Department of Mechanical and Materials Engineering: Faculty Publications

One of the limiting factors to high device performance in photovoltaics is the presence of surface traps. Hence, the understanding and control of carrier recombination at the surface of organic-inorganic hybrid perovskite is critical for the design and optimization of devices with this material as the active layer. We demonstrate that the surface recombination rate (or surface trap state density) inmethylammonium lead tribromide (MAPbBr3) single crystals can be fully and reversibly controlled by the physisorption of oxygen and water molecules, leading to a modulation of the photoluminescence intensity by over two orders of magnitude.We report an unusually low surface recombination …

Pulsed Laser Cutting Of Magnesium-Calcium For Biodegradable Stents, M. P. Sealy, Y. B. Guo, J. F. Liu, C. Li

Department of Mechanical and Materials Engineering: Faculty Publications

There is growing interests in the use of biodegradable magnesium implants for cardiovascular and pulmonary applications such as stents. Magnesium is a metal that has the ability to gradually dissolve and absorb into the human body after implantation. There is very little work discussing the relationship between process parameters and cut quality of magnesium stents by laser cutting. The objective of this research is to determine the effect of laser cutting conditions including peak laser power and cutting speed of a millisecond range pulsed laser on kerf geometry, surface topography, surface roughness, and microstructure. An assessment on the experimental work …

Impact Of Patient Factors On Operative Duration During Laparoscopic Cholecystectomy: Evaluation From The National Surgical Quality Improvement Program Database, Bethany Rose Lowndes, Cornelius A. Thiels, Elizabeth B. Habermann, Juliane Bingener, M. Susan Hallbeck, Denny Yu

Department of Mechanical and Materials Engineering: Faculty Publications

BACKGROUND: Patient factors impact laparoscopic cholecystectomy (LC) difficulty, specifically operative duration. This study quantifies the impact of patient factors on LC duration.

METHODS: The national surgery database (American College of Surgeons National Surgical Quality Improvement Program) was reviewed for all elective LC for biliary colic from 2005 to 2013. Multivariate general linear model and logistic regression were used to evaluate patient factors as predictors of operative duration greater than 60 minutes, adjusted for resident involvement and cholangiography.

RESULTS: A total of 24,099 LC met inclusion criteria. Regression analysis found procedure duration greater than 60 minutes was less likely for patients …

A Comparative Study On Machining Capabilities Of Wet And Dry Nanoscale Electro-Machining, Muhammad P. Jahan, Kamlakar P. Rajurkar, Ajay P. Malshe

Department of Mechanical and Materials Engineering: Faculty Publications

Presently, the nano scale electro-machining (nano-EM) process has been demonstrated in both the liquid and air dielectric mediums, which are known as wet and dry nano-EM respectively. In the current study, two important aspects of the nano-EM have been investigated: the minimum possible feature dimension and mass fabrication capability of nano-EM. Firstly, the investigation has been done on the capability of machining graphene at atomic scale with focus on obtaining smallest possible nano-feature using the wet nano-EM. Secondly, the ability of the nano-EM process for the fabrication of arrays of nano-holes has been investigated using dry nano-EM. It was found …

Bioink Properties Before, During And After 3d Bioprinting, Katja Holzl, Shengmao Lin, Liesbeth Tytgat, Sandra Van Vlierberghe, Linxia Gu, Aleksandr Ovsianikov

Department of Mechanical and Materials Engineering: Faculty Publications

Bioprinting is a process based on additive manufacturing from materials containing living cells. These materials, often referred to as bioink, are based on cytocompatible hydrogel precursor formulations, which gel in a manner compatible with different bioprinting approaches. The bioink properties before, during and after gelation are essential for its printability, comprising such features as achievable structural resolution, shape fidelity and cell survival. However, it is the final properties of the matured bioprinted tissue construct that are crucial for the end application. During tissue formation these properties are influenced by the amount of cells present in the construct, their proliferation, migration …

Development Of A Synthetic Gene Network To Modulate Gene Expression By Mechanical Forces, Zoltan Kis, Tania Rodin, Asma Zafar, Zhangxing Lai, Grace Freke, Oliver Fleck, Armando Del Rio Hernandez, Leila Towhidi, Ryan M. Pedrigi, Takayuki Homma, Rob Krams

Department of Mechanical and Materials Engineering: Faculty Publications

The majority of (mammalian) cells in our body are sensitive to mechanical forces, but little work has been done to develop assays to monitor mechanosensor activity. Furthermore, it is currently impossible to use mechanosensor activity to drive gene expression. To address these needs, we developed the first mammalian mechanosensitive synthetic gene network to monitor endothelial cell shear stress levels and directly modulate expression of an atheroprotective transcription factor by shear stress. The technique is highly modular, easily scalable and allows graded control of gene expression by mechanical stimuli in hard-to-transfect mammalian cells. We call this new approach mechanosyngenetics. To insert …

Portable Camera Aided Simulator (Portcas) For Minimally Invasive Surgical Training, Ka-Chun Sui, Carl Nelson, Mohsen Zahiri, Dmitry Oleynikov

Department of Mechanical and Materials Engineering: Faculty Publications

The present disclosure is directed to a system and method for surgical training with low cost, reusable materials and a highly customizable virtual environment for skill-building. According to various embodiments, a surgical training tool is usable in conjunction with a support structure configured to at least partially constrain the tool movement. Meanwhile, the tool is tracked in real-time with off-tool detectors to generate a tool path driving a virtual rendering of the surgical training tool in an operative environment. The virtual rendering may be visually observable via a display device and may include a customizable and/or selectable operative environment with …

Secondary Pool Boiling Effects, C. Kruse, A. Tsubaki, C. A. Zuhlke, T. P. Anderson, Dennis R. Alexander, George Gogos, Sidy Ndao

Department of Mechanical and Materials Engineering: Faculty Publications

A pool boiling phenomenon referred to as secondary boiling effects is discussed. Based on the experimental trends, a mechanism is proposed that identifies the parameters that lead to this phenomenon. Secondary boiling effects refer to a distinct decrease in the wall superheat temperature near the critical heat flux due to a significant increase in the heat transfer coefficient. Recent pool boiling heat transfer experiments using femtosecond laser processed Inconel, stainless steel, and copper multiscale surfaces consistently displayed secondary boiling effects, which were found to be a result of both temperature drop along the microstructures and nucleation characteristic length scales. The …

Experimental Explanation Of The Formation Mechanism Of Surface Mound-Structures By Femtosecond Laser On Polycrystalline Ni60Nb40, Edwin Peng, A. Tsubaki, Craig A. Zuhlke, Meiyu Wang, Ryan Bell, Michael J. Lucis, Troy P. Anderson, Dennis R. Alexander, George Gogos, Jeffrey E. Shield

Department of Mechanical and Materials Engineering: Faculty Publications

Femtosecond laser surface processing (FLSP) is an emerging technique for creating functionalized surfaces with specialized properties, such as broadband optical absorption or superhydrophobicity/ superhydrophilicity. It has been demonstrated in the past that FLSP can be used to form two distinct classes of mound-like, self-organized micro/nanostructures on the surfaces of various metals. Here, the formation mechanisms of below surface growth (BSG) and above surface growth (ASG) mounds on polycrystalline Ni₆₀Nb₄₀ are studied. Cross-sectional imaging of these mounds by focused ion beam milling and subsequent scanning electron microscopy revealed evidence of the unique formation processes for each class of …

Dose Dependence Of Radiation Damage In Nano-Structured Amorphous Sioc/Crystalline Fe Composite, Qing Su, Lloyd Price, Lin Shao, Michael Nastasi

Department of Mechanical and Materials Engineering: Faculty Publications

Through examination of radiation tolerance properties of amorphous silicon oxycarbide (SiOC) and crystalline Fe composite to averaged damage levels, from approximately 8 to 30 displacements per atom (dpa), we demonstrated that the Fe/SiOC interface and the Fe/amorphous Fe_xSi_yO_z interface act as efficient defect sinks and promote the recombination of vacancies and interstitials. For thick Fe/SiOC multilayers, a clear Fe/SiOC interface remained and no irradiation-induced mixing was observed even after 32 dpa. For thin Fe/SiOC multilayers, an amorphous Fe_xSi_yO_z intermixed layer was observed to form at 8 dpa, but no further …

Field-Scale Testing And Numerical Investigation Of Soil-Boulder Interaction Under Vehicular Impact Using Fem And Coupled Fem-Sph Formulations, Lynsey Reese, Tong Qiu, Daniel Linzell, Zoltan Rado

Department of Civil and Environmental Engineering: Faculty Publications

A computational approach that couples the Finite Element Method and the Smoothed Particle Hydrodynamics method may be advantageous for simulating the response of complex, physical systems involving large deformations. However, comparisons of this modeling technique against field-scale test data are remarkably sparse in literature. This study presents three field-scale tests involving vehicular impact into three landscape vehicular anti-ram barriers. Each barrier consisted of a single boulder embedded in compacted American Association of State Highway and Transportation Officials soil and physical testing resulted in one of the following outcomes: minimal boulder/soil movement (Test 1), moderate boulder/soil movement (Test 2), and severe …

Matl 260/360: Elements Of Materials Science—A Peer Review Of Teaching Project Benchmark Portfolio, Bai Cui

UNL Faculty Course Portfolios

The goal of MATL 260/360 Elements of Materials Science is to make undergraduate students understand the fundamental concepts of the microstructure-property relationship of materials. This course portfolio addresses several key questions in teaching, such as how to teach new knowledge more effectively, how to increase student engagement, how to promote students’ interests and motivations, and how to use this course to improve students’ analysis and critical thinking skills.

To address each of key questions, the course activities include: relating the new knowledge with daily-life and industry examples; giving PPT slides for after- class study; assigning homework questions after each lecture; …

Turning An Organic Semiconductor Into A Low-Resistance Material By Ion Implantation, Beatrice Fraboni, Alessandra Scidà, Piero Cosseddu, Yongqiang Wang, Michael Nastasi, Silvia Milita, Annalisa Bonfiglio

Nebraska Center for Energy Sciences Research: Publications

We report on the effects of low energy ion implantation on thin films of pentacene, carried out to investigate the efficacy of this process in the fabrication of organic electronic devices. Two different ions, Ne and N, have been implanted and compared, to assess the effects of different reactivity within the hydrocarbon matrix. Strong modification of the electrical conductivity, stable in time, is observed following ion implantation. This effect is significantly larger for N implants (up to six orders of magnitude), which are shown to introduce stable charged species within the hydrocarbon matrix, not only damage as is the case …

Experimental Investigation And Thermal Modeling On Electro Discharge Drilling Of Pcd, Farnaz Nourbakhsh

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

This study presents an experimental investigation and finite element simulation of Electro Discharge Drilling (ED-Drilling) of Polycrystalline Diamond (PCD). PCD has many outstanding properties including uniformly high hardness, high wear resistance and strong corrosion which are the main causes of widely using PCD. While PCD has many advantages and an important role in industrial applications, its high level of hardness and wear resistance cause this material to be difficult to form and machine by using traditional machining methods. EDM as a nontraditional machining process is an effective method among other non-traditional methods for PCDs due to its low cost and …

Imaging Thermal Conductivity With Nanoscale Resolution Using A Scanning Spin Probe, Abdelghani Laraoui, Halley Aycock-Rizzo, Yang Gao, Xi Lu, Elisa Riedo, Carlos A. Meriles

Department of Mechanical and Materials Engineering: Faculty Publications

The ability to probe nanoscale heat flow in a material is often limited by lack of spatial resolution. Here, we use a diamond-nanocrystal-hosted nitrogen-vacancy centre attached to the apex of a silicon thermal tip as a local temperature sensor. We apply an electrical current to heat up the tip and rely on the nitrogen vacancy to monitor the thermal changes the tip experiences as it is brought into contact with surfaces of varying thermal conductivity. By combining atomic force and confocal microscopy, we image phantom microstructures with nanoscale resolution, and attain excellent agreement between the thermal conductivity and topographic maps. …

System And Method For Estimating States Of Spacecraft In Planet-Moon Environment, Piyush Grover

Department of Mechanical and Materials Engineering: Faculty Publications

A method estimates a state of a spacecraft in a planet-moon environment by executing iteratively a particle filter. The particle filter comprising integrates individually states of each particle of the particle filter according to a probability-evolution equation using a model of the state of the spacecraft represented as a planar circular restricted three-body problem and determines a prior probability of each particle as a previous posterior probability of a corresponding particle during a previous iteration. A joint probability distribution of the state of the spacecraft is determines using the states of each particle and the prior probabilities of each particle …

An Estimate Of The Second-Order In-Plane Acceleration Sensitivity Of A Y-Cut Quartz Thickness-Shear Resonator, Huijing He, Jiashi Yang, John A. Kosinski

Department of Mechanical and Materials Engineering: Faculty Publications

We perform a theoretical analysis of the second-order in-plane acceleration sensitivity of a Y-cut quartz thick-ness-shear mode resonator. The second-order nonlinear theory of elasticity for anisotropic crystals is used to determine the biasing fields in the resonator under in-plane acceleration. The acceleration-induced frequency shift is determined from a per-turbation analysis based on the plate equations for small-amplitude vibrations superposed on a finite bias. We show that, whereas the first-order acceleration-induced frequency shift is zero for a structurally symmetric resonator under in-plane ac-celeration, the second-order frequency shift is nonzero and is quadratic in the acceleration. As the fourth-order nonlinear elastic constants …

Biodegradable Medical Device Having An Adjustable Degradation Rate And Methods Of Making The Same, Yuebin Guo, Michael Sealy, Meisam Salahshoor Pirsoltan

Department of Mechanical and Materials Engineering: Faculty Publications

Disclosed herein are biodegradable medical devices comprising biodegradable material (e.g., magnesium-calcium alloys) having an adjustable rate of degradation that can be used in various applications, including, but not limited to, drug delivery applications, cardiovascular applications, and orthopedic applications to make biodegradable and biocompatible devices. Also disclosed herein are methods of making biodegradable medical devices comprising biodegradable materials by using, for instance, hybrid dry cutting/hydrostatic burnishing.

Non-Wetting Surface-Driven High-Aspect-Ratio Crystalline Grain Growth For Efficient Hybrid Perovskite Solar Cells, Cheng Bi, Qi Wang, Yongbo Yuan, Zhengguo Xiao, Jinsong Huang

Department of Mechanical and Materials Engineering: Faculty Publications

Large-aspect-ratio grains are needed in polycrystalline thin-film solar cells for reduced charge recombination at grain boundaries; however, the grain size in organolead trihalide perovskite (OTP) films is generally limited by the film thickness. Here we report the growth of OTP grains with high average aspect ratio of 2.3–7.9 on a wide range of non-wetting hole transport layers (HTLs), which increase nucleus spacing by suppressing heterogeneous nucleation and facilitate grain boundary migration in grain growth by imposing less drag force. The reduced grain boundary area and improved crystallinity dramatically reduce the charge recombination in OTP thin films to the level in …

Local Control Robotic Surgical Devices And Related Methods, Eric Markvicka, Tom Frederick, Jack Mondry, Joe Bartels, Shane Farritor

Department of Mechanical and Materials Engineering: Faculty Publications

The various robotic medical devices include robotic devices that are disposed within a body cavity and positioned using a support component disposed through an orifice or opening in the body cavity. Additional embodiments relate to devices having arms coupled to a device body wherein the device has a minimal profile such that the device can be easily inserted through smaller incisions in comparison to other devices without such a small profile. Further embodiments relate to methods of operating the above devices.

Methods And Systems For Handling Or Delivering Materials For Natural Orifice Surgery, Carl Nelson, Jeff Midday, Dimitry Oleynikov, Alan Goyzueta

Department of Mechanical and Materials Engineering: Faculty Publications

The embodiments disclosed herein relate to various medical systems, including systems that can be used in conjunction with medical devices used in endoscopic surgery. Certain embodiments include various material handling devices that can transport materials between the inside and the outside of an endoscopic surgery patient.

Chloride Incorporation Process In Ch3Nh3Pbi3-XClX Perovskites Via Nanoscale Bandgap Maps, Jungseok Chae, Qingfeng Dong, Jinsong Huang, Andrea Centrone

Department of Mechanical and Materials Engineering: Faculty Publications

CH₃NH₃PbI_3-xCl_x perovskites enable fabrication of highly efficient solar cells. Chloride ions benefit the morphology, carrier diffusion length and stability of perovskite films; however, whether those benefits stem from the presence of Cl⁻ in the precursor solution or from their incorporation in annealed films is debated. In this work, the photothermal induced resonance (PTIR), an in situ technique with nanoscale resolution, is leveraged to measure the bandgap of CH₃NH₃PbI_3-xCl_x films obtained by a multicycle coating process that produces high efficiency (≈16 %) solar cells. Because chloride …

Role Of Interphase In The Mechanical Behavior Of Silica/Epoxy Resin Nanocomposites, Yi Hua, Linxia Gu, Sundaralingam Premaraj, Xiaodong Zhang

Department of Mechanical and Materials Engineering: Faculty Publications

A nanoscale representative volume element has been developed to investigate the effect of interphase geometry and property on the mechanical behavior of silica/epoxy resin nanocomposites. The role of interphase–matrix bonding was also examined. Results suggested that interphase modulus and interfacial bonding conditions had significant influence on the effective stiffness of nanocomposites, while its sensitivities with respect to both the thickness and the gradient property of the interphase was minimal. The stiffer interphase demonstrated a higher load-sharing capacity, which also increased the stress distribution uniformity within the resin nanocomposites. Under the condition of imperfect interfacial bonding, the effective stiffness of nanocomposites …

Relevance Of Blood Vessel Networks In Blast-Induced Traumatic Brain Injury, Yi Hua, Shengmao Lin, Linxia Gu

Department of Mechanical and Materials Engineering: Faculty Publications

Cerebral vasculature is a complex network that circulates blood through the brain. However, the role of this networking effect in brain dynamics has seldom been inspected. This work is to study the effects of blood vessel networks on dynamic responses of the brain under blast loading. Voronoi tessellations were implemented to represent the network of blood vessels in the brain. The brain dynamics in terms of maximumprincipal strain (MPS), shear strain (SS), and intracranial pressure (ICP) weremonitored and compared. Results show that blood vessel networks significantly affected brain responses.The increased MPS and SS were observed within the brain embedded with …

In Situ Longitudinal Pre-Stretch In The Human Femoropopliteal Artery, Alexey Kamenskiy, Andreas Seas, Grant Bowen, Paul Deegan, Anastasia Desyatova, Nick Bohlim, William Poulson, Jason N. Mactaggart

Department of Mechanical and Materials Engineering: Faculty Publications

In situ longitudinal (axial) pre-stretch (LPS) plays a fundamental role in the mechanics of the femoropopliteal artery (FPA). It conserves energy during pulsation and prevents buckling of the artery during limb movement. We investigated how LPS is affected by demographics and risk factors, and how these patient characteristics associate with the structural and physiologic features of the FPA. LPS was measured in n=148 fresh human FPAs (14–80 years old). Mechanical properties were characterized with biaxial extension and histopathological characteristics were quantified with Verhoeff-Van Gieson Staining. Constitutive modeling was used to calculate physiological stresses and stretches which were then analyzed …

Asphalt Composition, David Allen, Flavio Souza, Yong-Rak Kim, Roberto Soares

Department of Mechanical and Materials Engineering: Faculty Publications

A computational method is provided for predicting roadway failure due to degradation of the roadway over time as a function of the input loads, the roadway geometry, the material properties of the constituents in the asphaltic pavement, the shape, distribution, orientation and volume fractions of the constituents, and environmental conditions. The unique and new feature of the method is that it employs several physically based predictive methodologies simultaneously.

Extracting Continuum-Like Deformation And Stress From Molecular Dynamics Simulations, Lili Zhang, John Jasa, George Gazonas, Antoine Jerusalem, Mehrdad Negahban

Department of Mechanical and Materials Engineering: Faculty Publications

We present methods that use results from molecular dynamics (MD) simulations to construct continuum parameters, such as deformation gradient and Cauchy stress, from all or any part of an MD system. These parameters are based on the idea of minimizing the difference between MD measures for deformation and traction and their continuum counterparts. The procedures should be applicable to non-equilibrium and inhomogeneous systems, and to any part of a system, such as a polymer chain. The resulting procedures provide methods to obtain first and higher order deformation gradients associated with any subset of the MD system, and associated expressions for …

Blast-Induced Mild Traumatic Brain Injury Through Ear Canal: A Finite Element Study, Praveen Akula, Yi Hua, Linxia Gu

Department of Mechanical and Materials Engineering: Faculty Publications

Purpose The role of ear canal in transmitting blast waves to the brain is not clear. The goal of this work is to characterize the influence of ear canal on blast-induced mild traumatic brain injury through a computational approach.

Methods A three-dimensional human head model with single-side ear canal details was reconstructed from computed tomography images. The ear canal was positioned either facing the incident blast wave or facing away from the blast wave.

Results The blast wave-head interaction has demonstrated that the overpressure within the ear canal was substantially amplified when the ear directly faced the blast wave. When …