Nanomaterials

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4 pages, 195 KiB

Open AccessEditorial

Editorial for the Special Issue “Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29”

by Kunji Chen, Shunri Oda and Linwei Yu

Nanomaterials 2023, 13(18), 2594; https://doi.org/10.3390/nano13182594 - 20 Sep 2023

Viewed by 911

Abstract

The 29th International Conference on Amorphous and Nanocrystalline Semiconductors served as a continuation of the biennial conference that has been held since 1965 [...] Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

Research

Jump to: Editorial

12 pages, 2731 KiB

Open AccessEditor’s ChoiceArticle

A Flexible Piezocapacitive Pressure Sensor with Microsphere-Array Electrodes

by Shu Ying, Jiean Li, Jinrong Huang, Jia-Han Zhang, Jing Zhang, Yongchang Jiang, Xidi Sun, Lijia Pan and Yi Shi

Nanomaterials 2023, 13(11), 1702; https://doi.org/10.3390/nano13111702 - 23 May 2023

Cited by 6 | Viewed by 3601

Abstract

Flexible pressure sensors that emulate the sensation and characteristics of natural skins are of great importance in wearable medical devices, intelligent robots, and human–machine interfaces. The microstructure of the pressure-sensitive layer plays a significant role in the sensor’s overall performance. However, microstructures usually [...] Read more.

Flexible pressure sensors that emulate the sensation and characteristics of natural skins are of great importance in wearable medical devices, intelligent robots, and human–machine interfaces. The microstructure of the pressure-sensitive layer plays a significant role in the sensor’s overall performance. However, microstructures usually require complex and costly processes such as photolithography or chemical etching for fabrication. This paper proposes a novel approach that combines self-assembled technology to prepare a high-performance flexible capacitive pressure sensor with a microsphere-array gold electrode and a nanofiber nonwoven dielectric material. When subjected to pressure, the microsphere structures of the gold electrode deform via compressing the medium layer, leading to a significant increase in the relative area between the electrodes and a corresponding change in the thickness of the medium layer, as simulated in COMSOL simulations and experiments, which presents high sensitivity (1.807 kPa⁻¹). The developed sensor demonstrates excellent performance in detecting signals such as slight object deformations and human finger bending. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

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12 pages, 2488 KiB

Open AccessArticle

Structural, Electronic and Optical Properties of Some New Trilayer Van de Waals Heterostructures

by Beitong Cheng, Yong Zhou, Ruomei Jiang, Xule Wang, Shuai Huang, Xingyong Huang, Wei Zhang, Qian Dai, Liujiang Zhou, Pengfei Lu and Hai-Zhi Song

Nanomaterials 2023, 13(9), 1574; https://doi.org/10.3390/nano13091574 - 8 May 2023

Cited by 2 | Viewed by 2012

Abstract

Constructing two-dimensional (2D) van der Waals (vdW) heterostructures is an effective strategy for tuning and improving the characters of 2D-material-based devices. Four trilayer vdW heterostructures, BP/BP/MoS₂, BlueP/BlueP/MoS₂, BP/graphene/MoS₂ and BlueP/graphene/MoS₂, were designed and simulated using the [...] Read more.

Constructing two-dimensional (2D) van der Waals (vdW) heterostructures is an effective strategy for tuning and improving the characters of 2D-material-based devices. Four trilayer vdW heterostructures, BP/BP/MoS₂, BlueP/BlueP/MoS₂, BP/graphene/MoS₂ and BlueP/graphene/MoS₂, were designed and simulated using the first-principles calculation. Structural stabilities were confirmed for all these heterostructures, indicating their feasibility in fabrication. BP/BP/MoS₂ and BlueP/BlueP/MoS₂ lowered the bandgaps further, making them suitable for a greater range of applications, with respect to the bilayers BP/MoS₂ and BlueP/MoS₂, respectively. Their absorption coefficients were remarkably improved in a wide spectrum, suggesting the better performance of photodetectors working in a wide spectrum from mid-wave (short-wave) infrared to violet. In contrast, the bandgaps in BP/graphene/MoS₂ and BlueP/graphene/MoS₂ were mostly enlarged, with a specific opening of the graphene bandgap in BP/graphene/MoS₂, 0.051 eV, which is much larger than usual and beneficial for optoelectronic applications. Accompanying these bandgap increases, BP/graphene/MoS₂ and BlueP/graphene/MoS₂ exhibit absorption enhancement in the whole infrared, visible to deep ultraviolet or solar blind ultraviolet ranges, implying that these asymmetrically graphene-sandwiched heterostructures are more suitable as graphene-based 2D optoelectronic devices. The proposed 2D trilayer vdW heterostructures are prospective new optoelectronic devices, possessing higher performance than currently available devices. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

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8 pages, 6890 KiB

Open AccessCommunication

Room Temperature Light Emission from Superatom-like Ge–Core/Si–Shell Quantum Dots

by Katsunori Makihara, Yuji Yamamoto, Yuki Imai, Noriyuki Taoka, Markus Andreas Schubert, Bernd Tillack and Seiichi Miyazaki

Nanomaterials 2023, 13(9), 1475; https://doi.org/10.3390/nano13091475 - 26 Apr 2023

Cited by 2 | Viewed by 1423

Abstract

We have demonstrated the high–density formation of super–atom–like Si quantum dots with Ge–core on ultrathin SiO₂ with control of high–selective chemical–vapor deposition and applied them to an active layer of light–emitting diodes (LEDs). Through luminescence measurements, we have reported characteristics carrier confinement [...] Read more.

We have demonstrated the high–density formation of super–atom–like Si quantum dots with Ge–core on ultrathin SiO₂ with control of high–selective chemical–vapor deposition and applied them to an active layer of light–emitting diodes (LEDs). Through luminescence measurements, we have reported characteristics carrier confinement and recombination properties in the Ge–core, reflecting the type II energy band discontinuity between the Si–clad and Ge–core. Additionally, under forward bias conditions over a threshold bias for LEDs, electroluminescence becomes observable at room temperature in the near–infrared region and is attributed to radiative recombination between quantized states in the Ge–core with a deep potential well for holes caused by electron/hole simultaneous injection from the gate and substrate, respectively. The results will lead to the development of Si–based light–emitting devices that are highly compatible with Si–ultra–large–scale integration processing, which has been believed to have extreme difficulty in realizing silicon photonics. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

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11 pages, 5448 KiB

Open AccessArticle

Effect of a-SiC_xN_y:H Encapsulation on the Stability and Photoluminescence Property of CsPbBr₃ Quantum Dots

by Zewen Lin, Zhenxu Lin, Yanqing Guo, Haixia Wu, Jie Song, Yi Zhang, Wenxing Zhang, Hongliang Li, Dejian Hou and Rui Huang

Nanomaterials 2023, 13(7), 1228; https://doi.org/10.3390/nano13071228 - 30 Mar 2023

Cited by 2 | Viewed by 1411

Abstract

The effect of a-SiC_xN_y:H encapsulation layers, which are prepared using the very-high-frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) technique with SiH₄, CH₄, and NH₃ as the precursors, on the stability and photoluminescence of CsPbBr₃ [...] Read more.

The effect of a-SiC_xN_y:H encapsulation layers, which are prepared using the very-high-frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) technique with SiH₄, CH₄, and NH₃ as the precursors, on the stability and photoluminescence of CsPbBr₃ quantum dots (QDs) were investigated in this study. The results show that a-SiCxNy:H encapsulation layers containing a high N content of approximately 50% cause severe PL degradation of CsPbBr₃ QDs. However, by reducing the N content in the a-SiCxNy:H layer, the PL degradation of CsPbBr₃ QDs can be significantly minimized. As the N content decreases from around 50% to 26%, the dominant phase in the a-SiCxNy:H layer changes from SiNx to SiCxNy. This transition preserves the inherent PL characteristics of CsPbBr₃ QDs, while also providing them with long-term stability when exposed to air, high temperatures (205 °C), and UV illumination for over 600 days. This method provided an effective and practical approach to enhance the stability and PL characteristics of CsPbBr₃ QD thin films, thus holding potential for future developments in optoelectronic devices. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

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8 pages, 2350 KiB

Open AccessCommunication

Great Potential of Si-Te Ovonic Threshold Selector in Electrical Performance and Scalability

by Renjie Wu, Yuting Sun, Shuhao Zhang, Zihao Zhao and Zhitang Song

Nanomaterials 2023, 13(6), 1114; https://doi.org/10.3390/nano13061114 - 21 Mar 2023

Cited by 4 | Viewed by 1910

Abstract

The selector is an indispensable section of the phase change memory (PCM) chip, where it not only suppresses the crosstalk, but also provides high on-current to melt the incorporated phase change material. In fact, the ovonic threshold switching (OTS) selector is utilized in [...] Read more.

The selector is an indispensable section of the phase change memory (PCM) chip, where it not only suppresses the crosstalk, but also provides high on-current to melt the incorporated phase change material. In fact, the ovonic threshold switching (OTS) selector is utilized in 3D stacking PCM chips by virtue of its high scalability and driving capability. In this paper, the influence of Si concentration on the electrical properties of Si-Te OTS materials is studied; the threshold voltage and leakage current remain basically unchanged with the decrease in electrode diameter. Meanwhile, the on-current density (J_on) increases significantly as the device is scaling down, and 25 MA/cm² on-current density is achieved in the 60-nm SiTe device. In addition, we also determine the state of the Si-Te OTS layer and preliminarily obtain the approximate band structure, from which we infer that the conduction mechanism conforms to the Poole-Frenkel (PF) model. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

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11 pages, 2847 KiB

Open AccessEditor’s ChoiceArticle

Enhanced Electroluminescence from a Silicon Nanocrystal/Silicon Carbide Multilayer Light-Emitting Diode

by Teng Sun, Dongke Li, Jiaming Chen, Yuhao Wang, Junnan Han, Ting Zhu, Wei Li, Jun Xu and Kunji Chen

Nanomaterials 2023, 13(6), 1109; https://doi.org/10.3390/nano13061109 - 20 Mar 2023

Cited by 3 | Viewed by 1972

Abstract

Developing high-performance Si-based light-emitting devices is the key step to realizing all-Si-based optical telecommunication. Usually, silica (SiO₂) as the host matrix is used to passivate silicon nanocrystals, and a strong quantum confinement effect can be observed due to the large band [...] Read more.

Developing high-performance Si-based light-emitting devices is the key step to realizing all-Si-based optical telecommunication. Usually, silica (SiO₂) as the host matrix is used to passivate silicon nanocrystals, and a strong quantum confinement effect can be observed due to the large band offset between Si and SiO₂ (~8.9 eV). Here, for further development of device properties, we fabricate Si nanocrystals (NCs)/SiC multilayers and study the changes in photoelectric properties of the LEDs induced by P dopants. PL peaks centered at 500 nm, 650 nm and 800 nm can be detected, which are attributed to surface states between SiC and Si NCs, amorphous SiC and Si NCs, respectively. PL intensities are first enhanced and then decreased after introducing P dopants. It is believed that the enhancement is due to passivation of the Si dangling bonds at the surface of Si NCs, while the suppression is ascribed to enhanced Auger recombination and new defects induced by excessive P dopants. Un-doped and P-doped LEDs based on Si NCs/SiC multilayers are fabricated and the performance is enhanced greatly after doping. As fitted, emission peaks near 500 nm and 750 nm can be detected. The current density-voltage properties indicate that the carrier transport process is dominated by FN tunneling mechanisms, while the linear relationship between the integrated EL intensity and injection current illustrates that the EL mechanism is attributed to recombination of electron–hole pairs at Si NCs induced by bipolar injection. After doping, the integrated EL intensities are enhanced by about an order of magnitude, indicating that EQE is greatly improved. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

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12 pages, 4462 KiB

Open AccessArticle

Narrow UVB-Emitted YBO₃ Phosphor Activated by Bi³⁺ and Gd³⁺ Co-Doping

by Zhimin Yu, Yang Yang and Jiaming Sun

Nanomaterials 2023, 13(6), 1013; https://doi.org/10.3390/nano13061013 - 11 Mar 2023

Cited by 5 | Viewed by 1682

Abstract

Y_0.9(Gd_xBi_1−x)_0.1BO₃ phosphors (x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0, YGB) were obtained via high-temperature solid-state synthesis. Differentiated phases and micro-morphologies were determined by adjusting the synthesis temperature and the activator content of [...] Read more.

Y_0.9(Gd_xBi_1−x)_0.1BO₃ phosphors (x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0, YGB) were obtained via high-temperature solid-state synthesis. Differentiated phases and micro-morphologies were determined by adjusting the synthesis temperature and the activator content of Gd³⁺ ions, verifying the hexagonal phase with an average size of ~200 nm. Strong photon emissions were revealed under both ultraviolet and visible radiation, and the effectiveness of energy transfer from Bi³⁺ to Gd³⁺ ions was confirmed to improve the narrow-band ultraviolet-B (UVB) (⁶P_J→⁸S_7/2) emission of Gd³⁺ ions. The optimal emission was obtained from Y_0.9Gd_0.08Bi_0.02BO₃ phosphor annealed at 800 °C, for which maximum quantum yields (QYs) can reach 24.75% and 1.33% under 273 nm and 532 nm excitations, respectively. The optimal QY from the Gd³⁺-Bi³⁺ co-doped YGB phosphor is 75 times the single Gd³⁺-doped one, illustrating that these UVB luminescent phosphors based on co-doped YBO₃ orthoborates possess bright UVB emissions and good excitability under the excitation of different wavelengths. Efficient photon conversion and intense UVB emissions indicate that the multifunctional Gd³⁺-Bi³⁺ co-doped YBO₃ orthoborate is a potential candidate for skin treatment. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

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13 pages, 3422 KiB

Open AccessArticle

Controlling the Carrier Injection Efficiency in 3D Nanocrystalline Silicon Floating Gate Memory by Novel Design of Control Layer

by Hongsheng Hu, Zhongyuan Ma, Xinyue Yu, Tong Chen, Chengfeng Zhou, Wei Li, Kunji Chen, Jun Xu and Ling Xu

Nanomaterials 2023, 13(6), 962; https://doi.org/10.3390/nano13060962 - 7 Mar 2023

Cited by 1 | Viewed by 1497

Abstract

Three-dimensional NAND flash memory with high carrier injection efficiency has been of great interest to computing in memory for its stronger capability to deal with big data than that of conventional von Neumann architecture. Here, we first report the carrier injection efficiency of [...] Read more.

Three-dimensional NAND flash memory with high carrier injection efficiency has been of great interest to computing in memory for its stronger capability to deal with big data than that of conventional von Neumann architecture. Here, we first report the carrier injection efficiency of 3D NAND flash memory based on a nanocrystalline silicon floating gate, which can be controlled by a novel design of the control layer. The carrier injection efficiency in nanocrystalline Si can be monitored by the capacitance–voltage (C–V) hysteresis direction of an nc-Si floating-gate MOS structure. When the control layer thickness of the nanocrystalline silicon floating gate is 25 nm, the C–V hysteresis always maintains the counterclockwise direction under different step sizes of scanning bias. In contrast, the direction of the C–V hysteresis can be changed from counterclockwise to clockwise when the thickness of the control barrier is reduced to 22 nm. The clockwise direction of the C–V curve is due to the carrier injection from the top electrode into the defect state of the SiN_x control layer. Our discovery illustrates that the thicker SiN_x control layer can block the transfer of carriers from the top electrode to the SiN_x, thereby improving the carrier injection efficiency from the Si substrate to the nc-Si layer. The relationship between the carrier injection and the C–V hysteresis direction is further revealed by using the energy band model, thus explaining the transition mechanism of the C–V hysteresis direction. Our report is conducive to optimizing the performance of 3D NAND flash memory based on an nc-Si floating gate, which will be better used in the field of in-memory computing. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

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17 pages, 2722 KiB

Open AccessArticle

Amorphous As₂S₃ Doped with Transition Metals: An Ab Initio Study of Electronic Structure and Magnetic Properties

by Vladimir G. Kuznetsov, Anton A. Gavrikov, Milos Krbal, Vladimir A. Trepakov and Alexander V. Kolobov

Nanomaterials 2023, 13(5), 896; https://doi.org/10.3390/nano13050896 - 27 Feb 2023

Cited by 3 | Viewed by 1457

Abstract

Crystalline transition-metal chalcogenides are the focus of solid state research. At the same time, very little is known about amorphous chalcogenides doped with transition metals. To close this gap, we have studied, using first principle simulations, the effect of doping the typical chalcogenide [...] Read more.

Crystalline transition-metal chalcogenides are the focus of solid state research. At the same time, very little is known about amorphous chalcogenides doped with transition metals. To close this gap, we have studied, using first principle simulations, the effect of doping the typical chalcogenide glass As₂S₃ with transition metals (Mo, W and V). While the undoped glass is a semiconductor with a density functional theory gap of about 1 eV, doping results in the formation of a finite density of states (semiconductor-to-metal transformation) at the Fermi level accompanied by an appearance of magnetic properties, the magnetic character depending on the nature of the dopant. Whilst the magnetic response is mainly associated with d-orbitals of the transition metal dopants, partial densities of spin-up and spin-down states associated with arsenic and sulphur also become slightly asymmetric. Our results demonstrate that chalcogenide glasses doped with transition metals may become a technologically important material. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

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9 pages, 1952 KiB

Open AccessArticle

Enhancement of the Electroluminescence from Amorphous Er-Doped Al₂O₃ Nanolaminate Films by Y₂O₃ Cladding Layers Using Atomic Layer Deposition

by Yang Yang, Haiyan Pei, Zejun Ye and Jiaming Sun

Nanomaterials 2023, 13(5), 849; https://doi.org/10.3390/nano13050849 - 24 Feb 2023

Cited by 4 | Viewed by 1489

Abstract

Amorphous Al₂O₃-Y₂O₃:Er nanolaminate films are fabricated on silicon by atomic layer deposition, and ~1530 nm electroluminescence (EL) is obtained from the metal-oxide-semiconductor light-emitting devices based on these nanofilms. The introduction of Y₂O₃ [...] Read more.

Amorphous Al₂O₃-Y₂O₃:Er nanolaminate films are fabricated on silicon by atomic layer deposition, and ~1530 nm electroluminescence (EL) is obtained from the metal-oxide-semiconductor light-emitting devices based on these nanofilms. The introduction of Y₂O₃ into Al₂O₃ reduces the electric field for Er excitation and the EL performance is significantly enhanced, while the electron injection of devices and the radiative recombination of doped Er³⁺ ions are not impacted. The 0.2 nm Y₂O₃ cladding layers for Er³⁺ ions increase the external quantum efficiency from ~3% to 8.7% and the power efficiency is increased by nearly one order of magnitude to 0.12%. The EL is ascribed to the impact excitation of Er³⁺ ions by hot electrons, which stem from Poole-Frenkel conduction mechanism under sufficient voltage within the Al₂O₃-Y₂O₃ matrix. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

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14 pages, 7321 KiB

Open AccessArticle

A Wide-Range-Response Piezoresistive–Capacitive Dual-Sensing Breathable Sensor with Spherical-Shell Network of MWCNTs for Motion Detection and Language Assistance

by Shuming Zhang, Xidi Sun, Xin Guo, Jing Zhang, Hao Li, Luyao Chen, Jing Wu, Yi Shi and Lijia Pan

Nanomaterials 2023, 13(5), 843; https://doi.org/10.3390/nano13050843 - 24 Feb 2023

Cited by 13 | Viewed by 2790

Abstract

It is still a challenge for flexible electronic materials to realize integrated strain sensors with a large linear working range, high sensitivity, good response durability, good skin affinity and good air permeability. In this paper, we present a simple and scalable porous piezoresistive/capacitive [...] Read more.

It is still a challenge for flexible electronic materials to realize integrated strain sensors with a large linear working range, high sensitivity, good response durability, good skin affinity and good air permeability. In this paper, we present a simple and scalable porous piezoresistive/capacitive dual-mode sensor with a porous structure in polydimethylsiloxane (PDMS) and with multi-walled carbon nanotubes (MWCNTs) embedded on its internal surface to form a three-dimensional spherical-shell-structured conductive network. Thanks to the unique spherical-shell conductive network of MWCNTs and the uniform elastic deformation of the cross-linked PDMS porous structure under compression, our sensor offers a dual piezoresistive/capacitive strain-sensing capability, a wide pressure response range (1–520 kPa), a very large linear response region (95%), excellent response stability and durability (98% of initial performance after 1000 compression cycles). Multi-walled carbon nanotubes were coated on the surface of refined sugar particles by continuous agitation. Ultrasonic PDMS solidified with crystals was attached to the multi-walled carbon nanotubes. After the crystals were dissolved, the multi-walled carbon nanotubes were attached to the porous surface of the PDMS, forming a three-dimensional spherical-shell-structure network. The porosity of the porous PDMS was 53.9%. The large linear induction range was mainly related to the good conductive network of the MWCNTs in the porous structure of the crosslinked PDMS and the elasticity of the material, which ensured the uniform deformation of the porous structure under compression. The porous conductive polymer flexible sensor prepared by us can be assembled into a wearable sensor with good human motion detection ability. For example, human movement can be detected by responding to stress in the joints of the fingers, elbows, knees, plantar, etc., during movement. Finally, our sensors can also be used for simple gesture and sign language recognition, as well as speech recognition by monitoring facial muscle activity. This can play a role in improving communication and the transfer of information between people, especially in facilitating the lives of people with disabilities. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

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12 pages, 5159 KiB

Open AccessArticle

The Effect of Carbon Doping on the Crystal Structure and Electrical Properties of Sb₂Te₃

by Jie Zhang, Ningning Rong, Peng Xu, Yuchen Xiao, Aijiang Lu, Wenxiong Song, Sannian Song, Zhitang Song, Yongcheng Liang and Liangcai Wu

Nanomaterials 2023, 13(4), 671; https://doi.org/10.3390/nano13040671 - 9 Feb 2023

Cited by 5 | Viewed by 1987

Abstract

As a new generation of non-volatile memory, phase change random access memory (PCRAM) has the potential to fill the hierarchical gap between DRAM and NAND FLASH in computer storage. Sb₂Te₃, one of the candidate materials for high-speed PCRAM, has [...] Read more.

As a new generation of non-volatile memory, phase change random access memory (PCRAM) has the potential to fill the hierarchical gap between DRAM and NAND FLASH in computer storage. Sb₂Te₃, one of the candidate materials for high-speed PCRAM, has high crystallization speed and poor thermal stability. In this work, we investigated the effect of carbon doping on Sb₂Te₃. It was found that the FCC phase of C-doped Sb₂Te₃ appeared at 200 °C and began to transform into the HEX phase at 25 °C, which is different from the previous reports where no FCC phase was observed in C-Sb₂Te₃. Based on the experimental observation and first-principles density functional theory calculation, it is found that the formation energy of FCC-Sb₂Te₃ structure decreases gradually with the increase in C doping concentration. Moreover, doped C atoms tend to form C molecular clusters in sp² hybridization at the grain boundary of Sb₂Te₃, which is similar to the layered structure of graphite. And after doping C atoms, the thermal stability of Sb₂Te₃ is improved. We have fabricated the PCRAM device cell array of a C-Sb₂Te₃ alloy, which has an operating speed of 5 ns, a high thermal stability (10-year data retention temperature 138.1 °C), a low device power consumption (0.57 pJ), a continuously adjustable resistance value, and a very low resistance drift coefficient. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

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8 pages, 3547 KiB

Open AccessCommunication

Advantages of Ta-Doped Sb₃Te₁ Materials for Phase Change Memory Applications

by Mingyue Shao, Yang Qiao, Yuan Xue, Sannian Song, Zhitang Song and Xiaodan Li

Nanomaterials 2023, 13(4), 633; https://doi.org/10.3390/nano13040633 - 5 Feb 2023

Cited by 2 | Viewed by 1445

Abstract

Phase change memory (PCM), a typical representative of new storage technologies, offers significant advantages in terms of capacity and endurance. However, among the research on phase change materials, thermal stability and switching speed performance have always been the direction where breakthroughs are needed. [...] Read more.

Phase change memory (PCM), a typical representative of new storage technologies, offers significant advantages in terms of capacity and endurance. However, among the research on phase change materials, thermal stability and switching speed performance have always been the direction where breakthroughs are needed. In this research, as a high-speed and good thermal stability material, Ta was proposed to be doped in Sb₃Te₁ alloy to improve the phase transition performance and electrical properties. The characterization shows that Ta-doped Sb₃Te₁ can crystallize at temperatures up to 232 °C and devices can operate at speeds of 6 ns and 8 × 10⁴ operation cycles. The reduction of grain size and the density change rate (3.39%) show excellent performances, which are both smaller than that of Ge₂Sb₂Te₅ (GST) and Sb₃Te₁. These properties conclusively demonstrate that Ta incorporation of Sb₃Te₁ alloy is a material with better thermal stability and faster crystallization rates for PCM applications. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

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11 pages, 3384 KiB

Open AccessCommunication

Artificial HfO₂/TiO_x Synapses with Controllable Memory Window and High Uniformity for Brain-Inspired Computing

by Yang Yang, Xu Zhu, Zhongyuan Ma, Hongsheng Hu, Tong Chen, Wei Li, Jun Xu, Ling Xu and Kunji Chen

Nanomaterials 2023, 13(3), 605; https://doi.org/10.3390/nano13030605 - 2 Feb 2023

Cited by 5 | Viewed by 2189

Abstract

Artificial neural networks, as a game-changer to break up the bottleneck of classical von Neumann architectures, have attracted great interest recently. As a unit of artificial neural networks, memristive devices play a key role due to their similarity to biological synapses in structure, [...] Read more.

Artificial neural networks, as a game-changer to break up the bottleneck of classical von Neumann architectures, have attracted great interest recently. As a unit of artificial neural networks, memristive devices play a key role due to their similarity to biological synapses in structure, dynamics, and electrical behaviors. To achieve highly accurate neuromorphic computing, memristive devices with a controllable memory window and high uniformity are vitally important. Here, we first report that the controllable memory window of an HfO₂/TiO_x memristive device can be obtained by tuning the thickness ratio of the sublayer. It was found the memory window increased with decreases in the thickness ratio of HfO₂ and TiO_x. Notably, the coefficients of variation of the high-resistance state and the low-resistance state of the nanocrystalline HfO₂/TiO_x memristor were reduced by 74% and 86% compared with the as-deposited HfO₂/TiO_x memristor. The position of the conductive pathway could be localized by the nanocrystalline HfO₂ and TiO₂ dot, leading to a substantial improvement in the switching uniformity. The nanocrystalline HfO₂/TiO_x memristive device showed stable, controllable biological functions, including long-term potentiation, long-term depression, and spike-time-dependent plasticity, as well as the visual learning capability, displaying the great potential application for neuromorphic computing in brain-inspired intelligent systems. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

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7 pages, 2720 KiB

Open AccessCommunication

The Relationship between Electron Transport and Microstructure in Ge₂Sb₂Te₅ Alloy

by Cheng Liu, Yonghui Zheng, Tianjiao Xin, Yunzhe Zheng, Rui Wang and Yan Cheng

Nanomaterials 2023, 13(3), 582; https://doi.org/10.3390/nano13030582 - 31 Jan 2023

Cited by 4 | Viewed by 1481

Abstract

Phase-change random-access memory (PCRAM) holds great promise for next-generation information storage applications. As a mature phase change material, Ge₂Sb₂Te₅ alloy (GST) relies on the distinct electrical properties of different states to achieve information storage, but there are relatively [...] Read more.

Phase-change random-access memory (PCRAM) holds great promise for next-generation information storage applications. As a mature phase change material, Ge₂Sb₂Te₅ alloy (GST) relies on the distinct electrical properties of different states to achieve information storage, but there are relatively few studies on the relationship between electron transport and microstructure. In this work, we found that the first resistance dropping in GST film is related to the increase of carrier concentration, in which the atomic bonding environment changes substantially during the crystallization process. The second resistance dropping is related to the increase of carrier mobility. Besides, during the cubic to the hexagonal phase transition, the nanograins grow significantly from ~50 nm to ~300 nm, which reduces the carrier scattering effect. Our study lays the foundation for precisely controlling the storage states of GST-based PCRAM devices. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

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10 pages, 2463 KiB

Open AccessArticle

Highly Efficient Energy Transfer from Silicon to Erbium in Erbium-Hyperdoped Silicon Quantum Dots

by Kun Wang, Qiang He, Deren Yang and Xiaodong Pi

Nanomaterials 2023, 13(2), 277; https://doi.org/10.3390/nano13020277 - 9 Jan 2023

Cited by 5 | Viewed by 2200

Abstract

Erbium-doped silicon (Er-doped Si) materials hold great potential for advancing Si photonic devices. For Er-doped Si, the efficiency of energy transfer (η_ET) from Si to Er³⁺ is crucial. In order to achieve high η_ET, we used nonthermal [...] Read more.

Erbium-doped silicon (Er-doped Si) materials hold great potential for advancing Si photonic devices. For Er-doped Si, the efficiency of energy transfer (η_ET) from Si to Er³⁺ is crucial. In order to achieve high η_ET, we used nonthermal plasma to synthesize Si quantum dots (QDs) hyperdoped with Er at the concentration of ~1% (i.e., ~5 × 10²⁰ cm⁻³). The QD surface was subsequently modified by hydrosilylation using 1-dodecene. The Er-hyperdoped Si QDs emitted near-infrared (NIR) light at wavelengths of ~830 and ~1540 nm. An ultrahigh η_ET (~93%) was obtained owing to the effective energy transfer from Si QDs to Er³⁺, which led to the weakening of the NIR emission at ~830 nm and the enhancement of the NIR emission at ~1540 nm. The coupling constant (γ) between Si QDs and Er³⁺ was comparable to or greater than 1.8 × 10⁻¹² cm³·s⁻¹. The temperature-dependent photoluminescence and excitation rate of Er-hyperdoped Si QDs indicate that strong coupling between Si QDs and Er³⁺ allows Er³⁺ to be efficiently excited. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

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10 pages, 3871 KiB

Open AccessArticle

TiO₂/SnO₂ Bilayer Electron Transport Layer for High Efficiency Perovskite Solar Cells

by Xiaolin Sun, Lu Li, Shanshan Shen and Fang Wang

Nanomaterials 2023, 13(2), 249; https://doi.org/10.3390/nano13020249 - 6 Jan 2023

Cited by 8 | Viewed by 3006

Abstract

The electron transport layer (ETL) has been extensively investigated as one of the important components to construct high-performance perovskite solar cells (PSCs). Among them, inorganic semiconducting metal oxides such as titanium dioxide (TiO₂), and tin oxide (SnO₂) present great [...] Read more.

The electron transport layer (ETL) has been extensively investigated as one of the important components to construct high-performance perovskite solar cells (PSCs). Among them, inorganic semiconducting metal oxides such as titanium dioxide (TiO₂), and tin oxide (SnO₂) present great advantages in both fabrication and efficiency. However, the surface defects and uniformity are still concerns for high performance devices. Here, we demonstrated a bilayer ETL architecture PSC in which the ETL is composed of a chemical-bath-deposition-based TiO₂ thin layer and a spin-coating-based SnO₂ thin layer. Such a bilayer-structure ETL can not only produce a larger grain size of PSCs, but also provide a higher current density and a reduced hysteresis. Compared to the mono-ETL PCSs with a low efficiency of 16.16%, the bilayer ETL device features a higher efficiency of 17.64%, accomplished with an open-circuit voltage of 1.041 V, short-circuit current density of 22.58 mA/cm², and a filling factor of 75.0%, respectively. These results highlight the unique potential of TiO₂/SnO₂ combined bilayer ETL architecture, paving a new way to fabricate high-performance and low-hysteresis PSCs. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

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18 pages, 3805 KiB

Open AccessArticle

Nanocrystalline ZnSnN₂ Prepared by Reactive Sputtering, Its Schottky Diodes and Heterojunction Solar Cells

by Fan Ye, Rui-Tuo Hong, Yi-Bin Qiu, Yi-Zhu Xie, Dong-Ping Zhang, Ping Fan and Xing-Min Cai

Nanomaterials 2023, 13(1), 178; https://doi.org/10.3390/nano13010178 - 30 Dec 2022

Cited by 8 | Viewed by 1934

Abstract

ZnSnN₂ has potential applications in photocatalysis and photovoltaics. However, the difficulty in preparing nondegenerate ZnSnN₂ hinders its device application. Here, the preparation of low-electron-density nanocrystalline ZnSnN₂ and its device application are demonstrated. Nanocrystalline ZnSnN₂ was prepared with reactive sputtering. [...] Read more.

ZnSnN₂ has potential applications in photocatalysis and photovoltaics. However, the difficulty in preparing nondegenerate ZnSnN₂ hinders its device application. Here, the preparation of low-electron-density nanocrystalline ZnSnN₂ and its device application are demonstrated. Nanocrystalline ZnSnN₂ was prepared with reactive sputtering. Nanocrystalline ZnSnN₂ with an electron density of approximately 10¹⁷ cm⁻³ can be obtained after annealing at 300 °C. Nanocrystalline ZnSnN₂ is found to form Schottky contact with Ag. Both the current I vs. voltage V curves and the capacitance C vs. voltage V curves of these samples follow the related theories of crystalline semiconductors due to the limited long-range order provided by the crystallites with sizes of 2–10 nm. The I−V curves together with the nonlinear C⁻²−V curves imply that there are interface states at the Ag-nanocrystalline ZnSnN₂ interface. The application of nanocrystalline ZnSnN₂ to heterojunction solar cells is also demonstrated. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

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9 pages, 1765 KiB

Open AccessArticle

Nanostripe-Confined Catalyst Formation for Uniform Growth of Ultrathin Silicon Nanowires

by Yinzi Cheng, Xin Gan, Zongguang Liu, Junzhuan Wang, Jun Xu, Kunji Chen and Linwei Yu

Nanomaterials 2023, 13(1), 121; https://doi.org/10.3390/nano13010121 - 26 Dec 2022

Cited by 4 | Viewed by 1822

Abstract

Uniform growth of ultrathin silicon nanowire (SiNW) channels is the key to accomplishing reliable integration of various SiNW-based electronics, but remains a formidable challenge for catalytic synthesis, largely due to the lack of uniform size control of the leading metallic droplets. In this [...] Read more.

Uniform growth of ultrathin silicon nanowire (SiNW) channels is the key to accomplishing reliable integration of various SiNW-based electronics, but remains a formidable challenge for catalytic synthesis, largely due to the lack of uniform size control of the leading metallic droplets. In this work, we explored a nanostripe-confined approach to produce highly uniform indium (In) catalyst droplets that enabled the uniform growth of an orderly SiNW array via an in-plane solid–liquid–solid (IPSLS) guided growth directed by simple step edges. It was found that the size dispersion of the In droplets could be reduced substantially from

D_{cat}^{p l}

= 20 ± 96 nm on a planar surface to only

D_{cat}^{n s}

= 88 ± 13 nm when the width of the In nanostripe was narrowed to

W_{str} =

100 nm, which could be qualitatively explained in a confined diffusion and nucleation model. The improved droplet uniformity was then translated into a more uniform growth of ultrathin SiNWs, with diameter of only

D_{nw} =

28 ± 4 nm, which has not been reported for single-edge guided IPSLS growth. These results lay a solid basis for the construction of advanced SiNW-derived field-effect transistors, sensors and display applications. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

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9 pages, 2289 KiB

Open AccessArticle

Tracing the Si Dangling Bond Nanopathway Evolution ina-SiN_x:H Resistive Switching Memory by the Transient Current

by Tong Chen, Kangmin Leng, Zhongyuan Ma, Xiaofan Jiang, Kunji Chen, Wei Li, Jun Xu and Ling Xu

Nanomaterials 2023, 13(1), 85; https://doi.org/10.3390/nano13010085 - 24 Dec 2022

Cited by 3 | Viewed by 2044

Abstract

With the big data and artificial intelligence era coming, SiN_x-based resistive random-access memories (RRAM) with controllable conductive nanopathways have a significant application in neuromorphic computing, which is similar to the tunable weight of biological synapses. However, an effective way to detect [...] Read more.

With the big data and artificial intelligence era coming, SiN_x-based resistive random-access memories (RRAM) with controllable conductive nanopathways have a significant application in neuromorphic computing, which is similar to the tunable weight of biological synapses. However, an effective way to detect the components of conductive tunable nanopathways in a-SiN_x:H RRAM has been a challenge with the thickness down-scaling to nanoscale during resistive switching. For the first time, we report the evolution of a Si dangling bond nanopathway in a-SiN_x:H resistive switching memory can be traced by the transient current at different resistance states. The number of Si dangling bonds in the conducting nanopathway for all resistive switching states can be estimated through the transient current based on the tunneling front model. Our discovery of transient current induced by the Si dangling bonds in the a-SiN_x:H resistive switching device provides a new way to gain insight into the resistive switching mechanism of the a-SiN_x:H RRAM in nanoscale. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

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11 pages, 2476 KiB

Open AccessArticle

A Stable Rechargeable Aqueous Zn–Air Battery Enabled by Heterogeneous MoS₂ Cathode Catalysts

by Min Wang, Xiaoxiao Huang, Zhiqian Yu, Pei Zhang, Chunyang Zhai, Hucheng Song, Jun Xu and Kunji Chen

Nanomaterials 2022, 12(22), 4069; https://doi.org/10.3390/nano12224069 - 18 Nov 2022

Cited by 4 | Viewed by 2180

Abstract

Aqueous rechargeable zinc (Zn)–air batteries have recently attracted extensive research interest due to their low cost, environmental benignity, safety, and high energy density. However, the sluggish kinetics of oxygen (O₂) evolution reaction (OER) and the oxygen reduction reaction (ORR) of cathode [...] Read more.

Aqueous rechargeable zinc (Zn)–air batteries have recently attracted extensive research interest due to their low cost, environmental benignity, safety, and high energy density. However, the sluggish kinetics of oxygen (O₂) evolution reaction (OER) and the oxygen reduction reaction (ORR) of cathode catalysts in the batteries result in the high over-potential that impedes the practical application of Zn–air batteries. Here, we report a stable rechargeable aqueous Zn–air battery by use of a heterogeneous two-dimensional molybdenum sulfide (2D MoS₂) cathode catalyst that consists of a heterogeneous interface and defects-embedded active edge sites. Compared to commercial Pt/C-RuO₂, the low cost MoS₂ cathode catalyst shows decent oxygen evolution and acceptable oxygen reduction catalytic activity. The assembled aqueous Zn–air battery using hybrid MoS₂ catalysts demonstrates a specific capacity of 330 mAh g⁻¹ and a durability of 500 cycles (~180 h) at 0.5 mA cm⁻². In particular, the hybrid MoS₂ catalysts outperform commercial Pt/C in the practically meaningful high-current region (>5 mA cm⁻²). This work paves the way for research on improving the performance of aqueous Zn–air batteries by constructing their own heterogeneous surfaces or interfaces instead of constructing bifunctional catalysts by compounding other materials. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Semiconductors: Selected Papers from ICANS 29)

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