A General Vapor-Induced Coating Approach for Layer-controlled Organic Single Crystals

2D organic semiconductor crystals (2D OSCs) are vital for high-performance electronic and optoelectronic devices owing to their unique material merits. However, it is still challenging to fabricate high-quality and large-scale ultrathin 2D OSCs with controllable molecular layers due to the disordered molecular deposition and uncontrollable mass transport in solution-processing fabrication. Here, a vapor-induced meniscus modulating strategy for preparing unidirectional and stable Marangoni flow to guide contactless meniscus evolution is reported, which ensures uniform mass transport and ordered molecular deposition to achieve high-quality ultrathin 2D OSCs. Both the surface tension difference and the substrate wettability are critical to meniscus formation, which results in various meniscus deformation states and film morphologies. Based on the optimized vapor-solvent system, ultrathin 2D OSCs of C₈-BTBT with precise layer definition are prepared controllably. The discrepancies in liquid film height and solute concentration are decisive in controlling the molecular scale thickness ranging from mono to a few layers. Moreover, the layer-dependent electronic and optoelectronic properties of the ultrathin films are systematically investigated. Notably, high-performance polarization-sensitive solar-blind photodetectors are achieved with a dichroic ratio of photocurrent up to 2.26, and the corresponding polarimetric image sensor exhibits superior solar-blind polarization imaging capability thanks to the high crystalline quality.     

Azeotropic Binary Solvent Mixtures for Preparation of Organic Single Crystals

Here, a new approach is introduced to prepare large single crystals of π‐conjugated organic molecules from solution. Utilizing the concept of azeotropism, single crystals of tri‐isopropylsilylethynyl pentacene (TIPS‐PEN) with dimensions up to millimeters are facilely self‐assembled from homogeneous solutions comprising two solvents with opposing polarities and a positive azeotropic point. At solvent compositions close to the azeotropic point, an abrupt transition of morphology from polycrystalline thin‐films to large single crystals is found. How to adjust the initial ratio of the binary solvents so that the change in solvent composition during evaporation favors the specific H‐aggregation and promotes an efficient self‐assembly of TIPS‐PEN is explained. The charge‐carrier (hole) mobilities are substantially enhanced by a factor of 4 from the morphology of thin‐films to large single crystals used as active layer in field‐effect transistors. Additionally, this approach is extended to other π–π stacked organic molecules to elucidate its broad applicability.     

Molecular Self‐Doping Controls Luminescence of Pure Organic Single Crystals

Organic optoelectronics calls for materials combining bright luminescence and efficient charge transport. The former is readily achieved in isolated molecules, while the latter requires strong molecular aggregation, which usually quenches luminescence. This hurdle is generally resolved by doping the host material with highly luminescent molecules collecting the excitation energy from the host. Here, a novel concept of molecular self‐doping is introduced in which a higher luminescent dopant emerges as a minute‐amount byproduct during the host material synthesis. As a one‐stage process, self‐doping is more advantageous than widely used external doping. The concept is proved on thiophene–phenylene cooligomers (TPCO) consisting of four (host) and six (dopant) conjugated rings. It is shown that <1% self‐doping doubles the photoluminescence in the TPCO single crystals, while not affecting much their charge transport properties. The Monte‐Carlo modeling of photoluminescence dynamics reveals that host–dopant energy transfer is controlled by both excitonic transport in the host and host–dopant Förster resonant energy transfer. The self‐doping concept is further broadened to a variety of conjugated oligomers synthesized via Suzuki, Kumada, and Stille crosscoupling reactions. It is concluded that self‐doping combined with improved excitonic transport and host–dopant energy transfer is a promising route to highly luminescent semiconducting organic single crystals for optoelectronics.     

Selective Nucleation of Organic Single Crystals from Vapor Phase on Nanoscopically Rough Surfaces

Organic field‐effect transistors (OFETs) are attractive for microelectronic applications such as sensor arrays or flexible displays, due to their adequate performance and relatively low production costs. Organic single‐crystal transistors have emerged as benchmark devices for studying the intrinsic charge‐transport properties in organic semiconductor materials. Conventional approaches for growing organic single crystals result in uncontrollable dimensions and the formation of extremely fragile crystals. In addition, the hand‐selection and placement of individual crystals on a device structure represents a severe limitation for producing arrays of single‐crystal transistors with high density and reasonable throughput. As a result, the application of organic single‐crystal transistors has been restricted to fundamental charge transport studies, with their commercial application not yet realizable. We recently reported a materials‐general method of fabricating large‐area arrays of patterned organic single crystals. Microcontact‐printed octadecyltriethoxysilane (OTS) film domains on smooth, inert substrates were found to act as preferential nucleation sites for single crystals for a broad range of organic semiconductor materials, such as pentacene, tetracene, rubrene and C₆₀. In order to understand the underlying mechanism of preferential nucleation, the stamped OTS domains and the contact plane between the OTS domains and the organic crystals were inspected by atomic force microscopy (AFM) and optical microscopy. Our analysis suggests that crystals nucleate at the base of tall OTS pillars that form the significantly rough surface in the stamped domains. The selective nucleation inside the rough surface regions is discussed by means of a rate‐equation model of the growth process.     

Highly Efficient Organic THz Generator Pumped at Near‐Infrared: Quinolinium Single Crystals

A novel highly efficient ionic electro‐optic quinolinium single crystals for THz wave applications is reported. Acentric quinolinium derivatives, HMQ‐T (2‐(4‐hydroxy‐3‐methoxystyryl)‐1‐methylquinolinium 4‐methylbenzenesulfonate) and HMQ‐MBS (2‐(4‐hydroxy‐3‐methoxystyryl)‐1‐methylquinolinium 4‐methoxybenzenesulfonate) exhibit high order parameters cos³θ_p = 0.92 and cos³θ_p = 1.0, respectively, as well as a large macroscopic optical nonlinearity, which is in the range of the benchmark stilbazolium DAST (N,N‐dimethylamino‐N’‐methylstilbazolium 4‐methylbenzenesulfonate) and phenolic polyene OH1 (2‐(3‐(4‐hydroxystyryl)‐5,5‐dimethylcyclohex‐2‐enylidene)malononitrile) crystals. As‐grown unpolished bulk HMQ‐T crystals with a side length of about 6 mm and thickness of 0.56 mm exhibit 3.1 times higher THz generation efficiency than 0.37 mm thick OH1 crystals and about 8.4 times higher than 1 mm thick inorganic standard ZnTe crystals at the near‐infrared fundamental wavelength of 836 nm. Therefore, HMQ crystals with high order parameter obviously have a very high potential for high power THz‐wave generation and its applications.     

Hollow Mesoporous Metal Organic Framework Single Crystals Enabled by Growth Kinetics Control for Enhanced Photocatalysis

The tailored design of hollow mesoporous metal−organic framework (MOF) single crystals to realize the unimpeded mass transport and long-range carrier migration for advanced photoelectric applications is attractive while being a major challenge. Here, a kinetically mediated micelle assembly strategy is presented to synthesize hollow UiO-66(Ce) single crystals in 1,3,5-trimethylbenzene (TMB)-H₂O emulsion system with Pluronic F127/P123 as dual surfactants. This synthesis features the employment of modulator acetic acid, which can coordinate growth kinetics of MOFs, allowing the nucleation of MOF on block polymer micelles and transforming the self-assembly of block polymer/MOF composite monomicelles from water to TMB/H₂O emulsion interface and the growth of MOF from aggregation to oriented attachment, and thus ensuring the formation of hollow mesoporous UiO-66(Ce) single crystals. Moreover, a precise control in cavity diameter from ≈0 to ≈600 nm, mesopore structure from close to radial and dendritic can be achieved by tuning the amount of TMB and the ratio of F127/P123. As a result, the hollow mesoporous UiO-66(Ce) single crystals with large radial mesopores (≈25 nm) and high surface area (≈1061 m2 g) exhibit excellent photocatalytic performance for H₂ generation owing to enhanced permeability and suppressed electron-hole combination.     

Organic Phenolic Configurationally Locked Polyene Single Crystals for Electro‐optic and Terahertz Wave Applications

We investigate a configurationally locked polyene (CLP) crystal 2‐(3‐(4‐hydroxystyryl)‐5,5‐dimethylcyclohex‐2‐enylidene)malononitrile (OH1) containing a phenolic electron donor, which also acts as a hydrogen bond donor. The OH1 crystals with orthorhombic space group Pna2₁ (point group mm2) exhibit large second‐order nonlinear optical figures of merit, high thermal stability and very favorable crystal growth characteristics. Higher solubility in methanol and a larger temperature difference between the melting temperature and the decomposition temperature of OH1 compared to analogous CLP crystals, are of advantage for solution and melt crystal growth, respectively. Acentric bulk OH1 crystals of large sizes with side lengths of up to 1 cm with excellent optical quality have been successfully grown from methanol solution. The microscopic and macroscopic nonlinearities of the OH1 crystals are investigated theoretically and experimentally. The OH1 crystals exhibit a large macroscopic nonlinearity with four times larger powder second harmonic generation efficiency than that of analogous CLP crystals containing dimethylamino electron donor. A very high potential of OH1 crystals for broadband THz wave emitters in the full frequency range of 0.1–3 THz by optical rectification of 160 fs pulses has been demonstrated.     

有机聚合物CPU的结构形态

本文用扫描隧道显微镜（ＳＴＭ）研究了有机氰基－苯基－脲（ＣＰＵ）的表面结构。在不同的ＣＰＵ薄膜制备条件下，得到了不同的ＣＰＵ薄膜的ＳＴＭ像，表明制备条件与成膜结构的密切关系。观察到了ＣＰＵ薄膜中晶区和非晶区的存在，证实了聚合物晶体中晶区和非晶区的模型。     

四硼酸锂晶体的声表面波应用

介绍了新型压电晶体四硼酸锂的压电和声表面波特性，讨论了四硼酸锂晶体基片声表面波器件的制作工艺，总结了近年来四硼酸锂晶体压电器件的研究成果。     

磷扩散氧化锌单晶的性质

分别在550和800℃对CVT方法生长的非掺ZnO单晶进行闭管磷扩散. 通过Hall测试、X射线光电子谱（XPS) 、光致发光（PL）以及喇曼散射对扩散后的样品进行测试分析. 发现扩散掺杂后的ZnO单晶仍显示n型导电性,自由电子浓度比非掺样品增高,在800℃扩散后尤为明显. PL测试结果表明,掺杂样品在420~550nm范围的可见光发射与缺陷有关. XPS测试表明:在550℃掺杂,P原子更易代替Zn位;在800℃扩散时,P未占据Zn位,而似乎占据了O位. 最终在磷扩散后的ZnO单晶中形成了高浓度的浅施主缺陷,造成了自由电子的显著增加.     

磷扩散氧化锌单晶的性质

分别在550和800℃对CVT方法生长的非掺ZnO单品进行闭管磷扩散.通过Hall测试、X射线光电子谱(XPS)、光致发光(PL)以及喇曼散射对扩散后的样品进行测试分析.发现扩散掺杂后的ZnO单晶仍显示n型导电性,自由电子浓度比非掺样品增高,在800℃扩散后尤为明显.PL测试结果表明,掺杂样品在420～550nm范围的可见光发射与缺陷有关.XPS测试表明:在550℃掺杂,P原子更易代替Zn位;在800℃扩散时,P未占据Zn位,而似乎占据了O位.最终在磷扩散后的ZnO单晶中形成了高浓度的浅施主缺陷,造成了自由电子的显著增加.     

Conducting Domain Walls in Lithium Niobate Single Crystals

Ferroic materials play an increasingly important role in novel (nano)electronic devices. Recently, research on domain walls (DWs) receives a big boost by the discovery of DW conductivity (DWC) in BiFeO₃ and Pb(Zr_xTi_1‐x)O₃ ferroic thin films. Here, it is demonstrated that DWC is not restricted to thin films, but equally applies to millimeter‐thick wide‐bandgap, ferroic single crystals, such as LiNbO₃. In this material transport along DWs can be switched by super‐bandgap illumination and tuned by engineering the tilting angle of DWs with respect to the polar axis. The results are consistently obtained using conductive atomic force microscopy to locally map the DWC and macroscopic contacts, thereby in addition investigating the temperature dependence, DW transport activation energies, and relaxation behavior.     

Photoelectric Effects in Single Domain BiFeO3 Crystals

Energy harvesting from sunlight is essential in order to save fossil fuels, which are found in limited amount in the earth's crust. Photovoltaic devices converting light into electrical energy are presently made of semiconducting materials, but ferroelectrics are also natural candidates because of their internal built‐in electric field. Although they are clearly uncompetitive for mainstream applications, the possibility to output high photovoltages is making these materials reconsidered for targeted applications. However, their intrinsic properties regarding electronic transport and the origin of their internal field are poorly known. Here, it is demonstrated that under intense illumination and electric field, oxygen vacancies can be controllably generated in BiFeO₃ to dramatically increase the conductance of BiFeO₃ single crystals to a controllable value spanning 6 orders of magnitude while at the same time triggering light sensitivity in the form of photoconductivity, diode, and photovoltaic effects. Properties of the bulk and the Schottky interfaces with gold contacts are disentangled and it is shown that bulk effects are time dependent. The photocurrent has a direction that can be set by an applied field without changing the ferroelectric polarization direction. The self‐doping procedure is found to be essential in both the generation of electron hole pairs and the establishment of the internal field that separates them.     

Thermoelectric Properties of Li-Intercalated ZrSe2 Single Crystals

Zirconium diselenide (ZrSe₂) is one of many members of the layer-structured transition-metal dichalcogenide family. The structure of these materials features a weakly bonded van der Waals gap between covalently bonded CdI₂-type atomic layers that may host a wide range of intercalants. Intercalation can profoundly affect the structural, thermal, and electronic properties of such materials. While the thermoelectric potential of layer-structured transition-metal dichalcogenides has been formerly studied by several groups, to our best knowledge, neither the thermoelectric properties of ZrSe₂ nor the impact of intercalation on its thermoelectric properties have been reported (specifically, the full evaluation of the dimensionless figure of merit, ZT, which includes the thermal conductivity). In this proof-of-principle study, ZrSe₂ single crystals have been synthesized using an iodine-assisted vapor transport method, followed by a wet-chemistry lithium intercalation process. The results of resistivity, thermopower, and thermal conductivity measurements between 10 K and 300 K show that Li intercalation induced additional charge carriers and structural disorder that favorably affected the thermoelectric properties of the material. As a result, a dimensionless figure of merit ZT ≈ 0.26 has been attained at room temperature in a Li-intercalated sample, representing nearly a factor of three improvement compared with the pristine sample. These improvements, along with the abundance, relatively low toxicity, and low cost of such materials, merit further thermoelectric investigations of intercalated zirconium diselenide, especially in conjunction with a substitutional doping approach.     

Composition Engineering of Perovskite Single Crystals for High-Performance Optoelectronics

Composition engineering, with its advantages to effectively tune semiconductor properties by regulating chemical stoichiometry, is a proven strategy to boost the efficiency and stability of ABX₃ perovskite photoelectronic devices. Compared with its counterpart polycrystalline perovskite film, single crystalline is the ideal model for exploring its fundamental scientific issues. In this review, a critical overview of recent advances of the growth strategies, properties, and functional applications of multicomponent perovskite single crystals (SCs) is presented. First, the underlying advantages of composition engineering of perovskite SCs are discussed and then the different composition tuning strategies, including A-site, B-site, X-site, and simultaneous A- and X-site engineering, are systematically summarized. Subsequently, the benefits of composition engineering are highlighted for optimizing photovoltaic and photoelectronic devices. Lastly, controversies and remaining challenges for the development of composition engineering of perovskite SCs are discussed and a brief perspective regarding further investigation in this field is provided.     

铈掺杂稀土卤化物单晶的处理方法

为了解决铈掺杂稀土卤化物单晶中内部热应力大、难于加工的技术难题,该文提供了一种针对铈掺杂稀土卤化物单晶的原位退火处理方法。利用该方法对尺寸为?25.4 mm×25.4 mm和?76.2 mm×76.2 mm的Ce∶LaBr_3晶体进行退火处理,晶体经过切割、滚圆、研磨、抛光、封装等工艺过程后,均未出现开裂的现象。通过测试以上两种Ce∶LaBr_3器件能量谱图,其能量分辨率分别为2.92%和3.02%,该工艺未对晶体的闪烁性能造成影响。实验结果表明,该文提出的铈掺杂稀土卤化物单晶原位退火处理方法,可有效地消除晶体内部的热应力,并改善其机械性能,这对提高晶体加工成品率具有重要意义。     

高质量InAs单晶材料的制备及其性质

利用液封直拉法(LEC)生长了直径50mm〈100〉和〈111〉晶向的InAs单晶.分析研究了n型杂质Sn,S和p型杂质Zn,Mn的分凝特性、晶格硬化作用、掺杂效率等.利用X射线双晶衍射分析了晶体的完整性.对InAs晶片的抛光、化学腐蚀和清洗进行了分析,在此基础上实现了抛光晶片的开盒即用(EPI-READY).