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Direct Nanoprototyping of Functional Materials via Focused Electron Beam
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

During recent years the demand for nanoscale materials with tailor-made functional properties as bulk species, is continuously and progressively rising for such fields as e.g. micro- and nano-electronics, plasmonics, spintronics, bio-technology, bio-sensing and life sciences. Preserving and / or improving properties of functional materials with their simultaneous size reduction and high-resolution site-specific positioning is indeed very challenging, for both conductors and insulators.

One of the advanced nanoprototyping methods that can be utilized for this purpose is the Electron-Beam-Induced Deposition, or shortly EBID. This process is based on a local decomposition by a focused electron beam of a precursor gas molecules adsorbed on the sample’s surface. The beauty of this method is that it gives a unique possibility of rapid creation of site-specific nanoscale 3D structures of precise shape in a single operation. It’s an additive process that can be easily combined with other patterns.

However, besides all the benefits, EBID has some constraints, in particular low purity of the deposited materials, due to the organometallic nature of the used precursors. Chemical composition of EBID patterns is strongly dependent on the chosen gas chemistry, the substrate, many deposition parameters and post-treatment processes applied to the deposited structures.

In our research we focused on deposition of Co, Au, SiO2, C, W and Pt, their purification and shape control. And this thesis presents an overview of our accomplishments in this field.

Depending on the gas chemistry of interest, three major purification approaches of EBID-grown materials were tested out:

- Post-deposition annealing: in air and in the controlled atmosphere,

- Deposition onto a preheated substrate,

- Deposition in the presence of reactive gases.

As a result, a dramatic purity improvement was observed and a significant advancement was achieved in creation of high-purity gold, cobalt and silicon dioxide nanoscale structures. In particular:

1)   For the Me2Au(acac) precursor, we developed a nanofabrication routine combining application of wetting buffer layers, fine tuning of EBID parameters and subsequent post-annealing step, which led to formation of high-purity planar and high aspect ratio periodic Au nanopatterns. We also describe the adopted and gently adjusted wet etching method of undesirable buffer layer removal, required in some cases for the further device application.

2)   For the Co2(CO)8 precursor, in-situ seeded growth in conjunction with EBID at the elevated substrate temperature resulted in a deposition of pure nanocrystalline Co with magnetic and transport properties close to the bulk material.

3)   For the tetraethyl orthosilicate precursor, or shortly TEOS, assisting of the deposition process with the additional oxygen supply led to the EBID of carbon-free amorphous insulating Si-oxide, with the absorption and refraction properties comparable to those for fused silica.

Several applications of EBID nanopatterns are also discussed.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , x, 85 p.
Keyword [en]
EBID, nanoprototyping, nanopatterning, nanoscale, nanostructure, purification, Au, Co, SiO2, dimethyl gold acetylacetonate, dicobalt octacarbonyl, TEOS, Dual Beam
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-132365ISBN: 978-91-7501-907-9 (print)OAI: oai:DiVA.org:kth-132365DiVA: diva2:659580
Public defence
2013-11-15, F3, Lindstedtsvägen 26, Kungl Tekniska Högskolan, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20131028

Available from: 2013-10-28 Created: 2013-10-25 Last updated: 2013-10-28Bibliographically approved
List of papers
1. Pattern Shape Control for Heat Treatment Purification of Electron-Beam-Induced Deposition of Gold from the Me2Au(acac) Precursor
Open this publication in new window or tab >>Pattern Shape Control for Heat Treatment Purification of Electron-Beam-Induced Deposition of Gold from the Me2Au(acac) Precursor
2012 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, no 14, 6185-6191 p.Article in journal (Refereed) Published
Abstract [en]

Gold structures can be created in a scanning electron microscope (SEM) from the Me2Au(acac) precursor by direct writing with the electron beam. The as-deposited purity is usually poor, and a common purification approach is a post-annealing step that indeed is effective but also induces a volume reduction because of carbon loss and an undesirable reconfiguration of the gold structure, resulting in the loss of the original shape. We studied the shape change as a result of such purification, and to minimize this effect, the application of a tantalum and chromium buffer layer was investigated. These buffer materials are well-known for their good adhesion properties. We confirm by dedicated SEM, atomic force microscopy (AFM), and transmission electron microscopy (TEM) analysis that, for the creation of a uniform Au structure, tantalum is a better buffer layer material than chromium. Post-annealing of the Au electron-beam-induced deposition (EBID) patterns for 1 h at 600 degrees C in air resulted in a dramatic purity increase (from 8-12 atomic % Au to above 92 atomic % Au). The uncovered part of the tantalum layer can be easily etched away, resulting in a well-defined, high-purity, gold structure.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-94045 (URN)10.1021/la203599c (DOI)000302514800036 ()2-s2.0-84859575425 (Scopus ID)
Note
QC 20120508Available from: 2012-05-08 Created: 2012-05-07 Last updated: 2017-12-07Bibliographically approved
2. Gas-assisted electron-beam-induced nanopatterning of high-quality Si-based insulator
Open this publication in new window or tab >>Gas-assisted electron-beam-induced nanopatterning of high-quality Si-based insulator
Show others...
2014 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 25, no 15, 155301- p.Article in journal (Refereed) Published
Abstract [en]

An oxygen-assisted electron-beam-induced deposition (EBID) process, in which an oxygen flow and the vapor phase of the precursor, tetraethyl orthosilicate (TEOS), are both mixed and delivered through a single needle, is described. The optical properties of the SiO(2+delta) (-0.04 <= delta <= +0.28) are comparable to fused silica. The electrical resistivity of both single-needle and double-needle SiO(2+delta) are comparable (greater than 7 G Omega cm) and a measured breakdown field is greater than 400 V mu m(-1). Compared to the double-needle process the advantage of the single-needle technique is the ease of alignment and the proximity to the deposition location, which facilitates fabrication of complex 3D structures for nanophotonics, photovoltaics, micro- and nano-electronics applications.

Keyword
gas-assisted EBID, 3D nanopatterning, high-purity insulator, tetraethyl orthosilicate (TEOS), purification
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-132364 (URN)10.1088/0957-4484/25/15/155301 (DOI)000333394100005 ()2-s2.0-84897861464 (Scopus ID)
Funder
Swedish Research CouncilCarl Tryggers foundation
Note

QC 20140508. Updated from submitted to published.

Available from: 2013-10-25 Created: 2013-10-25 Last updated: 2017-12-06Bibliographically approved
3. Creation of Patterned Gold Nanostructures via Electron-Beam-Induced Deposition
Open this publication in new window or tab >>Creation of Patterned Gold Nanostructures via Electron-Beam-Induced Deposition
2013 (English)In: Materials Research Society Symposium Proceedings, ISSN 0272-9172, E-ISSN 1946-4274, Vol. 1546Article in journal (Refereed) Published
Abstract [en]

One of the methods to grow nanoscale three-dimensional (3D) Au patterns is to perform local electron-beam-induced deposition (EBID) using the Me2Au(acac) precursor inside the chamber of a scanning electron microscope (SEM). However, due to the organometallic nature of the chemical, the concentration of the metallic constituent in the as-deposited structure is dramatically low, at around 10 at. % of Au. Ex-situ post-annealing of Me2Au(acac) EBIDs is a very promising purification approach, resulting in an Au content of > 92 at. % after annealing at 600 °C. However, in most of the cases it also distorts the geometrical shape of the heat-treated structure, preserving of which is essential for the application. In this paper we present a systematic study of the dependence between the annealing parameters and resulting purity in combination with the shape of the Au structure. Optimized heat treatment conditions for the creation of well-purified high aspect ratio Au pillar array are presented; and for planar continuous structures, the importance of the parameter height to area ratio is identified.

Keyword
EBID, nanoprototyping, Au
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-132363 (URN)2-s2.0-84900311552 (Scopus ID)
Note

QC 20131028

Available from: 2013-10-25 Created: 2013-10-25 Last updated: 2017-04-28Bibliographically approved
4. Electron beam induced deposition at elevated temperatures: compositional changes and purity improvement
Open this publication in new window or tab >>Electron beam induced deposition at elevated temperatures: compositional changes and purity improvement
2011 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 22, no 5, 055302- p.Article in journal (Refereed) Published
Abstract [en]

Thermally assisted electron beam induced deposition can result in an improvement of the purity of nano-scale depositions. Six commonly used organic precursors were examined: W(CO) 6, TEOS (tetraethylorthosilicate), MeCpPtMe3, Co(CO)(3)NO, Co-2(CO)(8), and Me(2)Auacac. The last two precursors were also tested on two different instruments to confirm reproducibility of the results. The influence of the substrate temperature on the composition of the deposition has been quantified systematically in the temperature range 25-360 degrees C. It has been shown that most purities improve when applying an elevated temperature, while the shape of the deposition remains intact. The purity improvement is achieved at the cost of a lower deposition yield. The amount of improvement is different for each precursor. Within the maximum temperature range of 360 degrees C, the best improvement was found for W(CO)(6): from 36.7 at.% at 25 degrees C to 59.2 at.% at 280 degrees C. For both cobalt precursors an additional transition region between patterned electron beam induced deposition (EBID) and thermal thin film growth has been identified. In this region seeded growth occurs with strongly increased growth rates.

National Category
Materials Engineering Physical Sciences
Identifiers
urn:nbn:se:kth:diva-29360 (URN)10.1088/0957-4484/22/5/055302 (DOI)000285581600009 ()2-s2.0-79251566470 (Scopus ID)
Note
QC 20110204Available from: 2011-02-04 Created: 2011-02-01 Last updated: 2017-12-11Bibliographically approved
5. Rapid electron beam assisted patterning of pure cobalt at elevated temperatures via seeded growth
Open this publication in new window or tab >>Rapid electron beam assisted patterning of pure cobalt at elevated temperatures via seeded growth
Show others...
2011 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 22, no 14, 145305- p.Article in journal (Refereed) Published
Abstract [en]

A new method of direct, rapid nano- to micro-scale patterning of high purity cobalt is presented. The method utilizes a combination of electron beam induced deposition (EBID) and seeded growth at elevated temperatures below the temperature of spontaneous thermal decomposition. Dicobalt octacarbonyl Co-2(CO)(8) is used as the precursor and carbon as a seed layer. Seeded deposition is carried out in the substrate temperature range from 55 to 75 degrees C. Deposition yield is significantly higher than conventional EBID and magnetotransport measurements indicate that resistivity, 22 mu Omega cm, and saturation magnetization, 1.55 T, are much closer to the corresponding values for bulk Co than those for standard EBID.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-31610 (URN)10.1088/0957-4484/22/14/145305 (DOI)000287970000006 ()2-s2.0-79952670642 (Scopus ID)
Note

QC 20110325

Available from: 2011-03-25 Created: 2011-03-21 Last updated: 2017-12-11Bibliographically approved

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