27 research outputs found
Screening and the epidemic of thyroid cancer in China:an analysis of national representative inpatient and commercial insurance databases
Adsorption of adenine and phenylglycine on Cu(110) surfaces studied using STM and RAIRS
The adsorption of biologically active molecules, such as the DNA bases, amino acids, on solid surfaces has been the subject of a number of experimental and theoretical studies in the past years. The understanding of the self-assembly mechanism of bioactive molecules on surfaces not only is fundamentally important in the preparation of bioactive surfaces, but also provides us insight into the origins of life and homo-chirality in nature.
In this thesis, the adsorption behaviour of adenine and phenylglycine molecules on the Cu(110) surface has been investigated in order to understand the effect of experimental parameters like coverage, annealing temperature etc. on the molecular orientation and the ordering of the adlayer structures.
The thesis is organised in six parts:
Chapter I gives an introduction to the relevance of surface sciences studies, describing the phenomena of surface chirality and molecular adsorption behaviours on surfaces.
Chapter II gives an overview of the experimental techniques and introduces basic concepts of theoretical calculation.
Chapter III investigates the effect of experimental parameters, e.g. surface coverage, annealing temperature and substrate temperature on molecular diffusion, molecular orientation and ordering of the adlayer structures. LT-STM examination of the contrast variations of adenine chains and isolated adsorbate as a function of the tip-sample bias voltage is also presented with the aim to understand the tunnelling mechanism.
Chapter IV shows RAIR spectra studies of the evolution of phenylglycine molecular orientation as a function of surface coverage at room temperature. The adsorption geometry and binding nature of phenylglycine is discussed.
Chapter V concerns with the adsorption behaviours of phenylglycine and adenine on Cu(110) surface pre-covered with oxygen.
Chapter VI summarises the conclusions and describes the outlook of some future work
Role of Hydrogen Bonding in the Formation of Adenine Chains on Cu(110) Surfaces
Understanding the adsorption properties of DNA bases on metal surfaces is fundamental for the rational control of surface functionalization leading to the realisation of biocompatible devices for biosensing applications, such as monitoring of particular parameters within bio-organic environments and drug delivery. In this study, the effects of deposition rate and substrate temperature on the adsorption behavior of adenine on Cu(110) surfaces have been investigated using scanning tunneling microscopy (STM) and density functional theory (DFT) modeling, with a focus on the characterization of the morphology of the adsorbed layers. STM results revealed the formation of one-dimensional linear chains and ladder-like chains parallel to the [110] direction, when dosing at a low deposition rate at room temperature, followed by annealing to 490 K. Two mirror related, well-ordered chiral domains oriented at ±55° with respect to the [110] direction are formed upon deposition on a substrate kept at 490 K. The molecular structures observed via STM are rationalized and qualitatively described on the basis of the DFT modeling. The observation of a variety of ad-layer structures influenced by deposition rate and substrate temperature indicates that dynamic processes and hydrogen bonding play an important role in the self-assembly of adenine on the Cu(110) surface
Adsorption of adenine and phenylglycine on Cu(110) surfaces studied using STM and RAIRS
The adsorption of biologically active molecules, such as the DNA bases, amino acids, on solid surfaces has been the subject of a number of experimental and theoretical studies in the past years. The understanding of the self-assembly mechanism of bioactive molecules on surfaces not only is fundamentally important in the preparation of bioactive surfaces, but also provides us insight into the origins of life and homo-chirality in nature. In this thesis, the adsorption behaviour of adenine and phenylglycine molecules on the Cu(110) surface has been investigated in order to understand the effect of experimental parameters like coverage, annealing temperature etc. on the molecular orientation and the ordering of the adlayer structures. The thesis is organised in six parts: Chapter I gives an introduction to the relevance of surface sciences studies, describing the phenomena of surface chirality and molecular adsorption behaviours on surfaces. Chapter II gives an overview of the experimental techniques and introduces basic concepts of theoretical calculation. Chapter III investigates the effect of experimental parameters, e.g. surface coverage, annealing temperature and substrate temperature on molecular diffusion, molecular orientation and ordering of the adlayer structures. LT-STM examination of the contrast variations of adenine chains and isolated adsorbate as a function of the tip-sample bias voltage is also presented with the aim to understand the tunnelling mechanism. Chapter IV shows RAIR spectra studies of the evolution of phenylglycine molecular orientation as a function of surface coverage at room temperature. The adsorption geometry and binding nature of phenylglycine is discussed. Chapter V concerns with the adsorption behaviours of phenylglycine and adenine on Cu(110) surface pre-covered with oxygen. Chapter VI summarises the conclusions and describes the outlook of some future work.EThOS - Electronic Theses Online ServiceEastChemGBUnited Kingdo
AMLâderived mesenchymal stem cells upregulate CTGF expression through the BMP pathway and induce K562âADM fusiform transformation and chemoresistance
Energy Storage Properties of SolâGel-Processed SrTiO<sub>3</sub> Films
Dielectric films with a high energy storage density and a large breakdown strength are promising material candidates for pulsed power electrical and electronic applications. Perovskite-type dielectric SrTiO3 (STO) has demonstrated interesting properties desirable for capacitive energy storage, including a high dielectric constant, a wide bandgap and a size-induced paraelectric-to-ferroelectric transition. To pave a way toward large-scale production, STO film capacitors were deposited on Pt(111)/Ti/SiO2/Si(100) substrates by the solâgel method in this paper, and their electrical properties including the energy storage performance were studied as a function of the annealing temperature in the postgrowth rapid thermal annealing (RTA) process. The appearance of a ferroelectric phase at a high annealing temperature of 750 °C was revealed by X-ray diffraction and electrical characterizations (ferroelectric P-E loop). However, this high dielectric constant phase came at the cost of a low breakdown strength and a large hysteresis loss, which are not desirable for the energy storage application. On the other hand, when the RTA process was performed at a low temperature of 550 °C, a poorly crystallized perovskite phase together with a substantial amount of impurity phases appeared, resulting in a low breakdown strength as well as a very low dielectric constant. It is revealed that the best energy storage performance, which corresponds to a large breakdown strength and a medium dielectric constant, is achieved in STO films annealed at 650 °C, which showed a large energy density of 55 J/cm3 and an outstanding energy efficiency of 94.7% (@ 6.5 MV/cm). These findings lay out the foundation for processing high-quality STO film capacitors via the manufacturing-friendly solâgel method
Atomic Layer Deposition of Silicon Nitride Thin Films: A Review of Recent Progress, Challenges, and Outlooks
With the continued miniaturization of devices in the semiconductor industry, atomic layer deposition (ALD) of silicon nitride thin films (SiNx) has attracted great interest due to the inherent benefits of this process compared to other silicon nitride thin film deposition techniques. These benefits include not only high conformality and atomic-scale thickness control, but also low deposition temperatures. Over the past 20 years, recognition of the remarkable features of SiNx ALD, reinforced by experimental and theoretical investigations of the underlying surface reaction mechanism, has contributed to the development and widespread use of ALD SiNx thin films in both laboratory studies and industrial applications. Such recognition has spurred ever-increasing opportunities for the applications of the SiNx ALD technique in various arenas. Nevertheless, this technique still faces a number of challenges, which should be addressed through a collaborative effort between academia and industry. It is expected that the SiNx ALD will be further perceived as an indispensable technique for scaling next-generation ultra-large-scale integration (ULSI) technology. In this review, the authors examine the current research progress, challenges and future prospects of the SiNx ALD technique
Remote Plasma Oxidation and Atomic Layer Etching of MoS<sub>2</sub>
Exfoliated molybdenum
disulfide (MoS<sub>2</sub>) is shown to chemically
oxidize in a layered manner upon exposure to a remote O<sub>2</sub> plasma. X-ray photoelectron spectroscopy (XPS), low energy electron
diffraction (LEED), and atomic force microscopy (AFM) are employed
to characterize the surface chemistry, structure, and topography of
the oxidation process and indicate that the oxidation mainly occurs
on the topmost layer without altering the chemical composition of
underlying layer. The formation of SâO bonds upon short, remote
plasma exposure pins the surface Fermi level to the conduction band
edge, while the MoO<sub><i>x</i></sub> formation at high
temperature modulates the Fermi level toward the valence band through
band alignment. A uniform coverage of monolayer amorphous MoO<sub>3</sub> is obtained after 5 min or longer remote O<sub>2</sub> plasma
exposure at 200 °C, and the MoO<sub>3</sub> can be completely
removed by annealing at 500 °C, leaving a clean ordered MoS<sub>2</sub> lattice structure as verified by XPS, LEED, AFM, and scanning
tunneling microscopy. This work shows that a remote O<sub>2</sub> plasma
can be useful for both surface functionalization and a controlled
thinning method for MoS<sub>2</sub> device fabrication processes
Structural Changes in Self-Catalyzed Adsorption of Carbon Monoxide on 1,4-Phenylene Diisocyanide Modified Au(111)
The
self-accelerated adsorption of CO on 1,4-phenylene diisocyanide
(PDI)-derived oligomers on Au(111) is explored by reflectionâabsorption
infrared spectroscopy and scanning tunneling microscopy. PDI incorporates
gold adatoms from the Au(111) surface to form one-dimensional â(AuâPDI)<sub><i>n</i></sub>â chains that can also connect between
gold nanoparticles on mica to form a conductive pathway between them.
CO adsorption occurs in two stages; it first adsorbs adjacent to the
oligomers that move to optimize CO adsorption. Further CO exposure
induces PDI decoordination to form AuâPDI adatom complexes
thereby causing the conductivity of a PDI-linked gold nanoparticle
array on mica to decrease to act as a chemically drive molecular switch.
This simple system enables the adsorption process to be explored in
detail. DFT calculations reveal that both the â(AuâPDI)<sub><i>n</i></sub>â oligomer chain and the AuâPDI
adatom complex are stabilized by coadsorbed CO. A kinetic âfoot-in-the-doorâ
model is proposed in which fluctuations in PDI coordination allow
CO to diffuse into the gap between gold adatoms to prevent the PDI
from reattaching, thereby allowing additional CO to adsorb, to provide
kinetic model for allosteric CO adsorption on PDI-covered gold