CAMOS Director: Dr. Kurt Kolasinski

SELIM

CAMOS

Ultrafast Laser Lab

Previous Meetings

Director of CAMOS
Dr. Kurt W. Kolasinski

Department of Chemistry

University of Virginia
PO Box 400319
McCormick Road
Charlottesville, VA 22904-4319 USA

Tel. (434) 982-2075 (o), (434) 924-3974
Fax. (434) 924-3710
E-mail : Kolasinski@virginia.edu

Kurt W. Kolasinski , BA (Pittsburgh) PhD (Stanford) CChem MRSC
Director CAMOS Ultrafast Laser Facility since July 2004. Moving to the Department of Chemistry, West Chester University in August 2006.

Research Interests

surface science / reaction dynamics / laser photochemistry / laser-surface interactions / nanotechnology / physical chemistry / chemical physics

My research centers on the study of dynamical processes at the surfaces of metals and semiconductors with a special emphasis on structure formation and laser-surface interactions. Along these lines we are studying photochemical and thermal reactive processes on surfaces. Of special interest are etching and growth reactions to form nanoscale and larger structures.

Dynamics of Adsorption and Desorption
I've long studied the simplest of surface chemical reactions, the adsorption and thermal desorption of small molecules from surfaces, particularly hydrogen on silicon. I've also recently reviewed stimulated desorption of hydrogen from silicon.

Currently together with Professor Ian Harrison, we are examining the dynamics of methane adsorption on metal surfaces. CH₄ is a molecule that is very important in a range of catalytic chemistry. Methane is the primary component of natural gas and steam reforming of methane over a nickel catalyst is the primary industrial source of hydrogen.

Photochemical & Chemical Modification of Si and Porous Si

Si is a pure elemental semiconductor, the most widely used in integrated circuit applications. Irradiation with laser light fundamentally alters the surface chemistry of silicon. For instance, whereas clean crystalline Si is virtually inert to aqueous hydrofluoric acid, irradiation of a Si crystal immersed in HF(aq) with a cw visible laser can lead to the formation of porous Si . Once formed, the reactivity of porous Si can also be altered by irradiation. We are studying these processes in order to determine what factors affect the photochemical reactivity of Si surface and to develop a mechanistic understanding of the photochemical reactions involved.

We have also extended this work to investigate the formation of porous silicon by purely chemical methods, so-called stain etching. In stain etching an oxidant is mixed with fluoride to form an aqueous solution that spontaneously produces porous silicon once a silicon crystal has been dipped in it. We have already shown that the fluoride can be provided not only by HF but also by NH₄HF₂. We are now investigating the role of the oxidant and how it can be used to control both the photoluminescence spectrum and the morphology of the por-Si film.

There is great interest in obtaining light from nanoscale Si [see links ( 1 ), ( 2 ) and ( 3 )] structures for optoelectronic, nanoelectronic and biomedical applications, even fuel cells .

Working with porous silicon has its advantages. Not only is there a lively community of researchers in the field but we also like to meet at the beach in Tenerife or Catalonia or sometimes on a volcano such as El Teide in Tenerife.

Silicon Pillar formation

Laser irradiation of Si crystals under the appropriate conditions can lead to the spontaneous formation of conical structures. When made with a femtosecond laser, these pillars can be ten or so micrometers long. The tips, however, are on the order of a few hundred nanometers or less. Using a nanosecond laser, the pillars are much larger, up to 100 µm or more and a few micrometers at their tip.

We are currently investigating the optical and chemical parameters that influence the growth and morphology of these pillar films. We will also study the geometric and electronic structure of these films by means of scanning tunneling microsco py, Raman spectrsocpy and electron microscopy, among other techniques.

We are studying methods of pretreatment that lead to ordered arrays of pillars and post-irradiation chemical treatments that lead to porous pillars or sharpened pillars. As shown in the micrograph, we have used to KOH etching of the pillars to produce 10 nm tips on 100 µm tall pillars. These are perhaps the highest aspect ratio features ever made in silicon.

Ultrafast Surface Photochemistry in the VUV

In a collaborative effort with Professor RE Palmer (Nanoscale Physics Research Laboratory, Birmingham) and Dr JS Foord (Physical & Theoretical Chemistry Laboratory , Oxford), a rather unique machine to study ultrafast (about 1 ps or less) photochemistry in the vacuum ultraviolet regime has been constructed. We make the required photons through a laser-based technique: high harmonic generation with an Ar-ion-pumped Ti:sapphire laser . This laser produces roughly 80 fs pulses at a wavelength near 800 nm. The output of the Ti:sapphire laser is focused into a rare gas. A nonlinear interaction between the laser field and the atoms in the rare gas jet creates the photons that we are after: ~10-40 eV or 120-30 nm. We have studied the photochemistry of O₂ adsorbed on graphite. This was the first use of HHG to initiate surface photochemistry. To learn more about lasers, try this tutorial.

This project is part of a TMR Network which you can learn more about here . Being part of a TMR network is often hard work, including walking up snowy moutain roads and skiing.

Selected Recent Publications:

Laser assisted and wet chemical etching of silicon nanostructures, Kurt W. Kolasinski, David Mills and Mona Nahidi, J. Vac. Sci. Technol. A 24, 1474-1479 (2006).

Silicon nanostructures from electroless electrochemical etching, Kurt W. Kolasinski,Curr. Op. Solid State & Mater. Sci. 9, 73-83 (2005).

Surface photochemistry in the VUV and XUV: High harmonic generation, H₂O and O₂, Kurt W. Kolasinski, J. Phys Cond. Matter 18, S1655-S1675 (2006).

Solidification driven extrusion of spikes during laser melting of silicon pillars, David Mills and Kurt W. Kolasinski, Nanotechnology 17, 2741-2744 (2006).

Using effusive molecular beams and microcanonical unimolecular rate theory to characterize CH₄ adsorption on Pt(111), Kristy M. DeWitt, Leticia Valadez, Heather Abbott, Kurt W. Kolasinski and Ian Harrison, J. Phys. Chem. B 110, 6705-6713 (2006).

Effusive molecular beam study of C₂H₆ dissociation on Pt(111), Kristy M. DeWitt, Leticia Valadez, Heather Abbott, Kurt W. Kolasinski and Ian Harrison, J. Phys. Chem. B 110, 6714-6720 (2006).

The effects of stain etchant composition on the photoluminescence and morphology of porous silicon, Mona Nahidi and Kurt W. Kolasinski, J. Electrochem. Soc., 153, C19–C26 (2006).

The Composition of Fluoride Solutions, Kurt W. Kolasinski, J. Electrochem. Soc., 152 (9), J99–J104 (2005).

Non-Adiabatic and Ultrafast Dynamics of Hydrogen Adsorbed on Silicon, K.W. Kolasinski, Curr. Op. Solid State & Mater. Sci, 8, 332-333 (2004).

Non-lithographic method to form ordered arrays of silicon pillars and macropores, David Mills and Kurt W. Kolasinski, J. Phys D. 38 (2005) 632-636.

Laser-assisted restructuring of silicon over nano-, meso- and macro-scales, K.W. Kolasinski, in Recent Research Developments in Applied Physics, edited by S.G. Pandalai (Transworld Research Network, Kerala, India, 2004), Vol. 7, pp. 267-292.

Laser-etched silicon pillars and their porosification, David Mills and Kurt W. Kolasinski, J. Vac. Sci. Technol. A 22, 1647 (2004).

Arranged silicon conical spike structures from optical diffraction and ultrafast laser etching in halogen gas, D. Riedel, J.L. Hernández-Pozos, K.W. Kolasinski and R.E. Palmer, Appl. Phys. A 78, 381 2004 .

The mechanism of Si etching in fluoride solutions, K.W. Kolasinski, Phys. Chem. Chem. Phys., 5, 1270 (2003) .