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Radiative cooling to subambient temperatures can be efficiently achieved through spectrally selective emission, which until now has only been realized by using complex nanoengineered structures. Here, a simple dip-coated planar polymer emitter derived from polysilazane, which exhibits strong selective emissivity in the atmospheric transparency window of 8-13 μm, is demonstrated. The 5 μm thin silicon oxycarbonitride coating has an emissivity of 0.86 in this spectral range because of alignment of the frequencies of bond vibrations arising from the polymer. Furthermore, atmospheric heat absorption is suppressed due to its low emissivity outside the atmospheric transparency window. The reported structure with the highly transparent polymer and underlying silver mirror reflects 97% of the incoming solar irradiation. A temperature reduction of 6.8 °C below ambient temperature was achieved by the structure under direct sunlight, yielding a cooling power of 93.7 W m-2. The structural simplicity, durability, easy applicability, and high selectivity make polysilazane a unique emitter for efficient prospective passive daytime radiative cooling structures.

In this work, we employed the method of perhydropolysilazane (PHPS) conversion into silica for encapsulating flexible perovskite solar cells (PSCs). The conversion process was conducted by the vacu...

Perhydropolysilazane (PHPS), an inorganic polymer composed of Si-N and Si-H, has attracted much attention as a precursor for gate dielectrics of thin-film transistors (TFTs) due to its facile processing even at a relatively low temperature. However, an in-depth understanding of the tunable dielectric behavior of PHPS-derived dielectrics and their effects on TFT device performance is still lacking. In this study, the PHPS-derived dielectric films formed at different annealing temperatures have been used as the gate dielectric layer for solution-processed indium zinc oxide (IZO) TFTs. Notably, the IZO TFTs fabricated on PHPS annealed at 350 °C exhibit mobility as high as 118 cm

We successfully fabricated a stable, efficient, and easy-to-use CsPbBr3 perovskite nanocrystal (PeNC)-embedded inorganic polymer film through an encapsulation step with a Si–N/Si–O-based polysilaza...

Despite the excellent optical features of fully inorganic cesium lead halide (CsPbX3) perovskite quantum dots (PeQDs), their unstable nature has limited their use in various optoelectronic devices. To mitigate the instability issues of PeQDs, we demonstrate the roles of dual-silicon nitride and silicon oxide ligands of the polysilazane (PSZ) inorganic polymer to passivate the surface defects and form a barrier layer coated onto green CsPbBr3 QDs to maintain the high photoluminescence quantum yield (PLQY) and improve the environmental stability. The mixed SiNx/SiNxOy/SiOy passivated and encapsulated CsPbBr3/PSZ core/shell composite can be prepared by a simple hydrolysis reaction involving the addition of adding PSZ as a precursor and a slight amount of water into a colloidal CsPbBr3 QD solution. The degree of the moisture-induced hydrolysis reaction of PSZ can affect the compositional ratio of SiNx, SiNxOy, and SiOy liganded to the surfaces of the CsPbBr3 QDs to optimize the PLQY and the stability of CsPbB...

Polymer-derived ceramics (PDCs) have enabled the development of nonoxide ceramic coatings and fibers with exceptional thermo-mechanical stability. Here, we report the self-assembly based synthesis of gyroidal (space group Q230, Ia3d) mesoporous silicon oxynitride ceramic monoliths by pyrolysis of blends of commercially available preceramic polysilazane with a structure-directing triblock terpolymer up to temperatures of 1000 °C. Monoliths had pore diameters of 9.4 ± 1.1 nm and surface area of 160 m2/g. The three-dimensionally (3D) ordered periodic pore structure of the as-made hybrids acts to relieve stresses by allowing the escape of gases formed during ceramization. This process in turn enables the retention of smooth monoliths during ceramization under ammonia, a process that both adds nitrogen to the material and removes carbon pyrolysis products. The monoliths are appealing for high-temperature applications such as catalyst supports and microelectromechanical system (MEMS) devices including gas and ...

Amorphous SiHfBCN ceramics were prepared from a commercial polysilazane (HTT 1800, AZ-EM), which was modified upon reactions with Hf(NEt2)4 and BH3·SMe2, and subsequently cross-linked and pyrolyzed. The prepared materials were investigated with respect to their chemical and phase composition, by means of spectroscopy techniques (Fourier transform infrared (FTIR), Raman, magic-angle spinning nuclear magnetic resonance (MAS NMR)), as well as X-ray diffraction (XRD) and transmission electron microscopy (TEM). Annealing experiments of the SiHfBCN samples in an inert gas atmosphere (Ar, N2) at temperatures in the range of 1300-1700 °C showed the conversion of the amorphous materials into nanostructured UHTC-NCs. Depending on the annealing atmosphere, HfC/HfB2/SiC (annealing in argon) and HfN/Si3N4/SiBCN (annealing in nitrogen) nanocomposites were obtained. The results emphasize that the conversion of the single-phase SiHfBCN into UHTC-NCs is thermodynamically controlled, thus allowing for a knowledge-based preparative path toward nanostructured ultrahigh-temperature stable materials with adjusted compositions.

Ni–polysilazane precursors were synthesized from polysilazane and trans- [bis(2-aminoetanol-N,O)diacetato-nickel(II)]. The Ni–polysilazane precursors are superparamagnetic indicating formation of nanosized nickel particles (∼2−3 nm) confirmed by HRTEM as well. The as-obtained Ni–polysilazane precursors were thermolized at 700 °C and transformed to ceramic nanocomposites, manifesting a nanoporous structure, revealing a BET surface area of 215 m2 g–1, a micropore surface area of 205 m2 g–1, and a micropore volume of 0.113 cm3 g–1. Although Si–C–N–(O) ceramics derived from the native polysilazane are nonporous, the pronounced development of porosity in the Ni/Si–C–N–(O) system was attributed to (i) the stabilizing effect of carbosilane bonds, which prohibit the formation of macropores during thermolysis; (ii) the reduced barrier for heterogeneous pore nucleation as a result of in situ created nickel nanoparticles; and (iii) the reduced viscous flow of the pores due to the presence of nickel nanoparticles and...

We have reported the enhanced field emission properties of quasialigned 3C-SiC nanowires synthesized via catalyst assisted pyrolysis of polysilazane. The as-synthesized Al-doped SiC nanowires possess a tapered and bamboo-like structure with clear and tiny tips sized in several to tens of nanometers. The fabricated SiC nanowires have extremely low turn-on fields of 0.55−1.54 V μm−1 with an average of ∼1 V μm−1, which is the lowest one ever reported for any type of SiC emitters. The field-enhancement factor has been calculated to be 2983. The superior FE properties can be clearly attributed to the significant enhancements of the tapered and bamboo-like unique morphology and Al doping of SiC nanowires. Density functional theory calculations suggest that Al dopants in 3C-SiC nanowires could favor a more localized state near the Fermi energy, which improves the electron field emissions. We strongly believe that the present work will open a new insight in the fabrication of field emission sources with ultralow ...

Single-walled carbon nanotubes (SWNTs) were incorporated into precursor-derived ceramics made from a polysilazane. To improve the dispersion of the nanotubes in the liquid precursor and finally in the ceramic matrix, the SWNTs were chemically modified by (iodomethyl)trimethylsilane via a radical reaction. The functionalization degree of the modified SWNTs was determined to be 3 atom %. Microscopic investigation combined with viscosity measurements and thixotropy tests demonstrated that the functionalized SWNTs are more homogeneously dispersed in the liquid SWNT/polymer mixtures and the solid cross-linked precursor, as compared to pristine nanotubes. SWNT/Si−C−N ceramics with nanotube contents of up to 1 wt % were obtained through pyrolysis of cross-linked SWNT/polymer composites at 1000 °C. The presence of intact nanotubes in these composites could be verified by scanning transmission electron microscopy. The high viscosity of the SWNT/polysilazane mixtures was identified as an important prerequisite for ...

Stable gold clusters around 1 nm in size have been prepared by evaporation of the metal into an organosilicon polymer solution. A controlled particle growth of the entrapped gold particles was achieved by annealing in helium at ∼410 °C. Above 460 °C the growth rate is dramatically increased, concurrent with the onset of pyrolysis of polysilazane to form a porous solid. X-ray diffraction and simulation calculations using Debye functions of model clusters of different sizes and both crystallographic and noncrystallographic symmetry were used to characterize these particles. The exclusive presence of noncrystallographic (decahedral and icosahedral) multiply twinned particles (MTPs) in the as-prepared material is confirmed by EXAFS. The high precision of the XRD experiments and theoretical data fits gives detailed insight into the thermally induced growth process, during which the MTPs progressively disappear and are replaced by singly twinned fcc particles of larger size. This transition occurs in the range ...

In a search for a generic synthesis methodology to produce microporous, nonoxide ceramics, pyrolysis of silicon-based preceramic polymers has been studied in inert (He or Ar) and reactive (NH3) atmospheres over the temperature range 25−1300 °C. Pyrolysis of polysilazanes in an inert atmosphere in the absence of additives produced only low-density, nonmicroporous solids. However, four successful approaches to induce microporosity were developed, involving controlled reaction of selected low molecular weight polysilazane preceramic polymers. The first method employs the formation of colloidal polysilazane mixtures with micron-size particles of ceramics such as Si3N4, SiC, and AlN, followed by their pyrolysis in He or NH3 to form a ceramic−ceramic composite. The second method involves the synthesis of a nanoscale, polysilazane-stabilized metal colloid of a noble or transition metal and its conversion to a metal− or cermet−ceramic composite by pyrolysis in He or NH3. In the third method, a polysilazane is pyr...

The ionic ring-opening polymerization of cyclosilazane monomers is studied. Various cyclosilazanes have been reacted with both anionic and cationic initiators. Whereas cyclotrisilazanes and cyclotetrasilazanes give an equilibrated polymerization analogous to that observed with cyclosiloxanes, cyclodisilazanes with tert-butyl, isopropyl, or ethyl groups on the nitrogen only oligomerize. When the nitrogen substituent is a methyl group and for various silicon substituents, high molar mass polymers are obtained by both anionic and cationic processes

In the present study, a poly(isoprene-block-dimethylamino ethyl methacrylate) diblock copolymer (PI-b-PDMAEMA) is used to structure-direct a polysilazane pre-ceramic polymer, commercially known as Ceraset. To the polymer was added a 2-fold excess in weight of the silazane oligomer (Ceraset). The resulting composite was cast into films, and after cooperative self-assembly of block copolymer and Ceraset, the structure was permanently set in the hexagonal columnar morphology, as evidenced by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Cross-linking of the silazane oligomer was achieved with a radical initiator at 120 degrees C. Upon heating of the composite to 1500 degrees C under nitrogen, the structure is preserved and a mesoporous ceramic material is obtained, as demonstrated by SAXS and TEM. The pores are open and accessible, as evidenced by nitrogen sorption/desorption measurements indicating a surface area of about 51 m2 g-1 and a pore diameter of 13 nm, consistent with TEM analysis. These results suggest that the use of block copolymer mesophases may provide a simple, easily controlled pathway for the preparation of various high-temperature ceramic mesostructures.