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Zazpe R, Sopha H, Prikryl J, Krbal M, Mistrik J, Dvorak F, Hromadko L, Macak JM. A 1D conical nanotubular TiO 2/CdS heterostructure with superior photon-to-electron conversion. Nanoscale 2018; 10:16601-16612. [PMID: 30152830 PMCID: PMC6137607 DOI: 10.1039/c8nr02418a] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2018] [Accepted: 05/23/2018] [Indexed: 06/01/2023]
Abstract
Herein, a new strategy to efficiently harvest photons in solar cells is presented. A solar cell heterostructure is put forward, based on a 1D conical TiO2 nanotubular scaffold of high aspect ratio, homogenously coated with a thin few nm layer of CdS light absorber using atomic layer deposition (ALD). For the first time, a large variety of conical nanotube layers with a huge span of aspect ratios was utilized and ALD was used for the preparation of a uniform CdS coating within the entire high surface area of the TiO2 nanotubes. The resulting 1D conical CdS/TiO2 tubular heterostructure acts as a sink for photons. Due to the multiple light scattering and absorption events within this nanotubular sink, a large portion of photons (nearly 80%) is converted into electrons. It is the combination of the scaffold architecture and the light absorber present on the high surface area as a very thin layer, the optimized charge transport and multiple optical effects that make this heterostructure very promising for the next generation of highly performing solar cells.
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Affiliation(s)
- R. Zazpe
- Center of Materials and Nanotechnologies
, Faculty of Chemical Technology
, University of Pardubice
,
Nam. Cs. Legii 565
, 530 02 Pardubice
, Czech Republic
.
- Central European Institute of Technology
, Brno University of Technology
,
Purkynova 123
, Brno
, Czech Republic
| | - H. Sopha
- Center of Materials and Nanotechnologies
, Faculty of Chemical Technology
, University of Pardubice
,
Nam. Cs. Legii 565
, 530 02 Pardubice
, Czech Republic
.
- Central European Institute of Technology
, Brno University of Technology
,
Purkynova 123
, Brno
, Czech Republic
| | - J. Prikryl
- Center of Materials and Nanotechnologies
, Faculty of Chemical Technology
, University of Pardubice
,
Nam. Cs. Legii 565
, 530 02 Pardubice
, Czech Republic
.
| | - M. Krbal
- Center of Materials and Nanotechnologies
, Faculty of Chemical Technology
, University of Pardubice
,
Nam. Cs. Legii 565
, 530 02 Pardubice
, Czech Republic
.
| | - J. Mistrik
- Center of Materials and Nanotechnologies
, Faculty of Chemical Technology
, University of Pardubice
,
Nam. Cs. Legii 565
, 530 02 Pardubice
, Czech Republic
.
| | - F. Dvorak
- Center of Materials and Nanotechnologies
, Faculty of Chemical Technology
, University of Pardubice
,
Nam. Cs. Legii 565
, 530 02 Pardubice
, Czech Republic
.
| | - L. Hromadko
- Center of Materials and Nanotechnologies
, Faculty of Chemical Technology
, University of Pardubice
,
Nam. Cs. Legii 565
, 530 02 Pardubice
, Czech Republic
.
| | - J. M. Macak
- Center of Materials and Nanotechnologies
, Faculty of Chemical Technology
, University of Pardubice
,
Nam. Cs. Legii 565
, 530 02 Pardubice
, Czech Republic
.
- Central European Institute of Technology
, Brno University of Technology
,
Purkynova 123
, Brno
, Czech Republic
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Krbal M, Prikryl J, Zazpe R, Sopha H, Macak JM. CdS-coated TiO 2 nanotube layers: downscaling tube diameter towards efficient heterostructured photoelectrochemical conversion. Nanoscale 2017; 9:7755-7759. [PMID: 28580990 PMCID: PMC5471917 DOI: 10.1039/c7nr02841e] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2017] [Accepted: 05/16/2017] [Indexed: 06/02/2023]
Abstract
Herein, a novel photoelectrochemical heterostructure based on TiO2 nanotube layers uniformly coated by a CdS thin layer (using ALD) is presented. Downscaling the nanotube diameter (from 95 to 35 nm) resulted in a 2-fold enhancement of the UV and Vis light photocurrents. Further photocurrent improvement resulted from the prior annealing of the TiO2 nanotube layers from 300 to 600 °C.
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Affiliation(s)
- M. Krbal
- Center of Materials and Nanotechnologies , Faculty of Chemical Technology , University of Pardubice , Nam. Cs. Legii 565 , 530 02 Pardubice , Czech Republic . ; Tel: +420466037401
| | - J. Prikryl
- Center of Materials and Nanotechnologies , Faculty of Chemical Technology , University of Pardubice , Nam. Cs. Legii 565 , 530 02 Pardubice , Czech Republic . ; Tel: +420466037401
| | - R. Zazpe
- Center of Materials and Nanotechnologies , Faculty of Chemical Technology , University of Pardubice , Nam. Cs. Legii 565 , 530 02 Pardubice , Czech Republic . ; Tel: +420466037401
| | - H. Sopha
- Center of Materials and Nanotechnologies , Faculty of Chemical Technology , University of Pardubice , Nam. Cs. Legii 565 , 530 02 Pardubice , Czech Republic . ; Tel: +420466037401
| | - J. M. Macak
- Center of Materials and Nanotechnologies , Faculty of Chemical Technology , University of Pardubice , Nam. Cs. Legii 565 , 530 02 Pardubice , Czech Republic . ; Tel: +420466037401
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Mitrofanov KV, Kolobov AV, Fons P, Krbal M, Tominaga J, Uruga T. Study of band inversion in the PbxSn1-xTe class of topological crystalline insulators using x-ray absorption spectroscopy. J Phys Condens Matter 2014; 26:475502. [PMID: 25355606 DOI: 10.1088/0953-8984/26/47/475502] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Pb(x)Sn(1-x)Te and Pb(x)Sn(1-x)Se crystals belong to the class of topological crystalline insulators where topological protection is achieved due to crystal symmetry rather than time-reversal symmetry. In this work, we make use of selection rules in the x-ray absorption process to experimentally detect band inversion along the PbTe(Se)-SnTe(Se) tie-lines. The observed significant change in the ratio of intensities of L1 and L3 transitions along the tie-line demonstrates that x-ray absorption can be a useful tool to study band inversion in topological insulators.
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Affiliation(s)
- K V Mitrofanov
- Nanoelectronics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8562, Japan
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Simpson RE, Fons P, Kolobov AV, Fukaya T, Krbal M, Yagi T, Tominaga J. Interfacial phase-change memory. Nat Nanotechnol 2011; 6:501-5. [PMID: 21725305 DOI: 10.1038/nnano.2011.96] [Citation(s) in RCA: 188] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2011] [Accepted: 05/23/2011] [Indexed: 05/09/2023]
Abstract
Phase-change memory technology relies on the electrical and optical properties of certain materials changing substantially when the atomic structure of the material is altered by heating or some other excitation process. For example, switching the composite Ge(2)Sb(2)Te(5) (GST) alloy from its covalently bonded amorphous phase to its resonantly bonded metastable cubic crystalline phase decreases the resistivity by three orders of magnitude, and also increases reflectivity across the visible spectrum. Moreover, phase-change memory based on GST is scalable, and is therefore a candidate to replace Flash memory for non-volatile data storage applications. The energy needed to switch between the two phases depends on the intrinsic properties of the phase-change material and the device architecture; this energy is usually supplied by laser or electrical pulses. The switching energy for GST can be reduced by limiting the movement of the atoms to a single dimension, thus substantially reducing the entropic losses associated with the phase-change process. In particular, aligning the c-axis of a hexagonal Sb(2)Te(3) layer and the 〈111〉 direction of a cubic GeTe layer in a superlattice structure creates a material in which Ge atoms can switch between octahedral sites and lower-coordination sites at the interface of the superlattice layers. Here we demonstrate GeTe/Sb(2)Te(3) interfacial phase-change memory (IPCM) data storage devices with reduced switching energies, improved write-erase cycle lifetimes and faster switching speeds.
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Affiliation(s)
- R E Simpson
- Nanoelectronics Research Institute, National Institute of Applied Industrial Science and Technology, Tsukuba Central 4, 1-1-1 Higashi, Tsukuba 305-8562, Japan.
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Kolobov AV, Krbal M, Fons P, Tominaga J, Uruga T. Distortion-triggered loss of long-range order in solids with bonding energy hierarchy. Nat Chem 2011; 3:311-6. [PMID: 21430691 DOI: 10.1038/nchem.1007] [Citation(s) in RCA: 168] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2010] [Accepted: 02/08/2011] [Indexed: 11/09/2022]
Abstract
An amorphous-to-crystal transition in phase-change materials like Ge-Sb-Te is widely used for data storage. The basic principle is to take advantage of the property contrast between the crystalline and amorphous states to encode information; amorphization is believed to be caused by melting the materials with an intense laser or electrical pulse and subsequently quenching the melt. Here, we demonstrate that distortions in the crystalline phase may trigger a collapse of long-range order, generating the amorphous phase without going through the liquid state. We further show that the principal change in optical properties occurs during the distortion of the still crystalline structure, upsetting yet another commonly held belief that attributes the change in properties to the loss of long-range order. Furthermore, our results suggest a way to lower energy consumption by condensing phase change inducing energy into shorter pulses or through the use of coherent phonon excitation.
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Affiliation(s)
- A V Kolobov
- Nanodevice Innovation Research Center, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba 305-8562, Japan.
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Simpson RE, Krbal M, Fons P, Kolobov AV, Tominaga J, Uruga T, Tanida H. Toward the ultimate limit of phase change in Ge(2)Sb(2)Te(5). Nano Lett 2010; 10:414-419. [PMID: 20041706 DOI: 10.1021/nl902777z] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The limit to which the phase change memory material Ge(2)Sb(2)Te(5) can be scaled toward the smallest possible memory cell is investigated using structural and optical methodologies. The encapsulation material surrounding the Ge(2)Sb(2)Te(5) has an increasingly dominant effect on the material's ability to change phase, and a profound increase in the crystallization temperature is observed when the Ge(2)Sb(2)Te(5) layer is less than 6 nm thick. We have found that the increased crystallization temperature originates from compressive stress exerted from the encapsulation material. By minimizing the stress, we have maintained the bulk crystallization temperature in Ge(2)Sb(2)Te(5) films just 2 nm thick.
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Affiliation(s)
- R E Simpson
- Center for Applied Near-Field Optics Research, National Institute of Applied Industrial Science and Technology, Tsukuba Central4, 1-1-1 Higashi, Tsukuba 305-8562, Japan.
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Krbal M, Kolobov AV, Haines J, Fons P, Levelut C, Le Parc R, Hanfland M, Tominaga J, Pradel A, Ribes M. Initial structure memory of pressure-induced changes in the phase-change memory alloy Ge2Sb2Te5. Phys Rev Lett 2009; 103:115502. [PMID: 19792382 DOI: 10.1103/physrevlett.103.115502] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2009] [Indexed: 05/28/2023]
Abstract
We demonstrate that while the metastable face-centered cubic (fcc) phase of Ge2Sb2Te5 becomes amorphous under hydrostatic compression at about 15 GPa, the stable trigonal phase remains crystalline. Upon higher compression, a body-centered cubic phase is obtained in both cases around 30 GPa. Upon decompression, the amorphous phase is retained for the starting fcc phase while the initial structure is recovered for the starting trigonal phase. We argue that the presence of vacancies and associated subsequent large atomic displacements lead to nanoscale phase separation and loss of initial structure memory in the fcc staring phase of Ge2Sb2Te5.
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Affiliation(s)
- M Krbal
- Institut Charles Gerhardt, UMR 5253 CNRS-UM2-ENSCM-UM1, PMDP/PMOF, Université Montpellier II, Place Eugène Bataillon, Montpellier Cedex 5, France
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Wagner T, Krbal M, Gutwirth J, Nemec P, Vlcek M, Frumar M, Perina V, Mackova A, Hnatovitz V, Kasap SO, Vlcek M. Characterization of AgAsS and AgSbS amorphous films prepared by pulsed laser deposition. SURF INTERFACE ANAL 2004. [DOI: 10.1002/sia.1860] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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