In an effort to further the understanding of ligand-surface interactions, a combination of multi-nuclear (1H, 29Si, 31P) and multi-dimensional solid-state NMR techniques were utilized to characterize the phosphonic acid functionalization of fumed silica nanoparticles using methyl phosphonic acid (MPA) and phenyl phosphonic acid (PPA). Quantitative 31P MAS solid-state NMR measurements indicate that ligands favor a monodentate binding mode. Furthermore, 1H-1H single quantum-double quantum (SQ-DQ) back-to-back (BABA) 2D NMR spectra of silica functionalized with MPA and PPA indicate that the MPA and PPA are within 4.2±0.2 Å on the surface of the nanomaterial.
The ligand capping of phosphonic acid (PA) functionalized CdSe/ZnS core-shell quantum dots (QDs) was investigated with a combination of ligand exchange, solution and solid-state 31P NMR spectroscopy. In order to quantify the ligand populations on the surface of the QDs, ligand exchange facilitated by PPA resulted in the displacement of the PAs, and allowed for quantification of the free ligands using 31P liquid state NMR.
In addition to characterizing nanomaterials, the ionicity and transport properties of a series of diethylmethylamine (DEMA) based protic ionic liquids (PILs) were characterized, principally utilizing NMR. Gas phase proton affinity was shown to be a better predictor for the extent of proton transfer, and in turn the ionicity of the PIL, than using ∆pKa. Furthermore, pulsed field gradient (PFG) NMR was used to determine that the exchangeable proton diffuses with the cation or the anion based on the strength of the acid used to generate the PILs.
First, the surface electronic state configuration was examined with regards to the polarization bound 1013 charges/cm2 that increases with aluminum content. This large bound charge requires compensation either externally by surface states or internally by the space charge regions as relates to band bending. In this work, band bending was measured after different surface treatments of GaN and AlGaN to determine the effects of specific surface states on the electronic state configuration. Results showed oxygen-terminated N-face GaN, Ga-face GaN, and Ga-face Al0.25Ga0.75N surface were characterized by similar band bending regardless of the polarization bound charge, suggesting a Fermi level pinning state ~0.4-0.8 eV below the conduction band minimum. On oxygen-free Ga-face GaN, Al0.15Ga0.85N, Al0.25Ga0.75N, and Al0.35Ga0.65N, band bending increased slightly with aluminum content and thus did not exhibit the same pinning behavior; however, there was still significant compensating charge on these surfaces (~1013 charges/cm2). This charge is likely related to nitrogen vacancies and/or gallium dangling bonds.
In addition, this wozrk investigated the interface electronic state configuration of dielectric/GaN and AlGaN interfaces with regards to deposition conditions and aluminum content. Specifically, oxygen plasma-enhanced atomic layer deposited (PEALD) was used to deposit SiO2. Growth temperature was shown to influence the film quality, where room temperature deposition produced the highest quality films in terms of electrical breakdown. In addition, the valence band offsets (VBOs) appeared to decrease with the deposition temperature, which likely related to an electric field across the Ga2O3 interfacial layer. VBOs were also determined with respect to aluminum content at the PEALD-SiO2/AlxGa1-xN interface, giving 3.0, 2.9, 2.9, and 2.8 eV for 0%, 15%, 25%, and 35% aluminum content, respectively—with corresponding conduction band offsets of 2.5, 2.2, 1.9, and 1.8 eV. This suggests the largest difference manifests in the conduction band, which is in agreement with the charge neutrality level model.
Band engineering of Ge was achieved by alloying with Sn. Epitaxy of the alloy layers was conducted on virtual Ge substrates, and made use of the germanium hydrides Ge2H6 and Ge3H8, and the Sn source SnD4. These films exhibit stronger emission than equivalent material deposited directly on Si, and the contributions from the direct and indirect edges can be separated. The indirect-direct crossover composition for Ge1-ySny alloys was determined by photoluminescence (PL). By n-type doping of the Ge1-ySny alloys via P(GeH3)3, P(SiH3)3 and As(SiH3)3, it was possible to enhance photoexcited emission by more than an order-of-magnitude.
The above techniques for deposition of direct gap Ge1-ySny alloys and doping of Ge were combined with p-type doping methods for Ge1-ySny using B2H6 to fabricate pin heterostructure diodes with active layer compositions up to y=0.137. These represent the first direct gap light emitting diodes made from group IV materials. The effect of the single defected n-i¬ interface in a n-Ge/i-Ge1-ySny/p-Ge1-zSnz architecture on electroluminescence (EL) was studied. This led to lattice engineering of the n-type contact layer to produce diodes of n-Ge1-xSnx/i-Ge1-ySny/p-Ge1-zSnz architecture which are devoid of interface defects and therefore exhibit more efficient EL than the previous design. Finally, n-Ge1-ySny/p-Ge1-zSnz pn junction devices were synthesized with varying composition and doping parameters to investigate the effect of these properties on EL.
The objective of this experiment was to use water contact angle (WCA) to measure the effectiveness of adhesion, Atomic Layer Deposition (ALD), and cleaning techniques within different operations at Intel Corporation. Using the Sessile Drop Method, goniometer instrument, and a Video Contact Angle system (VCA), the water contact angle across silicon wafers at various operations were determined. Based on the results, it was concluded that Operation 5 and Step 4.4 within Operation 5 were suspected to cause lack of uniformity across the wafers, which is detrimental to the durability of the wafer and the overall high performance of a microchip. Due to proprietary reasons, it could not be disclosed as to whether adhesion, ALD, or cleaning techniques were implemented and suspected to cause non-uniformity across the wafer, but despite any operation, the topography of the wafer should be leveled. The absolute slopes of Operation 5 and Step 4.4 were 2.445 and 3.189, respectively. These slopes represented the change in contact angles across different positions of the wafer. In comparison, these showed the greatest variation of contact angles across the wafers, meaning the surface topography was more concentrated in certain areas of the wafer than others. Given these characteristics, Operation 5 and Step 4.4 are not qualified to produce high performing microchips because their techniques and methods are prone to cause surface defects, wafer stress, and wafer breakage.