THERMODYNAMICS OF NUCLEATION AND GROWTH

2002 ◽  
Vol 09 (03n04) ◽  
pp. 1565-1593 ◽  
Author(s):  
RUUD M. TROMP ◽  
JAMES B. HANNON

Nucleation and growth are often discussed in terms of kinetics, i.e. the adsorption of atoms from the gas phase or a solution onto a surface, the diffusion of these atoms on that surface, and their attachment to a growing nucleus, island or layer. In recent years, scanning tunneling and atomic force microscopy studies have tremendously improved our understanding of such kinetic processes for a wide range of materials. At relatively low temperatures where diffusion is slow, and where typical deposition rates result in adatom concentrations that far exceed the equilibrium concentration of adatoms on the surface, growth is indeed controlled by irreversible atomic scale kinetics. But at higher temperatures this is not necessarily the case. Indeed, the equilibrium concentration of adatoms can be so high that it is only slightly increased by an external flux. Diffusion can be so fast that spatially separated regions on the surface interact on a time scale that is not slow relative to the growth process. In such cases reversible, collective phenomena are more important than individual atomic events, and thermodynamics is more important than kinetics. In this paper we examine a number of cases related to nucleation and growth on surfaces, where a deep and quantitative insight into the growth process can be obtained by detailed consideration of the thermodynamics involved. It is our hope that this paper will help to bring about a balanced understanding of these phenomena, where kinetics and thermodynamics are two poles on a continuum with an importance that depends on the particulars of each experiment.

Author(s):  
M. Iwatsuki ◽  
S. Kitamura ◽  
A. Mogami

Since Binnig, Rohrer and associates observed real-space topographic images of Si(111)-7×7 and invented the scanning tunneling microscope (STM),1) the STM has been accepted as a powerful surface science instrument.Recently, many application areas for the STM have been opened up, such as atomic force microscopy (AFM), magnetic force microscopy (MFM) and others. So, the STM technology holds a great promise for the future.The great advantages of the STM are its high spatial resolution in the lateral and vertical directions on the atomic scale. However, the STM has difficulty in identifying atomic images in a desired area because it uses piezoelectric (PZT) elements as a scanner.On the other hand, the demand to observe specimens under UHV condition has grown, along with the advent of the STM technology. The requirment of UHV-STM is especially very high in to study of surface construction of semiconductors and superconducting materials on the atomic scale. In order to improve the STM image quality by keeping the specimen and tip surfaces clean, we have built a new UHV-STM (JSTM-4000XV) system which is provided with other surface analysis capability.


1999 ◽  
Vol 570 ◽  
Author(s):  
J. A. Venables ◽  
G. Haas ◽  
H. Brune ◽  
J.H. Harding

ABSTRACTNucleation and growth of metal clusters at defect sites is discussed in terms of rate equation models, which are applied to the cases of Pd and Ag on MgO(001) and NaCl(001) surfaces. Pd/MgO has been studied experimentally by variable temperature atomic force microscopy (AFM). The island density of Pd on Ar-cleaved surfaces was determined in-situ by AFM for a wide range of deposition temperature and flux, and stays constant over a remarkably wide range of parameters; for a particular flux, this plateau extends from 200 K ≤ T ≤ 600 K, but at higher temperatures the density decreases. The range of energies for defect trapping, adsorption, surface diffusion and pair binding are deduced, and compared with earlier data for Ag on NaCl, and with recent calculations for these metals on both NaCl and MgO


1998 ◽  
Vol 4 (S2) ◽  
pp. 600-601
Author(s):  
John Rakovan ◽  
F. Hochella Michael

Since its invention inl982 scanning probe microscopy (SPM) has become an important analytical tool in every branch of physical science. The two most widely used types of SPM are atomic force Microscopy (AFM) and scanning tunneling microscopy (STM). Both AFM and STM allow measurement of the microtopography of a surface down to the atomic scale. Many spin-off applications such as lateral force and magnetic force allow measurement of a variety of the physical properties of a surface while imaging its microtopography. SPM can be done in both air and liquid and hence can be used to observe the interactions that take place at a solid-solution interface.SPM has been used in mineralogy and geochemistry since 1989. Here as in other applications the great strength of SPM is in the characterization of the heterogeneous nature of mineral surfaces and the ability to observe many geochemical processes in real time.


1995 ◽  
Vol 3 (4) ◽  
pp. 6-7
Author(s):  
Stephen W. Carmichael

For biologic studies, atomic force microscopy (AFM) has been prevailing over scanning tunneling microscopy (STM) because it has the capability of imaging non-conducting biologic specimens. However, STM generally gives better resolution than AFM, and we're talking about resolution on the atomic scale. In a recent article, Franz Giessibl (Atomic resolution of the silicon (111)- (7X7) surface by atomic force microscopy, Science 267:68-71, 1995) has demonstrated that atoms can be imaged by AFM.


2019 ◽  
Vol 116 (13) ◽  
pp. 5872-5877 ◽  
Author(s):  
Qingqing Yang ◽  
Qian Ma ◽  
Kate M. Herum ◽  
Chonghe Wang ◽  
Nirav Patel ◽  
...  

Nanoscale multipoint structure–function analysis is essential for deciphering the complexity of multiscale biological and physical systems. Atomic force microscopy (AFM) allows nanoscale structure–function imaging in various operating environments and can be integrated seamlessly with disparate probe-based sensing and manipulation technologies. Conventional AFMs only permit sequential single-point analysis; widespread adoption of array AFMs for simultaneous multipoint study is challenging owing to the intrinsic limitations of existing technological approaches. Here, we describe a prototype dispersive optics-based array AFM capable of simultaneously monitoring multiple probe–sample interactions. A single supercontinuum laser beam is utilized to spatially and spectrally map multiple cantilevers, to isolate and record beam deflection from individual cantilevers using distinct wavelength selection. This design provides a remarkably simplified yet effective solution to overcome the optical cross-talk while maintaining subnanometer sensitivity and compatibility with probe-based sensors. We demonstrate the versatility and robustness of our system on parallel multiparametric imaging at multiscale levels ranging from surface morphology to hydrophobicity and electric potential mapping in both air and liquid, mechanical wave propagation in polymeric films, and the dynamics of living cells. This multiparametric, multiscale approach provides opportunities for studying the emergent properties of atomic-scale mechanical and physicochemical interactions in a wide range of physical and biological networks.


1998 ◽  
Vol 4 (S2) ◽  
pp. 302-303
Author(s):  
D. Janigian ◽  
E. Morales ◽  
T. Muir ◽  
B. Garcia ◽  
J. Vesenka

The tendency of poly-G oligonucleotides to undergo self-assembly into helical nucleic acid tetramers have been termed G-quartets. Also known as G-wires, these structures retain their crystallographic determined dimensions better than duplex DNA when imaged with the atomic force microscope (AFM). Relative humidity has been known to affect both the resolution and measured height DNA strands on mica. The results below aim to develop a model that can be used to define the mechanical properties of G-wires by scanning probe microscopy investigations. G-wires were examined under a wide range of relative humidity to determine their tolerance to shear forces under the AFM, and to establish imaging conditions for hydration scanning tunneling microscopy (HSTM).The relative humidity dependence of G-wires were taken with 125 μm long, 20 μm wide silicon nitride cantilevers in contact AFM mode (spring constant ∼ 0.4 N/m) (Fig. 1).


2017 ◽  
Vol 114 (13) ◽  
pp. E2556-E2562 ◽  
Author(s):  
Martin Setvin ◽  
Jan Hulva ◽  
Gareth S. Parkinson ◽  
Michael Schmid ◽  
Ulrike Diebold

Activation of molecular oxygen is a key step in converting fuels into energy, but there is precious little experimental insight into how the process proceeds at the atomic scale. Here, we show that a combined atomic force microscopy/scanning tunneling microscopy (AFM/STM) experiment can both distinguish neutral O2 molecules in the triplet state from negatively charged (O2)− radicals and charge and discharge the molecules at will. By measuring the chemical forces above the different species adsorbed on an anatase TiO2 surface, we show that the tip-generated (O2)− radicals are identical to those created when (i) an O2 molecule accepts an electron from a near-surface dopant or (ii) when a photo-generated electron is transferred following irradiation of the anatase sample with UV light. Kelvin probe spectroscopy measurements indicate that electron transfer between the TiO2 and the adsorbed molecules is governed by competition between electron affinity of the physisorbed (triplet) O2 and band bending induced by the (O2)− radicals. Temperature–programmed desorption and X-ray photoelectron spectroscopy data provide information about thermal stability of the species, and confirm the chemical identification inferred from AFM/STM.


2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Jiaxin Yu ◽  
Amit Datye ◽  
Zheng Chen ◽  
Chao Zhou ◽  
Omur E. Dagdeviren ◽  
...  

AbstractThe onset of yielding and the related atomic-scale plastic flow behavior of bulk metallic glasses at room temperature have not been fully understood due to the difficulty in performing the atomic-scale plastic deformation experiments needed to gain direct insight into the underlying fundamental deformation mechanisms. Here we overcome these limitations by combining a unique sample preparation method with atomic force microscopy-based indentation, which allows study of the yield stress, onset of yielding, and atomic-scale plastic flow of a platinum-based bulk metallic glass in volumes containing as little as approximately 1000 atoms. Yield stresses markedly higher than in conventional nanoindentation testing were observed, surpassing predictions from current models that relate yield stress to tested volumes; subsequent flow was then established to be homogeneous without exhibiting collective shear localization or loading rate dependence. Overall, variations in glass properties due to fluctuations of free volume are found to be much smaller than previously suggested.


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