共查询到20条相似文献,搜索用时 0 毫秒
1.
The pendant drop technique was used to characterize the adsorption behavior of n-dodecane-1-thiol and n-hexane-1-thiol-capped gold nanoparticles at the hexane–water interface. The adsorption process was studied by analyzing the
dynamic interfacial tension versus nanoparticle concentration, both at early times and at later stages (i.e., immediately
after the interface between the fluids is made and once equilibrium has been established). A series of gold colloids were
made using nanoparticles ranging in size from 1.60 to 2.85 nm dissolved in hexane for the interfacial tension analysis. Following
free diffusion of nanoparticles from the bulk hexane phase, adsorption leads to ordering and rearrangement of the nanoparticles
at the interface and formation of a dense monolayer. With increasing interfacial coverage, the diffusion-controlled adsorption
for the nanoparticles at the interface was found to change to an interaction-controlled assembly and the presence of an adsorption
barrier was experimentally verified. At the same bulk concentration, different sizes of n-dodecane-1-thiol nanoparticles showed different absorption behavior at the interface, in agreement with the findings of Kutuzov
et al. (Phys Chem Chem Phys 9:6351–6358, 2007). The experiments additionally demonstrated the important role played by the capping agent. At the same concentration, gold
nanoparticles stabilized by n-hexane-1-thiol exhibited greater surface activity than gold nanoparticles of the same size stabilized by n-dodecane-1-thiol. These findings contribute to the design of useful supra-colloidal structures by the self-assembly of alkane-thiol-capped
gold nanoparticles at liquid–liquid interfaces. 相似文献
2.
The photocurrent and spectral response characteristics of gallium arsenide (GaAs) are obtained by a multiinformation measurement system, and the evolution of the photocurrent versus the Cs:O flux ratio is investigated. The experimental results show that the photocurrent increases approximately exponentially after the first exposure to Cs until a maximum sensitivity is reached, the detailed evolution process and the ultimate photocurrent are different for different samples. These differences are analysed, and according to the process of coadsorption of Cs and oxygen on GaAs, an equation is presented to explain the increase of photocurrent. 相似文献
3.
The modulation reflectivity technique was used to detect the optical transition on clean cleaved (1 1 0) surfaces of III–V compounds. In the spectra obtained the optical transitions involving surface eigenstates were identified. 相似文献
4.
The adsorption and thermal chemistry of γ-butyrolactone (GBL) on the (1 1 1) surface of Pd and Pt has been investigated using a combination of high resolution electron energy loss spectroscopy (HREELS) and temperature programmed desorption (TPD). HREELS results indicate that GBL adsorbs at 160 K on both surfaces through its oxygenate functionality. On Pd(1 1 1), adsorbed GBL undergoes ring-opening and decarbonylation by 273 K to produce adsorbed CO and surface hydrocarbon species. On Pt(1 1 1), very little dissociation is observed using HREELS, with almost all of the GBL simply desorbing. TPD results are consistent with decarbonylation and subsequent dehydrogenation reactions on Pd(1 1 1), although small amounts of CO 2 are also detected. TPD results from Pt(1 1 1) indicate that a small proportion of adsorbed GBL (perhaps on defect sites) does undergo ring-opening to produce CO, CO 2, and H 2. These results suggest that the primary dissociation pathway for GBL on Pd(1 1 1) is through O-C scission at the carbonyl position. Through comparisons with previously published studies of cyclic oxygenates, these results also demonstrate how ring strain and functionality affect the ring-opening rate and mechanism. 相似文献
5.
GaAs spin-polarized electron source is a new kind of electron source, where the GaAs semiconductor crystal is used as a photocathode under the irradiation of helicity light. In this paper the activation process of the GaAs spin-polarized electron source is unvestigated experimentally in detail, during which the negative electron affinity of the photo cathode should be achieved more carefully by absorbing the caesium and oxygen on the surface of the GaAs crystal under ultrahigh vacuum conditions. Besides the different activation processes, the important physical parameters are studied to achieve the optimum activation results. At the same time the stability and lifetime of the polarized electron beam are explored for future experiments. Some important experimental data have been acquired. 相似文献
8.
The adsorption of CO molecules onto ytterbium nanofilms with their thickness varying from 1 to 16 monolayers is studied. The dependences of the number of adsorbed CO molecules (adsorption isotherms) and the work function of ytterbium films on the dose of carbon monoxide are examined. It is demonstrated that both the number of adsorbed molecules and the work function depend (under equal conditions) on the nanofilm thickness; in other words, a size effect is revealed. It is found that this size effect is induced by the electrostatic interaction between the conduction electrons of ytterbium and the electrons localized on the nanofilm surface, which establish bonding between the surface and CO molecules. This interaction depends on the film thickness and limits the number of CO molecules that may be adsorbed onto the surface of a film with a given thickness. 相似文献
9.
In this work, first-principles modeling techniques are used to investigate the mechanism(s) of adsorption of molecular oxygen on the GaAs(0 0 1)-(2 × 4) surface. The reaction of adsorption was modeled using ab-initio molecular dynamics at constant temperature for two thermal regimes, i.e. 300 K and 680 K, respectively. The resulting adsorbate configurations were relaxed using density functional theory and the adsorption energies were subsequently computed. Our results suggest a dominant mechanism of adsorption described by molecular dissociation, followed by oxygen insertion in the Ga-As bonds, bridging Ga-O-As chemical bonds. The electronic properties of the clean reconstructed GaAs(0 0 1) surface and the ones obtained after O 2 adsorption were computed. It is found that for the most stable adsorbate configuration, where oxygen is incorporated in a Ga-O-As unit, the associated density of electronic states is free of defect levels within the GaAs band gap region. 相似文献
10.
A magnetic memory effect is observed in the absorption of electromagnetic waves of 20–70 MHz in YBa 2Cu 3O 7at 77–300 K. 相似文献
11.
The adsorption and decomposition of formic acid on NiO(111)-p(2 × 2) films grown on Ni(111) single crystal surface were studied by temperature-programmed desorption (TPD) spectroscopy. Exposure of formic acid at 163 K resulted in both molecular adsorption and dissociation to formate. The adsorbed formate underwent further dissociation to H 2, CO 2 and CO. H 2 and CO 2 desorbed at the same temperatures of 340, 390 and 520 K, while CO desorbed at 415 and 520 K. The desorption features varied with the formic acid exposure. Two reaction channels were identified for the decomposition of formate under equilibrium with gas-phase formic acid with a pressure of 2.5 × 10 −4Pa, one preferentially producing H 2 and CO 2 with an activation energy of 22 ± 2 kJ mol −1 and the other preferentially producing CO and H 2O with an activation energy of 16 ± 2 kJ mol −1. The order of both reaction paths was 0.5 with respect to the pressure of formic acid. 相似文献
12.
This paper reports the formation of Ge nanoclusters in a multi-layer structure consisting of alternating thin films of Ge-doped
silica glass and SiGe, deposited by plasma-enhanced chemical vapor deposition (PECVD) and post annealed at 1100 °C in N 2 atmosphere. We studied the annealed samples by transmission electron microscopy (TEM) and Raman spectroscopy. As-deposited
and annealed samples were analyzed by secondary ion mass spectroscopy (SIMS). TEM investigation shows that Ge nanoclusters
were formed in the as-deposited SiGe layer and the SiGe layer was transformed into a silicon dioxide layer embedded with Ge
nanoclusters after annealing. These nanoclusters are crystalline and varied in size. There were no clusters in the Ge-doped
glass layer. Raman spectra verified the existence of crystalline Ge clusters. The positional shift of the Ge vibrational peak
with the change of the focus depth indicates that the distribution of the stress applied to the Ge clusters varies with depth.
SIMS measurements show clearly the dramatic O increase in the as-deposited SiGe layer after annealing. The creation of Ge
nanoclusters by the combination of PECVD and annealing makes possible the application in complicated waveguide components.
PACS 81.07.Bc; 78.66.Jg; 42.65.Wi 相似文献
13.
We studied the adsorption, surface diffusion, and penetration, i.e. the initial processes of a Ni adatom on the H-terminated Si(001)-(2×1) surface by the first-principles theoretical calculations. As concerns the adsorption, two different types were found. When Ni is deposited onto the Si dimer row, it once captures H from the dimer Si, though it eventually returns H, with no activation energy barrier. Then, Ni moves to the most stable site, which is the off-centered bridge (B) site between the dimer rows, with the activation energy of 0.65 eV. On the other hand, Ni deposited between the dimer rows captures no H and moves to the B site without the energy barrier. Thus an adsorbed Ni atom invariably arrives at the most stable B site at the room temperature. As for the surface diffusion, it needs the activation energies of 0.66 and 1.19 eV for Ni to migrate from the B site in the directions parallel and perpendicular to the dimer row, respectively. Therefore, we concluded that the surface diffusion of Ni is restricted in the valley between the dimer rows at the room temperature. Furthermore, since the penetration of Ni is blocked on this surface, it was also concluded that the surface hydrogenation suppresses silicidation. 相似文献
14.
Transient characteristics of the InGaP–GaAs–InGaAs (quantum well)-GaAs transistor laser are studied. Rate equations are numerically solved to obtain the response of current density and photon density. Expression of resonance frequency $f_{r}$ is obtained by solving the rate equations analytically. It has been found that the $f_{r}$ increases with decreasing spontaneous carrier lifetime and with increasing value of the bias current density. 相似文献
15.
Cross sectional and plane-view transmission electron microscopy (X- and PV-TEM) were used to investigate the initial growth phase of 5, 10, 20 and 40 nm thick Ni 1-xFe x ( x=0.6–0.8) films, prepared on MgO(0 0 1) covered with a buffer layer of Fe or Ni as well as on naked MgO(0 0 1). The 100 nm thick buffer layers of Fe and Ni were pre-grown on MgO(0 0 1). All of Ni 0.20Fe 0.80, Ni 0.40Fe 0.60, Fe and Ni films could be epitaxially grown at 250°C by dc-biased plasma sputtering at 2.9 kV in pure Ar gas.The films of Ni 0.20Fe 0.80 and Ni 0.40Fe 0.60 were grown in their own stable phase, bcc and fcc on MgO(0 0 1), respectively. However, Ni 0.20Fe 0.80 film could be grown in fcc phase pseudomorphic with Ni(0 0 1) up to 20 nm thick on Ni/MgO(0 0 1), while Ni 0.40Fe 0.60 film in bcc phase pseudomorphic with Fe(0 0 1) up to 10 nm thick on Fe/MgO(0 0 1). With increasing thickness, their growth phases transformed into their own stable phases. Whether or not the pseudomorphic phase may be induced and what its critical thickness may be should depend primarily on the lattice misfit between the crystal planes in contact. The growth mode of Ni 0.40Fe 0.60 film was investigated more in details to be compared with the simulations of the average strain energy versus thickness and with those of the critical thickness of the pseudomorphic films versus the lattice misfit between the contacted crystal planes. 相似文献
16.
The position of Cs on the (1 × 2) missing row reconstructed Ag(110) surface was determined by X-ray diffraction for two different Cs-coverages: θCs = 0.2 and θCs = 0.3. The Cs was found to be adsorbed in incommensurate chains in the troughs of the missing row with an average adsorption height of 1.7 Å ( θCs = 0.2) and 1.4 Å ( θCs = 0.3) above the topmost Ag layer. The apparent contradiction to the classical picture of alkali adsorption, which expects an increase of the Cs adsorption height with coverage, might be partly resolved by introducing a fraction of commensurately adsorbed Cs at θCs = 0.2. 相似文献
17.
一、前言负电子亲和势(NEA)材料的发现是光电发射材料领域中一项开拓性进展。尔后,人们对比GaAs带隙更窄的其它Ⅲ-V族半导体进行了更为广泛的研究,旨在获得NEA状态,为一些工作在1μm或更高波段的红外系统选择高效率光电阴极推动了研究工 相似文献
18.
The chemistry of Cr(CO) 6 on the Fe 3O 4(111) surface termination of α-Fe 2O 3(0001) was explored using temperature programmed desorption (TPD), Auger electron spectroscopy (AES), static secondary ion mass spectrometry (SSIMS) and low energy electron diffraction (LEED) both with and without activation from an oxygen plasma source. No thermal decomposition of Cr(CO) 6 was detected on the surface in the absence of O 2 plasma treatment, with first layer molecules desorbing in TPD at 215 K from a close-packed overlayer. The interaction of first layer Cr(CO) 6 with the Fe 3O 4(111)-termination was weak, desorbing only ~ 30 K above the leading edge of the multilayer state. Activation of multilayer coverages of Cr(CO) 6 with the O 2 plasma source at 100 K resulted in complete conversion of the outer Cr(CO) 6 layers, presumably to a disordered Cr oxide film, with Cr(CO) 6 molecules near the surface left unaffected. Absence of CO or CO 2 desorption states suggests that all carbonyl ligands are liberated for each Cr(CO) 6 molecule activated by the plasma. AES and SSIMS both show that O 2 plasma activation of Cr(CO) 6 results in a carbon-free surface (after desorption of unreacted Cr(CO) 6). LEED, however, shows that the Cr oxide film was disordered at 600 K and likely O-terminated based on subsequent water TPD. Attempts to order the film at temperatures above 650 K resulted in dissolution of Cr into the α-Fe 2O 3(0001) crystal based on SSIMS, an observation linked to the Fe 3O 4(111) termination of the surface and not to the properties of α-Cr 2O 3/α-Fe 2O 3 corundum interface. Nevertheless, this study shows that O 2 plasma activation of Cr(CO) 6 is an effective means of depositing Cr oxide films on surfaces without accompanying carbon contamination. 相似文献
19.
The adsorption characteristics of Cs on GaN(0001) and GaN(000) surfaces with a coverage from 1/4 to 1 monolayer have been investigated using the density functional theory with a plane-wave ultrasoft pseudopotential method based on first-principles calculations.The results show that the most stable position of the Cs adatom on the GaN(0001) surface is at the N-bridge site for 1/4 monolayer coverage.As the coverage of Cs atoms at the N-bridge site is increased,the adsorption energy reduces.As the Cs atoms achieve saturation,the adsorption is no longer stable when the coverage is 3/4 monolayer.The work function achieves its minimum value when the Cs adatom coverage is 2/4 monolayer,and then rises with Cs atomic coverage.The most stable position of Cs adatoms on the GaN(000) surface is at H3 site for 1/4 monolayer coverage.As the Cs atomic coverage at H3 site is increased,the adsorption energy reduces,and the adsorption is still stable when the Cs adatom coverage is 1 monolayer.The work function reduces persistently,and does not rise with the increase of Cs coverage. 相似文献
20.
It is determined by electron microscopy that the contact layer in the Sn–(Bi + 30 wt % Pb) system contains separate solid inclusions, while the contact layer in the Sn–(Bi + 40 wt % Pb) system is microheterogeneous. The observed structural states of alloys in the contact layers are explained by a change in the concentration of the initial contacting samples. The effect of the alloy structure and electromigration on the kinetics of contact melting is found. 相似文献
|