joseph michel mbengue - Academia.edu (original) (raw)
Papers by joseph michel mbengue
Materials Research Bulletin, Apr 1, 2016
Metal-assisted chemical etching (MACE) is a simple, low-cost and versatile method of fabricating ... more Metal-assisted chemical etching (MACE) is a simple, low-cost and versatile method of fabricating various silicon nanostructures. Due to the etching anisotropy of monocrystalline silicon, i.e. its different crystal orientation has different number of silicon back bonds needed to be broken in the etching process, the obtained silicon nanostructures are morphology variable. It has been demonstrated that, by choosing the species or morphologies of catalyst, adjusting the etchant composition or concentration, changing the doping species and level of the silicon substrate, or introducing extra physical fields, MACE method can be used to prepare various desired silicon nanostructures. This review summarizes the most recent contributions in the fabrication of designable monocrystalline silicon nanostructure by MACE. In order to provide a relatively complete comprehension of the MACE, the fundamental principle and basic manipulation process of a conventional MACE, as well as the main influence factors on the etching effects are given; and the common applications of MACE in silicon etching are briefly reviewed. This article also presents some new developed improved MACE technologies and their potential applications in the extended field.
RSC Advances, 2015
Metal-assisted chemical etching is a very popular method of fabricating silicon nanostructures. F... more Metal-assisted chemical etching is a very popular method of fabricating silicon nanostructures. For the dissolution and recrystallization of Ag, and the inertia of Au, we present a co-catalytic mechanism of silicon etching using non-overlapping Au and Ag nanofilms together, meanwhile, two kinds of novel nanostructures are obtained by changing their up and down positions. It is found that, no matter put the Ag or Au nanofilm on the upper layer, the Ag nanofilm will first participate in reaction, etch the silicon substrate into silicon nanowires (Si NWs). Afterwards, the Au nanofilm will re-etch the Si NWs into thick pillars (Ag upper) or ultrathin porous Si NWs (Au upper). It should be also noted that the vertical etching rates of the two layers don't exhibit observable difference, unlike using them separately, where the vertical etching rate of Ag nanofilm is much higher than that of Au nanofilm. This is because the subsequence re-etching process by the Au nanofilm actually conducts at multi-surfaces, arising from the physical feature that Au can generate excessive holes during the hydrogen peroxide decomposition. Furthermore, this study presents feasible ways for the fabrication of individual thick (~200nm) silicon pillars and ultrathin (~25nm) porous Si NWs. Such insights are of guide significance for the synthesizing of many nanostructures.
Scientific Reports, Apr 22, 2016
CrystEngComm, 2015
Anatase/TiO2-B hybrids are considered to be promising anode materials for lithium ion storage. He... more Anatase/TiO2-B hybrids are considered to be promising anode materials for lithium ion storage. Here, a modified synthesis process for the fabrication of anatase/TiO2-B hybrid TiO2 spheres is proposed. Compared to the conventional two-step method employing strong base and acid solutions with titanate as the intermediate, the modified process proposed here employs a one-step reaction which is more facile and moderate. The as-prepared anatase/TiO2-B hybrid TiO2 spheres are assembled from ultrathin anatase TiO2 nanosheets embedded with TiO2-B nanodomains, which take the advantages of both the anatase and TiO2-B phases, possessing a large surface area and a hybrid crystalline structure, which are beneficial for fast diffusion and reversible storage of the lithium ions. Therefore, the anodes with the anatase/TiO2-B hybrid TiO2 spheres have a capacity of 101 mA h g−1 even at a current density of 20C and good cycling stability. This work provides a facile process for the fabrication of TiO2 nanostructures with the TiO2-B phase, which also implies the potential application of anatase/TiO2-B hybrid spheres in many fields including lithium ion batteries and other electrochemical technologies.
Journal of materials chemistry. A, Materials for energy and sustainability, 2016
Journal of materials chemistry. A, Materials for energy and sustainability, 2017
RSC Advances, 2015
The surface defects of the organometallic perovskite play an important role in the photovoltaic p... more The surface defects of the organometallic perovskite play an important role in the photovoltaic performance of solar cells, which depress the conversion efficiency and cause photocurrent hysteresis.
Journal of materials chemistry. A, Materials for energy and sustainability, 2016
Photo-induced degradation of PSCs is caused by damage at the HTM/Au interface, which can be recov... more Photo-induced degradation of PSCs is caused by damage at the HTM/Au interface, which can be recovered by renewal of the Au electrode.
Carbon, May 1, 2017
Graphene has been considered an extraordinary platform for electronic applications, while it stil... more Graphene has been considered an extraordinary platform for electronic applications, while it still remains a challenge to fast synthesize large single-crystalline graphene (LSCG) for widespread use. Since the adsorption energy of single carbon on the substrate plays an important role in the nucleation and growth of graphene, we have considered adjusting its adsorption energy to synthesize LSCG. Here, our density functional theory (DFT) calculations expose that oxygen can significantly reduce (~1.03 eV) the adsorption energy of single carbon on oxygen-covered Cu compared with the bare Cu. Motivated by the calculation result that oxygen can induce weaker carbon adsorption energy, the sequential double oxygen passivation method through chemical vapor deposition is proposed to successfully grow the millimeter-scale single-crystalline graphene with the rate of about 100 mm min À1. This approach could provide a new sight into fast synthesizing LSCG facilely and economically.
Applied Physics Letters, Feb 29, 2016
InTech eBooks, Dec 16, 2015
The chemical vapor deposition technique is the most popular for preparing highquality graphene. S... more The chemical vapor deposition technique is the most popular for preparing highquality graphene. Surface energy will dominate the nucleation process of graphene; thus, the surface energy problems involved in thin film growth are introduced first. The experimental tools to describe the growth process in detail are insufficient. So, a mass of simulation investigations, which can give out a very fine description of the surface atomic process, have been carried out on this topic. We mainly summarized the density functional theory works in unearthing the graphene nuclei process and mechanisms. In addition, some studies using molecular dynamics methods are also listed. Such a summary will be helpful to stimulate future experimental efforts on graphene synthesis.
Journal of Materials Chemistry A, 2017
The embedded structure of perovskite solar cells (PSCs) is a novel structure, which possesses exc... more The embedded structure of perovskite solar cells (PSCs) is a novel structure, which possesses excellent photovoltaic performance and better long-term stability than the mesoporous or planar structure.
Applied Physics Letters, 2016
The degradation of organometallic perovskite solar cells (PSCs) is the key bottleneck hampering t... more The degradation of organometallic perovskite solar cells (PSCs) is the key bottleneck hampering their development, which is typically ascribed to the decomposition of perovskite (CH3NH3PbI3). In this work, the degradation of PSCs is observed to be significant, with the decrease in efficiency from 18.2% to 11.5% in ambient air for 7 days. However, no obvious decomposition or structural evolution of the perovskite was observed, except the notable degradation phenomenon of the device. The degradation of PSCs derives from deteriorated photocurrent and fill factor, which are proven to be induced by increased trap states for enlarged carrier recombination in degraded PSCs. The increased trap states in PSCs over storage time are probably induced by the increased defects at the surface of perovskite. The trap states induced degradation provides a physical insight into the degradation mechanisms of PSCs. Moreover, as the investigations were performed on real PSCs instead of individual perovs...
Journal of Materials Chemistry A, 2016
F4TCNQ interfacial layer passivates the perovskite and induces its p-type interfacial doping, lea... more F4TCNQ interfacial layer passivates the perovskite and induces its p-type interfacial doping, leading to high performance and stability of the PSCs.
Scientific Reports, 2016
Unique photon management (PM) properties of silicon nanowire (SiNW) make it an attractive buildin... more Unique photon management (PM) properties of silicon nanowire (SiNW) make it an attractive building block for a host of nanowire photonic devices including photodetectors, chemical and gas sensors, waveguides, optical switches, solar cells, and lasers. However, the lack of efficient equations for the quantitative estimation of the SiNW’s PM properties limits the rational design of such devices. Herein, we establish comprehensive equations to evaluate several important performance features for the PM properties of SiNW, based on theoretical simulations. Firstly, the relationships between the resonant wavelengths (RW), where SiNW can harvest light most effectively, and the size of SiNW are formulized. Then, equations for the light-harvesting efficiency at RW, which determines the single-frequency performance limit of SiNW-based photonic devices, are established. Finally, equations for the light-harvesting efficiency of SiNW in full-spectrum, which are of great significance in photovolt...
Materials Research Bulletin, 2016
Metal-assisted chemical etching (MACE) is a simple, low-cost and versatile method of fabricating ... more Metal-assisted chemical etching (MACE) is a simple, low-cost and versatile method of fabricating various silicon nanostructures. Due to the etching anisotropy of monocrystalline silicon, i.e. its different crystal orientation has different number of silicon back bonds needed to be broken in the etching process, the obtained silicon nanostructures are morphology variable. It has been demonstrated that, by choosing the species or morphologies of catalyst, adjusting the etchant composition or concentration, changing the doping species and level of the silicon substrate, or introducing extra physical fields, MACE method can be used to prepare various desired silicon nanostructures. This review summarizes the most recent contributions in the fabrication of designable monocrystalline silicon nanostructure by MACE. In order to provide a relatively complete comprehension of the MACE, the fundamental principle and basic manipulation process of a conventional MACE, as well as the main influence factors on the etching effects are given; and the common applications of MACE in silicon etching are briefly reviewed. This article also presents some new developed improved MACE technologies and their potential applications in the extended field.
Materials Research Bulletin, Apr 1, 2016
Metal-assisted chemical etching (MACE) is a simple, low-cost and versatile method of fabricating ... more Metal-assisted chemical etching (MACE) is a simple, low-cost and versatile method of fabricating various silicon nanostructures. Due to the etching anisotropy of monocrystalline silicon, i.e. its different crystal orientation has different number of silicon back bonds needed to be broken in the etching process, the obtained silicon nanostructures are morphology variable. It has been demonstrated that, by choosing the species or morphologies of catalyst, adjusting the etchant composition or concentration, changing the doping species and level of the silicon substrate, or introducing extra physical fields, MACE method can be used to prepare various desired silicon nanostructures. This review summarizes the most recent contributions in the fabrication of designable monocrystalline silicon nanostructure by MACE. In order to provide a relatively complete comprehension of the MACE, the fundamental principle and basic manipulation process of a conventional MACE, as well as the main influence factors on the etching effects are given; and the common applications of MACE in silicon etching are briefly reviewed. This article also presents some new developed improved MACE technologies and their potential applications in the extended field.
RSC Advances, 2015
Metal-assisted chemical etching is a very popular method of fabricating silicon nanostructures. F... more Metal-assisted chemical etching is a very popular method of fabricating silicon nanostructures. For the dissolution and recrystallization of Ag, and the inertia of Au, we present a co-catalytic mechanism of silicon etching using non-overlapping Au and Ag nanofilms together, meanwhile, two kinds of novel nanostructures are obtained by changing their up and down positions. It is found that, no matter put the Ag or Au nanofilm on the upper layer, the Ag nanofilm will first participate in reaction, etch the silicon substrate into silicon nanowires (Si NWs). Afterwards, the Au nanofilm will re-etch the Si NWs into thick pillars (Ag upper) or ultrathin porous Si NWs (Au upper). It should be also noted that the vertical etching rates of the two layers don't exhibit observable difference, unlike using them separately, where the vertical etching rate of Ag nanofilm is much higher than that of Au nanofilm. This is because the subsequence re-etching process by the Au nanofilm actually conducts at multi-surfaces, arising from the physical feature that Au can generate excessive holes during the hydrogen peroxide decomposition. Furthermore, this study presents feasible ways for the fabrication of individual thick (~200nm) silicon pillars and ultrathin (~25nm) porous Si NWs. Such insights are of guide significance for the synthesizing of many nanostructures.
Scientific Reports, Apr 22, 2016
CrystEngComm, 2015
Anatase/TiO2-B hybrids are considered to be promising anode materials for lithium ion storage. He... more Anatase/TiO2-B hybrids are considered to be promising anode materials for lithium ion storage. Here, a modified synthesis process for the fabrication of anatase/TiO2-B hybrid TiO2 spheres is proposed. Compared to the conventional two-step method employing strong base and acid solutions with titanate as the intermediate, the modified process proposed here employs a one-step reaction which is more facile and moderate. The as-prepared anatase/TiO2-B hybrid TiO2 spheres are assembled from ultrathin anatase TiO2 nanosheets embedded with TiO2-B nanodomains, which take the advantages of both the anatase and TiO2-B phases, possessing a large surface area and a hybrid crystalline structure, which are beneficial for fast diffusion and reversible storage of the lithium ions. Therefore, the anodes with the anatase/TiO2-B hybrid TiO2 spheres have a capacity of 101 mA h g−1 even at a current density of 20C and good cycling stability. This work provides a facile process for the fabrication of TiO2 nanostructures with the TiO2-B phase, which also implies the potential application of anatase/TiO2-B hybrid spheres in many fields including lithium ion batteries and other electrochemical technologies.
Journal of materials chemistry. A, Materials for energy and sustainability, 2016
Journal of materials chemistry. A, Materials for energy and sustainability, 2017
RSC Advances, 2015
The surface defects of the organometallic perovskite play an important role in the photovoltaic p... more The surface defects of the organometallic perovskite play an important role in the photovoltaic performance of solar cells, which depress the conversion efficiency and cause photocurrent hysteresis.
Journal of materials chemistry. A, Materials for energy and sustainability, 2016
Photo-induced degradation of PSCs is caused by damage at the HTM/Au interface, which can be recov... more Photo-induced degradation of PSCs is caused by damage at the HTM/Au interface, which can be recovered by renewal of the Au electrode.
Carbon, May 1, 2017
Graphene has been considered an extraordinary platform for electronic applications, while it stil... more Graphene has been considered an extraordinary platform for electronic applications, while it still remains a challenge to fast synthesize large single-crystalline graphene (LSCG) for widespread use. Since the adsorption energy of single carbon on the substrate plays an important role in the nucleation and growth of graphene, we have considered adjusting its adsorption energy to synthesize LSCG. Here, our density functional theory (DFT) calculations expose that oxygen can significantly reduce (~1.03 eV) the adsorption energy of single carbon on oxygen-covered Cu compared with the bare Cu. Motivated by the calculation result that oxygen can induce weaker carbon adsorption energy, the sequential double oxygen passivation method through chemical vapor deposition is proposed to successfully grow the millimeter-scale single-crystalline graphene with the rate of about 100 mm min À1. This approach could provide a new sight into fast synthesizing LSCG facilely and economically.
Applied Physics Letters, Feb 29, 2016
InTech eBooks, Dec 16, 2015
The chemical vapor deposition technique is the most popular for preparing highquality graphene. S... more The chemical vapor deposition technique is the most popular for preparing highquality graphene. Surface energy will dominate the nucleation process of graphene; thus, the surface energy problems involved in thin film growth are introduced first. The experimental tools to describe the growth process in detail are insufficient. So, a mass of simulation investigations, which can give out a very fine description of the surface atomic process, have been carried out on this topic. We mainly summarized the density functional theory works in unearthing the graphene nuclei process and mechanisms. In addition, some studies using molecular dynamics methods are also listed. Such a summary will be helpful to stimulate future experimental efforts on graphene synthesis.
Journal of Materials Chemistry A, 2017
The embedded structure of perovskite solar cells (PSCs) is a novel structure, which possesses exc... more The embedded structure of perovskite solar cells (PSCs) is a novel structure, which possesses excellent photovoltaic performance and better long-term stability than the mesoporous or planar structure.
Applied Physics Letters, 2016
The degradation of organometallic perovskite solar cells (PSCs) is the key bottleneck hampering t... more The degradation of organometallic perovskite solar cells (PSCs) is the key bottleneck hampering their development, which is typically ascribed to the decomposition of perovskite (CH3NH3PbI3). In this work, the degradation of PSCs is observed to be significant, with the decrease in efficiency from 18.2% to 11.5% in ambient air for 7 days. However, no obvious decomposition or structural evolution of the perovskite was observed, except the notable degradation phenomenon of the device. The degradation of PSCs derives from deteriorated photocurrent and fill factor, which are proven to be induced by increased trap states for enlarged carrier recombination in degraded PSCs. The increased trap states in PSCs over storage time are probably induced by the increased defects at the surface of perovskite. The trap states induced degradation provides a physical insight into the degradation mechanisms of PSCs. Moreover, as the investigations were performed on real PSCs instead of individual perovs...
Journal of Materials Chemistry A, 2016
F4TCNQ interfacial layer passivates the perovskite and induces its p-type interfacial doping, lea... more F4TCNQ interfacial layer passivates the perovskite and induces its p-type interfacial doping, leading to high performance and stability of the PSCs.
Scientific Reports, 2016
Unique photon management (PM) properties of silicon nanowire (SiNW) make it an attractive buildin... more Unique photon management (PM) properties of silicon nanowire (SiNW) make it an attractive building block for a host of nanowire photonic devices including photodetectors, chemical and gas sensors, waveguides, optical switches, solar cells, and lasers. However, the lack of efficient equations for the quantitative estimation of the SiNW’s PM properties limits the rational design of such devices. Herein, we establish comprehensive equations to evaluate several important performance features for the PM properties of SiNW, based on theoretical simulations. Firstly, the relationships between the resonant wavelengths (RW), where SiNW can harvest light most effectively, and the size of SiNW are formulized. Then, equations for the light-harvesting efficiency at RW, which determines the single-frequency performance limit of SiNW-based photonic devices, are established. Finally, equations for the light-harvesting efficiency of SiNW in full-spectrum, which are of great significance in photovolt...
Materials Research Bulletin, 2016
Metal-assisted chemical etching (MACE) is a simple, low-cost and versatile method of fabricating ... more Metal-assisted chemical etching (MACE) is a simple, low-cost and versatile method of fabricating various silicon nanostructures. Due to the etching anisotropy of monocrystalline silicon, i.e. its different crystal orientation has different number of silicon back bonds needed to be broken in the etching process, the obtained silicon nanostructures are morphology variable. It has been demonstrated that, by choosing the species or morphologies of catalyst, adjusting the etchant composition or concentration, changing the doping species and level of the silicon substrate, or introducing extra physical fields, MACE method can be used to prepare various desired silicon nanostructures. This review summarizes the most recent contributions in the fabrication of designable monocrystalline silicon nanostructure by MACE. In order to provide a relatively complete comprehension of the MACE, the fundamental principle and basic manipulation process of a conventional MACE, as well as the main influence factors on the etching effects are given; and the common applications of MACE in silicon etching are briefly reviewed. This article also presents some new developed improved MACE technologies and their potential applications in the extended field.