Graphene-enhanced metal oxide gas sensors at room temperature: a review

• Dongjin Sun,
• Yifan Luo,
• Marc Debliquy and
• Chao Zhang

Beilstein J. Nanotechnol. 2018, 9, 2832–2844, doi:10.3762/bjnano.9.264

• concentrations of NH3 and responded dramatically, which could be ascribed to the p–n heterojunctions formed between ZnO and rGO. However, the influence of humidity on the sensor response was not negligible due to the residual oxygen (high hydrophilicity) on rGO and the active sites (oxygen vacancies) on ZnO

Impact of the anodization time on the photocatalytic activity of TiO₂ nanotubes

• Jesús A. Díaz-Real,
• Geyla C. Dubed-Bandomo,
• Juan Galindo-de-la-Rosa,
• Luis G. Arriaga,
• Janet Ledesma-García and
• Nicolas Alonso-Vante

Beilstein J. Nanotechnol. 2018, 9, 2628–2643, doi:10.3762/bjnano.9.244

• is supported by the fact that atomic radii for O (48 pm) and F (42 pm) are similar enough to allow for the replacement of the former, effectively doping the material by creating oxygen vacancies and different energy states [29]. XPS To characterize the surface chemistry, high-resolution XPS

• N and F. Nevertheless, some physical phenomena such as light scattering (from the top part of the TNTs) and oxygen vacancies could also create distortions in the IPCE spectra. Furthermore, the bandgap (Eg) can be obtained from the Tauc plots, Figure 7b, plotting jph as a function of the wavelength

Exploring the photoleakage current and photoinduced negative bias instability in amorphous InGaZnO thin-film transistors with various active layer thicknesses

• Dapeng Wang and
• Mamoru Furuta

Beilstein J. Nanotechnol. 2018, 9, 2573–2580, doi:10.3762/bjnano.9.239

• oxygen-related defects, such as oxygen vacancies (VO), may be the origin of high-density electron traps near the EV in a-IGZO TFTs, which occupy the region near the valence band maximum with an energy width of ≈1.5 eV [26][27]. Figure 3a–d shows the variation in the transfer characteristics of a-IGZO

• required for the transition from VO to VO+ and VO2+, respectively. Moreover, the ionized oxygen vacancies of VO+ and VO2+ are located near the mid-gap and the bottom of the EC [15][29], respectively. It is sufficient to excite high-density VO defects to VO+/VO2+ and then to generate free electrons to EC

• oxygen vacancies in the bulk of the IGZO for the enhancement of electrical properties and stress stability of the TFTs, the following two aspects should be mainly considered: (i) oxidizing the densities of the defect state of oxide semiconductors to suppress charge trapping, for example by oxygen

Improved catalytic combustion of methane using CuO nanobelts with predominantly (001) surfaces

• Qingquan Kong,
• Yichun Yin,
• Bing Xue,
• Yonggang Jin,
• Wei Feng,
• Zhi-Gang Chen,
• Shi Su and
• Chenghua Sun

Beilstein J. Nanotechnol. 2018, 9, 2526–2532, doi:10.3762/bjnano.9.235

• indicates that the key role of OV is to activate O2 and release a highly active oxygen atom, although a barrier of 0.91 eV is found for O2 dissociation in the case of CuO(001), but the dehydrogenation from CHx becomes exothermic, confirming the importance of surface oxygen and oxygen vacancies, as suggested

Electrospun one-dimensional nanostructures: a new horizon for gas sensing materials

• Muhammad Imran,
• Nunzio Motta and
• Mahnaz Shafiei

Beilstein J. Nanotechnol. 2018, 9, 2128–2170, doi:10.3762/bjnano.9.202

• ]. Al-doped SnO2 NTs exhibit a high response to low concentrations of formaldehyde by Sn4+ by Al3+ in a SnO2 lattice as well as increase in oxygen vacancies [184]. Pure and 8Al-Sn NTs (i.e., the Al/(Al + Sn) ratio is 8%) have nearly the same average diameter (120 nm inner diameter and 200 nm outer

• to 64.9 due to an increase in oxygen vacancies. The response and the recovery time are about 7 s and 30 s, respectively [179]. WO3 NFs/NTs functionalized by Pt [168][187], Pd [107][188], Cu [101], Ru [189], Rh2O3 [106], Au NPs [109], RuO2 NPs [189], La2O3 [104] as well as Pd-loaded ZnO nanocubes [1

• resulting in high oxygen vacancies [215]. Similarly, Nd-doped In2O3 NTs showed enhanced formaldehyde sensing due to their porous and cracked morphology. Nd-doped In2O3 NTs have an average diameter of 200 nm as shown in Figure 10a–c. The optimum doping amount of Nd was 11 mol %. Nd-doped In2O3 porous NTs

Cr(VI) remediation from aqueous environment through modified-TiO₂-mediated photocatalytic reduction

• Rashmi Acharya,
• Brundabana Naik and
• Kulamani Parida

Beilstein J. Nanotechnol. 2018, 9, 1448–1470, doi:10.3762/bjnano.9.137

Understanding the performance and mechanism of Mg-containing oxides as support catalysts in the thermal dry reforming of methane

• Nor Fazila Khairudin,
• Mohd Farid Fahmi Sukri,
• Mehrnoush Khavarian and
• Abdul Rahman Mohamed

Beilstein J. Nanotechnol. 2018, 9, 1162–1183, doi:10.3762/bjnano.9.108

• . Therefore, the combination of Ce with Mg improves the catalyst basicity site. CeO2, commonly known for its oxygen storage capacity, contains a great concentration of highly mobile oxygen vacancies which could reduce the deposition of carbon on the catalyst surface [76]. In fact, CO2 molecules are more

• attracted to the base center (–Mg–OH group) and then dissociate on Ce2O3 via electron transfer to CO2 through oxygen vacancies to form CO2 and CeO2. Thus, the base center is most suitable for adsorbing the largest amount of CO2. The catalyst was stable for up to 50 h of reaction at 700 °C with an equal feed

Room-temperature single-photon emitters in titanium dioxide optical defects

• Kelvin Chung,
• Yu H. Leung,
• Chap H. To,
• Aleksandra B. Djurišić and
• Snjezana Tomljenovic-Hanic

Beilstein J. Nanotechnol. 2018, 9, 1085–1094, doi:10.3762/bjnano.9.100

• surface defect sites [59] and surface oxygen vacancies on anatase nanocrystal films [60]. Similar photoluminescence in the red was also observed from ZnO defects [7][8][9]. The photodynamics of D1 was also recorded and can be seen for a pump power of 82 μW in Figure 4b. The time trace shows photostability

• attributed their visible emission to surface states originating from oxygen vacancies associated with Ti3+ ions. The work of Zhang et al. [42] on anatase nanocrystals fabricated through a chemical process could not conclude definitively the origin of their broad visible emission band centred around 578 nm

Cyclodextrin inhibits zinc corrosion by destabilizing point defect formation in the oxide layer

• Abdulrahman Altin,
• Maciej Krzywiecki,
• Adnan Sarfraz,
• Cigdem Toparli,
• Claudius Laska,
• Philipp Kerger,
• Aleksandar Zeradjanin,
• Karl J. J. Mayrhofer,
• Michael Rohwerder and
• Andreas Erbe

Beilstein J. Nanotechnol. 2018, 9, 936–944, doi:10.3762/bjnano.9.86

• alternative explanation is a contribution from the β-CD HOMO to ZnO VBonset changes, since the β-CD HOMO onset was found 1.85 eV from the Fermi level. Intuitively, one would assume oxygen vacancies or zinc interstitials as dominating defects in the predominately n-type ZnO. The largest energy shift was

Effect of annealing treatments on CeO₂ grown on TiN and Si substrates by atomic layer deposition

• Silvia Vangelista,
• Rossella Piagge,
• Satu Ek and
• Alessio Lamperti

Beilstein J. Nanotechnol. 2018, 9, 890–899, doi:10.3762/bjnano.9.83

• equilibrium under standard conditions of temperature and pressure, stoichiometric CeO2 hosts Ce4+ and O2− ions in the cubic fluorite structure (space group Fm−3m in Pearson notation). However, Ce3+ ions can also be accommodated in the lattice structure in relation with oxygen vacancies, and Ce2O3 as minority

• growth and the oxygen vacancies, while preserving the cubic fluorite structure [12][13][14]. The electrical properties of CeO2 have been improved by performing post-deposition annealing at various temperatures [15]. In light of these previous studies, the interaction between substrate and annealing is

• atmosphere with the aim to passivate the film defects, namely the oxygen vacancies. A second set of samples has been annealed at high temperatures (600–900 °C) to induce full crystallization in CeO2 films and follow the corresponding structural and chemical changes induced by the annealing process

A review of carbon-based and non-carbon-based catalyst supports for the selective catalytic reduction of nitric oxide

• Shahreen Binti Izwan Anthonysamy,
• Syahidah Binti Afandi,
• Mehrnoush Khavarian and
• Abdul Rahman Bin Mohamed

Beilstein J. Nanotechnol. 2018, 9, 740–761, doi:10.3762/bjnano.9.68

• prepared using the sol–gel method had better catalytic activity than that of the impregnation method. Besides that, a huge amount of oxygen vacancies and superoxide ions was observed when cobalt metal was introduced via the sol–gel method, thereby enhancing the SCR performance. On the other hand, the co

Synthesis and characterization of two new TiO₂-containing benzothiazole-based imine composites for organic device applications

• Anna Różycka,
• Agnieszka Iwan,
• Krzysztof Artur Bogdanowicz,
• Michal Filapek,
• Natalia Górska,
• Damian Pociecha,
• Marek Malinowski,
• Patryk Fryń,
• Agnieszka Hreniak,
• Jakub Rysz,
• Paweł Dąbczyński and
• Monika Marzec

Beilstein J. Nanotechnol. 2018, 9, 721–739, doi:10.3762/bjnano.9.67

• both investigated imines. Similar interactions of oxygen vacancies existing on the TiO2 surface with SP1 and SP2 were observed. The imine:TiO2 mixtures showed good air stability and reusability, which demonstrates its potential for organic device applications. Keywords: azomethines; composites; HOMO

• hydrocarbon chains or aromatic rings are not visible. The observed changes confirmed the significant influence of titanium dioxide on the structural properties of both investigated compounds. It can be explained by the interactions of oxygen vacancies existing on the TiO2 surface with SP1 as well as SP2

Influence of the preparation method on the photocatalytic activity of Nd-modified TiO₂

• Patrycja Parnicka,
• Paweł Mazierski,
• Tomasz Grzyb,
• Wojciech Lisowski,
• Ewa Kowalska,
• Bunsho Ohtani,
• Adriana Zaleska-Medynska and
• Joanna Nadolna

Beilstein J. Nanotechnol. 2018, 9, 447–459, doi:10.3762/bjnano.9.43

• increasing the content of surface oxygen vacancies and defects [31][40]. These electron trapping sites can enhance the separation of photogenerated electron–hole pairs [24]. Furthermore, both pristine and Nd-TiO2 NPs exhibit obvious excitonic PL signals with a similar curve shape. The observed phenomena can

• amount of oxygen vacancies and defects was found on the surface of the 0.25% Nd-TiO2(HT) sample. As previously mentioned, the presence of oxygen deficient centres on the surface and surface defects such as Ti3+ can reduce the rate of electron–hole pair recombination [45][46][47]. Further, the light

Atomic layer deposition and properties of ZrO₂/Fe₂O₃ thin films

• Kristjan Kalam,
• Helina Seemen,
• Peeter Ritslaid,
• Mihkel Rähn,
• Aile Tamm,
• Kaupo Kukli,
• Aarne Kasikov,
• Joosep Link,
• Raivo Stern,
• Salvador Dueñas,
• Helena Castán and
• Héctor García

Beilstein J. Nanotechnol. 2018, 9, 119–128, doi:10.3762/bjnano.9.14

• reactive DC magnetron sputtering [7], also exhibited ferromagnetic properties. The undoped ZrO2 exhibited ferromagnetic properties mainly driven by oxygen vacancies. Monoclinic and tetragonal phases with similar amounts of oxygen vacancies were compared and ferromagnetism was only observed in the case of

• iron and zirconium oxides, the amount of defects (in particular oxygen vacancies) is increased due to the substitutive exchange between metal ions of different valence, resulting in an increase also in the leakage currents. Pure ZrO2 exhibited the lowest leakage current (Figure 7) and did not show any

Fabrication of CeO₂–MO_x (M = Cu, Co, Ni) composite yolk–shell nanospheres with enhanced catalytic properties for CO oxidation

• Ling Liu,
• Jingjing Shi,
• Hongxia Cao,
• Ruiyu Wang and
• Ziwu Liu

Beilstein J. Nanotechnol. 2017, 8, 2425–2437, doi:10.3762/bjnano.8.241

• independent forms. The formation of highly-dispersed copper species promotes the adsorption of CO molecules, while the presence of oxygen vacancies provided by CeO2 can in turn create active oxygen in the oxidation reactions [12][13]. Therefore, the creation of two-phase interfaces as numerous as possible and

• /and hierarchical architecture, which possess excellent redox properties and abundant oxygen vacancies, will be favorable for the enhancement of catalytic activity toward CO oxidation. CeO2-based hybrid oxides with hollow structure can be synthesized by a sacrificial-template method based on

• on various parameters, including the crystal defects, oxygen vacancies, phonon confinement, and inhomogeneous strain related to the reduced ceria [31][32]. Herein, the shift can be related to the interaction between the MOx species and CeO2 surface, which leads to lengthening and weakening of the M–O

Low-temperature CO oxidation over Cu/Pt co-doped ZrO₂ nanoparticles synthesized by solution combustion

• Amit Singhania and
• Shipra Mital Gupta

Beilstein J. Nanotechnol. 2017, 8, 1546–1552, doi:10.3762/bjnano.8.156

• dissolve into the ZrO2 lattice and thus creates oxygen vacancies due to lattice distortion and charge imbalance. High-resolution transmission electron microscopy (HRTEM) results showed Cu/Pt co-doped ZrO2 nanoparticles with a size of ca. 10 nm. X-ray diffraction (XRD) and Raman spectra confirmed cubic

• structure and larger oxygen vacancies. The nanoparticles showed excellent activity for CO oxidation. The temperature T50 (the temperature at which 50% of CO are converted) was lowered by 175 °C in comparison to bare ZrO2. Further, they exhibited very high stability for CO reaction (time-on-stream ≈ 70 h

• ). This is due to combined effect of smaller particle size, large oxygen vacancies, high specific surface area and better thermal stability of the Cu/Pt co-doped ZrO2 nanoparticles. The apparent activation energy for CO oxidation is found to be 45.6 kJ·mol−1. The CO conversion decreases with increase in

Synthesis of graphene–transition metal oxide hybrid nanoparticles and their application in various fields

• Arpita Jana,
• Elke Scheer and
• Sebastian Polarz

Beilstein J. Nanotechnol. 2017, 8, 688–714, doi:10.3762/bjnano.8.74

• photoluminescence (PL) band at 373 nm, which is due to the exciton recombination corresponding to the band edge emission, and a green emission peak is most commonly observed that arises from the defect of ZnO NPs such as oxygen vacancies, zinc vacancies, oxygen interstitials, and zinc interstitials [241]. Graphene

Impact of air exposure and annealing on the chemical and electronic properties of the surface of SnO₂ nanolayers deposited by rheotaxial growth and vacuum oxidation

• Monika Kwoka and
• Maciej Krzywiecki

Beilstein J. Nanotechnol. 2017, 8, 514–521, doi:10.3762/bjnano.8.55

• to its high and variable electrical conductivity in the range of 100 Ω−1·cm−1 to 102 Ω−1·cm−1 due to the existence of free electrons in oxygen vacancies. This effect has been widely applied for the construction of prototypical gas sensors devices with both thick and thin films [3][4][5][6][7][8]. The

Nanocrystalline ZrO₂ and Pt-doped ZrO₂ catalysts for low-temperature CO oxidation

• Amit Singhania and
• Shipra Mital Gupta

Beilstein J. Nanotechnol. 2017, 8, 264–271, doi:10.3762/bjnano.8.29

• conversion at 240 °C, which is the highest conversion rate reported for ZrO2 in literature to date. It is found that through solution combustion, Pt2+ ions replace Zr4+ ions in the ZrO2 lattice and because of this, oxygen vacancies are formed due to charge imbalance and lattice distortion in ZrO2. 1% Pt was

• oxygen mobility and oxygen vacancies and improves the activity and stability of the catalyst. The effects of gas hourly space velocity (GHSV) and initial CO concentration on the CO oxidation over Pt(1%)-ZrO2 were studied. Keywords: CO oxidation; nanomaterials; platinum; solution combustion method

• CO oxidation by different researchers [13][14][15][16]. The addition of precious metals such as Pd, Pt and Rh increased the reactivity of the support by increasing its oxygen mobility and number of oxygen vacancies (the source of oxygen in CO oxidation) [10][11][12]. In recent years, ZrO2 has been

Nanocrystalline TiO₂/SnO₂ heterostructures for gas sensing

• Barbara Lyson-Sypien,
• Anna Kusior,
• Mieczylaw Rekas,
• Jan Zukrowski,
• Marta Gajewska,
• Katarzyna Michalow-Mauke,
• Thomas Graule,
• Marta Radecka and
• Katarzyna Zakrzewska

Beilstein J. Nanotechnol. 2017, 8, 108–122, doi:10.3762/bjnano.8.12

• which the semiconducting behavior begins to prevail over water desorption/oxygen adsorption depends on the TiO2–SnO2 composition. The higher Tmax for TiO2-rich heterostructures can be explained on the basis of the higher ionic defect concentration (mainly oxygen vacancies) at the surface of TiO2. It is

• well known that oxygen vacancies act as water adsorption centers. Moreover, in the case of SnO2 water adsorption takes place because of the formation of weak van der Waals bonds between water dipoles and lattice ions (Sn4+ and O2−) [19]. This facilitates water desorption from the surface of SnO2-rich

• of oxygen vacancies VO, the following reaction could be proposed: The condition of lattice electroneutrality requires that: where k = 1 or 2 corresponds to singly or doubly ionized defects, respectively. Applying the law of mass action to Equation 11 (with k = 1 or 2) gives power-law coefficients of

Ordering of Zn-centered porphyrin and phthalocyanine on TiO₂(011): STM studies

• Piotr Olszowski,
• Lukasz Zajac,
• Szymon Godlewski,
• Bartosz Such,
• Rémy Pawlak,
• Antoine Hinaut,
• Res Jöhr,
• Thilo Glatzel,
• Ernst Meyer and
• Marek Szymonski

Beilstein J. Nanotechnol. 2017, 8, 99–107, doi:10.3762/bjnano.8.11

• investigation of molecular adsorption is titanium dioxide [11][12]. The most stable and the most studied face of TiO2 is the rutile (110) surface. In the context of adsorption studies, it is important to note that the (110) face of rutile usually contains numerous oxygen vacancies, often filled with hydroxy

Scanning probe microscopy studies on the adsorption of selected molecular dyes on titania

• Jakub S. Prauzner-Bechcicki,
• Lukasz Zajac,
• Piotr Olszowski,
• Res Jöhr,
• Antoine Hinaut,
• Thilo Glatzel,
• Bartosz Such,
• Ernst Meyer and
• Marek Szymonski

Beilstein J. Nanotechnol. 2016, 7, 1642–1653, doi:10.3762/bjnano.7.156

• either by the formation of oxygen vacancies [36], which are point defects commonly found in TiO2(110) surfaces, or by doping [37], and are redistributed among multiple Ti lattice sites in the subsurface layers [36][37][38][39][40][41]. Thus, a defect state in the band gap is formed. Such delocalized

• to the oxide takes place, and an interface dipole is formed. To further understand the energy level alignment between a semiconducting substrate and an organic adsorbate, Lackinger, Janson and Ho [59] studied interactions between zinc(II) etioporphyrin (ZnEP) and oxygen vacancies, which are point

• defects commonly found in TiO2(110) surfaces. The energy level alignment is of crucial importance for DSSC applications of titania. The authors took special care to prepare a sample with unsaturated oxygen vacancies [59] because it is known that they can be easily passivated even at very low partial

Photocurrent generation in carbon nanotube/cubic-phase HfO₂ nanoparticle hybrid nanocomposites

• Protima Rauwel,
• Augustinas Galeckas,
• Martin Salumaa,
• Frédérique Ducroquet and
• Erwan Rauwel

Beilstein J. Nanotechnol. 2016, 7, 1075–1085, doi:10.3762/bjnano.7.101

• -phase HfO2 nanoparticles, oxygen vacancies acting as luminescence trap states are present in large amounts [22]. In the variety of different techniques used to decorate CNTs, the first step is usually the dispersion of the CNTs in a liquid solution as they exist in the form of bundled ropes [23]. Acid

• close to the fundamental edge and commonly associated with oxygen vacancies [43][44]. With regard to the latter, a noteworthy discrepancy (at ≈0.1 eV) of the absorption thresholds in the case of CNT-embedded and free-standing HfO2 nanoparticles likely points towards different charge states of oxygen

• respect that theoretical calculations of the electronic properties of oxygen vacancies in monoclinic HfO2 [45] predict single- and double-ionized vacancy states at 4.7 eV and 4.9 eV above the valence band, which appear very close to the experimentally observed absorption thresholds in Figure 2b. The

NO gas sensing at room temperature using single titanium oxide nanodot sensors created by atomic force microscopy nanolithography

• Li-Yang Hong and
• Heh-Nan Lin

Beilstein J. Nanotechnol. 2016, 7, 1044–1051, doi:10.3762/bjnano.7.97

• Figure S1 in Supporting Information File 1.) We discussed the electrical properties of the sensors in our previous report [32]. A TiOx ND behaves like an n-type semiconductor due to oxygen vacancies. When NO molecules (or O2 molecules under ambient environment) adsorb on the ND surface, they become

Microscopic characterization of Fe nanoparticles formed on SrTiO₃(001) and SrTiO₃(110) surfaces

• Miyoko Tanaka

Beilstein J. Nanotechnol. 2016, 7, 817–824, doi:10.3762/bjnano.7.73

• surface is sputter-cleaned, it becomes severely disordered, forming oxygen vacancies in the uppermost layers [28]. Subsequent annealing induces oxygen diffusion and surface recrystallization at the same time, making various superstructures possible to appear. In our experiments, TEM STO(001) substrates

• , especially the presence of oxygen vacancies formed during UHV annealing. Our previous studies found that surfaces of both STO(001) and STO(110) have oxygen-depleted (1 × 1) structures [25]. Surface energies for these may differ from those of fully oxidized ones and may alter above values. Still, the present