Formation of conical microstructures upon laser evaporation of solids

Dolgaev, Sergei I; Lavrishev, S. V.; Lyalin, A.A.; Simakin, A.V.; Voronov, V. V.; Shafeev, G. A.

doi:10.1007/s003390100530

Cited by 128 publications

(91 citation statements)

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“…The ripples found in these studies on 2,5-DHB crystal targets (non-covalent solid) are comparable to those observed on covalent solids (metal and semiconductors) and likely the result of similar mechanisms such as thermal capillary waves [14 -17] or Kelvin-Helmhotz instabilities at the interface between the molten layer and the plume [18]. Interestingly, such instabilities would explain the formation of conical microstructures upon laser evaporation of Si [19]. Similar microstructures were also observed on 2,5-DHB single crystals irradiated by UV flat-top laser beam [10].…”

Section: Irradiation Effects On 25-dhb Single Crystalsupporting

confidence: 65%

Irradiation effects in MALDI, ablation, ion production, and surface modifications. Part II: 2,5-dihydroxybenzoic acid monocrystals

Fournier

Marinach

Tabet

et al. 2003

J. Am. Soc. Mass Spectrom.

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Irradiation effects at low and high laser fluence on 2,5-dihydroxybenzoic acid large crystals were investigated. Contrary to what was observed for matrices as cinnamic acid derivatives, no chemical degradation of matrix is evidenced and continuous ablation as well as ion production resulted of extended irradiation in all the fluence range corresponding to classical matrix-assisted laser desorption /ionization. Ripples are formed on the base of the crater for a limited number of laser shots under moderate fluence. For extended irradiation, conical shape craters are formed with the axis of the crater oriented along the incident direction of the laser beam. A study of the craters showed that ablation through the ablated volume slowly varied with the laser fluence when a strong increase of ion production (matrix and analyte) was recorded. Ablation volume was found to vary non-linearly with the number of laser shots. On a same spot, the ablated volume and the ion production were measured as a function of the laser energy. With an increasing laser energy (or fluence), the ablated volume slowly increases when the ion production strongly increases. This gives evidence of a decoupling between ablation and ionization. is now a powerful method to produce ions of large molecules and its coupling with mass spectrometry (MS) provides a major analytical tool, particularly in proteomic studies and synthetic polymers characterization. To date, many of the methodologies developed for MALDI have been empirically determined. Indeed, the mechanisms involved in the ion production are very complex and cannot be experimentally studied in detail in all the time range of elementary processes. Briefly, these mechanisms involve ablation of molecules and aggregates from a solid state, the expansion of a plume from a very dense state to a very dilute gas. Ionization processes are likely involved in all the steps of the ablation and expansion. In addition, it is still difficult to predict for a small molecule absorbing at the laser wavelength whether it will be an effective or an inefficient matrix for the analysis of a given analyte. Some recent reviews gave an overview of the common ideas on these ionization mechanisms [2, 3] involving specific chemical reaction, ion-molecule reaction [2] or proton transfer in aggregates [3,4]. Generally, the mechanisms in MALDI are studied in two different ways. One deals with the ablation phenomenon mainly by molecular dynamics simulation [5,6] at very short scale (Ͻ Ͻ1 ns) and experimentally on the plume expansion [7] at medium and long-time scale (a few s to a few tens of s). The second deals with the ions produced by MALDI at the time scale of the ion time-of-flight, the role of the laser parameters [8], the target preparations and the nature of analyte ions. This subject occupies most publications in this field.In this article, we will focus on the relationship between the ablated volume and the analyte ion production and on the irradiation effects using large 2,5-dihydroxybenzoic acid single crystals...

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Section: Irradiation Effects On 25-dhb Single Crystalsupporting

confidence: 65%

Irradiation effects in MALDI, ablation, ion production, and surface modifications. Part II: 2,5-dihydroxybenzoic acid monocrystals

Fournier

Marinach

Tabet

et al. 2003

J. Am. Soc. Mass Spectrom.

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“…The enhanced light capture due to multiple reflections on such micropatterned silicon surfaces has led to the suggestion that they could form improved solar cells [8]. Conical spikes have been demonstrated in metals and semiconductors [8,16,17,18,19,20], polymers [21,22,23,24,25], composites [26] and ceramics [6,27,28]. The formation mechanism of ablation spikes shares common features with penitente formation.…”

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confidence: 99%

Controlled Irradiative Formation of Penitentes

Bergeron

Berger²,

Betterton

2006

Phys. Rev. Lett.

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Spike-shaped structures are produced by light-driven ablation in very different contexts. Penitentes 1-4 m high are common on Andean glaciers, where their formation changes glacier dynamics and hydrology. Laser ablation can produce cones 10-100 µm high with a variety of proposed applications in materials science. We report the first laboratory generation of centimeter-scale snow and ice penitentes. Systematically varying conditions allows identification of the essential parameters controlling the formation of ablation structures. We demonstrate that penitente initiation and coarsening requires cold temperatures, so that ablation leads to sublimation rather than melting. Once penitentes have formed, further growth of height can occur by melting. The penitentes intially appear as small structures (3 mm high) and grow by coarsening to 1-5 cm high. Our results are an important step towards understanding and controlling ablation morphologies.PACS numbers: 89.75. Kd,81.16.Rf,92.40.Rm,92.40.Sn, Penitentes 1-4 m high are found on glaciers in high mountain regions; laser ablation of materials can produce similar structures 10-100 µm high (Fig. 1). These structures are initiated by the same underlying physics: ablation caused by direct and reflected radiation. When radiation illuminates a surface, small surface depressions receive more reflected light than high points, leading to greater ablation in troughs and surface instability [1,2,3]. Penitente formation alters glacial energy balances and therefore affects local water runoff and flooding, feedback in climate dynamics, and paleo-climatic reconstruction [4,5]. In materials science, surface micropatterning via laser ablation can produce problematic surface roughness [6,7], but also has several proposed applications, including improved solar cells and electron-field emitters [8,9].Here we report the first laboratory generation of snow penitentes 1-5 cm high (Fig. 1). We characterize lab penitente formation and measure penitente coarsening. The lab setting allows controlled environmental conditions, and we can measure the evolution of lab penitentes visually in real time. Our experiments provide a model system for studying ablation morphologies.Penitentes occur on high-altitude snowfields exposed to intense sunlight, particularly in South America [10]. Expeditions studying penitentes have invoked the importance of sunlight [4,5,10,11] and cold, dry conditions (dew point below 0 o C), where melting is disfavored and ablation proceeds by sublimation [5,10]. Concentrated reflections and protection from wind increase penitente growth; higher temperature and humidity in the troughs of penitentes allows melting in the troughs [10]. This effect accelerates penitente growth, because sublimation of ice at 0 o C requires 7.8 times more energy than melting an equivalent volume, while the sublimating surface is evaporatively cooled, further lowering the surface temperature. Thus initiation of penitente growth requires a low dew point, but melting can occur during later height growth....

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“…Such precipitation has been observed for arsenic implanted in silicon. 15 Precipitation of sulfur into inactive clusters requires diffusion of silicon out of an area with a high concentration of sulfur or diffusion of sulfur into this type of area. While we cannot rule out the possibility that sulfur forms precipitates, the likelihood of diffusion of either silicon or sulfur on this timescale and these temperatures is unlikely.…”

Section: Discussionmentioning

confidence: 99%

“…We reported previously that irradiation with femtosecond laser pulses in an SF 6 environment results in a high concentration of sulfur (~1%) in the disordered surface layer [9,15]. Sulfur, with its two extra valence electrons, should increase the mobile electron concentration in the laser-altered surface layer, producing a difference in carrier concentration across the junction between the laser-altered surface and the undisturbed substrate.…”

Section: Bodymentioning

confidence: 99%

“…This observation, combined with the low electron mobility observed in the disordered surface layer, suggests that the gain is due to collisional ionization. Because the impact ionization rate for holes is nearly 1000 times less than that of electrons at these low electric field strengths [14], devices on p-doped substrates exhibit no gain.We reported previously that irradiation with femtosecond laser pulses in an SF 6 environment results in a high concentration of sulfur (~1%) in the disordered surface layer [9,15]. Sulfur, with its two extra valence electrons, should increase the mobile electron concentration in the laser-altered surface layer, producing a difference in carrier concentration across the junction between the laser-altered surface and the undisturbed substrate.…”

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confidence: 99%

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Microtextured Silicon Surfaces for Detectors, Sensors & Photovoltaics

Carey¹,

Mazur²

2005

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Executive SummaryWith support from this award we studied a novel silicon microtexturing process and its application in silicon-based infrared photodetectors. By irradiating the surface of a silicon wafer with intense femtosecond laser pulses in the presence of certain gases or liquids, the originally shiny, flat surface is transformed into a dark array of microstructures. The resulting microtextured surface has near-unity absorption from near-ultraviolet to infrared wavelengths well below the band gap. The high, broad absorption of microtextured silicon could enable the production of silicon-based photodiodes for use as inexpensive, room-temperature multi-spectral photodetectors. Such detectors would find use in numerous applications including environmental sensors, solar energy, and infrared imaging.The goals of this study were to learn about microtextured surfaces and then develop and test prototype silicon detectors for the visible and infrared. We were extremely successful in achieving our goals. During the first two years of this award, we learned a great deal about how microtextured surfaces form and what leads to their remarkable optical properties. We used this knowledge to build prototype detectors with high sensitivity in both the visible and in the near-infrared. We obtained room-temperature responsivities as high as 100 A/W at 1064 nm, two orders of magnitude higher than standard silicon photodiodes. For wavelengths below the band gap, we obtained responsivities as high as 50 mA/W at 1330 nm and 35 mA/W at 1550 nm, close to the responsivity of InGaAs photodiodes and five orders of magnitude higher than silicon devices in this wavelength region.The following Project Summary includes: Summary of important resultsPrior to receipt of this contract, we developed a process for microtexturing silicon surfaces with laser-assisted etching [1, 2]. The silicon sample is irradiated with a train of high-power ultrashort (100 fs) laser pulses in the presence of SF 6 or Cl 2 . Where the laser strikes the surface, material is etched away in a pattern of conical spikes, with the spike tips at the level of the unetched surface and the spike bases tens of microns below the surface. The surrounding non-irradiated silicon is unaffected, so areas as small as tens of microns on a side can be made. Figure 1 shows a scanning electron micrograph of a microtextured silicon surface.After etching, the silicon surface appears black to the eye (see Figure 2), and the surface absorbs over 90% of incident light from 0.25 µm to 2.5 µm [3]. Flat crystalline silicon absorbs only about 65% of incident light for wavelengths shorter than 1 µm, and absorbs less than 20% at longer wavelengths, with very low absorptance from 1.1 to 1.4 µm. Creation of a prototype microtextured silicon based p-i-n detector.Much of the work done in Year One and Year Two characterized the effects of laser fluence, shot number, gas pressure, and ambient gas on the absorption properties of microtextured silicon [4][5][6][7]. Using this data, we attempted to make...

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Formation of conical microstructures upon laser evaporation of solids

Cited by 128 publications

References 0 publications

Irradiation effects in MALDI, ablation, ion production, and surface modifications. Part II: 2,5-dihydroxybenzoic acid monocrystals

Irradiation effects in MALDI, ablation, ion production, and surface modifications. Part II: 2,5-dihydroxybenzoic acid monocrystals

Controlled Irradiative Formation of Penitentes

Microtextured Silicon Surfaces for Detectors, Sensors & Photovoltaics

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