Umeå University's logo

umu.sePublications
Change search
Link to record
Permanent link

Direct link
Barzegar, Hamid RezaORCID iD iconorcid.org/0000-0002-1314-5407
Alternative names
Publications (10 of 36) Show all publications
Miranda la Hera, V., Mena Gómez, J., Canto-Aguilar, E., Barzegar, H. R., Carvajal, J. J., Wågberg, T. & Gracia-Espino, E. (2023). Electronic properties of hexagonal v-shaped gallium nitride pits. The Journal of Physical Chemistry C, 127(51), 24658-24665
Open this publication in new window or tab >>Electronic properties of hexagonal v-shaped gallium nitride pits
Show others...
2023 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 127, no 51, p. 24658-24665Article in journal (Refereed) Published
Abstract [en]

In this work, the morphology, surface composition, and electronic properties of porous GaN films containing hexagonal V-shaped pits were studied. The V-pits are orientated along the [0001] direction of GaN, and we observed a clear relation between the growth time with the surface composition, film thickness, and pit morphology, which in turn had a significant impact on the band gap, valence band maximum, and the work function. The effect on the position of the valence band maximum and work function is explained by the formation of superficial oxygen-rich phases such as Ga2O3 and nonstoichiometric GaNxOy as supported by X-ray photoelectron spectroscopy and density functional theory (DFT). We further show a change in the optical band gap with the thickness of the porous films explained by a change in the tensile strain caused by open-core screw dislocations that gives rise to the formation of V-pits. The correlation between strain and the band gap is supported by DFT calculations. Our study provides insights into the intricate relation between surface states and electronic properties of semiconducting materials and offers directions for designing GaN heterojunctions with specific optical and electronic properties.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2023
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:umu:diva-219532 (URN)10.1021/acs.jpcc.3c05878 (DOI)001134057500001 ()2-s2.0-85181028161 (Scopus ID)
Funder
Swedish Research Council, 2018-03937Swedish Research Council, 2021-04629Swedish Energy Agency, 45419-1Swedish Foundation for Strategic Research, SSF-Agenda 2030-PUSHCarl Tryggers foundation , CTS21-1581
Available from: 2024-01-19 Created: 2024-01-19 Last updated: 2024-01-19Bibliographically approved
Zhang, Y., Liu, S., Yao, Z., Dong, J., Liu, B., Liu, R., . . . Liu, B. (2022). Capture of novel sp3 hybridized Z-BN by compressing boron nitride nanotubes with small diameter. Diamond and related materials, 130, Article ID 109431.
Open this publication in new window or tab >>Capture of novel sp3 hybridized Z-BN by compressing boron nitride nanotubes with small diameter
Show others...
2022 (English)In: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 130, article id 109431Article in journal (Refereed) Published
Abstract [en]

Experimental synthesis of new sp3 hybridized carbon/boron nitride structures remains challenging despite that numerous sp3 structures have been proposed in theory. Here, we showed that compressed multi-walled boron nitride nanotubes (MWBNNTs) and boron nitride peapods (C60@BNNTs) with small diameters could transform into a new sp3 hybridized boron nitride allotrope (Z-BN). This strategy is considered from the topological transition point of view in boron nitride nanotubes upon compression. Due to the increased curvature in compressed small-diameter MWBNNTs, the uncommon 4- and 8-membered rings in Z-BN could be more favorably formed. And the irreversible tube collapse is proved to be a critical factor for the capture of the formed Z-BN, because of the competition between the resilience of tube before collapse and the stress limitation for the lattice stabilization of Z-BN upon decompression. In this case, Z-BN starts to form above 19.0 GPa, which is fully reversible below 45 GPa and finally becomes quenchable at 93.5 GPa. This collapse-induced capture of the high-pressure phase could also be extended to other tubular materials for quenching novel sp3 structures.

Place, publisher, year, edition, pages
Elsevier, 2022
Keywords
Boron nitride nanotubes (BNNTs), High pressure, Sp3 hybridized materials, Stacking sequence
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:umu:diva-200450 (URN)10.1016/j.diamond.2022.109431 (DOI)000880373100002 ()2-s2.0-85139593319 (Scopus ID)
Available from: 2022-10-25 Created: 2022-10-25 Last updated: 2023-09-05Bibliographically approved
Miranda la Hera, V., Wu, X., Mena, J., Barzegar, H. R., Ashok, A., Koroidov, S., . . . Gracia-Espino, E. (2022). Controlled synthesis of tellurium nanowires by physical vapor deposition. Nanomaterials, 12(23), Article ID 4137.
Open this publication in new window or tab >>Controlled synthesis of tellurium nanowires by physical vapor deposition
Show others...
2022 (English)In: Nanomaterials, E-ISSN 2079-4991, Vol. 12, no 23, article id 4137Article in journal (Refereed) Published
Abstract [en]

One-dimensional tellurium nanostructures can exhibit distinct electronic properties from those seen in bulk Te. The electronic properties of nanostructured Te are highly dependent on their morphology, and thus controlled synthesis processes are required. Here, highly crystalline tellurium nanowires were produced via physical vapour deposition. We used growth temperature, heating rate, flow of the carrier gas, and growth time to control the degree of supersaturation in the region where Te nanostructures are grown. The latter leads to a control in the nucleation and morphology of Te nanostructures. We observed that Te nanowires grow via the vapour–solid mechanism where a Te particle acts as a seed. Transmission electron microscopy (TEM) and electron diffraction studies revealed that Te nanowires have a trigonal crystal structure and grow along the (0001) direction. Their diameter can be tuned from 26 to 200 nm with lengths from 8.5 to 22 μm, where the highest aspect ratio of 327 was obtained for wires measuring 26 nm in diameter and 8.5 μm in length. We investigated the use of bismuth as an additive to reduce the formation of tellurium oxides, and we discuss the effect of other growth parameters.

Place, publisher, year, edition, pages
MDPI, 2022
Keywords
tellurium, bismuth, doping, nanowires, physical vapour deposition
National Category
Other Physics Topics
Identifiers
urn:nbn:se:umu:diva-200957 (URN)10.3390/nano12234137 (DOI)000896197300001 ()36500758 (PubMedID)2-s2.0-85143740574 (Scopus ID)
Note

Originally included in thesis in manuscript form. 

Available from: 2022-11-11 Created: 2022-11-11 Last updated: 2023-01-17Bibliographically approved
Rafei, M., Miranda la Hera, V., Barzegar, H. R., Gracia-Espino, E. & Wågberg, T. (2022). Study on the electronic and structural properties of oxidized copper films. AIP Advances, 12(10), Article ID 105203.
Open this publication in new window or tab >>Study on the electronic and structural properties of oxidized copper films
Show others...
2022 (English)In: AIP Advances, E-ISSN 2158-3226, Vol. 12, no 10, article id 105203Article in journal (Refereed) Published
Abstract [en]

A detailed study of the oxidation of Cu substrates was carried out under controlled conditions by regulating the pressure, atmosphere composition, process time, and temperature. By tuning the synthesis conditions, the formation of cuprous oxide (Cu2O) or cupric oxide (CuO) could be preferentially promoted. The oxidation temperature was varied from 400 to 1050 °C, and a gradual oxidation of metallic Cu to Cu2O was achieved at mild oxidation conditions (400-600 °C), while the formation of CuO was only observed at higher temperatures (≥900 °C). The surface morphology was also affected changing from a highly granular texture (400 °C) with grain sizes between 0.59 ± 0.15 μm to smooth large crystallites (≥900 °C) with a size within 2.76 ± 0.97 μm. We also show that by controlling the oxidation temperature (400-1050 °C), it is possible to tune the work function and the ionization potential of the resulting Cu2O/CuO film, properties that are important for various optoelectronic applications.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2022
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:umu:diva-203252 (URN)10.1063/5.0105281 (DOI)000869124200002 ()2-s2.0-85139759568 (Scopus ID)
Funder
Swedish Research Council, 2018-03937Swedish Research Council, 2017-04862Swedish Research Council, 2021-04629The Kempe Foundations, JCK-2132Carl Tryggers foundation , CTS 21-1581
Available from: 2023-01-17 Created: 2023-01-17 Last updated: 2023-03-28Bibliographically approved
Sandström, R., Gracia-Espino, E., Annamalai, A., Persson, P., Persson, I., Ekspong, J., . . . Wågberg, T. (2020). Microwave-Induced Structural Ordering of Resilient Nanostructured L10-FePt Catalysts for Oxygen Reduction Reaction. ACS Applied Energy Materials, 3(10), 9785-9791
Open this publication in new window or tab >>Microwave-Induced Structural Ordering of Resilient Nanostructured L10-FePt Catalysts for Oxygen Reduction Reaction
Show others...
2020 (English)In: ACS Applied Energy Materials, E-ISSN 2574-0962, Vol. 3, no 10, p. 9785-9791Article in journal (Refereed) Published
Abstract [en]

We show how structurally ordered L10 face-centered tetragonal (fct) FePt nanoparticles are produced by a solid-state microwave-assisted synthesis method. The structural phase as well as the incorporated Fe into the nanoparticles is confirmed by X-ray diffraction and high resolution high-angle annular dark field scanning transmission electron microscopy experiments. The prepared particles exhibit a remarkable resilience toward crystallite growth at high temperatures. Directly correlated to the L10 phase, the best oxygen reduction reaction (ORR) characteristics are achieved for particles with a 1:1 Fe:Pt atomic ratio and an average size of ~2.9 nm where Pt-specific evaluation provided a high mass and specific activity of ~570 A/gPt and ~600 μA/cm2Pt respectively. Our results demonstrate that well-structured catalysts possessing activities vastly exceeding Pt/C (~210 A/gPt & ~250 μA/cm2Pt), can be synthesized through a fast and highly eco-friendly method. We note that the achieved mass activity represent a significant leap toward the theoretical maximum for fully ordered FePt nanoparticles.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2020
Keywords
Proton exchange membrane fuel cell, platinum iron, Oxygen reduction reaction, microwave synthesis, L1(0) phase, FePt-nanoparticles, electrocatalysts, structural ordering, electron microscopy
National Category
Nano Technology Other Materials Engineering Condensed Matter Physics
Research subject
Materials Science; nanomaterials; nanoparticles; Solid State Physics
Identifiers
urn:nbn:se:umu:diva-158495 (URN)10.1021/acsaem.0c01368 (DOI)000586710300036 ()2-s2.0-85096581760 (Scopus ID)
Funder
Swedish Research Council, 2017-04862Swedish Energy Agency, 45419-1Interreg NordÅForsk (Ångpanneföreningen's Foundation for Research and Development), 15-483Swedish Research Council, 2016‐04412Swedish Foundation for Strategic Research , RIF 14‐0074Swedish Research Council, 2018-03937Olle Engkvists stiftelse, 186-0637
Note

Originally included in thesis in manuscript form  

Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2023-03-24Bibliographically approved
Sharifi, T., Xie, Y., Zhang, X., Barzegar, H. R., Lei, J., Coulter, G., . . . Ajayan, P. M. (2019). Graphene as an electrochemical transfer layer. Carbon, 141, 266-273
Open this publication in new window or tab >>Graphene as an electrochemical transfer layer
Show others...
2019 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 141, p. 266-273Article in journal (Refereed) Published
Abstract [en]

The capability of graphene to adopt a property from an adjacent material is investigated by measuring the electrochemical performance of a monolayer graphene placed on top of thin cobalt oxide (Co3O4) nanosheets. In this assembly, monolayer graphene works as an interfacial layer which inhibits the direct contact of the actual electroactive material and electrolyte during electrochemical reaction. The results show that while graphene is electrochemically inert, it behaves as an active material to catalyze oxygen evolution reaction (OER) once placed on top of Co3O4 nanosheets. The graphene-covered Co3O4 model system shows electrochemical performance similar to Co3O4 indicating complete transference of the electrochemical property of the metal oxide to the graphene. Based on density functional theory (DFT) calculations, charge transfer from graphene to Co3O4 is the key factor for turning the electrochemically inactive graphene to an apparent active material. 

Place, publisher, year, edition, pages
Elsevier, 2019
National Category
Materials Chemistry Condensed Matter Physics
Identifiers
urn:nbn:se:umu:diva-154021 (URN)10.1016/j.carbon.2018.09.056 (DOI)000450312600029 ()2-s2.0-85056148229 (Scopus ID)
Funder
Swedish Research Council, 2015-06462Swedish Research Council, 2015-00520
Available from: 2018-12-20 Created: 2018-12-20 Last updated: 2023-03-23Bibliographically approved
Gracia-Espino, E., Barzegar, H. R. & Zettl, A. (2018). Coronene-based graphene nanoribbons insulated by boron nitride nanotubes: electronic properties of the hybrid structure. ACS Omega, 3(10), 12930-12935
Open this publication in new window or tab >>Coronene-based graphene nanoribbons insulated by boron nitride nanotubes: electronic properties of the hybrid structure
2018 (English)In: ACS Omega, E-ISSN 2470-1343, Vol. 3, no 10, p. 12930-12935Article in journal (Refereed) Published
Abstract [en]

We present a theoretical study on the formation of graphene nanoribbons-via polymerization of coronene molecules-inside the inner cavity of boron nitride nanotubes. We examine the electronic property of the hybrid system, and we show that the boron nitride nanotube does not significantly alter the electronic properties of the encapsulated graphene nanoribbon. Motivated by previous experimental works, we examine graphene nanoribbons with two different widths and investigate probable scenarios for defect formation and/or twisting of the resulting graphene nanoribbons and their effect on the electronic properties of the hybrid system.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:umu:diva-153661 (URN)10.1021/acsomega.8b01617 (DOI)000449026500069 ()2-s2.0-85054729479 (Scopus ID)
Funder
Carl Tryggers foundation , CTS-16-161Swedish Research Council, 2015-00520
Available from: 2018-11-26 Created: 2018-11-26 Last updated: 2023-03-23Bibliographically approved
Barzegar, H. R., Larsen, C., Boulanger, N., Zettl, A., Edman, L. & Wågberg, T. (2018). Self-assembled PCBM nanosheets: a facile route to electronic layer-on-Layer heterostructures. Nano letters (Print), 18(2), 1442-1447
Open this publication in new window or tab >>Self-assembled PCBM nanosheets: a facile route to electronic layer-on-Layer heterostructures
Show others...
2018 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, no 2, p. 1442-1447Article in journal, Editorial material (Refereed) Published
Abstract [en]

We report on the self-assembly of semicrystalline [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) nanosheets at the interface between a hydrophobic solvent and water, and utilize this opportunity for the realization of electronically active organic/organic molecular heterostructures. The self-assembled PCBM nanosheets can feature a lateral size of >1 cm2 and be transferred from the water surface to both hydrophobic and hydrophilic surfaces using facile transfer techniques. We employ a transferred single PCBM nanosheet as the active material in a field-effect transistor (FET) and verify semiconductor function by a measured electron mobility of 1.2 × 10–2 cm2 V–1 s–1 and an on–off ratio of ∼1 × 104. We further fabricate a planar organic/organic heterostructure with the p-type organic semiconductor poly(3-hexylthiophene-2,5-diyl) as the bottom layer and the n-type PCBM nanosheet as the top layer and demonstrate ambipolar FET operation with an electron mobility of 8.7 × 10–4 cm2 V–1 s–1 and a hole mobility of 3.1 × 10–4 cm2V–1 s–1.

Keywords
Organic electronic; organic heterostructures; PCBM nanosheets; self-assembly
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:umu:diva-144566 (URN)10.1021/acs.nanolett.7b05205 (DOI)000425559700114 ()29364679 (PubMedID)2-s2.0-85042103585 (Scopus ID)
Available from: 2018-02-06 Created: 2018-02-06 Last updated: 2023-03-24Bibliographically approved
Dunn, G., Shen, K., Barzegar, H. R., Shi, W., Belling, J. N., Nguyen, T. N. .., . . . Zettl, A. (2017). Selective Insulation of Carbon nanotubes. Physica status solidi. B, Basic research, 254(11), Article ID 1700202.
Open this publication in new window or tab >>Selective Insulation of Carbon nanotubes
Show others...
2017 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 254, no 11, article id 1700202Article in journal, Editorial material (Refereed) Published
Abstract [en]

We demonstrate a method for the selective encapsulation of carbonnanotubes in thin parylene films using iron as a sacrificial lift-off layer. Theiron serves as an inhibitor of parylene deposition and prevents the parylenemolecules from linking, thus facilitating selective area coating after lift-off.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2017
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:umu:diva-144557 (URN)10.1002/pssb.201700202 (DOI)000417609800005 ()
Available from: 2018-02-06 Created: 2018-02-06 Last updated: 2019-11-21Bibliographically approved
Barzegar, H. R., Yan, A., Coh, S., Gracia-Espino, E., Ojeda-Aristizabal, C., Dunn, G., . . . Zettl, A. (2017). Spontaneous twisting of a collapsed carbon nanotube. Nano Reseach, 10(6), 1942-1949
Open this publication in new window or tab >>Spontaneous twisting of a collapsed carbon nanotube
Show others...
2017 (English)In: Nano Reseach, ISSN 1998-0124, E-ISSN 1998-0000, Vol. 10, no 6, p. 1942-1949Article in journal (Refereed) Published
Abstract [en]

We study the collapsing and subsequent spontaneous twisting of a carbon nanotube by in situ transmission electron microscopy (TEM). A custom-sized nanotube is first created in the microscope by selectively extracting shells from a parent multi-walled tube. The few-walled, large-diameter daughter nanotube is driven to collapse via mechanical stimulation, after which the ribbon-like collapsed tube spontaneously twists along its long axis. In situ diffraction experiments fully characterize the uncollapsed and collapsed tubes. The experimental observations and associated theoretical analysis indicate that the origin of the twisting is compressive strain.

Place, publisher, year, edition, pages
Tsinghua University Press, 2017
Keywords
multi-walled carbon nanotube, collapsed carbon nanotube, in situ TEM, electron diffraction, twisting, graphene nanoribbons
National Category
Biochemicals Composite Science and Engineering Condensed Matter Physics
Identifiers
urn:nbn:se:umu:diva-136050 (URN)10.1007/s12274-016-1380-7 (DOI)000401320700010 ()2-s2.0-85010792471 (Scopus ID)
Available from: 2017-06-20 Created: 2017-06-20 Last updated: 2022-04-04Bibliographically approved
Projects
Nano-cavity for encapsulation of small molecules; towards synthesis of one-dimensional hybrid structures and liquid cell for electron microscopy [2015-00520_VR]; Umeå University
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-1314-5407

Search in DiVA

Show all publications