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Aijaz, Asim
Publications (10 of 11) Show all publications
Vitelaru, C., Aijaz, A., Parau, A. C., Kiss, A. E., Sobetkii, A. & Kubart, T. (2018). Discharge runaway in high power impulse magnetron sputtering of carbon: the effect of gas pressure, composition and target peak voltage. Journal of Physics D: Applied Physics, 51(16), Article ID 165201.
Open this publication in new window or tab >>Discharge runaway in high power impulse magnetron sputtering of carbon: the effect of gas pressure, composition and target peak voltage
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2018 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 16, article id 165201Article in journal (Refereed) Published
Abstract [en]

Pressure and target voltage driven discharge runaway from low to high discharge current density regimes in high power impulse magnetron sputtering of carbon is investigated. The main purpose is to provide a meaningful insight of the discharge dynamics, with the ultimate goal to establish a correlation between discharge properties and process parameters to control the film growth. This is achieved by examining a wide range of pressures (2-20 mTorr) and target voltages (700-850 V) and measuring ion saturation current density at the substrate position. We show that the minimum plasma impedance is an important parameter identifying the discharge transition as well as establishing a stable operating condition. Using the formalism of generalized recycling model, we introduce a new parameter, 'recycling ratio', to quantify the process gas recycling for specific process conditions. The model takes into account the ion flux to the target, the amount of gas available, and the amount of gas required for sustaining the discharge. We show that this parameter describes the relation between the gas recycling and the discharge current density. As a test case, we discuss the pressure and voltage driven transitions by changing the gas composition when adding Ne into the discharge. We propose that standard Ar HiPIMS discharges operated with significant gas recycling do not require Ne to increase the carbon ionization.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2018
Keywords
magnetron sputtering, carbon sputtering, gas recycling, high power impulse magnetron sputtering (HiPIMS), diamond like carbon (DLC)
National Category
Fusion, Plasma and Space Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-353101 (URN)10.1088/1361-6463/aab590 (DOI)000428686500001 ()
Funder
VINNOVA
Available from: 2018-06-11 Created: 2018-06-11 Last updated: 2018-06-14Bibliographically approved
Ferreira, F., Aijaz, A., Kubart, T., Cavaleiro, A. & Oliveira, J. (2018). Hard and dense diamond like carbon coatings deposited by deep oscillations magnetron sputtering. Paper presented at 60th Annual Technical Conference of the Society-of-Vacuum-Coaters (SVC), APR 29-MAY 04, 2017, Providence, RI. Surface & Coatings Technology, 336, 92-98
Open this publication in new window or tab >>Hard and dense diamond like carbon coatings deposited by deep oscillations magnetron sputtering
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2018 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 336, p. 92-98Article in journal (Refereed) Published
Abstract [en]

Recent developments in the automotive industry to improve engine efficiency and minimize pollutant emissions are driving the need for higher operating temperatures and loading densities in internal combustion engines. Future engines for internal combustion engines will require coatings with increased temperature stability (up to 500 degrees C) and wear resistance as compared to present day solutions. Hard tetrahedral DLC coatings (ta-C coatings) very low coefficient of friction and performed very well under mixed and boundary lubrication, and, thus, they are very attractive for automotive industry. In this work, DLC coatings were deposited by deep oscillations magnetron sputtering (DOMS), a variant of high power magnetron sputtering (HiPIMS). The main objective is to increase the sp(3) content in the films, as compared to d.c. magnetron sputtering (DCMS), and thus extend their operating range to higher temperatures. Increasing the bias voltage results in denser and smoother films with increasing hardness, as measured by nano-indentation, and increasing mass density, as measured by x-ray reflectivity. Accordingly, the UV Raman spectroscopy analysis of the films shows that the sp(3)/sp(2) ratio in the films increases with increasing substrate biasing. However, the sp(3) bonds convert back to sp(2) upon annealing. Never the less, a significantly higher amount of sp(3) bonds is formed in the DLC films deposited by DOMS, as compared to the DCMS ones, showing that DOMS is a promising path for the development of hard DLC films.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2018
Keywords
DLC, DOMS, Mass density, Hardness, Temperature stability
National Category
Materials Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-348847 (URN)10.1016/j.surfcoat.2017.10.055 (DOI)000425478000015 ()
Conference
60th Annual Technical Conference of the Society-of-Vacuum-Coaters (SVC), APR 29-MAY 04, 2017, Providence, RI
Available from: 2018-04-20 Created: 2018-04-20 Last updated: 2018-05-02Bibliographically approved
Aijaz, A., Ferreira, F., Oliveira, J. & Kubart, T. (2018). Mechanical Properties of Hydrogen Free Diamond-Like Carbon Thin Films Deposited by High Power Impulse Magnetron Sputtering with Ne. Coatings, 8(11), Article ID 385.
Open this publication in new window or tab >>Mechanical Properties of Hydrogen Free Diamond-Like Carbon Thin Films Deposited by High Power Impulse Magnetron Sputtering with Ne
2018 (English)In: Coatings, ISSN 2079-6412, Vol. 8, no 11, article id 385Article in journal (Refereed) Published
Abstract [en]

Hydrogen-free diamond-like carbon (DLC) thin films are attractive for a wide range of industrial applications. One of the challenges related to the use of hard DLC lies in the high intrinsic compressive stresses that limit the film adhesion. Here, we report on the mechanical and tribological properties of DLC films deposited by High Power Impulse Magnetron Sputtering (HiPIMS) with Ne as the process gas. In contrast to standard magnetron sputtering as well as standard Ar-based HiPIMS process, the Ne-HiPIMS lead to dense DLC films with increased mass density (up to 2.65 g/cm(3)) and a hardness of 23 GPa when deposited on steel with a Cr + CrN adhesion interlayer. Tribological testing by the pin-on-disk method revealed a friction coefficient of 0.22 against steel and a wear rate of 2 x 10(-17) m(3)/Nm. The wear rate is about an order of magnitude lower than that of the films deposited using Ar. The differences in the film properties are attributed to an enhanced C ionization in the Ne-HiPIMS discharge.

Keywords
diamond-like carbon, HiPIMS, tribology, adhesion, ionized PVD
National Category
Materials Chemistry Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:uu:diva-371545 (URN)10.3390/coatings8110385 (DOI)000451152400012 ()
Funder
VINNOVA
Available from: 2018-12-21 Created: 2018-12-21 Last updated: 2018-12-21Bibliographically approved
Keller, J., Shariati, M.-N., Aijaz, A., Riekehr, L., Kubart, T., Edoff, M. & Törndahl, T. (2018). Using hydrogen‐doped In2O3 films as a transparent back contact in (Ag,Cu)(In,Ga)Se2 solar cells. Progress in Photovoltaics, 26(3), 159-170
Open this publication in new window or tab >>Using hydrogen‐doped In2O3 films as a transparent back contact in (Ag,Cu)(In,Ga)Se2 solar cells
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2018 (English)In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 26, no 3, p. 159-170Article in journal (Refereed) Published
Abstract [en]

This study evaluates the potential of hydrogen‐doped In2O3 (IOH) as a transparent back contact material in (Agy,Cu1‐y)(In1‐x,Gax)Se2 solar cells. It is found that the presence of Na promotes the creation of Ga2O3 at the back contact during (Agy,Cu1‐y)(In1‐x,Gax)Se2 growth. An excessive Ga2O3 formation results in a Ga depletion, which extends deep into the absorber layer. Consequently, the beneficial back surface field is removed and a detrimental reversed electrical field establishes. However, for more moderate Ga2O3 amounts (obtained with reduced Na supply), the back surface field can be preserved. Characterization of corresponding solar cells suggests the presence of an ohmic back contact, even at absorber deposition temperatures of 550°C. The best solar cell with an IOH back contact shows a fill factor of 74% and an efficiency (η) of 16.1% (without antireflection coating). The results indicate that Ga2O3 does not necessarily act as a transport barrier in the investigated system. Observed losses in open circuit voltage (VOC) as compared to reference samples with a Mo back contact are ascribed to a lower Na concentration in the absorber layer.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-363286 (URN)10.1002/pip.2977 (DOI)000424288000001 ()
Funder
Swedish Energy Agency, 2016-008376
Available from: 2018-10-16 Created: 2018-10-16 Last updated: 2019-06-27Bibliographically approved
Kubart, T. & Aijaz, A. (2017). Evolution of sputtering target surface composition in reactive high power impulse magnetron sputtering. Journal of Applied Physics, 121(17), Article ID 171903.
Open this publication in new window or tab >>Evolution of sputtering target surface composition in reactive high power impulse magnetron sputtering
2017 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 121, no 17, article id 171903Article in journal, Meeting abstract (Refereed) Published
Abstract [en]

The interaction between pulsed plasmas and surfaces undergoing chemical changes complicates physics of reactive High Power Impulse Magnetron Sputtering (HiPIMS). In this study, we determine the dynamics of formation and removal of a compound on a titanium surface from the evolution of discharge characteristics in an argon atmosphere with nitrogen and oxygen. We show that the time response of a reactive process is dominated by surface processes. The thickness of the compound layer is several nm and its removal by sputtering requires ion fluence in the order of 1016 cm−2, much larger than the ion fluence in a single HiPIMS pulse. Formation of the nitride or oxide layer is significantly slower in HiPIMS than in dc sputtering under identical conditions. Further, we explain very high discharge currents in HiPIMS by the formation of a truly stoichiometric compound during the discharge off-time. The compound has a very high secondary electron emission coefficient and leads to a large increase in the discharge current upon target poisoning.

Keywords
Sputtering, Sputter deposition, Ion-solid interaction, titanium oxide
National Category
Fusion, Plasma and Space Physics Condensed Matter Physics Other Materials Engineering
Identifiers
urn:nbn:se:uu:diva-316657 (URN)10.1063/1.4977814 (DOI)000400623700005 ()
Funder
Swedish Foundation for Strategic Research
Available from: 2017-03-06 Created: 2017-03-06 Last updated: 2017-06-02Bibliographically approved
Aijaz, A. & Kubart, T. (2017). Ion induced stress relaxation in dense sputter-deposited DLC thin films. Applied Physics Letters, 111(5), Article ID 051902.
Open this publication in new window or tab >>Ion induced stress relaxation in dense sputter-deposited DLC thin films
2017 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 111, no 5, article id 051902Article in journal (Refereed) Published
Abstract [en]

Deposition of high-density and low-stress hydrogen-free diamond like carbon (DLC) thin films is demonstrated using a pulsed ionized sputtering process. This process is based on high power impulse magnetron sputtering, and high C ionization is achieved using Ne as the sputtering gas. The intrinsic compressive stress and its evolution with respect to ion energy and ion flux are explained in terms of the compressive stress based subplantation model for DLC growth by Davis. The highest mass density was similar to 2.7 g/cm(3), and the compressive stresses did not exceed similar to 2.5 GPa. The resulting film stresses are substantially lower than those achieved for the films exhibiting similar mass densities grown by filtered cathodic vacuum arc and pulsed laser deposition methods. This unique combination of high mass density and low compressive stress is attributed to the ion induced stress relaxation during the pulse-off time which corresponds to the post thermal spike relaxation timescales. We therefore propose that the temporal ion flux variations determine the magnitude of the compressive stress observed in our films. Published by AIP Publishing.

National Category
Other Materials Engineering
Identifiers
urn:nbn:se:uu:diva-333517 (URN)10.1063/1.4997324 (DOI)000406782300007 ()
Funder
VINNOVA
Available from: 2017-11-14 Created: 2017-11-14 Last updated: 2017-11-14Bibliographically approved
Aijaz, A., Ji, Y.-X., Montero, J., Niklasson, G. A., Granqvist, C. G. & Kubart, T. (2016). Low-temperature synthesis of thermochromic vanadium dioxide thin films by reactive high power impulse magnetron sputtering. Solar Energy Materials and Solar Cells, 149, 137-144
Open this publication in new window or tab >>Low-temperature synthesis of thermochromic vanadium dioxide thin films by reactive high power impulse magnetron sputtering
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2016 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 149, p. 137-144Article in journal (Refereed) Published
Abstract [en]

Thermochromic (TC) vanadium dioxide thin films provide means for controlling solar energy throughput and can be used for energy-saving applications such as smart windows. One of the factors limiting the deployment of VO2 films in TC devices is the growth temperature tau(s). At present, temperatures in excess of 450 degrees C are required, which clearly can be an impediment especially for temperature-sensitive substrates. Here we address the issue of high tau(s) by synthesizing VO2 thin films from highly ionized fluxes of depositing species generated in high power impulse magnetron sputtering (HiPIMS) discharges. The use of ions facilitates low-temperature film growth because the energy of the depositing species can be readily manipulated by substrate bias. For comparison, films were also synthesized by pulsed direct current magnetron sputtering. Structural and optical characterization of VO2 thin films on ITO-coated glass substrates confirms previous results that HiPIMS allows tau(s) to be reduced from 500 to 300 degrees C. Importantly, we demonstrated that HiPIMS permits the composition and TC response of the films to be tuned by altering the energy of the deposition flux via substrate bias. An optimum ion energy of 100 eV was identified, which points at a potential for further reduction of tau(s) thereby opening new possibilities for industrially-relevant applications of VO2-based TC thin films. Weak TC activity was observed even at tau(s) approximate to 200 degrees C in HiPIMS-produced films.

Keywords
Vanadium oxide, Thermochromic thin films, Energy saving, HiPIMS, Ionized PVD, Low-temperature film growth
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-294656 (URN)10.1016/j.solmat.2016.01.009 (DOI)000373539900019 ()
External cooperation:
Funder
Swedish Research Council FormasEU, FP7, Seventh Framework Programme, 267234
Available from: 2016-06-08 Created: 2016-05-26 Last updated: 2018-08-30Bibliographically approved
Aijaz, A., Carreri, F. d., Sabelfeld, A., Gerdes, H., Bandorf, R., Kubart, T. & Bräuer, G. (2015). Industrial Scale Deposition of Diamond-like Carbon Thin Films using Ne-based HiPIMS Discharge. In: : . Paper presented at 6th International Conference on HiPIMS, June 2015, Braunshweig, Germany.
Open this publication in new window or tab >>Industrial Scale Deposition of Diamond-like Carbon Thin Films using Ne-based HiPIMS Discharge
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2015 (English)Conference paper, Poster (with or without abstract) (Other academic)
Abstract [en]

High power impulse magnetron sputtering (HiPIMS) has been successful in providing highly ionized deposition fluxes for most common metals (Cu, Al, Ti). However, it is challenged when non-metals such as carbon is considered. Highly ionized carbon fluxes (up to 100%) are essential for the synthesis of diamond-like carbon and tetrahedral amorphous carbon thin films. Earlier reports have shown that the C+/C0 ratio in HiPIMS does not exceed 5% and film densities and sp3/sp2 bond fractions are substantially lower than those achieved using ionized physical vapour deposition based methods such as filtered cathodic vacuum arc and pulsed laser deposition. In our previous work, we demonstrated that Ne-based HiPIMS discharge entails energetic electrons as compared to Ar-based HiPIMS discharge facilitating the generation of highly ionized C fluxes as well as diamond-like carbon thin films with mass densities in the order of 2.8 g/cm3

In this work, we perform industrial scale deposition of diamond-like carbon thin films using Ne- as well as Ar-based HiPIMS discharge. In order to investigate the effect of electron temperature enhancement and its correlation to generation of C1+ ion fluxes in Ne-based HiPIMS discharge, we perform time-averaged and time-resolved measurements of electron temperature as well as ion density at the substrate position using a flat probe. We also investigate the effect of plasma properties on the ionization of sputtered C as well as buffer gas species by measuring the optical emission from the discharge. In order to correlate the plasma and film properties, we synthesize C thin films under energetic deposition conditions and investigate structural (mass density, sp3/sp2 bond fraction, H content) and mechanical (hardness, elastic modulus, adhesion strength) properties of the resulting diamond-like carbon thin films.

Keywords
DLC; ta-C; carbon ionization; HiPIMS
National Category
Materials Engineering
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-271240 (URN)
Conference
6th International Conference on HiPIMS, June 2015, Braunshweig, Germany
Available from: 2016-01-07 Created: 2016-01-07 Last updated: 2016-04-22
Aijaz, A., Ji, Y.-X., Granqvist, C. G., Niklasson, G. A. & Kubart, T. (2015). Low-temperature synthesis of thermochromic vanadium dioxide thin films using reactive magnetron sputtering. In: Abstracts: . Paper presented at Oorgandagarna, Visby, Juni 15-17.
Open this publication in new window or tab >>Low-temperature synthesis of thermochromic vanadium dioxide thin films using reactive magnetron sputtering
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2015 (English)In: Abstracts, 2015Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-268235 (URN)
Conference
Oorgandagarna, Visby, Juni 15-17
Available from: 2015-12-03 Created: 2015-12-03 Last updated: 2018-08-30
Prusakova, L., Aijaz, A., Nyberg, T., Törndahl, T., Zhang, Z. & Kubart, T. (2015). Magnetron sputtering of InGaZnO and ZnSnO amorphous oxide semiconductors. In: E-MRS Spring meeting 2015, May 11-15, Lille, France: Symposium N (Synthesis, processing and characterization of nanoscale multi functional oxide films). Paper presented at E-MRS Spring meeting 2015, May 11-15, Lille, France.
Open this publication in new window or tab >>Magnetron sputtering of InGaZnO and ZnSnO amorphous oxide semiconductors
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2015 (English)In: E-MRS Spring meeting 2015, May 11-15, Lille, France: Symposium N (Synthesis, processing and characterization of nanoscale multi functional oxide films), 2015Conference paper, Poster (with or without abstract) (Other academic)
Abstract [en]

Amorphous oxide semiconductors (AOS) are exciting materials which combine optical transparency with high electron mobility. AOS are thus suitable for transparent electronics, or, on flexible substrates such as plastic foils, for wearable electronic devices. Although In-Ga-Zn-O is the best performing AOS so far, there is an interest in In-free alternatives. This is due to the concerns about limited In availability and its price. The alternative materials, however, normally require higher deposition temperatures.

Here we report on magnetron sputtering of In-Ga-Zn-O (IGZO) and Zn-Sn-O (ZTO) with focus on the effect of deposition conditions on the film properties.  IGZO films were deposited by RF sputtering from an oxide target while for ZTO, reactive sputtering from an alloy target was used. All films were deposited without substrate heating and characterized with respect to optical transparency, microstructure, electron mobility and resistivity. The best as-deposited IGZO films had resistivity of about 2∙10-2 ohm∙cm and electron mobility up to 10 cm2∙V-1∙s-1. The properties were very sensitive to the lateral position during deposition. Combination of simulations and experimental characterization was used to understand these effects. There is a strong influence of  the composition and energy of the material flux towards the substrate. Reactive deposition process provides more freedom in selecting optimum growth conditions as demonstrated for ZTO films.

Keywords
Amorphous oxide semiconductors, Sputtering, IGZO
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:uu:diva-269736 (URN)
Conference
E-MRS Spring meeting 2015, May 11-15, Lille, France
Funder
Carl Tryggers foundation
Available from: 2015-12-18 Created: 2015-12-18 Last updated: 2016-04-22
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