共查询到10条相似文献,搜索用时 203 毫秒
1.
C. Wesenberg O. Autzen E. Hasselbrink 《Applied Physics A: Materials Science & Processing》2007,88(3):559-569
The photochemistry of SO2 on thin epitaxial Ag films (5–60 nm) deposited on Si(100) has been studied using laser light with the wavelengths of 266,
355, and 532 nm. SO2 desorbs with cross sections of 1.7×10-19,1.7×10-20 and 2.9×10-21 cm2, respectively. The average translation energy, 〈Etrans/2k〉, is 440 K for 266 and 355 nm light, and 270 K for 532 nm light. Cross sections for a 60 nm thick Ag film are practically
identical to the ones for Ag(111) as the substrate. An increase by a factor of ∼3.5 is observed when the film thickness is
reduced to 5 nm for 266 and 355 nm light. No significant change is observed for 532 nm excitation. The film thickness has
no significant influence on the translational energy of the photodesorbed molecules. The data are discussed in connection
with the change of absorptivity of the metal film–semiconductor system. A model is put forward which takes into account the
light absorption in the Si substrate and the reduced relaxation of excited electrons in Si. Modelling indicates that electrons
excited in the Si substrate with energies and parallel momenta not allowed in Ag contribute to the surface chemistry after
crossing the gap in the projected band structure of Ag(111).
PACS 82.45.MP; 73.63.-b; 82.50.Bc 相似文献
2.
A simple method for patterning of thin (15–650 nm) aluminum films on glass substrates by direct, low-power, laser-thermal
oxidation in water under common laboratory conditions is demonstrated. Local heating of the metal film enhances the formation
of aluminum oxide (hydrargillite, Al2O3–3H2O) and provokes breakdown of the passivation layer followed by local corrosion at temperatures close to the boiling point
of water. Moving the focus of an Ar-ion laser (λ=488 nm) over the aluminum film with a speed of several μm/s yields grooves
flanked by hydrargillite. Upon through oxidation of the metal these structures act as electrically insulating domains. Depending
on the film thickness, the minimum width of the line structures measures between 266 nm and 600 nm. The required laser irradiation
power ranges from 1.7 mW to 30 mW. It is found that the photo-thermal oxidation process allows for writing of two-dimensional
electrode patterns.
Received: 16 July 2001 / Accepted: 23 July 2001 / Published online: 2 October 2001 相似文献
3.
M. Sanz M. López-Arias E. Rebollar R. de Nalda M. Castillejo 《Journal of nanoparticle research》2011,13(12):6621-6631
Nanostructured CdS and ZnS films on Si (100) substrates were obtained by nanosecond pulsed laser deposition at the wavelengths
of 266 and 532 nm. The effect of laser irradiation wavelength on the surface structure and crystallinity of deposits was characterized,
together with the composition, expansion dynamics and thermodynamic parameters of the ablation plume. Deposits were analyzed
by environmental scanning electron microscopy, atomic force microscopy and X-ray diffraction, while in situ monitoring of
the plume was carried out with spectral, temporal and spatial resolution by optical emission spectroscopy. The deposits consist
of 25–50 nm nanoparticle assembled films but ablation in the visible results in larger aggregates (150 nm) over imposed on
the film surface. The aggregate free films grown at 266 nm on heated substrates are thicker than those grown at room temperature
and in the former case they reveal a crystalline structure congruent with that of the initial target material. The observed
trends are discussed in reference to the light absorption step, the plasma composition and the nucleation processes occurring
on the substrate. 相似文献
4.
Hartmann L Gorbatschow W Hauwede J Kremer F 《The European physical journal. E, Soft matter》2002,8(2):145-154
The molecular dynamics in thin films (18 nm-137 nm) of isotactic poly(methyl methacrylate) (i-PMMA) of two molecular weights
embedded between aluminium electrodes are measured by means of dielectric spectroscopy in the frequency range from 50 mHz
to 10 MHz at temperatures between 273 K and 392 K. The observed dynamics is characterized by two relaxation processes: the
dynamic glass transition (α-relaxation) and a (local) secondary β-relaxation. While the latter does not depend on the dimensions
of the sample, the dynamic glass transition becomes faster (≤2 decades) with decreasing film thickness. This results in a
shift of the glass transition temperature T
g to lower values compared to the bulk. With decreasing film thickness a broadening of the relaxation time distribution and
a decrease of the dielectric strength is observed for the α-relaxation. This enables to deduce a model based on immobilized
boundary layers and on a region displaying a dynamics faster than in the bulk. Additionally, T
g was determined by temperature-dependent ellipsometric measurements of the thickness of films prepared on silica. These measurements
yield a gradual increase of T
g with decreasing film thickness. The findings concerning the different thickness dependences of T
g are explained by changes of the interaction between the polymer and the substrates. A quantitative analysis of the T
g shifts incorporates recently developed models to describe the glass transition in thin polymer films.
Received 12 August 2001 and Received in final form 16 November 2001 相似文献
5.
Laser-induced periodic surface structures (LIPSS) were generated on oriented and amorphous thick, as well as on spin-coated
thin, poly-carbonate films by polarized ArF excimer laser light. The influence of the film structure and thickness on the
LIPSS formation was demonstrated. Below a critical thickness of the spin-coated films the line-shaped structures transformed
into droplets. This droplet formation was explained by the laser-induced melting across the whole film thickness and subsequent
de-wetting on the substrate. The thickness of the layer melted by laser illumination was computed by a heat-conduction model.
Very good agreement with the critical thickness for spin-coated films was found. The original polymer film structure influences
the index of refraction of the thin upper layer modified by the laser treatment, as was proven by the dependence of the structure’s
period on the angle of incidence both for ‘s’- and ‘p’-polarized beams. The effect of the original surface roughness – grains in thick films or holes in thin films –
was studied using atomic force microscopy. It was shown that the oblique incidence of ‘s’-polarized beams results in an intensity confinement in the direction of the forward scattering and in asymmetrical interference
pattern formation around these irregularities. A new, two-dimensional grating-like structure was generated on spin-coated
films. These gratings might be used as a special kind of mask.
Received: 10 July 2001 / Accepted: 23 July 2001 / Published online: 30 August 2001 相似文献
6.
O.M. Hussain K. Srinivasa Rao K.V. Madhuri C.V. Ramana B.S. Naidu S. Pai J. John R. Pinto 《Applied Physics A: Materials Science & Processing》2002,75(3):417-422
Molybdenum trioxide thin films were prepared by reactive pulsed laser deposition on Corning 7059 glass substrates. The influence
of oxygen partial pressure and deposition temperature on the structure, surface morphology and optical properties of these
films was studied to understand the growth mechanism of MoO3 thin films. The films formed at 473 K in an oxygen partial pressure of 100 mTorr exhibited predominantly a (0k0) orientation,
corresponding to an orthorhombic layered structure of α-MoO3. The evaluated optical band gap of the films was 3.24 eV. The crystallite size increased with increase of deposition temperature.
The films formed at an oxygen partial pressure of pO2=100 mTorr and at a deposition temperature greater than 700 K exhibited both (0k0) and (0kl) orientations, representing α-β
mixed phases of MoO3. The films formed at an oxygen partial pressure less than 100 mTorr were found to be sub-stoichiometric with α-β mixed phases.
The investigation revealed the growth of polycrystalline and single-phase orthorhombic-layered-structure α-MoO3 thin films with composition nearly approaching the nominal stoichiometry at moderate substrate temperatures in an oxygen
partial pressure of 100 mTorr.
Received: 9 April 2001 / Accepted: 6 August 2001 / Published online: 17 October 2001 相似文献
7.
V. A. Svetlichnyi M. P. Samtsov O. K. Bazyl’ O. V. Smirnov D. G. Mel’nikov A. P. Lugovskii 《Journal of Applied Spectroscopy》2007,74(4):524-532
We present results of experimental and theoretical studies of the optical characteristics of a new indotricarbocyanine dye
that is capable of effectively limiting the power of laser radiation in the visible spectral range. The spectral-luminescent
and energy characteristics of the dye molecules and their absorption spectra from the excited state with nanosecond resolution
are investigated experimentally. Quantum-chemical methods are used to calculate electronic absorption spectra from the ground
(S0 → Sn) and excited (S1 → Sn) states and to determine the nature of electronic states of the molecule and the rate constants of intramolecular photophysical
processes. The results of the theoretical research agree with experimental data. It is shown that the investigated dye has
singlet-singlet absorption at 400–600 nm. Nonlinear absorption of the dye upon excitation by radiation of the second harmonic
of a Nd:YAG laser is studied by z-scanning with an open diaphragm. The ratio of dye absorption cross sections from the excited
and ground states at 532 nm is determined in the framework of a three-level model. The results are compared with those for
previously studied compounds.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 4, pp. 473–480, July–August, 2007. 相似文献
8.
Linear and nonlinear absorptance in Al2O3 films of different optical thicknesses are investigated using an ArF laser calorimeter. While the linear absorptance at 193
nm shows the expected linear increase, nonlinear absorptance increases quadratically with increasing film thickness. Thus,
it cannot be described by a constant nonlinear absorption coefficient β. The experimental findings are explained by a simple
phenomenological approach using excited states with a finite interaction length longer than the actual film thickness. a new
material constant Γ is introduced, which describes the nonlinear absorptance behavior correctly.
Received: 19 May 2000 / Accepted: 22 May 2000 / Published online: 13 July 2000 相似文献
9.
D.M. Bubb B. Toftmann R.F. Haglund Jr. J.S. Horwitz M.R. Papantonakis R.A. McGill P.W. Wu D.B. Chrisey 《Applied Physics A: Materials Science & Processing》2002,74(1):123-125
Thin films of the biodegradable polymer poly(DL-lactide-co-glycolide) (PLGA) were deposited using resonant infrared pulsed
laser deposition (RIR-PLD). The output of a free-electron laser was focused onto a solid target of the polymer, and the films
were deposited using 2.90 (resonant with O-H stretch) and 3.40 (C-H) μm light at macropulse fluences of 7.8 and 6.7 J/cm2, respectively. Under these conditions, a 0.5-μm thick film can be grown in less than 5 min. Film structure was determined
from infrared absorbance measurements and gel permeation chromatography (GPC). While the infrared absorbance spectrum of the
films is nearly identical with that of the native polymer, the average molecular weight of the films is a little less than
half that of the starting material. Potential strategies for defeating this mass change are discussed.
Received: 22 August 2001 / Accepted: 23 August 2001 / Published online: 17 October 2001 相似文献
10.
X.Y. Chen B. Yang T. Zhu K.H. Wong J.M. Liu Z.G. Liu 《Applied Physics A: Materials Science & Processing》2002,74(4):567-569
(110)-textured MgO films were grown on Si (100) with etching and without etching by pulsed laser deposition. The deposited
MgO films were shown to be droplets-free. The MgO film was used as a buffer layer to further grow Pt film on Si (100). A completely
(110)-oriented Pt film was obtained on such a buffer layer and its surface is very smooth with a roughness of about 7.5 nm
over 5×5 μm. This can be used as a new oriented Pt electrode on silicon for devices.
Received: 23 January 2001 / Accepted: 27 April 2001 / Published online: 27 June 2001 相似文献