摘要:

Evidence is presented which indicates that the way in which energetic ion bombardment accelerates the etching of Si in a fluorine environment is by a direct acceleration of the product formation step and not by damage‐enhanced chemistry. The use of fluorine coverage to characterize the etching process is discussed in detail and the assumption that the etch rate of Si can be decoupled into a spontaneous and an ion‐assisted contribution is questioned. Finally, examples of the influence of ion bombardment on Al(100)–Cl2, Cu(100)–Cl2at 310 °C, and Nb–XeF2are used to emphasize that some of the conclusions reached for the Si–XeF2system are not generally applicable to all gas–solid combinations.

ISSN:1071-1023    

DOI:10.1116/1.582996

出版商:American Vacuum Society    

年代:1985

数据来源: AIP

摘要:

The sputtering yield of Si when bombarded with a flux φAr+of low‐energy Ar+ions may be enhanced a few times when the Si surface is exposed simultaneously to Cl2fluxes φCl2about one order of magnitude larger than φAr+. The mechanism of this synergistic etching has been studied, using mass spectroscopy and time‐of‐flight techniques, for a φAr+of about 5×1014Ar+ cm−2 s−1at Ar+ion energies (Ep) from 0.25 to 5 keV, Cl2fluxes between 1015and 5×1016Cl2 cm−2 s−1andTin the range 300–625 K. As has been shown previously [J. Vac. Sci. Technol. A2, 487 (1984)] the main products of the synergistic reaction are atomic Si and Cl and molecular SiCl and SiCl2; the kinetic energy distributions of the molecular products consist of two parts, a Maxwell–Boltzmann and a collision cascade‐like distribution. The Maxwell–Boltzmann part decreases relative to the collision cascade‐like part whenTand/orEpare increased and/or φCl2is decreased. At the same time the collision cascade‐like part shifts to higher kinetic energies. These observations and the dependence of the relative contributions of the various products on φCl2,T, andEpcan be understood from the Ar+ion‐induced amorphization and Ar+ion‐induced mixing of adsorbed Cl into the top atomic layers of the Si, in which the molecular products SiCl and SiCl2are formed and also trapped, without further chemical binding to the surrounding bulk network; and for higherTalso by the competition between the thermal reaction, yielding SiCl4(and SiCl2), and synergistic etching. The yields of the molecular products SiCl and SiCl2show an increase relative to atomic Si and their binding energies are reduced when φCl2is enhanced and/orEpand/orTare decreased. It is suggested that this is due to an increasing concentration of Cl ion mixed into the top atomic layers of the Si.The experiments also suggest that the binding energy of atomic Si decreases systematically with increasing Cl concentration in the Si. The results show that the etching of Si with Cl2under simultaneous Ar+ion bombardment is not due to stimulation of the thermal reaction but to chemically enhanced physical sputtering.

ISSN:1071-1023    

DOI:10.1116/1.582997

出版商:American Vacuum Society    

年代:1985

数据来源: AIP

ISSN:1071-1023    

DOI:10.1116/1.582998

出版商:American Vacuum Society    

年代:1985

数据来源: AIP

摘要:

The use of surface‐enhanced Raman scattering as a tool for the elucidation of reaction mechanisms in heterogeneous catalysis is investigated. Following a short survey of surface analytical techniques, the advantages of surface Raman spectroscopy are discussed. Submonolayer sensitivity is achieved by making use of the surface enhancement effect. Adsorption and desorption phenomena of amines, which are of importance for catalytic dehydroamination reactions on copper surfaces, are studied using enhanced Raman scattering. Two models for the bonding of the amine to the surface are tested, by comparing the surface spectra with those of model compounds. Experiments are carried out on copper foils roughened by chemical etching, which exhibit strong surface enhancement. The design of the substrates is guided by advances in modeling the electromagnetic enhancement contribution. In particular the influences of particle size and of dipolar interactions between the particles on a surface must be taken into account.

ISSN:1071-1023    

DOI:10.1116/1.582999

出版商:American Vacuum Society    

年代:1985

数据来源: AIP

摘要:

Design considerations for a surface Raman spectrometer are reviewed. The behavior of the electromagnetic field near a conducting surface dictates the excitation and observation conditions for surface Raman spectroscopy; multichannel detection results in sufficient sensitivity to detect submonolayer quantities of material adsorbed on single crystal metal and semiconductor surfaces. Several examples, which illustrate the versatility of the technique, are presented.

ISSN:1071-1023    

DOI:10.1116/1.583000

出版商:American Vacuum Society    

年代:1985

数据来源: AIP

摘要:

Laser photons can interact with a gas‐solid system to promote heterogeneous reactions and to stimulate desorption. In this paper, a review is given on desorption processes induced by photon radiation. This includes laser‐induced thermal desorption and photodesorption by ultraviolet, visible, and infrared lasers. Relevant theories and recent experimental results are discussed with particular emphases on surface molecular dynamics and on assessing the quantum and the thermally assisted radiation effects.

ISSN:1071-1023    

DOI:10.1116/1.583001

出版商:American Vacuum Society    

年代:1985

数据来源: AIP

摘要:

The vibrational spectrum of molecules at or near an electrode surface can be obtained using subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) and electromodulated infrared spectroscopy (EMIRS). The large electric field existing at the electrode/solution interface is sufficient to induce dipole moments in highly polarizable molecules. The magnitude of the induced dipole moment is proportional to the electric field strength. As a result of this interaction some totally symmetric normal vibrations are made infrared active, and other bands appear in violation of the surface selection rule. This effect is known as the electrochemical Stark effect. Calculation of the expected absorption coefficients for the totally symmetric modes of adsorbed species gives values which are close to those observed experimentally. Experimental evidence ofAgmode activation of adsorbed pyrene is presented. The electric field dependence of the integrated absorption coefficient is demonstrated for acrylonitrile adsorbed on a gold electrode.

ISSN:1071-1023    

DOI:10.1116/1.583002

出版商:American Vacuum Society    

年代:1985

数据来源: AIP

摘要:

Multiatom cluster ions of 3 to 16 atoms/cluster have been observed in pulsed‐laser stimulated field desorption of silicon emitters. In a time‐of‐flight mass spectrum fine structures can be found in the mass line of every ion species, which are produced by isotope mixing in the clusters, and which will facilitate a correct identification of the charge state of the ions. The most abundant cluster ion species are Si2+4, Si2+5, and Si2+6. The numbers 4–6 may be called the magic numbers of the desorption process since they correspond to highly symmetric small units of atoms existing in Si surface layers. Most of the energy distributions of the ion species contain an exponentially decaying low energy tail which is produced by spontaneous dissociation of larger cluster ions, possibly due to photodissociation of larger cluster ions by the same laser pulses used for desorption. Water cluster ions of the form (H2O)mH+(m=1–12) can be observed in pulsed‐laser field desorption of ‘‘field condensed’’ water on a metal emitter surface. The appearance energy decreases monotonically with the cluster size, and also depends on the condition of the surface.

ISSN:1071-1023    

DOI:10.1116/1.583003

出版商:American Vacuum Society    

年代:1985

数据来源: AIP

摘要:

The photodesorption model of Gortel, Kreuzer, and collaborators in which a laser is resonantly coupled to an internal vibration mode of an absorbed molecule is considered. The importance of including anharmonicity of the internal vibration and a broadening of energy levels of a zero‐order Hamiltonian is demonstrated. A numerical calculation of the photodesorption as a function of a laser intensity is presented for a multilevel system of CH3F on NaCl and compared with experimental data. In comparison to previous assumption of only harmonic motion for the internal vibration where the values of the laser fluences for laser‐stimulated desorption are calculated to be too low, our results (saturation intensities ∼105–106W/cm2) are in closer agreement with experiment.

ISSN:1071-1023    

DOI:10.1116/1.583004

出版商:American Vacuum Society    

年代:1985

数据来源: AIP

摘要:

A technique is described for determining the surface diffusivity of a weakly bound adsorbate by measuring the kinetics of a spatially localized, laser‐beam‐driven surface photoreaction. The diffusivity is extracted from the experimental data by means of a Green’s function integral technique. The solution is numerically integrated in order to calculate the spatial and temporal evolution of the surface‐number‐density of parent and product molecules. The new technique has been applied to experiments with tetraethyl lead molecules adsorbed on sapphire.

ISSN:1071-1023    

DOI:10.1116/1.583005

出版商:American Vacuum Society    

年代:1985

数据来源: AIP