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Functional Metal Oxide Materials Deposited by Inkjet Printing Technique
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents a comprehensive study of the intrinsic room temperature ferromagnetism in 85 to 100nm thin films produced by in situ deposition of industrially important pristine MgO and ZnO by inkjet printing. It is suggested that the observed long range magnetic order, the so-called do magnetism in these oxides arises from cation vacancies. Wide range scanned XPS studies rule out any other source but of intrinsic nature in this first report on inkjetted oxide films. (Accepted for publication in APL 2010; and JPC Letters 2010)

The functional properties of the above oxide films have been exploited by inkjet patterning devices based on UV-sensing, photoconductivity and field-effect transistors with attractive features. Development of devices and prototypes is an area of growing importance among future technologies. Complementary to photolithography, inkjet printing is increasingly considered a cost-effective and flexible microfabrication method to structure functional materials. The ease of mass fabrication and the inherent flexibility of inkjet technology make it a suitable method for the manufacture of microsystems and components. The results presented in this dissertation summarize recent achievements in this relatively new technology for the development of miniaturized devices:

1)      RTFM in pure and Mn-doped ZnO thin films: (IEEE Trans. Magnetics 2010) Tailored RTFM in Mn-doped ZnO thin films synthesized by inkjet printing has been realized. Highly c-axis oriented 80 to 400 nm thin films are obtained with a magnetic moment as large as 2.1 μB/Mn2+. X-ray absorption and emission spectra measurements at the O K edge and the Mn L edge suggest strong p-d hybridization between the Mn2+ and O2-. Furthermore, Mn L edge XAS indicates the emergence of Mn3+/Mn4+ mixed valence states for films annealed above 500 °C that leads to suppression of ferromagnetic ordering.

2)      RTFM in MgO thin films (JPC Letters 2010) Solution processed homogeneous (200) oriented MgO ~85 nm thin films show room temperature ferromagnetism with a saturation magnetization MS as high as ~0.63 emu/g. X-ray photoelectron spectroscopy investigations show the absence of any contamination while the Mg 2p, and O 1s spectra indicate the role of defect structure at the Mg site. By controlling the pH values of the precursors the concentration of the defects can be varied and hence to tune the magnetization.

3)      Photoconductivity of pure and Al-doped ZnO thin films: (2009 MRS proceedings). Pure and Al-doped ZnO, 120-300 nm thin films are found to exhibit a transmittance above 85-90% in the visible wavelength range. The electrical conductivity of Al-doped ZnO thin films is found to be larger by two orders of magnitude than that for pure ZnO films while the photoconductivity is found to increase by about three orders of magnitude under UV irradiation.

4)      The photosensitivity of CaS-composited ZnO thin films: (JPC Letters 2010) We have engineered a 3 orders of magnitude enhancement of the ultraviolet photoresponse of ZnO thin films, fabricated by inkjet printing, and then capped with CdS nanoparticles by dip coating. As a consequence, the decay time of the photoresponse is reduced to about 4 ms. Capping with CdS not only suppresses the detrimental passivation layer of ZnO thin films, but also generates an interfacial carrier transport layer to reduce the probability of carrier recombination.

5)      Indium-doped Zinc oxide field effect transistors: (Materials Letters 2010) In darkness the In-doped zinc oxide field effect transistor (IZO-FET) exhibits a saturation current level of about 10 μA, an incremental mobility as high as 8 cm2 V-1 s-1, and a current on/off ratio of 104 ~105. When illuminated by 363 nm, 1.7 mW/cm2 UV light, the IZO-FET displays a photocurrent of 2 mA, and a darkness current of ~20 nA at an optimized gate voltage of -2V. The device is effectively turned on in about 5 ms and off in 10 ms.



Place, publisher, year, edition, pages
Stockholm: KTH , 2010. , xii, 63 p.
Keyword [en]
Inkjet printing, photoconductivity, ZnO, Al-ZnO, composite, electron transfer, CdS, field effect transistor, photosensitive, RT do-ferromagnetism, Mn-doped ZnO, MgO
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-13191ISBN: 978-91-7415-667-6 (print)OAI: oai:DiVA.org:kth-13191DiVA: diva2:321703
Public defence
2010-06-11, Salongen KTHB, Osquars Backe 31, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC20100706Available from: 2010-06-02 Created: 2010-06-02 Last updated: 2010-07-06Bibliographically approved
List of papers
1. Room Temperature Ferromagnetism and Fast Ultraviolet Photoresponse of Inkjet-Printed Mn-Doped ZnO Thin Films
Open this publication in new window or tab >>Room Temperature Ferromagnetism and Fast Ultraviolet Photoresponse of Inkjet-Printed Mn-Doped ZnO Thin Films
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2010 (English)In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 46, no 6, 2152-2155 p.Article in journal (Refereed) Published
Abstract [en]

We have synthesized Mn-doped ZnO thin films by inkjet printing using a two-step annealing process at 200 C for the decomposition of the organic compounds, and at various temperatures above 400 degrees C to tailor room temperature ferromagnetism. Highly c axis oriented 80 to 400 nm thin films on ( 001) Si substrates are obtained with a magnetic moment as large as 2.1 mu(B)/Mn2+. X-ray absorption and emission spectra measurements at the O K edge and the Mn L edge suggest strong p-d hybridization between the Mn2+ and O2-. Furthermore, Mn L edge XAS indicates the emergence of Mn3+ /Mn4+ mixed valence states for films annealed above 500 degrees C that leads to suppression of ferromagnetic ordering. All of these films show large and fast ultraviolet (UV) photoresponse with the decay times of about 0.5 ms, suggesting the potential for designing multifunctional UV sensors.

Keyword
Ferromagnetism, inkjet printing, Mn-doped ZnO, photoresponse, FIELD-EFFECT TRANSISTORS, MAGNETIC SEMICONDUCTORS, NANOPARTICLES, ZN1-XMNXO
Identifiers
urn:nbn:se:kth:diva-13940 (URN)10.1109/TMAG.2010.2043230 (DOI)000278037800227 ()2-s2.0-77952819931 (Scopus ID)
Note
QC20100705Available from: 2010-07-05 Created: 2010-07-05 Last updated: 2017-12-12Bibliographically approved
2. Room temperature ferromagnetism in pristine MgO thin films
Open this publication in new window or tab >>Room temperature ferromagnetism in pristine MgO thin films
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2010 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 96, no 23Article in journal (Refereed) Published
Abstract [en]

Robust ferromagnetic ordering at, and well above room temperature is observed in pure transparent MgO thin films (<170 nm thick) deposited by three different techniques. Careful study of the wide scan x-ray photoelectron spectroscopy rule out the possible presence of any magnetic contaminants. In the magnetron sputtered films, we observe magnetic phase transitions as a function of film thickness. The maximum saturation magnetization of 5.7 emu/cm(3) is measured on a 170 nm thick film. The films above 500 nm are found to be diamagnetic. Ab initio calculations suggest that the ferromagnetism is mediated by cation vacancies.

Keyword
ENERGY
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-13939 (URN)10.1063/1.3447376 (DOI)000278695900048 ()2-s2.0-77953525394 (Scopus ID)
Note

QC20100705

Available from: 2010-07-05 Created: 2010-07-05 Last updated: 2017-12-12Bibliographically approved
3. 'In-situ' Solution Processed Room Temperature Ferromagnetic MgO Thin Films Printed by Inkjet Technique
Open this publication in new window or tab >>'In-situ' Solution Processed Room Temperature Ferromagnetic MgO Thin Films Printed by Inkjet Technique
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(English)In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185Article in journal (Other academic) Submitted
Identifiers
urn:nbn:se:kth:diva-13952 (URN)
Note

QC20100706

Available from: 2010-07-06 Created: 2010-07-05 Last updated: 2017-12-12Bibliographically approved
4. Ultraviolet photoconductivity of pure and Al doped ZnO thin films by inkjet printing
Open this publication in new window or tab >>Ultraviolet photoconductivity of pure and Al doped ZnO thin films by inkjet printing
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2009 (English)In: NOVEL MATERIALS AND DEVICES FOR SPINTRONICS / [ed] Sanvito S, Heinonen O, Dediu VA, Rizzo N, Warrendale, PA: MATERIALS RESEARCH SOCIETY , 2009, Vol. 1183, 133-138 p.Conference paper, Published paper (Refereed)
Abstract [en]

Pure ZnO, and Al doped ZnO, 120-300 nm thin films on glass substrates, were synthesized by inkjet printing technique using zinc and aluminum acetate solution as precursors and a two stage heat treatment process to obtain polycrystalline hexagonal wurtzite structure with the mean grain size of 25 and 30 nm respectively. All films exhibit a transmittance above 85-90% in the visible wavelength range below 700 nm. In the Al doped films the UV absorption spectra show a strong absorption onset below 380nm followed by shoulders centered around 325 nm depending on the film thickness. The electrical conductivity of Al doped ZnO thin films is larger by two orders of magnitude than that for pure ZnO films while the photoconductivity increases by about three orders of magnitude under UV irradiation. The photoresponse of the films with UV irradiation in terms of the rise and decay times in the frequency range from 5 to 500 Hz is also presented and discussed.

Place, publisher, year, edition, pages
Warrendale, PA: MATERIALS RESEARCH SOCIETY, 2009
Series
Materials Research Society Symposium Proceedings, ISSN 0272-9172 ; 1183
Keyword
Absorption onset; Acetate solutions; Al doped; Al doped ZnO thin films; Al-doped ZnO; Decay time
Identifiers
urn:nbn:se:kth:diva-13956 (URN)10.1557/PROC-1161-I03-22 (DOI)000284863300020 ()2-s2.0-77951016000 (Scopus ID)
Conference
Symposium on Novel Materials and Devices for Spintronics San Francisco, CA, APR 14-17, 2009
Note
QC20100705Available from: 2010-07-05 Created: 2010-07-05 Last updated: 2011-02-04Bibliographically approved
5. Enhanced photoresponse of inkjet printed ZnO thin films induced by chemically capped CdS nanoparticles by dip coating
Open this publication in new window or tab >>Enhanced photoresponse of inkjet printed ZnO thin films induced by chemically capped CdS nanoparticles by dip coating
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2009 (English)In: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, E-ISSN 1996-756X, Vol. 7402, no 740207Article in journal (Refereed) Published
Abstract [en]

Monodispersed CdS nanoparticles (NP) are dip coated on porous ZnO thin film deposited by inkjet printing. Optical absorption characteristics of the composite films show that the composite exhibits two main peaks centered at 355 nm due to the absorption at UV region from ZnO, and 433 nm arising from CdS NP. On UV radiations the electrical conductivity of CdS/ZnO composite thin film with 5 dip cycles is found to be enhanced more than three orders magnitude compared with that of the ZnO which we attribute to be the effect of interfacial charge transfer. Also, the UV photoresponse of ZnO shows pronounced enhancement after CdS capping. 

Identifiers
urn:nbn:se:kth:diva-13969 (URN)10.1117/12.827022 (DOI)2-s2.0-70350169940 (Scopus ID)
Note
QC20100706Available from: 2010-07-06 Created: 2010-07-06 Last updated: 2017-12-12Bibliographically approved
6. Enhanced Photoresponse of Inkjet-Printed ZnO Thin Films Capped with CdS Nanoparticles
Open this publication in new window or tab >>Enhanced Photoresponse of Inkjet-Printed ZnO Thin Films Capped with CdS Nanoparticles
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2010 (English)In: J PHYS CHEM LETT, ISSN 1948-7185, Vol. 1, no 1, 89-92 p.Article in journal (Refereed) Published
Abstract [en]

Composite semiconductors provide routes for realizing high-performance electronic devices, but for many applications of such devices, low-cost manufacturing techniques are desirable. We have engineered a 3 orders of magnitude enhancement of the ultraviolet photoresponse of ZnO thin films, fabricated "in situ" by drop-on-demand inkjet printing, and then capped with CdS nanoparticles by dip. coating. As a consequence, the decay time of the photoresponse is. reduced to about 4 ms. Thus, capping with CdS not only suppresses the detrimental passivation layer of ZnO thin films, but also generates an interfacial carrier transport layer to reduce the probability of carrier recombination.

Keyword
ZINC-OXIDE, PHOTOCONDUCTIVITY, SEMICONDUCTORS
Identifiers
urn:nbn:se:kth:diva-13954 (URN)10.1021/jz900008y (DOI)000276905600020 ()2-s2.0-77149149744 (Scopus ID)
Note
QC 20100705Available from: 2010-07-05 Created: 2010-07-05 Last updated: 2011-02-04Bibliographically approved
7. Unusual ferromagnetism above room temperature in undoped thin films and nanoparticles of MgO
Open this publication in new window or tab >>Unusual ferromagnetism above room temperature in undoped thin films and nanoparticles of MgO
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(English)Manuscript (Other academic)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-10162 (URN)
Note
QC 20101108Available from: 2009-03-27 Created: 2009-03-27 Last updated: 2010-11-08Bibliographically approved

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