Device Performance and Strain Effect of Sub-5 nm Monolayer InP Transistors

Indium phosphide (InP) has higher electron mobility, electron saturation velocity, and drain current than silicon (Si), and the ultra-thin (UT) InP field-effect transistor (FET) probably possesses a better device performance...

Aminophosphine-Derived, High-Quality Red-Emissive InP Quantum Dots by Use of an Unconventional In Halide

Thanks to the synthetic maturity and environmental benignity of indium phosphide (InP) quantum dots (QDs), they have acquired a dominant position as efficient, sustainable visible emitters for next-generation display devices....

Aminophosphine Reduction Mechanisms and the Synthesis of Indium Phosphide Nanomaterials

<p>Indium phosphide (InP) nanomaterials are attractive for countless technological applications due to their well-placed band gap energies. The quantum confinement of these semiconductors can give rise to size-dependent absorption and emission features throughout the entire visible spectrum. Therefore, InP materials can be employed as low-toxicity fluorophores that can be implemented in high value avenues such as biological probes, lighting applications, and lasing technologies. However, large scale development of these quantum dots (QDs) has been stymied by the lack of affordable and safe phosphorus precursors. Syntheses have largely been restricted to the use of dangerous chemicals such as tris(trimethylsilyl)phosphine ((TMS)₃P), which is costly and highly sensitive to oxygen and water. Recently, less-hazardous tris(dialkylamino)phosphines have been introduced to produce InP QDs on par with those utilizing (TMS)₃P. However, a poor understanding of the reaction mechanics has resulted in difficulties tuning and optimizing this method. In this work, density functional theory (DFT) is used to identify the mechanism of this aminophosphine precursor conversion. This understanding is then implemented to design an improved InP QD synthesis, allowing for the production of high-quality materials outside of glovebox conditions. Time is spent understanding the impact of different precursor salts on the reaction mechanisms and discerning their subsequent effects on nanoparticle size and quality. The motivation of this work is to formulate safer and less technical indium phosphide quantum dot syntheses to foster non-specialist and industrial implementation of these materials.</p>

Aminophosphine Reduction Mechanisms and the Synthesis of Indium Phosphide Nanomaterials

<p>Indium phosphide (InP) nanomaterials are attractive for countless technological applications due to their well-placed band gap energies. The quantum confinement of these semiconductors can give rise to size-dependent absorption and emission features throughout the entire visible spectrum. Therefore, InP materials can be employed as low-toxicity fluorophores that can be implemented in high value avenues such as biological probes, lighting applications, and lasing technologies. However, large scale development of these quantum dots (QDs) has been stymied by the lack of affordable and safe phosphorus precursors. Syntheses have largely been restricted to the use of dangerous chemicals such as tris(trimethylsilyl)phosphine ((TMS)₃P), which is costly and highly sensitive to oxygen and water. Recently, less-hazardous tris(dialkylamino)phosphines have been introduced to produce InP QDs on par with those utilizing (TMS)₃P. However, a poor understanding of the reaction mechanics has resulted in difficulties tuning and optimizing this method. In this work, density functional theory (DFT) is used to identify the mechanism of this aminophosphine precursor conversion. This understanding is then implemented to design an improved InP QD synthesis, allowing for the production of high-quality materials outside of glovebox conditions. Time is spent understanding the impact of different precursor salts on the reaction mechanisms and discerning their subsequent effects on nanoparticle size and quality. The motivation of this work is to formulate safer and less technical indium phosphide quantum dot syntheses to foster non-specialist and industrial implementation of these materials.</p>

Aptamer Conjugated Indium Phosphide Quantum Dots with a Zinc Sulphide Shell as Photoluminescent Labels for Acinetobacter baumannii

Acinetobacter baumannii is a remarkable microorganism known for its diversity of habitat and its multi-drug resistance, resulting in hard-to-treat infections. Thus, a sensitive method for the identification and detection of Acinetobacter baumannii is vital. However, current methods used for the detection of pathogens have not improved in the past decades and suffer from long process times and low detection limits. A cheap, quick, and easy detection mechanism is needed. In this work, we successfully prepared indium phosphide quantum dots with a zinc sulphide shell, conjugated to a targeting aptamer ligand, to specifically label Acinetobacter baumannii. The system retained both the photophysical properties of the quantum dots and the folded structure and molecular recognition function of the aptamer, therefore successfully targeting Acinetobacter baumannii. Confocal microscopy and transmission electron microscopy showed the fluorescent quantum dots surrounding the Acinetobacter baumannii cells confirming the specificity of the aptamer conjugated to indium phosphide quantum dots with a zinc sulphide shell. Controls were undertaken with a different bacteria species, showing no binding of the aptamer conjugated quantum dots. Our strategy offers a novel method to detect bacteria and engineer a scalable platform for fluorescence detection, therefore improving current methods and allowing for better treatment.

Solution Phase Syntheses of Nanoparticles and Nanowires

<p>This thesis is concerned with the preparation of metal and semiconductor nanostructures in solution, specifically bismuth and indium metal nanoparticles, gallium nitride nanoparticles, indium phosphide nanowires and zinc phosphide nanoparticles. There were two aims: firstly to study if gallium nitride nanoparticles with improved crystallinity and size distribution could be synthesized and secondly to find and develop new methods to prepare crystalline indium phosphide nanowires and zinc phosphide nanoparticles using precursors that are safe and cheap. The crystallinity, structures, morphologies and chemical compositions of the nanostructures synthesized in this thesis were studied primarily by transmission electron microscopy (TEM), powder X-ray diffraction (PXRD) and energy dispersive X-ray spectrometry (EDS). For the synthesis of gallium nitride, two approaches were taken. The first revolves around the direct metathesis reaction between gallium trichloride and lithium nitride under ambient pressure. A range of solvents with different polarities has been tested and only in highly polar solvents crystalline nanostructures were produced. These crystalline nanostructures however are not of gallium nitride. The second approach involves thermally decomposing an organometallic precursor. Organometallic compounds [Ga2(NMe2)6] (compound 1) and [(Me3C)2Ga(u-NHNHCMe3)] (compound 2) were chosen from the literature as precursors. Compound 1 was synthesized in a very small yield together with by-products. Thermal decomposition of the mixture produced no nanoparticles. A compound (compound S2) which is structurally similar to compound 2 was successfully synthesized and was subjected to thermal decomposition in ammonia to produce crystalline monodispersed nanoparticles. However, these nanoparticles could not be confidently identified as gallium nitride. The outcome from the reaction of lithium borohydride and indium trichloride was found to be strongly solvent dependent. In toluene a white precipitate was obtained. Both in isobutylamine and N,N-diethylaniline indium metal nanoparticles were produced as black solutions. Only in isobutylamine, small monodispersed indium nanoparticles can be produced. The isobutylamine method was extended to prepare bismuth metal nanoparticles. However, the bismuth nanoparticles prepared were moderately polydispersed in size. Two new methods were developed to prepare indium phosphide nanowires from red phosphorus and phosphorus pentabromide via Solution-Liquid-Solid growth. Borohydride reagents are required in both methods to produce chemically active intermediates which further react to form indium phosphide nanowires in the presence of pre-synthesized indium metal or bismuth nanoparticles. The diameter of indium phosphide nanowires prepared from red phosphorus depends strongly on the reaction sequences. If indium metal nanoparticles are formed prior to the addition of red phosphorus, large nanowires (> 300 nm) are produced. Reversing the sequences, small nanowires (50-100 nm) are produced. Red phosphorus residue remains in the products regardless of the reaction sequences and is difficult to remove completely by chemical means. The reaction which employs phosphorus pentabromide as precursor proceeds via intermediates of hydrogen phosphide and indium metal to form indium phosphide. The reaction temperature dictates the crystallinity of the product and needs to be >170 oC to produce crystalline indium phosphide. The way hydrogen phosphide is introduced to the reaction and the presence or absence of pre-synthesized metal seeds together control the morphology of indium phosphide synthesized. The best set of conditions established in this thesis allows the preparation of indium phosphide in ~100% nanowire morphology. The hydrogen phosphide method was adapted to produce zinc phosphide nanoparticles. The choice of the reaction solvent was found to be most critical. Amorphous particles were produced in trioctylphosphine at as high as 330 oC whereas in oleylamine and N,Ndiethylaniline crystalline zinc phosphide (a-Zn3P2) nanoparticles were produced at ~200 oC. An overall conclusion is given in the last chapter comparing the methods developed in this thesis with literature methods paying particular foci on the level of hazard and the costs of the chemical reagents involved.</p>

Solution Phase Syntheses of Nanoparticles and Nanowires

<p>This thesis is concerned with the preparation of metal and semiconductor nanostructures in solution, specifically bismuth and indium metal nanoparticles, gallium nitride nanoparticles, indium phosphide nanowires and zinc phosphide nanoparticles. There were two aims: firstly to study if gallium nitride nanoparticles with improved crystallinity and size distribution could be synthesized and secondly to find and develop new methods to prepare crystalline indium phosphide nanowires and zinc phosphide nanoparticles using precursors that are safe and cheap. The crystallinity, structures, morphologies and chemical compositions of the nanostructures synthesized in this thesis were studied primarily by transmission electron microscopy (TEM), powder X-ray diffraction (PXRD) and energy dispersive X-ray spectrometry (EDS). For the synthesis of gallium nitride, two approaches were taken. The first revolves around the direct metathesis reaction between gallium trichloride and lithium nitride under ambient pressure. A range of solvents with different polarities has been tested and only in highly polar solvents crystalline nanostructures were produced. These crystalline nanostructures however are not of gallium nitride. The second approach involves thermally decomposing an organometallic precursor. Organometallic compounds [Ga2(NMe2)6] (compound 1) and [(Me3C)2Ga(u-NHNHCMe3)] (compound 2) were chosen from the literature as precursors. Compound 1 was synthesized in a very small yield together with by-products. Thermal decomposition of the mixture produced no nanoparticles. A compound (compound S2) which is structurally similar to compound 2 was successfully synthesized and was subjected to thermal decomposition in ammonia to produce crystalline monodispersed nanoparticles. However, these nanoparticles could not be confidently identified as gallium nitride. The outcome from the reaction of lithium borohydride and indium trichloride was found to be strongly solvent dependent. In toluene a white precipitate was obtained. Both in isobutylamine and N,N-diethylaniline indium metal nanoparticles were produced as black solutions. Only in isobutylamine, small monodispersed indium nanoparticles can be produced. The isobutylamine method was extended to prepare bismuth metal nanoparticles. However, the bismuth nanoparticles prepared were moderately polydispersed in size. Two new methods were developed to prepare indium phosphide nanowires from red phosphorus and phosphorus pentabromide via Solution-Liquid-Solid growth. Borohydride reagents are required in both methods to produce chemically active intermediates which further react to form indium phosphide nanowires in the presence of pre-synthesized indium metal or bismuth nanoparticles. The diameter of indium phosphide nanowires prepared from red phosphorus depends strongly on the reaction sequences. If indium metal nanoparticles are formed prior to the addition of red phosphorus, large nanowires (> 300 nm) are produced. Reversing the sequences, small nanowires (50-100 nm) are produced. Red phosphorus residue remains in the products regardless of the reaction sequences and is difficult to remove completely by chemical means. The reaction which employs phosphorus pentabromide as precursor proceeds via intermediates of hydrogen phosphide and indium metal to form indium phosphide. The reaction temperature dictates the crystallinity of the product and needs to be >170 oC to produce crystalline indium phosphide. The way hydrogen phosphide is introduced to the reaction and the presence or absence of pre-synthesized metal seeds together control the morphology of indium phosphide synthesized. The best set of conditions established in this thesis allows the preparation of indium phosphide in ~100% nanowire morphology. The hydrogen phosphide method was adapted to produce zinc phosphide nanoparticles. The choice of the reaction solvent was found to be most critical. Amorphous particles were produced in trioctylphosphine at as high as 330 oC whereas in oleylamine and N,Ndiethylaniline crystalline zinc phosphide (a-Zn3P2) nanoparticles were produced at ~200 oC. An overall conclusion is given in the last chapter comparing the methods developed in this thesis with literature methods paying particular foci on the level of hazard and the costs of the chemical reagents involved.</p>