1
|
Chi L, Nogami J, Singh CV. Phase Transformation-Induced Quantum Dot States on the Bi/Si(111) Surface. ACS APPLIED MATERIALS & INTERFACES 2022; 14:36217-36226. [PMID: 35900138 DOI: 10.1021/acsami.2c07015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Nanopatterns at near atomic dimensions with controllable quantum dot states (QDSs) are promising candidates for the continued downscaling of electronic devices. Herein, we report a phase transition-induced QD system achieved on the √3 × √3-Bi/Si(111) surface reconstruction, which points the way to a novel strategy on QDS implementation. Combining scanning tunneling microscopy, scanning tunneling spectroscopy, and density functional theory (DFT) calculations, the structure, energy dispersion, and size effect on band gap of the QDs are measured and verified. As-created QDs can be manipulated with a dot size down to 2 nm via Bi phase transformation, which, in turn, is triggered by thermal annealing at 700 K. The transition mechanism is also supported by our DFT calculations, and an empirical analytical model is developed to predict the transformation kinetics.
Collapse
Affiliation(s)
- Longxing Chi
- Department of Materials Science and Engineering, University of Toronto, 184 College Street, Toronto, Ontario M5S 3E4, Canada
| | - Jun Nogami
- Department of Materials Science and Engineering, University of Toronto, 184 College Street, Toronto, Ontario M5S 3E4, Canada
| | - Chandra Veer Singh
- Department of Materials Science and Engineering, University of Toronto, 184 College Street, Toronto, Ontario M5S 3E4, Canada
- Department of Mechanical and Industrial Engineering, University of Toronto, 5 King's College Road, Toronto, Ontario M5S 3G8, Canada
| |
Collapse
|
2
|
Kim TH, Zhao H, Ong PV, Jensen BA, Cui B, King AH, Ke L, Zhou L. Kinetics of Magnetic Skyrmion Crystal Formation from the Conical Phase. NANO LETTERS 2021; 21:5547-5554. [PMID: 34185540 DOI: 10.1021/acs.nanolett.1c00923] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The particle-like magnetic skyrmion or skyrmion lattice (SkX) formation has promoted strong application and fundamental science interests. Despite extensive research, the kinetic of the SkX development is much less understood because of the ultrafast spin rotation and high sensitivity to external perturbations. Here, using in situ Lorentz transmission electron microscopy, we successfully measured the dynamics of SkX formation from the conical phase with precise control of both the temperature and the magnetic field. We discovered that the Avrami equation can accurately describe the transition process with an initial Avrami constant around 1, suggesting that the rate-limiting step for the quasiparticle lattice formation is one-dimensional heterogeneous nucleation of individual skyrmions. A modified Arrhenius rate law is established, with an energy barrier that has a square-root dependence on temperature and a quadratic dependence on the magnetic field. This study paves the way toward precise and predictable manipulation of topological spin structures.
Collapse
Affiliation(s)
- Tae-Hoon Kim
- Ames Laboratory, U.S. Department of Energy, Ames, Iowa 50011, United States
- Department of Materials Science and Engineering, Chonnam National University, Gwangju 61186, Republic of Korea
| | - Haijun Zhao
- School of Physics, Southeast University, Nanjing 211189, China
| | - Phuong-Vu Ong
- Ames Laboratory, U.S. Department of Energy, Ames, Iowa 50011, United States
| | - Brandt A Jensen
- Ames Laboratory, U.S. Department of Energy, Ames, Iowa 50011, United States
| | - Baozhi Cui
- Ames Laboratory, U.S. Department of Energy, Ames, Iowa 50011, United States
| | - Alexander H King
- Ames Laboratory, U.S. Department of Energy, Ames, Iowa 50011, United States
- Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011, United States
| | - Liqin Ke
- Ames Laboratory, U.S. Department of Energy, Ames, Iowa 50011, United States
| | - Lin Zhou
- Ames Laboratory, U.S. Department of Energy, Ames, Iowa 50011, United States
| |
Collapse
|
3
|
Seper BC, Ko A, Abma AF, Folkerts AD, Tristram-Nagle S, Harper PE. Methylene volumes in monoglyceride bilayers are larger than in liquid alkanes. Chem Phys Lipids 2019; 226:104833. [PMID: 31738879 DOI: 10.1016/j.chemphyslip.2019.104833] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2019] [Revised: 09/26/2019] [Accepted: 10/09/2019] [Indexed: 11/26/2022]
Abstract
The densities as a function of temperature of four fully hydrated saturated monoglycerides with even chain lengths ranging from eight to fourteen were determined by vibrating tube densitometry and their phase transition temperatures were determined by differential scanning calorimetry (DSC). We find the volume of a methylene group in a monoglyceride bilayer is 2% larger than in liquid alkanes at physiological temperatures, similar to the methylene group volumes found in phosphatidylcholine (PC) bilayers. Additionally, we carefully consider the traditional method of calculating component volumes from experimental data and note potential difficulties in this approach. In the literature, the ratio of terminal methyl volume (CH3) to methylene (CH2) volumes is typically assumed to be 2. By analysis of literature alkane data, we find this ratio actually ranges from 1.9 to 2.3 for temperatures ranging from 0 °C to 100 °C. For a rough sense of scale, we note that to effect a 2% reduction in volume requires of order 200 atmospheres of pressure, and pressures of this magnitude are biologically relevant. For instance, this amount of pressure is sufficient to reverse the effect of anesthesia. The component volumes obtained are an important parameter used for determining the structure of lipid bilayers and for molecular dynamics simulations.
Collapse
Affiliation(s)
- Brian C Seper
- Department of Physics and Astronomy, Calvin University, Grand Rapids, MI 49546, USA
| | - Anthony Ko
- Biological Physics Group, Physics Department, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, USA
| | - Aaron F Abma
- Department of Physics and Astronomy, Calvin University, Grand Rapids, MI 49546, USA
| | - Andrew D Folkerts
- Department of Physics and Astronomy, Calvin University, Grand Rapids, MI 49546, USA
| | - Stephanie Tristram-Nagle
- Biological Physics Group, Physics Department, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, USA
| | - Paul E Harper
- Department of Physics and Astronomy, Calvin University, Grand Rapids, MI 49546, USA.
| |
Collapse
|
4
|
Wang Z, Ma Y, Khalil H, Wang R, Lu T, Zhao W, Zhang Y, Chen J, Chen T. Fusion between fluid liposomes and intact bacteria: study of driving parameters and in vitro bactericidal efficacy. Int J Nanomedicine 2016; 11:4025-36. [PMID: 27574430 PMCID: PMC4993285 DOI: 10.2147/ijn.s55807] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Background Pseudomonas aeruginosa represents a good model of antibiotic resistance. These organisms have an outer membrane with a low level of permeability to drugs that is often combined with multidrug efflux pumps, enzymatic inactivation of the drug, or alteration of its molecular target. The acute and growing problem of antibiotic resistance of bacteria to conventional antibiotics made it imperative to develop new liposome formulations for antibiotics, and investigate the fusion between liposome and bacterium. Methods In this study, the factors involved in fluid liposome interaction with bacteria have been investigated. We also demonstrated a mechanism of fusion between liposomes (1,2-dipa lmitoyl-sn-glycero-3-phosphocholine [DPPC]/dimyristoylphosphatidylglycerol [DMPG] 9:1, mol/mol) in a fluid state, and intact bacterial cells, by lipid mixing assay. Results The observed fusion process is shown to be mainly dependent on several key factors. Perturbation of liposome fluidity by addition of cholesterol dramatically decreased the degree of fusion with P. aeruginosa from 44% to 5%. It was observed that fusion between fluid liposomes and bacteria and also the bactericidal activities were strongly dependent upon the properties of the bacteria themselves. The level of fusion detected when fluid liposomes were mixed with Escherichia coli (66%) or P. aeruginosa (44%) seems to be correlated to their outer membrane phosphatidylethanolamine (PE) phospholipids composition (91% and 71%, respectively). Divalent cations increased the degree of fusion in the sequence Fe2+ > Mg2+ > Ca2+ > Ba2+ whereas temperatures lower than the phase transition temperature of DPPC/DMPG (9:1) vesicles decreased their fusion capacity. Acidic as well as basic pHs conferred higher degrees of fusion (54% and 45%, respectively) when compared to neutral pH (35%). Conclusion Based on the results of this study, a possible mechanism involving cationic bridging between bacterial negatively charged lipopolysaccharide and fluid liposomes DMPG phospholipids was outlined. Furthermore, the fluid liposomal-encapsulated tobramycin was prepared, and the in vitro bactericidal effects were also investigated.
Collapse
Affiliation(s)
- Zhao Wang
- Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, Shaanxi; Shaanxi Liposome Research Center, Xi'an, Shaanxi
| | - Yufan Ma
- Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, Shaanxi; Xi'an Libang Pharmaceuticals Co, Ltd, Xi'an; School of Medicine, Xi'an Jiaotong University, Xi'an, People's Republic of China
| | - Hayssam Khalil
- Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, Shaanxi
| | - Rutao Wang
- Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, Shaanxi; Shaanxi Liposome Research Center, Xi'an, Shaanxi; Xi'an Libang Pharmaceuticals Co, Ltd, Xi'an
| | - Tingli Lu
- Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, Shaanxi
| | - Wen Zhao
- Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, Shaanxi
| | - Yang Zhang
- Xi'an Libang Pharmaceuticals Co, Ltd, Xi'an
| | - Jamin Chen
- Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, Shaanxi; Shaanxi Liposome Research Center, Xi'an, Shaanxi
| | - Tao Chen
- Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, Shaanxi; Shaanxi Liposome Research Center, Xi'an, Shaanxi; Xi'an Libang Pharmaceuticals Co, Ltd, Xi'an
| |
Collapse
|
5
|
Reese CW, Strango ZI, Dell ZR, Tristram-Nagle S, Harper PE. Structural insights into the cubic-hexagonal phase transition kinetics of monoolein modulated by sucrose solutions. Phys Chem Chem Phys 2015; 17:9194-204. [PMID: 25758637 PMCID: PMC4381959 DOI: 10.1039/c5cp00175g] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Using DSC (differential scanning calorimetry), we measure the kinetics of the cubic-HII phase transition of monoolein in bulk sucrose solutions. We find that the transition temperature is dramatically lowered, with each 1 mol kg(-1) of sucrose concentration dropping the transition by 20 °C. The kinetics of this transition also slow greatly with increasing sucrose concentration. For low sucrose concentrations, the kinetics are asymmetric, with the cooling (HII-cubic) transition taking twice as long as the heating (cubic-HII) transition. This asymmetry in transition times is reduced for higher sucrose concentrations. The cooling transition exhibits Avrami exponents in the range of 2 to 2.5 and the heating transition shows Avrami exponents ranging from 1 to 3. A classical Avrami interpretation would be that these processes occur via a one or two dimensional pathway with variable nucleation rates. A non-classical perspective would suggest that these exponents reflect the time dependence of pore formation (cooling) and destruction (heating). New density measurements of monoolein show that the currently accepted value is about 5% too low; this has substantial implications for electron density modeling. Structural calculations indicate that the head group area and lipid length in the cubic-HII transition shrink by about 12% and 4% respectively; this reduction is practically the same as that seen in a lipid with a very different molecular structure (rac-di-12:0 β-GlcDAG) that makes the same transition. Thermodynamic considerations suggest there is a hydration shell about one water molecule thick in front of the lipid head groups in both the cubic and HII phases.
Collapse
Affiliation(s)
- Caleb W Reese
- Department of Physics and Astronomy, Calvin College, 1734 Knollcrest Circle SE, Grand Rapids, MI, USA.
| | | | | | | | | |
Collapse
|
6
|
A bacterial monorhamnolipid alters the biophysical properties of phosphatidylethanolamine model membranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1828:2083-90. [DOI: 10.1016/j.bbamem.2013.04.024] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2012] [Revised: 04/16/2013] [Accepted: 04/17/2013] [Indexed: 11/23/2022]
|